1. Life

Definition of life

not clear-cut

alternative biologies

silicon instead of carbon

ammonia instead of water

significance of finding life on other planets

any kind will do!

2. Fact, Fiction, Belief

BEWARE:

``inevitable'' =

can't really explain, but gut reaction is YES

Historical trends:

utopianism

optimism

realism

pessimism

Historical precedents: scientific revolutions

Ptolemaic vs. Copernican world view

Newton's Physics:

Classical Mechanics and Gravity

Einstein's Physics:

Quantum Mechanics & General Relativity

3. Green Bank Equation

The best way we know how to 'parametrize' our ignorance!

Why "Green Bank"?

7 terms:

1. star formation rate (number per year)

2. stars with planets (fraction)

3. planets suitable for life /10 (number per star)

4. habitable planets with life (fraction)

5. planets with intelligent life (fraction)

6. intelligent life with technology (fraction)

7. lifetime of civilization ???

The book chooses the last term as the variable !!!

4. Speed of light rears its ugly head

Suppose civilizations with technology last for 10⁶ years ...

... and are randomly distributed in the disk of our galaxy.

Average separation: 150 light years

But if ...

10,000 year lifetime 1,500 light years

100 year lifetime 15,000 light years

5. Bottom line: (my opinion)

Life exists elsewhere in the Universe (certainty)

Chances are we won't know about it unless we learn how to break the light barrier.

Sheer fancy?

Hope not! (but don't count on it in our lifetime)

(a) direct evidence for other intelligent life in the solar system

(b) other "biologies" based on silicon and ammonia are impossible

(c) we are not alone as sentient creatures in the universe

(d) Earth colonization of planets is possible

(e) life on Earth is less likely to be a freak accident

(a) star formation rate

(b) fraction of planets with intelligent life

(c) stellar lifetimes

(d) fraction of potential life-bearing planets

(e) size of planetary habitable zones around stars