[extropy-chat] Singularity heat waste

[Martin Striz]

On 7/15/06, Eugen Leitl <eugen at leitl.org> wrote:
> On Sat, Jul 15, 2006 at 07:27:30AM -0400, Martin Striz wrote:
>
> > 1) Why do we use silicon for computation in most microprocessors, as
> > opposed to some other substrate?
>
> Silicon is a particular sweet spot (single-element
> semiconductor with a particular bandgap, easy to purify,
> forms solid oxides, plays well with other elements, etc)
> for a particular technology (photolithography, the only
> massively parallel processing technology apart from classical
> chemistry and biotechnology we currently command).
> In fact, we're already using some 20-odd other elements in a modern
> (CPU or memory) process. The next major advance will most likely
> use carbon (both as diamond and graphene), with minor additives
> (just as life does CHNOPS, and almost the entire PSE, in traces).

Is the heat generated due to internal resistance or information loss? :)

> > No.  It takes a goot bit of energy to reinstate the action potential.
> > It doesn't show up as heat though because chemical transformations are
> > efficient.  Silicon literally RELIES on internal resistance to do
> > computation, which produces waste energy by its nature.  What I'm
> > asking you is why we use that to do computation in the first place.
>
> It's an evolutionary fluke. Biology has been using gradients for a very
> long time, and with switchable ion channels you can make gradients
> collapse temporarily.

The larger point is that energy is well conserved in most chemical
transformations.  It just gets shuffled around from chemical bonds in
the reagents to chemical bonds in the products, hot potato style.
Only a small fraction of chemical transformations are significantly
endo/exothermic.  Neuron spike trains are a series of such
transformations:  the voltage changes across the plasma membrane, an
ion channel undergoes a conformational change in response, ions pass
through, phosphate gets removed from ATP and the energy released is
used to cause a conformational change in a pump which tosses Na+ and
K+ across the plasma membrane, etc.  Energy is conserved.

A semiconductor gets hot because it has a particular internal
resistance, so the energy associated with electrons passing through it
that can't go very fast gets dissipated as heat.  It's a physical
property of the system.  I don't understand what informaton loss has
to do with it.  Presumably we can use substrates without such
properties, we just happen to use semiconductors for the reasons you
elucidated.

> > waste heat, as I said. Your head is kept warm through fluid conduction
> > thanks to the vasculature.  The point is that there's a reason for
> > that: enzyme kinetics.  If you drop the system below ~34C, enzyme
> > rates slow down enough that the system goes kaput.  If you take it
> > above ~40C, enough enzymes start denaturing that that system also goes
> > kaput.  They are remarkably temperature sensitive (trust me, I have
> > loads of empirical evidence to back this up :), and that's why
> > thermoregulation matters so much to warm blooded species.
>
> Extremophiles manage to operate at 120 C or so, but they don't
> form complex tissues. There's no particular reason we operate
> at 37 C but that our normothermic homeostasis is adapted to
> a specific heat loss rate, which is a function of the environment
> temperature. If you cool too far down, the kinetics of chemical
> reactions plummets too far down to homeostate the system.

> > The question of why mammals have converged on 35-40C is an interesting
> > one.  I personally hypothesize that it has to do with fighting
> > pathogens, but one way or another, it's dictated by environment, not
>
> Possible, but I think it's a co-evolution drive for fast fight/flight
> reflexes. If you run too hot, however, you need more food for metabolism
> to maintain, and might starve.

The most efficient temperature at which to operate is ambient air
temperature, because it minimizes the effort that you have to make to
constantly fight heat gain/loss.  That range as a global average is
20-30C.  I hypothesize that the reason we operate 5-10C above that
(which introduces an energy cost through the homeostatic mechanism) is
because pathogens have also evolved for ambient temperatures and we
can fight them off by denaturing their proteins when we maintain
slightly elevated temperatures.  Unfortunately, many human (or
mammalian) pathogens have evolved optimal metabolic rates also at
35-40C in response.

Martin