# Accelerating charges and frames of reference

1. Feb 25, 2015

### lavinia

An accelerating charge radiates light. But in its own frame of reference it is stationary. So it does not emit light.
How is this explained?

Extreme Example:

A charge inside an elevator is falling in a gravitational field. The elevator is lined with a light sensitive sensor that triggers a chemical explosion that obliterates the elevator in mid-air.

Inside the elevator a man is reading a book. The charge is stationary in his free fall frame. The man finishes the book just as the elevator hits the ground.

2. Feb 25, 2015

### Staff: Mentor

Acceleration is invariant, meaning that it is actually felt by the object ubdergoing acceleration and all observers will agree that the object is actually accelerating. The acceleration due to gravity is not an actual acceleration in the sense that an accelerometer would not know whether it is floating in space or in free fall under the influence of gravity. So a charge falling in a gravitational field shouldnt radiate, but this has not been experimentally verified as far as i know.

3. Feb 25, 2015

### mrspeedybob

4. Feb 25, 2015

### zoki85

5. Feb 25, 2015

### Staff: Mentor

Got a reference or an explanation for this?

6. Feb 26, 2015

### zoki85

Accelerated charge (with respect to stationary observers) emits EM radiation regardless of the cause of acceleration. But detection of EM radiation is relative, not absolute. It depends on the motion of receiver/antenna and EM field. Antenna of the observer in uniformly accelerated frame of the charge should not detect radiation from co-moving accelerated charge.

7. Feb 26, 2015

### Staff: Mentor

If a charge and an observer are both under acceleration, shouldn't the charge experience back-reaction from the emitted radiation? And why wouldn't the observer pick up this radiation?

8. Feb 26, 2015

### zoki85

I said why: Becouse detection of EM radiation is relative. I'm positive that can be rigorously shown by appropriate transformation of coordinates between the two systems in framework of GR (and probably is standard result).

9. Feb 26, 2015

### Staff: Mentor

Can you elaborate on that?

10. Feb 27, 2015

### zoki85

Most preceise elaboration is derivation. Luckily, I've just found a nicely written paper which backs up the statement:
http://arxiv.org/abs/gr-qc/9903052
Even without going through all the steps of derivations, I can say I have at least two reasons why I can thrust it.

11. Feb 27, 2015

### Staff: Mentor

Interesting read. Thanks, zoki.

12. Feb 27, 2015

### Vanadium 50

Staff Emeritus
It seems to be the general consensus that the OP's issue is that the problem wasn't complicated enough. Instead of a straightforward question on electromagnetism, we have to throw in gravity. Then gravitational radiation. Then semiquantum gravity.

13. Feb 27, 2015

### Staff: Mentor

Welcome to PF!

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