Posted by
Rob on Tuesday, May 05, 2009 3:51:44 PM
A response to Roddy Bullock's post:
Life: (More Than) Some Assembly Required
When I took college physics in the 70's from Howard Claussen, who
co-invented Teflon (and we whispered in the halls, deserved the Nobel
prize), he used to ask us "what is the entropy difference between a live
cow and a dead cow?"
None of us knew how to answer that question. Nor did any of my graduate
school profs. The problem is that physics did not have a very good
handle on the entropy of anything, much less the entropy of life. Oh
sure, we could calculate the entropy of mono-atomic ideal gases, but
even diatomic gasses became a challenge, much less a living organism.
Reductionism, as any biologist will tell you, is the sin of physicists.
So when you asked about cats, I couldn't help but think of my esteemed
professor's question. In the 30 years since, I think I have the
beginning of an answer.
Entropy, as the textbook would say, is proportional to the logarithm of
the number of states of the system: S=k ln Ω. "The system" being
the 6-dimensional phase space for (mono-atomic gas) particles
f(x,y,z,vx,vy,vz). But then it is illustrated with marbles in a shoebox,
and we are led to believe that only (x,y,z) are important. If instead we
try keep track of (vx,vy,vz) of the particles, we end up with a LOT more
states because each particle can be going in just about any direction!
Just for fun I argue, lets take the Fourier transform of phase space, F,
and note that here the position "disappears" but the velocity comes into
focus. Then a good approximation to the total entropy of the
(mono-atomic ideal gas) is
S_total = S(f(x,y,z)) + S(F(vx,vy,vz)).
I like to think of it as the sum of space-entropy and time-entropy.
The consequences for cats and cows, is that the elements of the dead cat
are all in the same places as the live one, but the velocities are all
different. That is, when a cat is alive, everything in it is in motion,
the blood through the heart, the electricity through the brain, the ATP
through the cells; but when it is dead, everything stops.
The consequences for scientists who want to make "life from scratch", is
that they not only have to get all the right ingredients together, but
they have to get all the motion too. Getting Frankenstein's monster to
sit up takes more than electricity, but a heart-lung machine, a
alpha-wave machine, (cellular bots?) etc.
If they think that "just add water" is proof of artificial life, then
bacterial spores have been continuous proof of spontaneous generation
for 200 years despite Pasteur's miserable failure to convince us
otherwise. Which perhaps is the only good thing to come out of this
hopeless religiously-driven research: that perhaps we can understand how
bacterial spores can go into suspended animation, seemingly without
time-entropy, and yet come to life with water.