State of the Universe if we increase/decrease the binding energy of deuterium

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Main Question or Discussion Point

[Sorry for the vague title, had a limit.]

I have a question given in my Astronomy class:
Below is a list of possible ways in which the universe could have been different. Some of these changes would make life as we know it impossible in our universe.

Tick the boxes next to all the changes that would definitely make life as we know it impossible. You may assume that there were many more protons than neutrons even before neutrons start to decay.

1) Decreasing the binding energy of deuterium, so that deuterium cannot form until an hour after the Big Bang.

2) Increasing the binding energy of deuterium so that it can form less than ten seconds after the Big Bang

The explanation for why the first one is true and not the second one is given as follows:
"If the binding energy of Deuterium were decreased, neutrons would decay before being combined into nuclei, making heavy element formation impossible. Increasing the binding energy would make less difference."

However, if you decrease the binding energy of deuterium, wouldn't it make it easier for neutrons to combine into nuclei? And if you increase the binding energy, wouldn't there be less Hydrogen which would later fuse to Hydrogen and so on to make life possible?

Thanks!
 

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  • #2
D H
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However, if you decrease the binding energy of deuterium, wouldn't it make it easier for neutrons to combine into nuclei?
A decreased binding energy would make it easier for a newly formed deuteron to split back into a proton and a neutron. Our universe had to cool down to about 109 kelvins before deuterium could form. Reducing the binding energy would have required an even longer cooling off period before deuterium could form. Reduce it enough and the waiting period will be so long that almost all of the neutrons will have decayed into protons.[/QUOTE]
 

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