Realism and Physical Laws

Are you a realist about the laws of nature? Most people, I would warrant, would not know how to answer the question, which is fair enough. It is only physicists and philosophers of science who tend to worry about such things. But it is, at least, a bit interesting.

The question is whether we think that a physical law is correct and really describes the world, or whether a law is a relation inhering in the world. The difference is in the words ‘inhere’ and ‘describe’. A view in which the laws describe the world can be traced back the David Hume, the Scottish Empiricist. A law which inheres in the world is a metaphysical entity which controls the world.

Most people, including most physicists, do not worry about the difference too much. But taking the laws of nature as inhering in the world can lead to some odd sorts of effects in our thinking. Hence, we can start to believe that every time a quantum event occurs in a way that affects the macroscopic universe (a cat in a box with a phial of poison which opens when a radioactive decay occurs) the universe splits into two, and we go down one branch or another (the cat is, when we look at it, alive, or dead, but not both).

If we take the view that laws of nature only describe the universe to us, there is less of a problem with unknowable branching universes. In a sense, it seems to me, the Humean version of physical laws are a bit more humble than metaphysical laws of nature. In the Humean case, what matters is the description of the universe as it appears to us. We might be grasping at each advance of science towards a better understanding of what is going on, but each step is not getting at a final truth, but simply a better understanding.

I think there might be an analogy with theology here; indeed, some authors about the problems surrounding quantum mechanics reach for God-like beings to give a total explanation of the theory. But that is not accessible to us as limited humans. Ian Ramsey once noted that the early Church Fathers were giving the best descriptions they could of the Godhead, but they were not dialling Chalcedon 451 for updates on the Trinity every week and writing it down. Human descriptions of the Trinity are exactly that: human descriptions of the indescribable in human terms.

We can see, perhaps, that we might be over-egging our quantum pudding by claiming that quantum mechanics gives a complete description of the quantum scale. Quantum Mechanics gives rise to some paradoxes, grated, but the paradoxes are human paradoxes, grounded on our ignorance of what is really going on at the quantum scale (the very, very small), in a similar way to Trinitarian theology, which is grounded on our ignorance of what is going on in the Godhead.

Therefore, when physicists or philosophers of science come up with ideas like the multiple emerging universes of branching quantum mechanics and argue (quite coherently, admittedly) that this is all fine and no counterargument can really stand against it, we have the right to be a little sceptical. Quantum mechanics might be the best theory we have which describes the micro-world, but that does not mean it is giving us the constraints that the micro-world acts under. Just because it is correct (i.e., gives accurate predictions) does not mean that quantum mechanics is a metaphysical entity controlling the world.

Again, caution is suggested by the analogy with Trinitarian theology. Just because something is a deduction from an idea about the Trinity, does not mean that the deduction is right. Theology works with a host of images and metaphors for God and the Godhead. Running one of them to death is liable to land the theologian in heresy. Similarly, running one idea of quantum mechanics to death is liable to land the philosopher of science in a but of a muddle, claiming that, for example, each time the cat is placed in a box and is later observed, the universe splits into two identical universes, one with a live cat and the other with a dead one.

The quantum world is a great deal weirder than we can imagine, I think. We do not know what it is like to ‘be’ and electron. How does an electron experience a magnetic field and emitting photons by moving through it? We have no idea. To claim that we do have is to argue that quantum mechanics is an absolute, cast-iron physical law. In fact, I would suggest, quantum mechanics is simply a human language construct (that language being mathematics, of course) which predictions which can be experimentally verified as being reasonably (and certainly usefully) accurate.

If this is correct, then arguments about multiple emerging universes start to look a little superfluous. The problems which such theories claim to solve – the relation between the Schrodinger equation and the Born rule, one being a solvable wave equation and the other being probabilistic, dissolves. It is simply the result of having to use two bits of a human construct to explain what we see.

Similarly, the problem of wavefunction collapse vanishes as well, I think. This is the issue that before we look in the box, the cat exists in a superposition of states – it is either alive or dead. When we make an observation, it is either one or the other, the wavefunction as suddenly collapsed into one state. The question is then asked about how the collapse happens, physically. The answer is that it does not happen, because the collapse of the wavefunction is something that emerges from the human level description of the universe. It does not necessarily happen in the quantum level because the quantum level is inaccessible to us.

Quantum mechanics is quite weird enough, it seems to me, not to require additional counter-intuitive ideas to further complicate matters. While emergent universes might not be ruled out specifically by the theories of quantum mechanics, they are an unnecessary and, perhaps, rather arrogant addition to the laws of nature. We simply do not know what is happening at the quantum level; that knowledge is unavailable to us.