Is life an extremely rare thing in the universe?

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No you are completely incorrect. If you subject hydrogen to sufficient pressure that it would solidify, that would press the hydrogen atoms closer together, but it would not make the atoms smaller. As the pressure increases the end result is not a smaller hydrogen atoms, it is hydrogen fusion, creating helium.



How many different ways do I have to say this: the binding energy never changes, regardless of the environmental temperature. The nature of a C-H bone or a Si-H bond is exactly the same in every environment in which the bonds can be created. Carbon will always be a more efficient bond for free hydrogen than silicon--nothing in an environment with change that, other than the absence of carbon.

In a low temperature environment you certainly won't get complex hydrocarbons. But you will have methane. Available carbon will lock away hydrogen four atoms at a time, and in a low temperature state, the methane will be virtually indestructible--certainly silicon won't be able to dislodge it. The only way for silanes and more complex hydrosilicons to be created is for carbon to be absent--or present in insufficient quantity to capture the available hydrogen.



Which does not change the fact that there is nothing else that we have observed in nature that behaves the same way.



Fine, describe for me a Pressure/Temperature environment in which hydrocarbons cannot form, but hydrosilicons can? Describe for me any combination of temperature and pressure in which silicon becomes more effective at capturing free hydrogen than carbon.

The simple fact is, you can't. Because silicon will always be a bigger atom than carbon--always. And that means that C-H bonds will always be stronger than Si-H ones. Always. Methane will be stable at a much wider range of temperatures and pressures than silane--always. Whatever variations of pressure and temperature will do to carbon, they will do sooner to silicon.

Once you get environments that are so hot, and so dense as to permit iron precipitation, then no complex molecules of any type will be able to be sustained, because the energy in the environment will be ripping them apart as soon as they are made. Going to the other extreme, in cold and low pressure environments, complex molecules will not be able to be created because the environment will lack the energy to create them in the first place.

Let's understand, we are talking about life: an ordered system that is capable of capturing and storing energy from the environment, and releasing that energy in a controlled fashion to perpetuate, expand or reproduce the system. This is an incredibly difficult set of circumstances to create, and both high energy and low energy environments are likely to be completely inimical to their creation.

I am looking at the big picture. I am looking at the fundamental nature of the building blocks of matter.

But the individual atoms don't change.

When hydrogen atoms are finally force very close together and the strong force becomes operative they fuse and become helium with a loss of mass and and production of energy.

ruveyn

http://en.wikipedia.org/wiki/Metallic_hydrogen

http://en.wikipedia.org/wiki/High_pressure



fragile molecules brake because of thermal oscillation(assuming no reactans). If its cold enough, a molecule can be deemed stable.



I'm saying its observation bias.



This is not just about Si.

C/H2O is observation bias, because we use that. I think you underestimate the potential of alternate chemistries in hugely different conditions. We barely tried to studied other biochemistries. With all that oil, and watter, its the cheapest stuff to make stuff with, that we have.

My understanding for life is to be able to build a long molecule that is stable enough. It will fold on it self in some complicated way, and will have some kind of useful effect. With just that, you can in theory build a working cell. Just a long molecule, its not that improbable.

While boron-hydrogen compounds(boranes)are far more unstable(in an oxidizing atmosphere) than hydrocarbons due to the hydride bridge( -H-), if you substitute the hydride with an amide or an oxy bridge(-O-) the result is a far more stable molecule that behaves chemically very much like a hydrocarbon. Boron based life, if it does exist, would require a planet much colder than Earth as covalently bonded boron molecules are far more stable; especially in an ammonia.

A definition change because in the 1990's, well respected scientists doubted the existence of Eris and coutnless other small objects rivaling pluto in size.

Your comment was a bit too cryptic. You meant that they would have redefined it earlier. (not every one knows the definition of a dwarf planet)

Neither of these articles suggest that hydrogen atoms change their size under pressure.

All elements undergo phase transitions. At their melting points they transition from solid to liquid; at their boiling points they transition from liquid to gas. All that "metallic hydrogen" means is that when hydrogen is sufficiently frozen and compressed, its electrons will be torn away from their protons.

But once we enter that kind of environment, what is the potential for any kind of biochemistry? How are molecules supposed to stay in one piece when hydrogen atoms can't hold on to their electrons?



But not if it hasn't been created in the first place. Biochemical reactions are reactions that capture and release energy. If it's too cold, then none of these complex molecules can get created in the first place.



Which is why I have been careful never to say that what you propose is impossible. Merely extremely improbable.



We haven't studied other biochemistries because as far as we know, they don't exist, and we haven't yet conceived of an environmental system in which they are likely to exist.

"Just a long molecule?" That's incredibly improbably. Even in ideal circumstances its improbable. And for life you have to get those long molecules to create themselves over and over again.

So again, I say, possible--but extremely improbable.



This is more interesting, but it is challenged by the fact that boron was not produced by the big bang and is not a product of stellar fusion. Of all of the elements lighter than iron boron is the second rarest, after Beryllium. To support boron biochemistry, an environment would have to have abundant free boron, and that would mean that it would necessarilly have to be heavily bombarded with cosmic rays, since that is the only mechanism for the creation of boron. If complex amide-boron or oxy-boron molecules were to be created, the cosmic rays that created the boron in the first place would have to have diminished.

While the chemistry is attractive enough, I see the environmental needs as particularly challenging because of the rarity of the base element.