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It's not about humans looking at it. It's about collapsing the wave function. The only to "look" at a particle is to make it interact with something (trigger so

by hasenj 15y ago

It's not about humans looking at it. It's about collapsing the wave function. The only to "look" at a particle is to make it interact with something (trigger some chain reaction that ultimately sends a signal to one of your senses, e.g. a photo multiplier). The moment it interacts with that thing, the wave function collapses. This part is not mysterious. The mysterious part is, what in the world could be the thing that acts as a wave function and then collapse to a single point when it interacts with something else? What underlying reality does this hint at?

Anderkent 15y ago
That part is not mysterious either - the collapse simply doesn't occur. Say you have a photon in a superposition of state A and state B - think position. If it is in state A it hits a detector, if it is in state B it does not. If the detector is hit, it displays 'HIT' on its screen - otherwise it does not. If 'HIT' is displayed, the researcher thinks photon was in state A, otherwise the researcher thinks it is in state B. The result of the experiment, without any wavefunction collapse, is a superposition of two states of the entire system: State 1: Photon is in A, Detector was Hit, Researcher thinks photon is in A + State 2: Photon is in state B, detector was not hit, researcher thinks photon is in B. As you can see, the fact that the researcher never sees a photon in a superposition of states a+b (he doesn't ever see the detector both lit up and not) is explained without any wavefunction collapse.
- hasenj 15y ago
  > Say you have a photon in a superposition of state A and state B - think position. Why are you assuming the particle has got to have a "position"? The fact that a quantum particle can interfere with itself would be experimental evidence that it doesn't in fact have a definite position.
Cushman 15y ago
You would think this, but the quantum erasure experiment appears to demonstrate that a photon which has been marked so as to determine its path and then subsequently randomly unmarked so as to irretrievably destroy that information once again displays interference. The delayed choice quantum eraser appears to demonstrate that this decision to either record or destroy path information may be delayed until after the reference photon has arrived at the detector, with corresponding absence or presence of interference. It's not just about interaction causing collapse, or, if it is, a particle which has been interacted with and collapsed may be subsequently uninteracted with and uncollapse back into a wave. http://en.wikipedia.org/wiki/Quantum_eraser http://en.wikipedia.org/wiki/Quantum_eraser http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser

by hasenj 15y ago

Anderkent 15y ago

That part is not mysterious either - the collapse simply doesn't occur. Say you have a photon in a superposition of state A and state B - think position. If it is in state A it hits a detector, if it is in state B it does not. If the detector is hit, it displays 'HIT' on its screen - otherwise it does not. If 'HIT' is displayed, the researcher thinks photon was in state A, otherwise the researcher thinks it is in state B. The result of the experiment, without any wavefunction collapse, is a superposition of two states of the entire system: State 1: Photon is in A, Detector was Hit, Researcher thinks photon is in A + State 2: Photon is in state B, detector was not hit, researcher thinks photon is in B. As you can see, the fact that the researcher never sees a photon in a superposition of states a+b (he doesn't ever see the detector both lit up and not) is explained without any wavefunction collapse.

hasenj 15y ago
> Say you have a photon in a superposition of state A and state B - think position. Why are you assuming the particle has got to have a "position"? The fact that a quantum particle can interfere with itself would be experimental evidence that it doesn't in fact have a definite position.

Cushman 15y ago

You would think this, but the quantum erasure experiment appears to demonstrate that a photon which has been marked so as to determine its path and then subsequently randomly unmarked so as to irretrievably destroy that information once again displays interference. The delayed choice quantum eraser appears to demonstrate that this decision to either record or destroy path information may be delayed until after the reference photon has arrived at the detector, with corresponding absence or presence of interference. It's not just about interaction causing collapse, or, if it is, a particle which has been interacted with and collapsed may be subsequently uninteracted with and uncollapse back into a wave. http://en.wikipedia.org/wiki/Quantum_eraser http://en.wikipedia.org/wiki/Quantum_eraser http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser