Questions tagged [time-travel]

Time travel is the concept of moving between different points in time, often instigated by non-trivially topology of space-time, such as a wormhole. DO NOT USE THIS TAG for questions on changes of coordinate systems, changes of time coordinate, or topologically trivial 'twin paradox' settings.

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If I was to take light and loop it between two iron cores, like a transformer with copper; what would happen?

Precursor: I am not a physicist, and don’t claim to be. I’m sorry if the question is easily answered. Question: If I were to take light and loop it between two iron cores, similar to the way copper in ...
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3 votes
1 answer
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Why does a null entropy variation along a closed timelike curve imply a reversible process?

Carlo Rovelli in one of his articles from 2019 (reference: https://arxiv.org/abs/1912.04702) argues that time travel into the past are thermodynamically impossible: For instance, if we want to travel ...
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3 answers
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FTL travel without time travel (again)

In discussions about FTL communication and time travel, there is a simple thought experiment: the relativistic duel which is used to demonstrate that FTL travel implies time travel (I know it has a ...
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Who is traveling in future? [duplicate]

According to theory of relativity time dilation $$t=t_0 \gamma \text{ where }\gamma= \frac{1}{\sqrt{1-\frac{v^2}{c^2}}}$$ suppose time for a person $A$ is $t$ and time for a person $B$ is $t_0$ ...
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Has the possibility of time travel been proven or demonstrated? [duplicate]

This study by Lesovik et al., 2019 seems to claim they have either sent information or an electron back in time. What is the current status of the idea of time travel (at least on the scale of ...
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Impossibility of closed timelike curves

Hawking's Chronology Protection Conjecture says that the laws of nature must always conspire to prevent a CTC from forming. Why can't we conclude that this is proven? An inconsistent CTC is s ...
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2 votes
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Are non-linear extensions to QM equivalent to time travel?

I recently learned of the existence of Objective Collapse theories which add non-linear terms to QM to explain wave function collapse. Per the 2014 paper Treating Time Travel Quantum Mechanically, the ...
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0 votes
1 answer
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Thought experiment with the speed of light

Every time we look at a star we are looking to the past. That's because the light of that star needed to travel long distances at the speed of light. When the light reaches our sight maybe the star no ...
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Could Gott's Cosmic String Time Machine hypothetically be used as a poor man's Alcubierre drive?

I have read much speculation about Gott's theoretical use of cosmic strings for time travel, but if the colliding cosmic strings accelerated the spacecraft faster than light, as Gott theorizes, could ...
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1 vote
1 answer
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Travelling backward in time? [closed]

An event requires 4 coordinates - spatial $x,y,z,$ and time $t$. Multiple objects cannot occupy the same $x,y,z$ at the same time $t$. Given this fact how can a subpart of the universe travel back in ...
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Can different BH orbits allow time travel?

Consider two spaceships in orbit around a black hole. After synchronizing clocks, both start a calculation on an electronic computer that takes a known number of clock ticks to complete. One of the ...
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1 vote
2 answers
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Could Matter Go Backwards in Time?

In the real world, it seems that traveling backwards in time is impossible, but do we have a theorem in physics that would imply this fact? Some people (including Feynman) describe antiparticles as ...
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Why would an FTL-drive imply time travel? (other answers and questions unsatisfactory)

I've been spending quite some time trying to understand why an FTL-drive would also imply time-travel, but every answer I can find seems to mainly be about semantics and perception. I will break it ...
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Wouldn't time travel also require space travel to be practical? [closed]

If we somehow move back in time, say 6 months back, earth would be on the opposite side of the sun relative to its position in the present. Earth is moving relative to sun. Sun is moving relative to ...
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3 votes
1 answer
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What's the big deal with interacting tachyons?

I understand that any spacelike path appears to move backward in time from some reference frames, so e.g. a "reflected" tachyon can be absorbed before it was emitted. But I don't see how ...
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Why does FTL imply that BACKWARDS time travel is possible? - Very Detailed! [closed]

I know this question has been asked before and I have read and understand the answers however imo none of them still imply that backward time travel is possible. I understand moving forward in time ...
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How does time travel work through superluminal travel, as mentioned in Stephen Hawking's "A brief history of time"?

I quote the part I don't quite understand: If it is possible for a rocket traveling below the speed of light to get from event A (say, the final of the 100-meter race of the Olympic Games in 2012) to ...
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Chronology Protection Conjecture with a wormhole time machine-Mechanisms in layman's terms

I remember hearing about Steven Hawking making a Chronology Protection Conjecture back a couple of decades ago. He seemed to be arguing that the properties of the universe would conspire to prevent a ...
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0 votes
1 answer
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Does non-local interepretations of quantum mechanics imply FTL communication? [closed]

For example the pilot wave theory... And if this is the case then does FTL commuincation imply time travel (i.e: information going back in time).
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3 votes
1 answer
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Warp drive causality issue, and a possible error in a paper?

Take a look at this paper on "Warp Drives and Causality:" https://doi.org/10.1103/PhysRevD.53.7365 The author attempts to argue that the Alcubierre Drive spacetime could exhibit Closed ...
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0 votes
2 answers
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Do wormholes really allow us to travel back in time?

Theories surrounding wormhole based time travel are annoying me tonight... So the way time works is relative, right? The closer you are to the frame of reference, the faster time moves. So, if we use ...
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-4 votes
2 answers
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Law of Conservation of Time? [closed]

So, it may or may not seem to be stupid, but if we think that there is a person named John who travels back in time by any means, and he met his past lets say him small John then the past small John ...
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0 votes
2 answers
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Possibility of having a spacetime trajectory that cuts the $t=$constant at more than one point

Can we have a spacetime trajectory like the blue curve (shown in the figure) inside the lightcone such that the trajectory cuts a $t={\rm constant}$ line at more than one point (three points in the ...
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6 votes
5 answers
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Can we use Heisenberg Uncertainty Principle to prove that time travel to past is impossible?

Suppose the case that someone in future makes a time machine which can be used to time travel in past. Now s/he can accurately measure momentum of a particle without caring about the particle's ...
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7 votes
4 answers
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Are wormholes evidence for traversal of a higher dimension?

Warning, pop science coming.. please correct what I’m getting wrong. Einstein’s equations of relativity showed the potential for existence of wormholes that can connect different points in space time....
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0 votes
1 answer
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Novikov self-consistency and computability

The Wikipedia article on the Novikov self-consistency principle has a section on time loop logic, where it discusses using time travel to solve any NP problem by finding an algorithm where the only ...
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-1 votes
2 answers
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What happens with time when we travel at the speed of light? [closed]

I always wonder how time is related to traveling at the speed of light and what actually happens when we travel at the speed of light. Why does time slow down and what can be the physical explanation ...
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4 votes
4 answers
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Why would FTL imply time travel? [duplicate]

Edit: Thank you all for the explanations, but I think until I fully grok special relativity, Lorentz transformations and relativity of simultaneity, the answers won't make any sense to me. Maybe the ...
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-4 votes
1 answer
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I was researching on time travel and got an idea. Is free fall a case of time travel?

A person standing in a huge lift which is free falling. Observation: for that person gravity will be relatively zero. As we know the weaker the gravity is the faster time flows and stronger the ...
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2 votes
0 answers
63 views

Is it possible for a particle to cross the event horizon of a black hole via traveling back in time?

Let us suppose we have a particle that is near the event horizon of a black hole. The Shroedinger equation for particle without interacting with itself in a gravitational field is given as: $$ i \hbar ...
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-2 votes
1 answer
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What Ron Mallett doing for time machine here? [duplicate]

Here Ron Mallett pouring liquid chemical on array of lasers for progress of time machine. I didn't understand it. Source What exactly Ron Mallett doing for time machine here?
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3 votes
2 answers
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Is temporal causality broken by quantum entanglement?

When one particle of an entangled pair is measured, it forces the state of the other particle. This effect propagates faster than we can measure, certainly faster than light and possibly ...
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4 votes
1 answer
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Travelling to the future while seemingly standing still?

Some time ago I thought about this possibility, knowing about the time dilation from general relativity. What would theoretically happen if I travelled at near the speed of light in a circle that has ...
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-1 votes
1 answer
306 views

Need help understanding the argument that "faster than light motion does not imply time travel" [closed]

The paper in question is https://arxiv.org/abs/1407.2528 . But it contradicts known theory. Could someone ELI5? Is it legit? Are there any gotchas or catches? Abstract Seeing the many examples ...
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2 answers
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Does the Novikov self-consistency principle rule you being another conscious observer in history? [closed]

The Novikov self-consistency principle at its simplest form is that you can't go back in time and change the past in a way that would affect your existence. Does that mean that it is automatically ...
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0 answers
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Law of conservation of mass-energy and time travelling (repeat question)

Although there are already atleast four questions on it (most of them closed as off-topic), asking the same since none of the answers made much sense to me and did not seem off-topic to me (...
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4 votes
1 answer
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How does a tachyonic antitelephone work?

Based on my current knowledge on physics (which is not a lot), a tachyonic antitelephone is a hypothetical device that will allow information to travel back in time, created based on the theory of the ...
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0 votes
1 answer
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Is there any experimental evidence of CTC?

One consequence of general relativity is a solution called the closed time like curve or CTC...which could allow you to view a place at an earlier point in time or possibly even travel back in time. ...
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-2 votes
1 answer
961 views

Time travel in 4th dimension [duplicate]

Can we travel in past in 4rth dimension because according to physics it is not possible to travel in past in even 4rth dimension we can only go in future.pls explain.
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2 votes
1 answer
135 views

Can you go back and forth through time when inside a black hole?

Inside the event horizon of a Schwarzschild black hole the radial coordinate becomes timelike and the time coordinate becomes spacelike (they change signatures). I read that timelike coordinates are ...
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1 vote
1 answer
122 views

Pair creation and annihilation and Wheeler's one electron universe

I stumbled upon Wheeler's idea that there could be only one electron. If I understood correctly, basically the idea is that one electron moves forward and backward in time such that it appears as if ...
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2 votes
1 answer
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Is reversing the arrow of time that same as going backward into the past?

I read an article today that somwhat confused me. Is this the same as time travel...which I have always thought was a contradiction. Are they talking about reversing law of thermodynamics? In which ...
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-2 votes
1 answer
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Time travel to the past via solutions of General Relativity [closed]

Are there any solutions in General Relativity which allow for time travel to the past without introducing a closed timelike curve?
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1 vote
1 answer
154 views

Are tachyons time travelers?

If tachyons are faster than light, that means they have passed a certain point before anyone or anything can “see” them. Theories have mentioned that if anything can go faster than light, then it can ...
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1 vote
0 answers
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Gödel Universe and second law of thermodynamics

In the Gödel universe, which contains closed timelike curves and is a solution to Einstein’s G=T field equation, time travel is thought to be physically possible. But as you need a spaceship (which ...
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2 votes
1 answer
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Time Travel, CTC and Causal Loop

What is the difference between a closed timelike curve and a causal loop? If someone is travelling in a closed timelike curve, are they also in a causal loop?
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2 votes
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Brouwer fixed point theorem

How does the Brouwer fixed point theorem (which provides a solution to the photo camera paradox of a causal loop) generalise to show that objects in closed time-like curves do not violate the second ...
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2 votes
1 answer
166 views

Hawking said virtual particles can almost become real particles, following closed trajectories. What does that mean?

Here's hawking quote from his latest book. Brief Answers to the Big Questions "When space-time gets warped almost enough to allow travel into the past, virtual particles can almost become real ...
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10 votes
4 answers
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Does time dilation mean that faster than light travel is backwards time travel? [duplicate]

Ok. So my question is, I've always heard it that Faster Than Light travel is supposedly backwards time travel. However, the time dilation formula is $$T=\frac{T_0}{\sqrt{1-v^2/c^2}}$$ And while it ...
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5 votes
1 answer
2k views

Is time travel a violation of second law of thermodynamics?

According to the increase of entropy principle, the entropy of the universe is always increasing. So, does going back in time violates the second law of thermodynamics? Because entropy of the universe ...
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