Suppose we assume that the universe is an extremely “regular” sort of place, so that everything that happens happens in a “lawlike” way, in accordance with the laws of physics. This assumption has guided physics since Newton’s day. With that assumption in place, apparently “random” events – those that do not occur with the otherwise universal regularity – can seem to present a problem. Why did this rather than that happen, given that both possibilities seemed to be equally “ordained” or “unordained” by law? What “made” this rather than that happen? Why was one possibility realized and the other one not realized when there is nothing to choose between them?

One “solution” to this supposed “problem” is to say that both things actually did happen – that the universe split into two, no less. One universe contains one possibility – what we actually see happening. And the other universe contains the other possibility – what our new twins in the other universe presumably see happening instead.

I have put sneering quotation marks around the word ‘problem’ to indicate that I do not see “random” occurrences as a problem at all. But even if we do see them as a problem, and accept the above “solution”, a new “problem” arises: how is it that we find ourselves in “this” universe? How did it come to pass that I am located on this rather than that “branch” of the ever-expanding “tree of possibilities”? The pathway that can be traced back from my particular “branch” down towards the root of the “tree” takes apparently “random” turns in exactly the same places as the entire universe did before we posited multiple universes to avoid the apparent randomness!

So we are left with a supposed “explanation” that leaves as much unexplained as it began with – and now we also have to countenance an innumerable, unimaginable number of universes into the bargain! William of Ockham – whose “razor” tells us to choose the simplest possible explanation – would not be pleased. The idea is that “entities must not be multiplied beyond necessity” – and by “entities” Ockham wasn’t even thinking of entire universes but the posits of explanatory hypotheses.  Allowing entire universes to work as explanatory posits is to multiply entities beyond sanity.

Apart from being a remarkably bad bit of thinking in itself, the fact that this “multiverse” theory (as it is known) is so widely accepted, or at least taken seriously, exemplifies some other remarkably bad habits of thought. Ordinary people – i.e. non-scientists – do not point at it and ridicule it. Why not? Physicists do not blush when it comes up in conversation. Why not? Both bloody well ought to!

Physics is a remarkably good science. For most of its life, from Newton’s time to the present, its theories have had great explanatory and predictive powers. But something strange happened in the twentieth century. The “lowest level” of physics – quantum theory – turned into a formalism. This formalism has breathtaking predictive powers, and almost all of the marvels of recent technology rely on it. But it has almost no explanatory power, because no one understands it. You don’t have to take my word for that: Richard Feynman, himself one of the most important contributors to quantum theory, said “it is safe to say that no one understands quantum theory”.

The subatomic world is so unlike the macroscopic world, and it is populated by such unfamiliar objects, which interact with each other in such an unusual way, that we don’t know how to interpret the mathematical formalism that so successfully predicts its workings. Honest, reflective physicists admit that. But there is a less honest, less reflective type of physicist too, one who is flattered by public admiration for the predictive powers of physics and for the seemingly miraculous modern technology it makes possible. This type of physicist comes to believe that he is himself a sort of miracle-worker.

This is exacerbated by a sad fact about humans. When we don’t understand something, we tend to fall back on the supernatural and the “spiritual”. If it seems to us that some interaction is taking place but don’t understand how, we tend to start talking about minds and ghostly mind-like kinds of stuff. We can see this in many places in physics, from the yin-and-yang symbol that Niels Bohr chose for his coat of arms to the current usage of the word ‘information’ in physics (to mean something quite different from what we normally mean by the word).

Some physicists are so firmly in the grip of the idea that they are the unique purveyors of “spirituality” that, like their religious forbears, they do not trouble themselves to consult others who have given such matters more thought than they have.

For example, consider the thought I began with, that the universe is an extremely “regular” sort of place, so that everything that happens happens in a “lawlike” way. Why should anyone expect this to be the case? A scientific law is just a special sort of description – a far-reaching generalization (as in “what goes up must come down”). It does not “make” things happen, as Hume was the first to recognize. I used the word ‘ordained’ above, again in sneering quotations-marks, because scientific laws don’t “do stuff”. They’re just bits of human language that purport to describe stuff. The events they purport to describe either do happen in a regular pattern (so that Xs always follow Ys), or else they don’t. If they don’t, our descriptions or understanding are lacking in some way. That is an appropriate moment for modesty, and for scepticism, rather than the ludicrous extravagance of “multiple universes”.

We don’t have any compelling reason to believe that everything that happens in the universe does conform to regular patterns. Practically the only reason we can have to think that way is: we tend to assume the universe is “intelligible”. And I submit that that assumption comes from the vague idea that God designed it to be “orderly”. We don’t get the assumption from the universe being so orderly than we can imagine nothing but orderliness, because we would have the idea even if the universe was less orderly than it really is. (To see this, imagine that atoms of the same isotope differ from each other slightly – we would still assume they were indistinguishable below the level of our ability to discern between them.) The assumption of orderliness may guide science, but it isn’t one of the deliverances of science.

Physicists who have read Hume or at least thought about Hume’s most celebrated ideas will be aware of that. And physicists who haven’t won’t be. And the latter are condemned to rehearse a play of ideas that has already been staged, by philosophers, quite some time ago. (‘Condemned’ is too harsh a word, as they still enjoy the adulation of the general public.)

Physicists who do not bother to reflect on the insights that philosophers have already had make worse physicists than those who do, just as philosophers who do not bother to reflect on the insights of physicists make worse philosophers.

We need each other. We need to criticize each other. Philosophers need to be less timid about physics. Some of it is obviously stupid crap. And physicists need to think more deeply – and more – about possibility, cause, scientific laws, explanation, the place of the mind in the physical world, and so on. Philosophers have much to contribute here. And the general public needs to be more skeptical of extravagant claims made by people they look up to. Everyone wants to call himself a “sceptic”, and hardly anyone even knows what the word ‘gull’ means. But the gull population greatly exceeds that of genuine sceptics.