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> There is no simple logical connective in ordinary language that captures that Yes, I'd agree with this. I was trying to say something aproximately true to co

by gpsx 8y ago

> There is no simple logical connective in ordinary language that captures that Yes, I'd agree with this. I was trying to say something aproximately true to convey a point. In your post you did agree with my salient point - the electric field moves with the electron, it doesn't do something funny when the elestron has some spread in its wavefuntion for position. This seemed to be the what the article was talking about, that the gravitational field behaved differently for a superposition of states. I will try a more concrete example. Suppose you have an electron gun and shoot a single elctron at a metal plate. Suppose the wavefunction is such that it is uniform over the surface of the plate (So the electron has an equal probability of hitting anywhere on the plate.) What does the damage to the plate look like? Is it spread uniformly over the plate? No. It is a single small mark at some specific place on the plate. The electron is not smeared over the plate, the probability of finding the electron is smeared over the plate. The electron is still a point particle (to the extent of our current laws of physics) and it will only interact with the plate at one point. (Some people will not like my language and tell me I am wrong. But it is true the electron will hit the plate at a single point - not smeared out like the wavefunction is.) In actuality the electron didn't cause the damage to the plate. The electric field did. The electric field moves with the electron almost like you would expect in classical physics. It's not like the electric field is smeared around because the electron is in a superposition of states. I'd expect gravity to work the same way. But seeing how we don't have a theory it is possible it could violate the above idea. To me that would be a pretty weird violation too. (This short writeup doesn't really do that justice.) I'd bet against it.

Armisael16 8y ago
Please explain single-electron double-slot experiments. If the electron is simply a point particle how does it interfere with itself?
- pdonis 8y ago
  > If the electron is simply a point particle It isn't. It's a wave function (or, if we take relativity into account, a quantum field).
- gpsx 8y ago
  You can google "electron size" and you get different classical estimations and hopefully a statement that there is no measuarable size and that it is considered a point particle. But that doesn't mean it can't have interference. Interference occurs because of the wave function. The wave function for the electron and the electron itself are two different things. They did a electon double split experiment where they fired electons one at a time. The electrons each made a single point (or small mark) on the measuring screen, but over time, the interference pattern formed. (To be honest I heard this back when I was learning physiscs, which was along time ago. It could have actually been a thought experiment or it could have been something besides an electron. Anyway I believe it is true.)
pdonis 8y ago
> the electric field moves with the electron Sort of. Describing it as an "electric field" assumes the electron is not moving; if it's moving, at the very least there will be a magnetic field as well as an electric field. Also, as I said, when we take quantum effects into account we need to quantize the electromagnetic field as well as the electron, so the field is no longer just something that "moves with" the electron; it's a separate thing of its own that happens to interact with the electron in a certain way. > The electron is still a point particle (to the extent of our current laws of physics) and it will only interact with the plate at one point. Not a point; the damage on the plate will have a finite size. But you're right that the damage on the plate won't look like the wave function as a whole. Also see below. > In actuality the electron didn't cause the damage to the plate. The electric field did. If this is true, you can't deduce that the electron is a point particle from the damage at all, since the damage tells you about the field, not about the electron. > It's not like the electric field is smeared around because the electron is in a superposition of states. You're mixing up two different things. If the electron hits the plate, it's no longer in a superposition, and neither is the field. If the electron is in a superposition, it's because it hasn't hit the plate yet, so we haven't measured it--and in that case, the field is in a superposition too. So the "smearing" of the electron and the field go together (in the oversimplified model we're using). > I'd expect gravity to work the same way. The issue with gravity is that the "field" in the case of gravity is the spacetime metric. All of the reasoning about the electron and the electric field assumed that the spacetime metric was known. But if gravity is quantized, the spacetime metric itself would be in a superposition if its source (say some massive object) were in a superposition. That's a crucial aspect that's unique to gravity.

by gpsx 8y ago

Armisael16 8y ago

Please explain single-electron double-slot experiments. If the electron is simply a point particle how does it interfere with itself?

pdonis 8y ago
> If the electron is simply a point particle It isn't. It's a wave function (or, if we take relativity into account, a quantum field).
gpsx 8y ago
You can google "electron size" and you get different classical estimations and hopefully a statement that there is no measuarable size and that it is considered a point particle. But that doesn't mean it can't have interference. Interference occurs because of the wave function. The wave function for the electron and the electron itself are two different things. They did a electon double split experiment where they fired electons one at a time. The electrons each made a single point (or small mark) on the measuring screen, but over time, the interference pattern formed. (To be honest I heard this back when I was learning physiscs, which was along time ago. It could have actually been a thought experiment or it could have been something besides an electron. Anyway I believe it is true.)

pdonis 8y ago

> the electric field moves with the electron Sort of. Describing it as an "electric field" assumes the electron is not moving; if it's moving, at the very least there will be a magnetic field as well as an electric field. Also, as I said, when we take quantum effects into account we need to quantize the electromagnetic field as well as the electron, so the field is no longer just something that "moves with" the electron; it's a separate thing of its own that happens to interact with the electron in a certain way. > The electron is still a point particle (to the extent of our current laws of physics) and it will only interact with the plate at one point. Not a point; the damage on the plate will have a finite size. But you're right that the damage on the plate won't look like the wave function as a whole. Also see below. > In actuality the electron didn't cause the damage to the plate. The electric field did. If this is true, you can't deduce that the electron is a point particle from the damage at all, since the damage tells you about the field, not about the electron. > It's not like the electric field is smeared around because the electron is in a superposition of states. You're mixing up two different things. If the electron hits the plate, it's no longer in a superposition, and neither is the field. If the electron is in a superposition, it's because it hasn't hit the plate yet, so we haven't measured it--and in that case, the field is in a superposition too. So the "smearing" of the electron and the field go together (in the oversimplified model we're using). > I'd expect gravity to work the same way. The issue with gravity is that the "field" in the case of gravity is the spacetime metric. All of the reasoning about the electron and the electric field assumed that the spacetime metric was known. But if gravity is quantized, the spacetime metric itself would be in a superposition if its source (say some massive object) were in a superposition. That's a crucial aspect that's unique to gravity.