Physics Stack Exchange
Physics 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.

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.

228 questions
80
votes
7 answers

How does faster than light travel violate causality?

Let's say I have two planets that are one hundred thousand lightyears away from each other. I and my immortal friend on the other planet want to communicate, with a strong laser and a tachyon communication device. I record a message on the tachyon…
markovchain
  • 1,531
35
votes
6 answers

Is time travel possible? Is it possible to go back in time?

I read somewhere that according to relativity, it is possible - involving black holes and other stuff - to jump into the past. Is it possible for anything to go back in time either continuously or by jumping?
SMUsamaShah
  • 5,507
31
votes
5 answers

Wormholes & Time Machines - for *experts* in GR/maths

EDIT: Further clarification in the context of answers/comments received to 20 Jan has been appended EDIT: 21 Jan - Response to the Lubos Expansion appended [in progress, not yet complete] EDIT: 23 Jan - Visser's calculations appended EDIT: 26 Jan -…
Julian Moore
  • 792
28
votes
4 answers

What are some scenarios where FTL information transfer would violate causality?

I've always heard people saying, "Faster than light information transfer can't happen because it would violate causality! Effects can precede their causes!" However, I'm trying to think of a situation where this would happen. I'm sure it has…
Justin L.
  • 6,090
17
votes
6 answers

How to argue that time travel to past would not be possible even in future?

I am a science fiction writer. I know how to time travel to the future (using black hole or speed). But I need to argue in my novel that time travel to the past might not be possible. Is there a way to do this without using a formula? And how basic…
BioHazard
  • 355
16
votes
2 answers

Is the "Doctor Who" spacetime affected by Hawking's chronology protection mechanism?

Recently, there has been a paper1 (and an accompanying layman-ized white paper2) on "Traversable Achronal Retrograde Domains In Spacetime", TARDIS for short. It proposes a spacetime geometry that contains closed timelike curves. Now, Hawking once…
Manishearth
  • 19,167
  • 6
  • 64
  • 104
15
votes
8 answers

Is time travel impossible because it implies total energy in the universe is non-constant over time?

I have always argued with my friends regarding Time Travel that it is impossible. My argument has been that it will destroy the theory that all the energy in the universe is constant since when one travels to a different time, the universe at that…
John Paul
  • 159
13
votes
2 answers

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 inner gravitational pull towards the singularity…
Bagho
  • 131
13
votes
2 answers

Gödel's solutions to Einstein's relativity equations and their consequences

Gödel gave certain solutions to Einstein's relativity equations that involved a rotating universe or something unusual like that; that predicted stable wormholes could exist and therefore time travel, if one could travel through a wormhole. He was a…
201044
  • 295
  • 2
  • 9
12
votes
4 answers

Is time travel possible?

Time travel -- often featured in movies, books, or facetiously in conversation. There are also theories treating time as simply another dimension, which to the layperson might imply forward and backward movement is possible at will. But what do we…
DuckMaestro
  • 245
12
votes
3 answers

Height Issues of the Time Traveler

A person from the year 2250 goes back in time. They go back 60 Million years, because they want to observe dinosaurs. Imagine their surprise when they see T-Rex's running around like little chickens!! That's because they neglected the Hubble…
Jiminion
  • 2,673
12
votes
3 answers

Closed timelike curves in the region beyond the ring singularity in the maximal Kerr spacetime

The region beyond the ring singularity in the maximal Kerr spacetime is described as having closed timeline curves. Why and/or how is the question. Now if you look a Kruskal-Szkeres Diagram (or a Penrose Diagram as above) you can see that the Kerr…
Timaeus
  • 26,055
  • 1
  • 36
  • 71
12
votes
3 answers

Is it possible to produce gravitational waves artificially?

Why don't they make a ball with irregularities, say the size of a tennis ball, then spin it very rapidly, so it would produce gravitational waves like a spinning star with irregularities on it? Is that not possible with our current technology?…
user43783
  • 1,137
11
votes
2 answers

Energy balance of closed timelike curves in Gödel's universe

I recently read Palle Yourgrau's book "A World Without Time" about Gödel's contribution to the nature of time in general relativity. Gödel published his discovery of closed timelike curves in 1949. Many years later (in 1961), S. Chandrasekhar and…
Thomas Klimpel
  • 931
10
votes
4 answers

Does time dilation mean that faster than light travel is backwards time travel?

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 is true that speeds greater than $c$ turn the…
Guthrie Douglas Prentice
  • 355
1
2 3
…
15 16