“our physical laws might be explained “anthropically,” meaning that they are as they are because if they were otherwise, no one would be around to notice them.”

There has to be a way of explaining this that saves it from its prima facie air of total unreasonableness. If such-and-such, no one would be around to notice does not normally establish that such-and-such can’t be the case. For example: if a tree falls in a forest on an unpopulated island then no one would be around to notice. This doesn’t prove the non-existence of unpopulated islands. For another example: if you read your book while hiding in a cupboard, then no one will see you reading. It doesn’t show that you couldn’t read while hiding in a cupboard. Provided, of course, you had a light of some kind. So come on, someone, explain it in terms that don’t appear plainly absurd.

I think he might have the wrong end of the stick. The point of this isn’t to deny the possibility that universes could turn out differently even though no form of life could exist in them. It’s instead to assert that they could and that, therefore, the fact this one has turned out like this, capable of supporting our existence, needs to be explained.

A form of explanation is to say that, from our point of view, it couldn’t be otherwise. It’s therefore unremarkable. Whatever the probability might be that the universe turned out like this one, that’s what happened – and this is absolutely fine, mathematically: one chance in however many squillion is still expected to happen, just not very often.

The anthropic principle is also used as an argument for the existence of God. Given there are an almost infinite – perhaps infinite – number of possible universes and only this one could support life, what made it be this one? Could it really be chance?

This assumes there are lots of possible kinds of universe. It turns out, there might be. There have been theories about the multiverse for a while, but at the end of last year, a group claimed to have found evidence of other universes from looking at the cosmic microwave background. They claimed to be able to detect ‘bruising’ where other universes had ‘bumped’ into ours. They had found areas which possess symmetry that, they feel, probably could not have appeared without some kind of event.

Another assumption is that our type of universe is rare, perhaps unique. This brings us back to the opening quotation. Here’s how I understand it: in this universe, there are now four basic laws in which physical reality can be described: the weak nuclear force, the strong nuclear force, electromagnetism and gravity. These are the things the opening quote was referring to. If you take one and change the way it works slightly, then do the sums, it turns out the universe would be very different to the way it actually is. Maybe no molecules heavier than helium could form. Life couldn’t exist; there would be almost no chemistry.

There’s also something called the cosmological constant. This is a term Einstein had to introduce into his equations in order to be able to have an expanding universe. I’m vague about this, but it represents something like the mass you can attribute to the vacuum. In effect it’s a weighting that can – as you slide the value up or down – make the universe one that will ultimately contract, or expand endlessly, or be static. Nobody’s sure of the value, but you can say that if it were outside a certain range then the universe would just be a big blob, or a vast emptiness as everything rushed apart. But it’s in the sweet zone, like the four laws above.

Incidentally, Stephen Wolfram argues* that, while it’s true that varying one of the physical laws throws thing out of kilter, you can often adjust by tweaking one or more of the others.

Wolfram has a particular interest in this because he has invented a new kind of science. This turns the normal approach on its head. Instead of looking at the world and trying to figure out the laws that govern it, he has started with the sets of possible laws, in steps of increasing complexity, starting with the simplest possible set. He is, among other things, looking for the simplest set of laws that produce the characteristics of this universe.

Snoopy picked this up and made me think. He commented:

I would dearly wish physicists considered themselves a bit less of philosophers and a bit more of trained dogs that bring the philosophers new trinkets to get busy with.

Physics used to be called Natural Philosophy, as did chemistry and all the sciences. I wonder whether, as the hard sciences crystallized, what was left behind was the mush, the syntactically correct, meaningless questions epitomized by “Why are we here?”. And I have a feeling the anthropic principle is more mush than crystalline. If there are an infinite number of possible universes or just one, or anything between, it doesn’t matter. This one exists.

* He said this in a video talk, maybe at TED. It would take forever to hunt down.

The left-hand image, obtained by the European Space Agency’s Huygens probe, shows rounded rocks from the surface of Saturn’s moon Titan. Huygens rode with NASA’s Cassini spacecraft to the Saturn system. The right-hand image, taken by amateur photographer Sandra M. Matheson, shows river rocks on Earth. (Credit: NASA/JPL/ESA/University of Arizona and S.M. Matheson)