schapel wrote:I think it's more correct to say that an electron emitting a photon is an "electromagnetic interaction" rather than an example of the electromagnetic force. The latter term seems to imply there's a force acting between the electron and the photon. Well, there is actually a force between them, because the photon shoots one way, so the electron must experience an equal force in the opposite direction. But the electron and photon are not actually repelling each other electrically or magnetically.
An electron which emits a photon experiences a change in mass-energy and a change in momentum at the moment of emission; however, that is where the interaction ends. There can be no interaction after the photon is emitted because that would require the interaction to take place faster than the speed of light (because the photon is moving away at the speed of light).
PM 2Ring wrote:It's sometimes said that neutronium is held together by gravity, but that's not quite right. The formation of neutron-degenerate matter requires very high pressure, gravity is merely a way of achieving that pressure.
But neutron-degenerate matter will not remain in a bound state except under the influence of gravity. Perhaps we could say more accurately that neutron-degenerate interactions allow gravity to hold neutronium more densely than it would otherwise be able to?