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Possible to mathematically demonstrate that evolution doesnt violate the 2nd law?

  1. Nov 21, 2005 #1
    I was wondering if it was possible, via biological thermodynamics, to demonstrate that evolution does not violate the 2nd law of thermodynamics in mathematical terms. From my understanding, the Earth is a closed system (this seemed odd, but I read this in a book on biological thermodynamics. I always figured the Earth was an open system.) I know it gets energy from the sun — is there a way to mathematically demonstrate that this energy is more than enough to account for the evolution occuring on the planet?
     
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  3. Nov 21, 2005 #2

    Bystander

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    Couple things you gotta do: 1) define "evolution;" 2) define the system you're going to analyze.

    For the first point, does "evolution" mean just a longer DNA molecule? Or, are you going to play with a more complex definition?

    The second point is going to depend on what your definition is for the first point; remember, you get to define the system. That means, you can include everything you need in a "closed system," and completely bypass the misstatements of the second law and the pointless jawboning that goes on over that point. Go ahead and shoot down the anti-evolutionary arguments in a closed system, and be done with it rather than fighting "yes, but" arguments.

    "Gotta" passes spellcheck?!?!?!
     
  4. Nov 21, 2005 #3
    I don't know about "evolution", but you might be able to prove that the presence of life does not violate the 2nd thermo law (albeit, in a back-of-the-envelope calculation sort of way):

    1) From the amount of light that reaches the earth from the Sun, calculate what the temperature of the earth should be. (Treat the Sun as a black-body radiator to simplify this calculation).

    2) Show that the actual temperature of the earth is much colder than this. If we ignore geophysical/weather phenomena, then we can make the approximation that the vast remainder of this energy is stored in life processes.

    3) Estimate the number of cells on earth.

    4) Calculate the amount of entropy per cell (using the energy difference calculated above).

    5) Using arguments based upon biological metabolism and efficiency, show that the actual entropy of a cell is not more than this.
     
    Last edited: Nov 21, 2005
  5. Nov 21, 2005 #4

    Moonbear

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    Um, biologists use the same laws of thermodynamics as everybody else does. I don't know where you read that there is something different, or that Earth is a closed system. Of course it isn't. If someone is trying to use that to discredit evolution, then it seems they're making up the data to suit their claims rather than using the actual evidence available, which doesn't suit their claims.
     
  6. Nov 22, 2005 #5

    Phobos

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    The creationist’s claim that evolution violates the 2nd law of thermo is based on their simplification/misrepresentation that evolution means increasing complexity in all cases and the 2nd law requires decreasing complexity in all cases. Neither assumption is accurate.
    Evolution is change…even into a less “complex” form (assuming you can define that well). And as noted, applying the second law requires correctly defining the “system” such that it is “closed”. Entropy within a closed system increases or stays the same.
    So basically, there’s no free lunch. The energy driving generations of life comes from ultimately, the sun (or in some cases, geothermal energy). I suppose you could go & try to show that the sum total of energy used by life is less than that released by the sun and earth or you could focus down on a single DNA mutation (evolution need not increase DNA length…it can just change components within the same DNA length) and show that the energy required for that change was input into the system and not created out of nothing from that system itself.
    Better yet, a scientific theory is falsifiable. You just need to show a case where evolution does violate the second law of thermo in order to cause a ripple effect throughout the rest of the theory. So far, no such examples have been found.
     
  7. Nov 23, 2005 #6

    Ouabache

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    A closed system, hmmmmm.. So besides the sun, we essentially ignore other inputs such as photons from other stars, extrasolar cosmic radiation, matter from bits of asteroids. Shall we forget that much of the matter in biological lifeforms orginated with elements made in stars far across as well as beyond our galaxy? (So much for a closed system) :biggrin:

    (Carl Sagan's poignant quote, "We are all made of star-stuff")
     
  8. Nov 23, 2005 #7

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    Demonstrate an "increase in order" (for the people who get their thermo from Roget's) accompanied by an increase in entropy for a closed system, and be done with the abuse of the second law. The open-closed system tangent to discussions of evolution is unnecessary, appears evasive to the lay audience, and just "leaves the door open" for the same, tired, argument to start all over again.
     
  9. Nov 23, 2005 #8

    selfAdjoint

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    The following argument is a statement in words of one that can be, and has been, made fully quantitative.

    The incoming solar photons are characteristic of the temperature of the photosphere of the sun, about 8000 degrees F, so they are of a high individual energy. But because the earth only intercepts a tiny fraction of the sun's rays, there are relatively few of them (relative to what? I'll get to that).

    The earth is warmed by these photons to its own characteristic temperaure (about 80 degrees F on the average) and radiates infra-red photons appropriate to that temperature into space.

    These two radiations, the incoming and outgoing, are in energy balance. If they weren't, the earth would have to heat up or cool down a bit till they were (that's thermodynamics).

    But because of the different compositions of the two, the makeup of that energy is different in each case:

    Sum of energy of a great many low energy photons = sum of energy of a few high energy photons.

    The incoming radiation, with its energy packed into fewer sources, is at lower entropy than the outgoing radiation wich uses many low energy sources, subject to random permutations and combinations.

    So the process by which the earth is heated to equilibrium by sunshine in and its own earth glow out is a powerfully entropy increasing one.

    Photosynthesis, which builds sugars out of sunshine, carbon dioxide and water, is an entropy increasing process, but it increases entropy slower than the background sunshine-earthglow process.

    All the rest of the life on the earth's surface (ocean depths are different) depends on the sugars produced by photosynthesis and uses them in entropy increasing processes which still don't match the rate of entropy increase of the background process. So relative to the background it exists in life seems to decrease entropy.
     
    Last edited: Nov 23, 2005
  10. Nov 23, 2005 #9

    Ouabache

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    Lots of excellent thoughts here, I've enjoyed reading them... :smile:
     
  11. Nov 24, 2005 #10
    I found the statement of a closed system strange as well. I believe the book defined a closed system as one that does not exchange matter with it's exterior. According to the book I checked out, a closed system can exchange heat energy (which would allow sunlight.) I did find this odd, seeing as, as was mentioned before, we get bits of matter from asteroids, meteorites, etc.

    The reason I was unable to use the 2nd law, is because — well, I'm not a master physicist (yet) and I only how it applies in terms of pressure and heat. I believe I've read different equations for biological systems.

    Don't worry — I'm not a Creationist :)

    Thank you for the responses!
     
  12. Nov 24, 2005 #11

    Moonbear

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    The author of that book seems to be making up a definition of a closed system to suit their purpose; you were right to be suspicious of it. By definition, any exchange of energy or matter with the exterior makes it an open system.
     
  13. Nov 26, 2005 #12
    energetically speaking, this doesn't account for much. the vast majority of energy that allows us all to live on this nice little rock comes from the sun. its like comparing a puddle to the pacific ocean.

    yes, but our own star-stuff, as in sun-stuff.
     
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