Why does life not exist on other planets like our planet earth?

1 Answer
Jul 21, 2016

We don't know if it does or does not.


Consider the following:

  • #13.8# billion years have elapsed since the Big Bang (assuming our current theory is more or less correct).

  • #4.5# billion years have elapsed since the formation of our planet.

  • Primitive life formed (or arrived) on Earth at least #3.7# billion years ago, maybe as early as #4# billion years ago or so.

  • Anatomically modern humans have existed on Earth for only about #200,000# years.

  • Even relatively short periods of separation seem to lead to evolutionary divergence.

  • We have found that life exists on Earth in unexpected forms (extremophiles).

  • There are #100# billion stars in the observable universe.

  • A significant proportion of the stars have planetary systems.

  • A significant proportion of those planetary systems probably have planets in the "goldilocks zone", with liquid water and suitable chemistry to support life.

  • It is difficult or impossible to travel the distance between the stars in practical useful time frames.

So it seems likely that:

  • Primitive life exists in much of the universe.

  • Higher forms of life may be significantly rarer and may take forms somewhat different from us.

  • Intelligent life may exist in millions of separate planets, but they may be so far from us that we would not detect activity similar to our own (radio communication etc) and it would be difficult for us to meet.