Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: Anthropic principle

Learn more physics!

Most recent answer: 06/28/2009
Q:
Is the "anthropic principle" to be taken seriously? Just because the developing universe supports human life for a span of time at one location in the universe, does that really mean the universe is "fine tuned" for human life? What about the universe in the 13.699 billion years prior to the existence of humans? What about the future when humans as we know the species are extinct? What about whatever other forms of complex objects that might have developed elsewhere in the universe? The concept seems merely homocentric to me.
- Bill Cantrell (age 53)
Bellingham, WA USA
A:
Many eminent scientists tout the principle.  Many other eminent scientists poo-poo the idea.  In my own opinion there is no compelling evidence for or against it.   Instead of saying the universe is "fine tuned" for human life, you might say that human life is "fine tuned" for the universe.  But, in itself, the "anthropic principle" is a non-trivial argument and deserves discussion.  Take your pick.  There is a discussion ad nauseam in the Wiki article:
      

LeeH

For a slightly different take: I agree with you and Lee that any 'fine-tuning' specifically for  humans consists of
1)picking a suitable planet
2) evolution tuning all the organisms here, including us, to the local environment.

The problem comes in when you consider the basic physical constants that pervade the entire universe. These include the cosmological constant, the relative strengths of the different forces, the ratios of the masses of the common particles... If you made modest changes in any of these, you would have a universe with no complex chemistry, and hence no ability to support any sort of life so far as we know.  One possible way to make sense of this is similar to the way we make sense of the Earth having a reasonable temperature- nobody lives on the planets which are too hot or too cold. That sort of explanation could only make sense if there are many universes  to  choose from, just as there are many planets within a universe.  Just as life will only get started on suitable planets, suitable planets would only be found in the small fraction of universes that have suitable tuning. There are several lines of thought that had independently led to that 'multiverse' hypothesis. Needless to say, it's not easy to test.
MikeW.




(published on 06/28/2009)

Follow-up on this answer.