Entropy and the Big Bang

[theIndigoVervet]

Hi guys,

not to put too fine a point on it, I suspect I've probably gone wrong somewhere, but I'm a curious chimp and I'd love to know where...

It seems to me that if the Big Bang shoots out energy randomly in all directions, this energy will coalesce into particles that are also moving randomly in all directions, so it would be overwhelmingly probable that the universe would start out in a high entropy state and no (or very little) work could be done because everything would be the same temperature.

However, this is obviously not the case.

Since the Second Law of Thermodynamics is a mathematical law, not a physical law (it is based on statistics in statistical mechanics), I think it should apply to the Big Bang (and any "quantum foam" or whatnot that preceded it) as well as to everything else.

Also, I don't think the Anthropic Principle and infinite universes can be invoked to explain this, because there's much more free energy around than the minimum required for us to evolve.

Is there a well-accepted explanation? Or any theories? Or is it a mystery? Or have I made some laughably simple mistake?

thanks

IV

[timo]

I don't see why "...so it would be overwhelmingly probable that the universe would start out in a high entropy state..." seems to be a contradiction to the 2nd law of thermodynamics to you. What exactly do you think the 2nd law of thermodynamics states? My first guess is that you mistake the big bang scenario for the one point where distance between any two points in space becomes zero and the theory breaks down. The big bang scenario is everything except this point. My 2nd guess is that you expect statements like "dS>=0" to trivially hold for non-equilibrium states and non-quasi-static processes. I'm absolutely no expert on non-equilibrium thermodynamics, but the assumption seems a bit naive to me.

Edited June 19, 2011 by timo

[MajorTom]

I don't think anyone reading this should write this question off (not that anyone is), it is a good one.

 

Entropy is about available energy for useful work. Increasing entropy (or loss of heat) does not always correspond to human notions of order and disorder. While related, order and disorder are separate concepts who's flow do not soley depend on entropy flow. In other words, order can increase along with entropy, but most of the time order does decrease as entropy increases. 300,000 years after the initial expansion of the BB, the CMBR reveals lower entropy than today and lots of potential usable energy. This energy has been converted over 13.7 billion years to matter and other forms of energy, increasing entropy. This is in accordance with the 2nd law of thermodynamics.

 

That may seem strange. How is it that entropy has increased, yet we now have more ordered forms like planets, stars and galaxy. Realize that this is a problem with human notions of order and disorder. What order and disorder are, are in fact much different than what human notions say they are. The formation of planets and stars are a condition of moving from order and less entropy to disorder and more entropy. The total energy of the universe was much more uniform and distributed much more evenly 300,000 years after the BB. Now when you look at the universe, the distribution of energy is inconsistent, available energy to do work has decreased and large pockets of the Universe are filled with near no usable energy.

 

The interesting part of the question, is how did the Universe start off with such low entropy and high order to begin with?

[csmyth3025]

I don't think anyone reading this should write this question off (not that anyone is), it is a good one.

 

Entropy is about available energy for useful work. Increasing entropy (or loss of heat) does not always correspond to human notions of order and disorder. While related, order and disorder are separate concepts who's flow do not soley depend on entropy flow. In other words, order can increase along with entropy, but most of the time order does decrease as entropy increases. 300,000 years after the initial expansion of the BB, the CMBR reveals lower entropy than today and lots of potential usable energy. This energy has been converted over 13.7 billion years to matter and other forms of energy, increasing entropy. This is in accordance with the 2nd law of thermodynamics.

 

That may seem strange. How is it that entropy has increased, yet we now have more ordered forms like planets, stars and galaxy. Realize that this is a problem with human notions of order and disorder. What order and disorder are, are in fact much different than what human notions say they are. The formation of planets and stars are a condition of moving from order and less entropy to disorder and more entropy. The total energy of the universe was much more uniform and distributed much more evenly 300,000 years after the BB. Now when you look at the universe, the distribution of energy is inconsistent, available energy to do work has decreased and large pockets of the Universe are filled with near no usable energy.

 

The interesting part of the question, is how did the Universe start off with such low entropy and high order to begin with?

(bold added by me for emphasis)

 

I'm not sure you have the idea of entropy quite right concerning the CMB 300,000 years after the big bang and today, 13.7 billion years later.

 

First, no energy has been converted to matter since about one trillionth of a second after the big bang, as far as I know. (ref. http://en.wikipedia....ectroweak_epoch )

 

Second, the CMB started with a temperature of about 3000^o Kelvin 300,000 years after the big bang and there were minute irregularities (anisotropies) in its distribution due, at least in part, to the distribution of matter that was already present:

 

The power spectrum of the cosmic microwave background radiation temperature anisotropy in terms of the angular scale (or Multipole moment). The data shown come from the WMAP (2006), Acbar (2004), Boomerang (2005), CBI (2004), and VSA (2004) instruments. Also shown is a theoretical model (solid line).The anisotropy of the cosmic microwave background is divided into two sorts: primary anisotropy, due to effects which occur at the last scattering surface and before; and secondary anisotropy, due to effects such as interactions of the background radiation with hot gas or gravitational potentials, which occur between the last scattering surface and the observer.

 

The structure of the cosmic microwave background anisotropies is principally determined by two effects: acoustic oscillations and diffusion damping (also called collisionless damping or Silk damping). The acoustic oscillations arise because of a competition in the photon–baryon plasma in the early universe. The pressure of the photons tends to erase anisotropies, whereas the gravitational attraction of the baryons—moving at speeds much slower than light—makes them tend to collapse to form dense haloes. These two effects compete to create acoustic oscillations which give the microwave background its characteristic peak structure. The peaks correspond, roughly, to resonances in which the photons decouple when a particular mode is at its peak amplitude.

 

The peaks contain interesting physical signatures. The angular scale of the first peak determines the curvature of the universe (but not the topology of the universe). The next peak—ratio of the odd peaks to the even peaks—determines the reduced baryon density. The third peak can be used to pull information about the dark matter density.

 

The locations of the peaks also give important information about the nature of the primordial density perturbations. There are two fundamental brands of density perturbations—called adiabatic and isocurvature. A general density perturbation is a mixture of both, and different theories that purport to explain the primordial density perturbation spectrum predict different mixtures...

(ref. http://en.wikipedia....mary_anisotropy )

 

I'm not sure what to make of your last statement (bold added). Although I agree that the entropy ("Unavailability of energy for useful work", to correct your implied definition) of the universe has increased over the last 13.7 billion years, this notion is a odds with your statement that the present distribution of energy is inconsistent. It is the inconsistent distribution of energy that makes energy available for useful work:

 

The second law of thermodynamics states that in general the total entropy of any system will not decrease other than by increasing the entropy of some other system. Hence, in a system isolated from its environment, the entropy of that system will tend not to decrease. It follows that heat will not flow from a colder body to a hotter body without the application of work (the imposition of order) to the colder body. Secondly, it is impossible for any device operating on a cycle to produce net work from a single temperature reservoir; the production of net work requires flow of heat from a hotter reservoir to a colder reservoir...

(ref. http://en.wikipedia...._thermodynamics )

 

To be sure, since the present average temperature of the CMB is now about 2.73^o Kelvin the temperature gradient available for useful work is a lot less than it was 13.7 billion years ago.

 

Chris

 

Edited to correct syntax and spelling errors

Edited June 28, 2011 by csmyth3025

[pantheory]

Entropy: A thermodynamic quantity representing the unavailability of a system's thermal energy for conversion into mechanical work.

 

In the universe entropy accordingly increases with time. Entropy: Lack of order or predictability; gradual decline into disorder.

 

From the extreme order following the Big Bang to the extreme homogeneity and disorder of galaxies, clusters, life, humans, etc. disorder today. The theory concerning increasing entropy in the universe over time makes total sense to me, NOT!

Edited June 30, 2011 by pantheory

[csmyth3025]

Entropy: A thermodynamic quantity representing the unavailability of a system's thermal energy for conversion into mechanical work.

 

In the universe entropy accordingly increases with time. Entropy: Lack of order or predictability; gradual decline into disorder.

 

From the extreme order following the Big Bang to the extreme homogeneity and disorder of galaxies, clusters, life, humans, etc. disorder today. The theory concerning increasing entropy in the universe over time makes total sense to me, NOT!

(bold added by me)

 

It seems odd that galaxies can be described as being both extremely homogenous and extremely disordered in the same sentence. It sounds a bit self-contradictory. In the context of entropy, though, homgenous and disordered have essentially the same meaning as far as I know.

 

Although the early universe was, indeed, extremely homogenous, it still had fluctuations in its temperature as I mentioned in my previous post. Additionally, the matter in the universe possessed a lot of potential energy that could then be converted into kinetic energy as it clumped together. This is essentially what happened in order to form galaxies, stars, planets and ourselves. Each step in the process that results in a more ordered state (locally) is at the expenditure of energy that is globally less available to do work.

 

Eventually, all the matter in the universe that is gravitationally bound to other matter will clump together and attain a minimal energy state. At the same time, all the kinetic energy released by the clumping of matter - as well as the ambient flux of radiation - will become both more widely dispersed and more evenly distributed. At some point way in the future the unavailability of energy to do work (entropy) will reach its maximum level because:

 

...it is impossible for any device operating on a cycle to produce net work from a single temperature reservoir; the production of net work requires flow of heat from a hotter reservoir to a colder reservoir...

(ref. http://en.wikipedia...._thermodynamics )

 

Chris

 

Edited to correct mis-statement in the first paragraph.

Edited June 30, 2011 by csmyth3025

[MigL]

Forget order and disorder as those are human ideas, look at it instead, in terms of an increase or decrease of degrees of freedom. Bound states obviously have less degrees of freedom and are therefore more ordered.

[pantheory]

csmythe3025,

 

Good over-all answer Chris. Even with my best mainstream-perspective "insights" I don't believe I could have done very well concerning a non-frivolous explanation By being a little flippant in my posting I was trying to show how the second law of thermodynamics does not seem to fit with the standard model of cosmology, in my opinion. And it appears the O.P. also has a problem with a connection. Gravity for one thing and evolution for another, seem to work contrary to the second law.

 

If they are not congruent/ consistent with each other, implying maybe one is correct and the other is wrong, which one would you want to bet on?

 

`if your theory is ... against the second law of thermodynamics ... there is nothing for it but to collapse in deepest humiliation' (Eddington)

 

I think most realize that there are no guarantees that either the standard model of cosmology is correct, or that the second law of thermodynamics (including increasing entropy) should apply in its present wording, to the universe as a whole.

Edited June 30, 2011 by pantheory

[csmyth3025]

csmythe3025,

 

...I was trying to show how the second law of thermodynamics does not seem to fit with the standard model of cosmology, in my opinion. And it appears the O.P. also has a problem with a connection. Gravity for one thing and evolution for another, seem to work contrary to the second law.

 

If they are not congruent/ consistent with each other, implying maybe one is correct and the other is wrong, which one would you want to bet on?

 

`if your theory is ... against the second law of thermodynamics ... there is nothing for it but to collapse in deepest humiliation' (Eddington)

 

I think most realize that there are no guarantees that either the standard model of cosmology is correct, or that the second law of thermodynamics (including increasing entropy) should apply in its present wording, to the universe as a whole.

A more complete rendering of Sir Arthur Eddington's comment:

The practical measure of the random element which can increase in the universe but can never decrease is called entropy. Measuring by entropy is the same as measuring by the chance explained in the last paragraph, only the unmanageably large numbers are transformed (by a simple formula) into a more convenient scale of reckoning. Entropy continually increases. We can, by isolating parts of the world and postulating rather idealised conditions in our problems, arrest the increase, but we cannot turn it into a decrease. That would involve something much worse than a violation of an ordinary law of Nature, namely, an improbable coincidence. The law that entropy always increases-the second law of thermodynamics-holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations-then so much the worse for Maxwell's equations. If it is found to be contradicted by observation-well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.

(ref: Eddington, A.S., "The Nature of the Physical World," [1928], The Gifford Lectures 1927, Cambridge University Press: Cambridge UK, 1933, reprint, pp.74-75. )

 

The question of whether the concepts of entropy and evolution are compatible or contradictory is probably best addressed in a separate thread. It's one of those "hot button" topics that will no doubt draw more opinions than logical arguments .

 

The "purely scientific" questions of whether the standard cosmological model and/or our current theory of gravity (general relativity) conflict with the second law of thermodynamics is an interesting one.

 

I'm certainly no expert, but I'm thinking that the entropy of a closed system (in this case, the universe) increases over time not only due to the flow of heat from warmer regions to cooler regions, but also due to the flow of mass from areas of higher gravitational potential energy to areas of lower gravitational energy.

 

I'll limit my reply to this observation for now. I'll have to think about this for a while. Perhaps a more knowledgeable member can respond more completely.

 

Chris

[pantheory]

csmythe3025,

 

....I'm thinking that the entropy of a closed system (in this case, the universe) increases over time not only due to the flow of heat from warmer regions to cooler regions,

 

... but also due to the flow of mass from areas of higher gravitational potential energy to areas of lower gravitational energy.

I agree that your understanding of the flow of mass is in line with the meaning of entropy concerning gravitational flow but not what has happened concerning the evolution of the universe in my opinion, no matter what cosmological model one adheres to.

 

I'll limit my reply to this observation for now. I'll have to think about this for a while. Perhaps a more knowledgeable member can respond more completely.

That's why I like talking with you Chris. Logic is an important constituent in your postings. To me logic trumps everything else providing the logic is good enough A "more knowledgeable member" might provide better insight for some, but for me logic alone is gold such as I perceive the best of your logic is You have my ear.

Edited July 1, 2011 by pantheory

[IM Egdall]

There is an excellent discussion of this entropy/cosmology issue in Brian Greene's book, The Fabric of the Cosmos. And it is in plain English.

 

He says that the universe began in a highly ordered (low entropy) state, and this state was highly unlikely. The entropy (disorder) of the universe has been increasing ever since.

 

He goes on to say this highly ordered state came from inflation. As the inflation field slid down to lower energy, it relinquished pent-up energy, producing about 10^^80 particles of matter and radiation, resulting in a huge amount of entropy. Ever since the end of inflation, entropy has continued to increase due to the effects of gravity.

 

OK, so my question is: where did this inflation come from? And what was the entropy of the universe before inflation? And does this violate the second law of thermodynamic? Unfortunately, I don't think anyone has an answer for these questions outside of speculation. Perhaps a new quantum gravity theory will shed more light on this issue.

Edited July 1, 2011 by I ME

[pantheory]

I ME,

 

OK, so my question is: where did this inflation come from? And what was the entropy of the universe before inflation? And does this violate the second law of thermodynamic? Unfortunately, I don't think anyone has an answer for these questions outside of speculation. Perhaps a new quantum gravity theory will shed more light on this issue.

There are hypothesis that address these questions; some might be considered mainstream and others not. Non-mainstream theorists also consider the mainstream to be nothing more than speculation. There may be a true answer for such questions but maybe not within the mainstream arena of speculation. Brian Green's applicable speculations are considered mainstream hypothesis.

Edited July 1, 2011 by pantheory

[MajorTom]

(bold added by me for emphasis)

 

 

I'm not sure you have the idea of entropy quite right concerning the CMB 300,000 years after the big bang and today, 13.7 billion years later.

 

 

First, no energy has been converted to matter since about one trillionth of a second after the big bang, as far as I know. (ref. http://en.wikipedia....ectroweak_epoch )

 

 

If you read carefully you'll notice I said over 13.7 billion years. I included energy to matter conversion in the "over 13.7 billion years", not because it has happened over all of that amount of time, but because it was easier to lump it in without being specific. I do realize that NEARLY all energy to matter conversion happened very early on.

 

I say nearly because all is not accurate, to my knowledge. Particle accelerators have created other forms of matter, although that matter does not contribute in any practical measurable way to total entropy of the Universe. Other places in the Universe where conditions are similar to that of partical accelerators here on Earth could also produce new forms of matter. Also, and someone correct me if I'm incorrect here, but I do believe that very small amounts of matter do get created from energy at the event horizon of black holes. I have not had time to look this up and verify it. So someone feel free to correct this or verify it if you wish.

 

But that's all really beside the point.

 

 

Second, the CMB started with a temperature of about 3000o Kelvin 300,000 years after the big bang and there were minute irregularities (anisotropies) in its

distribution due, at least in part, to the distribution of matter that was already present:

 

 

I'm not sure what you're getting at here in terms of how this applies to my response.

 

 

I'm not sure what to make of your last statement (bold added). Although I agree that the entropy ("Unavailability of energy for useful work", to correct your implied definition)

 

 

Thank you for clarifying the "implied" definition. But I'm not sure there is a difference between saying:

 

 

"availability of energy to do work has decreased" (work should be assumed to be "useful" if it has any affect, not sure there's any reason to speficy that)

 

 

or

 

 

"unavailability of energy to do work has increased"

 

 

In the context of the discussion, it's saying the same thing. If I'm wrong here, please enlighten me as to why.

 

 

Although I agree that the entropy of the universe has increased over the last 13.7 billion years, this notion is a odds with your statement that the present distribution of energy is inconsistent. It is the inconsistent distribution of energy that makes energy available for useful work:

 

 

I'm not sure I understand this, could you explain in more detail?

 

 

I'm not so sure we disagree here, I think we may actually be on the same page but I may not have explained myself well. It all depends on what you mean by this. Please explain in more detail if you don't mind. Thanks.

Edited July 2, 2011 by MajorTom

[csmyth3025]

csmyth3025,

 

...I agree that your understanding of the flow of mass is in line with the meaning of entropy concerning gravitational flow but not what has happened concerning the evolution of the universe in my opinion, no matter what cosmological model one adheres to...

The role of gravity (and the consequent flow of mass) in the universe is something about which I'm still working to understand. The role that gravity played in upsetting the thermal equilibrium of the very early universe is well described in the following excerpt:

 

Up until this time, the constant interaction between photons and matter had kept the temperature of the universe quite uniform. But when the radiation decoupled, it did more than create atoms and clear up the view-it also marked a turning point. The universe had departed from thermal equilibrium. Ever since the radiation era had begun, the universe had been dominated by electromagnetism, in the form of the sea of photons. Now electromagnetism took a back seat, and gravity, the weakest force, took over. The most important processes would now be caused by the gravitational attraction of matter. In Volume I we talked about the preoccupation at the turn of the 20th century with the heat death of the universe; an imagined time when everything has fallen into thermal equilibrium and no useful work can be done. It's debatable whether such a thing will ever happen in the future, but in a way, it already happened in the past. For hundreds of thousands of years after the Big Bang, the universe was indeed in a state of thermal equilibrium. It was a bit like an early, scorching version of the heat death.

 

What changed? If thermal equilibrium is an absence of useful potential energy, where did the potential come from? It came from the expansion of the universe. As the universe expanded, it stretched out the photons until they couldn't keep the universe in equilibrium. It had been a temporary, high-energy equilibrium, not a terminal, lowest-energy one, because of the potential energy of expansion. Once the photons decoupled, this allowed the potential of the electromagnetic attraction between electrons and photons to go to work, snapping together the first atoms. After that happened, the electromagnetic potential was mostly used up, because the positive and negative forces more or less balanced each other.

 

This let the universe go further out of equilibrium, as gravity took over. Gravity may be weak, but it only works in one direction - it is always attractive, which means it can never cancel itself out like electric charge can. Gravity thus tends to work against equilibrium. It causes matter to clump, not to spread out evenly. From our perspective this is vital. As users of potential energy, we ultimately live on gravity. Gravity eventually caused matter to clump, sometimes into stars. When this happened, the potential energy of gravity compressed stars enough to liberate the energy of mass in fusion reactions. Not only did this create the elements we're made of, but it also provided the source of energy we live on - the energy of hot starlight, radiated into cold space. Our star, the sun, is so much hotter than the space around it that it is an enormous source of potential energy, one that will last for 5000 million more years. And ultimately, it's fueled by the energy of gravity.

 

This complicates the simple interpretation of the second law of thermodynamics; that entropy and disorder will always increase as the universe moves toward equilibrium. Gravity tends to pull the universe away from equilibrium, and today scientists are not quite sure what this means for entropy on the largest scales of space and time. Gravity may modify the second law, or it may just hold it at bay for a while. We are not quite sure which. Maybe a quantum theory of gravity will help answer this question. In any case, matter and gravity had taken the reins from the photons...

(ref. http://www.knowledge...eginningweb.htm )

 

By the way, the home site of which this article on the early universe is just one part is a very comprehensive and interesitng collection of articles about natural science and history. Although I can't be sure of the technical correctness of Ross Mays' description as cited above (he has a Masters degree in Psychology), it seems to conform to other descriptions of the standard big bang model of cosmology that I've read.

 

Chris

 

There is an excellent discussion of this entropy/cosmology issue in Brian Greene's book, The Fabric of the Cosmos. And it is in plain English.

 

He says that the universe began in a highly ordered (low entropy) state, and this state was highly unlikely. The entropy (disorder) of the universe has been increasing ever since.

 

He goes on to say this highly ordered state came from inflation. As the inflation field slid down to lower energy, it relinquished pent-up energy, producing about 10^^80 particles of matter and radiation, resulting in a huge amount of entropy. Ever since the end of inflation, entropy has continued to increase due to the effects of gravity.

 

OK, so my question is: where did this inflation come from? And what was the entropy of the universe before inflation? And does this violate the second law of thermodynamic? Unfortunately, I don't think anyone has an answer for these questions outside of speculation. Perhaps a new quantum gravity theory will shed more light on this issue.

From what I've read most cosmologists agree that the requiste pre-inflationary conditions are high temperature and (to resolve the "flatness problem") an almost perfectly uniform density - within 1 part in 10⁶⁰ according to John Gribbin's "Inflation for Beginners" (ref. http://www.lifesci.s...ibbin/cosmo.htm ). Additionally, inflationary theory in big bang cosmology requires that the pre-inflationary universe was in thermal equilibrium (a state of maximum entropy) in order to explain the "horizon problem":

 

If correct, inflation solves the horizon problem by suggesting that prior to the inflationary period the entire universe was causally connected, and it was during this period that the physical properties evened out. Inflation then expanded it rapidly, freezing in these properties all over the sky; at this point the universe would be forced to be almost perfectly homogeneous, as the information needed to change it from that state was no longer causally connected...

(ref. http://en.wikipedia....oblem#Inflation )

(bold added by me)

 

As I understand it, this period of thermal equilibrium essentially ended about 380,000 years after the big bang when the temperature of the universe was low enough for neutral atoms to form and for photons to decouple from the preceding "fog" of plasma.

 

If my understanding of these concepts is correct then it would seem the the universe must have started with very high entropy even prior to inflation. As the excerpt in my post #14 indicates, gravity seems to have reversed this situation. I'm still trying to figure out how all this ties in with the second law of thermodynamics. It may be that the combined effects of the (global) expansion of the universe and the (local) movement of matter from large regions of higher gravitational potential energy to small regions of lower gravitaional potential energy may in some way "balance the books".

 

Any help from the experts out there is welcome.

 

Chris

 

csmyth3025, on 28 June 2011 - 02:08 AM, said:

Although I agree that the entropy of the universe has increased over the last 13.7 billion years, this notion is a odds with your statement that the present distribution of energy is inconsistent. It is the inconsistent distribution of energy that makes energy available for useful work...

 

I'm not sure I understand this, could you explain in more detail?

 

 

I'm not so sure we disagree here, I think we may actually be on the same page but I may not have explained myself well. It all depends on what you mean by this. Please explain in more detail if you don't mind. Thanks.

If the distribution of energy is consistent (homogenous), then there is essentially a single temperature reservoir:

 

...it is impossible for any device operating on a cycle to produce net work from a single temperature reservoir; the production of net work requires flow of heat from a hotter reservoir to a colder reservoir...

(ref. http://en.wikipedia...._thermodynamics )

 

If the entropy of the universe has increased over time, it seems to me that the present distribution of energy (albeit inconsistent) would have to be less inconsistent than it was in the past.

 

Chris

[pantheory]

I agree Chris,

 

Your quotation seems like a good summary according to the standard model perspective. I showed my skepticism because I am skeptical concerning the standard L CDM model or any BB version for that matter. The OP question involves increasing entropy over time and is based, I believe, upon theory alone and has no observational basis which I believe adds to his and others questioning of such cosmological interpretations which require increasing entropy over time.

 

regards Forrest

Edited July 3, 2011 by pantheory

[IM Egdall]

I agree Chris,

 

Your quotation seems like a good summary according to the standard model perspective. I showed my skepticism because I am skeptical concerning the standard L CDM model or any BB version for that matter. The OP question involves increasing entropy over time and is based, I believe, upon theory alone and has no observational basis which I believe adds to his and others questioning of such cosmological interpretations which require increasing entropy over time.

 

regards Forrest

 

I believe Chris said "From what I've read most cosmologists agree that the requiste pre-inflationary conditions are high temperature and (to resolve the "flatness problem") an almost perfectly uniform density ."

 

I think this is not quite right. I beleive the almost perfectly uniform density of the universe is a result of inflation, not a pre-inflationary condition.

[pantheory]

I believe Chris said "From what I've read most cosmologists agree that the requiste pre-inflationary conditions are high temperature and (to resolve the "flatness problem") an almost perfectly uniform density ."

 

I think this is not quite right. I believe the almost perfectly uniform density of the universe is a result of inflation, not a pre-inflationary condition.

(bold added)

 

According to BB models in general, the observable universe should not be uniform in density. For observing most of it we must look back in time. In an expanding universe model (expanding distances between galaxies) the universe should have been eight times more dense 7 billion years ago (the volume of a sphere pi x r^3). As you said the universe appears to be of a uniform density no matter how far back in time we look, which I also think is what we have observed. The direct implication, I believe, is that the universe may not be expanding at all, which would also explain contradictions of entropy as questioned by the O.P. If so there would be a different reason for the observed redshifts.

 

There does seem to be a contradiction IMO concerning continuously increasing entropy, the standard model, and what is being observed. If the universe is not expanding then gravity could seemingly keep pace with entropy to accordingly find the equilibrium that we may be now observing.

Edited July 3, 2011 by pantheory

[csmyth3025]

I ME, on 3 July 2011 - 09:16 AM, said:

I believe Chris said "From what I've read most cosmologists agree that the requisite pre-inflationary conditions are high temperature and (to resolve the "flatness problem") an almost perfectly uniform density ."

 

I think this is not quite right. I believe the almost perfectly uniform density of the universe is a result of inflation, not a pre-inflationary condition.

(bold added)

 

According to BB models in general, the observable universe should not be uniform in density. For observing most of it we must look back in time. In an expanding universe model (expanding distances between galaxies) the universe should have been eight times more dense 7 billion years ago (the volume of a sphere pi x r^3). As you said the universe appears to be of a uniform density no matter how far back in time we look, which I also think is what we have observed. The direct implication, I believe, is that the universe may not be expanding at all, which would also explain contradictions of entropy as questioned by the O.P. If so there would be a different reason for the observed redshifts.

 

There does seem to be a contradiction IMO concerning continuously increasing entropy, the standard model, and what is being observed. If the universe is not expanding then gravity could seemingly keep pace with entropy to accordingly find the equilibrium that we may be now observing.

First, I apologize for my lengthy post #14. I submitted three separate replies (to pantheory, I Me and MajorTom). For some reason these separate replies appear in the same post.

 

Regarding the earliest time during which the universe must have been in thermal equilibrium, I repeat that this state of thermal equilibrium must have existed prior to the inflationary epoch:

 

If correct, inflation solves the horizon problem by suggesting that prior to the inflationary period the entire universe was causally connected, and it was during this period that the physical properties evened out. Inflation then expanded it rapidly, freezing in these properties all over the sky; at this point the universe would be forced to be almost perfectly homogeneous, as the information needed to change it from that state was no longer causally connected...

(ref. http://en.wikipedia....oblem#Inflation )

(bold added by me)

 

I Me is correct that the process of inflation resolves the flatness problem and that flatness is not a pre-condition. In fact, one of the reasons that inflationary theory has been incorporated in the standard model is that it eliminates the need for flatness as an initial condition of the universe.

 

I mistakenly related the flatness problem to the pre-inflationary universe's distribution of matter and energy. Rather, the almost perfectly uniform density of the pre-inflationary universe is required to explain the large scale homogeneity and isotropy observed in the universe today:

 

All of these problems would be resolved if something gave the Universe a violent outward push (in effect, acting like anti-gravity) when it was still about a Planck length in size. Such a small region of space would be too tiny, initially, to contain irregularities, so it would start off homogeneous and isotropic. There would have been plenty of time for signals traveling at the speed of light to have criss-crossed the ridiculously tiny volume, so there is no horizon problem -- both sides of the embryonic universe are "aware" of each other. And spacetime itself gets flattened by the expansion, in much the same way that the wrinkly surface of a prune becomes a smooth, flat surface when the prune is placed in water and swells up. As in the standard Big Bang model, we can still think of the Universe as like the skin of an expanding balloon, but now we have to think of it as an absolutely enormous balloon that was hugely inflated during the first split second of its existence.

(ref. http://www.lifesci.s...ibbin/cosmo.htm )

 

It's my understanding that the BB model is based on the assumption that the universe is homogeneous and isotropic (the cosmological principle). It's true that the universe today is larger and that matter and energy are more spread out now than they were 7 billion years ago. But for each slice of time in the past that we examine, observations indicate that "...the universe appears to be of a uniform density no matter how far back in time we look..." A lengthy (but pretty thorough) explanation relating the standard model with what is being observed can be found here:

 

Science and Reason: The Big Bang

 

Chris

 

Edited to correct syntax error

Edited July 4, 2011 by csmyth3025

[pantheory]

csmyth3025,

 

It's my understanding that the BB model is based on the assumption that the universe is homogeneous and isotropic (the cosmological principle). It's true that the universe today is larger and that matter and energy are more spread out now than they were 7 billion years ago. But for each slice of time in the past that we examine, observations indicate that "...the universe appears to be of a uniform density no matter how far back in time we look..." A lengthy (but pretty thorough) explanation relating the standard model with what is being observed can be found here:

Yeah, Chris, I think that all agree that the universe has uniform density in any particular time frame. But from any perspective in the observable universe you should be able to progressively look back in time with a large telescope and "watch" an "expanding universe" (expanding space between galaxies), the universe becoming progressively more dense. To do so you observe a galaxy panning across its diameter, lets say .03 arcseconds, then you would pan the entire volume diameter being observed in the same focus relative to .03 arcseconds. There should be more galaxies per volume of what is being observed than in the present time according to an expanding universe model (expanding distances between galaxies). Instead what we see is generally the same density in the distant universe as we see locally. What we see is that no matter how distant we look the universe seems to be of the same density that we can see in our local neighborhood which seems totally contrary to the BB model. This problem with the standard model is rarely discussed but when it is, the explanations seem totally contrived and unconvincing.

 

If we did see decreasing density going forward in time we could infer increasing entropy based upon observations rather than just theory; since we accordingly do not it may imply that gravity is keeping pace with entropy in a Steady State (SS) universe, but with no particular SS model in mind. The problem, if it exists, is with any expanding universe model, not just BB models. Such a SS model would not include an expanding universe as Hoyle's models do. Such a model must explain redshifts in a logical/ understandable way, as being caused by another reason than an expanding universe and preferably one where there is evidence to support an expanding universe other than just the observed redshifts themselves which is the only evidence that I know of for proposing an expanding universe or increasing entropy.

Edited July 4, 2011 by pantheory

[csmyth3025]

csmyth3025,

 

 

Yeah, Chris, I think that all agree that the universe has uniform density in any particular time frame. But from any perspective in the observable universe you should be able to progressively look back in time with a large telescope and "watch" an "expanding universe" (expanding space between galaxies), the universe becoming progressively more dense. To do so you observe a galaxy panning across its diameter, lets say .03 arcseconds, then you would pan the entire volume diameter being observed in the same focus relative to .03 arcseconds. There should be more galaxies per volume of what is being observed than in the present time according to an expanding universe model (expanding distances between galaxies). Instead what we see is generally the same density in the distant universe as we see locally. What we see is that no matter how distant we look the universe seems to be of the same density that we can see in our local neighborhood which seems totally contrary to the BB model...

I'll try to respond to the remainder of your post in a separate reply. Concerning the portion cited above, cosmologist Ned Wright offers the following:

 

 

The Steady State model makes some definite predictions. The first one to be tested involved the number of faint radio sources. In the 1950's astronomers found that radio sources were typically much more distant than typical optical galaxies, so modifications to the usual source count law due to cosmology were expected. For the standard Big Bang model the counts were expected to fall below the usual "8 times more sources for 4 times fainter limit" law by an amount given approximately by 1/(1+z)⁴ where z is the redshift of the sources. This law assumes that radio sources are conserved, so a given section of the Universe has the same number of radio sources at all times. Because the volume of the section was smaller by a factor of (1+z)³ at early times, the actual density of radio sources was higher by a factor of (1+z)³. The density was constant in the Steady State model, of course, so the count correction factor would be given by 1/(1+z)⁷. The diagram below shows what was expected and actually seen:

The Big Bang should have a deficit of faint sources, the Steady State should have an even bigger deficit, but the observations showed a surplus of faint sources. The Steady State model has no adjustable parameters to correct for this error, but the Big Bang does. The assumption of conserved radio sources (CRS) can be dropped in favor of an excess of radio sources 1-3 Gyr after the Big Bang. Thus the Steady State failed the radio source count test, while the Big Bang passed by "winning ugly" - introducing a new parameter to describe a new datum. See Maran's review of Hoyle's book, Galaxies, Nuclei, and Quasars. Maran describes the birth and death of the Steady State theory without reference to the microwave background.

(ref. Errors in the Steady State and Quasi-SS Models )

 

The entire article covers other aspects of the differences between what the steady state model (and the revised quasi-steady state model) predict and what is observed.

 

Chris

[pantheory]

Thanks Chris, nice article and explanations.

 

Both the SS model and the QSS model involve an expanding universe just like the BB models do. I was talking about a SS model that does not include the expansion of the universe which could imply an explanation concerning the O.P. question(s) of entropy and why entropy may not be a big player in the universe as a whole.

 

Any further detail/ discussion of such a model would seemingly diverge from the O.P.'s quandary and my attempt at humor in posting #5.

Edited July 5, 2011 by pantheory

[csmyth3025]

Thanks Chris, nice article and explanations.

 

Both the SS model and the QSS model involve an expanding universe just like the BB models do. I was talking about a SS model that does not include the expansion of the universe which could imply an explanation concerning the O.P. question(s) of entropy and why entropy may not be a big player in the universe as a whole.

 

Any further detail/ discussion of such a model would seemingly diverge from the O.P.'s quandary and my attempt at humor in posting #5.

Any model of the evolution of the universe that doesn't include the expansion of the universe is going to be problematic. Observations that distant galaxies seem to be rushing away from each other have been noted since before 1917:

 

Edwin Hubble was generally incorrectly credited with discovering the redshift of galaxies; these measurements and their significance were understood before 1917 by James Edward Keeler (Lick & Allegheny), Vesto Melvin Slipher (Lowell), and William Wallace Campbell (Lick) at other observatories.

 

Combining his own measurements of galaxy distances with Vesto Slipher's measurements of the redshifts associated with the galaxies, Hubble and Milton Humason discovered a rough proportionality of the objects' distances with their redshifts. This redshift-distance correlation, nowadays termed Hubble's law, was formulated by Hubble and Humason in 1929 and became the basis for the modern model of the expanding universe.

(ref. http://en.wikipedia....i/Vesto_Slipher )

 

 

 

In this century there have been studies conducted using three separate instruments that have confirmed the recessional velocity of distant galaxies and refined the value of the Hubble constant:

 

Using Hubble space telescope data

The Hubble Key Project (led by Dr. Wendy L. Freedman, Carnegie Observatories) used the Hubble space telescope to establish the most precise optical determination in May 2001 of 72 ± 8 (km/s)/Mpc, consistent with a measurement of H₀ based upon Sunyaev-Zel'dovich effect observations of many galaxy clusters having a similar accuracy.

 

 

Using WMAP data

The most precise cosmic microwave background radiation determinations were 71 ± 4 (km/s)/Mpc, by WMAP in 2003, and 70.4 +1.5

−1.6 (km/s)/Mpc, for measurements up to 2006. The five year release from WMAP in 2008 found 71.9 +2.6

−2.7 (km/s)/Mpc using WMAP-only data and 70.1 ± 1.3 (km/s)/Mpc when data from other studies was incorporated, while the seven year release in 2010 found H₀ = 71.0 ± 2.5 (km/s)/Mpc using WMAP-only data and H₀ = 70.4 +1.3

−1.4 (km/s)/Mpc when data from other studies was incorporated.

 

These values arise from fitting a combination of WMAP and other cosmological data to the simplest version of the ΛCDM model. If the data is fitted with more general versions, H₀ tends to be smaller and more uncertain: typically around 67 ± 4 (km/s)/Mpc although some models allow values near 63 (km/s)/Mpc.

 

 

Using Chandra X-ray Observatory data

In August 2006, using NASA's Chandra X-ray Observatory, a team from NASA's Marshall Space Flight Center (MSFC) found the Hubble constant to be 77 (km/s)/Mpc, with an uncertainty of about 15%. The consistency of the measurements from all these methods lends support to both the measured value of H₀ and the ΛCDM model.

 

 

(ref. http://en.wikipedia....Hubble_constant )

 

As far as I know, tired light as first proposed by Fritz Zwicky in 1929 is the only proposed hypothesis claiming to explain the observed cosmological red shift while allowing for a non-expanding universe.

 

"...Despite periodic re-examination of the concept, tired light has not been supported by observational tests..."

(ref. http://en.wikipedia....iki/Tired_light )

 

Regarding the OP's quandary: "...It seems to me that if the Big Bang shoots out energy randomly in all directions, this energy will coalesce into particles that are also moving randomly in all directions, so it would be overwhelmingly probable that the universe would start out in a high entropy state and no (or very little) work could be done because everything would be the same temperature...", he seems to be thinking of the big bang as a physical explosion from some central point that "...shoots out energy randomly in all directions..."

 

As has been stated many times in this and other threads, the big bang was characterized by the uniform expansion of the space between every particle and every other particle throughout the universe. The universe itself expanded and carried all the particles it contained along with it. This expansion simply "stretched" the distance between every adjacent particle uniformly to accommodate the increasing volume.

 

The Op's claim of initial high entropy in the universe is, in my mind, only partially correct. For the first 380,000 years or so the observable universe at that time was in thermal equilibrium. Radiation kept the particles (electrons,protons and helium nuclei, mostly) at a uniform (but constantly falling) temperature as the universe expanded. Even at this time, though, there were gravity "wells" - perhaps as a result of dark matter - that tended to concentrate matter. The observed CMB anisotropies bear witness to these early precursors to the structure we see in the universe today. At this stage one might imagine that the "stuff" of the universe was balanced between the outward pressure of radiation and the inward pull of gravity - similar to the way our sun is also balanced between these competing forces.

 

Once recombination allowed photons to decouple from the preceding "fog" of ions, gravity could then take hold and start clumping the matter particles together - converting gravitational potential energy into kinetic energy. The rest, as they say, is history.

 

The high state of entropy that the OP attributes to the early universe was a sort of pseudo-entropy. It could only exist for as long as the temperature of the universe remained high enough to sustain the ionic "fog" that allowed the radiation of the early universe to keep matter particles in thermal equilibrium.

 

Chris

[pantheory]

csmyth3025,

Any model of the evolution of the universe that doesn't include the expansion of the universe is going to be problematic. Observations that distant galaxies seem to be rushing away from each other have been noted since before 1917:

 

(ref. http://en.wikipedia....i/Vesto_Slipher )

 

In this century there have been studies conducted using three separate instruments that have confirmed the recessional velocity of distant galaxies and refined the value of the Hubble constant :

 

(ref. http://en.wikipedia....Hubble_constant )

 

Chris, the Hubble constant is no longer thought to be a constant. Instead it is thought to be a variable according to the Dark Energy hypothesis. These instruments can only observe redshifts. Only by inference is a recession velocity suggested. They can correlate distances with redshifts but the idea that redshifts are related to a recession velocity is assumed. There is no evidence (that I know of) to this effect.

 

As far as I know, tired light as first proposed by Fritz Zwicky in 1929 is the only proposed hypothesis claiming to explain the observed cosmological red shift while allowing for a non-expanding universe.

 

"...Despite periodic re-examination of the concept, tired light has not been supported by observational tests..."

(ref. http://en.wikipedia....iki/Tired_light )

 

Tired light is primarily contradicted by the time dilation of supernova. For this reason few presently accept the tired light hypothesis including me. However I believe there is another explanation that I won't discuss here. If you Google "alternative theories explaining galactic redshifts" you will find a number of hypothesis. Mine is probably one of them although probably deep in the pile

 

Regarding the OP's quandary: "...It seems to me that if the Big Bang shoots out energy randomly in all directions, this energy will coalesce into particles that are also moving randomly in all directions, so it would be overwhelmingly probable that the universe would start out in a high entropy state and no (or very little) work could be done because everything would be the same temperature...", he seems to be thinking of the big bang as a physical explosion from some central point that "...shoots out energy randomly in all directions..."

 

As has been stated many times in this and other threads, the big bang was characterized by the uniform expansion of the space between every particle and every other particle throughout the universe. The universe itself expanded and carried all the particles it contained along with it. This expansion simply "stretched" the distance between every adjacent particle uniformly to accommodate the increasing volume.

I agree yours is a good description according to the standard model, concerning its beginning stages and expansion in general.

 

The Op's claim of initial high entropy in the universe is, in my mind, only partially correct.

I also agree this may not be a good theoretical characterization of the initial conditions.

 

For the first 380,000 years or so the observable universe at that time was in thermal equilibrium. Radiation kept the particles (electrons,protons and helium nuclei, mostly) at a uniform (but constantly falling) temperature as the universe expanded. Even at this time, though, there were gravity "wells" - perhaps as a result of dark matter - that tended to concentrate matter. The observed CMB anisotropies bear witness to these early precursors to the structure we see in the universe today. At this stage one might imagine that the "stuff" of the universe was balanced between the outward pressure of radiation and the inward pull of gravity - similar to the way our sun is also balanced between these competing forces.

 

Once recombination allowed photons to decouple from the preceding "fog" of ions, gravity could then take hold and start clumping the matter particles together - converting gravitational potential energy into kinetic energy. The rest, as they say, is history.

 

The high state of entropy that the OP attributes to the early universe was a sort of pseudo-entropy. It could only exist for as long as the temperature of the universe remained high enough to sustain the ionic "fog" that allowed the radiation of the early universe to keep matter particles in thermal equilibrium.

I also think your theoretical characterizations seem accurate and reasonable. My own related theories are contrary to the standard model and belong in the Speculations forum if you wish to visit me there where presently I have an open thread.

Edited July 6, 2011 by pantheory

[BJC]

csmyth3025,

 

 

Yeah, Chris, I think that all agree that the universe has uniform density in any particular time frame. But from any perspective in the observable universe you should be able to progressively look back in time with a large telescope and "watch" an "expanding universe" (expanding space between galaxies), the universe becoming progressively more dense. To do so you observe a galaxy panning across its diameter, lets say .03 arcseconds, then you would pan the entire volume diameter being observed in the same focus relative to .03 arcseconds. There should be more galaxies per volume of what is being observed than in the present time according to an expanding universe model (expanding distances between galaxies). Instead what we see is generally the same density in the distant universe as we see locally. What we see is that no matter how distant we look the universe seems to be of the same density that we can see in our local neighborhood which seems totally contrary to the BB model. This problem with the standard model is rarely discussed but when it is, the explanations seem totally contrived and unconvincing.

 

If we did see decreasing density going forward in time we could infer increasing entropy based upon observations rather than just theory; since we accordingly do not it may imply that gravity is keeping pace with entropy in a Steady State (SS) universe, but with no particular SS model in mind. The problem, if it exists, is with any expanding universe model, not just BB models. Such a SS model would not include an expanding universe as Hoyle's models do. Such a model must explain redshifts in a logical/ understandable way, as being caused by another reason than an expanding universe and preferably one where there is evidence to support an expanding universe other than just the observed redshifts themselves which is the only evidence that I know of for proposing an expanding universe or increasing entropy.

 

 

"Instead what we see is generally the same density in the distant universe as we see locally. What we see is that no matter how distant we look the universe seems to be of the same density that we can see in our local neighborhood which seems totally contrary to the BB model. This problem with the standard model is rarely discussed but when it is, the explanations seem totally contrived and unconvincing"

Are you trying to say that the density of the universe has never changed with time? Does that imply the density at (say) +200,000 years is the same as (say) +13. billion years?

[pantheory]

BJC,

Are you trying to say that the density of the universe has never changed with time? Does that imply the density at (say) +200,000 years is the same as (say) +13. billion years?

I cannot make such an assertion concerning the observable universe in this forum but I would in the Speculation Forum I know of a few observation papers over the many years that have concluded that densities vary, but such assertions in my readings over the years, are few and far between. If you have such a link to a scholarly paper concerning observations where the conclusion is otherwise, I would need to read it.

 

best regards

Edited July 7, 2011 by pantheory