# A question about the double slit experiment

1. Apr 11, 2013

### capcom1983

Is there any evidence that when the electrons pass through the single slit as a wave rather than a particle? Just curious because a single wave should provide the same Pattern as a particle.

2. Apr 11, 2013

### Staff: Mentor

Modern quantum mechanics does not have "object is a particle" and "object is a wave" as different concepts. A wavefunction of the electron, passing through both slits, is a good (but not the only) description of the system.

3. Apr 11, 2013

### capcom1983

I don't think you understand the question I understand the duality of an electron. I was wondering if when electrons were fired the the single slit ( not the two slits) if there was evidence that they passed through as a wave?

4. Apr 11, 2013

### Staff: Mentor

Sure, you get single-slit diffraction.

5. Apr 11, 2013

### capcom1983

Yes but is the electron passing through as a particle or wave?

6. Apr 11, 2013

Staff Emeritus

7. Apr 11, 2013

### capcom1983

What observations have been made of electrons going through the single slit?

8. Apr 11, 2013

### fluidistic

That if the slit is small enough as to be comparable with the de Broglie's wavelength of the electron(s) in question, there will be diffraction.
If you fire the electrons one by one and you have a screen that makes light where the electron hit it and if you mark the spot of where the electrons have hit the screen you'd get a diffraction pattern.
Or if you fire a lot of them at once, you'd see the diffraction pattern shining over your screen.
Edit: See http://arxiv.org/abs/1210.6243v1

Last edited: Apr 11, 2013
9. Apr 24, 2013

### Double-Slit

Accoring to the Coppenhagen interpretation the electron is a wave until measured.Mathematically we can describe it with a ψ wavefunction,as being a probability distribution of the electron.But physically is a wave until measured.If it's unmeasured it will produce an interference pattern so it will behave like a wave until it hits the screen,then it will become a particle.If it's observed before it enters the slit then it will enter as a particle and will form the 2 strips on the screen.I personally belive that in wave form the electron physically doesn't exists yet only as a wave of probability and it only materializes itself upon interaction,measurement sufficient to cause the quantum decoherence of that wave.

10. Apr 24, 2013

Many:

And for a couple of bucks you can try it out yourself:

Last edited by a moderator: Sep 25, 2014
11. Apr 24, 2013

### fluidistic

DevilsAvocado, photons aren't electrons. :)

12. Apr 24, 2013

Ouch (need new glasses ;) but they are both best friends of Schrödinger, aren’t they?

Last edited by a moderator: Sep 25, 2014
13. Apr 24, 2013

### fluidistic

Nice video, thanks for sharing. Although the OP asked for the single slit (not the double one).

14. Apr 24, 2013

### Double-Slit

What is with the 2nd video's ending (2:28),where the guy says the photon takes every single path from the Moon to Alpha Centauri,he must be kidding,the probability distribution of the photons can't be that big...

Last edited by a moderator: Sep 25, 2014
15. Apr 25, 2013

No worries mate, I like to quote my dear friend Red Bart – “The slit is in the eye of the beholder”.

16. Apr 25, 2013

The path integral in quantum-mechanical interpretation

17. Apr 26, 2013

### crissyb1988

Wrong. Even when the electron is observed it will still act like a wave. The only thing that changes is the wavefunction as it collapses into a definite state. This state is still a wavefunction and still acts like a wave. Only difference is that its not a superposition of waves. I any case the OP was talking about a single slit problem NOT double slit.

An electron going through a SINGLE slit whether it is observed or not will produce a diffraction pattern. Observation plays NO role in this particular case. The wavefunction will indeed collapse if we observe but this will not change the pattern we see when we measure. Also its better to think of particles as wavefunctions because they dont suddenly jump from being a particle to then being a wave...

EDIT: Diffraction only occurs when the slit is comparable to the debroglie wavelength

18. Apr 27, 2013

### Double-Slit

Yes it depends how you interpret particles.If you go by point-like objects in the classical sense then you're wrong because we know it doesn't act like that.A wavefunction will evolve according to the evolution operator until something interferes with it and collapses it to a definite and irreversible state.Whether the previous information is lost or it is preserved in "multiverses" thats a question of debate.In the modern sense we could imagine the particle as being a localized part of a wave while a wave being non-local and propagating through the entire system.The Uncertainty Principle can be much easily understood this way.

On the other hand i`m interested in this experiment,can you explain in detail why the electron doesnt form a stip if measured.Could it be because the edges are less smooth and look like an interference pattern while in reality it is only a strip,or we couldn't track the position of the particle (Uncertainty Principle) like in the 2 slit experiment ,so it will show up as a wave.

19. Apr 28, 2013

### crissyb1988

The layman/classical definition of a particle can not be brought into a conversation, and i think (if i read your post correct) we both agree on that. In terms of the scientific definition of a particle I would say that in what ever state, local or non-local, superposition or definite it is still a particle. Whether you observe the particle or not it will still exhibit wave-like properties. Take for example the single slit experiment, observation has no effect on the system. This is because in the double slit we have a superposition of states (ie. particle goes through both slits A and B simultaneously when NOT observed). In the single slit we don't have that kind of superposition. So the resulting pattern for a single slit experiment is a diffraction pattern which appears when the slit width is comparable to the wavelength of the particle. If the slit is too big then we will just see an "image" of a single slit on the screen which is what you are saying. The reason why diffraction happens at all is because waves in general tend to bend around obstacles. So no matter what has happened to a particle it is still a wave.

Ironically diffraction is a classical phenomenon. And as explained in the wiki article all kinds of waves will exhibit these properties
http://en.wikipedia.org/wiki/Diffraction

20. Apr 28, 2013

### Double-Slit

Totally agreed,but the single slit can be explained also with the uncertainty principle,since with 1 slit we can't detect it's position.So the wavefunction won't collapse.And if you come with an argument that the particle detector will interfere with the system then it won't be enough,like in Einstein's slit thought experiment,the uncertainty is passed on,so the interference must be logical,like in the 2 slit experiment,since it can't be in 2 places when observed because that would violate energy/mass conservation.It's just a matter of point of view whether if you describe it with wave or with particle,but i should guess that the term quantum (pl quanta) is more appropiate than particle.