All Questions
Tagged with spacetime reference-frames
38
questions
13
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3
answers
6k
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Distance in relativistic circular motion in invariant spacetime
I understand that the closer something travels to the speed of light, that time will stretch by a factor, and distance will compress by the same factor.
My question is, if something travels in a ...
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32
votes
4
answers
9k
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Why isn't the center of the galaxy "younger" than the outer parts?
I understand that time is relative for all but as I understand it, time flows at a slower rate for objects that are either moving faster or objects that are near larger masses than for those that are ...
- 469
7
votes
1
answer
903
views
Doesn't dating the universe violate the concept of spacetime's inseparability?
It would seem that measuring an age of the universe from the big bang requires separating spacetime into a 3D coordinate system and a time track. I fail to understand why it is appropriate to take ...
- 121
21
votes
4
answers
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Does velocity or acceleration cause time dilation?
What causes time dilation? Acceleration or velocity?
I've seen multiple comments on this forum that assert velocity is the cause, but that doesn't seem right to me. You can't have velocity without ...
- 663
6
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1
answer
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What is the relativistic calculation of travel time to Proxima Centauri?
It has already been asked here how fast a probe would have to travel to reach Alpha Centauri within 60 years. NASA has done some research into a probe that would take 100 years to make the trip. But ...
- 4,973
6
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5
answers
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What if two twins flew off in opposite directions and were reunited in a perfectly symmetric way, would they have aged same? [duplicate]
If No, well this can't be, as there is perfect symmetry, you can't tell one from the other.
If Yes, they had relative velocities all along, then their times must have dilated and somehow they must ...
user218113
5
votes
3
answers
4k
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A sees B's clock running slow and B sees A's clock running slow?
This paradox is very common it seems, in which A sees B's clock running slow and B sees A's clock running slow. Here is the question a little more concretely.
Let's say B flies by A's spaceship. If B'...
- 815
3
votes
3
answers
460
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If an astronaut had stationed in International Space Station for the duration of mission, 17 years, would he be older?
Today the NASA International Space Station started the 100000 orbit after 17 years in the space.
I just wonder if there were a team of astronauts which were in the Lab for all the duration of last 17 ...
- 1,659
2
votes
2
answers
609
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How to define the proper time of a photon?
I'm writing a paper about the motion of photons near a Schwarzschild black hole. At some point there's a derivative of the Hamiltonian of the system with respect to time $\tau$. I need to explain what ...
- 41
12
votes
2
answers
3k
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How fast can time flow? A question of time dilation
(I would describe myself as an illiterate physics enthusiast, so I hope you'll forgive me if my ignorance is borderline offensive.)
If I've understood anything of the concept of time dilation, your ...
- 141
9
votes
4
answers
3k
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Can we show that time is orthogonal to space?
It's easy to show that the time we measure is "in a different direction" from the space directions we measure. However, it's not immediately obvious to me that these directions are orthogonal.
How do ...
- 313
8
votes
1
answer
755
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What coordinate system is used to describe planets positions in the universe?
How are planets positions described in the space and in respect to what?
For example is Sun the reference point and right now at this moment, the Earth has coordinates X, Y and Z?
Edit1:
I found ...
- 181
3
votes
3
answers
537
views
Why is proper time $d\tau$ equated to spacetime length $ds$?
Follow-up to this question: Why proper time is a measure of space?.
The selected answer to me tells us why proper time is an invariant quantity, but I'm still wondering why we equate it to $ds$. Can ...
- 1,261
3
votes
4
answers
677
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How close should you get to speed of light, in order for time to be dilated?
Recently I was watching Carl Sagan's Cosmos: A Personal Voyage. In episode 8 ("Journeys in Space and Time") there is a scene presenting the idea of time dilation, due to traveling close to the speed ...
user187075
1
vote
9
answers
25k
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If an event happens 10 light years away and we observe it here, did it actually happen 10 years ago?
I'm sorry if this question has been answered a squillion times; I need someone with smarts to explain it to me. If an event happens at a distance of 10 light years away, and we observe it here, at a ...
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