Can Entropy Ever be Reversed?

Yo Mamma

So, the galaxies are flying apart and so far our instruments haven't detected enough mass in the universe to make them reverse and collapse down into another big bang.

there's the theory of "dark matter"... but it's still completely unproven.

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.

so is that it?

sounds pretty crap to me.

nesf

And this has what to do with entropy?

Yo Mamma

1: A measure of the disorder or randomness in a closed system.
2: A measure of the loss of information in a transmitted message.
3: The tendency for all matter and energy in the universe to evolve toward a state of inert uniformity.
4: Inevitable and steady deterioration of a system or society.

I mean Entropy in the sense of no 4. in this case relating to the steady expansion of our Universe and thus the deterioration of all the systems therein !!

Does that make it easier for you ?

nesf

I meant what has this got to do with entropy in the physics sense of the word.

It wasn't meant as an insult or jibe but as a query into what form of entropy you were refering.


Oh and btw, I study physics, I don't need an easier explanation. You can take the universe as coming from a highly chaotic state, i.e. the big bang, to a symettrical one if you so wish.

Static

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.

Yo Mamma

Apologies for the btichiness

Got out the wrong side of bed this morn................a wee bit cranky........................;)

Winning Hand

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?

nesf

Originally posted by Yo Mamma
Apologies for the btichiness

Got out the wrong side of bed this morn................a wee bit cranky........................;)

No problems boy Same here.

bonkey

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

DeVore

/me puts on his maths head.

Well, both of these are interesting questions and slightly related but there is a big difference.

In very simple terms (and afaik )
1. Entropy is the general tendancy for complicated (high energy) things to break, fall apart, stop working.... rather then the other way around. the way it was explained to me in lectures was that there are hundreds of ways of dropping a cup and breaking it into little pieces (release of the energy in the bonds that go to hold it together) but not many ways of dropping bits and ending up with a properly formed "cup" (partially because we chose one particular arrangement of molecules to term: cup... but the point still stands because higher energy states are less likely to form then lower states).

2. The expansion of the universe is caused (or not caused) by the gravitational pull of the mass inside it on all the other mass inside it
Currently it *appears* to be slowing a LOT faster then we would have expected. Scientists HATE surprises and so have postulated dark matter. Thats not as cuckcoo as it sounds.
When you exclude the impossible, whatever explanation remains, no matter how improbable, must be the answer. (Einstein or Holmes said that, cant recall which).
Couple that with Occams razor which says "the most likely answer is the one you must accept for the moment if you are to proceed with postulating" and hence:
If the mass inside the universe causes it to slow, and its slowing faster then all the mass we can see should cause it to, then there must be more mass here then we can see. Dark Matter QED

(may my maths lecturers forgive me for such simplifcation )



Where these two theories/questions intersect is not in the collapse or expansion of the universe (though some postulate that the collapse of the universe would lead to a reversal of the arrow of entropy). But rather in the gradual evening out of the "clumps" of mass we have wandering around in the universe.

It would make sense that complex, high energy states such as ... oooh... planets would *tend* to break up, radiate, get ripped apart etc and become space dust. It may take a lot of time but hey, the universe can wait

<opinion>
I'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...

I hate paradoxes.

DeV.

bonkey

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

DeVore

Black hole radiation is quite simple really, quatum particles are made up of two waves. Think of them as positive and negative if you like (at that level those terms have little meaning except that they are opposites).

Now think of the event horizon of the black hole. The very edge where one micron closer means being sucked in and one micron further means escape-velocity can be attained.

Now, quantum particles are hypothesised to be split into +/- waves and then collide again destroying each. This happens extremely quickly.

However think of those particles right on the edge of the evetn horizon, when they split one gets dragged into the black hole and the other wanders off with no partner to destroy itself against. Charged particles wandering around space are called radiation

When this theory was suggested, it was easy to prove. Point your telescope up at a suspected blackhole and look for these particles. What they found was what is now referred to as Hawking Radiation and it simulataneously strengthened and advanced quantum mechanics and black hole theory.

Black holes are not black at all, using this method they shine quite brightly.


JC is quite right, though, the second law doesnt have to apply at every point but must be obeyed in a closed system. 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...

DeV.

bonkey

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

MiCr0

/me goes in search of "a brief history of time"

OT: any one read hawking's new book yet?

bonkey

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

Yo Mamma

Currently it *appears* to be slowing a LOT faster then we would have expected. Scientists HATE surprises and so have postulated dark matter.

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 !

This was the recent bleak news, that our universe (as we see it with our blind stick) is getting further and further apart and will probably continue doing so until the end (whatever that may be).

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.

Then again I could (and prolly am) wrong.

bonkey

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