Slide 1

Dark Energy

Slide 2

Conclusions from Hubbles Law The universe is expanding Space itself is expanding Galaxies are held together by gravity on small distance scales R. Knob - Creative Commons

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Expansion Causes Redshifting Cosmological redshift (vs doppler shift or gravitational redshifting) Observed evidence of expanding universe and big bang R. Knob - Creative Commons

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More evidence CMB radiation Cosmic Microwave Background radiation T space = 2.7 K Emitted when universe was very hot, then was redshifted over billions of years Evidence of continued cosmological redshift NASA

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What the CMB Tells Us Critical density ( 0 ) density of the universe that would result in a critically expanding universe Average density () actual density of the universe 0 = / 0 If < 0, then 0 < 1 negative curvature If = 0, then 0 = 1 flat (no curvature) If > 0, then 0 > 1 positive curvature Our universe NASA/WMAP Science Team

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Curvature of the Universe On VERY large scales Could be: Positive (>180 ) [closed universe] Negative (