All Questions
Tagged with special-relativity observers
148
questions
108
votes
12
answers
15k
views
How can time dilation be symmetric?
Suppose we have two twins travelling away from each other, each twin moving at some speed $v$:
Twin $A$ observes twin $B$’s time to be dilated so his clock runs faster than twin $B$’s clock. But twin ...
67
votes
10
answers
172k
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Would time freeze if you could travel at the speed of light?
I read with interest about Einstein's Theory of Relativity and his proposition about the speed of light being the universal speed limit.
So, if I were to travel in a spacecraft at (practically) the ...
33
votes
4
answers
9k
views
How does a photon experience space and time?
To an an external observer it appears that time has stopped for photon. But this relation is reflexive, so for an observer travelling with the photon it appears the universe has stopped everywhere.
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- 13.1k
52
votes
8
answers
14k
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How is the classical twin paradox resolved?
I read a lot about the classical twin paradox recently. What confuses me is that some authors claim that it can be resolved within SRT, others say that you need GRT. Now, what is true (and why)?
- 3,711
25
votes
8
answers
5k
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In the theory of special relativity speed is relative so who decides which observer’s time moves slower? [duplicate]
If for example we have 2 people one moving in speed v relative to the other, according to special relativity the time passing for the moving person is slower than for the stationary person. However ...
- 375
2
votes
5
answers
6k
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Special Relativity - Regarding the Simultaneity of Events During the Train Paradox
My questions concerns that classic train paradox, wherein there is a train and a tunnel of equal length, and the train is traveling and some fraction of the speed of light towards the tunnel.
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- 1,395
24
votes
10
answers
7k
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What are the mechanics by which Time Dilation and Length Contraction occur?
What are the mechanics of time dilation and length contraction? Going beyond the mathematical equations involving light and the "speed limit of the universe", what is observed is merely a phenomenon ...
- 241
15
votes
3
answers
3k
views
The reference frame of $c$
I don't have a lot of knowledge of special relativity and associated topics; some of the few things I know are that "all motion is relative" (that is, there is no 'stationary reference frame'), and ...
5
votes
4
answers
1k
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Equivalence of two definitions of proper time in special relativity
According to Wikipedia,
proper time along a timelike world line is defined as the time as measured by a clock following that line.
This makes sense to me, but my book defines proper time in the ...
user63248
12
votes
3
answers
2k
views
Is energy content of a system different depending on the observer?
For the sake of simplicity, let's imagine that the entire universe is empty except for a single lump of (classical) matter with mass $m$. In its center of momentum frame, it is clear that the total ...
- 121
6
votes
2
answers
3k
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Schutz's geometrical proof that spacetime interval is invariant
I'm trying to understand the proof that spacetime interval is invariant under for any two inertial observers. I know it's easy to arrive at the result using Lorentz transformation but I'm trying to ...
- 777
27
votes
5
answers
5k
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Hole-and-nail paradox in special relativity
Yesterday we started relativity on our physics class, and my professor taught us a few concepts. We did some examples on how things changed by looking them from different reference systems, and a ...
- 381
12
votes
4
answers
2k
views
Which clock is the fastest inside an accelerating body?
The picture shows an accelerating spaceship with two clocks inside it. It is so far away from all other bodys that gravity is of no importance.
Will the bottommost clock be slower than the topmost ...
- 495
8
votes
3
answers
4k
views
Does superluminal travel imply travelling back in time?
Is this statement true?
You can not travel back in time. If I travel fast enough the clock will start to go backwards, but that does not mean I am traveling back in time. It would only mean that ...
- 113
26
votes
8
answers
9k
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In the twin paradox does the returning twin also come back permanently length contracted flatter than the twin on Earth?
This video from Brian Greene suggests this is so:
https://www.youtube.com/watch?v=2sZUNud6rRw&list=PLj6DWzIvBi4PFDXCCV1bNhVUgDLTwVbFc&index=60
It shows if you stop a pole in the barn (...
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