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Author Topic: 2 slit experiment !..why not 3 slits or more ?  (Read 6930 times)

Offline neilep

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2 slit experiment !..why not 3 slits or more ?
« on: 15/11/2005 16:21:10 »
As you may or may not know I am 'attemtping ' (badly) to get to grips with the kindergarten subject of Quantum stuff !

I've been reading about the two slit experiment which is of course pretty freaky in it's results, but I have seen no mention of a three slit experiment or four etc etc.....has this been done ?...am I silly in asking ?

Am I silly ? (rhetorical question , i already know the answer !;))

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Offline stinkinstudentlamo

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Re: 2 slit experiment !..why not 3 slits or more ?
« Reply #1 on: 15/11/2005 17:20:40 »
interesting question neilp
I'm not all that familiar with the quantum implications of the experiment however for the people that want to understand science;)

i believe that youngs original double slit experiment was to prove the wave nature of light by producing two beams of light that were in phase, therebye showing where constructive and destructive interference takes place.

I would assume that since any experiment of more than one slit would produce several different beams of light that are in phase, they would produce roughly the same results ie light and dark bands.

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Offline DoctorBeaver

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Re: 2 slit experiment !..why not 3 slits or more ?
« Reply #2 on: 15/11/2005 21:09:25 »
I refuse to join this thread on the grounds that I'm thick as 2 short planks[:o)]
 

Offline rosy

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Re: 2 slit experiment !..why not 3 slits or more ?
« Reply #3 on: 15/11/2005 22:08:09 »
Yes 3 slits will produce a series of light and dark bands, there will be extra weaker bands in between the original ones where you get 2 of the slits at the opposite phase to the other one.

You can increase the number of slits to approximately infinity (a few hundred in this case) and you get a diffraction grating, here all the intermediate peaks become tiny and you get very bright fringes as much more light comes through, as you have much more hole.

Apparently you can also make a subtractive double slit experiment where you have two obstructions rather than two slits, one day I will try this...

The reason you allways hear about the double slit experiment is that it is simple so you have less things to think about.
 

Offline neilep

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Re: 2 slit experiment !..why not 3 slits or more ?
« Reply #4 on: 15/11/2005 22:43:30 »
Well there you go...question answered , concisely and succinctly.

Thank You Rosy.....

...also..thanks Daniel for your contribution, and Eth, thank you for opting out !!....:D;):D

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Re: 2 slit experiment !..why not 3 slits or more ?
« Reply #5 on: 16/11/2005 04:28:31 »
An ancillary question I have to this (that demonstrates exactly how naïve I can be) is how do you know that the particles can only go through the slits.

In classical physics, one deals in certainties, and one can say A can or cannot by at place X, and you can talk about absolute transparency and absolute opacity.  As I understand it, quantum physics only deals in uncertainty, and probability.  How do you design an experiment that only deals with uncertainty, and yet can be certain that the material between the slits is 100% opaque?
 

Offline daveshorts

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Re: 2 slit experiment !..why not 3 slits or more ?
« Reply #6 on: 16/11/2005 09:39:06 »
It probably isn't 100% opaque to tunneling, but it can be 99.9999999999% (tunneling probabilities reduce very rapidly with thickness) opaque, so it doesn't make much difference.

Most of physics is actually working out which bits of the equation are not going to make a significant effect so can be ignored, making the problem more soluble...
 

Offline Solvay_1927

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Re: 2 slit experiment !..why not 3 slits or more ?
« Reply #7 on: 16/11/2005 13:37:41 »
Interestingly (well, interesting to me - probably very dull to many people), this is allegedly how Richard Feynman came up with his "sum over histories" approach to the motion of photons and electrons (whereby, to calculate how a photon/electron moves from point A to point B, you have to assume that it simultaneously moves via EVERY possible path through space between the two points).

He thought of a two slit experiment (where the particle follows the two paths - i.e. through the two slits - simultaneously), then 3 slits, then 4, ... and reasoned that, as the number of slits grows to infinity (i.e. the screen disappears and you're left with free space), you end up having to accept that the particle is effectively following every possible path simultaneously.

I'd strongly recommend Feynman's book "QED" for a nice short (and cheap) layperson's introduction to how light phenomena (slit experiments, reflection, diffraction, etc.) can be explained neatly and simply by quantum mechanics. (That is, after you've finished reading "Quantum", Neil.)


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Re: 2 slit experiment !..why not 3 slits or more ?
« Reply #7 on: 16/11/2005 13:37:41 »

 

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