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Name: James
Status: other
Grade: 12+
Location: NC
Country: USA
Date: April 4, 2011


Question:
Does a quantum wave function actually physically collapse or is this purely mathematical? The double slit experiment leads me to believe the former. If so, where does the energy go?



Replies:
No, sir. The "area under the curve", the mass-energy of the particle, and any conserved quantum numbers: when they disappear from one place, they always go somewhere else. In the double-slit experiment, the electron-presence lost in the null zones is made up in the peak zones. If you somehow arranged wave-function cancellation everywhere in the roughly forward direction, that just means the electron was not allowed to go forward, and was probably reflected backward. But in the slit experiment this deflection is just small amounts to the left and right, not 180 to the rear. The only weirdness in it, is that a simple flat distribution modulated only by line-of-sight masking, surprisingly flowers into ripply interference (something waves always do). Combined distributions {flat }+{flat} = {high in some places, low in others, but the integral is preserved}.

Jim Swenson


James,

There are various interpretations. As I understand it, the energy does not disappear. When an electron passes through both slits, it is not as two electrons. When a wave functions consists of a distribution over several states, it is possible for the same object to have both energy levels at the same time. Every state conserves energy within its version of reality. When a measurement is made, one of the possible states is selected. The sequences of previous and future events that agree with the selection are selected. There is no disappearing energy, because previous events that require the unselected states have been eliminated: they never happened.

Time is not absolute at the quantum level. What happens now can affect what happened before now. Reality is not a sequence of events set in stone. When not measured, and when not restricted by other measurements, all possible realities exist. Each reality is consistent within itself. When measured, each reality has a probability of continuing. Those that do not agree with the measurement are removed. When a second measurement is made, more realities are removed. Each measurement will agree with at least one reality. The result of the measurement depends on the probability of each reality. One is more likely to see a result that agrees with a high probability reality, but any existing reality has a chance of providing the result. These realities are often called "timelines".

Dr. Ken Mellendorf


Your question is one that I think is still debated, but to my knowledge, is not resolved by experts in the field. Quantum mechanics behaves differently than classical mechanics, so we have to be very wary about transferring classical concepts to quantum concepts. In the case of the double slit (or other "double" experiments"). Even when the pairs are separated at distances that exceed the speed of light x the distance, the particle pair seem to know what its partner is "doing". Classically, that makes no sense. But we are not dealing with classical processes.

Personally, I am not convinced by wave functions "collapsing" only when they are observed. Particles do not think! You can write down wave functions analytically for simple systems -- before and after -- and there is no mathematical term that I can find dormant in the steady-state wave functions that "collapses". This must mean that the wave function that we write is only an approximation.

Vince Calder


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