Putting it all together: The Big Bang Model

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Astronomy & Astrophysics
Michael Reid

AST201 Thursday, April 4, 2013. The Milky Way is mostly Dark Matter - There are small amounts of baryonic matter Dark energy - Accounts for majority of the universe - Almost 70% of universe - About 27% is dark matter - About 5% is ordinary matter - 95% of universe is mysterious dark stuff *Clicker Question: According to Hubble’s Law, distant galaxies are: - Receding from us at an ever-increasing rate - Getting farther away at speeds proportional to their distances (THIS ONE) - Moving through space, with farther ones moving faster o Galaxies are not MOVING, but are getting FARTHER AWAY o Distance to a galaxy is proportional to its redshift *Clicker Question: What effect should all the matter in the universe (dark plus luminous) have on the expansion of the universe? - Slow it down (THIS ONE) - No effect - Speed it up o Every mass produces gravity o Gravity can NEVER push, only pull o As it cannot push, it can never speed things up If expansion is slowing down, we would expect distant galaxies to have larger redshifts than predicted by Hubble’s Law - Would expect deviations in the upward curve of Hubble’s Law (decelerating expansion) - We actually find an accelerating expansion curve - Today, universe is expanding faster than it was millions of years ago - Lower redshifts, and slower expansions farther back in history of universe - We observe an accelerating universe, not a decelerating universe (which was what was initially expected) We call the driver of the acceleration dark energy o Require unit of energy to produce accelerating universe o We do not know what this energy is, so we call it dark energy AST201 Thursday, April 4, 2013. o Dark energy is powering the expansion of the universe o It is not causing the expansion; the Big Bang caused the expansion o Dark energy only makes the pre-existing expansion proceed faster PUTTING IT ALL TOGETHER Big Bang Model - Observation: universe is getting bigger o According to Hubble’s Law, universe was once filled with hot, dense plasma o To prove Big Bang theory, look for the light produced by all that hot plasma  The further away we look, the further back in time we can see.  Any dense object emits blackbody spectrum  Universe was a blackbody at its origins; it would have had very short wavelengths
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