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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In the Twin Paradox, can one twin travel backwards in time?
In the Twin Paradox, if the travelling twin, Betty, instead of returning to her brother Albert at home, continues her journey after a period of rest, why is causality not violated due to her brother, ...
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Apparent time travel paradox from oscillating worldlines
I was trying to make a desmos graph that takes the spacetime worldline of let's say spaceship A (viewed from an inertial reference frame) as an input and draws its constant time/space axis (still ...
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Assuming you could go faster than light in Minkowski spacetime, how could you close your worldline?
I've been looking into how faster-than-light travel implies time travel. I'm familiar with the simplest example to show that causality is violated with faster-than-light communication (the example I ...
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What are some highly unstable phenomena you can observe from lightyears away?
I'm currently drafting some scifi story where the protagonist is in a long timeloop and wants to figure out when the loop starts exactly based on observing some unstable phenomena, like atomic decay ...
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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, ...
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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 $(M, g)$...
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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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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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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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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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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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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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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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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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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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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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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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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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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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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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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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 ...
