**Ask a monkey a physics question thread**

[MadMojoMonkey]

More silly questions.

How dare you suggest these are silly questions!

If a photon is absorbed, does its wave disappear?

Ummm. Words.
Disappear? :/

Dis-appear... yeah. A photon being absorbed is exactly that. Dis-appearing. Oh wait. Actually it's the fact that the photon was absorbed which allowed it to "appear" to the observing particle. :/ words.

A photon being absorbed means before there was 1 photon and now there are 0 photons. So yes, the wave of the photon collapses. The energy carried by the photon will be transferred to the particle which absorbed it, in accordance with the Law of Conservation of Energy (and accepting that mass may be one expression of energy).

Say one photon was created in a vacuum in an area of space that was completely devoid of energy.

We really need at least 2 photons to have any hope of preserving said conservation law, and all his stern-looking friends, who are giving me the stink-eye and waving their fists,

but I'll play along.

The wave from that photon could propagate for light years without encountering anything. Say you had an array of detectors that provided complete coverage of half of the sphere of 1 light year radius from the source of the wave. Would those detectors have a 50% likelihood of seeing the photon, and then would the other half of the wave disappear if they did?

Given a perfectly random initial trajectory of the photon, then yes, 50%... assuming the detector has 100% efficiency.

Other half? You lost me.
At any rate, the entire wave packet that is the photon is absorbed.

Think of the single slit experiment. The rippled pattern looks like wave interference. It is also true that when a photon is detected, it always has the energy of exactly 1 photon. Never half a photon here and the other half over there.
This is the meaning of "quantum." They come in discrete bits. They act like waves in many ways, but they act like particles, all the same.