Talk:Second law of thermodynamics

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The text states, "The is regarded as the only true isolated system, the Earth can be viewed as a closed system, although this is not entirely accurate, it is a fairly good approximation." I think something vital is missing after the first "is" - but what? The universe? I'm not sure.--Bob_M (talk) 04:32, 23 May 2007 (CDT)

My guess is, it was supposed to be "This is" (meaning the universe), not "The is". I've reworded it slightly, working under that assumption. If I'm wrong, hopefully someone will fix it. --jtltalk 04:41, 23 May 2007 (CDT)


Good article. I think even I understand what this is about now. High school never managed to do that. :D --AKjeldsen 08:57, 23 May 2007 (CDT)

Contents

[edit] Subtle distinction in rebuttal to creationists' misuse of the second law

The usual rebuttal to the creationists' bogus claim that evolution violates the Second Law is to say that the earth is not an isolated system and it receives a large amount of energy from the sun. While these two statements are both true, it doesn't really refute the claim.

The change of entropy of an object is defined as the amount of heat energy transferred in or out of the object divided by the temperature at which the transfer occurs. If heat flows out of the object, then the object's entropy decreases. So it is not correct to say that the entropy reduction on the earth is enabled by a larger entropy increase on the sun, because the sun's entropy actually tends to decrease as it radiates energy and the solar energy that hits the earth tends to increase its entropy.

What actually happens is more subtle. The earth is radiatively coupled to two "objects": the sun and the rest of the universe. As we know from the physics of global warming, the thermal power the earth receives from the sun at optical and infrared wavelengths must equal the outbound radiation of thermal power at long infrared wavelengths or the earth heats or cools until the radiation balance is restored. This power balance satisfies the first law of thermodynamics, the conservation of matter/energy.

But the earth is much warmer (300 K) than most of the sky (3 K, the cosmic background temperature) so that the decrease in the earth's entropy associated with the radiation of each unit of heat energy is much less than the resulting increase in the entropy of the universe as a whole.

So it is actually more correct to say that the reason life can evolve and survive on the earth is that solar energy flows through the earth from a very hot source (the sun at 5785 K) to a very cold sink (the rest of the universe). This is analogous to how the high temperature heat from burning fuel flows through a gas or steam turbine, producing useful work plus low-temperature waste heat that must be dumped into the environment. Just as a heat engine cannot run without both fuel and a heat sink, life on the earth could not survive without both the sun and the rest of the universe into which to dump its low-temperature waste heat energy. 

Karn 03:39, 21 June 2007 (CDT)

Indeed, feel free to edit. MiddleMan 09:54, 21 June 2007 (CDT)

[edit] Hmn

This edit is not exactly clear to me. Are you defining the universe to cover what is necessary to make it an isolated system? If so, you could just say "The universe is defined in such a way that it is an isolated system." Heart♥GoldTeach me about your father Satan 12:12, 17 July 2007 (CDT)

No, because that's not how it is defined, although the definitions are equivalent. The universe is in laymen's terms: everything there is, all space, all energy there is is stored in the universe. MiddleMan 12:17, 17 July 2007 (CDT)

Okay, if that is not how it is defined, you should be able to cite a reference that prooves the universe is an isolated system. Or is this pseudoscience? Heart♥GoldCry Like a little girl 12:19, 17 July 2007 (CDT)

No, there is no space-time (yes, no time) outside the universe, so heat currents cannot flow there. MiddleMan 12:21, 17 July 2007 (CDT)

Original research on your part, definitional, or can you cite a scientific proof to this effect? Heart♥GoldShow me your intolerance 12:36, 17 July 2007 (CDT)

[edit] Another

Again, this edit is not exactly clear to me. Couldn't the Earth also gain potential energy, e.g., the creation of mountain ranges? Heart♥GoldCry Like a little girl 12:19, 17 July 2007 (CDT)

Well I suppose the better way to say it is that high-grade energy from the sun interacts with the earth, where some of it is stored and eventually released as low-grade energy into space. But the creation of mountain ranges is not fueled by the sun, thats storage of energy from the core and mantle. Most of the sun's energy that gets stored is stored in plants/bacteria or trapped as heat. tmtoulouse nettle 12:35, 17 July 2007 (CDT)
Hence, my comment (somewhere) about being integrated (and by implication) averaged over time. Heart♥GoldShow me your intolerance 12:38, 17 July 2007 (CDT)
Assume I am ignorant of all previous discussion (which I am)...what are you attempting to integrate? tmtoulouse persecute 12:39, 17 July 2007 (CDT)
The energy into and out of Earth. Heart♥GoldTeach me about your father Satan 13:04, 17 July 2007 (CDT)
So you mean integration of the difference between the energy entering the earth and leaving the earth? That gets exceedingly complicated depending upon what exactly you are looking at. Sources of external energy include extra-terrestrial objects, and extra-terrestrial sources of radiation, the bast majority of that is not "stored" in the earth and just continues on unchanged. So if we only look at external energy thats stored I would say that currently it would currently integrate to a positive number since there is plenty of "stored" energy left. However, as we let the time axis expand eventually we would integrate to 0 if we only count energy released that was originally stored from external sources. But if you want to count ALL energy that will ultimately be released the difference between energy in and energy out will ultimately be negative since the earth has its on energy left over from its formation that will eventually be released...............but why does this matter? tmtoulouse pester 13:12, 17 July 2007 (CDT)

I think it is actually possible to store potential energy in the Earth like that, it would however be insignificant, and extra energy is far more likely to manifest itself as kinetic energy or heat. Not that the influx has to equal the outflux to make Earth an open system. MiddleMan 13:09, 17 July 2007 (CDT)

Hmmm... I'm going to have to work on this a bit at some point. In the world of chemistry, people are moving away from the misapplied term "disorder" to "degree of dispersion of energy." It turns out the disorder analogy isn't such a good one, and a lot of the social analogies are even worse. ŠтΈṜȳŁЁand...? 13:12, 17 July 2007 (CDT)
Yes the order/disorder stuff is problematic, I usually respond to creationist attempts at using 2nd LOT by asking them what the rules governing transfer of heat have to do with evolution anyway? tmtoulouse persecute 13:20, 17 July 2007 (CDT)
Exactly; in chemical terms how the quanta of energy are always distributed statistically among the energy at equilibrium; it's just when two systems interact, they need to redistribute that energy. Hence why all energy ends up as heat. All gen. chem books (or at least the decent ones) have in their last edition taken out a lot of (if not all of) their references to disorder, and certainly the messy room or desk analog. It's been acknowledged that 40 years of chemical pedagogy were all crap. ŠтΈṜȳŁЁand...? 13:28, 17 July 2007 (CDT)
"It turns out the disorder analogy isn't such a good one, and a lot of the social analogies are even worse." Bad social analogies are not caused by actual words used, in my opinion. It just happens. See social darwinism and the eugenics movement. Heart♥GoldDeny you're a communist 21:25, 17 July 2007 (CDT)

You mean that Einstein and Fermi were wrong, because people turned their ideas into weapons of mass destruction? MiddleMan 21:28, 17 July 2007 (CDT)

[edit] Rewrite

Sterile, I would like to put the example of the room and some other things back in. So, a curious homeschooler can understand how entropy works and what is actually meant by "disorder". Not that there's anything factually wrong with your version, but it might a bit hard to follow for laymen. MiddleMan 21:22, 17 July 2007 (CDT)

Go ahead--I was worried it was a bit "elevated." You will find I'm not particularly possessive about most articles. ŠтΈṜȳŁЁand...? 10:31, 18 July 2007 (CDT)

[edit] hydraulic ram

Two useful bits to read:

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