From: Martin Striz (mstriz@gmail.com)
Date: Thu Aug 25 2005 - 12:16:42 MDT
On 8/25/05, Phil Goetz <philgoetz@yahoo.com> wrote:
> Mikko Särelä <msarela@cc.hut.fi> wrote:
> > You're assuming that the human brain is operating at more than 1%
> > of its theoretical computational power here (and I'd be interested to see
> > how you plan to calculate or prove that).
>
> Evolution doesn't construct machines that operate at < 1% of the
> efficiency possible with the given materials. Photosynthesis is
> about 12% efficient, comparable to solar cells, which are made
> out of human-selected materials rather than proteins.
> Fat is more efficient than our best power storage cells.
> Birds are probably much more efficient flyers than airplanes?
> Bicycles enable a human to be more efficient than walking
> animals, but only on roads. (There is a case to be made that
> a wheel could not evolve, except at microscopic sizes.)
There are two possible metrics by which you can judge efficiency, and
it seems you folks are confusing the two. You can judge the
efficiency of a system either 1) by measuring how much output you get
from a given input, or 2) measuring the rate at which the system is
operating versus its maximum possible/theoretical rate.
Take a car as an example. There's a certain miles-per-gallon
efficiency that your car has. If you use the most expensive gasoline,
change the oil regularly, and drive properly (without accelerating or
breaking too fast, or driving too fast), you'll probably get close to
100% efficiency out of that car (close to the advertised miles/ga).
If you neglect the car, don't change the oil or give it necessary
repairs, and drive erratically, you'll get far less efficiency.
That's one metric. However, the amount of output (let's say as
mechanical energy) given the input (as chemical energy) is far worse.
That's a different metric.
When you say that photosynthesis operates at 12% efficiency, you're
simply comparing the output versus the input, say in Joules. But
given the nature of the system -- conjugated molecules absorbing
radiant energy, proteins catalyzing energy tranfers, etc. -- evolution
has probably maximized the efficiency that's possible by this method
(and by this standard, photosynthesis operates at close to 100%
efficiency).
So when you say that the brain operates at <1% efficiency, you should
mean according to what's theoretically possible (all information
currently available in the environment as input vs any theoretically
possible computational output), but I think you mean according to
*what's possible with neurons.* Except that, what's possible with 1)
plama membrane-bound cells that 2) send actions potentials and 3) rely
on enzyme reaction rates, is a lot different than what's possible with
65 nm silicon wires or 10 nm carbon nanotubes. Evolution has come
close to maximizing what's computationally possible with neural
wetware (given a particular synaptic organization). Our brains are
functioning at close to 100% efficiency for what they are designed to
do.
Martin Striz
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