Thought experiment with electron and proton

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  • #26
BruceW
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speaking totally classically, the electron would spiral further in towards the proton, and would get arbitrarily close to the proton, releasing an arbitrarily large amount of radiation energy. clearly not something that we want in our physical theory. yay for quantum!
 
  • #27
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Crash or landing, either one is fine by me. The point is that whatever you call it, it doesn't happen.

If it did happen then we wouldn't have any atoms. Electrons would continue getting closer and closer to the protons until the Coulomb forces got so large that you would get the electron and proton fusing into a neutron (inverse beta decay).

You wouldn't form a neutron because the neutron's mass is higher than the combined electron+proton mass. What would happen is that the electron would keep falling in, emitting photons, losing energy, until the system's total energy would be negative (Including the rest masses) creating exotic matter. That bottomless pit is a catastrophic failure of classical physics.
 
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  • #28
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You wouldn't form a neutron because the neutron's mass is higher than the combined electron+proton mass. What would happen is that the electron would keep falling in, emitting photons, losing energy, until the system's total energy would be negative (Including the rest masses) creating exotic matter. That bottomless pit is a catastrophic failure of classical physics.

Do we know enough about the quarks to tell how they would classically change this analysis ? Or is that already taken into account in this analysis ?
 
  • #29
Dale
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There are no quarks classically.
 
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  • #30
Dale
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You wouldn't form a neutron because the neutron's mass is higher than the combined electron+proton mass. What would happen is that the electron would keep falling in, emitting photons, losing energy, until the system's total energy would be negative (Including the rest masses) creating exotic matter. That bottomless pit is a catastrophic failure of classical physics.
OK, either way we would not have atoms. Since we observe that we do have atoms the classical analysis fails.
 
  • #31
BruceW
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yeah, it is kind of silly to talk about 'how would things work if we allowed some of quantum mechanics but not other parts'. For anything to properly make sense, either stay fully classical, or go into the quantum regime. Anything in the middle is not so useful. Well, maybe there are some exceptions, like how semi-classically, the electron in the atom feels a magnetic force from the proton, since from its viewpoint, the proton is moving around it. But really, it is better to do these things the proper (fully-quantum) way.
 
  • #32
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No matter how you look at it it is simply not correct that it winds up "going back and forth forever".

Why not ? Are there observations that rule it out ?
 
  • #33
Dale
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Yes. Atoms at rest are observed to not emit synchotron radiation.
 
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  • #34
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Yes. Atoms at rest are observed to not emit synchotron radiation.

That seems to rule out only curved electron orbits.
 
  • #35
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Yes. Atoms at rest are observed to not emit synchotron radiation.

You mean atoms in a stationary state.
 
  • #36
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Electrons in a stationary atom are moving, since they have kinetic energy. So in a sense they are eternally moving back and forth.
 
  • #37
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It is contrary to observation.

All of it's kinetic and potential energy, yes.

Classically the electron would, by radiating, increase its kinetic energy and decrease its potential energy indefinitely. That is possible because classical point charges have infinite electromagnetic self energy. The total energy would never become negative.
 
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  • #38
OmCheeto
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Classically the electron would, by radiating, increase its kinetic energy and decrease its potential energy indefinitely.
Indefinitely? If something is radiating energy away, how can this go on indefinitely?
 
  • #39
Dale
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That seems to rule out only curved electron orbits.
Obviously. The Coulomb potential couldn't lead to any others.
 
  • #40
Dale
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Electrons in a stationary atom are moving, since they have kinetic energy. So in a sense they are eternally moving back and forth.
They may have KE, but their expected position is not changing. They are not moving back and forth.

Classically the electron would, by radiating, increase its kinetic energy
You have this exactly backwards. An electron loses KE by radiating.

In any case, atoms are not observed to radiate indefnitely either.
 
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  • #41
Dale
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This thread is such a mess of classical and quantum concepts and blatant misinformation that it is not useful any more, if it ever was useful.

The question in the OP was clearly and correctly answered back in post 2. If forcefield does not like the answer then he/she is free to consult an actual textbook.
 
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