… or, The Real Anthropic Principle…
I was musing, as one does, about the relation between physics and biology. Usually we think of biology as some domain that can (or, depending on your personal position, cannot) be reduced to physics. I, on the other hand think of biology, like chemistry, psychology and librarianship, as what physics does in some part of the the universe. This led me to Avoid Work (a technical manoeuvre I often engage in) by doing some simplistic math on the matter.
The Anthropic Principle is basically the claim that the universe is fine tuned to produce life, and intelligent life at that. I wondered how fine tuned. How hospitable is the universe towards life? Basically, what’s the ratio of life-friendliness in the physical world to inhospitability?
We know that the biosphere of earth is roughly a shell of 100km thickness on the earth, from about 20km below sea level to 80km above it. This is, generously, the part of the universe that we know is life-friendly. Taking the volume of the sphere of the earth’s radius plus 80km, and subtracting the volume of the earth’s radius minus 20km, we get 46,412,331,509 km3. Not bad. 46 billion cubic kilometers in which life can exist. What’s the ratio of the observable universe to life-friendly volume?
The observable universe is roughly 8.8 × 1023 km across, so the volume is roughly 3.5 × 1071 km3. The ratio of life to nonlife volume is therefore around 1 in 1.361. It’s pretty much zero. So let’s assume biospheres are common; say, around a billion biospheres per galaxy and a hundred billion galaxies in that space, each around the size of ours. That gives us 4,641,233,150,851,590,000,000,000,000,000 km3. That brings the ratio to 1 in 1.341. Still pretty much zero.
So if biology is what physics does, it’s what physics does in an infinitesimally small part of the universe. On that basis, should we expect biology to have laws like physics? Are there biological universals? Is this the best universe God could have made for life? Does the design argument still make an impact here?
Have fun chewing on that…