# Questions tagged [special-relativity]

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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### How do two observers see the same photon?

Here's what I'm trying to solve. Suppose we have two observers (call them A and B). Both are inertial. Their frames of reference are represented on the following space-time diagram (the black axes ...
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### What kind of tensor is $\psi^\dagger\psi$?

I'm trying to find how does this quantity $$\psi^\dagger\psi$$ transforms under a Lorentz transformation. Where $\psi$ is a Dirac spinor. What I've tried so far: It is known that a Dirac spinor ...
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### Demonstration of Electromagnetic Tensor antisymmetry

I've already made a post about this topic here, but I realized that I didn't understand the explanation on that post. in Chapter 7 of Rindler's book on relativity, in section about electromagnetic ...
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### Is special relativity falsified by the Aharonov Bohm effect?

The Lorenz gauge is the only Lorentz invariant electrodynamic gauge. If the vector potential has physical meaning, as in the Aharonov–Bohm effect, then the gauge condition can not be arbitrarily ...
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### How does the period of an oscillating mass-spring system comply with the relativistic time dilation as viewed by a moving observer?

Consider a simple mass-spring system. The spring is attached to the ceiling in the lab frame of reference and a block of mass $m'$ is suspended from the spring. The mass starts to oscillate with ...
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### Inertial mass and gravitational mass [closed]

I would like to ask about gravitational mass. I know inertial mass is changing by motion (speed) according to $m=\frac{m_o}{(1-v^2/c^2)^{1/2}}$ And also that is inertial mass which sits in $E=mc^2$. ...
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### Special relativity basic concept [closed]

When someone travels really fast, do things seem to slow down around him or do things go faster around him?
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### Does matter exits in quantum realm? [closed]

I have been taught that matter exists but with double split experiment I was shocked to know that the matter doesn't even exits, it's the state we are which we feel as matter but in real scenario we (...
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### What do I need to build special relativity?

If I postulate the principle of relativity and the constancy of the speed of light for every inertial observer can I then prove all SR? Or do I need some other postulate? For example: do I need to ...
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### Why is the photon clock equivalent to all clocks?

I can understand why, if the speed of light is invariant, a photon clock would tick slower. I find this explanation very useful in terms of introducing the idea of time dilation (also because it ...
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### Lorentz spinor in Lorentz $\rm Spin(3,1)$ signature and the real structure?

In this paper: J. Wang, X. Wen and E. Witten, "A new ${\rm SU}(2)$ anomaly", J. Math. Phys. 60 (2019) 052301, arXiv:1810.00844, it says the following in p.2, It says for $3+1$ dimensional ...
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### Is mass actually relativistic? [duplicate]

Is mass physically relativistic in any way? I have seen many places online--such as derivations of relativistic momentum--where entities have a relativistic mass (where relativistic mass=rest mass* ...
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### Which postulates did Einstein really use in his 1905 derivation of the Lorentz transformations? [closed]

Einstein explicitly states in "Zur Elektrodynamik bewegter Körper" that the only two postulates he requires for his derivation of the Lorentz transformations are 1) the principle of ...
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### What would be the increase of gravity if we create a new world slightly bigger than the earth? [closed]

I need to know what would happen if I increased the earth's size by a small percentage to make a fictional world similar to earth. So my thought process is this: My thinking started with increasing ...
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### Light catching up with a uniformly accelerating object

Is there a formula for how long it takes light to catch up with a constantly accelerating object given initial distance?
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### Neglected effects of special relativity for the case of a fall into a black hole?

It has been said that falling into a black hole and crossing the event horizon would appear as "nothing out the ordinary" for the in-faller (especially for a super-massive BH, but lack of ...
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### How relative is speed?

A short question, because the math got me confused. If in my inertial reference frame, I see a dude going away from me at a speed $v$. Then, from his frame of reference (which is also inertial) he ...
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### Einstein: 'SR is a theory of invariants, not relativity' — source? [migrated]

It is occasionally remarked that Einstein was unhappy that SR became referred to as a ‘theory of relativity’, when in his eyes it was, much more importantly, a theory of invariants (Invariantentheorie)...
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### In relativity, why does spacetime diagram have position on $x$-axis and time on $y$-axis?

In regular Newtonian physics, we use $x(t) - t$ graph to under position of a particle but why is it that in special relativity that we switch up the axis notation? I was seeing the lecture by Leonard ...
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### For Einstein's equation $E= mc^2$ is it energy that increases or mass as the velocity increases? [duplicate]

I will be surprised if no one asked this before and I would be happy if it is answered already although I haven't located it just yet! From Einstein's original paper "Does The Inertia of a Body ...
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### Time dilation in Einstein's train

Wikipedia states that a clock that is moving relative to [observer] will be measured to tick slower than a clock that is at rest in their frame of reference and they explain it using two pictures: ...