Why is the strength of weak nuclear force important ?

[thatoekhant]

I am just a student. I read that if the strength of weak nuclear force were stronger than current value, this would cause the rarity of neutrons. And, if the strength of weak nuclear force were weaker than current value, this would cause most of hydrogen to convert to helium. I can't understand those statement. Why ? Please !

Thanks in advance.

 

[Hawkwind]

Well, the weak force is responsible for the beta decays. Thus, a larger coupling constant would result in reduced lifetimes of the decaying particles - e.g. the neutron.
The beta decay also plays a role in the fusion process H + H -> He.
In the 1st step, a deuterium nucleus will be formed
p + p -> p + n + positron + neutrino
So, a beta+ decay of the proton is involved. A higher coupling constant would increase the fusion H + H -> He

 

[thatoekhant]

Thanks. But, some say that if there were rarity of neutrons, number of helium atom would be rare during big bang. But, I think even if there had not been sufficient heliums and only hydrogen atoms exists, formed stars would have converted hydrogens to helium by changing a proton to a neutron so helium will not be rare anyway. That will make the production of heavier elements without problems cos there are helium atoms produced by stars by converting hydrogens to helium. So, I think rarity of helium atom during big bang is not a problem. Is that right ? Please !
Thanks in advance.

 

[llynne]

The fact that the weak nuclear force is at a critical point of balance is significant. The events of the big bang (if there was such a thing) would not affect things so much as an ongoing effect of shorter particle lifetimes or reduced stability in atoms. The values of various forces hold atoms in a balanced way. The strong and weak nuclear forces and electromagnetic forces set up repulsive/attractive fields which locate each particle within a certain zone of an atom or molecule. Our understanding of it depends upon careful study of what we can measure of nanoscopic interactions. I think a little knowledge is a bad thing. How can you propose that it wouldn't matter if the weak nuclear force were different? And please rather than "some say" grab a reference. Tell us who says it, that really helps to explain what you mean.

 

[thatoekhant]

Thanks a lot. I would like to ask some questions. If there were no weak nuclear force, the sun would not burn because there would be no deuterium . And, di protons are extremely unstable. So, The sun would not burn . Is that right ? Besides, may I know the life time of a di proton , please. And also, May I know whether the mass of the formed diproton is less than the two H1 hydrogen atoms or not . Does a proton decay to a neutron every 10 minutes in the sun ?
Thanks in advance!

 

[mfb]

If there would be no weak force, the big bang would have happened completely different. So different that I have no idea how our universe would look like.

Assuming the weak force would have "vanished" in some way after the big bang: neutrons would be stable and fuse with protons quickly, so deuterium would not be an issue. Could shorten the lifetime of stars, as deuterium fusion is way quicker than the proton-proton reaction.

Diprotons are so short-living, the decay process has to happen "nearly at the same time".

Does a proton decay to a neutron every 10 minutes in the sun ?

I don't think that question makes sense.

 

[thatoekhant]

I would like to ask a question . As far as I know , number of protons is greater than that of neutrons in the universe. I have read that it is because the mass of neutron is slightly greater than that of proton. Could someone explain me relationship between mass of particles and their present numbers ?
Thanks in advance!

 

[mfb]

A particle cannot decay to a heavier particle - that would need additional energy from somewhere.
It is possible that a particle can decay to lighter particles - not all processes are possible, but neutrons can decay to protons.

As a result, the universe has more protons than neutrons.