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kevin1981
2011-Sep-27, 01:55 AM
When an electron gets fired once every hour, giving it enough time to hit the detector, after a while we see an interference patten. So what is actually happening ?

Does the electron go through both slits and interfere with itself, like a wave giving rise to the patten ? Or can we not fully understand what is happening ?

Thanks.

AGN Fuel
2011-Sep-27, 03:38 AM
Provided the experiment is not designed in such a way as to determine which slit the electron went through, then that is my understanding - the electron will have in effect passed through both slits, interfered with itself and given rise to the interference pattern.

WayneFrancis
2011-Sep-27, 03:54 AM
That is my understanding too. Can't think of the electron, or any other object, as simply a little ball. The larger the object the more it will act like a ball but even buckyballs work
http://physicsworld.com/cws/article/news/2952

Jens
2011-Sep-27, 03:57 AM
Does the electron go through both slits and interfere with itself, like a wave giving rise to the patten ? Or can we not fully understand what is happening ?


It may be that the electron goes through one slit, but that there is a possibility that it goes through either of the slits, and it is interfering with those possibilities. I think, though, that "we cannot fully understand" is correct. We do understand a lot of it, but I think there is at a certain level something that we don't understand, and in fact whenever we come to understand something at one level, there is always a deeper level that appears. So I think it is impossible to "fully understand".

korjik
2011-Sep-27, 05:54 AM
It may be that the electron goes through one slit, but that there is a possibility that it goes through either of the slits, and it is interfering with those possibilities. I think, though, that "we cannot fully understand" is correct. We do understand a lot of it, but I think there is at a certain level something that we don't understand, and in fact whenever we come to understand something at one level, there is always a deeper level that appears. So I think it is impossible to "fully understand".

While I am not going to disagree with the sentiment, wave/particle duality is pretty well understood. Lots and lots of things that we have no clue on, but electrons acting like waves isnt really all that special.

kevin1981
2011-Sep-27, 12:56 PM
Is this a better way to think about it: When the electron leaves the electron gun, as long as it is sealed off from the outside environment, it no longer act's like a particle, it act's like a wave. So the particle does not go through both slits because we are no longer looking at it from a particle point of view.

Rather, it goes through both slits because it is acting like a wave, so now, we are looking at it from the wave perspective.

The electron act's like a wave and acts like a particle depending on how we measure it, or if the electron is in an isolated environment.

Ken G
2011-Sep-28, 01:40 AM
That's probably a reasonable way to frame it, but I prefer to go a bit farther. First of all, there are two very different ways that a wave can act like a classical particle trajectory. One way is to simply make the wavelength very small compared to the length scale of the slits it is passing through. That's like using an X-ray rather than a radio wave to image your bones, and waves with very short wavelengths behave exactly like particle trajectories with one exception-- the wave still goes through both slits. But it does not make an interference pattern if its wavelength is short-- you just get two spots behind the two slits, and it seems random which slit each particle goes through. This is just like flipping a coin-- that also seems random if it is done in a fair way. So short-wavelength waves do everything coins do, there is never a need to choose a description that is not a wave.

But there is a second way to get particles to act like they have trajectories, and that is to track where the individual particle is going at each step along the way (or if you prefer, watch which slit it goes through, the idea is similar). With a classical wave, like a sound wave, you can watch the air very carefully and the wave doesn't do anything different. The same holds for quantum mechanical waves in the classical limit-- you can watch the amplitude of an electromagnetic field, for example, and the photons will still make an interference pattern. They don't mind if you watch the field, because the field is an averaged quantity-- they only mind if you watch the photons individually. If you do that, you get no interference pattern-- the watched photon establishes which slit it goes through, and cannot interfere with anything happening with the other slit. This type of trajectory has a very different quality-- it is a case of culling the information, so the particle is in a sense forced to make choices, it is not allowed to slip into indeterminacy like waves do.

So I think the clear conclusion from this is that the reality itself is agnostic on the issue of which slit unless something is put into the reality that can tell which slit, for each individual photon. The question never asked is also never answered. So it's not that the photon goes through both slits, or that we don't know which slit, it's that the language "going through slits" simply doesn't mean anything, it's gibberish, when applied to an apparatus that does not establish which slit the photons go through. That holds even if you watch the combined fields very closely, in the case of many photons at once. If there's no way to establish the slit an individual photon goes through, then there's no such thing as "going through a slit" for that photon, even though the amplitudes that contribute to what the photon does do account for both slits and in some sense "go through" both slits. The amplitudes can be pictured that way, not the photons, but the amplitudes don't actually do it-- because amplitudes don't really move at all, they just vary with time according to the wave equation.

kevin1981
2011-Sep-28, 03:44 PM
Thanks, Ken. That has given me plenty of food for thought !