# Absolute rest

1. Jan 19, 2005

### beckett

Hi,

I'm looking into electromagnetic radiation at the moment and something has just entered my head. If its true that an electron will not radiate unless its velocity changes with time then could this property be used to determine absolute rest. That is, how can we know that if something is really at rest in the universe, even the wire (and thus the electrons) i am holding is accelerating at the rate of the rotation of the earth so even it must be radiating even though i consider it to be at rest relative to me.

2. Jan 19, 2005

### chroot

Staff Emeritus
If an object is not accelerating, it is not necessarily at rest -- it could also be moving at a constant velocity. Acceleration is not "relative" in the same way as uniform motion.

- Warren

3. Jan 19, 2005

### Gonzolo

Welcome to special relativity. A wire is neutral, but if it was a static-charged balloon instead, you would seem to have a paradox. This what Einsteins's 1905 paper is about. It is apparent that you have radiation in the rest frame, yet none in the accelerating frame.

4. Jan 20, 2005

### Crosson

You: "Ah, a charge that is not radiating, it must not be accelerating!"

<Your friend in a free falling gravity frame that is locally equivalent to yours. He can toss a balll back and forth between his hands the same way that you can.>

"I see the charge radiating man, its accelerating."

The point is, physics laws in his frame of reference are equivalent to yours*, and you both measure different values for the acceleration of a charge. Therefore acceleration is relative, if you want it to be.

*with the proper tensor formulation of the laws of physics.