Re: "A Universe Without Weak Interactions"

Jonathan L Cunningham wrote:
Erik Max Francis <max@xxxxxxxxxxx> wrote:

This one's right up rec.arts.sf.science's alley:

http://arxiv.org/abs/hep-ph/0604027

That reminds me of something I've been wondering about (for SF
purposes).

Suppose you had a universe with almost the same laws of physics as ours,
except tweaked so that the masses of protons and neutrons were swapped,
keeping everything else as much the same as possible.

Anyone care to speculate what the effects would be?


The di-neutron would probably be stable. It's only narrowly unstable in
our universe. The trineutron might be also.

For star formation, the ability to radiate away energy is important.
Once the temperature has dropped low enough that typical collisions
don't have enough energy to put either particle in an excited state,
the cloud largely stops radiating, which sets a floor on the gas cloud's
temperature, and pressure.

Pure helium won't form stars efficiently for this reason. Pure dineutron
clouds would have the same problem. You need to come out of
nucleogenesis with enough deuterium to avoid this, though I couldn't
estimate what the minium requirements are.

Any other obvious effects? I don't see why life shouldn't be possible in
such a universe... or is it?


Life as we know it, perhaps not. Life of some kind, quite probably.
There would still be energy gradients, and complex chemistry.

Another interesting option is to weaken gravity, relative to
electromagnetism. Everything where gravity is significant ends
up being bigger, with longer timescales.

If gravity is 100-fold weaker, stars would need to be 1000 times
heavier, to ignite fusion, but would last roughly 100 times longer.
Similar elemental abundances to now would be reached after a similar
number of stellar generations, around a trillion years. The stars
would be about ten-fold brighter than ours, but roughly the same
temperature, so habitable planets would circle at a little over
3 a.u.

The heavier sun would outweigh the weaker gravity, giving shorter
years than ours, but the typical size of a planet would be larger.
The largest living land creaures, which can barely hold up their
own weight, would also be larger, and so on.

This gives life much longer to evolve, and a wider range of
length scales to explore, which could be interesting.

Make gravity too weak, and you do run into problems, but there
should be room to make it somewhat weaker.



--
Matter is fundamentally lazy:- It always takes the path of least effort
Matter is fundamentally stupid:- It tries every other path first.
That is the heart of physics - The rest is details.- Robert Shaw
.

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