Anthropic Principal

The following post appeared at Cosmic Variance

Unusual Features of Our Place In the Universe That Have Obvious Anthropic Explanations

Sean at 5:02 pm, August 7th, 2007

The “sensible anthropic principle” says that certain apparently unusual features of our environment might be explained by selection effects governing the viability of life within a plethora of diverse possibilities, rather than being derived uniquely from simple dynamical principles. Here are some examples of that principle at work.

• Most of the planetary mass in the Solar System is in the form of gas giants. And yet, we live on a rocky planet.
• Most of the total mass in the Solar System is in the Sun. And yet, we live on a planet.
• Most of the volume in the Solar System is in interplanetary space. And yet, we live in an atmosphere.
• Most of the volume in the universe is in intergalactic space. And yet, we live in a galaxy.
• Most of the ordinary matter in the universe (by mass) consists of hydrogen and helium. And yet, we are made mostly of heavier elements.
• Most of the particles of ordinary matter in the universe are photons. And yet, we are made of baryons and electrons.
• Most of the matter in the universe (by mass) is dark matter. And yet, we are made of ordinary matter.
• Most of the energy in the universe is dark energy. And yet, we are made of matter.
• The post-Big-Bang lifespan of the universe is very plausibly infinite. And yet, we find ourselves living within the first few tens of billions of years (a finite interval) after the Bang.

That last one deserves more attention, I think.

If you go to the post (by clicking on the link at the top) you will find many erudite comments and it would be impossible to summarise the debate, but my favourites are short:

From Allyson: "This is one of posts that is awesome to read to stoned people"

From Neil B.: "How did life start? From atom and eV".

This issue relates to the "Fine Tuned Universe" which is described at this wikipedia article:

http://en.wikipedia.org/wiki/Fine-tuned_universe

and in the books:

Just Six Numbers by Martin J. Rees
and
The Goldilocks Enigma by Paul Davies

I am planning a future post on these issues.