Quantum Mechanics

The theory of quantum mechanics poses a well-known problem: at the atomic level, particles must be described as waveforms, but at the macroscopic level, they must be described as particles. The well-known double-slit experiment shows that if we, at the macroscopic level, remain ignorant of the location of the particle, it acts as a wave. However, if we measure the location of the particle, it acts as a particle. This is often described as “collapse of the wave function” or the “measurement problem.” As far as we can tell, this is reality, despite the complete defiance of common sense. The question that needs to be solved is why it looks different at the microscopic and macroscopic levels.

The traditional explanation of the measurement problem is known as the “Copenhagen interpretation,” so named because it was developed by Neils Bohr and Werner Heisenberg in Copenhagen. In this explanation, the wave function collapses when it is “measured.” Unfortunately, the nature of “measurement” is left undefined. It is often assumed that “measurement” occurs when a conscious observer becomes aware of the occurrence. However, if we take a materialistic world view, as I do, this does not make sense. Consciousness is created by atoms like other atoms, and they obey the laws of quantum mechanics just like everything else. It does not make sense to assign consciousness any special powers.

As far as I can see, there are two supportable theories to describe waveform collapse (ignoring various detailed differences between theories, and just focusing on the highest level approach). The first is one described in Roger Penrose’s book Shadows of the Mind (which is, by the way, in general a terrible book, continuing and expanding the deep confusion about the nature of consciousness which he first demonstrated in The Emperor’s New Mind). In this theory the waveform collapses when there is too much energy involved in it. That is, as particles interact with each other, the waveform grows to encompass more particles and hence more energy, until it eventually collapses. I have no idea if this is completely coherent, but let’s assume that it is.

The second theory is the Many Worlds Interpretation, originally proposed by Hugh Everett, which simply says that the wave function never collapses. In this theory, our consciousness gets bound up in one version of the wave function, and so it appear to us that the waveform has collapsed. This process of getting bound up is now known as “quantum decoherence.”

These theories can be experimentally distinguished in principle, so we could in principle determine that one of them was wrong. We can determine an upper limit on the amount of energy which would cause a waveform collapse in Penrose’s theory–evidently once a human brain is entangled the waveform collapses. We can then in principle construct an isolated quantum entanglement, make it contain more energy than a human brain, and then try to replicate waveform effects. In practice the isolation requirement would be fiendishly difficult.

The Many Worlds Interpretation is often assumed to suggest that all possible worlds exist. For example, the suggestion is that in some other path of the universal wave function I started this essay with the word “the” instead of the word “a.” While this argument may make for some good science fiction stories, I believe it is an error. The supposition that in some sense every choice is made at the subatomic level does not imply that every choice is made at the macroscopic level. There are many choices that I will never make, even though they are technically possible. It is not the case that my consciousness depends critically on quantum waveforms in my brain, or that my decisions are in way controlled by wavefunction collapse (Penrose might disagree, but that is because he is seeking a last redoubt for his confused view of consciousness). It is not the case that everything that we can imagine is actually possible.

On the other hand, one could argue that perhaps all the atoms in my brain will simultaneously change position, thus giving me a different personality, while still retaining my memory, causing me to make different choices. Of course, this would be a vanishingly improbable event, much less likely than my sudden spontaneous explosion. The most disturbing aspect of the Many Worlds Interpretation is that it suggests not only that there is a vanishingly small chance that I will suddenly explode–all interpretations of quantum mechanics suggest that–it suggests that in some sense I am in fact exploding all the time. I don’t know of any way to deal with this infinitesimally small possibility other than the time honored technique of not worrying about it.

Sticking to higher probability branches, the main problem with the Many Worlds Interpretation is trying to explain why we humans don’t see an entangled wave function, but only see a collapsed one. There is no immediately obvious reason why we could not operate on a quantum view of the universe, and even simultaneously choose different actions. That might sound odd, but it is more or less what quantum computers do, and they seem to work under laboratory conditions. Why can’t we do it?

If the Many Worlds Interpretation is true, I think the answer has to be that for some reason it was evolutionary advantageous to our remote ancestors to only perceive a single version of the wave function. Perhaps it is as simple as that when there are two slightly different high probability locations of food, choosing to move toward one causes the entire organism to act as though a single instance of the wave function were reality, effectively causing quantum decoherence.

I believe that life in some form is bound to be common in the universe, though I see no reason to believe that intelligence is common. It is interesting to speculate about the possibility of discovering a life form which was able to simultaneously choose different actions. Would such a being appear to us to behave almost randomly? Or would it seem to be able to solve problems almost magically?