# Wavefunction collapse

Hi Everyone

I am not sure of what exactly happens when a wavefunction collapses but I have some ideas about which I would be grateful for your thoughts.

Firstly, it is often said that wavefunctions collapse when they are "observed" or "measured". To be honest, I do not think that wavefunction collapse depends upon being "observed" by a conscious, cognitive, multicellular organism. I think that it is much simpler than that. I think that the wavefunction of a particle can collapse when it is in some way "touched" buy another particle. What this "touching" exactly means I don't realy know but I would like to know if the people on this forum think I am on the right track here.

Imagine a simplified scenario of a particle whose wavefunction consists of four "spikes" of equal length in four positions. This means that the particle has a 1/4 probability of being in each position. Now imagine that another particle (a "measuring" particle) "touches" one of the four "spikes". As I see it, this can have the following two possible results:

1. The "measuring" particle has a 1/4 probability of receiving a "reply" from the wavefunction. If this happens then the wavefunction completely collapses and the particle being "measured" definitely is (or was) in the position of the spike which was "touched".

2. The "measuring" particle has a 3/4 probability of not receiving a "reply" from the wavefunction. If this happens then the "spike" which was "touched" dissapears and redistributes itself to the remaining three "spikes". This is a partial collapse of the wavefunction.

I would be very grateful if anyone could let me know if I am right of wrong here.

Thank you very much.

Kind regards

Tim

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bhobba
Mentor
I think that the wavefunction of a particle can collapse when it is in some way "touched" buy another particle.
Sort of.

It's when it becomes entangled with it. Technically it converts it from a superposition to a mixed state.

Susskinds QM book gives a good look at the detail of this:
https://www.amazon.com/dp/0465036678/?tag=pfamazon01-20&tag=pfamazon01-20

Thanks
Bill

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