# Electron orbital the earth will radiate?

1. Oct 26, 2013

### magnetar

If an electron orbital the earth only influence by gravity,does it emit electromagnetic waves? if so, the radius will decay,eventually falling on earth?

2. Oct 26, 2013

### HallsofIvy

Staff Emeritus
I have no idea what you mean by "an electric orbital the earth only". Are you postulating an electron orbiting the earth? Why bother with such a strange example? Using the "planetary model", an electron orbiting the nucleus of an atom is accelerating and so must be emitting waves- which would result in its losing energy until it cannot orbit the nucleus. That is one of the things that led to the development of quantum physics. The "planetary model" is invalid and an electron emits electromagnetic waves only when goes from one "energy level" to another.

3. Oct 26, 2013

### snorkack

Quantum theory approaches classical theory for large quantum numbers. An electron orbiting Earth by gravity alone is on an orbit with a large quantum number. Therefore it has a large number of lower energy levels, and can and will emit electromagnetic waves as it goes to lower energy levels.

The relativistic problem is whether an electron held stationary in a field of gravity would be emitting electromagnetic waves?

4. Oct 26, 2013

### WannabeNewton

It would not.

5. Oct 26, 2013

### snorkack

Sorry, the original problem was relativistic after all.

Principle of equivalence says that free fall has to be indistinguishable from inertial movement.

Since a charge carrier moving in a straight line does not radiate, is a charge carrier in free fall allowed to radiate?

6. Oct 26, 2013

### WannabeNewton

Let's clear some stuff up first. The principle of equivalence says that free fall is locally equivalent to inertial movement. It also says that being at rest in a static gravitational field (meaning following orbits of the time translation symmetry) is locally equivalent to acceleration. All these things presuppose that the system one is working with is local in space-time. An electron carries an electromagnetic field which fails to satisfy this requirement so the equivalence principle does not apply here.