[ceptimus]

Originally Posted by peacegirl

So are they part the source, or are they independent of the source?

The photons are emitted by the source, but after emission they are independent of it.

Once the photons are travelling away from the source, nothing that happens at the source can affect them. For something to affect the photons, it would need to catch up with them. This would involve travelling faster than the photons themselves and nothing can do that.

Note that the emission source may have an associated gravitational field that can affect the photons as they move away (red shifting them). However, it's the field at the time of emission that matters. In the unlikely event that the gravitational field of the object changes after the photons have been emitted, then even that can't affect the photons. It may cause a gravity wave to pursue the photons, but even gravity waves can't travel faster than light.

An analogy is a gun shooting bullets. After the bullets have been fired, the gun could be moved, painted blue, dropped in a bucket of water or be crushed. None of this would affect the flight of the bullets in any way.