On Fri, May 02, 2014 at 12:36:37AM -0400, Richard Aiken wrote:
> I'm currently re-reading H. Beam Piper's "Uller Uprising" and I'm
> curious: How accurate are the chemistry essays which form the book's
> introduction, which describe the rationale behind silicon-based
> alien life?

They're very brief, so it's hard to say what might have been used as a
foundation.

I noticed on reading (and confirmed on re-reading just now) that the
essay only talks about water being replaced in the circulatory system,
without talking at all about the all-pervading role of water within
the tissues.  We have about 6 times as much water outside the
circulatory system as within it, for example.  Water within our cells
is a fundamental part of our biochemistry and could not be replaced by
silicones without scrapping everything from amino acids upward and
starting over.

In short, I'm not sure I buy a gradual transition from carbon/water to
silicon/silicone life.  Life having originally evolved on such a
planet based on silicones would be perfectly fine.  The descendants of
complex organisms changing in fundamental biochemistry to the point
where they have nothing in common with its ancestors seems much less
likely.

The other part I take issue with is the assumption that a change in
solvent from water to silicones would make an organism essentially
immune to temperature changes.

The principle is much more fundamental: biochemistry is still
chemistry, a massively complex system of reactions.  Most reactions
are temperature dependent for fundamental physical reasons, and
variations in those reaction rates change the balance of the
biochemistry.  Reactions that dissipate less energy are generally more
prone to vary with temperature, so there's a trade-off involved
between biological efficiency and temperature sensitivity.  It's
certainly reasonable for one to win out over the other in an
evolutionary context, but a change of solvent alone won't suffice to
force the issue one way or the other.

So, overall: I find the outcomes described to be quite plausible, but
some of the stated reasoning behind them to be dubious.  Of course,
this should be taken in professional context.  The writer of that
piece was a professional chemist and literal rocket scientist, while I
am neither.

- Tim