Life in the Universe
100 billion+ star systems in the Milky Way
◦ New exoplanets being discovered every day
100 billion+ galaxies in observable universe
Carbon can arrange in many, many ways…
◦ Given that and the amount of matter, nature can experiment practically an infinite number of times.
Stuff. Lots of stuff.
We hope that we can:
◦ Find microbial life in our Solar System
◦ Find EM signals from extra-solar civilizations
Two Possibilities
Earth was born 4.5 billion years ago
Heavy bombardment from 4.2 to 3.9 billion years ago
Life was thriving prior to 3.85 billion years ago
Life on Earth
So just as soon as the oceans quit getting vaporized by asteroids, life sprang into action – in an instant!
Life on Earth
Timeline
“Mats” of bacteria build layered rocks
We see them today, we see similar ones from long ago
Dated to 3.5 billion years
Stromatolites
Oldest microbes (from DNA standpoint):
◦ Live near “black smokers” in the ocean
◦ Live in hot springs in Yellowstone
Life In Extremes
Why did early life hang around extremes?
Earth may not have had an ozone layer yet; hide out from UV
First Living Organisms
“Ice worms” live in glacial ice
Life In Extremes
Lakes, rivers and thick atmosphere of basic organic molecules have been observed
Titan (a moon of Saturn)
Chemists have recreated the pressure, temperature, and chemistry of Titan’s atmosphere
They found:◦ Nucleotide bases◦ Amino acids
Titan (a moon of Saturn)
Source of nutrients to build living cells◦ Organic molecules all over the Solar System
Energy for activity◦ Sunlight, internal heat from a planet
Liquid water◦ That’s the tough one.
What do we need?
Liquid water requirement leaves us with:
◦ Mars
◦ Jovian moons, particularly Europa
Life in the Solar System
Evidence: Mars once thriving waterworld
Martian meteorite may show evidence for life
Life on Mars
Tidal heating
Evidence for water flow
Thick water-ice surfaces◦ But not much energy from sunlight
Life on Jovian Moons
Jovian Under-Water Worlds (?)
Europa Ganymede Callisto
Enceladus Titan
Life may only take ten thousand years to form
Intelligent life may take a few billion years
◦ Excludes blue stars; they only last 100 million years
◦ Sun-like stars and red dwarfs good candidates
Life Around Other Stars
Habitable zone: Smaller and closer for smaller stars
Life Around Other Stars
Outer galaxy:◦ Too few heavy
elements
Inner galaxy:◦ More crowded,
supernovas would nuke everything
Galactic Habitability
When an exoplanet transits a star, starlight passes through the planet’s atmosphere
◦ This is a cutting-edge technique, but does reveal chemical composition of the planet
◦ Look for carbon dioxide, ozone, methane, and water vapor
◦ Oxygen abundance on Earth result of biology
Signs of Life
It is entirely possible that extraterrestrial civilizations could be using this technique to monitor our progress. Perhaps at some point:
◦ We become cool enough to make friends
◦ We become advanced enough to pose a threat
Signs of Life
Jovian planets launched trillions of objects into the Oort Cloud
These objects now pose no danger to Earth
Might “comet launchers” be a prerequisite for intelligent civilizations?
Jovian Planets: Comet Launchers
The Drake Equation
Number of “Contactable” Civilizations = NHP x flife x fciv x fnow
NHP = Number of habitable planets in the galaxy
flife = Fraction of planets that are habitable
fciv = Fraction of planets that can communicate
fnow = Fraction of planets that have a civilization now
EM waves travel forever – but get weaker
Look for signs of communication
SETI (Search for ExtraTerrestrial Intelligence) does that all day
Another Approach
We have deliberately sent high-power signals into space to “make contact”
Used Arecibo in 1974 to send to M13 (21k LY away)
And Just The Opposite
Einstein’s Theory of Relativity limits all speeds to the speed of light
Out fastest spacecraft are travelling 1/10,000 the speed of light◦ 100,000 years to Alpha Centauri (but not pointing
there)
Time dilation and length contraction: ◦ At 99.9% the speed of light, 2 years pass for the
astronauts while 50 years pass on Earth
Interstellar Travel
Detonate atomic bombs to propel the ship
Scoop up hydrogen and fuse it
Interstellar Travel Ideas
So we either build generational ships or we figure out how to warp space and time
We don’t know how to warp space and time, but current laws of physics don’t seem to prevent it
Interstellar Travel
Even our “slow” spaceships could populate stars within a few hundred LY
◦ Would take about 10,000 years – an instant in the overall scheme of the Universe
◦ In a few million years, we could colonize the galaxy
A few million years? This should have been done a long time ago.
Aliens
1 in 1 million chance a star will have life
100 billion stars in Milky Way: 100,000 civilizations
Suppose intelligent civilizations arise after 5 billion years◦ Galaxy is 12 billion years old◦ 100,000 civilizations should have arisen 7 billion
years ago – billions of years ahead of us
Aliens
Aliens
So… where are the aliens?
Galactic civilization should already exist! Three possibilities
◦ We are alone … and therefore precious. The only part of the Universe that is
self-aware.
◦ Civilizations are common but they haven’t bothered colonizing the galaxy We explore every chance we get. Do they always end up
destroying themselves?
◦ The galactic civilization hasn’t gotten around to us Are we not yet invited?
Aliens