# Tagged Questions

The special theory of relativity describes the motion and dynamics of objects moving at significant fractions of the speed of light.

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### Special relativity paradox and gravitation/acceleration equivalence

One of the features of the black hole complementarity is the following : According to an external observer, the infinite time dilation at the horizon itself makes it appear as if it takes an ...
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### Relativity gedanken experiment

Lets consider the following thought experiment: A spaceship is in circular orbit around Earth traveling at 99% of $c$ (the orbital distance is chosen in such a way that inside the ship there are no ...
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### Why do we write the lengths in the following way? Question about Lorentz transformation

Yesterday we have studied the Lorentz transformation in school. So we have two frames of reference, $S$ and $S'$ . $S$ is stationary and $S'$. $S'$ has a constant velocity $v$, relative to the $S$ ...
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### Diagonal lorentz invariant matrix

Is there any general way to show that diagonal Lorentz invariant matrix must be proportional to $g^{\mu \nu}$? I can show it is true, but my proof is not clean enough for such a simple problem.
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### Invariance of Mass in SR: Comparing Taylor and Wheeler's Spacetime Physics with a Comment made in Purcell and Morin's Electricity and Magnetism

Purcell and Morin's Electricity and Magnetism mentions on pp. 241: Mass is not invariant in the same way (in a relativistic theory). We know that the energy of a paritcle is changed by its motion, ...
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### Length Contraction in Relativity

Let's suppose we have a one dimensional rod made of elementary point particles, in contact with each other placed along the x-axis.If the rod is moving along x-axis then we know (because of relativity)...
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### Why does time dilation cause you to age slower? And is time considered relative to the observer?

I understand that the higher your velocity the slower light will move. But how does time itself slow down while you are moving faster?
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### Why would speed of light be directional if spacetime is discrete?

In Feynman's Simulating Physics with Computers, Feynman states that "we might change the idea that space is continuous to the idea that space perhaps is a simple lattice and everything is ...
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### Has relativity of simultaneity been directly observed?

I know that thought experiment about trains when a flash of light in the middle reaches the both end simultaneously for a passenger but different times for the bystander. So were there (non-thought) ...
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### Alternative view on mass energy equivalence? E=mv^2 instead of E=mc^2 [closed]

(this is old thread, but i have edited this question to be more brief) In the paper, http://arxiv.org/pdf/physics/0206061.pdf "Fundamental Disagreement of Wave Mechanics with Relativity", and few ...
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### Can we work out how fast we are traveling by looking at our mass?

If we (the galaxy) were traveling close to the speed of light; relativity says we would need proportionally more energy to go faster. Given that relative to the cosmic microwave background, the Local ...
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### Is there energy output when mass moves between two spacetimes [closed]

Is there energy output when mass $m$ moves between two spacetimes? Say, it starts in a flat spacetime and then falls into a black hole (other examples don't come to mind, but this doesn't mean they ...
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### The “Other” mechanical clock appears to click slower from both observers point of view. How? [duplicate]

In professor Shankar's Yale University lecture Lorentz transformation video, https://www.youtube.com/watch?v=202fU9qIVK4 , at the time period between 49:00 to 53:00, he describes light clocks and how ...
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### Why Sun light can reach us if Time is dilating?

I understand that if something is moving with constant speed in respect to an observer, the time of the moving one runs slower, so the more your speed is, the more your time ticks slower. Which ...
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### Watching a live stream in spaceship traveling away from earth close to speed of light

My name is Dennis. This might sound just straight up ignorant of basic concepts of physics. I was having a conversation with my friend in regards to streaming a live event on earth to a spaceship ...
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### What is the velocity of the photon through the fourth dimension x4? [closed]

Photons are real, physical objects. The fourth dimension is a real, physical entity. Therefore, photons must have a relationship with the fourth dimension. They must have some velocity relative to ...
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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 "...