All Questions
Tagged with spacetime speed-of-light
36
questions
27
votes
7
answers
22k
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Why are objects at rest in motion through spacetime at the speed of light? [closed]
I read that an object at rest has such a stupendous amount of energy, $E=mc^2$ because it's effectively in motion through space-time at the speed of light and it's traveling through the time dimension ...
- 4,607
10
votes
5
answers
3k
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Reducing General Relativity to Special Relativity in limiting case
I understand that general relativity is applicable to gravitational fields and special relativity is applicable to case when there is no gravity. But is there a derivation on how to reduce General ...
- 2,566
10
votes
1
answer
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How is it that distortions in space can be measured as distances? [duplicate]
Imagine yourself and anything you're able to perceive to be drawn onto a rubber band. Any means of determining distances would be affected by the stretching/contracting of the rubber band. The ...
- 211
20
votes
8
answers
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How does velocity cause time dilation?
I've been trying to learn about the speed of light and time dilation, but I'm at an impasse.
The presented facts say that if I travel around the solar system at 50% the speed of light and then come ...
- 317
17
votes
3
answers
3k
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Proving invariance of $ds^2$ from the invariance of the speed of light
I've started today the book of Landau and Lifshitz Vol.2: The Classical Theory of Fields $\S 2$. They start from the invariance of the speed of light, express it as the fact that $$c^2(\Delta t)^2-(\...
- 171
4
votes
5
answers
745
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Is everything relative? Length and time?
Yesterday I woke up in the night after having a dream (after sleeping late watching a SciFi film on space). It had this:
Suppose you are told that the linear size of everything in the universe has ...
- 592
2
votes
5
answers
1k
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The vacuum light speed: Is it really constant, i.e., independent of location in space-time?
I am by no means an expert in this field, however something puzzles me about the speed of light and the relativity of time and space (space-time).
Is is universally acknowledged that the speed of ...
- 171
2
votes
1
answer
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Twin Paradox Without Acceleration [duplicate]
So I've been doing a lot of reading about the twin paradox and have encountered several different explanations that strive to resolve it. First off let me start by saying general relativity is not an ...
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11
votes
3
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Is the edge of our Hubble Sphere within our Cosmic Event Horizon and why?
I was recently shown a pretty cool video about common cosmological misconceptions. It got me reviewing the different between event horizon (current distance within which we will see/interact), ...
- 14.2k
10
votes
5
answers
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Measuring the speed of light and defining the metre - absolute or relative?
If the metre is now defined as the distance light travels in vacuum in $1/299\,792\,458^{\textrm{th}}$ of a second and the speed of light is accepted to be $299\,792\,458\ \textrm{m}\,{\rm s}^{-1}$, ...
- 1,187
9
votes
5
answers
1k
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Speed of gravitational waves vs speed of light
I own an educational YouTube channel on physics and astronomy. I am currently working on a gravitational waves video extension to my "How Fast Is It" video book on relativity theory. I have a question ...
- 107
6
votes
3
answers
3k
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If something is not moving in space, is it moving on the time axis at the speed of light? [duplicate]
I heard this theory yesterday:
If something is not moving in space, then it is moving on the time axis at the speed of light.
I realize that in essence there is no object which can be considered as "...
- 163
0
votes
3
answers
1k
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Why are the coordinate axes of a moving frame $K'$ tilted in spacetime diagrams?
I am currently trying to self-teach special relativity (if relevant, I am still in school). I think that I already have a good intuitive understanding of, for example, time dilation and length ...
- 3,778
4
votes
4
answers
380
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Why is the speed of light used to define the fourth axis of spacetime?
The four axes of spacetime are $x, y, z$ and $ct$, where $c$ is the speed of light, and $t$ is time. Why is the speed of light (not any other speed) used to define the fourth axis of spacetime? If ...
- 1,653
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 ...
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