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Thread: Problems with classical thermodynamics

  1. #1 Problems with classical thermodynamics 
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    Jul 2008
    I was recently interested by some news that it's possible to drain energy from pure heat - absorb infrared thermal radiation:
    Other problem is for example that while spontaneous crystallization entropy goes in 'forbidden' direction:

    It would be nice to localize simplifications of looking to be such general theory like thermodynamics.
    One way of their reasons can be simplifying physics for thermodynamical model, like
    - it corresponds to molecules, while we can say that their electrons live in completely different world - on a scaffolding made of molecules. Their energies doesn't correspond straightforwardly,
    - thermodynamics usually ignores thermal radiation and it's energy.

    But maybe there are deeper problems - thermodynamics usually ignores internal structure - for example from two states of the same energy one can be easier accesable...

    What do You think about it?

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  3. #2  
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    Jul 2008
    Here is simple counter example to 2nd law of thermodynamics -
    converting heat into work.
    Everything is in vacuum, without gravity:

    Take a tube with interior covered with mirror.
    Fix two transparent separators inside and place hot gas between them.
    Now place two mirrors on both sides, which can freely move inside the

    Some of thermal infrared photons will be bounced by a mirror - giving
    part of own momentum, thanks of momentum conservation law.
    The heat of the gas will be slowly converted into momentum of mirrors,
    which can be converted into work.

    Above example uses that despite that kinetic energy of molecules
    behave randomly, each one has specific movement/oscillation, which
    energy can be changed into ordered one - electromagnetic oscillation
    of photon.
    Thermodynamics of photons is very 'simplified' - they practically don't interact
    with each other, so they don't equilibrate their energies, increase
    their randomness. They also vanish when their energy goes to 0.

    Are there some problems with this counter example?
    The real question is if it can be used in practice - there are made
    nanoantennas to catch thermal infrared:
    Can it be changed into electricity without difference of
    The problem is with diodes which looks like Maxwell's demons...


    If You don't like idealized unpractical models, there are also two
    very practical: one for us and one for organisms which lives hundreds
    of meters below and have extremely weak access to chemical energy, but
    they have plenty of energy around in heat (and tectonic

    Both of them uses microscopic mechanisms. Usually released microscopic
    energy quickly escape and change into heat. We can use that sometimes
    these releases are spatially localized, so local 'mechanisms' can help
    to put this energy into more stable form like potential energy of
    electron in a circuit or chemical energy of some molecule (like ATP).

    The first example uses that thermal infrared can not only be emitted/
    absorbed by single molecules, usually using their vibrational/
    rotational energy, but also for example by a free electron in a circuit
    - by nanoantenna. The energy of this electron when it absorbs photon is
    relatively huge - it's highly improbable that it gain this energy thanks
    of thermal energy only and emit a photon - absorption will dominate
    here. The problem is to rectify this electricity, but we can use that it
    is highly localized. This electron will naturally equilibrate its energy
    with environment, but this process is relatively slow, require some
    length of way through circuit. So the nearer electron is to the antenna,
    the higher average energy it statistically have.

    The whole electricity generator could look like (parallel):
    -conductor-threshold-antenna-conductor-threshold- and electrons should
    more likely go left, because after absorbing a photon, they equilibrate
    their energy while going through conductor. If the antennas are printed
    as in the work of prof. Novack I've linked, required threshold could be
    just narrowing/ gap.

    Before going to the second example, let's think about crystallization.
    It obviously increases ordering (reduce entropy), but total entropy
    doesn't decrease because the binding energy (difference between energy
    of the molecule in solution (larger) and after binding (smaller) ) is
    stored in unstable form of energy (kinetic/vibration/rotation energy)
    that quickly equilibrate its energy with environment, increasing heat/
    entropy. But what if this binding energy would be stored in stable form,
    like chemical energy (ATP)/conformation ? Such energy stored in ATP can
    be used in order way to create work (for example using myosin). Remember
    that joining to growing 'crystal' is localized reaction - could use help
    of an enzyme as catalyst, which additionally stores part of binding
    energy in stable form like in ATP.

    The second example uses just two molecules instead of whole crystal.

    Let say that we have two molecules(A,B) which has larger total energy
    separated(E1) than when they are bind (E2<E1). Additionally there is
    energy barrier between these states (as usual).

    Now when they are bind in solution, their thermal energy statistically
    sometimes exceed the barrier and they split, taking require energy from
    heat -reducing temperature! But to bind them back, they not only have to
    reach the barrier, but they have also to find each other in the solution
    - it's not very likely, so statistically concentration of AB is
    relatively small comparing to concentration of separated molecules.

    Now we will need a catalyst which reduce the barrier, but then use the
    energy difference for example to bind ADP and phosphate. For example it
    catches all required molecules and uses just gained energy or energy
    stored in own structure to take A and B closer, to make them reach the
    top of the barrier, then use energy they produce to bind ADP + P and
    restore own energy.

    I know - this enzyme would work in both directions, but concentration of
    AB should be relatively small, it doesn't have to use whole binding
    energy, such that the wanted direction should dominate. Organisms can
    enforce required optimal concentrations.

    Returning to thermodynamics - it's derived averaging local behaviors.
    It's kind of mean field approximation - forgets about correlations ...
    which can give very different behaviors/interactions ... like different
    stability of stored energy. I agree that it can pass simplified models
    or tests like Maxwell's demon, but it's far from being proved to be
    universal property.

    Remember that 2nd law is not required to forbid machine which creates
    work for infinity, conservation of energy/momentum already forbids it.
    2nd law forbids only ordering energy stored in chaotic thermal movement.
    But if this law isn't always true, there would be other counter
    intuitive implications, like that computation could need no energy...
    But remember that quantum computation would theoretically also offer it
    - computation is invertible - doesn't use energy. Energy is required
    only to read result.


    I completely agree that we usually don't observe entropy reductions, but maybe it's because such reductions has usually extremely low efficiency, so they are usually just imperceptible, shadowed by general entropy increase... ?

    2nd law is statistical mathematical property of model with assumed physics.
    But it was proven for extremely simplified models!
    And still for such simplified models was used approximation - while introducing functions like pressure, temperature we automatically forget about microscopic correlations - it's mean field approximation.
    Maybe these ignored small scale interactions could be use to reduce entropy...
    For example thermodynamics assumes that energy quickly equilibrate with environment ... but we have eg.ATP, which stores own energy in much more stable form then surrounding molecules, be converted into work...

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