21_universe1 - UCSD Physics 8 2008 The Place of Humans in...

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Unformatted text preview: UCSD: Physics 8; 2008 The Place of Humans in the Cosmos Many Other Parts of Physics Life in the Universe? 1 UCSD: Physics 8; 2008 Sub-fields of Physics Astrophysics and Astronomy Geophysics Plasma Physics Biophysics Condensed Matter Physics Particle Physics Atomic and Molecular Physics Gravitational Physics Economic Physics 2 UCSD: Physics 8; 2008 Our Place in Space The universe is unimaginably big our galaxy is one of > 100 billion visible to us our sun is one of ~100 billion stars in the galaxy if earth is the size of a pea, the sun is a beach ball 100 m away, and the next star is 3/4 of the way around the earth even in the solar system, earth is only a grain earth mass is <0.0003% of solar system mass and humans are tiny compared to the earth We are not at the center of: the solar system the galaxy the universe attention 3 UCSD: Physics 8; 2008 Our Place in Time Modern humans have been around maybe 200,000 years This is about 0.001% the age of the universe 2 105/2 1010 = 10-5 Compared to distance scale, this is sort-of like the size of a galaxy compared to the size of the whole universe 4 UCSD: Physics 8; 2008 Are We Alone? Hard to believe that we are Assumptions (restrictive version): must have solid planet to start life planet must be in habitable zone (liquid water) >10% of stars have planets already see >5% life forms given energy input and non-destructive environment no supernovae nearby, limited comet bombardment, etc. 5 UCSD: Physics 8; 2008 100 billion stars in Milky Way 10% with planetary systems 10 billion planetary systems The Numbers Say 1% of planetary systems have habitable planets 100 million planets Pick very long odds for life formation: one-in-a-million now 100 life-bearing planets in Milky Way Now multiply by 100 billion galaxies in visible universe 10 trillion life-bearing planets in visible universe How many have (or have at one time had) intelligent life? very difficult to know--related question: how long does intelligent life persist? Why don't they visit? same reason we haven't gone farther than our own moon: space is way too vast we may never venture even to the nearest star 6 UCSD: Physics 8; 2008 Planetary systems known to date Over 150 planetary systems discovered in last 10 years 170 planets total 18 multi-planet systems Discovered by seeing star wiggle under gravitational influence of planet tends to find BIG planets CLOSE to the parent star (biased) red points are individual measurements (with error bars) black line is best-fit elliptical orbit 8 MJUP at 2.88 A.U., 0.29 ecc. 7 sun's path in 65 years UCSD: Physics 8; 2008 http://exoplanets.org 8 UCSD: Physics 8; 2008 Galaxies: Islands of stars Central Virgo Cluster Andromeda Galaxy: our closest "big" neighbor 9 UCSD: Physics 8; 2008 How do we know: by their spectra 10 UCSD: Physics 8; 2008 Galaxies as far as we can see Montage of the Hubble Ultra-Deep Field: ALL are galaxies! 11 ...
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This note was uploaded on 04/10/2008 for the course PHYS 8 taught by Professor Tytler during the Spring '08 term at UCSD.

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