Cosmology and the Origin of Life

Making Helium:

But, deuterium is a very fragile nucleus and can easily be broken apart by a high energy photon:

pn + photon --> p + n (which will decay in 900 seconds)

Now there is an interesting race condition:

Will deuterium combine with another proton to make a nucleus with 3 nucleons or will it be photodissociated before it can do this?

This race condition depends on the density of protons:

• if the density is high then deuterium will fuse with another proton to make Helium-3
• if the density is low then most of the deuterium will be photo- dissociated before making Helium-3.
• a high density universe means a low density of deuterium
• a low density universe means a low density of Helium (3 and 4).

So things are trying to proceed as follows:

The end result is the conversion of 2 protons and 2 neutrons into 1 Helium-4 nucleus.

Before the Reaction:

• 14 protons and 2 neutrons

After the reaction

• 12 protons and 1 Helium-4 nucleus

The mass of 1 Helium-4 nucleus is about 4 times the mass of a proton

Now we can make a prediction:

The helium abundance reflects three things:

1. The p/n ratio at the time that nucleosynthesis starts
2. The ratio of photons to baryons
3. The actual baryon density

Element Production beyond helium:

• Lithium/Boron Production
• It stops at Boron

We have now finished the first step in the process

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