It is common knowledge that when you fire electrons through a double slit you se

Question

It is common knowledge that when you fire electrons through a double slit you see an interference pattern indicating it is behaving as a wave in transit. Firstly, would you consider that it transforms into a particle on impact with the back wall in a position semi-predictable by a probability distribution that relates to the waves interference pattern. It is said that if the electron is observed it returns to behaving as a particle. Where is the particle observed? If you observed the particle before in entered the slits would it then return to behaving as a wave just before it entered them. If you observed the particle after it has exited the slit, would it be on a path determined by the interference it has encountered up till then. I.e. do you have to observe the particle exactly in the space of the slit to get the require result. Furthermore, is observation interchangable with interaction, i.e. could you just have something that measures the electron but isn't observed?

Explanation / Answer

These are all incredibly interesting questions.

For your first question, it is considered in many different ways. The way you suggest is one explanation, and another explanation is that before the electron passes through the two slits, it splits, passes through both at the same time, and interferes with itself to create the pattern. Either way, the probability distribution governs the effect.

Now onto observation: It is impossible to observe something without altering it in some way. For an electron, we would observe measuring its magnetic field, which would use a coil that would in turn create a magnetic field altering the electron's path. Regardless, observation only changes the interference pattern AFTER the electron passed through the slit. Any observation before does not change anything. So therefore, wave-like behavior is only affected by observing after. But when observing after, the only point that is helpful in determining which slit the electron passed through is right after the slit. And yes, measurement and observation are the same thing.

This all goes back to Heisenberg's uncertainty principal. With these experiments, we know the momentum of the particle because we shoot them out with some known speed. But if we try to measure their positions, we alter the particles and they no longer behave the same- in the case of altering right after the slit, they lose their wave-like properties

Source:

Princeton University Physics Major

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