My comment is with regards to Young's double slit experiment showing how diffraction patterns disappear when you measure which slit the electron passes through.(adsbygoogle = window.adsbygoogle || []).push({});

The standard interpretation is that the electron wave propagates through both slits, unless you measure which slit it passed through. Once you measure it, you force it to pass through one specific slit. No component passes through the other slit, and there is no "two source like terms" to interfere with each other, and produce a diffraction pattern.

My comment

Q: How (when I say how, I mean show/describe me the math) does measuring which slit the electron passes through force it into pass through one slit?

A: Consider Young's system. We identify which slit the electron passes through by using a laser monitoring each slit. If part of the laser beam is scattered (which we can detect), we know the electron entered that specific slit. The electron is treated as a free particle with wave vector k.

Now treat the laser as a small travelling/standing wave perturbation potential in the Schrodinger equation. Similar perturbation potentials (Kronig Penny Model, and free electron gas in a metal) have already shown (using time dependent perturbation theory) how a perturbation of this form causes the electron to transition from a momentum eigenstate with wave vector k into two a super position of different momentum eigenstates with wave vectors k+q and k-q, where q is the laser wave vector. This scattering process iterates over and over again until the electron is in a superposition of momentum eigenstates with wave vectors k-n*q where n is an integer spanning -infty to +infty.

As shown in any intro quantum textbook, as the electron wave-function broadens in k-space, it narrows in r-space. That is, the light forces the electron spatial distribution to narrow and have a well defined position.

implications: If one knew the exact state of a system, one could predict how/where an electron would localize. And the universe is, again, deterministic?

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I am assuming some one has thought of this before. Any one know who?

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# New look at Youngs experiment

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