Tim Tyler  wrote in
news:cfh516$13j6$1{at}darwin.ediacara.org: 

> William Morse  wrote or quoted:

>> I think the definition of life has to encompass the use of fuel, but
>> it should be something like "the ability to maintain a structure
>> against an energy gradient by using an available energy source."
 
> Practically any self-organising system does that.
> 
> Look at a whirlpool - for example.

I disagree. Self-organising systems all maintain a structure by using an 
available energy source, but I do not think that all that many can 
maintain the structure against an energy gradient, at least for any 
significant length of time. 

 
>> This gets around the crystal question because their structure is the 
>> lowest energy solution, not a structure maintained against a
>> gradient. 
 
> Don't get me going on the crystal subject.  Crystals can be
> *extremely* complex.  One of the main reasons is that they are *not*
> normally at the lowest energy level for such a structure.
 
> Their energy is usually at a local minima - not a global one.
 
> The imperfections are manifested as fault structures within the
> crystal. These are ubiquitous.  The faster crystals grow, the more
> faults and dislocations they exhibit.
 
> Out of all the natural but non-biological self-organising systems I am
> aware of, I classify crystals as the most life life.  Indeed, there's
> a whole theory of the origin of life that says that life came from
> clay crystals.
 
> One of my web pages on the subject:
> http://originoflife.net/cairns_smith/ 

OK, I may have to retract my statement, at least with regard to some 
crystal structures.
 
>> Flames utilize an energy source but do not maintain a structure.
 
> Unless they are at the top of a candle ;-)

And not in the presence of an energy gradient such as a puff of wind ;-)

>> Tornados might qualify as alive under this definition - I don't
>> really know whether their structure is a lowest energy solution but I
>> suspect it is not.
> 
> The "lowest possible energy" wasn't part of your definition of life
> anyway. 

This was implied by maintaining structure against an energy gradient. 
 
> Tornadoes and whirlpools *do* seem to qualify under your definition -
> as do fractal drainage systems, waterfalls, sand dunes - and all
> manner of other things.
 
> However, I reckon most people would agree that such things are not
> alive. 
> 
>> The definition could be qualified further by requiring the use of
>> electron transport for energy - I hesitate to do this because it
>> might eliminate non-earth life that should still qualify. But perhaps
>> electron transport is in fact a requirement for any true life?
 
> Definitions of life should not make any mention of electron transport
> - IMHO.

Actually you might be happier with a definition that included electron 
transport. It would exclude tornados and whirlpools but would include 
complex crystals. And electron transport is still a general enough 
quality that it would not exclude things such as robots or non-carbon 
based life. Hmmm...


Yours,

Bill Morse
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