Double Slit Experiment: Questions and Answers

[underworld]

so - i understand the basic double slit experiment - and like any sane person, am having a hard time understanding the electron-at-a-time outcome. but i have some questions...

1) why do we assume that an electron is a single "object" or whatever that would pass through one or the other slit? is it possible that the electron, in some way, does pass through both slits? that a wave or particle is not necessarily a single thing, but instead something fundamentally different that can pass through both slits and interfere with itself...

2) what are the limits of how it passes through them? in other words - if the "emitter" is inside a cylinder - how far apart can the slits be before the outcome is not an interference pattern?

thanks ...

 

[NateTG]

so - i understand the basic double slit experiment - and like any sane person, am having a hard time understanding the electron-at-a-time outcome. but i have some questions...

1) why do we assume that an electron is a single "object" or whatever that would pass through one or the other slit? is it possible that the electron, in some way, does pass through both slits? that a wave or particle is not necessarily a single thing, but instead something fundamentally different that can pass through both slits and interfere with itself...

2) what are the limits of how it passes through them? in other words - if the "emitter" is inside a cylinder - how far apart can the slits be before the outcome is not an interference pattern?

The double-slit experiment is the classic example of the electron behaving like a wave. The photo-electric effect is the classic example of the electron behaving like a particle.(http://en.wikipedia.org/wiki/Photoelectric_effect).

At least theoretically, the interference pattern occurs for any distance. Obviously, as the experiment gets larger, external factors become more and more difficult to control.

 

[ZapperZ]

so - i understand the basic double slit experiment - and like any sane person, am having a hard time understanding the electron-at-a-time outcome. but i have some questions...

1) why do we assume that an electron is a single "object" or whatever that would pass through one or the other slit? is it possible that the electron, in some way, does pass through both slits? that a wave or particle is not necessarily a single thing, but instead something fundamentally different that can pass through both slits and interfere with itself...

If this is true, then if I put a detector at BOTH slits, I would detect a simultaneous signal coming from both slits even when I am only shooting one electron at a time, no? Yet, how come this doesn't happen? Not only that, but how come when I do use such a detector, I no longer get the same interference pattern that I did before?

It is more profound than what you have explained.

Zz.

 

[DeepQ]

1) why do we assume that an electron is a single "object" or whatever that would pass through one or the other slit? is it possible that the electron, in some way, does pass through both slits?

I encourage you to investigate the experimental results. They are interesting. The specific case regarding electrons is rather recent (1989), and if you Google "Hitatchi single slit" you can find a summary online.

However, it should be noted that the electron-based experiment setup is not quite the same as the dual slit method. Instead of slits, a small charged filament (1 micron in width, called an electron biprism) is placed within an electron microscope. An interference pattern results, even when the electron emission intensity is quite low (no more than one electron in the device at anyone time). It should be noted that this result was noticed much earlier by others.

 

[JesseM]

I encourage you to investigate the experimental results. They are interesting. The specific case regarding electrons is rather recent (1989), and if you Google "Hitatchi single slit" you can find a summary online.

According to this article, the 1989 experiment was actually not the first:

But in 1961 Claus Jönsson of Tübingen, who had been one of Möllenstedt's students, finally performed an actual double-slit experiment with electrons for the first time (Zeitschrift für Physik 161 454). Indeed, he demonstrated interference with up to five slits. The next milestone - an experiment in which there was just one electron in the apparatus at anyone time - was reached by Akira Tonomura and co-workers at Hitachi in 1989 when they observed the build up of the fringe pattern with a very weak electron source and an electron biprism (American Journal of Physics 57 117-120). Whereas Jönsson's experiment was analogous to Young's original experiment, Tonomura's was similar to G I Taylor's. (Note added on May 7: Pier Giorgio Merli, Giulio Pozzi and GianFranco Missiroli carried out double-slit interference experiments with single electrons in Bologna in the 1970s; see Merli et al. in Further reading and the letters from Steeds, Merli et al., and Tonomura at the end of this article.)

 

[DeepQ]

According to this article, the 1989 experiment was actually not the first:

Yes, thanks. That's why I mentioned "others". But, did Claus Jönsson prove it for single electrons? (I've not read the paper.)

 

[JesseM]

Yes, thanks. That's why I mentioned "others". But, did Claus Jönsson prove it for single electrons? (I've not read the paper.)

Just going by that paragraph, I would assume not--after discussing his experiment, they say "The next milestone - an experiment in which there was just one electron in the apparatus at anyone time - was reached by Akira Tonomura and co-workers at Hitachi in 1989". But then they added that paranthetical revision to the paragraph indicating that "Pier Giorgio Merli, Giulio Pozzi and GianFranco Missiroli carried out double-slit interference experiments with single electrons in Bologna in the 1970s", so I suppose this was the first experiment demonstrating interference with single electrons.