'We can't imagine life without water'-but can YOU?

Well, like I said I think carbon is the only suitable basis of life. Silicon is a far, far second. Si-Si bonds are very difficult to make, and Si=Si double bonds are even more difficult. The likelihood of catalytic silicon-based macromolecules developing spontaneously would be far lower than for carbon. Even in a highly exotic environment. Further reasons for the necessity of carbon (and water) are given in the first few pages of Voet and Voet’s Biochemistry. (This means I don’t feel like looking for it, but I’ll quote some if anyone really wants it.) Silicon-based life might be possible, but I don’t think it could be adequately hypothesized with our (read: my) current understanding of Si chemistry. Maybe in the future we’ll discover that silicon can do things we don’t now know it can do.

If C is vastly better than Si, then Si is even more vastly than the next-best alternative. I honestly can’t see chalcogens, pnictogens or halogens forming the basis of life. They simply cannot concatenate to the degree necessary to form catalysts. I suppose it might be vaguely possible to use a different catalytic paradigm for life that would emphasize inorganic catalysis – this would take some of the emphasis off carbon, but it would be much less likely to arise spontaneously and would lack much of the specificity of organic catalysts.

**Solvents:**I can see how sulfur dioxide could be a decent solvent. I disagree with ammonia because of its reactivity. In the real world, ammonia-water oceans would be suitable for life, as has been mentioned, but the OP excludes that.

I hadn’t thought of liquid CO, but that’s very intriguing. Unfortunately I can’t find a phase diagram, so I don’t know what conditions would be required. But CO is an excellent feedstock for organic synthesis. CO oceans – especially ones with abundant dissolved metals – would give rise to all kinds of organic compounds. The compounds would be different than terrestrial biological molecules, but they could easily be catalytic. Assuming the right atmospheric conditions, any organisms that happened to evolve would likely be able to sustain themselves by oxidizing CO to CO[sub]2[/sub].

The only problem is that these organisms would be constantly surrounded by a fairly reactive substance. Keeping CO out would be a priority, and they would have to find a way to protect themselves against it. One idea: with all that CO around, perhaps they could use polymers instead of lipid membranes. A polyalkane or polyketone ‘shell’ could be used to keep out CO and sustain an internal environment of some other solvent.

It’s not inconceivable that that solvent could be water. If there were hydrogen in the atmosphere, molecular hydrogen rather than water could be used as the hydrogen and proton source. And it’s possible that some water could be produced as the byproduct of CO-based organic synthesis. This water could be used inside the organisms as a less reactive solvent – and then a very different biochemistry would begin to appear. I don’t think it violates the OP to introduce water after the beginning of life. Remember, most of the oxygen in the Earth’s atmosphere is the result of life, so it’s not inconceivable that an initially waterless planet could have water in abundance after a couple billion years of life.

A highly unusual property of water is it can dissolve both organic and inorganic materials, plus it has a very high specific heat, and that it actually conducts electricity with impurities added.

So water is not as simple as a solvent, though that is a very important role.

Well, if we must try to imagine life without water and carbon based organics, the we are looking at different kinds of self perpetuating complexity; this complexity also has to be self-replicating, with a capacity for storing information…
I have tried to imagine high energy life-like complexities, for instance in high temperature plasmas- the trouble is a high temperature seems to defeat the object of storing information, as high temperature conditions are generally chaotic.
Some geological events are quite complex, especially during the crystalisation phase; perhaps a low order life-like self-perpetuating complexity could emrge in certain exotic lavas out there in the universe somewhere;
(as I have depicted in this piece of fiction, without giving any real coherent details of course)
but I don’t really expect that such life-like lava really exists, or if it does, it wil be short-lived and restricted to a narrow range of temperatures and chemistries,
while organic life can adapt to its environment and even modify it.

One thing to consider are the relative frequencies of different elements in the universe, and on planets. If we look at volatile compounds, hydrogen is the most common, followed by helium, then a grab bag of carbon, nitrogen and oxygen, and then everything else.

So we can imagine that the most common compounds in the universe would be water, methane, and ammonia. But how common would liquid helium be? Sure there’s lots of helium, but most of it is in stars. How much helium could there be in the Kuiper belt, and would conditions there permit liquid helium? Since we don’t know much about liquid helium, we can imagine all sorts of interesting properties for life in a helium solvent without being too constrained by awkward facts.

Or do we already know too much? Any experts on liquid helium physics want to weigh in?

I can’t imagine liquid helium being a solvent, as helium is the most insert element there is.

I can’t imagine liquid helium being a solvent, as helium is the most insert element there is.

Yes, helium is chemically unreactive. But that doesn’t mean it can’t act as a solvent, does it? Sure, the helium itself wouldn’t be part of the chemistry of helium organisms, but perhaps there could be interesting superfluid properties of helium. Would any normal carbon organic chemistry be possible at liquid helium tempertures?

how about life in the form of magnetic configurations in a star. its obvious to everyone that magnetic feilds can be used to store information, they also can be used to effect eachother and so interact and arrange themselfs.

of course this is unlikely to form life, but there are MANY stars out there and they are VERY big and VERY long lived.