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- Thread starter George5
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...otherwise there wouldn't be an interference pattern if only one electron is sent through the apparatusat a time.

this is what I meant

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Fredrik

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There will be an interference pattern even if you send one photon (or electron) through at a time. (I think it's easier to do it with photons). I don't think it's hard to get one photon at a time to go through. You should just have to lower the intensity of the light source until it emits one photon at a time.

Feynman's book "QED: The strange theory of light and matter" explains this stuff very well. Everyone who's interested in physics should read it.

I would say that the claim that the "photon takes both paths" is misleading. Given an emission event, we can calculate the probability of each possible detection event. We can, in principle, do this by associating a probability amplitude (a complex number) which each*path* from the emission event to the detection event, and add them up to get a final amplitude, which then tells us the probability.

Quantum mechanics isn't very confusing as long as you think about it as an algorithm that lets you calculate probabilities of possibilities. It's when you start to think about what "really happens" that it gets confusing. This might mean that it's simply*wrong* to think that quantum mechanics *describes* the universe. A theory doesn't have to describe anything to be scientific. It just have to be able to predict the outcomes of experiments, and quantum mechanics does that better than any other theory.

Feynman's book "QED: The strange theory of light and matter" explains this stuff very well. Everyone who's interested in physics should read it.

I would say that the claim that the "photon takes both paths" is misleading. Given an emission event, we can calculate the probability of each possible detection event. We can, in principle, do this by associating a probability amplitude (a complex number) which each

Quantum mechanics isn't very confusing as long as you think about it as an algorithm that lets you calculate probabilities of possibilities. It's when you start to think about what "really happens" that it gets confusing. This might mean that it's simply

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- #4

Cthugha

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There will be an interference pattern even if you send one photon (or electron) through at a time. (I think it's easier to do it with photons). I don't think it's hard to get one photon at a time to go through. You should just have to lower the intensity of the light source until it emits one photon at a time.

Both have their problems. From an experimental point of view, creating electron beams is a bit more complicated than creating photon beams, just as a crt is a bit more complicated than a flashlight, but when it gets to single electrons versus single photons electrons are usually better as they are fermions and therefore the the Pauli exclusion principle works for them and they have the tendency to show antibunching anyway. I think there was even a report on a coherent single electron source somewhere in Science last year.

Photons are bosons and have the tendency to bunch. Lowering the intensity of the light source leads to a thermal or coherent state with low average photon number, which is still a superposition of several Fock states (photon number states). If you really want to have just one photon at a time, you need to get the field to the n=1 Fock state, which is possible by using single atoms or single quantum dots as a light source, but complicated.

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subtle for quantum mechanics.

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subtle for quantum mechanics.

In other words?

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From the moment you start to think of a particle as a probability wave, it gets straight forward ...

If two slits are open and we see an interference pattern, I agree that it is straight forward. But if there is only one slit open ...? In this case I usually imagine something analogous to the typical water wave after throwing a stone into the pond. The screen recording the photons would be analogous to a cross cut through the water wave at some point in time. But then I don't understand why there is no wavy pattern on the screen when only one slit is open. It would be more regular than the interference pattern, but still not just a single-maximum curve?

What is wrong with my analogy of the water wave here?

Harald.

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However after thousands of electrons were fired, one at a time, the pattern spots of the screen looked like a classic interference pattern for waves. It was as if each electron "knew" where all it's predecessors had gone, where all electrons coming behind it would go, and where it was supposed to be in the pattern.

It was very weird....yet it is true.

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This analogy would include that if one of the servers is swallowed by a shark and leaves a red patch of blood on the surface, all other surfers disappear at the same instant without a trace Not each one represents a photon, but collectively they represent a single photon.

Harald.

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