# Double slit experiment with magnetic traps

That may be your goal, but I don't think you've achieved this. I think all you've done is exactly what @PeroK said: devised n elaborate mechanism for detecting which slit the electron went through.
I disagree, because after the measurement of magnetic induction in both traps I still know nothing about the paths of individual electrons.

PeterDonis
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I disagree, because after the measurement of magnetic induction in both traps I still know nothing about the paths of individual electrons.
Yes, you do: you know that there is an electron in one trap and no electron in the other. So you know the electron went through the slit in front of the trap that has an electron in it.

vanhees71
Yes, you do: you know that there is an electron in one trap and no electron in the other. So you know the electron went through the slit in front of the trap that has an electron in it.
You are right on one condition: that there was a collapse. But you can know it only by the measurement. You can't use the ad infinitum argumentation: the electron is in just one of the traps, because there was a collapse. Why there was a collapse? Because the electron is in just one of the traps.

PeterDonis
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You are right on one condition: that there was a collapse.
No, what I have said is true for any interpretation of QM, including no collapse interpretations. In a no collapse interpretation like the MWI, there are two branches of the wave function after the measurement, one in which the electron is in the trap behind slit #1 and the magnetic induction measurement shows it there (and the observer observes that), and one in which the electron is in the trap behind slit #2 and the magnetic induction measurement shows it there (and the observer observes that).

you can know it only by the measurement.
The magnetic induction measurement...is a measurement. That's why we use expressions like, oh, say, "measure the magnetic induction" (which is what you said in the OP of this thread) to describe it.

vanhees71 and PeroK
PeroK
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You are right on one condition: that there was a collapse. But you can know it only by the measurement. You can't use the ad infinitum argumentation: the electron is in just one of the traps, because there was a collapse. Why there was a collapse? Because the electron is in just one of the traps.
This is perhaps a good time to pause, reflect and consider learning a bit more about QM, what it says and what it doesn't say.

There is not a lot of point in arguing about things that are well-established, theoretically and experimentally.

vanhees71
This is perhaps a good time to pause, reflect and consider learning a bit more about QM, what it says and what it doesn't say.

There is not a lot of point in arguing about things that are well-established, theoretically and experimentally.

The magnetic induction measurement...is a measurement. That's why we use expressions like, oh, say, "measure the magnetic induction" (which is what you said in the OP of this thread) to describe it.
Correct. The difference is that I don't measure the effect or presence of a single electron, but the effect caused by the whole bunch of them. This is my idea of preventing the collapse of individual electrons, however stupid it sounds.

PeterDonis
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I don't measure the effect or presence of a single electron, but the effect caused by the whole bunch of them.
In other words, you run a large number of electrons through the experiment, and then measure the magnetic induction in each of the traps?

This is my idea of preventing the collapse of individual electrons
It won't.

First, you'll have the problem that magnetic traps can't store large numbers of electrons--the Pauli exclusion principle prevents it (there are only a small number of states the electrons in the trap can be in, and once those states are filled you're done, the trap can't hold any more electrons).

Second, when you do the magnetic induction measurement, you'll just get two numbers for magnetic induction that will be approximately equal (since each electron has basically a 50-50 chance to go into one trap vs. the other). You won't get anything that shows interference between the electrons (which pretty much invalidates the point of doing a double slit experiment in the first place).

Third, even though you have multiple electrons in both traps, you haven't "prevented collapse"; you've just changed the states that the electrons collapse into when you make the magnetic induction measurement, as compared to the case where you only have one electron and it has a 50-50 chance to be in either trap. (The states change because if the presence of multiple electrons in the trap affects the energy levels of the states, due to the Coulomb repulsion between the electrons.)

vanhees71 and Marcin
@PeterDonis I get it, you've made it clear. Thank you.

dlgoff and berkeman