Exploring the End of the Universe: Thermodynamics

[Billy T]

...Hey Spock, how bout that translation please.

Not sure I am your "spock" but if you did not understand what I was saying in post 32, please ask some specific question(s) - I thought I was relatively straight forward and clear - compared to what I am like often

 

[misskitty]

We are just starting to talk about this stuff in my physics class. We haven't hit relativity yet, but we're getting there within the next week and a half or so.

I'm not sure if it was you Billy, it might be me. The electrons joining with the protons to make a neutral nucleus was ok I think. The elements above z aren't stable thing, you lost me there. The short range thing also comes into that too. Baryon diameters? I don't know what that is. Mutual repulsion of protons was confusing because I'm not sure I know where that fits into everything, especially the inverse square thing. What did you mean by protons "falling off"? Do they literally fall off of an atom that is trying to form?

What did you mean about the prevention of a black hole? There is a force in space that can prevent a black hole? I know very little about this stuff, but I do know that light can not even escape a black hole.

Anyone else who might be able to explain any of this please do! Your input would be an excellent addition to the thread.

Billy your information is great. I'm not saying it isn't. I just don't want this to turn into a thread where you and I are the only people posting. Keep posting.

 

[Janus]

We are just starting to talk about this stuff in my physics class. We haven't hit relativity yet, but we're getting there within the next week and a half or so.

I'm not sure if it was you Billy, it might be me. The electrons joining with the protons to make a neutral nucleus was ok I think. The elements above z aren't stable thing, you lost me there. The short range thing also comes into that too. Baryon diameters? I don't know what that is. Mutual repulsion of protons was confusing because I'm not sure I know where that fits into everything, especially the inverse square thing. What did you mean by protons "falling off"? Do they literally fall off of an atom that is trying to form?

Z = atomic number = number of protons in the nucleus.
Baryon diameters: Essentially the diameters of the Neutron and Proton.

Nuclei are composed of protons and neutrons. The Protons all have a postive charge thus they mutually repel each other. Something has to hold the nucleus together against this tendency to fly apart. Thus the strong force which is acts between the Neutrons and protons. This forms the nuclear "glue" that holds the nucleus together.

Now, the repulsion between the Protons "falls off" (gets weaker) by the inverseof the square of the distance. (two protons that are separated by a given distance will repel each other by 1/4 as much as two protons that are half as far apart from each other.)

The strong force, while stronger than this repulsion at short range, gets weaker a lot faster with distance. As the number of protons increase in a nucleus ( As you move up the periodic table of elements) the nuclei tend to get larger. As they get larger, it becomes harder for the strong force to "reach across" the entire width of the nucleus with enough strength to hold all the protons from flying off. The nuclei tend to become unstable and undergo radioactive decay. (There are also other reasons for radioactive decay of nuclei, such as neutron deficiency or excess in certain isotopes, etc, but that's another discussion)

 

[misskitty]

Ah, ok that makes sense. Thanks Janus.

Stupid questions for 100: Is there anyway to reduce the entropy of a substance that has reached maximum entropy? How do you do it?

 

[Nereid]

Someone else earlier said it - our understanding of cosmology is sufficiently new, and its history shows sufficiently drastic changes, that anything we think now about 100 trillion years in the future is as close to 100% wrong as to not matter!

Perhaps it's fun to look at what our current best theories say ... about the distant future, and whether there are inconsistencies? I have a soft spot for neutrinos - shall the meek inherit the universe?

 

[Billy T]

Z = atomic number = number of protons in the nucleus.
Baryon diameters: Essentially the diameters of the Neutron and Proton.

Nuclei are composed of protons and neutrons. The Protons all have a postive charge thus they mutually repel each other. Something has to hold the nucleus together against this tendency to fly apart. Thus the strong force which is acts between the Neutrons and protons. This forms the nuclear "glue" that holds the nucleus together.

Now, the repulsion between the Protons "falls off" (gets weaker) by the inverseof the square of the distance. (two protons that are separated by a given distance will repel each other by 1/4 as much as two protons that are half as far apart from each other.)

The strong force, while stronger than this repulsion at short range, gets weaker a lot faster with distance. As the number of protons increase in a nucleus ( As you move up the periodic table of elements) the nuclei tend to get larger. As they get larger, it becomes harder for the strong force to "reach across" the entire width of the nucleus with enough strength to hold all the protons from flying off. The nuclei tend to become unstable and undergo radioactive decay. (There are also other reasons for radioactive decay of nuclei, such as neutron deficiency or excess in certain isotopes, etc, but that's another discussion)

Well said. Thanks for saving me the trouble. I have been quite busy at a higher level in the thread "First Stars - how big - Black Holes now?" which has warped into another thread about small black holes evaporating away etc. Perhaps you should have also helped misskitty on her confusion:
"The elements above z aren't stable thing, you lost me there."
but I am not sure if it is about iron being the most stable or fact that few (if any) with z>100 are at all stable. The "iron is the bottom of the stability well" is very important as this is why no stellar fusion is possible even in big stars after they have fused elements with z less than iron. And why the they then implode as the still fusing layers above the core press down on the core.
"

 

[misskitty]

Billy, I understand your dilemma. A friend of mine had been involved in higher courses of study for so long he had begun to do simple steps in his head and word explanations in such a way that would confuse me because I was not well versed in that level of vocabulary yet. Its ok, not big thing.

My class mentioned the Z particle thing a few days ago. It sort of made sense, but not at the same time. It had something to do with the big bang theory and how we can get within 10^-43 seconds of the actual event.

 

[Crosson]

Stupid questions for 100: Is there anyway to reduce the entropy of a substance that has reached maximum entropy? How do you do it?

Sure, you refridgerator reduces the entropy (and with it the temperature) of your food.

It is just that the process of cooling your food makes more entropy than the food decreases by. So the net change is an increase.

 

[misskitty]

Crosson, funny you should mention a refridgerator. My latest physics test had a question asking us (the test takers) to describe how a refridgerator works and what states the refridgerant was in through every step of the process.

The ONE THING I continuously reviewed and thought about...and then moved on to the other equations and material and such...ended up MISSING an imortant step of the process. I wanted to kick myself for that! :grumpy: Probably a good thing I can't. Thank goodness for partial credit.

 

[misskitty]

By the way, if we can reduce the entropy of the refriderant and increase the entropy of the surrounding environment, can we do that to space too? I don't know if my question makes sense...

 

[moving finger]

For those of you who are disconsolate over the prospect of heat death - there's still hope:
Spontaneous Inflation and the Origin of the Arrow of Time
http://arxiv.org/abs/hep-th/0410270

I still have a problem reconciling the 2nd Law of Thermodynamics and the prospect of eternal inflation.

Briefly : The entropy of the universe tends to increase over time. This implies that the entropy at the beginning of the universe (Big Bang) should be much (much!) lower than towards the end. Carroll & Chen in the cited paper estimate that the present-day entropy is some 10^22 lower than it will be when most matter ends up in black holes, and the entropy of the early universe was probably some 10^11 lower than today. And their guesstimate for the entropy of the "proto-inflationary" universe (some 10^6 Planck lengths in size) that is supposed to have existed at the time of inflation is at least some 10^70 lower still. Even if the final state of our universe is one of increasingly rarified radiation and no black holes (which would be the case for a space containing a finite amount of mass-energy which is continually expanding), Carroll & Chen show that this is then actually the state with larger entropy.

If there is some mechanism of 'eternal inflation', what is the origin (cause) of the low entropy starting conditions each time a new universe is created?

Are we simply a statistical fluctuation?

I know Carroll & Chen go into this issue in great depth in their paper - but I haven't been able to fathom the solution to the problem yet - can anyone summarise it?

Thanks!

MF

 

[misskitty]

MF, I don't think we are just a statistical fluctuation.

I'm not sure I completely comprehend what you are getting at though. The second law of thermo makes sense to me. I'm not sure I see where you are having an issue.

 

[selfAdjoint]

Are we simply a statistical fluctuation?

I know Carroll & Chen go into this issue in great depth in their paper - but I haven't been able to fathom the solution to the problem yet - can anyone summarise it?

Thanks!

Look at section four and the beginning of section five of their paper. In section four they review Penrose's argument that in a universe with gravity and zero vacuum energy, the evolution inevitable takes you to isolated black holes. Here there are a lot of diagrams to help you follow the argument.

In section five they show that in the special but plausible deSitter case of general relativity, a slight vacuum energy, caused by a small cosmological constant, is "unstable toward inflation". Fluctuations from average behavior will tend to fall into inflation states. And they show that inflation pumps entropy into the universe, providing that arrow of time they mention. And of course this gives a sort of anthropic reason for that small cosmological constant (which has been measured from the CMB but which is regarded as a problem for theory); we see the c.c. as positive but small because that is what it had to be in order to produce the arrow of time, which in turn was necessary for the physics, chemistry, and evolution which produced us.

 

[DaveC426913]

Could absolute zero theoretically be achieved in the universe?

It's not that the universe will eventually cool to absolute zero, it's that it will reach equilibrium. Cooling can only happen when heat flows from a hotter place to a cooler place. But eventually all atoms will have the same amount of energy and there will be no further transfer.

That is, unless we account for infinite expansion. If we presume universe expands infinitely, then it will continue to cool, merely because there will be fewer atoms in any given volume of space.

 

[1123581321]

right now, we really don't know what will happen. if you are familiar with the Hubble constant/ deceleration parameter are, you will understand what will happen. the huble constant says that the universe is expanding anywhere from 50 km/s to 70 km/s per 3.2 million lightyears. (which means that every 3.2 mill lightyears, the universe is expanding 50 to 70 km/s faster than the last 3.2. the deceleration parameter measures the rate at which cosmic expansion is slowing. as far as i know, we don't know the answer to this, but if we did, we could know what the mass density of the universe is. with all of this we could determine the fate of the universe. to make things simple, all this mumbo-jumbo was condensed into 'omega'. if omega is under 1, then the universe will endlessly expand (because the expansion is too great for deceleration or something like that) and will suffer a heat death. if it is over one, the universe will suffer a big crunch, the big bang in reverse. if one, than the universe will be critical density, and i don't know what that is. I got that almost directly from the book "the big shebang", so if i am wrong, don't yell at me.

Regards,
Fabinacci

 

[misskitty]

Well, seems as though we are eventually screwed either way. Hmm, all the more reason to live life to the fullest.

 

[moving finger]

In section five they show that in the special but plausible deSitter case of general relativity, a slight vacuum energy, caused by a small cosmological constant, is "unstable toward inflation". Fluctuations from average behavior will tend to fall into inflation states. And they show that inflation pumps entropy into the universe, providing that arrow of time they mention. And of course this gives a sort of anthropic reason for that small cosmological constant (which has been measured from the CMB but which is regarded as a problem for theory); we see the c.c. as positive but small because that is what it had to be in order to produce the arrow of time, which in turn was necessary for the physics, chemistry, and evolution which produced us.

Thank you! I see it now.
I was stuck in terms of thinking of a finite phase space and coudn't get my head around how eternal inflation managed to reduce entropy at some stage - but I see my error now. Eternal inflation does not reduce entropy; the total entropy of all the "universes" created continues increasing, but the phase space of the "ensemble" of universes is unbounded, hence entropy can keep increasing without limit, even though there is a maximum possible entropy for anyone universe.

Not sure I agree that the c.c. in our universe has to be non-zero to produce an arrow of time however - I agree in the paper the non-zero c.c. is the reason why a "parent universe" might produce a "daughter universe" by spontaneous inflation, but does that necessarily mean every "daughter universe" (including ours) must therefore have a non-zero c.c.? Is the value of the c.c. carried over from parent to daughter?

MF

 

[moving finger]

if omega is under 1, then the universe will endlessly expand (because the expansion is too great for deceleration or something like that) and will suffer a heat death. if it is over one, the universe will suffer a big crunch, the big bang in reverse. if one, than the universe will be critical density, and i don't know what that is. I got that almost directly from the book "the big shebang", so if i am wrong, don't yell at me.

Regards,
Fabinacci

Not quite correct. Your interpretation is based on the "old" version which assumes a zero cosmological constant (lambda). If lambda is zero then it is only the energy density (of matter plus radiation) which determines omega, and there is then a simple relationship between omega, "flatness" and whether we expand forever or recollapse.

However if lambda is not zero (and there is mounting evidence that lambda is non-zero and positive) then there is no longer a simple relationship between omega, "flatness" and crunch/expansion.

The important parameters are the energy density of matter/radiation (rho.m), the energy density due to the vacuum (vacuum energy, rho.v), and the relationship between vacuum energy density and vacuum energy pressure (p.v).

If rho.v = -p.v (and that seems to be a likely equation of state for vacuum energy), then even a "closed" universe would expand forever if rho.m < 2 x rho.v at any time when H approaches zero; and an "open" universe would recollapse if rho.v < 0.

The conclusion is that it is mainly the vacuum energy density and equation of state, and not (as was thought in the past) geometry, which determines the ultimate fate of the universe.

For more details see http://arxiv.org/abs/astro-ph/9904020

MF

 

[Chronos]

Look at section four and the beginning of section five of their paper. In section four they review Penrose's argument that in a universe with gravity and zero vacuum energy, the evolution inevitable takes you to isolated black holes. Here there are a lot of diagrams to help you follow the argument.

In section five they show that in the special but plausible deSitter case of general relativity, a slight vacuum energy, caused by a small cosmological constant, is "unstable toward inflation". Fluctuations from average behavior will tend to fall into inflation states. And they show that inflation pumps entropy into the universe, providing that arrow of time they mention. And of course this gives a sort of anthropic reason for that small cosmological constant (which has been measured from the CMB but which is regarded as a problem for theory); we see the c.c. as positive but small because that is what it had to be in order to produce the arrow of time, which in turn was necessary for the physics, chemistry, and evolution which produced us.

Brilliant.

 

[Billy T]

Brilliant.

Please someone give clear reference to this paper/ book. If Chronos thinks it "brilliant" I want to at least look at it.

 

[misskitty]

I would like to get a look at what you are all citing as well. If that's alright. I may not comprehend it entirely, but that just means more clarification questions. I hope no one is bothered by that.

 

[moving finger]

Please someone give clear reference to this paper/ book. If Chronos thinks it "brilliant" I want to at least look at it.

Chronos did that already in this thread , it's at ;
http://arxiv.org/abs/hep-th/0410270

Chronos, selfAdjoint, could you comment on the idea that the non-zero cosmoligcal constant (c.c.) we see in our universe may be "responsible" for the arrow of time (in our universe)? (ie an anthropic explanation for the non-zero c.c.)

Does it necessarily follow that the emergence of time in our universe requires a non-zero c.c., and if so, why?

Ta

MF