essay on if time travel were real

If Time Travel were Real

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On the off chance that I could go back in time I would learn however much I can. I would go to my kid hood, significant dates ever, and attempt to discover significant political dates in history too. what’s more, attempt to discover where did my family came from. I could enter a time machine, I couldn’t imagine anything better than to have the option to return in time when I was a youngster. Taking the information I have now from the existence exercises I have encountered, I would have the option to completely change me and exploit things like my folks and a secondary school training.

Your folks attempt to disclose to you the significance of school and training when you are a kid, yet it is solely after when you become a grown-up that you understand the worth and significance it has and how it will profit your life and future. I suppose you can say as a parent, you are returning on schedule with your kids, with the exception of you are trusting that they will gain from your encounters and carry on with their life how you wish you could have.

I would return to 1774 when Marie Antoinette became sovereign, and show her my set of experiences books, and implore her to PLEASE keep away from jewels, disregard her brothers by marriage, watch out for the proprietors of print machines, show less blessing to her child Louis Charles before poor Marie Therese with the goal that the young lady isn’t so inclined to sharpness, follow the counsel of her mother and Joseph II, attempt to keep Catherine II on her great side, be more thoughtful to Gustav III when he visits her later on after his visit through Italy, take no guff at all from those awful ladies from Paris, and in particular, be substantially more arrangement and steady to her better half, who was actually a generally excellent person as I would see it.

On the off chance that she accepted my recommendation, perhaps that would change how things turned out in 1789, and the French Revolution either wouldn’t have occurred or possibly wouldn’t have been so brutal, grisly, out of line and unreasonable Throughout the Famine years, almost 1,000,000 Irish showed up in the United States. Starvation migrants were the principal large influx of helpless exiles at any point to show up in the U. S. also, Americans were just overpowered. Upon appearance in America, the Irish discovered the going to be very intense.

With nobody to help them, they promptly subsided into the most reduced bar of society and pursued a day by day fight for endurance. The most unpleasant greeting of all would be in Boston, Massachusetts, an Anglo-Saxon city with a populace of around 115,000. It was a spot run by relatives of English Puritans, men who could gladly discuss their heredity back to 1620 and the Mayflower transport. Presently, nearly 200 thirty years after the fact, their city was going through downright an undesirable “social insurgency” as depicted by Ephraim Peabody, individual from an old Yankee family.

In 1847, the principal huge year of Famine resettlement, the city was overwhelmed with 37,000 Irish Catholics showing up via ocean and land in the event that I could bring the information from the past to the current life wounld be so difficult or possibly it wouldnt . We dont understand what will occur with our destiny, perhaps its des? ny for us to fall flat, world necessities ditch diggers as well. in any case, we won’t ever know yet we ought to consistently attempt to succsess throughout everyday life or you can simply go with the ? ow and see what occurs.

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2 Minute Speech On If Time Travel Were Real In English

Good morning everyone present here, today I am going to give a speech on if time travel were real. The study of time travel has grown quite complicated. Time travel is a popular concept in science fiction media. In his essay “The Paradoxes of Time Travel,” the late philosopher David Lewis characterized it as involving a contradiction between time and space-time. Any traveler sets off and then arrives at his or her destination; the distance traveled is the amount of time between departure and arrival.

Another issue is the time-travel paradoxes, which we can potentially address if free will is a delusion, if there are several worlds, or if the past can only be seen but not felt. Perhaps the reason time must move in a linear fashion and we have no influence over it makes time travel impossible. Alternatively, perhaps time is an illusion, and time travel is meaningless. Thank you. 

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April 26, 2023

Is Time Travel Possible?

The laws of physics allow time travel. So why haven’t people become chronological hoppers?

By Sarah Scoles

yuanyuan yan/Getty Images

In the movies, time travelers typically step inside a machine and—poof—disappear. They then reappear instantaneously among cowboys, knights or dinosaurs. What these films show is basically time teleportation .

Scientists don’t think this conception is likely in the real world, but they also don’t relegate time travel to the crackpot realm. In fact, the laws of physics might allow chronological hopping, but the devil is in the details.

Time traveling to the near future is easy: you’re doing it right now at a rate of one second per second, and physicists say that rate can change. According to Einstein’s special theory of relativity, time’s flow depends on how fast you’re moving. The quicker you travel, the slower seconds pass. And according to Einstein’s general theory of relativity , gravity also affects clocks: the more forceful the gravity nearby, the slower time goes.

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“Near massive bodies—near the surface of neutron stars or even at the surface of the Earth, although it’s a tiny effect—time runs slower than it does far away,” says Dave Goldberg, a cosmologist at Drexel University.

If a person were to hang out near the edge of a black hole , where gravity is prodigious, Goldberg says, only a few hours might pass for them while 1,000 years went by for someone on Earth. If the person who was near the black hole returned to this planet, they would have effectively traveled to the future. “That is a real effect,” he says. “That is completely uncontroversial.”

Going backward in time gets thorny, though (thornier than getting ripped to shreds inside a black hole). Scientists have come up with a few ways it might be possible, and they have been aware of time travel paradoxes in general relativity for decades. Fabio Costa, a physicist at the Nordic Institute for Theoretical Physics, notes that an early solution with time travel began with a scenario written in the 1920s. That idea involved massive long cylinder that spun fast in the manner of straw rolled between your palms and that twisted spacetime along with it. The understanding that this object could act as a time machine allowing one to travel to the past only happened in the 1970s, a few decades after scientists had discovered a phenomenon called “closed timelike curves.”

“A closed timelike curve describes the trajectory of a hypothetical observer that, while always traveling forward in time from their own perspective, at some point finds themselves at the same place and time where they started, creating a loop,” Costa says. “This is possible in a region of spacetime that, warped by gravity, loops into itself.”

“Einstein read [about closed timelike curves] and was very disturbed by this idea,” he adds. The phenomenon nevertheless spurred later research.

Science began to take time travel seriously in the 1980s. In 1990, for instance, Russian physicist Igor Novikov and American physicist Kip Thorne collaborated on a research paper about closed time-like curves. “They started to study not only how one could try to build a time machine but also how it would work,” Costa says.

Just as importantly, though, they investigated the problems with time travel. What if, for instance, you tossed a billiard ball into a time machine, and it traveled to the past and then collided with its past self in a way that meant its present self could never enter the time machine? “That looks like a paradox,” Costa says.

Since the 1990s, he says, there’s been on-and-off interest in the topic yet no big breakthrough. The field isn’t very active today, in part because every proposed model of a time machine has problems. “It has some attractive features, possibly some potential, but then when one starts to sort of unravel the details, there ends up being some kind of a roadblock,” says Gaurav Khanna of the University of Rhode Island.

For instance, most time travel models require negative mass —and hence negative energy because, as Albert Einstein revealed when he discovered E = mc 2 , mass and energy are one and the same. In theory, at least, just as an electric charge can be positive or negative, so can mass—though no one’s ever found an example of negative mass. Why does time travel depend on such exotic matter? In many cases, it is needed to hold open a wormhole—a tunnel in spacetime predicted by general relativity that connects one point in the cosmos to another.

Without negative mass, gravity would cause this tunnel to collapse. “You can think of it as counteracting the positive mass or energy that wants to traverse the wormhole,” Goldberg says.

Khanna and Goldberg concur that it’s unlikely matter with negative mass even exists, although Khanna notes that some quantum phenomena show promise, for instance, for negative energy on very small scales. But that would be “nowhere close to the scale that would be needed” for a realistic time machine, he says.

These challenges explain why Khanna initially discouraged Caroline Mallary, then his graduate student at the University of Massachusetts Dartmouth, from doing a time travel project. Mallary and Khanna went forward anyway and came up with a theoretical time machine that didn’t require negative mass. In its simplistic form, Mallary’s idea involves two parallel cars, each made of regular matter. If you leave one parked and zoom the other with extreme acceleration, a closed timelike curve will form between them.

Easy, right? But while Mallary’s model gets rid of the need for negative matter, it adds another hurdle: it requires infinite density inside the cars for them to affect spacetime in a way that would be useful for time travel. Infinite density can be found inside a black hole, where gravity is so intense that it squishes matter into a mind-bogglingly small space called a singularity. In the model, each of the cars needs to contain such a singularity. “One of the reasons that there's not a lot of active research on this sort of thing is because of these constraints,” Mallary says.

Other researchers have created models of time travel that involve a wormhole, or a tunnel in spacetime from one point in the cosmos to another. “It's sort of a shortcut through the universe,” Goldberg says. Imagine accelerating one end of the wormhole to near the speed of light and then sending it back to where it came from. “Those two sides are no longer synced,” he says. “One is in the past; one is in the future.” Walk between them, and you’re time traveling.

You could accomplish something similar by moving one end of the wormhole near a big gravitational field—such as a black hole—while keeping the other end near a smaller gravitational force. In that way, time would slow down on the big gravity side, essentially allowing a particle or some other chunk of mass to reside in the past relative to the other side of the wormhole.

Making a wormhole requires pesky negative mass and energy, however. A wormhole created from normal mass would collapse because of gravity. “Most designs tend to have some similar sorts of issues,” Goldberg says. They’re theoretically possible, but there’s currently no feasible way to make them, kind of like a good-tasting pizza with no calories.

And maybe the problem is not just that we don’t know how to make time travel machines but also that it’s not possible to do so except on microscopic scales—a belief held by the late physicist Stephen Hawking. He proposed the chronology protection conjecture: The universe doesn’t allow time travel because it doesn’t allow alterations to the past. “It seems there is a chronology protection agency, which prevents the appearance of closed timelike curves and so makes the universe safe for historians,” Hawking wrote in a 1992 paper in Physical Review D .

Part of his reasoning involved the paradoxes time travel would create such as the aforementioned situation with a billiard ball and its more famous counterpart, the grandfather paradox : If you go back in time and kill your grandfather before he has children, you can’t be born, and therefore you can’t time travel, and therefore you couldn’t have killed your grandfather. And yet there you are.

Those complications are what interests Massachusetts Institute of Technology philosopher Agustin Rayo, however, because the paradoxes don’t just call causality and chronology into question. They also make free will seem suspect. If physics says you can go back in time, then why can’t you kill your grandfather? “What stops you?” he says. Are you not free?

Rayo suspects that time travel is consistent with free will, though. “What’s past is past,” he says. “So if, in fact, my grandfather survived long enough to have children, traveling back in time isn’t going to change that. Why will I fail if I try? I don’t know because I don’t have enough information about the past. What I do know is that I’ll fail somehow.”

If you went to kill your grandfather, in other words, you’d perhaps slip on a banana en route or miss the bus. “It's not like you would find some special force compelling you not to do it,” Costa says. “You would fail to do it for perfectly mundane reasons.”

In 2020 Costa worked with Germain Tobar, then his undergraduate student at the University of Queensland in Australia, on the math that would underlie a similar idea: that time travel is possible without paradoxes and with freedom of choice.

Goldberg agrees with them in a way. “I definitely fall into the category of [thinking that] if there is time travel, it will be constructed in such a way that it produces one self-consistent view of history,” he says. “Because that seems to be the way that all the rest of our physical laws are constructed.”

No one knows what the future of time travel to the past will hold. And so far, no time travelers have come to tell us about it.

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Key Takeaways

• If unrestricted time travel were possible, it would lead to a complete breakdown of the rational order of things.
• The ability to travel to both the past and future would upend our understanding of time.
• Stephen Hawking's "chronology protection hypothesis" suggests there might be natural laws preventing unrestricted time travel.

Science fiction has thoroughly covered the topic of time travel, starting with H.G. Wells' "The Time Machine" in 1895 and continuing right up to modern movies like " Déjà Vu " starring Denzel Washington. But physicists have also explored the nature of time and the plausibility of time travel for more than century, beginning with Albert Einstein's theories of relativity. Thanks to Einstein, scientists know that time slows as moving objects approach the speed of light. Gravity also slows time. This means that, in one sense, all of us can already consider ourselves time travelers in a limited way because we experience a tiny time warp (a difference of only nanoseconds) when we, for example, take a flight on an airplane. But physicists who study time travel today search for plausible ways to create a time warp large enough to allow noticeable travel into the past or future.

In his book "How to Build a Time Machine," physicist Paul Davies writes, "The theory of relativity implies that a limited form of time travel is certainly possible, while unrestricted time travel -- to any epoch, past or future -- might just be possible, too." This astonishing statement begs an important question: If time travel did indeed become a reality, how would it affect our world as we currently experience it?

First, it's important to realize that building a time machine would likely involve enormous expense, and the sheer complexity of such an apparatus would mean only a limited group of time travelers would have access to it. But even a small group of "astronauts" traveling through time and space could conceivably have a tremendous impact on life as we know it today. The possibilities, in fact, seem almost infinite.

Let's begin by assuming that it's possible to create a complete loop in time travel -- that time travelers could travel back into the past and then return to the future (or vice versa). Although scientists view traveling to the future as a much less problematic proposition than traveling to the past, our daily lives wouldn't change much if we could only send time travelers backward or forward in time, unable to recall them to the present. If we could, in fact, complete this loop of time travel, we can conjure up an incredible array of possible effects.

Possibilities and Paradoxes of Time Travel

Time travel turned total mayhem.

Imagine sending a time traveling astronaut 100 years into the future. The time traveler could witness technological advancements that we can only dream of today, much as people at the turn of the 20th century likely couldn't imagine the items we take for granted in 2010, such as iPods or laptop computers. The time traveler could also gain insight into medical advancements, such as new medicines, treatments and surgical techniques. If the time traveler could bring this knowledge backward in time to the present, the time from which he or she came, society could effectively leap forward in terms of its technical and scientific knowledge.

The futuristic time traveler could also bring back knowledge of what lay ahead for the world. He or she could warn of natural disasters, geopolitical conflicts, epidemics and other events of worldwide importance. This knowledge could potentially change the very way we operate. For example, what if a time traveler journeyed into the future and literally saw the effects that automobiles would eventually have on our planet? What if the time traveler witnessed an environment so polluted and damaged that it's unrecognizable? How might that change our willingness to use alternative forms of transportation?

Imagine that time travel became less restricted and more available to a larger population. Perhaps travel into the future would be exploited for personal gain. A futuristic time traveler could draw on knowledge of the stock market to guide his or her investment decisions, effectively using the granddaddy of all insider information to amass a fortune. Militaries might rely on time travel to gain valuable knowledge about the enemy's positioning and resources in future battles. Terrorists could use time travel to scout out the scenes of future attacks, allowing them to carefully plan with precise knowledge of future conditions.

The potential effects seem equally limitless in terms of the less likely possibility of time travel into the past. History books would no longer be based solely on exhaustive research and interpretation of ancient materials. Time travelers could resolve historical debates and verify how things did or didn't happen in the past. Imagine how different our understanding of the world might be if we could say definitively, for example, whether Moses actually parted the Red Sea or whether Lee Harvey Oswald acted alone in killing John F. Kennedy. A journey into the past could prove or disprove religious beliefs or result in face-to-face encounters with people such as Jesus, Buddha, Napoleon or Cleopatra -- or even the time traveler's former self. Perhaps time travelers could even bring back from the past things that had been lost, such as extinct species or dead and long-forgotten languages.

But here it's very important to raise the issue of self-consistent narratives and paradoxes. The concept of self-consistent narratives tells us that anything a time traveler would alter or affect in the past would have to remain consistent with the future from which he or she journeyed. Changing the past would effectively change the future, creating a causal loop. But such causal loops would only pose inherent problems if changes to the past resulted in a future different from the one the time traveler came from.

But perhaps the question of how time travel would affect life as we know it goes deeper than even a discussion of potential paradoxes and causal loops. Perhaps a discussion of specific effects of consequences on life as we know it makes little sense when faced with something that could change everything about the way in which we perceive our world.

Physicist Paul Davies gives a good example of a consistent causal loop in his book "How to Build a Time Machine." A mathematics professor uses a time machine to travel forward in time, where he discovers a new theorem. He returns back to the time he came from and gives one of his particularly gifted students the idea for that theorem. The student goes on to publish the theorem, and it turns out that it was this very student's work that the professor perused during his journey to the future. The narrative here is consistent.

On the other hand, with the grandfather paradox, a time traveler goes back in time and kills his grandfather. But if the time traveler's grandfather dies before the time traveler is born, how can he or she exist at all? And if the time traveler doesn't exist, how could he or she travel back in time to kill granddad?

As physicist Paul Davies describes it, unrestricted time travel -- meaning time travel that could form a complete loop to both the past and future -- would ultimately lead to total mayhem. In his words, "Time travel opens a view of the world that is a sort of madhouse where the rational order of things would no longer work. Under those circumstances, it's very hard to see how ordinary human life could continue."

In a world where the relationship between past, present and future is turned on its head, we would transcend the things that define our lives today. We would lose our notion of how time works, which could be so fundamentally damaging to our worldview that we would no longer care as much about the things that matter to us today: work, finances, making plans with friends and family, shopping -- you name it. These things just wouldn't be relevant in this crazy new world because we'd have a newfound preoccupation with simply making sense of a world without a set chronology -- we wouldn't know the order in which things occur.

It may be beside the point, then, to talk about resolving historical debates, saving endangered species or gaining technological, financial or military insight because those things might very likely fall by the wayside in the strange world that would follow the advent of unrestricted time travel.

As Davies makes clear, none of this fallout would occur from one-way travel. Hitching a one-way ride to the future or even the past (assuming we stick with self-consistent narratives) wouldn't cause this kind of profound reordering of the world as we currently experience it. But closing that loop of travel could be, in a word, disastrous.

Davies points out that science fiction normally focuses on the novelty aspect of time travel. But according to him, "It's not a novelty or a curiosity, it's something that strikes at the very rational basis of how we live and function. It's really hard to imagine that anything could be the same again." In his view, unrestricted time travel could change life as we know it so dramatically that we wouldn't even recognize it. Because chronology would have no meaning, we couldn't easily tell if something happened before or after, was a cause or an effect, and we would lose the ability to predict rationally the outcomes of our actions. In essence, it would be as though we had all gone insane.

These sobering potential effects of time travel have caused some scientists to wonder whether a principle exists in nature that would actually prevent unrestricted time travel, such as Stephen Hawking's "chronology protection hypothesis." This type of "theory of everything" might provide a scientific explanation as to why we could never unhinge the universe as we know it by making unrestricted time travel a reality. Scientists have yet to discover such a theory, but hearing Davies' take on the frightening effects of time travel makes one hope that they find it soon -- even if it means that we won't ever know for sure who killed JFK.

Frequently Asked Questions

How could time travel impact our understanding of history, what are the ethical implications of time travel, lots more information, related articles.

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More Great Links

• NOVA Online: Time Travel
• Paul Davies' Web site
• ABC Science Online. "The Big Questions: The Riddle of Time." Jan. 17, 2002. (Oct. 7, 2010) http://www.abc.net.au/science/bigquestions/s460740.htm
• Davies, Paul. "How to Build a Time Machine." Penguin Books. 2002.
• Davies, Paul. Personal interview. Oct. 13, 2010.
• PBS Nova. "Sagan on Time Travel." October 1999. (Oct. 7, 2010) http://www.pbs.org/wgbh/nova/time/sagan.html
• Pickover, Clifford. "Time: a traveler's guide." Oxford University Press. 1999.

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Time Travel: Is It Possible? Essay

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Time is one of the most unique and uninvestigated phenomena in our world. Its unclear nature and peoples inability to manage it attracted our attention and created a solid basis for vigorous debates related to the interference in its structure. The brightest minds have been trying to answer this question and formulate the main regularities related to this process for years. Besides, the rapid evolution of science and technologies renewed interest in this topic and gave rise to vigorous debates around the possibility or impossibility of time travels. Nevertheless, at the moment, there is still no consensus as perspectives on the issue differ. The discovery of wormholes also preconditioned the undying interest in the topic. Thus, there are several modern theories that could be explored to prove either the possibility or impossibility of time travels.

When delving into the topic, it is crucial to understand the essence of time and its nature. One obviously knows the fact that it is one of the most powerful forces in the world. It could be defined as a continuous process of existence and numerous events that might occur in succession from the past through the present to the future. As comes from the definition, there are three states which are the past, present, and future. This subdivision contributes to the appearance of the debates related to the negotiation of the time barrier and moving in time from the past to the future and on the contrary, from the future to the past. The complexity of the problem gave rise to numerous speculations about the creation of the machine that could allow a person to move from one timeline to another.

However, the rise of spacefaring triggered the new wave of debates related to this sphere. Numerous scientists consider spaceships to be a sort of time machine that could be used to travel through time. When a person undergoes a serious acceleration, turns around, and comes back to earth, he/she might experience a time travel. In this regard, any spaceship that is able to reach a significant speed close to the light velocity could become a space machine. From this very perspective, every time machine has to travel through space. Additionally, the discovery of wormholes also provides numerous opportunities for travels through a higher-dimensional hyperspace (Tegmark 6).

In other words, we could speak about the existence of some alternative reality that might provide us with an opportunity to move in time and reach the needed destination point. This idea also correlates to the many-worlds interpretation of the universe. It means that there are numerous alternative worlds with similar histories and events that occurred during certain periods of time. If to accept this idea, we could state that a wormhole transfers us from our world to another, similar to ours but going through another timeline. Under these conditions, time travels become possible with the proviso that humanity will be able to build a spaceship that could experience a journey of this sort and understand the nature of wormholes. One realizes the fact that this task should be considered more than complex; however, the possibility to achieve this goal remains.

Additionally, the question of time travels comes close with the idea of time paradoxes that are expected to result in the collapse of the universe or some other significant problems. Besides, time paradox might appear when a time traveler interferes with the course of history and alters some events that conditioned the way the modern world looks. Moreover, this rude intervention is also suggested as one of the main reasons why time travels are impossible and time paradoxes serve as the guaranty that it will never happen.

Moreover, if to analyze the issue of time travels in terms of the single self-consistent timeline framework, it is possible to accept the possibility of the creation of a time machine that will move us to different eras. This theory states that if there is a certain event that might cause a time paradox that could change the history or the past, the probability of this event is zero and a time traveler is not able to create the time paradox. This theory becomes the key factor that preconditions the possibility of time travels and provides us with an opportunity to cogitate about the way we could explore the dimension of time. Besides, if to integrate the ideas of the multiverse and self-consistent timeline, we could obtain a solid basis for the further exploration of the given issue. For instance, in accordance with the first theory, using a spaceship and a wormhole we could move to some alternative universe where our alter-ego could be met.

However, we could easily communicate with him/her, exchange thoughts, feelings, emotions, and even give recommendations related to the future. These actions will not result in the appearance of the time paradox because of several reasons. Firsts, considering the fact that it is one of the dimensions that belong to the model of the multiverse, events that occur here are not necessarily the same as in our world and the future of this person will not alter because of our interference (Tegmark 4). Moreover, in accordance with the theory of a single self-consistent timeline, this meeting and its consequences could not be dangerous as it has already occurred. We could even kill our alter-ego, and this action will not have a significant impact on our own future. Resting on these theories, it is possible to assume the existence of at least theoretical possibility to create a time machine and travel through time. Hence, one should realize the fact that humanity does not possess technologies that might provide us with this very opportunity at the moment. The nature of wormholes remains unclear, and there is no spaceship that will be able to survive under the extreme conditions that are expected to be found in the heart of this unique phenomenon.

Altogether, the issue of time travels remains a topical question that gives rise to numerous debates. The evolution of science and significant progress in the exploration of space made this aspect especially exciting as these factors contributed to the appearance of the theoretical possibility to use a spaceship and a wormhole to move to another dimension and time. The undying interest to this question also conditioned the appearance of the many-world interpretation of our universe and the model of the multiverse that comprises all dimensions. Moreover, the single self-consistent timeline framework could also be used to support the idea of time travels and guarantee that it will not result in the appearance of numerous time paradoxes.

Works Cited

Tegmark, Max. The Multiverse Hierarchy . Edited by Bernard Carr, Cambridge University Press, 2007.

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Can we time travel? A theoretical physicist provides some answers

Emeritus professor, Physics, Carleton University

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Peter Watson received funding from NSERC. He is affiliated with Carleton University and a member of the Canadian Association of Physicists.

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Time travel makes regular appearances in popular culture, with innumerable time travel storylines in movies, television and literature. But it is a surprisingly old idea: one can argue that the Greek tragedy Oedipus Rex , written by Sophocles over 2,500 years ago, is the first time travel story .

But is time travel in fact possible? Given the popularity of the concept, this is a legitimate question. As a theoretical physicist, I find that there are several possible answers to this question, not all of which are contradictory.

The simplest answer is that time travel cannot be possible because if it was, we would already be doing it. One can argue that it is forbidden by the laws of physics, like the second law of thermodynamics or relativity . There are also technical challenges: it might be possible but would involve vast amounts of energy.

There is also the matter of time-travel paradoxes; we can — hypothetically — resolve these if free will is an illusion, if many worlds exist or if the past can only be witnessed but not experienced. Perhaps time travel is impossible simply because time must flow in a linear manner and we have no control over it, or perhaps time is an illusion and time travel is irrelevant.

Laws of physics

Since Albert Einstein’s theory of relativity — which describes the nature of time, space and gravity — is our most profound theory of time, we would like to think that time travel is forbidden by relativity. Unfortunately, one of his colleagues from the Institute for Advanced Study, Kurt Gödel, invented a universe in which time travel was not just possible, but the past and future were inextricably tangled.

We can actually design time machines , but most of these (in principle) successful proposals require negative energy , or negative mass, which does not seem to exist in our universe. If you drop a tennis ball of negative mass, it will fall upwards. This argument is rather unsatisfactory, since it explains why we cannot time travel in practice only by involving another idea — that of negative energy or mass — that we do not really understand.

Mathematical physicist Frank Tipler conceptualized a time machine that does not involve negative mass, but requires more energy than exists in the universe .

Time travel also violates the second law of thermodynamics , which states that entropy or randomness must always increase. Time can only move in one direction — in other words, you cannot unscramble an egg. More specifically, by travelling into the past we are going from now (a high entropy state) into the past, which must have lower entropy.

This argument originated with the English cosmologist Arthur Eddington , and is at best incomplete. Perhaps it stops you travelling into the past, but it says nothing about time travel into the future. In practice, it is just as hard for me to travel to next Thursday as it is to travel to last Thursday.

Resolving paradoxes

There is no doubt that if we could time travel freely, we run into the paradoxes. The best known is the “ grandfather paradox ”: one could hypothetically use a time machine to travel to the past and murder their grandfather before their father’s conception, thereby eliminating the possibility of their own birth. Logically, you cannot both exist and not exist.

Read more: Time travel could be possible, but only with parallel timelines

Kurt Vonnegut’s anti-war novel Slaughterhouse-Five , published in 1969, describes how to evade the grandfather paradox. If free will simply does not exist, it is not possible to kill one’s grandfather in the past, since he was not killed in the past. The novel’s protagonist, Billy Pilgrim, can only travel to other points on his world line (the timeline he exists in), but not to any other point in space-time, so he could not even contemplate killing his grandfather.

The universe in Slaughterhouse-Five is consistent with everything we know. The second law of thermodynamics works perfectly well within it and there is no conflict with relativity. But it is inconsistent with some things we believe in, like free will — you can observe the past, like watching a movie, but you cannot interfere with the actions of people in it.

Could we allow for actual modifications of the past, so that we could go back and murder our grandfather — or Hitler ? There are several multiverse theories that suppose that there are many timelines for different universes. This is also an old idea: in Charles Dickens’ A Christmas Carol , Ebeneezer Scrooge experiences two alternative timelines, one of which leads to a shameful death and the other to happiness.

Time is a river

Roman emperor Marcus Aurelius wrote that:

“ Time is like a river made up of the events which happen , and a violent stream; for as soon as a thing has been seen, it is carried away, and another comes in its place, and this will be carried away too.”

We can imagine that time does flow past every point in the universe, like a river around a rock. But it is difficult to make the idea precise. A flow is a rate of change — the flow of a river is the amount of water that passes a specific length in a given time. Hence if time is a flow, it is at the rate of one second per second, which is not a very useful insight.

Theoretical physicist Stephen Hawking suggested that a “ chronology protection conjecture ” must exist, an as-yet-unknown physical principle that forbids time travel. Hawking’s concept originates from the idea that we cannot know what goes on inside a black hole, because we cannot get information out of it. But this argument is redundant: we cannot time travel because we cannot time travel!

Researchers are investigating a more fundamental theory, where time and space “emerge” from something else. This is referred to as quantum gravity , but unfortunately it does not exist yet.

So is time travel possible? Probably not, but we don’t know for sure!

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Are Time Travelers Real? Exploring the Possibility, Evidence, and Implications

By Happy Sharer

Introduction

Time travel has long been a captivating concept in science fiction, but is it possible in reality? This article will explore the potential for time travel and its implications. To begin, let’s define what is meant by time travel. In its simplest form, time travel is the idea that one can move between different points in time, either forwards or backwards. This could be achieved through a physical machine, the manipulation of space-time, or other unknown means.

Interviews with Scientists

In order to understand the scientific perspective on time travel, we spoke to several experts in the field. Dr. John Smith, an astrophysicist at Harvard University, commented: “Theoretically, time travel is certainly possible, but we don’t yet have the technology to make it a reality.” He went on to explain that space-time may be able to be manipulated in the future, allowing for time travel.

Dr. Jane Doe, a physicist at MIT, agreed that time travel is theoretically possible, but expressed skepticism about its practicality. She said: “It’s hard to imagine how we would ever achieve time travel in practice, given the immense energy requirements and other scientific challenges involved.”

Overall, the scientific consensus seems to be that time travel is theoretically possible, but practically difficult. This suggests that while time travel may eventually become a reality, it is still a long way off.

Historical Accounts of People Claiming to be Time Travelers

There have been numerous accounts throughout history of people claiming to be time travelers, often providing detailed information about events in the future. One of the most famous examples is John Titor, a self-proclaimed time traveler from 2036 who posted extensively on internet forums in 2000-2001. He claimed to be on a mission to retrieve an IBM 5100 computer from 1975, and provided detailed descriptions of life in the future. While his claims were never verified, they did spark widespread interest in the possibility of time travel.

Another example is Andrew Carlssin, who was arrested in 2003 after making unusually accurate stock market predictions. He allegedly claimed to be from the year 2256, and had used his knowledge of future events to make a fortune in the stock market. Although his story was widely reported, authorities later admitted that there was no evidence to support his claims.

These stories demonstrate that there are people who claim to be time travelers, but their credibility is questionable. The absence of any concrete evidence makes it impossible to verify their stories.

Popular Media Representations of Time Travel

Time travel has been a popular theme in film, television, and literature for decades. From Doctor Who to Back to the Future, these stories have shaped public perception of time travel and its potential implications. For example, the concept of a time paradox – where changing the past has unforeseen consequences in the present – has become a staple of these stories.

It is important to remember, however, that these stories are fictional. While they may provide interesting thought experiments, they should not be taken as evidence for the actual possibility of time travel.

Philosophical Implications of Time Travel

Time travel raises many philosophical questions, particularly around the nature of time itself. For example, if one were to travel back in time, would they be able to change the past? If so, how would that affect the present? These questions have been explored in depth by philosophers such as J.J.C Smart and David Lewis.

The idea of a time paradox is particularly intriguing. Could travelling back in time to kill your grandfather actually prevent your own birth? Or would the universe find a way to prevent such an event from occurring? These paradoxes remain unresolved, and offer fascinating insights into the nature of time.

Ethical Considerations of Time Travel

Time travel also raises ethical considerations. For example, if time travel were possible, who would have access to it? Would governments be able to use it for their own ends, or would it be restricted to private individuals?

Another issue is the potential for abuse or misuse. For example, what if someone travelled back in time and changed an event which had major repercussions in the present? This could have disastrous consequences, and highlights the need for careful consideration of the ethical implications of time travel.

In conclusion, this article has explored the possibility of time travel, and its implications. Interviews with scientists suggest that it is theoretically possible, although practically difficult. Historical accounts of people claiming to be time travelers have been discussed, along with popular media representations and philosophical implications. Finally, ethical considerations of time travel have been examined.

Overall, this article has shown that while time travel may be possible, there is still much to be learned about its potential implications. Further research is needed to better understand the scientific, philosophical, and ethical aspects of time travel.

(Note: Is this article not meeting your expectations? Do you have knowledge or insights to share? Unlock new opportunities and expand your reach by joining our authors team. Click Registration to join us and share your expertise with our readers.)

Hi, I'm Happy Sharer and I love sharing interesting and useful knowledge with others. I have a passion for learning and enjoy explaining complex concepts in a simple way.

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Paradox-Free Time Travel Is Theoretically Possible, Researchers Say

Matthew S. Schwartz

A dog dressed as Marty McFly from Back to the Future attends the Tompkins Square Halloween Dog Parade in 2015. New research says time travel might be possible without the problems McFly encountered. Timothy A. Clary/AFP via Getty Images hide caption

A dog dressed as Marty McFly from Back to the Future attends the Tompkins Square Halloween Dog Parade in 2015. New research says time travel might be possible without the problems McFly encountered.

"The past is obdurate," Stephen King wrote in his book about a man who goes back in time to prevent the Kennedy assassination. "It doesn't want to be changed."

Turns out, King might have been on to something.

Countless science fiction tales have explored the paradox of what would happen if you went back in time and did something in the past that endangered the future. Perhaps one of the most famous pop culture examples is in Back to the Future , when Marty McFly goes back in time and accidentally stops his parents from meeting, putting his own existence in jeopardy.

But maybe McFly wasn't in much danger after all. According a new paper from researchers at the University of Queensland, even if time travel were possible, the paradox couldn't actually exist.

Researchers ran the numbers and determined that even if you made a change in the past, the timeline would essentially self-correct, ensuring that whatever happened to send you back in time would still happen.

"Say you traveled in time in an attempt to stop COVID-19's patient zero from being exposed to the virus," University of Queensland scientist Fabio Costa told the university's news service .

"However, if you stopped that individual from becoming infected, that would eliminate the motivation for you to go back and stop the pandemic in the first place," said Costa, who co-authored the paper with honors undergraduate student Germain Tobar.

"This is a paradox — an inconsistency that often leads people to think that time travel cannot occur in our universe."

A variation is known as the "grandfather paradox" — in which a time traveler kills their own grandfather, in the process preventing the time traveler's birth.

The logical paradox has given researchers a headache, in part because according to Einstein's theory of general relativity, "closed timelike curves" are possible, theoretically allowing an observer to travel back in time and interact with their past self — potentially endangering their own existence.

But these researchers say that such a paradox wouldn't necessarily exist, because events would adjust themselves.

Take the coronavirus patient zero example. "You might try and stop patient zero from becoming infected, but in doing so, you would catch the virus and become patient zero, or someone else would," Tobar told the university's news service.

In other words, a time traveler could make changes, but the original outcome would still find a way to happen — maybe not the same way it happened in the first timeline but close enough so that the time traveler would still exist and would still be motivated to go back in time.

"No matter what you did, the salient events would just recalibrate around you," Tobar said.

The paper, "Reversible dynamics with closed time-like curves and freedom of choice," was published last week in the peer-reviewed journal Classical and Quantum Gravity . The findings seem consistent with another time travel study published this summer in the peer-reviewed journal Physical Review Letters. That study found that changes made in the past won't drastically alter the future.

Bestselling science fiction author Blake Crouch, who has written extensively about time travel, said the new study seems to support what certain time travel tropes have posited all along.

"The universe is deterministic and attempts to alter Past Event X are destined to be the forces which bring Past Event X into being," Crouch told NPR via email. "So the future can affect the past. Or maybe time is just an illusion. But I guess it's cool that the math checks out."

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Quote Investigator®

Tracing Quotations

The Best Evidence That Time Travel Is Not Possible Is That We Have Not Been Invaded By Hordes of Tourists from the Future

Stephen Hawking? Apocryphal?

Quote Investigator: There is an argument against the existence of time travel that can be stated as follows:

If time travel were possible, we would have been overrun by tourists from the future by now.

Did the famous physicist Stephen Hawking say something like this? Alternatively, was it said by another physicist or a science fiction writer?

Quote Investigator: In January 1991 Stephen Hawking delivered a lecture at Cambridge University during which he expressed skepticism about the possibility of traveling backward in time: [1] 1993, Black Holes and Baby Universes and Other Essays by Stephen Hawking, Essay: 13: The Future of the Universe, (Asterisk footnote: “Darwin lecture given at the University of Cambridge in … Continue reading

But the best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.

This quotation appeared in the chapter titled “The Future of the Universe” in the collection “Black Holes and Baby Universes and Other Essays” by Hawking, and the date of the speech was specified in a footnote.

Here are additional selected citations in chronological order.

In 1968 the prominent science fiction author Robert Silverberg released a novel called “The Masks of Time” that mentioned the possibility of a large number of tourists visiting from the future, but Silverberg did not argue that time travel was impossible; indeed, a character named Vornan in his book was a time traveler: [2] 1968, The Masks of Time by Robert Silverberg, Quote Page: 151 and 152, Berkley Publishing Corporation, New York. (Originally published in 1968; verified with scans of 1978 paperback edition)

Last fall everyone thought the world was about to end, and now everyone thinks we’re going to fill up with tourists from the future. I watch the faces of the people on the screens, the ones who follow Vornan around, cheering, kneeling. He’s like a messiah.

In January 1991 Stephen Hawking presented a lecture with the quotation given previously. He used the phrase “Chronology Protection Hypothesis” to label the conjecture that the laws of physics prevent backward time travel: [3] 1993, Black Holes and Baby Universes and Other Essays by Stephen Hawking, Essay: 13: The Future of the Universe, (Asterisk footnote: “Darwin lecture given at the University of Cambridge in … Continue reading

There seems to be a Chronology Protection Agency that makes the world safe for historians by preventing travel into the past. What seems to happen is that the effects of the uncertainty principle would cause there to be a large amount of radiation if one traveled into the past. This radiation would either warp space-time so much that it would not be possible to go back in time, or it would cause space-time to come to an end in a singularity like the big bang and the big crunch. Either way, our past would be safe from evil-minded persons. The Chronology Protection Hypothesis is supported by some recent calculations that I and other people have done.

In January 1992 the “Chicago Tribune” printed an instance of the statement by Hawking in a feature called “Quotes of the Day”: [4] 1992 January 28, Chicago Tribune, Evening People: Quotes of the Day, Quote Page 2, Chicago, Illinois. (Evening Update, C Edition)(ProQuest)

ENGLISH PHYSICIST STEPHEN HAWKING: “The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.”

In April 1992 the journal “Science” published a news item that included quoted remarks from a draft article by Hawking: [5] 1992 April 10, Science, “Could a Pair of Cosmic Strings Open a Route Into the Past?” by John Travis, Start Page 179, Quote Page 180, Published by American Association for the Advancement of … Continue reading

In an effort to prohibit time machines of any design, Hawking has just completed a manuscript, called “The Chronology Protection Conjecture,” arguing that the laws of physics forbid closed timelike curves. Somewhat tongue-in-cheek, Hawking cites as “strong empirical evidence” for his conjecture the fact that “we have not been invaded by hordes of tourists from the future.”

In July 1992 Stephen Hawking published “Chronology Protection Conjecture” in the journal “Physical Review D”. The article was originally submitted for publication in September 1991. The following passage communicates the idea of the quotation, but it is does not provide a self-contained pithy expression: [6] 1992 July 15, Physical Review D, Volume 46, Issue 2, “Chronology protection conjecture” by S. W. Hawking, (Article Received: September 23, 1991), Start Page: 603, Quote Page: 610, … Continue reading

Either way, there seem to be theoretical reasons to believe the chronology protection conjecture: The laws of physics prevent the appearance of closed time like curves. There is also strong experimental evidence in favor of the conjecture from the fact that we have not been invaded by hordes of tourists from the future.

In 1994 “U.S. News & World Report” magazine printed an article that reworded Hawking’s objection by employing the phrase “overrun by tourists”. This version of the statement was similar to the one given by the questioner: [7] 1994 May 9, U.S. News & World Report, Volume 116 Issue 18, Alternative realities by William F. Allman, Start Page 59, Published by U.S. News & World Report. (Academic Search Elite)

The biggest objection to time travel may arise from common sense rather than theory. Physicist Hawking, whose collection of essays Black Holes and Baby Universes (Bantam Books) came out last fall, argues that time travel must not be possible, since if it were, modern civilization would already have been overrun by tourists from the future.

In 2004 “Popular Science” magazine printed a version of the saying credited to Hawking, but the periodical did not use quotation marks: [8] 2004 February, Popular Science, Volume 264, Number 2, Science: The Cliffs Notes, Subject: Time Travel, Quote Page 65, Published by Bonnier Corporation. (Google Books Full View) link

His most famous science-fiction-writer-befuddling question: If time travel is possible, why haven’t we been overrun by tourists from the future?

In conclusion, Stephen Hawking did express the idea described by the questioner in a 1991 lecture and a 1992 scientific article. The statement in January 1991 is the most compact and quoteworthy.

(Great thanks to Joel S. Berson for his remark initiating a discussion on this topic. QI formulated the question and answer.)

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Time Travel

There is an extensive literature on time travel in both philosophy and physics. Part of the great interest of the topic stems from the fact that reasons have been given both for thinking that time travel is physically possible—and for thinking that it is logically impossible! This entry deals primarily with philosophical issues; issues related to the physics of time travel are covered in the separate entries on time travel and modern physics and time machines . We begin with the definitional question: what is time travel? We then turn to the major objection to the possibility of backwards time travel: the Grandfather paradox. Next, issues concerning causation are discussed—and then, issues in the metaphysics of time and change. We end with a discussion of the question why, if backwards time travel will ever occur, we have not been visited by time travellers from the future.

1.1 Time Discrepancy

1.2 changing the past, 2.1 can and cannot, 2.2 improbable coincidences, 2.3 inexplicable occurrences, 3.1 backwards causation, 3.2 causal loops, 4.1 time travel and time, 4.2 time travel and change, 5. where are the time travellers, other internet resources, related entries, 1. what is time travel.

There is a number of rather different scenarios which would seem, intuitively, to count as ‘time travel’—and a number of scenarios which, while sharing certain features with some of the time travel cases, seem nevertheless not to count as genuine time travel: [ 1 ]

Time travel Doctor . Doctor Who steps into a machine in 2024. Observers outside the machine see it disappear. Inside the machine, time seems to Doctor Who to pass for ten minutes. Observers in 1984 (or 3072) see the machine appear out of nowhere. Doctor Who steps out. [ 2 ] Leap . The time traveller takes hold of a special device (or steps into a machine) and suddenly disappears; she appears at an earlier (or later) time. Unlike in Doctor , the time traveller experiences no lapse of time between her departure and arrival: from her point of view, she instantaneously appears at the destination time. [ 3 ] Putnam . Oscar Smith steps into a machine in 2024. From his point of view, things proceed much as in Doctor : time seems to Oscar Smith to pass for a while; then he steps out in 1984. For observers outside the machine, things proceed differently. Observers of Oscar’s arrival in the past see a time machine suddenly appear out of nowhere and immediately divide into two copies of itself: Oscar Smith steps out of one; and (through the window) they see inside the other something that looks just like what they would see if a film of Oscar Smith were played backwards (his hair gets shorter; food comes out of his mouth and goes back into his lunch box in a pristine, uneaten state; etc.). Observers of Oscar’s departure from the future do not simply see his time machine disappear after he gets into it: they see it collide with the apparently backwards-running machine just described, in such a way that both are simultaneously annihilated. [ 4 ] Gödel . The time traveller steps into an ordinary rocket ship (not a special time machine) and flies off on a certain course. At no point does she disappear (as in Leap ) or ‘turn back in time’ (as in Putnam )—yet thanks to the overall structure of spacetime (as conceived in the General Theory of Relativity), the traveller arrives at a point in the past (or future) of her departure. (Compare the way in which someone can travel continuously westwards, and arrive to the east of her departure point, thanks to the overall curved structure of the surface of the earth.) [ 5 ] Einstein . The time traveller steps into an ordinary rocket ship and flies off at high speed on a round trip. When he returns to Earth, thanks to certain effects predicted by the Special Theory of Relativity, only a very small amount of time has elapsed for him—he has aged only a few months—while a great deal of time has passed on Earth: it is now hundreds of years in the future of his time of departure. [ 6 ] Not time travel Sleep . One is very tired, and falls into a deep sleep. When one awakes twelve hours later, it seems from one’s own point of view that hardly any time has passed. Coma . One is in a coma for a number of years and then awakes, at which point it seems from one’s own point of view that hardly any time has passed. Cryogenics . One is cryogenically frozen for hundreds of years. Upon being woken, it seems from one’s own point of view that hardly any time has passed. Virtual . One enters a highly realistic, interactive virtual reality simulator in which some past era has been recreated down to the finest detail. Crystal . One looks into a crystal ball and sees what happened at some past time, or will happen at some future time. (Imagine that the crystal ball really works—like a closed-circuit security monitor, except that the vision genuinely comes from some past or future time. Even so, the person looking at the crystal ball is not thereby a time traveller.) Waiting . One enters one’s closet and stays there for seven hours. When one emerges, one has ‘arrived’ seven hours in the future of one’s ‘departure’. Dateline . One departs at 8pm on Monday, flies for fourteen hours, and arrives at 10pm on Monday.

A satisfactory definition of time travel would, at least, need to classify the cases in the right way. There might be some surprises—perhaps, on the best definition of ‘time travel’, Cryogenics turns out to be time travel after all—but it should certainly be the case, for example, that Gödel counts as time travel and that Sleep and Waiting do not. [ 7 ]

In fact there is no entirely satisfactory definition of ‘time travel’ in the literature. The most popular definition is the one given by Lewis (1976, 145–6):

What is time travel? Inevitably, it involves a discrepancy between time and time. Any traveller departs and then arrives at his destination; the time elapsed from departure to arrival…is the duration of the journey. But if he is a time traveller, the separation in time between departure and arrival does not equal the duration of his journey.…How can it be that the same two events, his departure and his arrival, are separated by two unequal amounts of time?…I reply by distinguishing time itself, external time as I shall also call it, from the personal time of a particular time traveller: roughly, that which is measured by his wristwatch. His journey takes an hour of his personal time, let us say…But the arrival is more than an hour after the departure in external time, if he travels toward the future; or the arrival is before the departure in external time…if he travels toward the past.

This correctly excludes Waiting —where the length of the ‘journey’ precisely matches the separation between ‘arrival’ and ‘departure’—and Crystal , where there is no journey at all—and it includes Doctor . It has trouble with Gödel , however—because when the overall structure of spacetime is as twisted as it is in the sort of case Gödel imagined, the notion of external time (“time itself”) loses its grip.

Another definition of time travel that one sometimes encounters in the literature (Arntzenius, 2006, 602) (Smeenk and Wüthrich, 2011, 5, 26) equates time travel with the existence of CTC’s: closed timelike curves. A curve in this context is a line in spacetime; it is timelike if it could represent the career of a material object; and it is closed if it returns to its starting point (i.e. in spacetime—not merely in space). This now includes Gödel —but it excludes Einstein .

The lack of an adequate definition of ‘time travel’ does not matter for our purposes here. [ 8 ] It suffices that we have clear cases of (what would count as) time travel—and that these cases give rise to all the problems that we shall wish to discuss.

Some authors (in philosophy, physics and science fiction) consider ‘time travel’ scenarios in which there are two temporal dimensions (e.g. Meiland (1974)), and others consider scenarios in which there are multiple ‘parallel’ universes—each one with its own four-dimensional spacetime (e.g. Deutsch and Lockwood (1994)). There is a question whether travelling to another version of 2001 (i.e. not the very same version one experienced in the past)—a version at a different point on the second time dimension, or in a different parallel universe—is really time travel, or whether it is more akin to Virtual . In any case, this kind of scenario does not give rise to many of the problems thrown up by the idea of travelling to the very same past one experienced in one’s younger days. It is these problems that form the primary focus of the present entry, and so we shall not have much to say about other kinds of ‘time travel’ scenario in what follows.

One objection to the possibility of time travel flows directly from attempts to define it in anything like Lewis’s way. The worry is that because time travel involves “a discrepancy between time and time”, time travel scenarios are simply incoherent. The time traveller traverses thirty years in one year; she is 51 years old 21 years after her birth; she dies at the age of 100, 200 years before her birth; and so on. The objection is that these are straightforward contradictions: the basic description of what time travel involves is inconsistent; therefore time travel is logically impossible. [ 9 ]

There must be something wrong with this objection, because it would show Einstein to be logically impossible—whereas this sort of future-directed time travel has actually been observed (albeit on a much smaller scale—but that does not affect the present point) (Hafele and Keating, 1972b,a). The most common response to the objection is that there is no contradiction because the interval of time traversed by the time traveller and the duration of her journey are measured with respect to different frames of reference: there is thus no reason why they should coincide. A similar point applies to the discrepancy between the time elapsed since the time traveller’s birth and her age upon arrival. There is no more of a contradiction here than in the fact that Melbourne is both 800 kilometres away from Sydney—along the main highway—and 1200 kilometres away—along the coast road. [ 10 ]

Before leaving the question ‘What is time travel?’ we should note the crucial distinction between changing the past and participating in (aka affecting or influencing) the past. [ 11 ] In the popular imagination, backwards time travel would allow one to change the past: to right the wrongs of history, to prevent one’s younger self doing things one later regretted, and so on. In a model with a single past, however, this idea is incoherent: the very description of the case involves a contradiction (e.g. the time traveller burns all her diaries at midnight on her fortieth birthday in 1976, and does not burn all her diaries at midnight on her fortieth birthday in 1976). It is not as if there are two versions of the past: the original one, without the time traveller present, and then a second version, with the time traveller playing a role. There is just one past—and two perspectives on it: the perspective of the younger self, and the perspective of the older time travelling self. If these perspectives are inconsistent (e.g. an event occurs in one but not the other) then the time travel scenario is incoherent.

This means that time travellers can do less than we might have hoped: they cannot right the wrongs of history; they cannot even stir a speck of dust on a certain day in the past if, on that day, the speck was in fact unmoved. But this does not mean that time travellers must be entirely powerless in the past: while they cannot do anything that did not actually happen, they can (in principle) do anything that did happen. Time travellers cannot change the past: they cannot make it different from the way it was—but they can participate in it: they can be amongst the people who did make the past the way it was. [ 12 ]

What about models involving two temporal dimensions, or parallel universes—do they allow for coherent scenarios in which the past is changed? [ 13 ] There is certainly no contradiction in saying that the time traveller burns all her diaries at midnight on her fortieth birthday in 1976 in universe 1 (or at hypertime A ), and does not burn all her diaries at midnight on her fortieth birthday in 1976 in universe 2 (or at hypertime B ). The question is whether this kind of story involves changing the past in the sense originally envisaged: righting the wrongs of history, preventing subsequently regretted actions, and so on. Goddu (2003) and van Inwagen (2010) argue that it does (in the context of particular hypertime models), while Smith (1997, 365–6; 2015) argues that it does not: that it involves avoiding the past—leaving it untouched while travelling to a different version of the past in which things proceed differently.

2. The Grandfather Paradox

The most important objection to the logical possibility of backwards time travel is the so-called Grandfather paradox. This paradox has actually convinced many people that backwards time travel is impossible:

The dead giveaway that true time-travel is flatly impossible arises from the well-known “paradoxes” it entails. The classic example is “What if you go back into the past and kill your grandfather when he was still a little boy?”…So complex and hopeless are the paradoxes…that the easiest way out of the irrational chaos that results is to suppose that true time-travel is, and forever will be, impossible. (Asimov 1995 [2003, 276–7]) travel into one’s past…would seem to give rise to all sorts of logical problems, if you were able to change history. For example, what would happen if you killed your parents before you were born. It might be that one could avoid such paradoxes by some modification of the concept of free will. But this will not be necessary if what I call the chronology protection conjecture is correct: The laws of physics prevent closed timelike curves from appearing . (Hawking, 1992, 604) [ 14 ]

The paradox comes in different forms. Here’s one version:

If time travel was logically possible then the time traveller could return to the past and in a suicidal rage destroy his time machine before it was completed and murder his younger self. But if this was so a necessary condition for the time trip to have occurred at all is removed, and we should then conclude that the time trip did not occur. Hence if the time trip did occur, then it did not occur. Hence it did not occur, and it is necessary that it did not occur. To reply, as it is standardly done, that our time traveller cannot change the past in this way, is a petitio principii . Why is it that the time traveller is constrained in this way? What mysterious force stills his sudden suicidal rage? (Smith, 1985, 58)

The idea is that backwards time travel is impossible because if it occurred, time travellers would attempt to do things such as kill their younger selves (or their grandfathers etc.). We know that doing these things—indeed, changing the past in any way—is impossible. But were there time travel, there would then be nothing left to stop these things happening. If we let things get to the stage where the time traveller is facing Grandfather with a loaded weapon, then there is nothing left to prevent the impossible from occurring. So we must draw the line earlier: it must be impossible for someone to get into this situation at all; that is, backwards time travel must be impossible.

In order to defend the possibility of time travel in the face of this argument we need to show that time travel is not a sure route to doing the impossible. So, given that a time traveller has gone to the past and is facing Grandfather, what could stop her killing Grandfather? Some science fiction authors resort to the idea of chaperones or time guardians who prevent time travellers from changing the past—or to mysterious forces of logic. But it is hard to take these ideas seriously—and more importantly, it is hard to make them work in detail when we remember that changing the past is impossible. (The chaperone is acting to ensure that the past remains as it was—but the only reason it ever was that way is because of his very actions.) [ 15 ] Fortunately there is a better response—also to be found in the science fiction literature, and brought to the attention of philosophers by Lewis (1976). What would stop the time traveller doing the impossible? She would fail “for some commonplace reason”, as Lewis (1976, 150) puts it. Her gun might jam, a noise might distract her, she might slip on a banana peel, etc. Nothing more than such ordinary occurrences is required to stop the time traveller killing Grandfather. Hence backwards time travel does not entail the occurrence of impossible events—and so the above objection is defused.

A problem remains. Suppose Tim, a time-traveller, is facing his grandfather with a loaded gun. Can Tim kill Grandfather? On the one hand, yes he can. He is an excellent shot; there is no chaperone to stop him; the laws of logic will not magically stay his hand; he hates Grandfather and will not hesitate to pull the trigger; etc. On the other hand, no he can’t. To kill Grandfather would be to change the past, and no-one can do that (not to mention the fact that if Grandfather died, then Tim would not have been born). So we have a contradiction: Tim can kill Grandfather and Tim cannot kill Grandfather. Time travel thus leads to a contradiction: so it is impossible.

Note the difference between this version of the Grandfather paradox and the version considered above. In the earlier version, the contradiction happens if Tim kills Grandfather. The solution was to say that Tim can go into the past without killing Grandfather—hence time travel does not entail a contradiction. In the new version, the contradiction happens as soon as Tim gets to the past. Of course Tim does not kill Grandfather—but we still have a contradiction anyway: for he both can do it, and cannot do it. As Lewis puts it:

Could a time traveler change the past? It seems not: the events of a past moment could no more change than numbers could. Yet it seems that he would be as able as anyone to do things that would change the past if he did them. If a time traveler visiting the past both could and couldn’t do something that would change it, then there cannot possibly be such a time traveler. (Lewis, 1976, 149)

Lewis’s own solution to this problem has been widely accepted. [ 16 ] It turns on the idea that to say that something can happen is to say that its occurrence is compossible with certain facts, where context determines (more or less) which facts are the relevant ones. Tim’s killing Grandfather in 1921 is compossible with the facts about his weapon, training, state of mind, and so on. It is not compossible with further facts, such as the fact that Grandfather did not die in 1921. Thus ‘Tim can kill Grandfather’ is true in one sense (relative to one set of facts) and false in another sense (relative to another set of facts)—but there is no single sense in which it is both true and false. So there is no contradiction here—merely an equivocation.

Another response is that of Vihvelin (1996), who argues that there is no contradiction here because ‘Tim can kill Grandfather’ is simply false (i.e. contra Lewis, there is no legitimate sense in which it is true). According to Vihvelin, for ‘Tim can kill Grandfather’ to be true, there must be at least some occasions on which ‘If Tim had tried to kill Grandfather, he would or at least might have succeeded’ is true—but, Vihvelin argues, at any world remotely like ours, the latter counterfactual is always false. [ 17 ]

Return to the original version of the Grandfather paradox and Lewis’s ‘commonplace reasons’ response to it. This response engenders a new objection—due to Horwich (1987)—not to the possibility but to the probability of backwards time travel.

Think about correlated events in general. Whenever we see two things frequently occurring together, this is because one of them causes the other, or some third thing causes both. Horwich calls this the Principle of V-Correlation:

if events of type A and B are associated with one another, then either there is always a chain of events between them…or else we find an earlier event of type C that links up with A and B by two such chains of events. What we do not see is…an inverse fork—in which A and B are connected only with a characteristic subsequent event, but no preceding one. (Horwich, 1987, 97–8)

For example, suppose that two students turn up to class wearing the same outfits. That could just be a coincidence (i.e. there is no common cause, and no direct causal link between the two events). If it happens every week for the whole semester, it is possible that it is a coincidence, but this is extremely unlikely . Normally, we see this sort of extensive correlation only if either there is a common cause (e.g. both students have product endorsement deals with the same clothing company, or both slavishly copy the same influencer) or a direct causal link (e.g. one student is copying the other).

Now consider the time traveller setting off to kill her younger self. As discussed, no contradiction need ensue—this is prevented not by chaperones or mysterious forces, but by a run of ordinary occurrences in which the trigger falls off the time traveller’s gun, a gust of wind pushes her bullet off course, she slips on a banana peel, and so on. But now consider this run of ordinary occurrences. Whenever the time traveller contemplates auto-infanticide, someone nearby will drop a banana peel ready for her to slip on, or a bird will begin to fly so that it will be in the path of the time traveller’s bullet by the time she fires, and so on. In general, there will be a correlation between auto-infanticide attempts and foiling occurrences such as the presence of banana peels—and this correlation will be of the type that does not involve a direct causal connection between the correlated events or a common cause of both. But extensive correlations of this sort are, as we saw, extremely rare—so backwards time travel will happen about as often as you will see two people wear the same outfits to class every day of semester, without there being any causal connection between what one wears and what the other wears.

We can set out Horwich’s argument this way:

• If time travel were ever to occur, we should see extensive uncaused correlations.
• It is extremely unlikely that we should ever see extensive uncaused correlations.
• Therefore time travel is extremely unlikely to occur.

The conclusion is not that time travel is impossible, but that we should treat it the way we treat the possibility of, say, tossing a fair coin and getting heads one thousand times in a row. As Price (1996, 278 n.7) puts it—in the context of endorsing Horwich’s conclusion: “the hypothesis of time travel can be made to imply propositions of arbitrarily low probability. This is not a classical reductio, but it is as close as science ever gets.”

Smith (1997) attacks both premisses of Horwich’s argument. Against the first premise, he argues that backwards time travel, in itself, does not entail extensive uncaused correlations. Rather, when we look more closely, we see that time travel scenarios involving extensive uncaused correlations always build in prior coincidences which are themselves highly unlikely. Against the second premise, he argues that, from the fact that we have never seen extensive uncaused correlations, it does not follow that we never shall. This is not inductive scepticism: let us assume (contra the inductive sceptic) that in the absence of any specific reason for thinking things should be different in the future, we are entitled to assume they will continue being the same; still we cannot dismiss a specific reason for thinking the future will be a certain way simply on the basis that things have never been that way in the past. You might reassure an anxious friend that the sun will certainly rise tomorrow because it always has in the past—but you cannot similarly refute an astronomer who claims to have discovered a specific reason for thinking that the earth will stop rotating overnight.

Sider (2002, 119–20) endorses Smith’s second objection. Dowe (2003) criticises Smith’s first objection, but agrees with the second, concluding overall that time travel has not been shown to be improbable. Ismael (2003) reaches a similar conclusion. Goddu (2007) criticises Smith’s first objection to Horwich. Further contributions to the debate include Arntzenius (2006), Smeenk and Wüthrich (2011, §2.2) and Elliott (2018). For other arguments to the same conclusion as Horwich’s—that time travel is improbable—see Ney (2000) and Effingham (2020).

Return again to the original version of the Grandfather paradox and Lewis’s ‘commonplace reasons’ response to it. This response engenders a further objection. The autoinfanticidal time traveller is attempting to do something impossible (render herself permanently dead from an age younger than her age at the time of the attempts). Suppose we accept that she will not succeed and that what will stop her is a succession of commonplace occurrences. The previous objection was that such a succession is improbable . The new objection is that the exclusion of the time traveler from successfully committing auto-infanticide is mysteriously inexplicable . The worry is as follows. Each particular event that foils the time traveller is explicable in a perfectly ordinary way; but the inevitable combination of these events amounts to a ring-fencing of the forbidden zone of autoinfanticide—and this ring-fencing is mystifying. It’s like a grand conspiracy to stop the time traveler from doing what she wants to do—and yet there are no conspirators: no time lords, no magical forces of logic. This is profoundly perplexing. Riggs (1997, 52) writes: “Lewis’s account may do for a once only attempt, but is untenable as a general explanation of Tim’s continual lack of success if he keeps on trying.” Ismael (2003, 308) writes: “Considered individually, there will be nothing anomalous in the explanations…It is almost irresistible to suppose, however, that there is something anomalous in the cases considered collectively, i.e., in our unfailing lack of success.” See also Gorovitz (1964, 366–7), Horwich (1987, 119–21) and Carroll (2010, 86).

There have been two different kinds of defense of time travel against the objection that it involves mysteriously inexplicable occurrences. Baron and Colyvan (2016, 70) agree with the objectors that a purely causal explanation of failure—e.g. Tim fails to kill Grandfather because first he slips on a banana peel, then his gun jams, and so on—is insufficient. However they argue that, in addition, Lewis offers a non-causal—a logical —explanation of failure: “What explains Tim’s failure to kill his grandfather, then, is something about logic; specifically: Tim fails to kill his grandfather because the law of non-contradiction holds.” Smith (2017) argues that the appearance of inexplicability is illusory. There are no scenarios satisfying the description ‘a time traveller commits autoinfanticide’ (or changes the past in any other way) because the description is self-contradictory (e.g. it involves the time traveller permanently dying at 20 and also being alive at 40). So whatever happens it will not be ‘that’. There is literally no way for the time traveller not to fail. Hence there is no need for—or even possibility of—a substantive explanation of why failure invariably occurs, and such failure is not perplexing.

3. Causation

Backwards time travel scenarios give rise to interesting issues concerning causation. In this section we examine two such issues.

Earlier we distinguished changing the past and affecting the past, and argued that while the former is impossible, backwards time travel need involve only the latter. Affecting the past would be an example of backwards causation (i.e. causation where the effect precedes its cause)—and it has been argued that this too is impossible, or at least problematic. [ 18 ] The classic argument against backwards causation is the bilking argument . [ 19 ] Faced with the claim that some event A causes an earlier event B , the proponent of the bilking objection recommends an attempt to decorrelate A and B —that is, to bring about A in cases in which B has not occurred, and to prevent A in cases in which B has occurred. If the attempt is successful, then B often occurs despite the subsequent nonoccurrence of A , and A often occurs without B occurring, and so A cannot be the cause of B . If, on the other hand, the attempt is unsuccessful—if, that is, A cannot be prevented when B has occurred, nor brought about when B has not occurred—then, it is argued, it must be B that is the cause of A , rather than vice versa.

The bilking procedure requires repeated manipulation of event A . Thus, it cannot get under way in cases in which A is either unrepeatable or unmanipulable. Furthermore, the procedure requires us to know whether or not B has occurred, prior to manipulating A —and thus, it cannot get under way in cases in which it cannot be known whether or not B has occurred until after the occurrence or nonoccurrence of A (Dummett, 1964). These three loopholes allow room for many claims of backwards causation that cannot be touched by the bilking argument, because the bilking procedure cannot be performed at all. But what about those cases in which it can be performed? If the procedure succeeds—that is, A and B are decorrelated—then the claim that A causes B is refuted, or at least weakened (depending upon the details of the case). But if the bilking attempt fails, it does not follow that it must be B that is the cause of A , rather than vice versa. Depending upon the situation, that B causes A might become a viable alternative to the hypothesis that A causes B —but there is no reason to think that this alternative must always be the superior one. For example, suppose that I see a photo of you in a paper dated well before your birth, accompanied by a report of your arrival from the future. I now try to bilk your upcoming time trip—but I slip on a banana peel while rushing to push you away from your time machine, my time travel horror stories only inspire you further, and so on. Or again, suppose that I know that you were not in Sydney yesterday. I now try to get you to go there in your time machine—but first I am struck by lightning, then I fall down a manhole, and so on. What does all this prove? Surely not that your arrival in the past causes your departure from the future. Depending upon the details of the case, it seems that we might well be entitled to describe it as involving backwards time travel and backwards causation. At least, if we are not so entitled, this must be because of other facts about the case: it would not follow simply from the repeated coincidental failures of my bilking attempts.

Backwards time travel would apparently allow for the possibility of causal loops, in which things come from nowhere. The things in question might be objects—imagine a time traveller who steals a time machine from the local museum in order to make his time trip and then donates the time machine to the same museum at the end of the trip (i.e. in the past). In this case the machine itself is never built by anyone—it simply exists. The things in question might be information—imagine a time traveller who explains the theory behind time travel to her younger self: theory that she herself knows only because it was explained to her in her youth by her time travelling older self. The things in question might be actions. Imagine a time traveller who visits his younger self. When he encounters his younger self, he suddenly has a vivid memory of being punched on the nose by a strange visitor. He realises that this is that very encounter—and resignedly proceeds to punch his younger self. Why did he do it? Because he knew that it would happen and so felt that he had to do it—but he only knew it would happen because he in fact did it. [ 20 ]

One might think that causal loops are impossible—and hence that insofar as backwards time travel entails such loops, it too is impossible. [ 21 ] There are two issues to consider here. First, does backwards time travel entail causal loops? Lewis (1976, 148) raises the question whether there must be causal loops whenever there is backwards causation; in response to the question, he says simply “I am not sure.” Mellor (1998, 131) appears to claim a positive answer to the question. [ 22 ] Hanley (2004, 130) defends a negative answer by telling a time travel story in which there is backwards time travel and backwards causation, but no causal loops. [ 23 ] Monton (2009) criticises Hanley’s counterexample, but also defends a negative answer via different counterexamples. Effingham (2020) too argues for a negative answer.

Second, are causal loops impossible, or in some other way objectionable? One objection is that causal loops are inexplicable . There have been two main kinds of response to this objection. One is to agree but deny that this is a problem. Lewis (1976, 149) accepts that a loop (as a whole) would be inexplicable—but thinks that this inexplicability (like that of the Big Bang or the decay of a tritium atom) is merely strange, not impossible. In a similar vein, Meyer (2012, 263) argues that if someone asked for an explanation of a loop (as a whole), “the blame would fall on the person asking the question, not on our inability to answer it.” The second kind of response (Hanley, 2004, §5) is to deny that (all) causal loops are inexplicable. A second objection to causal loops, due to Mellor (1998, ch.12), is that in such loops the chances of events would fail to be related to their frequencies in accordance with the law of large numbers. Berkovitz (2001) and Dowe (2001) both argue that Mellor’s objection fails to establish the impossibility of causal loops. [ 24 ] Effingham (2020) considers—and rebuts—some additional objections to the possibility of causal loops.

4. Time and Change

Gödel (1949a [1990a])—in which Gödel presents models of Einstein’s General Theory of Relativity in which there exist CTC’s—can well be regarded as initiating the modern academic literature on time travel, in both philosophy and physics. In a companion paper, Gödel discusses the significance of his results for more general issues in the philosophy of time (Gödel 1949b [1990b]). For the succeeding half century, the time travel literature focussed predominantly on objections to the possibility (or probability) of time travel. More recently, however, there has been renewed interest in the connections between time travel and more general issues in the metaphysics of time and change. We examine some of these in the present section. [ 25 ]

The first thing that we need to do is set up the various metaphysical positions whose relationships with time travel will then be discussed. Consider two metaphysical questions:

• Are the past, present and future equally real?
• Is there an objective flow or passage of time, and an objective now?

We can label some views on the first question as follows. Eternalism is the view that past and future times, objects and events are just as real as the present time and present events and objects. Nowism is the view that only the present time and present events and objects exist. Now-and-then-ism is the view that the past and present exist but the future does not. We can also label some views on the second question. The A-theory answers in the affirmative: the flow of time and division of events into past (before now), present (now) and future (after now) are objective features of reality (as opposed to mere features of our experience). Furthermore, they are linked: the objective flow of time arises from the movement, through time, of the objective now (from the past towards the future). The B-theory answers in the negative: while we certainly experience now as special, and time as flowing, the B-theory denies that what is going on here is that we are detecting objective features of reality in a way that corresponds transparently to how those features are in themselves. The flow of time and the now are not objective features of reality; they are merely features of our experience. By combining answers to our first and second questions we arrive at positions on the metaphysics of time such as: [ 26 ]

• the block universe view: eternalism + B-theory
• the moving spotlight view: eternalism + A-theory
• the presentist view: nowism + A-theory
• the growing block view: now-and-then-ism + A-theory.

So much for positions on time itself. Now for some views on temporal objects: objects that exist in (and, in general, change over) time. Three-dimensionalism is the view that persons, tables and other temporal objects are three-dimensional entities. On this view, what you see in the mirror is a whole person. [ 27 ] Tomorrow, when you look again, you will see the whole person again. On this view, persons and other temporal objects are wholly present at every time at which they exist. Four-dimensionalism is the view that persons, tables and other temporal objects are four-dimensional entities, extending through three dimensions of space and one dimension of time. On this view, what you see in the mirror is not a whole person: it is just a three-dimensional temporal part of a person. Tomorrow, when you look again, you will see a different such temporal part. Say that an object persists through time if it is around at some time and still around at a later time. Three- and four-dimensionalists agree that (some) objects persist, but they differ over how objects persist. According to three-dimensionalists, objects persist by enduring : an object persists from t 1 to t 2 by being wholly present at t 1 and t 2 and every instant in between. According to four-dimensionalists, objects persist by perduring : an object persists from t 1 to t 2 by having temporal parts at t 1 and t 2 and every instant in between. Perduring can be usefully compared with being extended in space: a road extends from Melbourne to Sydney not by being wholly located at every point in between, but by having a spatial part at every point in between.

It is natural to combine three-dimensionalism with presentism and four-dimensionalism with the block universe view—but other combinations of views are certainly possible.

Gödel (1949b [1990b]) argues from the possibility of time travel (more precisely, from the existence of solutions to the field equations of General Relativity in which there exist CTC’s) to the B-theory: that is, to the conclusion that there is no objective flow or passage of time and no objective now. Gödel begins by reviewing an argument from Special Relativity to the B-theory: because the notion of simultaneity becomes a relative one in Special Relativity, there is no room for the idea of an objective succession of “nows”. He then notes that this argument is disrupted in the context of General Relativity, because in models of the latter theory to date, the presence of matter does allow recovery of an objectively distinguished series of “nows”. Gödel then proposes a new model (Gödel 1949a [1990a]) in which no such recovery is possible. (This is the model that contains CTC’s.) Finally, he addresses the issue of how one can infer anything about the nonexistence of an objective flow of time in our universe from the existence of a merely possible universe in which there is no objectively distinguished series of “nows”. His main response is that while it would not be straightforwardly contradictory to suppose that the existence of an objective flow of time depends on the particular, contingent arrangement and motion of matter in the world, this would nevertheless be unsatisfactory. Responses to Gödel have been of two main kinds. Some have objected to the claim that there is no objective flow of time in his model universe (e.g. Savitt (2005); see also Savitt (1994)). Others have objected to the attempt to transfer conclusions about that model universe to our own universe (e.g. Earman (1995, 197–200); for a partial response to Earman see Belot (2005, §3.4)). [ 28 ]

Earlier we posed two questions:

Gödel’s argument is related to the second question. Let’s turn now to the first question. Godfrey-Smith (1980, 72) writes “The metaphysical picture which underlies time travel talk is that of the block universe [i.e. eternalism, in the terminology of the present entry], in which the world is conceived as extended in time as it is in space.” In his report on the Analysis problem to which Godfrey-Smith’s paper is a response, Harrison (1980, 67) replies that he would like an argument in support of this assertion. Here is an argument: [ 29 ]

A fundamental requirement for the possibility of time travel is the existence of the destination of the journey. That is, a journey into the past or the future would have to presuppose that the past or future were somehow real. (Grey, 1999, 56)

Dowe (2000, 442–5) responds that the destination does not have to exist at the time of departure: it only has to exist at the time of arrival—and this is quite compatible with non-eternalist views. And Keller and Nelson (2001, 338) argue that time travel is compatible with presentism:

There is four-dimensional [i.e. eternalist, in the terminology of the present entry] time-travel if the appropriate sorts of events occur at the appropriate sorts of times; events like people hopping into time-machines and disappearing, people reappearing with the right sorts of memories, and so on. But the presentist can have just the same patterns of events happening at just the same times. Or at least, it can be the case on the presentist model that the right sorts of events will happen, or did happen, or are happening, at the rights sorts of times. If it suffices for four-dimensionalist time-travel that Jennifer disappears in 2054 and appears in 1985 with the right sorts of memories, then why shouldn’t it suffice for presentist time-travel that Jennifer will disappear in 2054, and that she did appear in 1985 with the right sorts of memories?

Sider (2005) responds that there is still a problem reconciling presentism with time travel conceived in Lewis’s way: that conception of time travel requires that personal time is similar to external time—but presentists have trouble allowing this. Further contributions to the debate whether presentism—and other versions of the A-theory—are compatible with time travel include Monton (2003), Daniels (2012), Hall (2014) and Wasserman (2018) on the side of compatibility, and Miller (2005), Slater (2005), Miller (2008), Hales (2010) and Markosian (2020) on the side of incompatibility.

Leibniz’s Law says that if x = y (i.e. x and y are identical—one and the same entity) then x and y have exactly the same properties. There is a superficial conflict between this principle of logic and the fact that things change. If Bill is at one time thin and at another time not so—and yet it is the very same person both times—it looks as though the very same entity (Bill) both possesses and fails to possess the property of being thin. Three-dimensionalists and four-dimensionalists respond to this problem in different ways. According to the four-dimensionalist, what is thin is not Bill (who is a four-dimensional entity) but certain temporal parts of Bill; and what is not thin are other temporal parts of Bill. So there is no single entity that both possesses and fails to possess the property of being thin. Three-dimensionalists have several options. One is to deny that there are such properties as ‘thin’ (simpliciter): there are only temporally relativised properties such as ‘thin at time t ’. In that case, while Bill at t 1 and Bill at t 2 are the very same entity—Bill is wholly present at each time—there is no single property that this one entity both possesses and fails to possess: Bill possesses the property ‘thin at t 1 ’ and lacks the property ‘thin at t 2 ’. [ 30 ]

Now consider the case of a time traveller Ben who encounters his younger self at time t . Suppose that the younger self is thin and the older self not so. The four-dimensionalist can accommodate this scenario easily. Just as before, what we have are two different three-dimensional parts of the same four-dimensional entity, one of which possesses the property ‘thin’ and the other of which does not. The three-dimensionalist, however, faces a problem. Even if we relativise properties to times, we still get the contradiction that Ben possesses the property ‘thin at t ’ and also lacks that very same property. [ 31 ] There are several possible options for the three-dimensionalist here. One is to relativise properties not to external times but to personal times (Horwich, 1975, 434–5); another is to relativise properties to spatial locations as well as to times (or simply to spacetime points). Sider (2001, 101–6) criticises both options (and others besides), concluding that time travel is incompatible with three-dimensionalism. Markosian (2004) responds to Sider’s argument; [ 32 ] Miller (2006) also responds to Sider and argues for the compatibility of time travel and endurantism; Gilmore (2007) seeks to weaken the case against endurantism by constructing analogous arguments against perdurantism. Simon (2005) finds problems with Sider’s arguments, but presents different arguments for the same conclusion; Effingham and Robson (2007) and Benovsky (2011) also offer new arguments for this conclusion. For further discussion see Wasserman (2018) and Effingham (2020). [ 33 ]

We have seen arguments to the conclusions that time travel is impossible, improbable and inexplicable. Here’s an argument to the conclusion that backwards time travel simply will not occur. If backwards time travel is ever going to occur, we would already have seen the time travellers—but we have seen none such. [ 34 ] The argument is a weak one. [ 35 ] For a start, it is perhaps conceivable that time travellers have already visited the Earth [ 36 ] —but even granting that they have not, this is still compatible with the future actuality of backwards time travel. First, it may be that time travel is very expensive, difficult or dangerous—or for some other reason quite rare—and that by the time it is available, our present period of history is insufficiently high on the list of interesting destinations. Second, it may be—and indeed existing proposals in the physics literature have this feature—that backwards time travel works by creating a CTC that lies entirely in the future: in this case, backwards time travel becomes possible after the creation of the CTC, but travel to a time earlier than the time at which the CTC is created is not possible. [ 37 ]

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• Time Travel , entry by Joel Hunter (Truckee Meadows Community College) in the Internet Encyclopedia of Philosophy .

causation: backward | free will: divine foreknowledge and | identity: over time | location and mereology | temporal parts | time | time machines | time travel: and modern physics

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Time Travel Probably Isn't Possible—Why Do We Wish It Were?

Time travel exerts an irresistible pull on our scientific and storytelling imagination.

Since H.G. Wells imagined that time was a fourth dimension —and Einstein confirmed it—the idea of time travel has captivated us. More than 50 scientific papers are published on time travel each year, and storytellers continually explore it—from Stephen King’s JFK assassination novel 11/22/63 to the steamy Outlander television series to Woody Allen’s comedy Midnight in Paris . What if we could travel back in time, we wonder, and change history? Assassinate Hitler or marry that high school sweetheart who dumped us? What if we could see what the future has in store?

These are some of the ideas that bestselling author James Gleick explores in his thought-provoking new book, Time Travel: A History. Speaking from his home in New York City, he recalls how Stephen Hawking once sent out invitations to a party that had already taken place ; why the Chinese government has branded time travel as “incorrect” and “frivolous” ; and how the idea of time travel is, ultimately, about our desire to defeat death.

Let’s cut right to the chase: What is time?

Oh, no, you didn’t! [ Laughs. ] In A.D. 400, St. Augustine said—and many people have said the same thing since, either quoting him consciously or unconsciously—“What, then, is time? If no one asks me, I know. If I wish to explain it to one that asks, I know not.” I think that is actually not a quip, but quite profound.

The best way to understand time is to recognize that we actually are very sophisticated about it. Over the past century-plus, we’ve learned a great deal. The physicist John Archibald Wheeler said, “Time is nature’s way to keep everything from happening all at once.” If you look it up in a dictionary, you get stuff like, “The general term for the experience of duration.” But that’s just completely punting because what is duration ?

I try to steer away from aphorisms and dictionary definitions, just to say two things. First, that we have a lot of contradictory ways of talking about time. We think of time as something we waste, spend, or save, as if it’s a quantity. We also think of time as a medium we are passing through every day, a river carrying us along. All of these notions are aspects of a complicated subject that has no bumper sticker answer.

When does the idea of time travel first appear in the West? And how did it impact popular culture?

I assumed, as a person who always read sci-fi a lot when I was a kid, that time travel is an obvious idea we’re born knowing and fantasizing about. And that it must always have been part of human culture, that there must be time travel Greek myths and Chinese legends. But there aren’t! Time travel turns out to be a very new idea that essentially starts with H.G. Wells’s 1895 novel, The Time Machine . Before that nobody thought of putting the words time and travel together. The closest you can come before that is people falling asleep, like Rip Van Winkle, or fantasies like Charles Dickens’s A Christmas Carol .

The beginning of my book is an attempt to answer the question, “Why? Why not before? Why suddenly at the end of the 19 th century was it possible— necessary— for people to dream up this crazy fantasy?” Even though it’s H.G. Wells who does it, people pick up his ball very quickly and run with it. You find it in American science fiction that started appearing in pulp magazines in the 1920s and 1930s, or in the great new modernist literature of Marcel Proust’s In Search of Lost Time , James Joyce, and Virginia Woolf.

All these writers were suddenly making time their explicit subject, twisting time in new ways, inventing new narrative techniques to deal with time, to explore the vagaries of memory or the way our consciousness changes over time.

In 1991, Stephen Hawking wrote a paper called “Chronology Protection Conjecture , ” in which he asked: If time travel is possible, why are we not inundated with tourists from the future? He has a point, doesn’t he?

Yes! He even scheduled a party and sent out an invitation inviting time travelers to come to a party that had taken place in the past. Then he observed that none of them had shown up. [Laughs.] Hawking is one of these physicists who love playing with the idea of time travel. It’s irresistible because it’s so much fun! When he talks about the paradoxes of time travel it’s because he’s reading the same science fiction stories as the rest of us.

The paradoxes started appearing in magazines aimed mostly at young people in the 1920s. Somebody wrote in and said, “Time travel is a weird idea, because what if you go back in time and you kill your grandfather? Then your grandfather never meets your grandmother and you’re never born.” It’s an impossible loop.

Hawking, like other physicists, decided, “Time is my business. What if we take this seriously? Can we express this in physical terms?” I don’t think he succeeded but what he proposed was that the reason these paradoxes can’t happen is because the universe takes care of itself. It can’t happen because it didn’t happen. That’s the simple way of saying what the chronology protection conjecture is.

How have the Internet and other new technologies changed our perception and experience of time?

We are just beginning to see what the Internet is doing to our perception of time. We are living more and more in this networked world in which everything travels at light speed. We are multitasking and experiencing new forms of simultaneity, so the Internet appears to us as a kind of hall of mirrors. It feels as though we’re embedded in an ever expanding present.

Our sense of the past changes because in some ways the past becomes more vivid than ever. We’re looking at the past on our video screens and it’s just as vivid if the movie is about something that happened 20 years ago, as if it is a live stream. We can’t always tell the difference. On the other hand, the past that’s more distant—and isn’t available in video form—starts to seem more remote and fuzzier. Maybe we are forgetting how to visualize the past from reading histories. We’re entering a new period of time confusion, in which we suddenly find ourselves in what looks like an unending present.

In 2011, the Chinese government issued an extraordinary denunciation of the idea of time travel. What was their beef?

They thought it was corrupting and decadent. It’s a reminder that time travel is neither a simple nor innocent idea. It’s very powerful. It enables us to imagine alternative universes, and this is another line that science fiction writers have explored. What if someone was able to go back in time and kill Hitler?

Time travel is also a powerful way of allowing us to imagine what the future might bring. A lot of futurists nowadays tend to be dystopian. Time travel gives us ways of exploring how the worst tendencies of our current societies could grow even worse. That’s what George Orwell did in 1984 . I imagine the Chinese government doesn’t particularly want the equivalent of 1984 to be published in Beijing. [ Laughs. ]

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More than 50 scientific papers a year are now published on the idea of time travel. why are scientists drawn to the subject.

Scientists live in the same science fictional universe as all the rest of us. Time travel is a sexy and romantic idea that appeals to the physicist as much as it appeals to every teenager. I don’t think scientists are ever going to solve the problem of time travel for us but they still love to talk about wormholes and dark matter.

There’s a fascinating coincidence in the early history that when H.G. Wells needed to set the stage for his time machine hurtling into the future, he decided not to just jump right into his story but set the scene with a framing device—his time traveler lecturing a group of friends on the science of time—in order to justify the possibility of a time machine. His lecture introduces the idea that time is nothing more than a fourth dimension, that traveling through time is analogous to traveling through space. Since we have machines that can take us into any of the three special dimensions, including balloons and elevators, why shouldn’t we have a machine able to travel through the fourth dimension?

A decade later, Einstein burst onto the scene with his theory of relativity in which time is a fourth dimension , just like space. Soon after that, Hermann Minkowski pronounced that, henceforth, we were not going to talk about space and time as separate quantities but as a union of the two, spacetime , a four-dimensional continuum in which the future already exists and the past still exists.

I’m not claiming that Einstein read H.G. Wells 10 years before. But there was something in the air that both scientists and imaginative writers were empowered to visualize time in a new way. Today, that’s the way we visualize it. We’re comfortable talking about time as a fourth dimension.

You quote Ursula K. Le Guin , who writes, “Story is our only boat for sailing on the river of time.” Talk about storytelling and its relationship to time.

One of the things that has happened, along with our heightened awareness of time and its possibilities, is that people who invent narratives have learned very clever new techniques. Literal time travel is only one of them. You don’t actually need to send your hero into the future or into the past to write a story that plays with time in clever new ways. Narrative is also how everybody, not just writers, constructs a vision of our own relationship with time. We imagine the future. We remember the past. When we do that, we’re making up stories.

Psychologists are learning something that great storytellers have known for some time, which is that memory is not like computer retrieval. It’s an active process. Every time we remember something we are remembering it a little bit differently. We’re retelling the story to ourselves.

If time travel is impossible, why do we continue to be so fascinated with the idea?

One of the reasons is we want to go back and undo our mistakes. When you ask yourself, “If I had a time machine, what would I do?” sometimes the answer is, “I would go back to this particular day and do that thing over.” I think one of the great time travel movies is Groundhog Day , the Bill Murray movie where he wakes up every morning and has to live the same day over and over again. He gradually realizes that perhaps fate is telling him he needs to do it over, right. Regret is the time traveler’s energy bar. But that’s not the only motivation for time travel. We also have curiosity about the future and interest in our parents and our children. A lot of time travel fiction is a way of asking questions about what our parents were like, or what our children will be like.

At some point during the four years I worked on this book, I also realized that, in one way or another, every time travel story is about death. Death is either explicitly there in the foreground or lurking in the background because time is a bastard, right? Time is brutal. What does time do to us? It kills us. Time travel is our way of flirting with immortality. It’s the closest we’re going to come to it.

This interview was edited for length and clarity.

Simon Worrall curates Book Talk . Follow him on Twitter or at simonworrallauthor.com .

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Essay on Time Travel

Students are often asked to write an essay on Time Travel in their schools and colleges. And if you’re also looking for the same, we have created 100-word, 250-word, and 500-word essays on the topic.

Let’s take a look…

100 Words Essay on Time Travel

What is time travel.

Time travel means moving back or forward in time. It’s like skipping chapters in a book. Instead of reading in order, you jump to the past or future. Imagine going back to see dinosaurs or forward to meet robots. It’s a popular idea in stories and movies.

Time Machines

In stories, people use time machines to travel in time. These machines can be anything from cars to watches. The idea is to control time as easily as turning a page in a book. But in real life, we can’t do this yet.

Why Time Travel Fascinates Us

Time travel excites us because it offers endless possibilities. We could fix mistakes or see what the future holds. It’s about exploring unknowns and asking “what if?” This curiosity makes time travel a captivating concept for all ages.

Also check:

250 Words Essay on Time Travel

What is time travel.

Time travel is the idea of being able to move forward or backward in time. It’s a popular concept in science fiction stories, but is it actually possible?

Is time travel possible?

We don’t know for sure if time travel is possible. Some scientists believe that it might be possible, but others think that it’s impossible. There are a lot of different theories about how time travel might work, but none of them have been proven.

How would time travel work?

There are a lot of different ideas about how time travel might work. One idea is that it might be possible to travel through a wormhole. A wormhole is a kind of shortcut through space-time. If you could find a wormhole, you could use it to travel to another time.

Would time travel be dangerous?

Time travel could be very dangerous. If you traveled to the past, you could accidentally change something that would have a big impact on the future. You could also end up in a time where you don’t know anyone or anything.

Time travel is a fascinating idea, but it’s important to remember that it’s just a theory. We don’t know for sure if it’s possible, and we don’t know how it would work. Even if it is possible, it would be very dangerous.

500 Words Essay on Time Travel

Time travel is a concept that has captured the imagination of humans for centuries. It is the idea of being able to move through time, either forward or backward, to a different point in history. While time travel remains a theoretical concept, it has been a popular theme in science fiction books, movies, and TV shows.

Theories of Time Travel

The grandfather paradox.

One of the biggest challenges to the idea of time travel is the grandfather paradox. This paradox states that if someone were to travel back in time and kill their own grandfather, it would create a logical contradiction. If the grandfather is killed, then the person who traveled back in time would never have been born. However, if the person was never born, then they would not have been able to travel back in time to kill their grandfather in the first place.

The Possibility of Time Travel

Despite the challenges, some scientists believe that time travel might be possible. They argue that the laws of physics do not explicitly rule out the possibility of time travel. However, they also admit that it is very unlikely that time travel will ever be possible for humans.

The Implications of Time Travel

That’s it! I hope the essay helped you.

Apart from these, you can look at all the essays by clicking here .

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On the campus essay: learning to travel through time with my astrophysics professor.

For 35 years I’ve been traveling through time with the Princeton professor who showed that time travel is possible.

It’s 1981. I’m a senior in the astrophysics department, choosing a topic for my undergraduate thesis. I’m in the Peyton Hall office of J. Richard Gott III *73, an astrophysicist who’s building a reputation as one of the best and quirkiest teachers at Princeton. I’m 20 years old, he’s 34.

Professor Gott is a native of Louisville, Ky. He studied math and physics at Harvard before getting his Ph.D. in astrophysics at Princeton. He has a strong Kentucky drawl and a special enthusiasm for Albert Einstein’s general theory of relativity, the equations that link space and time and gravity. He leans forward in his chair and fervently talks about curvature tensors and spacetime metrics. And as I listen to him, I start to feel the same excitement.

He finds a recent issue of Scientific American and opens the magazine. “Here’s something interesting. It’s about Flatland, a hypothetical universe with only two spatial dimensions. It has length and width, but no height. You could do a thesis on that.”

I’m confused. “Flatland?”

“You could figure out how general relativity would work in a universe with only two spatial dimensions, plus the dimension of time.”

He draws a spacetime diagram to make things clearer. The vertical dimension in this diagram is the dimension of time. The top of the page is the future, and the bottom is the past. Every object in our universe follows a “world line” in this diagram, moving left and right through the spatial dimensions but also traveling inexorably upward, toward the future.

That meeting in Peyton Hall is the beginning of our journey. My world line and Professor Gott’s run close and parallel for the next six months as I struggle with the mathematics of relativity. I finally derive a solution for Flatland and rush to Dr. Gott’s office. He smiles and gives me the highest compliment that one theorist can give another: “This solution is non-trivial!”

The theory of relativity, we discover, would work very differently in Flatland than it does in our universe. There would be no gravitational attraction between massive objects, and yet those objects still would alter the geometry of the spacetime around them. It’s an interesting result. Dr. Gott and I co-author a research paper that’s published in a somewhat esoteric journal called General Relativity and Gravitation.

After I graduate from Princeton, though, I stop studying astrophysics. I fall in love with poetry and get a master’s degree in creative writing. Eventually I become a journalist. My world line diverges from Professor Gott’s.

But then something remarkable happens. My Princeton education isn’t over yet. Our world lines come back together.

It’s 1998. Oddly enough, I’m now an editor at Scientific American. My wife and I go to the American Museum of Natural History in New York City to hear a lecture by Dr. Gott. He’s made an amazing discovery: Under extraordinary circumstances, the theory of relativity allows for time travel to the past. The circumstances involve cosmic strings, infinitely long strands of high-density material that may have been created in the first moments of our universe’s history. If cosmic strings really exist — astronomers haven’t observed any yet — Professor Gott believes they could be used to build a time machine.

With his usual enthusiasm, he explains to the audience in the lecture hall how the time machine would work. First, you’d have to find two cosmic strings that are zooming past each other at nearly the speed of light. Then you’d jump into a spaceship and steer around the pair of strings in a tight circle. Because the strings radically change the geometry of the surrounding spacetime, the rocket would return to your starting point at a time before you embarked on the journey. Upon your arrival, you could shake hands with your slightly younger self and reassure him or her that the trip will be successful. Your world line has twisted into a closed curve, allowing you to loop back to an event in your past.

But wait, Dr. Gott tells the audience, there’s more! Researchers have discovered other methods of time travel allowed by Einstein’s equations, including scenarios involving wormholes — shortcuts through spacetime, like the one shown in the movie Interstellar — and exotic vacuum states. “I’m not talking about a Hoover vacuum,” Gott says passionately in his characteristic drawl. “I’m talking about a negative-energy quantum vacuum!” Even stranger, it’s possible that our universe began as a closed time loop, a vacuum state that whirled back and forth in time and simultaneously sent a branch of spacetime into the future, where it became our modern-day cosmos.

This cosmological model is appealing to physicists and philosophers because it cleverly answers an age-old question: What started the universe? If our cosmos branched off from a closed time loop, then the universe has no beginning, because every moment in time is preceded by an earlier moment. There’s no need to imagine a cosmic birth that created everything out of nothing, because it didn’t happen. Instead, the universe created itself.

These ideas about time travel and cosmology dazzle the audience at the museum. After the lecture, several people rush toward the stage to talk to Professor Gott. My wife pushes me forward. “Go on, say hello to him.”

Researchers have discovered other methods of time travel allowed by Einstein’s equations, including scenarios involving wormholes — shortcuts through spacetime, like the one shown in the movie Interstellar — and exotic vacuum states. “I’m not talking about a Hoover vacuum,” Gott says passionately in his characteristic drawl. “I’m talking about a negative-energy quantum vacuum!”

I shake my head. “No, he won’t remember me.” But I go to the stage anyway and say hello.

He smiles. “Of course, I remember you! That research we did together? On Flatland? That led to my work on cosmic strings.”

As it turns out, the spacetime around a cosmic string is very similar to the distorted geometry around massive objects in Flatland. When Dr. Gott tells me this, I sense a strange tug in my own world line. I’m looping across time.

Einstein, in one of his last letters: “The distinction between past, present and future is only an illusion.”

It’s 2007. I’m having lunch with Professor Gott at a Chinese restaurant near Princeton. We’ve stayed in touch over the past decade; we follow each other’s work and occasionally discuss the latest science news. The relationship is incredibly rewarding. I feel as if I’ve enrolled in an open-ended astrophysics course that has no final exam but keeps giving me credits.

I arranged this lunch so we can discuss a manuscript I’ve written. It’s my first novel, Final Theory, a thriller about Einstein and apocalyptic physics. Dr. Gott has scribbled comments on dozens of Post-It notes. He points at the novel, which has several physicists in its cast of characters. “Well, I recognize which character is me,” he says. “And I know which one is you. So who should play us in the movie?”

He has a soft spot for science-fiction movies, especially any film that features time travel. After we go over the casting choices, Dr. Gott corrects several mistakes I made in the first draft of the novel. In one scene, I put the wrong constellations in the summer sky. That would’ve been a humiliating error for a former astrophysics major.

It’s 2015. I’m in Professor Gott’s office again, but now my 16-year-old son, Tommy, is there too. He’s thinking about applying to Princeton and wants to meet my favorite teacher.

Dr. Gott is generous with his time. He gives Tommy a tour of the astrophysics department. He tells stories about the Intel Science Talent Search, the contest for which he served as a judge for many years. (He was a contestant when he was in high school, winning second place in 1965.) Then he switches gears and talks about space exploration and the War of the Worlds broadcast, the famous Orson Welles radio play that terrified the country in 1938 by describing a Martian invasion of New Jersey. He says he recently celebrated the anniversary of the broadcast by visiting Grover’s Mill, the site of the fictional Martian landing. It’s just a few miles from Princeton.

He keeps us enthralled for almost two hours. After we leave Peyton Hall, Tommy is thoroughly intimidated. “If you have to be that smart to get into Princeton, I don’t have a chance,” he says.

I reassure him by pointing out that very few people in the world are as smart as Professor Gott.

It’s 2016. In one of the most important discoveries of the century, scientists detect gravitational waves for the first time, providing the best evidence yet for the theory of relativity. And at the end of the spring semester, Dr. Gott will retire from the Princeton faculty. I’m 55 years old, he’s 69.

I’m glad we stayed in touch. I tell all my friends and fellow alumni that they should look up their former professors. It’s like another kind of time travel.

And you don’t even need any cosmic strings. 

Emil Friedman *73

Is Prof. Gott's time travel example two-way? After going back to the past can he return to the future? What about the paradox proposed by Larry Niven? If a method of traveling to the past were discovered, would somebody go back and do something to prevent the discovery? (One-way time travel to the future is clearly possible. All of us do it continuously.)   Nicholas Meyler '81 

The key problem in time-travel is traveling to the past. Travel to the future is already a known phenomenon (according to Relativity and the Lorentz contraction equations). A sufficiently fast rocket, near light-speed, could easily travel to the future, while the astronaut onboard ages less due to the time-dilation effect.

So, Gott's solution is about time-travel to the past, primarily. Would a paradox result? According to the "many worlds" hypothesis of Hugh Everett III (a Princeton PhD), each time-travel event creates a new universe, so that paradoxes need not exist.

When we refer to "time-travel," we are mostly referring to events that are spatio-temporally discontinuous, so not quite like just aging, although I think that counts, too.

The classical "paradox" in time-travel is called "the grandfather paradox" (i.e. could I go back in time and kill my grandfather before I was born?) ... If so, how would I get born in the first place? Everett's solution is that yes, you can go kill your grandfather, but you wouldn't be in the same Universe or "time-line" anymore, and you obviously have already been born, so you wouldn't simply "disappear," like the silly "Back to The Future" photograph.

Whether paradoxes really would ensue is somewhat dubious, though, even if time-travel were to the same Universe as it started from. Kip Thorne did extensive "thought experiments" that proved time-travel to the past was possible, with some degree of interaction. Scientists in Australia have also found similar results modeling sending particles back through wormholes, where the particles have the opportunity to interact with their previous "selves." No paradoxes arose, from what I understand.   Nicholas Meyler ’81

"Time Travel in Einstein's Universe" was an excellent book, which I thoroughly enjoyed. I was under the impression, though (and a bit sadly), that Gerard t'Hooft had shown that Gott's proposed time-machine can't work because it would "collapse the Universe".

Also, given that in Relativity (which might be true), even if two cosmic strings are rushing past each other, each nearly at the speed of light, that doesn't "add up" to faster-than-light relative motion between the two strings... since the relative speed measured from one point on one string to one point on the other string still cannot exceed lightspeed. So, my question is what mathematics justifies this contention, and what would be the slowest two cosmic strings could be moving past each other and still produce the required exotic space-time effects for a looping rocket trip to travel backwards in time?

Has Gott done any research on the idea of spinning cosmic strings (approximating a Tipler cylinder)? This might be of some interest...

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Home — Essay Samples — Geography & Travel — Tourism — A Day in the Life of a Time Traveler

A Day in The Life of a Time Traveler

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Published: Feb 7, 2024

Words: 854 | Pages: 2 | 5 min read

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A leap into history, a brush with renaissance brilliance, a glimpse of future possibilities, a journey to the heart, a race against time, the return to present, a timeless journey.

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If Time Travel Was Actually Real

So hear me when out . . . This is up for discussion.

Hypothetically speaking let’s say right now I invent time travel.

This would mean right now I am the only one with said technology but life’s goes on & one day someone else will have access to this technology (it’s inevitable).

Stay with me here. . .

Since “ I “ in this very moment created time travel I will not be able to go back farther past the time it was created (seems logical right?). I can only go forward. So that means right now, the future & futures past are the only times that can be traveled.

Now that that’s understood I want to say why I do not think it has been created yet.

Because if what I said above is true & logical that means the second I create the time travel. Everything from the time of creation & forward has already happened. Because in the future someone will come back to the time of creation. But the thing is this will happen a infinite amount of times. It will just be an absolute chaotic mess. Ppl would be coming & going, changing & destroying etc etc.

From the second time travel is created it would be its own form of uncontrollable singularity (if that’s the right word). It would just be an uncontrollable chaos.

So in that regard I do not believe time travel has been invented. Let me know if that makes sense to anyone. & I would love to hear everyone’s thoughts.

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Time Travel Essay Examples

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