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Lecture 27

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McMaster University
Laura Parker

Lecture 27Wednesday November 16 20111230 PMThe threshold density doesnt add up to 100 meaning we will expand foreverIn WMAP we see we are at the threshold densityWe have an extra component thats just extra energy which makes the universe expand fasterDark energy is uniformly distributed but has no gravityRecall about WMAPThe degree of lumpiness tells us the total amount of massenergy in spaceIf very smooth then not much mass in space universe would expand foreverIf very clumpy then lots of massenergy in space universe expansion would stop and recollapseThere is a threshold density of massenergy below which expansion would continue foreverVisible starsgas makes up 4 of this thresholdIndirectly detected dark matter makes up 23But WMAP picture says that the total massenergy density is very nearlyto threshold densityThe remaining 73 is now suggested to be composed of pure energy in space dark energyThis dark energy could be the same kind of energy held within spacetime grid that was in the early inflation epoch but just at a much lower levelDark Matter vs Dark EnergyDM any type of mass that does not emit light Detectable through its gravitySeveral possible kinds of objects in this categoryMany times as much mass in Dark form as in luminous stars and gasDE pure energy does not produce gravity Even harder to detect evidence for itWhat is it and how does it show upDark energyCame from looking at supernovas incredibly bright we can see them from 7 billi
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