6 votes

Moving in the same direction as a photon

The speed of the photon is the speed of light, and that remains constant regardless of what speed you are moving at. So the answer is the latter - the photon moves at the speed of light.
  • 18.1k
4 votes

Does it actually make sense to talk about "An inertial frame" instead of a collection of frames that are inertial with respect to another?

Newton's first law of motion says that an object that starts moving at a constant velocity, and isn't acted on by an external force, will continue moving at that velocity forever. Let me define two ...
  • 41.5k
2 votes

How does SR explain constant light speed where the distance between observer and light source is increasing?

You are neglecting the relativity of simultaneity and length contraction. All three are needed to explain the invariance of $c$. Specifically, the usual derivation is to assume the invariance of $c$ ...
  • 78k
2 votes

Is there a Lorentz contraction of the radius of the rotating disk, after all?

I suspect the problem is that we are missing context, and Einstein is referring to some of the specific variables used in Petzoldt's derivation. Looking at the whole letter (this is Einstein to Joseph ...
1 vote

Conceptual relations between tick indications of a clock and corresponding tick-response indications of a receiver observing that clock

It's called the Doppler Shift: $$ f'_{\rm received} = \sqrt{\frac{1+\beta}{1-\beta}} \times f_{\rm rest} $$ This differs from the thought-experiment observed clock rate: $$ f_{\rm observed}' = f_{\rm ...
  • 26.9k
1 vote

How does SR explain constant light speed where the distance between observer and light source is increasing?

The key to understanding SR is to understand the relativity of simultaneity, which is the cause of effects such as time dilation and length contraction. Suppose you walk East past a stationary person ...
  • 22.1k
1 vote
Accepted

How would a stationary observer perceive an object moving near the speed of light on a closed loop?

We know what the train would look like because we have a practical experiment - the Large Hadron Collider. Although this has bunches of protons instead of a train and a vacuum tube surrounded by ...
  • 39.6k
1 vote

How do emitted photons in a moving light clock keep moving sideways with the clock when photons have no mass and therefore no inertia?

Just follow your own logic in another direction and you will see that your conclusion is nonsense. Imagine the light clock is stationary, so that according to your intuition the laser is 'pointing ...
  • 22.1k
1 vote

What is the relevance of the Lorentz factor in general relativity?

The Lorentz factor turns up in GR when physical observables are involved, particularly under transformations between different (local) frames. Sadly there is usually little attention given to such ...
1 vote

How do emitted photons in a moving light clock keep moving sideways with the clock when photons have no mass and therefore no inertia?

The light moves on a slant because it is emitted on a slant. The wave propagates perpendicular to its lines of constant phase, which in a stationary laser a parallel to the aperture, say: $$ \phi(x, z,...
  • 26.9k
1 vote

How do emitted photons in a moving light clock keep moving sideways with the clock when photons have no mass and therefore no inertia?

Once emitted, light travels in a straight line. In the moving light clock thought experiment, the light is emitted (from the point of view of an observer who sees the clock under motion) in a diagonal ...
1 vote

How meaningful is the notion of 'now' here on Earth?

scale of relativistic effects To get a sense of scale, the Lorentz factor appears in many S.R. equations and gives the general scale of relativistic effects. $$\gamma = \frac{1}{\sqrt{1-\left(\frac{v}{...
  • 6,143
1 vote
Accepted

Measurement of an Inertial frame according to two other inertial frames at the same position

This can be solved in a straightforward (but not particularly simple) manner using the Lorentz transforms. Here there are 3 reference frames of interest, the reference frame of the drawings $S$, the ...
  • 78k

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