Qualities of electrons

[K^2]

OK, genuine question then. What happens when an atom absorbs a photon? My understanding was that the photon disappears and the atom is placed into some kind of excited state.

You start out with excited electromagnetic field, which carries energy, momentum, and angular momentum. It transfers these quantities to an atom. So an atom is now in excited state, and electromagnetic field went down to ground state. Nothing actually stops being. The photon state is still there. It just lost excitation. The field is there. All of the conserved quantities are there.

There are two self-consistent ways of interpreting what is a photon here. You can call it a collection of all relevant quantum numbers. These get transferred to the atom. I know it's a bit weird to think of it this way, but it's logically consistent, and sometimes useful, to consider atom as "holding" and extra photon. But a more conventional interpretation is that photon is just the state labeled with its quantum numbers, including the four-momentum. And that state remains intact regardless of whether it is excited or not.

It all comes back to the fact that "particles" are really just a result of us quantizing the fields. It's purely a mathematical trick. We have the electromagnetic field, and instead of dealing with all possible configurations of it, we introduce particle operators which "add a particle" or "remove a particle" from the field. But all they do is change field configuration.

Where are those particles if you can't detect them anymore?

Which particle? A proton? You seriously can't find a proton where you are? And yes, it is the proton you're looking for, because they're all the same.

Do you have one evidence to support your claim that they're "somewhere"?

Are you seriously asking me to prove that other protons exist?

I do understant that concept, of course, but I don't understand how you're defending something completely opposite from what my professors of physics were talking to me.

Are you studying Relativistic Quantum Field Theory and doing research in Particle Theory? Because I simplify it a lot for students in lower level QM courses. I know professors do to, because it's impossible to talk about all of this in precise terms until you start doing field quantization.

[Seret]

That's the perspective K^2 uses

I think that's what's at issue here. Concepts such as "particle" and "wave" are just models that can be used to communicate about the physical state of a system. They don't literally describe reality, there are no little balls flying around or wiggly things in the air, although for the purposes of instruction it's perfectly valid to teach that they are until the student is ready to move on to a more subtle interpretation. So it might not be strictly correct from an expert point of view to describe particles vanishing, it's correct enough for a neophyte.

[KSK]

You start out with excited electromagnetic field, which carries energy, momentum, and angular momentum. It transfers these quantities to an atom. So an atom is now in excited state, and electromagnetic field went down to ground state. Nothing actually stops being. The photon state is still there. It just lost excitation. The field is there. All of the conserved quantities are there.

There are two self-consistent ways of interpreting what is a photon here. You can call it a collection of all relevant quantum numbers. These get transferred to the atom. I know it's a bit weird to think of it this way, but it's logically consistent, and sometimes useful, to consider atom as "holding" and extra photon. But a more conventional interpretation is that photon is just the state labeled with its quantum numbers, including the four-momentum. And that state remains intact regardless of whether it is excited or not.

It all comes back to the fact that "particles" are really just a result of us quantizing the fields. It's purely a mathematical trick. We have the electromagnetic field, and instead of dealing with all possible configurations of it, we introduce particle operators which "add a particle" or "remove a particle" from the field. But all they do is change field configuration.

That makes sense - thanks for getting back to me. Or at least it makes qualitative sense - the maths would be way over my head and I suspect that thinking too hard about it would break my brain. As a very distinguished man once said "For those who are not shocked when they first come across quantum theory cannot possibly have understood it."

[Duxwing]

You're getting into particle-wave duality here, this is difficult stuff to grasp without a good idea of how either particles or waves work.

The way I suggest you visualize it is to imagine a photon as a wave packet:

http://www.upscale.utoronto.ca/GeneralInterest/Harrison/SpecRel/Superluminal/WavePacket.gif

The peaks and valleys are related the probability that you'll encounter a photon in that position. This entire packet moves through space at the speed of light.

Basically, as you add multiple waves of different frequencies you can shape your wave into a little packet as you see above. The more frequencies you add the less certain you can be about your frequency but the sharper you can make that peak. So yea, technically photons can be everywhere at once. Even a billion miles to the right of this packet the packet still won't be zero, it still has a very very small amplitude.

Is that indeterminism of location a mathematical trick or a property of the Kantian thing-in-itself?

-Duxwing

[K^2]

Is that indeterminism of location a mathematical trick or a property of the Kantian thing-in-itself?

Particle formalism is a mathematical trick. Particle's indeterminate momentum/position is a consequence of said formalism. And the reason we rely on particle formalism is that we are dealing with an object we cannot directly experience, and that is very different from anything we can. So either of these works, depending on which aspect of it you focus on.

[Duxwing]

Particle formalism is a mathematical trick. Particle's indeterminate momentum/position is a consequence of said formalism. And the reason we rely on particle formalism is that we are dealing with an object we cannot directly experience, and that is very different from anything we can. So either of these works, depending on which aspect of it you focus on.

Ok.

-Duxwing