Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

-4
votes
0answers
60 views

Time travel possible? [on hold]

Now we have found that neutrinos can travel faster than the speed of light.Does this enable time-travelling machines?
2
votes
1answer
62 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 ...
1
vote
1answer
61 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 ...
2
votes
1answer
227 views

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 ...
-2
votes
1answer
69 views

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?
1
vote
1answer
91 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 ...
0
votes
0answers
33 views

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 ...
2
votes
1answer
73 views

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?
1
vote
0answers
34 views

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 ...
1
vote
1answer
126 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 ...
10
votes
5answers
958 views

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 ...
4
votes
1answer
322 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 ...
-4
votes
1answer
78 views

How is traveling back in time different from traveling at a negative velocity? [closed]

A simplified explanation of why you can't travel through space faster than the speed of light is that you are already traveling at the speed of light, through spacetime. If you are stationary in ...
1
vote
1answer
70 views

Why do wormholes necessarily alter time? Why don't they just make two places causally linked?

I've heard many-an-explanation of wormholes. From as a kid with the hole punch through paper, to the sci-fi something something magic, to popular YouTube science channels talking about how it could ...
1
vote
2answers
103 views

Wormholes and Time Machines

According this paper: Morris, Michael S. and Thorne, Kip S. and Yurtsever, Ulvi (1988) Wormholes, time machines, and the weak energy condition. Physical Review Letters, 61 (13). pp. 1446-1449. ...
-4
votes
1answer
72 views

Is Quantum teleportation possible for large objects like a cat, for example? [duplicate]

Ok, here's the idea. This isn't really connected to what is usually referred to as 'quantum teleportation', but assuming that all particles can tunnel to a different location given the right ...
0
votes
1answer
70 views

How does going faster than light cause going backward in time? [duplicate]

I have read in many places that some virtual particles can "travel faster than light (1)" and thereby "go backwards in time (2)". My question is about the connection between these two. I have always ...
0
votes
2answers
125 views

Causality (time travel) question

This bugs me, and I don't know if I would be able to understand reasoning in answers on this thought experiment. Let say observer is on the earth in this example. Let him use quantum entangled pair of ...
0
votes
0answers
42 views

Is a time loop possible? [duplicate]

Let's say that hypothetically we could travel faster than light. Would a ship travelling at lightspeed or faster than light travel create a time loop where it makes the same trip over and over again ...
0
votes
0answers
61 views

Effects of negative energy density on properties of black hole horizon (and nearby spacetime)

Some background: Hawking's radiation (https://en.wikipedia.org/wiki/Hawking_radiation) is counter-intuitive in at least two sense. First is that it leads to a complete evaporation of the black hole in ...
0
votes
1answer
77 views

Would communication of information from the future require a block time structure? [closed]

If faster-than-light travel (through wormhole tunneling or some other exotic means) was discovered in future, such that it allows information to be communicated from the future to the present, what ...
1
vote
0answers
61 views

Can someone review this mathematical derivation that in Special Relativity FTL implies Time Travel

I am looking to show mathematically (i.e. with derivations and algebraic relationships) that FTL implies time travel. Here's what I got: Suppose we have 2 ships $O_1, O_2$ traveling at $0.9c$ in ...
0
votes
1answer
84 views

What is time travel and why is the grandfathers Paradox a Paradox?

While watching a talk given by Neil DeGrase Tyson, he says that if something happens on earth, it would take light 2 million years to get to Andromeda. In theory, if you could generate a wormhole and ...
-1
votes
3answers
128 views

Scientific book about time travel? [closed]

Is there any book which is related with time travel? I want to read something scientific about it. I read Michio Kaku's Physics of the Impossible but in there just one chapter was about time travel. I ...
0
votes
3answers
293 views

Closed spacelike vs Closed timeline curves (or rather loops)

Reading John Rennie's answer, it made it very clear as to why it is justified to talk of time as a coordinate. So, for now we put time and space on the same footing i.e. consider them dynamical ...
1
vote
1answer
72 views

Could I enter in a wormhole?

Reading a question on sci-fi stack exchange I find the wikipedia article on Novikov self-consistency principle in which is described the Polchinski paradox and the solution proposed by Thorne and some ...
-3
votes
1answer
94 views

Is this statement defensible? [duplicate]

If I contend that time travel into the past is not possible in any possible version of future reality that we can access since no time traveller from the future has yet presented themselves to rebuff ...
-3
votes
1answer
50 views

Matter beyond the event horizon should time travel? [duplicate]

when anything passes the event horizon of a blackhole, it must be moving faster than light as even light cannot escape. So then, shoundnt it time travel?
-1
votes
1answer
127 views

What is the gravity and effect of a Black Hole with two connected cones cut from it?

Any question about Black Holes or time travel seems to have some untested theory or incredibly complicated and prohibitively expensive solution, this question is no different. While the second half ...
1
vote
1answer
243 views

How is faster than light travel analogous to time travel? [duplicate]

According to this video, faster than light travel is analogous to time travel. Does this mean that if I could instantly teleport 1 light year away, and then sent a laser pulse to my friend, my friend ...
2
votes
1answer
95 views

The Time Freezing Room - Theoretically possible?

Imagine a room in your basement with a very special property: The time inside this room runs 60 times faster compared to the outside world. That means when you enter the room and spend there 1 day ...
1
vote
1answer
60 views

Tipler cyllinder shouldn't have to be infinitely long

Since information can only travel at the speed of light, the information that the cylinder is infinitely long will never arrive to any point of the cylinder. And if the information that its infinite ...
-1
votes
1answer
49 views

If time travel possible then we able to travel to future or past [duplicate]

If time travel possible? If we can travel in future? If we can travel in past? Or Both actually?
0
votes
1answer
92 views

Time travel, possibility? [duplicate]

It is said that if we travel at the speed of light,we will go into future,please could you explain how?Is it possible to make a time machine ever? Please give an easy answer, a simple one!
3
votes
1answer
170 views

What kind of discovery would prove the impossibility of time travel? [closed]

Bearing in mind that: "Time travel" does not have one fixed definition. "Proof" in physics is never absolute or final as in mathematics. Except logical arguments which lead to paradoxes, what kind ...
1
vote
1answer
911 views

What slows down time relative to an observer: super gravity or super speed? [duplicate]

Sounds like after the Interstellar movie, ppl are talking much more about time slowing down near a black hole, instead of traveling close to the speed of light. My personal hobbyist experience was ...
4
votes
2answers
1k views

Are time loops real?

I'm new to physics and I was wondering if time loops (like those seen in the movies Groundhog Day or Edge of Tomorrow) possible?
-7
votes
1answer
107 views

Faster than light travel??? Would this process work? [closed]

This first and foremost could not be done now with todays tech- so bear with me. I have put a lot of thought into the physics based notion that nothing could travel faster than the speed of light... ...
0
votes
1answer
214 views

Contradiction to the law of conservation of energy while time travelling [duplicate]

If time travelling backward were possible,(by a wormhole, one opening of which has been kept near a massive body, for instance) wouldn't it contradict the law of conservation of energy, since a ...
2
votes
1answer
251 views

Does general relativity make time travel impossible or just very difficult? [duplicate]

I was hoping to get some technical answers to this question, and was really asking because I thought it'd be a fun question. Have at it folks.
1
vote
1answer
325 views

Help me understand this example about FTL = time travel [duplicate]

Searching for clear explanations of why FTL equals time travel I found this http://www.physicsmatt.com/blog/2016/8/25/why-ftl-implies-time-travel Go at the bottom, when he draws the blue lines. He ...
-1
votes
2answers
86 views

Can we travel forward in time like this?

An object in spacetime warps it and creates like a pit. If the object had such a huge mass and gravity that the pit edges were touching or were anyway very close would it be possible to skip a portion ...
1
vote
2answers
329 views

Entropy and time travel

Suppose that time travel is possible. Can then we circumvent the law of increasing entropy (second law of thermodynamics) transferring entropy from the future to the past?
-1
votes
2answers
138 views

Opinions on the Grandfather Paradox [closed]

According to the grandfather paradox, the notion of changing events that have occurred in the past is logistically impossible due to the fact that the events have already occurred. This has lead many ...
0
votes
0answers
46 views

Time- the stubborn illusion? [duplicate]

BACKGROUND: As I was happily watching "Genius" tele-drama's teaser Genuis, I came across this very popular and subtle comment: The past,present and the future all exist simultaneously. Time is ...
0
votes
1answer
82 views

Are there any theories out there that explain this time travel paradox [duplicate]

I was quite perplexed by a paradox that I thought of, for instance, say I am a person who completely understand einsteins field equations. In this case, Einstein formulated his theory. Now, say I have ...
11
votes
2answers
941 views

If you hover just above the event horizon of a black hole, would you see the future of the universe?

Let's do this thought experiment. You have an insanely powerful rocket and it can accelerate to 0.999999c. Now you fly to a supermassive black hole and hover just above its event horizon, where the ...
1
vote
0answers
182 views

Faster than light movement and time travel simple explanation

I've read Stephen Hawking's Briefer History of Time and when it got to time travel back at faster than light speeds it felt natural to me. However a few months later when I talked to a friend I couldn'...
1
vote
1answer
86 views

Time Wormholes Detection

Was reading the possibility of time travel. Now Hawkings states that they haven't invented time travel, because we haven't had a visit from a time machine yet. But he also states that there exists ...
1
vote
3answers
1k views

Can a telescope look into the future?

If a telescope can see the past, can it look into the opposite direction and see the future? I suppose I am trying to put time into a single line. (timeline) with a beginning and end, and we are in ...