Transcript Search for Life in the Universe

Search for Life in the Universe
Chapter 1
A Universe of Life?
(Part 1)
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Announcement
• Astronomy Open Night: talks to the public
about astronomical topics of interest,
followed by observing on the roof of the
ESS Building, weather permitting
• Time and place: First Friday of each month
at 7:30 PM in ESS 001 (big lecture hall)
• See the Fall 2005 Program
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Outline
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Is There Life Elsewhere?
Life in the Solar System
Nearby Stars
Distant Stars in Our Galaxy
Numbers of Stars
Distances of Stars
Communications and Travel
Universal Astrophysics (Part 1)
– Expansion and Finite Lifetime of the Universe
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Is There Life Elsewhere?
• Hollywood picture ignores basic physics,
chemistry, biology, and astronomy
• No credible UFO sighting (TBD in detail)
• Our task: scientific search for life, based
on physics, chemistry biology, and
astronomy
• Science evolves: we know today much
more than we knew before
• But science is also always incomplete
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Life in the Solar System
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No civilization except ours, present or past
Look for habitable worlds
Evidence that Mars once had water
Evidence for water under the ice of Europa
Evidence for microbal life on Earth under
harsh conditions
 Search for evidence of microbes
• Controversial Martian microbes
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Nearby Stars
• Many extrasolar giant planets (like Jupiter)
discovered since 1995
• Detection by reflex motion of parent star
• A few transitions seen
• Terrestrial planets still below detection limit
• Giant extrasolar planets very prevalent in
nearby stars
• No information, so far, on habitability
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Distant Stars in Our Galaxy
• Harder to detect microbal life
• Search for Extraterrestrial Intelligence:
SETI
• Main signature: radio transmission
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Numbers of Stars
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The Solar System has just one star: the Sun
~1011 stars in our Milky Way galaxy
~109 galaxies in the observable universe
With planets so prevalent, shouldn’t we expect
life to exist elsewhere?
• Can we calculate the probability of life?
• Can we detect extraterrestrial life?
• Is it intelligent?
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Sizes to scale, distances not to scale
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Distances of Stars
• 1 astronomical unit (AU) = Earth-Sun
distance: 1.5 x 108 km (9.3 x 107 miles)
• Equals 500 light seconds (8 min. 20 sec.)
• Distance to nearest star,  Cen: 4 light
years
• Distance to Galactic Center: 2.5 x 104 light
years
• Distance to the nearest big galaxy,
Andromeda (M31): 2 x 106 light years
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Communications & Travel
• Communication at the speed of light c:
– 4 years to  Cen
– 2.5 x 104 years to the Galactic Center
– 2 x 106 years to Andromeda
• Travel at ~10-4x c:
– 4 x 104 years to  Cen
– 2.5 x 107 years to the Galactic Center
– 2 x 109 years to Andromeda
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Universal Astrophysics (Part 1)
• Universal laws of physics ultimately
govern all processes
• Homogenous expansion of the universe 
similar physical development everywhere:
– Gravity  Galaxies, stars, and planets
– Nucleosynthesis  abundances of elements
• Instabilities & chaos  different objects at
different places (galaxies/stars/planets,
intergalactic/stellar/planetary space)
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Expansion and Finite Lifetime of
the Universe
• Hubble expansion v12  r12:
– Finite age
– Early universe dense and hot
• Cosmic Microwave Background (CMB):
– Detected, present temperature 2.7 K
• Big-bang nucleosynthesis:
– Correctly predicts primordial abundances of the light elements
– There is further nucleosynthesis in stars  heavier elements
• Small-scale CMB anisotropies:
– Detected primordial perturbations  gravitational instabilities
– Deduced precise age of the universe (2003): 13.7±0.2 x 109 yr
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