ASTRON 1F03 Lecture Notes - Lecture 28: Cold Dark Matter, Hot Dark Matter, Grand Unification Energy

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As the universe cooled after the big bang: Matter-antimatter annihilation, leaving many photons, neutrinos and a little normal matter. Pairs of particles and antiparticles were created and annihilated in the early universe. Higher energy means a particle with greater mass can be created. At early times, almost equal numbers of particles and antiparticles. After annihilation slightly more particles than anti-particles. Processes that occurred after inflation do leave behind a lot of junk. When matter-anti-matter annihilated, it left behind lots of neutrinos and anti-neutrinos that did not billions per regular atom (they don"t weigh much, so don"t effect the evolution of the universe). Gravitational instabilities in the early universe collapsed matter to form galaxies. Need: amount of dark matter and dark energy, size of original density variations, complete list of all ingredients. Suggest hierarchical clustering: small objects formed first, then grouped together. Recombination: normal matter is hot, density uniform to 1/100,000: gravity cannot grow galaxies from just regular matter.

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