PCS 181 Lecture Notes - Lecture 3: Cyclic Model, Elementary Particle, Parsec

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< 1 s, t = 1 x 1012 k. All types of elementary particles in existence. Matter and anti-matter begin annihilation to produce energetic photons. Recombination era = photon energies have declined enough such that hydrogen and helium. Vr = hod where we use a hubble parameter of 75 km/s. Recall that d = vt and replace d in above equation: 1 = hot t = 1/ho = hubble time = age of universe. = t = 3. 09 x 109 km = t = 4. 12 x 1017s = t =13. 1 x 109 years. *note: today it is = t = 13. 8 x 109 years. Open universe: density of matter is low = gravity is weak = universe expands forever. Closed universe: density of matter is high = gravity will halt the expansion and re- contract the universe. If this happens repeatedly, we have an oscillating universe.

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