Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: kasparovitch on 25/06/2016 13:53:11
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The second law of Thermodynamics states that a system tends to disorganization, and thus the Universe so tends.
It's easy to notice that my house will become very disorganized in future if I do nothing, and perhaps my head, too.
This happens in the first instance because I have my house organized, otherwise it couldn't tend to disorganization.
My FIRST question is how can the Universe be organized first so that it will tend to disorganization as stated by the second law of Thermodynamics, thus first violating it?
This is my SECOND question:
It's a tenet that life is an exception to that law and this is accepted because the global entropy doesn't stop increasing because of the creation of law.
This tenet is evident given the paucity of life in such a huge universe. However, for it to be true that life can originate as long as it doesn't imply that entropy will decrease, then there must be a physical process that guaranteed that the global entropy won't decrease even when there are violations as the creation of life.
These are perhaps philosophical questions which I find very interesting unless something very basic is escaping me. This is challenge.
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By definition of entropy change: ΔS = ∫(dq/T).
For heat flows from body 1 to body 2 (both isolated from the surroundings), and for small heat flow so that each temperature change very little, ΔS = Δq1/T1 + Δq2/T2. By conservation of energy, Δq1 + Δq2 = 0. So ΔS = Δq * ( 1/T2 - 1/T1 ), where positive heat flow is assigned to body 2 that is receiving heat. ΔS ≥0 because T1 ≥ T2, or heat flows from hotter to colder bodies.
1) About your first question, according to the big bang model, the entire universe was at first a dense and hot spot. And now we have hot parts (the stars) and cold parts (the planets and other non radiant bodies). It seems against the second law, because for an uniform temperature universe to become what it is now, heat was transfered from colder to hotter parts. Unless that hot and dense spot was not homogeneous.
2) About the second question, the photosynthesis reaction can be seen as the bridge from inorganic to organic world. It absorbs energy from sunlight, so it is endothermic. If the entropy of the reaction products (C6H12O6 + 6O2) were lower than that of the input molecules (6CO2 + 6H2O) the process would not be spontaneous as it is. So, while the living cell seems more organized than its inorganic origin, its entropy is really bigger.
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It's a tenet that life is an exception to that law and this is accepted because the global entropy doesn't stop increasing because of the creation of law.
Entropy of a system can be reduced by adding energy from outside of the system. Hence life is not an exception to the law.
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2) About the second question, the photosynthesis reaction can be seen as the bridge from inorganic to organic world. It absorbs energy from sunlight, so it is endothermic. If the entropy of the reaction products (C6H12O6 + 6O2) were lower than that of the input molecules (6CO2 + 6H2O) the process would not be spontaneous as it is. So, while the living cell seems more organized than its inorganic origin, its entropy is really bigger.
Entropy of a system can be reduced by adding energy from outside of the system. Hence life is not an exception to the law.
Both your answers seem interesting and I'd ask if you can offer a bibliographical source, but please nothing for graduates in astrophysics, something at the level of a Scientific American article, or Science at most.
Thanks a lot in advance.
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according to the big bang model, the entire universe was at first a dense and hot spot. And now we have hot parts (the stars) and cold parts (the planets and other non radiant bodies). It seems against the second law, because for an uniform temperature universe to become what it is now, heat was transferred from colder to hotter parts.
If you consider the universe to be an inert gas, as it expanded, it should cool down.
The temperature of the whole universe should now be about 2.7K.
However, the universe is not composed of an inert gas - most of it is Hydrogen, the stuff of Hydrogen bombs.
Just due to statistics, you will get density fluctuations in this gas, and high densities are self-reinforcing.
If you get enough Hydrogen together in one place, it is held together by gravity, and the central pressure increases. Once the internal temperature exceeds about 4 million Kelvin, it will start Hydrogen fusion (https://en.wikipedia.org/wiki/Stellar_nucleosynthesis#Hydrogen_fusion), releasing more energy and increasing in temperature.
These hot glowing balls of plasma that are powered by hydrogen fusion we call stars.
Lesser balls of glowing iron and silicates we call rocky planets. These don't undergo fusion in the core, but they are still hot from the collision of the rocky objects that formed them, assisted by the decay of radioactive elements formed in supernova events, as earlier stars died violently.
Neither stars nor planets violate the second law of thermodynamics.
Unless that hot and dense spot was not homogeneous.
The theory of inflation suggests that for a while, the microscopic universe expanded faster than the speed of light.
This allowed some small differences in temperature to persist, which are now being studied in the Cosmic Microwave Background Radiation - but the differences are relatively small.
See: https://en.wikipedia.org/wiki/Inflation_(cosmology)#Few_inhomogeneities_remain
It is hoped that some future sensitive gravitational wave detector might be able to detect relic gravitational waves representing density differences in the early universe.
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Just googled it
http://curious.astro.cornell.edu/about-us/136-physics/general-physics/thermodynamics/816-does-evolution-contradict-the-second-law-of-thermodynamics-intermediate
If you want to go a bit deeper
http://www.talkorigins.org/faqs/thermo.html
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Just googled it
http://curious.astro.cornell.edu/about-us/136-physics/general-physics/thermodynamics/816-does-evolution-contradict-the-second-law-of-thermodynamics-intermediate
If you want to go a bit deeper
http://www.talkorigins.org/faqs/thermo.html
I'm afraid the second link, and perhaps the first one, too, is inappropriate in that it assumes the reader is a creationist.
Not that I'm one, but because I prefer to use information not flawed by an argumentation based on a false dilemma, first of all, and last but not least because I discard people who teach me how to think unless I'm stupid in their [superior] opinion.
I prefer pure scientific information, based on a categorical imperative and not on hypothetical ones as Kant would put it. Not information constructed so as to conform religious, evolutionist, creationist or whatever tenets outside their areas. Every jack to his trade.
The second question confronts the empirical existence of life, however simple or complex it may be, with the second law of thermodynamics. I wouldn't think that if Darwin was alive he would be the best authority to answer it.
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If you consider the universe to be an inert gas, as it expanded, it should cool down.
The temperature of the whole universe should now be about 2.7K.
The birth of a star can then be described as an exothermical process. Potential gravitational and strong nuclear energy transform in heat, that flows (radiates) to the surroundings.
It really follows the second law the same way that forest fires in the dry season.
Some real gases will cool down when expanding. Loss of molecular kinetic energy (temperature) and increase of potential energy (binding forces are smaller when the average space increases).
It can be a methaphor for the cooling down effect of an expansion universe, but I think there is no relation.