question about the photoelectric effect

[swansont]

You can tell where the particle was, but the photon imparts momentum to the particle, so it will have moved. You can't know the energy (and thus momentm) of the detected photon perfectly, either. And to better know the position you have to use smaller wavelengths, imparting more momentum; longer wavelengths will diffract rather than reflect.

[gib65]

Thanks swansont. Your answers are invaluable.

 

Something else I was wondering was who came up with the idea of a "probability wave"? I'm not even sure if any one particular person did or if it just evolved as quantum mechanics did. I'm not even sure if "probability wave" is the standard term physicists use.

 

What I mean by "probability wave" is idea that as a particle travels through space in the form of a wave, like in the double-slit experiment, what constitutes the wave isn't really a "something" - that is, it isn't like a wave of energy, or a smearing out of the particle, or anything like that. It's the region of space where one is most likely to find the particle if one tries to measure its position. In a sense, it's really just an abstract/mathematical concept rather than a real thing with substance. The only thing that's real is that the particle's position is undetermined but mostly confined to this region.

 

Anyway, that's my understanding of a "probability wave", and assuming I've got it right (even remotely right), I was just wondering if there's one character in history that we can credit with presenting this model.

[swansont]

Thanks swansont. Your answers are invaluable.

 

Something else I was wondering was who came up with the idea of a "probability wave"? I'm not even sure if any one particular person did or if it just evolved as quantum mechanics did. I'm not even sure if "probability wave" is the standard term physicists use.

 

What I mean by "probability wave" is idea that as a particle travels through space in the form of a wave, like in the double-slit experiment, what constitutes the wave isn't really a "something" - that is, it isn't like a wave of energy, or a smearing out of the particle, or anything like that. It's the region of space where one is most likely to find the particle if one tries to measure its position. In a sense, it's really just an abstract/mathematical concept rather than a real thing with substance. The only thing that's real is that the particle's position is undetermined but mostly confined to this region.

 

Anyway, that's my understanding of a "probability wave", and assuming I've got it right (even remotely right), I was just wondering if there's one character in history that we can credit with presenting this model.

 

 

It's Schroedinger's wave equation, but there were a lot of contributors to what we call QM and probability waves.

 

There have been a number of investigations into what's "real" and what's representation, and you can get into an argument about it depending on who you talk to. Are photons real, or are they just the name we give to an excitation of a particular electromagnetic vibrational mode of the universe? You can do experiments that point in one direction and you think you have a handle on it, and then someone comes along with a counterexample that trashes the whole argument. At some level it doesn't matter; e.g. nature behaves as if photons are real, and that's what you need to describe how nature behaves — that's the goal of science. How nature really is is a question of philosophy and metaphysics, which is a separate topic of discussion.

[gib65]

Next question: who discovered quantum entanglement? Or was it "discovered" at all? I mean, I can imagine that quantum entanglement is just a logical consequence of other well-known facts about particle physics. I can see the production of an electron with one value for spin and a positron with the opposite value for spin being produced by a J/psi particle being well-known already. And if spin is one of these "uncertain" variables, then gleening knowledge about the spin of one, say the electron, will give you instant knowledge of the spin of the other, leading to the EPR paradox. No experiment or accidental discovery needs to be done in order to come to this conclusion.

 

But I'm not sure. Was quantum entanglement discovered - or at least, officially confirmed through some kind of formal experiment - or was it just deduced from other well-known facts about quantum mechanics?

[swansont]

AFAIK the concept was proposed in the EPR scenario (that was 1935), but I don't know if there were earlier mentions of it. One could check that paper for references.

[Mr Skeptic]

Next question: who discovered quantum entanglement? Or was it "discovered" at all? I mean, I can imagine that quantum entanglement is just a logical consequence of other well-known facts about particle physics. I can see the production of an electron with one value for spin and a positron with the opposite value for spin being produced by a J/psi particle being well-known already. And if spin is one of these "uncertain" variables, then gleening knowledge about the spin of one, say the electron, will give you instant knowledge of the spin of the other, leading to the EPR paradox. No experiment or accidental discovery needs to be done in order to come to this conclusion.

 

But I'm not sure. Was quantum entanglement discovered - or at least, officially confirmed through some kind of formal experiment - or was it just deduced from other well-known facts about quantum mechanics?

 

Well, you don't actually know anything you didn't know already about the second particle. That is, you already knew its spin was opposite of that of its twin. What bothers me more is how the second particle knows that the first has been measured:confused:

[swansont]

Well, you don't actually know anything you didn't know already about the second particle. That is, you already knew its spin was opposite of that of its twin. What bothers me more is how the second particle knows that the first has been measured:confused:

 

One problem is thinking about it that way. There is no "second particle;" they are an entangled pair, meaning they comprise one system. The spooky part is the one that was in state A wasn't in state A all the way along.