What Happens When an Electron Interacts with a Photon in an Empty Space?

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Discussion Overview

The discussion revolves around the interaction between electrons and photons in a nearly empty space, focusing on the implications of wave function collapse, the persistence of quantum states, and the nature of these interactions. Participants explore theoretical aspects of quantum mechanics, particularly regarding the behavior of particles in isolation and during interactions.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that an electron's wave function collapses upon interaction with a photon, resulting in a definite spin state until further interaction occurs.
  • Others argue that the electron always carries spin and question the interpretation of wave function collapse, suggesting that the term should not be taken literally.
  • A participant raises the question of how long the collapsed state persists and whether a physical state can change instantaneously, expressing uncertainty about the concept of "zero time."
  • There is a discussion about the evolution of the wave function, with some asserting it follows the Schrödinger equation, while others suggest that the state remains unchanged if no further interactions occur.
  • One participant acknowledges a misunderstanding regarding stationary states and the conservation of probability in the context of wave function evolution.

Areas of Agreement / Disagreement

Participants express differing views on the nature of wave function collapse and the implications of quantum state persistence. There is no consensus on the interpretation of these concepts or the specifics of how interactions affect the electron's state.

Contextual Notes

Limitations include varying interpretations of wave function collapse, the conditions under which states are observed, and the implications of quantum mechanics in a nearly empty space. The discussion does not resolve these complexities.

frogsong
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The other day the following question occurred to me and I was wondering if anyone here might have the answer. Imagine a large piece of space that is really quite empty. Just a few electrons and photons whizzing about. Since these particles rarely interact, most of the time their wave funtions are not collapsed. Now let us suppose that an electron has an encounter with a photon and the electron's wave function collapses and it now has a spin etc. For how long does this collapsed state persist before we can no longer "see" the electron? And furthermore, since most of the particles in this system are not collapsed most of the time, would this system exhibit any unusual properies? I would think that, in fact, a good deal of the universe is rather like this. Thanks for your attention
Frogsong
 
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frogsong said:
For how long does this collapsed state persist before we can no longer "see" the electron?

Hi frogsong, great handle! Since we can't see the electron without bouncing at least one photon off it, it will keep those observable values until it next meets something. The wave function carries along the state (it is better to think of states: the electron is presumably in a superposition of all possible states before the interaction, and after, it is in a particular state; it will stay in that state till something happens to change it.
 
frogsong said:
The other day the following question occurred to me and I was wondering if anyone here might have the answer. Imagine a large piece of space that is really quite empty. Just a few electrons and photons whizzing about. Since these particles rarely interact,


What do you mean...?They interract whenever they meet.

frogsong said:
most of the time their wave funtions are not collapsed.

What's your idea of "wavefunction collapse"...?

frogsong said:
Now let us suppose that an electron has an encounter with a photon and the electron's wave function collapses and it now has a spin etc.

The electron ALWAYS CARRIES SPIN... :wink:

frogsong said:
For how long does this collapsed state persist before we can no longer "see" the electron?

That's just a weird question...If is doesn't interact ever again,his evolution would be dictated by the free particle Hamiltonian.(See SE).

frogsong said:
And furthermore, since most of the particles in this system are not collapsed most of the time,

Weird... :rolleyes:

I'd suggest to reread the V-th principle.And don't take the word "collapse" literally.

Daniel.
 
Last edited:
Ok thanks for the response. I know the electron (for example) has a number of properties assiciated with it but for siimplicity let's just think about spin. So as I understand it, before the interaction with the photon there is no definite spin, just a probability that the spin is x or y. After the interaction the spin is definite. No more nasty probabilities. Then some time later the photon comes back (or another photon comes along) and Whack! the spin is now indefinite again. So we look once, we see the electron, we look twice and it disappears.
OK, now here is a related question. When the photon interacts with the photon, how long does the interaction take? And what is going on while the photon is adjusting the wave function of the electron? What I am really asking here is can a physical state (like spin) change in zero time. And a change can be going from unknown to known. It would seem a strange world where things could change in zero time. I don't think I even know what zero time means.

Thanks again for your thoughts
 
dextercioby said:
If is doesn't interact ever again,his wavefunction would stay the same.

No. The wavefunction evolves according to the Schrödinger equation.
 
Sorry,of course,you're right...I was thinking of a stationary state and the conservation of probability...

Daniel.
 

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