Universe Scale and Probability of Life

• Observable universe: 90 billion light years diameter
• Contains at least 100 billion galaxies
• Each galaxy has 100-1,000 billion stars
• Planets very common throughout universe
• Trillions of habitable planets should exist
• Should create lots of opportunity for life development

Galactic Limitations and Focus

• Alien civilizations in other galaxies unreachable
• Everything outside local group out of reach forever due to universe expansion
• Even with fast spaceships, would take billions of years to reach distant galaxies
• Focus narrowed to Milky Way galaxy

Milky Way Statistics

• Home galaxy with up to 400 billion stars
• Counting 1 star per second = 100 lifetimes to count all
• 20 billion sun-like stars in Milky Way
• 1/5 of sun-like stars have earth-sized planet in habitable zone
• If only 0.1% of those planets harbored life = 1 million planets with life
• Milky Way age: 13 billion years old
• First habitable planets born after 1-2 billion years
• Earth only 4 billion years old
• Trillions of chances for life development in past
• Single space-traveling super civilization would be noticeable by now

Civilization Types (Kardashev Scale)

• Type 1: Access whole energy available on planet
  • Humans currently 0.73 on scale
  • Should reach Type 1 in next couple hundred years
• Type 2: Harness all energy of home star
  • Requires serious science fiction technology
  • Dyson sphere concept: giant complex surrounding sun
• Type 3: Controls whole galaxy and its energy
  • Would appear god-like to humans

Galactic Colonization Timeline

• Generation spaceships sustaining population 1,000 years
• Could colonize whole galaxy in 2 million years
• Millions/billions of planets sustain life in Milky Way
• Other life forms had considerably more time than humans

Fermi Paradox Introduction

• Central question: "Where are all the aliens?"
• Nobody has definitive answer
• Multiple theoretical explanations exist

Great Filter Theory - Option 1: Filters Behind Us

• Complex life development much harder than assumed
• Life beginning process not completely understood
• Required conditions may be extremely complicated
• Past universe was more hostile
• Only recently cooled down for complex life
• Humans may be unique or among first civilizations in universe

Great Filter Theory - Option 2: Filters Ahead of Us

• Described as "really really bad" scenario
• Life at our level exists everywhere but gets destroyed at certain advancement point
• Advanced technology activation destroys planets
• Last words of civilizations: "This new device will solve all problems once I push this button"
• Humans closer to end than beginning of existence
• Ancient Type 3 civilization monitors universe
• Advanced civilizations eliminated instantly when detected
• Something exists better not to discover

Existential Implications

• Possibility humans completely alone
• No evidence of other life exists
• Universe appears empty and dead
• No messages received, no responses to calls
• Humans trapped on "tiny moist mud ball" in eternal universe
• If life on Earth dies, maybe no life left in universe
• Life could be gone forever
• Humans must venture to stars, become first Type 3 civilization
• Spread life until universe's final breath
• Universe too beautiful not to be experienced

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