[FoRK] Water != Life (other solvents may work too)

Eugen Leitl eugen at leitl.org
Mon Jan 31 10:40:22 PST 2005


On Mon, Jan 31, 2005 at 12:39:40PM -0500, damien morton wrote:

> >Are we talking naturally emerged, or designed? Designed indeed doesn't
> >require chemistry, see ALife.
> 
> Greg Egan wrote a lovely short story about an emergent 'ALife' that 

"Wang's Carpets", a short story, later integrated into "Diaspora".

> existed 'inside' a substrate formed by the plants on an ocean planet,

Not plants. Floating sheets of natural polysaccharide polymer.
 
> whose movement and grouping behavior was individually simple, but as a 
> whole formed a computing substrate capable of supporting ALife.

Yes. Egan has no clue about sugar chemistry, reaction rates, the size of
"universe" these floating objects would have spanned. Or he speculates none
of his readers do, so he can play loose with his science.

In comparison to that world, hydrocarbon lakes, methane/water volcanism,
photosmog and organic polymer precipitates, washed by a rain of liquid
methane and ethane are completely trivial.

If you were bound to cite "There are more...", I proactively have to remind
you that nucleosyntheses and preplanetary nebula accretion are pretty well
understood.
 
> Fanciful, perhaps, but I have a feeling that the definition of life will 
>  eventually have to be stretched to include such.

Once again, I absolutely have no trouble with ALife, in designed settings.
However, given our current knowledge of this spacetime, Wang's Carpets and
variations upon natural-physical-structure-simulated-a-virtual-universe
need not apply.
 
> >>In my mind, all thats needed is a substrate that supports enogh 
> >>compelxity.
> >
> >For natural processes, we seem to be stuck to condensed phase.
> >Gas and plasma doesn't support persistent structures. There might be life
> >based on strange/dark matter, but we currently have no evidence that's
> >possible.
> 
> Thats not true. Gas certainly supports persistent structures, for 

Persistant enough to encode its own structure and fork off related
structures.

> example, clouds. cf 100-year old storms on the face of jupiter. As to 
> whether gas supports structures capable of life, I dont know, but it 
> likely depends on what you define as life.

I define life loosely enough (most biologists would laugh derisively) to
include any evolutionary structure (iterative replication with errors in a
limited-resource-context).

How do you define life? 
 
> Assuming, that life depends on chemistry.

Life emerged within this spacetime must depend on chemistry, according to
our current knowledge. 

There's no point to speculate upon something for which there is absolutely no
evidence. (Unless you want to sell science fiction, of course).
 
> >>Greg Egan is the sci-fi writer who explores this best (IMO).
> >
> >Greg Egan's physics is frequently b0rken.
> 
> Your spelling appears to be brok3d.

That's on purpose. Egan's physics is better than most, but it's still jarring
enough to provide these disillusionment moments (which make most of Hollywood SF
flix unwatchable). Vinge (another of my favourites) has this, too.

-- 
Eugen* Leitl <a href="http://leitl.org">leitl</a>
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