Can Entropy Ever be Reversed?

We'll become so advanced that we'll be able to create a new universe for everyone who wants one 8)

Might take a few millennia, so put on the kettle.

Originally posted by Yo Mamma

4: Inevitable and steady deterioration of a system or society.

Your body cells do it all the time, having to maintain a system totally different to the outside world, this is done by the constant input of energy, otherwise entropy 'takes over' and your body disintegrates into the surrounding enviroment (which is what happens when you die, no energy = no maintainance of order = disorder= decomposition)

So in theory, i suppose if there was enough energy available entropy 'could' be reversed, however to cause a reversal energy in > energy out which the first law of thermodynamics puts paid to.

So this 'dark matter' you speak of could be your only hope of reversing entropy. Next question is why bother?

Originally posted by Yo Mamma
It looks like the universe will age and die, just like everything else... expanding and cooling until all that's left is some lumps of lead where neutron stars once were. and even those will eventually evaporate as their atoms decay away into their constituent particles and fly apart.

sounds pretty crap to me.

Well, the other options would be :

1) The universe stops expanding, and collapses to a point again, with varying results depending on which model you subscribe to (Relativity, Quantum Mecahmics and String Theory all produce different results after you shrink below Planck Length)

2) The universe miraculously reaches a steady state in terms of size, and remains there for infinity, until everything eventually goes the same way as with an expansionist theory, only with a higher density per cubic area.

Both of which should sound "equally crap" to you as well, so I guess its all doom and gloom

As to your question....there is no known mechanism whereby entropy can be reduced, except possibly the "collapsing universe" scenario at the big crunch.

jc

Originally posted by DeVore
[BI'm not sure where black holes come into all this, because the theories above would indicate a likely evening out of the energy in the universe (remember mass ~= energy, energy ~= mass)
so how come its being gobbled up by black holes which never release it...
[/B]

Black holes can emit radiation (Hawking radiation, IIRC) through some funky interaction of the event horizon and virtual quantum particles. Can supply more information if requested.

Interestingly, this means that were the unverse to be expansionary, then black holes would eventually "die out" into the great evening out which deV just mentioned.

Also, it is worth noting that black holes are a rare case where entropy is decreased. However, the Second Law of Thermodynamics does not apply necessarily to "bits" of the universe - it is applied as a whole. In otherwords, because a black hole is not a "closed environment", it cannot be taken on its own to show a discrepancy in the SLoT.

jc

Originally posted by DeVore
What I'm questioning is, if the universe was expanding permanently and will generally even out the matter in it over time... how will the matter *currently* tied up in black holes get released as the theory says it has to over time...
[/B]

This is actually something that has puzzled me about Hawking radiation, so if anyone else has read up on it, some clarification would be good. Heres my understanding

From my reading, Hawking radiation is caused when empty space "spontaneously" splits into two virtual elementary particles - one virtual particle of matter, and its corresponding virtual anti-matter particle. These particles are referred to as virtual because normally when matter and anti-matter meet, they cancel each others mass out, releasing huge amounts of energy.

In the case of the virtual particles, the energy to create the particles seems to have been "borrowed" from the universe, and this is ok as long as it is paid back in short order. Thus, when the particles recombine, cancelling each other, the energy balance is restored - the loan repaid if you will.

Yes - this is bloody head-bending - maybe have a coffee and think about that last paragraph before proceeding

Anyway, when a virtual pair like this get created at (or near) the event horizon of a black hole, it is probable that in some cases, one particle will fall into the black hole, and the other will not.

So what, I initially thought to myself. An equal number of particles and anti-particles will fall in, and their opposites will escape, so it all evens out. Black holes may emit radiation, but they dont shrink.

But then I thought some more.....and I'm still confused.

I cannot see how a black hole shrinks. Assuming that the virtual particle falls into the black hole, the virtual anti-particle becomes a real anti-particle, and goes on its merry way until it meets a particle, and they destroy each other. The virtual particle, in the mean time, has become a real particle, and has fallen into the black hole, making it more massive (surely). This, of course, is offset by the reverse situation where the virtual particle escapes and the virtual anti-particle falls into the black hole and destroys some matching particle in there, making teh black hole less massive.

I know I'm missing something. Hawking radiation is believed to cause black holes to shrink over time, as they are radiating energy (obviously). So, in asnwer to DeVores question, in an expansionary universe, the black holes will actually decay over time, which is how the matter currently tied up in them will get released.

As a speculative side, I think my confusion comes from a lack of understanding of how the "energy debt" is repaid to the universe after the virtual particles become sufficiently seperated to become real particles. I am assuming it is when the no-llonger-virtual anti-particle bumps into a particle, but this is probably where my error is.

jc

BHOT isnt a bad read on this stuff. Interestingly, "The Elegant Universe" is also very good at explaining it, despite being mostly about string theory! Essentially, the author gives you a crash course in the "conventional" theory of something before looking at the string equivalent.

Havent read Hawkings new book yet - whats it called?

jc

Originally posted by Yo Mamma
I could be wrong here, but I think they discovered that instead of the universe slowing down and eventually stopping altogether and collapsing in upon itself, it is actually speeding up and the rate at which the galaxies are moving away from each other is getting faster all the time !

There have been theories to that extent. However, they are geerally "fringe theories" which are not widely accepted, and/or theories which have later been shown to be based on bad data, or based on incorrect assumptions.

AFAIK, the theory in the link you gave (dated 1998) has since been discarded, but I dont have anything close to hand. The general scientific community still think the universe is slowing. Like you, however, I could be wrong

Which turns the whole Big-Bang scene on its cosmic ear!
Because the basis of the big-bang theory relies heavily on a Big-Crunch.

Absolutely not. The big bang theory does not rely at all on a big crunch, for one major reason :

The big-bang theory has several "conclusions". Our universe could be bounded or unbounded, and could contine expanding for ever (expansionary universe), reach a "balance point (steady-state universe) or collapse again (collapsing universe). All three are possible, with the steady-state being the most improbable. Any of these "end-points" can be reached from a big-bang model, and therefore the expansionary model that you mentioned does not cause a problem

As a matter of interest, the whole argument about dark-matter and the so-called cosmological constant essentially revolves around why the universe is expanding at its current rate, and where that rate will lead us.....continued expansion or contraction.

jc