# Tag Info

## New answers tagged special-relativity

### Far field approximation for massive Klein-Gordon equation in 3+1D

You don't need to take $t' \rightarrow +\infty$ and $r' \rightarrow +\infty$ individually. The quantity that should be large is the proper distance i.e. $\sqrt{t' ^{2} - r' ^{2}} \rightarrow +\infty$. ...
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1 vote

### Relative velocity of light beam and rocket (special relativity)

It is useful to draw a diagram $t \times x$. Then calculate the equations for the straight lines of the beam and of the rocket trajectory. The interception is the event $t,x$ where the light reach the ...
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### Moving clocks tick slow and time dilation

The statement that 'moving clocks tick more slowly' is misleading in two important ways. Firstly, if while you sit at your desk reading this you are passed by two spaceships in line, one ahead of the ...
• 18.8k
Accepted

### Is this proof that massless objects cannot be charged?

As was pointed out in the comments above, one has to use relativistic mechanics to talk meaningfully about massless particles; you can't just write $F = ma$ and expect it to work. And, indeed, it ...
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### Is this proof that massless objects cannot be charged?

I disagree with your conclusion that $qE=0$ if $m=0$. My interpretation is that in such a case the acceleration is infinite, so the product is well defined. It is only natural to think that in ...
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### Is this proof that massless objects cannot be charged?

I think a massless electron traveling at $c$ under classical Maxwell's Eq. would be problematic, but: The Standard Model says electrons were massless and charged before Spontaneous Symmetry Breaking, ...
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### Moving clocks tick slow and time dilation

Let’s say Alice measures two events separated in time by ΔtA according to her own watch, and she measures those events in the same place, so she has measured her own proper time. Technically, the ...
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### Moving clocks tick slow and time dilation

$\Delta t_{B}'$ is the time the moving observer (Bob) measures between the events for which Alice measured $\Delta t_{A}$. Do not conflate this with proper time though. Proper time refers to the ...
• 611
1 vote

### Relative velocity of light beam and rocket (special relativity)

But that would imply that it doesn't matter whether the rocket is stationary, or moving at v = 0.8c towards the light beam? What am I missing exactly? You are not missing anything. That is correct. ...
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### Why do particle accelerators need to smash particles together?

We use particle accelerators to put different kinds of particles close enough together for them to experience interactions, which we can then detect. The easiest way to do this difficult job is to ...
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1 vote

### Why do particle accelerators need to smash particles together?

Why doesn’t the kinetic energy produce new particles before the collision? I assume that it is because there is an inertial frame moving with the particles in which they don’t have any more energy ...
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1 vote

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### Why is proper time equated to $ds$?

In general, the separation between two events contains a spatial component and a time component. If the separation is time like, the time is large and the distance is small. You can travel between the ...
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