[extropy-chat] Scientists Confront 'Weird Life' on Other Worlds

[Robert J. Bradbury]

On Fri, 14 May 2004, BillK wrote:

> <http://www.space.com/searchforlife/seti_carbon_040415.html>
> Silicon may be carbon’s chemical cousin, but it’s a poor relation.
> Because the silicon atom is larger, its bonds with other elements are
> weaker.

Not so fast there Bill -- though there has been some commentary that
some of the bonds are weaker not all of them are.  Extend the hypothesis
that "large atoms have weaker bonds" to metallic tungsten, or Titanium
Carbide or Tantalum carbide or Hafnium carbide -- each of which has extremely
high melting points (~2-3x higher than various forms of diamond -- in the
3000-4000K range...).

[Tungsten, titanium, tantalum and hafnium are all relatively large atoms...]

> While carbon hooks up with two oxygen atoms to make carbon
> dioxide, a nice waste product for both humans and SUV's, the silicon
> equivalent, silicon dioxide, quickly assembles itself into a crystalline
> lattice.

*So*??? CO2 assembles itself into a nice crystalline lattice for shipments
of biological products I want to send somewhere as well as for commercial
activities generally involving my ice cream truck salesperson.

> It's better known as sand, and would make exhaling a gritty experience.

Not in environments where the ambient temperature is above ~2504 deg K.
At that temperature SiO2 is a gas just like CO2 is at 195K at normal
atmospheric pressure.  This analysis is simplistic if larger molecules form
weaker bonds and yet the boil at higher temperatures...  The intermolecular
bonds are not broken when a compound converts from a solid to a liquid
to a gas -- yet the interaction capability after these transitions changes
things significantly.  [Hypothesis: perhaps the higher transition temperatures
of Silicon molecules to more highly interactive forms results in the destruction
of molecules that it would need to interact with to optimize the development
of "life".  Not an exclusive hypothesis mind you but one that may skew
the probabilities in a negative direction.]

> The weaker bonds of silicon also preclude the easy formation
> of those long, same-atom molecular chains that underlie many biological
> compounds.

Caca.  The DNA and RNA backbones are both poly-phosphate compounds (Voet & Voet,
"Biochemistry", pgs 792 & 860).  Only proteins and perhaps lipids can be considered
poly-carbon compounds and even then one gets into some questionable definition
issues based on what fraction of the molecules require poly-carbon based structures.
It is certainly true that the molecules in biology based on poly-phosphates
are much larger than those based on poly-carbons.

> A slew of complex carbon-based molecules are easily produced
> in comets, interstellar dust, and university glassware. But if you check
> out nature's chemistry lab for silicon (consider volcanic lava), the
> products are far less interesting.

Oh, but who knows what Nature's chemistry lab produces at temperatures
where silicon based compounds are liquids or gases?  Do we really know?

> Non-carbon based life-forms seem to be mainly sf speculation in order to
> make a good story. Possible life on the surface of a sun? Life which
> creates an atomic reactor inside it's body for energy? Yea, sure.

The surface of the sun has a temperature of between 5,500 and 6000 deg. C.
This is hot enough to break all hydrogen, ionic and covalent bonds (thus
destroying all molecules) and ionize all atoms (thus producing a plasma).
So speculation about life on the surface of the sun has to be based in
speculation on the feasibility of life in a plasma (which is far outside
our base of experience).  If one wants to use current experience one has
to base speculation on known experience (i.e. where molecules can form
and chemical reactions can occur and where molecular structures (e.g.
enzymes) might develop to speed reactions up or slow them down).  And
there is no "rule" that I'm aware of that says those criteria *MUST*
occur at liquid water temperatures.

Now with regard to a pseudo-nuclear reactor inside the a life-form's body,
this has already been discussed in Nanomedicine Volume I, section 6.3.7
with respect to using Gadolinium-148 to power nanorobots.  There have been
more recent ideas circulating for the powering of reactors using X-ray
bombardment, perhaps of hafnium-178 to generate energy (though there
is some controversy around these claims).

So -- present a case tnat non-carbon based life-forms are by default
more difficult than carbon based life-forms in a non-intelligence
impacted universe.  Then present a case that carbon based life-forms
are the dominant life-form in the universe given that the evidence
(Lineweaver & group) suggest that most of the Earth's in the Universe
are much older than ours suggesting that many have already gone through
the singularity.

Go on... I'm waiting...  And you might want to leave out the space.com
references since we can assume from the above THAT THEY HAVEN'T DONE
THEIR HOMEWORK...

:-; (somewhat strained...)
Robert