Why Are the Physical Constants of the Universe So Perfect for Life?

Arthur T Knackerbracket has processed the following story:

When we look out into the universe, we know it can support life - if it couldn't, we wouldn't exist. This has been stated in different ways over the years, but the essential thrust makes up the core of a philosophical argument known as the anthropic principle. It sounds obvious, even tautological, but it isn't quite as simple as that.

To get your head around it, start with what scientists call the fine-tuning problem, the fact our universe seems perfectly balanced on the knife's edge of habitability. Many fundamental constants, from the mass of a neutron to the strength of gravity, must have very specific values for life to be possible. Some of these constants, if you make them too large, you just destabilise every atom," says Luke Barnes at Western Sydney University in Australia.

The anthropic principle began as an attempt to explain why the universe is in this seemingly improbable state, and it boils down to a simple idea: the universe has to be this way, or else we wouldn't be here to observe it.

There are two main formulations of the principle, both of which were set out in a 1986 book by cosmologist-mathematicians John Barrow and Frank Tipler. The weak principle states that because life exists, the universe's fundamental constants are - at least here and now - in the range that allows life to develop. The strong principle adds the powerful statement that the fundamental constants must have values in that range because they are consistent with life existing. The must" is important, as it can be taken as implying that the universe exists in order to support life.

If the weak principle is I heard a tree fall in the forest, and therefore I must be in a place where trees can grow", the strong principle says A tree has fallen nearby, and therefore this planet was destined to have forests all along."

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