Tagged Questions
3
votes
0answers
109 views
Going through a ring of black holes
Mathematician here with a speculative physical question -- feel free to boot me if the level isn't right.
Suppose one finds, or builds, a constellation of several black holes arranged in a circle. ...
4
votes
1answer
102 views
How is the direction of time determined in general relativity?
In special relativity every frame has its own unique time axis, represented in Minkowski diagrams by a fan-out of time vectors that grows infinitely dense as you approach the surface of the light cone ...
4
votes
3answers
360 views
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 ...
3
votes
1answer
97 views
An issue about the compactness and the existence of CTCs
There is a well known fact that a compact spacetime necessarily contains a closed timelike curve (CTC). Proof can be found in several books on GR (e.g. Hawking, Ellis, Proposition 6.4.2), and in ...
0
votes
1answer
149 views
Information faster-than-light and GR vs. QM
What is meant by the statement that information cannot travel faster than light?
If I write down something on a paper, isn't there according to QM a non-zero probability that an identical paper can ...
5
votes
3answers
89 views
Analyticity and Causality in Relativity
A few weeks ago at a conference a speaker I was listening to made a comment to the effect that a function (let's say scalar) cannot be analytic because otherwise it would violate causality. He didn't ...
3
votes
2answers
81 views
What is wrong in this representation of relative reference systems?
Up until now I've explained relative time to myself as looking at the 3D world from different four-dimensional perspectives, analogous to how looking at a 2D-ish object (eg. a sheet of paper) from ...
4
votes
3answers
251 views
Is causality synonymous with continuity?
In general relativity, we use the term "time-like" to state that two events can influence one another. In fact, in order for an event to physically interact with another one, they have to be ...
2
votes
4answers
331 views
Does time have a special status in general relativity?
In a lot of laymen explanations of general relativity it is implied that the four dimensions of the space-time are equivalent, and we perceive time as different only because it is embedded in our ...
