Enropy paradox ? or , tell me why?

[Alireza_M]

Hi all,
I've been around with this question for a while,I googled it and I found some information,But I want you to help me more, The question is :
From the beginning of the universe,Anywhere of the Universe you see,there is reactions that due to them new materials are being produced,and definitely it is getting structured , and that is decreasing the entropy of the universe... Is this in paradox with the second law of thermodynamics that says:anything that happens in the world is toward the increasing of entropy
I appreciate your help

 

[Drakkith]

The reactions still result in an increase in entropy. You must expend some energy to take those compounds apart and make them back into their original states. Just like how stars convert Hydrogen to Helium. This results in an increase in entropy with each reaction.

Edit: Hrmm. I might not be understanding entropy correctly. Someone correct me if I am mistaken.

 

[Alireza_M]

The reactions still result in an increase in entropy. You must expend some energy to take those compounds apart and make them back into their original states. Just like how stars convert Hydrogen to Helium. This results in an increase in entropy with each reaction.

Thanks , So that is the matter of enthalpy of the reactions somehow?

 

[Drakkith]

I can't explain it very well. See here for more info.

http://en.wikipedia.org/wiki/Introduction_to_entropy

 

[Alireza_M]

I can't explain it very well. See here for more info.

http://en.wikipedia.org/wiki/Introduction_to_entropy

I've seen it all , Thanks anyway.

 

[Drakkith]

All I can say is that whatever happens, the total entropy of the universe is increasing. You can definitely decrease entropy locally, but it always results in an increase in entropy somewhere else.

 

[Alireza_M]

Yes,that is the second LAW of thermodynamics but I don't understand where's entropy is increasing,As anywhere you see there is materials being produced with less entropy,and in such reactions of course some heat will be produced too,If that heat is increasing the total entropy,so why the temperature of the universe is decreasing? Because the universe is expanding? Be my guest,so what is the evidence on increasing the entropy?!
I hope I could say what I was about to say

 

[Drakkith]

I kind of like this quote from wikipedia from: http://en.wikipedia.org/wiki/Entropy_(energy_dispersal )

In this approach, the second law of thermodynamics is introduced as "Energy spontaneously disperses from being localized to becoming spread out if it is not hindered from doing so."

 

[dimension10]

Yes,that is the second LAW of thermodynamics but I don't understand where's entropy is increasing,As anywhere you see there is materials being produced with less entropy,and in such reactions of course some heat will be produced too,If that heat is increasing the total entropy,so why the temperature of the universe is decreasing? Because the universe is expanding? Be my guest,so what is the evidence on increasing the entropy?!
I hope I could say what I was about to say

When youre pressing a syringe, youre increasing the entropy of the surrounding air while decreasing that of a syrings.

 

[Dale]

them new materials are being produced,and definitely it is getting structured , and that is decreasing the entropy of the universe...

This doesn't make sense to me. Can you show me which nuclear reaction you believe decreases the entropy of the universe?

 

[netheril96]

The key is gravity. Statistical mechanics don't take into account gravitational interactions between particles and empirical proof for thermodynamics are objects on earth.
I have read about two kinds of thought. One claims that gravity can reduce entropy, as in near uniform gas condensing into a star system. The other thinks that entropy still increases, but gravitation systems are unstable, and therefore there is no equilibrium, i.e., no upper bounds for entropy. So it increases, but it never ends, and in local areas, complexity can still arise.

 

[Naty1]

"...definitely it is getting structured , and that is decreasing the entropy of the universe.."

That idea would be true in the absence of gravity...less structure without gravity means increasing entropy. But WITH gravity, maximum entropy is associated with structure...planets for example. When gravity matters clumpiness...not uniformity...is the norm...it's not an obvious situation.

Most discussions of entropy are based on non gravitational situations such as the increasingly uniform distribution of gas molecules in a container. With gravity, our thinking needs a BIG change in perspective: clumpiness tends to ensue and with gravity present THAT is increasing entropy...less order.

An extreme example illustrating why your supposition is NOT correct are black holes...which continue to form... they are structured and have the maximum entropy possible within their volume.

As another example, all life forms are conduits for taking in low entropy energy and giving off high entropy energy...

There is a good discussion of all this in Brian Greene's FABRIC OF THE COSMOS beginning around page 168...The puzzle, or "paradox" if you prefer, is why our universe started in such a highly ordered nearly uniform low entropy big bang.

 

[Alireza_M]

"...definitely it is getting structured , and that is decreasing the entropy of the universe.."

That idea would be true in the absence of gravity...less structure without gravity means increasing entropy. But WITH gravity, maximum entropy is associated with structure...planets for example. When gravity matters clumpiness...not uniformity...is the norm...it's not an obvious situation.

Most discussions of entropy are based on non gravitational situations such as the increasingly uniform distribution of gas molecules in a container. With gravity, our thinking needs a BIG change in perspective: clumpiness tends to ensue and with gravity present THAT is increasing entropy...less order.

An extreme example illustrating why your supposition is NOT correct are black holes...which continue to form... they are structured and have the maximum entropy possible within their volume.

As another example, all life forms are conduits for taking in low entropy energy and giving off high entropy energy...

There is a good discussion of all this in Brian Greene's FABRIC OF THE COSMOS beginning around page 168...The puzzle, or "paradox" if you prefer, is why our universe started in such a highly ordered nearly uniform low entropy big bang.

Thanks! that really helped

 

[Alireza_M]

This doesn't make sense to me. Can you show me which nuclear reaction you believe decreases the entropy of the universe?

For example : H --> He + 2 positron + 2 neutrino + energy.
I know that the energy increases the entropy of the surrounding and that overally the entropy increases but i wanted to know any more information or situations or reasons.

 

[Andrew Mason]

Yes,that is the second LAW of thermodynamics but I don't understand where's entropy is increasing,As anywhere you see there is materials being produced with less entropy,and in such reactions of course some heat will be produced too,If that heat is increasing the total entropy,so why the temperature of the universe is decreasing? Because the universe is expanding? Be my guest,so what is the evidence on increasing the entropy?!
I hope I could say what I was about to say

What has happened to all the energy that the galaxies have been spewing into inter-galactic space since the Big Bang? Why does the universe not keep getting hotter? Interesting question. I don't know the answer to that. You should probably post that question on the cosmology board. Like you, I suspect it has to do with the expansion of the universe.

But I don't see entropy as a problem. All the second law says is that in any thermodynamic process, entropy must increase.

So, for example, consider the following: a hydrogen gas cloud compresses itself into a ball through gravity and fusion begins to occur. The temperature of that gas cloud, now a star, definitely increases. And since that heat flow is coming from fusion at the centre of the star and not from some external thermal source, there is net heat flow into the universe. The galaxy in which that star resides now radiates more energy so the galaxy's blackbody temperature increases as a result of the new star (assuming all the other sources of energy in the galaxy do not change).

Lets examine the entropy: Heat flows from the universe into the star through the fusion process at the very hot centre of the star and is radiated out into the universe from the cooler surface:

\Delta S_{universe} = \int dQ_{h}/T_{h} + \int dQ_{c}/T_{c} > 0 since the dQs are the same magnitude and opposite in sign (Qh is - and Qc is +) and Th is higher than Tc.

That radiant energy is absorbed on the surface of a distant, cooler planet that contains plant life. The radiant energy drives non-reversible thermodynamic processes in the plant that cause the plant to build complex structures and complex chemical energy storage and delivery systems. Because the processes are non-reversible, entropy increases further on the the planet.

End result is: more complexity locally; increase in heat flow into the universe, increase in entropy of the universe;

AM

 

[Naty1]

If that heat is increasing the total entropy,so why the temperature of the universe is decreasing?

[why does the heat of a thermonuclear explosion decrease? Does that mean entropy is decreasing?]

Heat is just one form of energy. What about gravitational energy, dark energy, kinetic energy, etc. You could also ask why potential energy is trending in whatever direction it is...It's the total energy in the universe that is believed to stay constant at zero. gravitational energy exactly balances all other energies.


But different observers will measure different energy values...take the Unruh effect for example. We only measure the same cosmic background radiation because we agree on a standard approach...which yields about 2.7 degrees C. A different approach is equally valid but will have a different value...

[As an example, a free falling observer passes a black hole horizon without incident; a stationary observer there is instantaneously burned by radiation. Leonard Susskind in his BLACK HOLE WAR has a great and detailed discussion on this.))

It's like asking does everybody measure the same age of the universe...no, every measure from a different frame or point in the universe will in general be different...so we establish some references and use those for discussion.

You can read about vacuum energy here:http://en.wikipedia.org/wiki/Vacuum_energy

The opening paragraph about the disparate range of vacuum energy and the cosmological constant reveals one of the greatest puzzles in theoretical physics...

 

[Alireza_M]

What has happened to all the energy that the galaxies have been spewing into inter-galactic space since the Big Bang? Why does the universe not keep getting hotter? Interesting question. I don't know the answer to that. You should probably post that question on the cosmology board. Like you, I suspect it has to do with the expansion of the universe.

But I don't see entropy as a problem. All the second law says is that in any thermodynamic process, entropy must increase.

So, for example, consider the following: a hydrogen gas cloud compresses itself into a ball through gravity and fusion begins to occur. The temperature of that gas cloud, now a star, definitely increases. And since that heat flow is coming from fusion at the centre of the star and not from some external thermal source, there is net heat flow into the universe. The galaxy in which that star resides now radiates more energy so the galaxy's blackbody temperature increases as a result of the new star (assuming all the other sources of energy in the galaxy do not change).

Lets examine the entropy: Heat flows from the universe into the star through the fusion process at the very hot centre of the star and is radiated out into the universe from the cooler surface:

\Delta S_{universe} = \int dQ_{h}/T_{h} + \int dQ_{c}/T_{c} > 0 since the dQs are the same magnitude and opposite in sign (Qh is - and Qc is +) and Th is higher than Tc.

That radiant energy is absorbed on the surface of a distant, cooler planet that contains plant life. The radiant energy drives non-reversible thermodynamic processes in the plant that cause the plant to build complex structures and complex chemical energy storage and delivery systems. Because the processes are non-reversible, entropy increases further on the the planet.

End result is: more complexity locally; increase in heat flow into the universe, increase in entropy of the universe;

AM

Thank you.good explanation.but one thing. Absorbed energy by a planet I think will lead reactions to less complex structures I think.

 

[Naty1]

Here is a view I have not quite seen before:

Since a finite universe is an isolated system then, by the Second Law of Thermodynamics, its total entropy is constantly increasing. It has been speculated, since the 19th century, that the universe is fated to a heat death in which all the energy ends up as a homogeneous distribution of thermal energy, so that no more work can be extracted from any source.

If the universe can be considered to have generally increasing entropy, then—as Roger Penrose has pointed out—gravity plays an important role in the increase because gravity causes dispersed matter to accumulate into stars, which collapse eventually into black holes. The entropy of a black hole is proportional to the surface area of the black hole's event horizon.[56] Jacob Bekenstein and Stephen Hawking have shown that black holes have the maximum possible entropy of any object of equal size. This makes them likely end points of all entropy-increasing processes, if they are totally effective matter and energy traps. Hawking has, however, recently changed his stance on this aspect.[citation needed]



The role of entropy in cosmology remains a controversial subject. Recent work has cast some doubt on the heat death hypothesis and the applicability of any simple thermodynamic model to the universe in general. Although entropy does increase in the model of an expanding universe, the maximum possible entropy rises much more rapidly, moving the universe further from the heat death with time, not closer. This results in an "entropy gap" pushing the system further away from the posited heat death equilibrium.[57] Other complicating factors, such as the energy density of the vacuum and macroscopic quantum effects, are difficult to reconcile with thermodynamical models, making any predictions of large-scale thermodynamics extremely difficult.[58]

The entropy gap is widely believed to have been originally opened up by the early rapid exponential expansion of the universe.

http://en.wikipedia.org/wiki/Entropy

 

[Naty1]

Here are some posts I saved from an earlier discussion :

I also had a lot of difficulty with Penrose's Chapter 27 until I remembered a discussion in THE FABRIC OF THE COSMOS, Brian Greene, Entropy and Gravity page 171-173 following quotes from there.

(1) Penrose explains (in Chapter 27) that in an ordinary gas the configuration with the highest entropy is that in which particles are uniformly distributed. So one expects the uniform early universe to have high entropy.
second part not so!
"ordinary" means low gravity. Normally a uniform gas distribution, say sitting on a table top here on earth, IS in it's highest state of entropy when equilibrium is reached BECAUSE GRAVITY IS NEGLIGIBLE.
Greene:

When gravity matters as it did in the high density early universe, clumpiness - not uniformity- is the norm.

So shortly after the big bang uniformity actually means LOW entropy as gravity was huge...one DOES NOT expect uniformity under such conditions of high gravity to reflect high entropy. (I think Penrose agrees.)

(2) Post #6
Then he points out (by invoking the Bekenstein-Hawking formula) that a universe which has gravitationally condensed into black holes has an even higher entropy. (One must of course remember, as Space Tiger emphasizes in this thread, that high and low are relative terms.)
Black hole entropy IS maximum because gravity is maximum in a given region of space.
Greene:

When gravity flexes it's muscles to the limit it becomes the most efficient generator of entropy in the universe. Since we can't see inside a black hole, it's impossible for us to detect any rearrangements

..,meaning hidden information (entropy) is maximized.


(3) Post#6:
Penrose also argues (his Fig. 27.10) --- without seeming to provide any proof --- that any gravitational condensation (perhaps into galaxies or stars) will increase the entropy of a uniform distribution of matter, and hence conform with the Second Law of thermodynamics.
Greene:

In calculating entropy you need to tally up the contributions from all sources. For the initially diffuse gas cloud you find that the entropy decrease through the formation of orderly clumps is more than compensated by the heat generated as the gas compresses, and ultimately, by the enormous heat and light released when nuclear processes begin to take place...The overwhelming drive towards disorder does not mean that orderly structures like stars and planets...can't form...the entropy balance sheet is still in the black even though certain constitutents have become more ordered.

 

[Andrew Mason]

Thank you.good explanation.but one thing. Absorbed energy by a planet I think will lead reactions to less complex structures I think.

Why less complex?

A plant cell takes in energy from the sun to build-up a chemical energy supply (eg. ATP) that can then drive bio-chemical processes in living cells. The cells operate like little machine shops building all sorts of complex molecules that carry out various functions within the cells. The cell's energy drives the processes that create complex macroscopic structures: tree trunks, bark, branches, leaves, roots, etc. Some of the plant cells are ingested by mammals who use the energy contained in those complex molecules to carry out various animal functions - building nests, burrows, making tools, houses, factories (eg that make computers on which other higher order animals discuss plant cells building up chemical energy supply ... etc.)...

All of this results in an increase in entropy through heat flow. Heat flow has the potential to do work. Heat flow will always be into a body from a higher temperature and, after extracting work, expelled from the body at a lower temperature, meaning entropy increases.

The creation of complex structures requires work. All work is ultimately derived from heat flow. So when heat flow occurs, entropy always increases.

AM

 

[Vespa71]

Flow of entropy can be harnessed in any "trap" to build high-value energy. That is the case in a cars engine, and in a windmill. Same even in a hydropower-turbine, if you include the sun vaporizing the water, wind pushing the clouds up to colder air over mountains, condensing and then harnessing the potential energy through dropping liq water. Any local arrangement that reduces entropy, also the building of higher value materials, are possible, if the conditions are present, man made or natural. In any case the total entropy increases, though such local system might structurize.

The universe is approaching even temperature, isn't that the theory? Heat capacity of universe is constant, no matter what size it reaches. What temperature are we at then?