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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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Explain post-selected teleportation [closed]

I'd be grateful for an explanation of post-selected teleportation (PCTCs). Please provide a step-by-step description of how the process should be performed (Alice and Bob style). Please also explain ...
yoav.aviram's user avatar
5 votes
4 answers
760 views

Relativity of Time from an Observer Perspective

We have established that time is relative and goes slower for objects in motion and we have experimentally proven with the ISS. A thought experiment: What if the ISS was moving at much higher speeds, ...
Niccola Tartaglia's user avatar
2 votes
2 answers
165 views

Does causality forbid time travel?

If causality is an axiom or a fundamental law in physics, would the existence of causality be a reason which forbids time travel? Because time travel could break causality so we see first the effect ...
Jose Perez's user avatar
2 votes
1 answer
165 views

No inconsistencies due to closed timelike curves in General Relativity

Is there anything wrong with the following argument ruling out inconsistencies with closed timelike curves? Math A solution in the context of General Relativity is a pseudo-Riemannian manifold $(M, g)$...
TomS's user avatar
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0 answers
32 views

Why can't travel through a closed timelike curve violate the Novikov self-consistency principle? [duplicate]

The Novikov self-consistency principle prevents a paradox in which a billiard ball is sent to its past through a closed timelike curve (allowed under general relativity) such that it collides with its ...
T Scherer's user avatar
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1 vote
2 answers
192 views

Why can't travel through a closed timelike curve violate the Novikov self-consistency principle?

The Novikov self-consistency principle prevents a paradox in which a billiard ball is sent to its past through a closed timelike curve (allowed under general relativity) such that it collides with its ...
T Scherer's user avatar
  • 129
2 votes
2 answers
177 views

Past and Future

I'm new to physics we've had and argument in our class about: we know that present (and/or past) can and will affect future. But how do we know if the future can affect past or present? Is that even ...
MpH81679's user avatar
0 votes
2 answers
90 views

If antimatter can be interpreted as matter moving back in time, could we in theory send information to the past? [closed]

I am pretty sure the answer is going to bo "no", but I would still like to have a physicist explanation. If I can create a device that can change the probability of a positron annihilation, ...
Guillaume Chereau's user avatar
1 vote
1 answer
813 views

Why Going Faster-Than-Light (FTL) Leads to Time Paradoxes? [duplicate]

In this video: https://www.youtube.com/watch?v=an0M-wcHw5A&lc=UgxqC71gefTRIuVubGt4AaABAg.9jI6ltMIeu59jx2P8cpn_z In the video the following events happen: A supernova goes off. Earth sees the ...
Rick's user avatar
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1 vote
0 answers
66 views

Why do we assume that we can change the past by sending signals backwards in time? [closed]

This might be a stupid question, but hang in with me- From what I've seen, the biggest argument against superluminal signaling is that you would be able to send a message backwards in time that could ...
Scott's user avatar
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1 vote
0 answers
53 views

Does the tachyonic antitelephone actually show a time-travel paradox? [duplicate]

The tachyonic antitelephone paradox is, roughly, this: Alice is in a space station and watches Bob go past at relativistic speed in a spaceship. Some time later she sends him a message at ...
Spitemaster's user avatar
0 votes
3 answers
233 views

If the future already exists, why can't we travel to it?

since time is actually distance, and if the future already exists, why wouldn't we be able to travel to the future? I understand humanity will never be able to, even if it was possible because our ...
Wyatt's user avatar
  • 17
1 vote
1 answer
112 views

Does travel through static wormhole(s) allow time-travel to the past? (Does one-way Tachyonic antitelephone compatible with reality?)

I'm trying to understand if faster-than-light travel via static wormholes is compatible with our current view of the Universe. https://en.wikipedia.org/wiki/Tachyonic_antitelephone gives two examples: ...
Alex Martian's user avatar
1 vote
3 answers
189 views

Are Temporal Paradoxes possible within the Many Worlds Interpretation?

Are Temporal Paradoxes possible within the universe of the MWI, or is the idea not possible within this interpretation? I guess if one would alter something in the past within the MWI universe, they ...
42piratas's user avatar
  • 165
1 vote
1 answer
39 views

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 ...
Always learning never preachin's user avatar
5 votes
1 answer
300 views

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 ...
MattG88's user avatar
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-5 votes
3 answers
589 views

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 ...
Carm's user avatar
  • 7
0 votes
1 answer
95 views

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 $t_0$ ...
Naman's user avatar
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0 votes
0 answers
33 views

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 ...
foggy's user avatar
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0 votes
1 answer
183 views

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 ...
JeffK's user avatar
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3 votes
0 answers
85 views

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 ...
Logan R. Kearsley's user avatar
0 votes
1 answer
79 views

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 ...
myst1c's user avatar
  • 103
1 vote
1 answer
114 views

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 ...
Ben Warner's user avatar
1 vote
1 answer
68 views

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 ...
Sandip Chitale's user avatar
1 vote
2 answers
566 views

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 ...
Hans's user avatar
  • 94
2 votes
1 answer
624 views

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 ...
Achi's user avatar
  • 133
1 vote
0 answers
61 views

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 ...
GunJack's user avatar
  • 127
4 votes
1 answer
211 views

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 ...
Adam Herbst's user avatar
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1 vote
6 answers
2k views

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 ...
Mucker's user avatar
  • 127
0 votes
1 answer
317 views

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 ...
J. Schmidt's user avatar
0 votes
1 answer
61 views

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).
Omar Hossam Ahmed's user avatar
4 votes
1 answer
298 views

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 ...
Joeseph123's user avatar
0 votes
2 answers
319 views

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 ...
Hazel へいぜる's user avatar
-5 votes
2 answers
248 views

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 ...
Krrish Dhaneja's user avatar
0 votes
2 answers
88 views

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 ...
Solidification's user avatar
6 votes
5 answers
2k views

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 ...
anantagni's user avatar
  • 143
7 votes
4 answers
1k views

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....
Michael James's user avatar
0 votes
1 answer
98 views

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 ...
Yair Halberstadt's user avatar
-1 votes
2 answers
408 views

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 ...
Er Arpit Tiwari's user avatar
4 votes
4 answers
6k views

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 ...
PoultryMan's user avatar
-4 votes
1 answer
132 views

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 ...
Darshan Padia's user avatar
2 votes
0 answers
72 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 ...
Struggling_Student's user avatar
-2 votes
1 answer
236 views

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?
Polly Man's user avatar
5 votes
2 answers
4k views

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 ...
Guy Inchbald's user avatar
  • 7,428
4 votes
1 answer
114 views

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 ...
AndryCraft69's user avatar
-1 votes
1 answer
392 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 ...
pete's user avatar
  • 220
-1 votes
2 answers
1k views

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 ...
Nederealm's user avatar
  • 135
0 votes
0 answers
97 views

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 (...
Ravindra HV's user avatar
6 votes
1 answer
2k views

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 ...
Ricky Hu's user avatar
0 votes
1 answer
136 views

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. ...
Joeseph123's user avatar

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