Thanks for your comments on my post, JB and Daniel. I see clearly the point you mention (one cannot apply the 2nd law to open systems such as living beings or the earth), but I keep on wondering what kind of system is the universe itself...In all our thermodynamical calculations, the universe is always considered as an isolated system, and that’s the reason why it is expected to end as a thermal soup, isn’t it? One of my questions is if it is possible to have ¿spontaneous? forces (and flows) in an isolated system... I would like to know an example of spontaneous macroscopic forces and flows in an isolated system. If there are no exchanges with the surroundings, where comes the energy from to drive changes? In other words, if the only natural state for an isolated system is that of maximal entropy, why the universe has not remained as an entropy soup from the very beginning?. It is difficult to imagine an isolated system that evolves to anything more organized...unless it starts to exchange heat, work, any kind of energy with the surroundings and hence, it is not isolated any more. The point is that isolated systems do not get organized with time, but become more and more “disordered“– or more exactly, evolve to states of maximum probability and multiplicity, the macrostates with the higher number of microstates or configurations available, is that right? Apparently the universe has not evolved in that sense: the old universe the infrarred techniques can detect seems a lot more homogeneous, disordered and probable that the one we can see today....Where’s the increasing entropy to satisfy the 2nd law? Another point is that to have organization one must be far from equilibrium, and one cannot maintain this state in an isolated system. Perhaps there is a lot of entropy in black holes, or other universes and big bangs as some hypothesis suggest...who knows. Anyway, if “The End” of all this is a boring thermal soup – or a big crunch...- it is even more amazing what thermodynamical laws heve been able to create in the middle...
I would like also to comment the integrins paper, and to ask about the phenomenon of entropy-enthalpy compensation that is mentioned by the authors. Years ago I read a paper that suggested the possibilty that the surprisingly good correlation that exists between entropy and enthalpy increase in some processes ( a plot of ∆S versus ∆H can give almost a straight line with a slope dependent on T, I think) could be a sign that we were measuring or observing the same physical variable from two different points of view..(I suppose, something like the particle-wave duality?). Anyone knows an explanation for this phenomenon, or is it just an artifact?
2 comments:
if it is possible to have ¿spontaneous? forces (and flows) in an isolated system...
yes, in an isolated system that is not at equilibrium. This is what we saw in the class, that flows can arise from differences in the system and can be related to a fundamental forces. For example, energy flux induced by a temperature gradient, mass flux induced by a density gradient, current (flux of electron) induced by a temperature gradient in a metal, etc.
The universe seems to be in a far-from-equilibrium state, as we can see in the stars constant nuclear reactions and fluxes of energy are going on. The density of particules, for example, is far from being homogenous. Thus, the apparent organization of the universe is not in contradiction with thermodynamics. As it has been said, there is a constant entropy production.
why the universe has not remained as an entropy soup from the very beginning?
Concerning the evolution of the universe from its very beginning (big-bang), it clearly falls out of my reach as a poor statistical physics student ;) I just wonder about the validity of thermodynamics as after the big-bang the huge amount of initial energy is transformed into matter (a lot of different particles are created), a phenomena that is not taken into account in this theory.
Can you find the reference of the article you mention? it seems an interesting question...
Interesting thermodynamic questions, Laura, even if slightly outside biophysics...
The point is that isolated systems do not get organized with time, but become more and more “disordered“– or more exactly, evolve to states of maximum probability and multiplicity, the macrostates with the higher number of microstates or configurations available, is that right?
Yes, that's right as far as I know.
Apparently the universe has not evolved in that sense: the old universe the infrarred techniques can detect seems a lot more homogeneous, disordered and probable that the one we can see today....Where’s the increasing entropy to satisfy the 2nd law?
Interesting question. The answer is double as far as I understand. On the one hand, the initial state was not an exactly thermal state, but a slighly perturbed thermal state. Actually those deviations from exact thermality is what the CMB experiments (COBE, WMAP) detect, and they are the seeds for all the structure we observe today (galaxies, stars, planets, life).
On the other hand, one has to take into account not only the entropy of the matter, but also the entropy of the gravitational field, which is very important in the early stages of the universe expansion. Actually, it looks like that the entropy of a uniformely-filled expanding universe is comparatively low when one takes into account the gravitational field.
Perhaps there is a lot of entropy in black holes, or other universes and big bangs as some hypothesis suggest...who knows.
If I remember well, for a given size the black hole is the object with the maximum possible entropy, so your idea might be intersting...
Anyway as far as I know there is no contradiction with the laws of thermodinamics and the current standard model of the universe expansion (this is not to say that there are no interesting quesions one can pose, like yours).
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