Dark Energy. Conclusions from Hubble’s Law The universe is expanding Space itself is expanding Galaxies are held together by gravity on “small” distance.

Dark Energy

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

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

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

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

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

Dark Energy. Conclusions from Hubble’s Law The universe is expanding Space itself is expanding Galaxies are held together by gravity on “small” distance.

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evidence of expanding

closed universe negative

positive curvature

negative curvature

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gravitational redshifting