Re: Why is oxygen more abundant than carbon in the universe?

I suppose the simple answer would be to say that "energy isn't 
everything" but that wouldn't really address the issue you raised. 

Nucleosynthesis of the heavy elements - that is, anything other than 
hydrogen and helium and their respective isotopes - requires different 
processes due to the beryllium problem. You simply can't take two 
helium's and stick them together to get beryllium. It doesn't work very 
well. So, making carbon is tricky, requiring the fusion of three helium 
nuclei at the "same time" - an improbably 3-body collision has to occur 
which is aided by the momentary stability of the 2-body product. All of 
this sort of puts a log jam in the way of making the heavier elements.

Hence, we typically only find carbon in large quantities in second 
generation stars and in super novae just before they explode. Further, 
once carbon is formed, it is readily burnt to oxygen through the addition 
of another helium nuclei. The explosion of a super nova seeds the 
galaxies with carbon and oxygen rich clouds. These elements are, in turn, 
incorporated into new stars where they engage in the CNO process. In 
essense, this is a series of competing reactions - each with a different 
rate and all of which are temperature dependent. The result of the 
competing rate processes is that the equilibrium struck by the star with 
respect to its C/O ratio is not necessarily driven by a consideration of 
the relative energy levels of the nuclei but by the processes driving 
their formation and destruction. Kinetics wins out over thermodynamics is 
one way to view it. The net result is that since carbon and oxygen 
burning stages occur either just prior to a super nova explosion or 
within second-generation stars of high mass, the ratio of the two 
elements essentially doesn't change and is the same pretty much 
everywhere - at 0.6. It is a consequence of relative rates and not 
relative energy.

I hope that this answers your question.