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Are the starting conditions for life truly random?

Post of the Month: October 2007


Subject:    | Origins and Mental Activity
Date:       | 29 Oct 2007
Message-ID: |

Zoe said:

> I would like to work with the current understanding of the Big Bang
> activity before continuing to chew on the laws of intelligence.

> Taking it for granted that there is no certain answer as to how the
> elements formed after the big bang -- except maybe helium and hydrogen
> -- but that they most assuredly made their appearance eventually (maybe
> from supernovas), I would like to work from that point on.

> Okay, so here we have some basic elements distributed randomly
> throughout the universe, and in great quantity. Space would look
> something like this, multiplied many many times over, I guess?

Robert Grumbine replies:

As explained many times, but repetition seems needed, no.

He begins by running time's clock backward to explain how we got here:

Let us start from the other way around. We observe that the universe is expanding -- all points are separating from all other points. We can then ask what happens if we look backwards in time -- our expectation is, first, that points would be getting closer together. From elementary physics, we know that if you stuff things (gases in particular, and they are most of the observable matter in the universe) closer together, they heat up. We can take this elementary bit of physics back to a point where the temperature of the universe would be, instead of the current 3 K, about 3000 K. At such temperatures (a bit cooler than the sun's observable 'surface') hydrogen is fully ionized and opaque to radiation (at least if densities are high enough, which they are for the early universe).

We can continue running the universe back in time, if using less obvious physics. We continue to compress the universe and its gas (whatever it may be) until it reaches stellar core densities and temperatures. At that point (we're approaching from the cold side, remember, the modern side) fusion of hydrogen to helium is efficient. As we pass this point (going away from the present), the cores get hotter and denser -- so hot and dense that heavy elements, like oxygen and carbon -- are knocked apart in the collisions at least as fast as they're assembled by fusion processes. Much before that and there aren't nuclear particles to worry about. In any case, the outcome of this stellar core stage in the universe's history is that it erases anything larger that might have been formed in the earlier history and leaves us with only a (computable, and observed) distribution of hydrogen, helium, and a trace of lithium.

Then he takes a look at how things are evolving now:

All elements heavier than that (perhaps a nod need be taken for vanishing quantities of beryllium) are distinctly _not_ uniformly distributed through the universe. They are all produced from stellar cores and distributed by novae and supernovae. Neither the location of stars nor distribution of such eruptions is random in space. Stars, for instance, are far more common inside galaxies than outside, and galaxies are far from uniformly distributed. Further, galaxies themselves evolve. New stars (such as our sun) are formed from the ashes of old stars. This happens with greater frequency where there are more (and larger -- so as to produce supernovae) stars. So much more frequent towards cores of galaxies, or the arms of spiral galaxies.

Now wait a while after the bang for some heavy elements, like oxygen, carbon, etc. to get formed and blasted into the interstellar medium of a galaxy of interest. The overwhelming majority of atoms are _still_ hydrogen and helium. The novae and supernovae lend only a trace (by mass, even smaller by number) of heavy elements to the clouds.

Let's jump ahead and consider a real cloud. (This is several steps ahead of where you are.) Real clouds (I'm selecting, by the way, the ones most relevant) are cold, relatively dark due to shielding by dust grains and ice particles, and still essentially vacuum density. Certainly a better grade vacuum than we generate here on earth in labs. Cold means 10-100 K, which we can match in the lab.

What kinds of things happen inside this cloud? Well, the hydrogen was long since largely locked up in H2 molecules (as the cloud cooled). But let's ignore that and consider (reality notwithstanding) all atoms to be solo. Consider a billion atomic mass units at a time (c.f. 93% are hydrogen atoms, with most of the rest being Helium. As I said, only a trace of other things are tossed into the mix. So mostly what goes on in our atomic cloud is that hydrogen atoms bounce into hydrogen atoms. If they're moving fast enough, they 'stick' and become an H2 molecule. If they're moving too fast, they bounce off each other (possibly ionizing one of them). And if they're moving too slowly, they, again, just bounce off each other. If they (or anything else) bounce into a helium, they bounce off. Ditto heliums meeting heliums.

The 'fast enough' qualifier means you have to study chemistry if you want to understand what's going on in any more detail. The topic involved is reaction kinetics and/or thermodynamics.

Among those trace of heavy elements, the same rules apply. If they collide with something which it is chemically permissible to combine (an O and and H) then they combine with a probability related to the conditions (pressure, relative velocity, possible electronic excited state in a participant) of the collision. This also applies to collisions between the H2 molecules and the still-bare (in our conceptualization) heavy atoms. In an astrophysically short time, the H atoms combine to H2 molecules.

Heavy elements molecules build up more slowly. Particles build up when/where it's easy to simply stack yet another molecule on to a structure -- as for H2O or CO2 ice, which are fairly happy under astrophysical conditions to glom on to each other. Once there's a shield of these, reactions can occur untrammeled inside the cloud. Low temperatures follow, which slows things down, but this is balanced by the increased density, and there being no photo-disruption of the molecules by outside stellar light.

As mentioned earlier, quite an array of molecules have been found in space, particularly the Great Nebula in Orion (relatively close and easy to observe).

None of this is instantaneous, none of it is an 'absolutely only one thing can possibly happen', notwithstanding your malicious misreading of people to that effect. Kinetics is statistical. Certain outcomes are more likely, and occur at rates depending on their conditions. Change the conditions, and different things are more likely. Given a universe of clouds to run reactions in, quite a few things are liable to happen.

More, perhaps, to the point, is that the gas cloud has limited relevance to concerns of forming terrestrial life. We don't live in giant molecular gas clouds. We live on a planet, whose formation involved a different seriously non-random process [1] -- forming a locale in the universe where astrophysically very minor elements, like silicon, oxygen, carbon, iron, etc., were made vastly more common than hydrogen and helium. Further, to form a locale wherein gas was not the dominant phase of matter, instead setting up a three phase system where gas, liquid, and solids could interact physically and chemically.

  1. Solar system formation, that is. Gravity, thermodynamics, and chemistry suffice, however, to construct earthlike planets. (And the more common non-earthlike, of course.)

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