The anthropic principle

The view which has emerged after the quantum revolution is that the Universe we inhabit is quite a unique place indeed. Many processes and forces must have been in a perfect balance for human life to evolve in it. We are talking about the mass of a proton, the density of the Universe, the quantitative relationship between various particles after the Big Bang, the magnitude of the strong nuclear force etc. If any of these numbers were off by as much as one billionth (!) of the observed value the humans would not be here to witness the proceedings. There is any number of catastrophic (from our viewpoint) scenarios even a tiniest imbalance would have caused. Atomic nuclei would be torn apart, galaxies would not form, heavy elements would not be created, water would not exist etc. The Universe appears to be perfectly fine-tuned for humans. Actually – impossibly so.

It is a legitimate scientific question how come the forces of nature are in such a perfect balance, from a human viewpoint? Enter the anthropic principle (AP) explanation. First postulated by Brandon Carter, it was subsequently refined and expanded by others. In simple terms it claims that the Universe we are part of is the way it is BECAUSE we are in it. Humans can only exist in a Universe where this incredibly precise balance of the various forces of nature is present. It is no wonder, the AP exponents claim, that say the observed mass of a proton is what it is. Otherwise we would not be here to measure it!

This explanation may sound almost redundant but it has some staggering implications. Assuming the mass of a proton could hypothetically be different there should exist billions of other Universes unsuitable for human life, in parallel  with the one we inhabit. In essence this is similar to a tadpole hatching in a pond somewhere and wondering how come it is surrounded by all the things it needs to live like water, algae, light etc. From a human perspective this is perfectly logical – tadpoles can only hatch in water, there is no mystery in that at all. There are countless other habitats like mountains, deserts or ice shields where a tadpole would never hatch.

The philosophical angle makes the AP theory abhorrent to most physicists. AP turns the tables on reductionist science. Instead of looking at why things appear the way they do it postulates that of the countless Universes on offer we popped up where conditions were just right for our set of tendencies. Otherwise we would not be here to blog about it.

Whacky, eh?


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