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