Lecture 24: Is There Other Intelligent Life in the Universe?
"Sometimes I think we're alone. Sometimes I think we're not. In
either case, the thought is staggering."
-- Buckminster Fuller
To put the cosmos in perspective,
click here and
follow the slide show.
How did life evolve on Earth?
- in 1859, Charles Darwin
publishes The Origin of Species
- most revolutionary work in the history of science?
- basic idea is very simple -- so simple it is frequently misunderstood
- recognized a
purely natural way to obtain highly adapted complex organisms
- complexity can arise as result of cumulative effect of small
- adaptation can arise as result of selection effect
- if mutation confers advantage to chance that organism will survive,
mutation will be adopted and passed on to next generation
- if, however, mutation reduces chance of survival, then that mutation is less likely to be passed on to
next generation because organism may perish before it reproduces
- thus, over many generations, survivors will
be those organisms that are best able to adapt and
survive -- this selection effect is called Natural Selection
- unlike evolution by artificial selection, evolution
by natural selection, is undirected and goal-free
- there is no aim -- what survives is
what works best at that moment in that environment
- if evolution by natural selection
has occurred on Earth, then can it occur elsewhere, but result may be different due to different conditions
So, life adapts to suit its environment -- the successful (not necessarily
the best!) adaptations continue, the unsuccessful ones disappear.
Let's concentrate on life close to what we know
(as it's hard to imagine everything
we don't know!)...
So, Are We Alone?
- Milky Way contains about 100 billion stars, and known Universe contains
about as many galaxies
- given such huge numbers, it is reasonable to ask if we are alone
- and, if we believe that other life is likely, to ask whether some of it could be
- basic building blocks of carbon-based life as we know it are organic molecules
- such molecules are spread throughout the Universe
- how easy is it to go from these simple organic molecules to building blocks of life?
- in 1952, question answered in
classic experiment performed by the chemists Stanley Miller and Harold Urey
- showed that simple molecules can
combine to form molecular building blocks of carbon-based life forms under
conditions that are believed to have existed on Earth in its early history
- but this success is only first step towards life
- we still have to get from amino acids to self-replicating molecules
- natural selection proves crucial
- can obtain self-replicating molecule
by cumulative effect of small random changes in a large pool
of randomly-created molecules
- over time, population of the more stable,
better-adapted molecules grows at the expense of less stable, less well-adapted molecules
How Do We Find Other Intelligent Life?
To learn about the physics of interstellar travel,
The Drake Equation
To read an interview with Frank Drake,
To make your own estimate of the probability of other intelligent life using
the Drake equation,
- many uncertainties associated with terms in equation (some terms are more uncertain
than others -- which ones and why?)
- one possibility is Earth harbors the only intelligent, communicative organisms in Galaxy
- OR a few (relatively) short-lived technological civilizations are scattered
far apart among stars, never contacting each other before disappearing
- OR there is a large number of life-bearing planets
- estimates of number of other intelligent civilizations range from 0 to 10 trillion!!!
- development of astrobiology
- convergence of wide range of scientific disciplines
- astronomy, biology, paleontology, oceanography, microbiology, geology, and genetics, among others
- consideration of entire planets as ecological systems
- life on Earth considered only single example of how life might work, rather than only example
- suggestions of simple life on Mars and
undersea life on Europa...
- Galileo spacecraft took measurements of Europa's magnetic field during January 2000 flyby
218 miles above this moon of Jupiter
- magnetic north pole reverses every 5 1/2 hours
(something that would make a compass difficult to use!)
- underground layer of conductive liquid -- like saltwater -- best explains the
- Europa has cracked, icy surface, suggesting floating, colliding ice on liquid ocean
- coupled with discoveries
of extrasolar planets and extremophiles...
- make some people think that life elsewhere is
likely (fl and fp terms might be large ---> N large?)