23 votes

What exactly would it take to show (hypothetically) that the speed of light (in vacuum) is not constant?

You are correct and in good modern treatments, people are careful to say that it's only meaningful to say that dimensionless quantities change with time. The "grown up version" of looking at ...
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11 votes
Accepted

What exactly would it take to show (hypothetically) that the speed of light (in vacuum) is not constant?

In the Minkowski metric the $dt$ is the time I measure on my clock and the $dx$, $dy$ and $dz$ are the distances I measure with my ruler. That's how those coordinates are defined. Suppose we choose ...
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11 votes

How to prove that time stops at the speed of light using general relativity in a flat spacetime?

Let's try to do the computation from the start, so you can see where you missed some things,first of all the Minkowsky metrix is: \begin{equation}g_{\mu\nu} = \begin{pmatrix} 1 & 0\\ 0 & -1 \...
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  • 551
10 votes
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How to prove that time stops at the speed of light using general relativity in a flat spacetime?

You have claimed that $v_x=v$, in other words that the X component of the four velocity is the classical velocity, but this is not correct and in fact you want $v=v_x/v_t.$ Once that is clarified then ...
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5 votes

Is Feynman right? Does mass change with speed?

Because speeds are relative to an observer, if I as an observer move quickly away from an object, is there some sense in which I change its mass? This is one reason that modern physicists have ...
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4 votes

What exactly would it take to show (hypothetically) that the speed of light (in vacuum) is not constant?

The answer was already said by others, but I will rephrase it a little differently: Spacetime metric is not the end. You also need other physics than just structure of spacetime, like, for example, ...
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3 votes

What is wrong with these ways of measuring one-way speed of light?

There is no way to measure the one way speed of light (OWSOL), so this experiment is no exception. To measure the OWSOL it must be treated as a variable and then the equations of the experiment need ...
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2 votes

If during the resistance of a resistor against an electric current particles are colliding why not say that they produce a lot of gamma rays?

Each current carrying electron in a wire has an energy of the order of ten electron Volts (see this Wikipedia article). To create a gamma ray you need energy of around ten thousand electron Volts or ...
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  • 33.9k
2 votes

Surpassing 70%c of spinning black holes - projection

The quote in the OP is not exactly right. I guess this is the typical case where a scientific report is misinterpreted and reposted in a news article. The source of the article you quote is this ...
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2 votes

Do objects outside the Hubble sphere violate special relativity?

Yes, this violates special relativity. Special relativity is only valid in a region of spacetime which is small enough that curvature effects are negligible. The Hubble sphere is not a small region of ...
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1 vote

If a proton travels exactly at 99% of speed of light are the individual velocities of the quarks inside it also exactly 99% of $c$?

The quarks inside a proton do not have well-defined trajectories. The reason is basically the same set of problems as the “planetary orbits” of electrons in the Bohr model, only more so because the ...
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  • 71.8k
1 vote

How can gravity change the wavelength of a photon without the two peaks or troughs to accelerate one from the other?

How can gravity change the wavelength of a photon without the two peaks or troughs to accelerate one from the other? So is it possible that gravity accelerates light? Yes. In general relativity the ...
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1 vote

At which fraction of light speed could I expand ten times, and 100 times, my clock's ticking?

You need to use the Lorentz transformation from your frame of reference to the reference frame moving relative to you. The calculation becomes simpler if you assume that the measurement between the ...
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  • 165
1 vote
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Calculating the one-direction speed of light

The flaw is that you can't assume the clocks stay synchronized. Assuming they stay synchronized is equivalent to adopting Einstein synchronization, and thus adopting the convention that the one-way ...
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