Physics and Physicalism

Sorry for the lack of posting recently- not surprisingly, I’ve been a little busy with classes. But, my philosophy class is discussing physicalism, and I thought I’d say something about it really quickly, as a physics major. Physicalism is essentially the theory that everything can be explained through physical explanations- i.e. everything is reducible to the laws of physics. In our recitation this was formally defined as the theory that “all facts are entailed by physical facts”, where a physical fact is one that would eventually be described by a complete theory of physics. For Christians, this is problematic because a physicalist denies the reality of anything that isn’t “physical”, that is, things like souls and God.

However, I’d like to discuss this theory as a physicist. At first, it seems like physicists would love this theory, since it implies they can explain everything. However, physicalism is actually incompatible with physics, at least under the Copenhagen interpretation of quantum mechanics. I discussed other possible interpretations here, but for this argument I will assume the Copenhagen interpretation, which is virtually unanimously accepted among physicists. The Copenhagen interpretation explains the wave nature of particles in quantum mechanics as the probability that a particle will be measured in a particular state. So, when a particle is observed, the wave collapses RANDOMLY into one of the states in the wave equation (assuming there are multiple states in the wave equation). The probability that the wave will collapse into a state can be found mathematically, but as to why any given particle collapses into a certain state, it is vital to the Copenhagen interpretation that it happens randomly (which I discussed in this article). Thus, it cannot be explained by any further laws of physics, and a completely theory of physics still will not tell us why any particular particle collapses into a particular state.

But, it is a fact that a certain particle collapses into a certain state, and according to physicalism, this fact must be entailed by physics. That is, the physical laws must be such that this particle had to collapse into that certain state. In formal logic, if the laws of physics are A1 & A2 & A3 … and the other physical knowledge (boundary/initial conditions, etc) and B1 & B2 & B3 …, and the particle collapsing into a given state is P, then ((A1 & A2 & A3 …) & (B1 & B2 & B3 …)) → P, or (~P) & ((A1 & A2 & A3 …) & (B1 & B2 & B3 …)) is a contradiction. However, physics (as we understand it today, anyway) tells us that the particle could have collapsed into other states without violating the laws of physics, since the particle collapses randomly. Hence, this fact is not entailed by the laws of physics, and physicalism fails.

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