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Author Topic: double slit experiment question.  (Read 3378 times)

Offline hamza

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double slit experiment question.
« on: 21/12/2007 05:01:12 »
Why does it happen in a double slit experiment that if just one electron is made to pass through the slit, interferrance fringes are observed? I read somewhere that the same electron passes through both slits. How can that be possible.?




Edit:
Hamza. i have changed the title of your topic. This will help people know what your topic is about, helping them to read / respond.
Hope you don't mind. paul
« Last Edit: 21/12/2007 05:09:19 by paul.fr »


 

Offline Soul Surfer

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double slit experiment question.
« Reply #1 on: 21/12/2007 10:40:33 »
This is a true fact of quantum mechanical wierdness.  Yes electrons do behave as waves and do interfere with themselves even if they are sent one at a time through the apparatus.  The experiment has been done many times and you just have to accept that's the way the universe works!

Of course if you arrange to detect which slit each electron goes through as a particle, the interference pattern vanishes and that is even wierder.
 

lyner

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double slit experiment question.
« Reply #2 on: 22/12/2007 01:00:40 »
One electron in the double slit experiment would 'probably' land in line with one slit or the other. It is only when you have a lot of electrons that the probability density would begin to show a diffraction like pattern.
THIS HAPPENS -you can't argue with the evidence but you can suggest other reasons, if you like, other than waves and diffraction. You will have a job though!.
 

Offline thebrain13

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double slit experiment question.
« Reply #3 on: 22/12/2007 06:08:22 »
thats not true sophie, the diffraction pattern will be shown even if you send them one at a time.
 

Offline lightarrow

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double slit experiment question.
« Reply #4 on: 22/12/2007 10:41:30 »
thats not true sophie, the diffraction pattern will be shown even if you send them one at a time.
Yes, it is what he intended.
 

lyner

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double slit experiment question.
« Reply #5 on: 22/12/2007 12:08:22 »
Quote
thats not true sophie, the diffraction pattern will be shown even if you send them one at a time.
I didn't say it didn't but you can't have 'statistics' for just one particle. All one can say is that one particle is most likely to turn up as if it went directly through one slit or the other i.e. at  one of the two central peaks of the diffraction pattern (probability distribution pattern) these peaks correspond to the direct paths through the slits.  Yes - a single particle could end up way over on the left or the right - that's statistics / probability theory.

What you are saying, goes for a number of particles - which will build up the pattern. 'One at a time' still implies more than one, doesn't it? Even in a shower of them, they will arrive one at a time - just short time intervals!
« Last Edit: 22/12/2007 12:09:53 by sophiecentaur »
 

Offline Soul Surfer

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double slit experiment question.
« Reply #6 on: 22/12/2007 12:42:44 »
The point is that it works even if there is only one electron travelling through the apparatus at one during the time t takes for the electron to be emitted until it is detected after passing through the slits.

This quantum mechanical weirdness does seem to cause lots of people problems but the behaviours are completely proved.  however there are hopes for those who must have a more rational explanation of things.  this problem is sometimes called the EPR problem after the people who first posed it  Einstein Podolsky and Rosen

The critical work by Bell that clearly proved that quantum mechanics could not be explained by hidden variables had a limitation this was that the variables were subject to the normal rules of arithmetic.  Now this may not always be the case

If for example the variables were non commutative there could be hidden variables a non commutative process is one in which the order in which you do things is critical so if you do A then B to something that is not the same as doing B then A a good example of this is doing a 90 degree rotation in one dimension on an asymmetrical object like a book.

A fuller report is given in the New Scientist 3rd November pages 36 - 39

The original paper is in  http://www.arxiv.org/abs/quant-ph/0703179

« Last Edit: 22/12/2007 12:50:38 by Soul Surfer »
 

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double slit experiment question.
« Reply #6 on: 22/12/2007 12:42:44 »

 

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