# Question about Quantum Theory regarding hydrogen atom and photon

1. Mar 11, 2012

### euquila

Assume the universe consists of a single photon, a single atom of hydrogen and a spherical detector (like an encompassing shell) with a semi-infinite radius.

The photon gets "absorbed" by the hydrogen atom.

Moments after the photon is emitted.

My question is the following: from the time the photon is emitted until it is detected, is it correct to say that the photon is everywhere* along a 2D spherical front? When it gets detected, will it show up as a point at a random location on the detector?

*I get the nagging feeling that the word everywhere is not accurate.

Also, does this example require more assumptions about the uncertainty in the electron/proton's momentum and position?

Thank you.

2. Mar 11, 2012

### Staff: Mentor

QM does not address this question. Rather, it is the subject of interpretations of QM. There are a number of interpretations of QM, all of which use the same math for predicting the the results of actual observations, and therefore cannot be distinguished by experiment. Some people here argue a lot about interpretations of QM, based on philosophical or metaphysical preferences.

Yes.

3. Mar 24, 2012

### euquila

jtbell: What is your opinion/interpretation on what is happening?

Photons assuredly do not blank out of existence simply because physics/mathematics is missing part of the story. Do you think string theory will eventually provide a better interpretation?

4. Mar 25, 2012

### Jano L.

It is also fair to say that QM does not describe dynamics of electromagnetic field at all. In Schroedinger's equation, there is nothing corresponding to radiation. No photons.

Electromagnetic radiation is addressed by quantum theory of field and there the photons are introduced. But this theory in turn has difficulties describing atoms exactly, so we do not have exact calculation of what happens even for the simplest case like that you mentioned.

The answer in quantum theory of fields depends also on how you look at quantum field $A$ (EM field). If you understand it as a probability function that photons will appear somewhere and do something, then (I think) the collapse of A happens instantaneously on the whole spherical surface, because it is only update of our knowledge about the state of the photon.

If you think A is something objective independent of the observer, then the collapse cannot be instantaneous in relativistic theory, so, if it happens at all, it has to be continuous process.

I am trying to discuss similar question "Are there quantum jumps?" here: