# Thread: Double Slit - Electron as a wave with only one slit.

1. Hi all,

Just something I was wondering about the Double Slit experiement, but first I'd better give a brief explanation of my understanding of the experiement in case thats flawed, I'm using the cheezy Dr Quantum youtube video for much of my interpretation which you can view at http://www.youtube.com/watch?v=DfPeprQ7oGc

As I understand it :-

1, With a single slit the electrons (photons? protons?) act as particles and either go through the slit or don't, making a pattern on the detector screen (if 'detector screen' is the right term) roughly the same shape as the slit.

2, Electrons (again, photons? protons?) through two slits give an interference pattern, as though waves had gone though rather than particles, the waves from each slit interfering with each other to give the pattern.

3, If the electrons are fired one at a time there is still an interference pattern, implying that electrons are waves, or at least act as waves when unonbserved.

4, If the single electrons are measured to see which slit they went though then they go back to acting like particles.

My Questions :-

1, Why don't the unobserved electrons act as a wave when there is only one slit? ie why don't we see a wave pattern which is brighter in the center then tapers off to the egdes as we would if waves went through? The Dr Quantum video on youtube shows what happens when waves pass through a single slot, link to that video above.

2, In the video it explains that with two slits each electron somehow passes through both slits, one slit, the other slit and neither slit when unobserved, so with only one slit does the electron both pass through the slit and not pass through it when unobserved? ie does every electron fired result in a hit on the 'detector screen' at the back as though it passed through the slit even though some inevitably should have missed the slit and bounced back?

Thank you for your time and any light you can shed on this.

-Pete-

2.

3. Originally Posted by Vasteel
My Questions :-

1, Why don't the unobserved electrons act as a wave when there is only one slit? ie why don't we see a wave pattern which is brighter in the center then tapers off to the egdes as we would if waves went through? The Dr Quantum video on youtube shows what happens when waves pass through a single slot, link to that video above.
They do still act as a wave, but single slit waves don't exhibit the cancellation effect you see when you've got two or more waves. With two or more waves interfering with each other, there are certain areas that never get any light because the positive part of one wave and the negative part of the other wave are always reaching that point at the same time.

So what draws all the interest about the double slit experiment is that, if you put a detector on one slit (or both slits), it starts creating two separate single slit patterns instead of a double slit pattern. There's no longer any cancellation.

2, In the video it explains that with two slits each electron somehow passes through both slits, one slit, the other slit and neither slit when unobserved, so with only one slit does the electron both pass through the slit and not pass through it when unobserved? ie does every electron fired result in a hit on the 'detector screen' at the back as though it passed through the slit even though some inevitably should have missed the slit and bounced back?

Thank you for your time and any light you can shed on this.

-Pete-
It's not that this doesn't happen. It does. But the experiment is only set up to watch for the ones that make it through the slit. The ones that don't make it through the slit are just being ignored.

4. Thanks for the information,
I thought that in the electrons and single slit version you should get a pattern like waves passing through a single slit rather than a single slit particle pattern, but obviously thats not the case.

Thanks Again.

5. There actually is a diffraction pattern with a single slit.

http://en.wikipedia.org/wiki/Fileiffraction1.png

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