Life in the Universe
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Life in the Universe. Stuff. Lots of stuff. 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…

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Life in the Universe

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Life in the Universe

Stuff. Lots of stuff.

  • 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.

Two Possibilities

  • We hope that we can:

    • Find microbial life in our Solar System

    • Find EM signals from extra-solar civilizations

Life on Earth

  • 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!



  • “Mats” of bacteria build layered rocks

  • We see them today, we see similar ones from long ago

  • Dated to 3.5 billion years

Life In Extremes

  • Oldest microbes (from DNA standpoint):

    • Live near “black smokers” in the ocean

    • Live in hot springs in Yellowstone

First Living Organisms

  • Why did early life hang around extremes?

  • Earth may not have had an ozone layer yet; hide out from UV

Life In Extremes

  • “Ice worms” live in glacial ice

Titan (a moon of Saturn)

  • 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

What do we need?

  • 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.

Life in the Solar System

  • Liquid water requirement leaves us with:

    • Mars

    • Jovian moons, particularly Europa

Life on Mars

  • Evidence: Mars once thriving waterworld

  • Martian meteorite may show evidence for life

Life on Jovian Moons

  • Tidal heating

  • Evidence for water flow

  • Thick water-ice surfaces

    • But not much energy from sunlight

Jovian Under-Water Worlds (?)






Life Around Other Stars

  • 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

Galactic Habitability

  • Outer galaxy:

    • Too few heavy elements

  • Inner galaxy:

    • More crowded, supernovas would nuke everything

Signs of Life

  • 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

Jovian Planets: Comet Launchers

  • 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?

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

Another Approach

  • EM waves travel forever – but get weaker

  • Look for signs of communication

  • SETI (Search for ExtraTerrestrial Intelligence) does that all day

And Just The Opposite

  • We have deliberately sent high-power signals into space to “make contact”

  • Used Arecibo in 1974 to send to M13 (21k LY away)

Interstellar Travel

  • 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 Ideas

  • Scoop up hydrogen and fuse it

  • Detonate atomic bombs to propel the ship

Interstellar Travel

  • 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


  • 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.


  • 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


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?

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