Cosmology and the Origin of Life
Two main observations:
Universal Expansion --> means the universe used to be a small place where all the matter was together --> as the universe expands (ages) its density goes down
The Microwave Background:
Now we know something real important. If the Universe is cooling then it was hotter in the past. Hence the Universe used to be a real hot and dense place. The average energy per photon depends on the temperature of the Universe and therefore, at early times, photons have a large amount of energy.
The observed ratio of photons (400 per cubic centimeter) to hydrogen in the Universe is about 1 billion to 1. That is, for every H-atom there are one billion microwave background photons. This will be extremely important later.
Now remember the Principle of Equivalence . Why is this a big deal?
A Framework for describing the Thermal Evolution of the Universe:
photon + photon <-----> particle +antiparticle
Average photon energy depends on the Temperature of the Universe
This temperature is steadily in decline and therefore the average energy per photon declines as the Universe expands and cools
At any given time in the Universe, the distribution of photon energies looks like this (this is the blackbody curve):
If Ephoton < mpc2 then that photon has insufficient energy to spontaneously convert itself to mp + its anti-particle
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