Talk about entropy and cyclical cosmology from spacetime thread

[Michael Mooney]

"Cosmic Hide and Seek: the Search

for the Missing Mass", Chris Miller

Dark Matter

 

Intro:

Scientists using different methods to determine the mass of galaxies have found a discrepancy that suggests ninety percent of the universe is matter in a form that cannot be seen. Some scientists think dark matter is in the form of massive objects, such as black holes, that hang out around galaxies unseen. Other scientists believe dark matter to be subatomic particles that rarely interact with ordinary matter. This paper is a review of current literature. I look at how scientists have determined the mass discrepancy, what they think dark matter is and how they are looking for it, and how dark matter fits into current theories about the origin and the fate of the universe.

 

The thing is that a page full of math might look very "scientific" and impressive, but it is the ultimate conceit to believe all the energy/matter in the universe has already been found and that it falls way short of the critical mass required for a gravitational reversal and a cyclic, Bang/Crunch cosmos. Yet this is what Modest is saying above, complete with all that math to "back it up!

 

BTW, NASA is quite proud of their orbiting "Chandra" observatory and all the new (previously undetected) matter/energy it has been finding and continues to find.

 

What astounds me is that Modest can make the assumptions he does above, dress it all up in a bunch of formulae, and no one but me challenges him.

It was the same on the spacetime thread.... about so many issues, like distances between objects varying with relative perspective, tho the *objective* distances between bodies in our solar system and many beyond are well known and published. But he weasels out of the criticism every time.

I can hardly wait for his maneuver out of this one.

Michael

[freeztar]

"Cosmic Hide and Seek: the Search

for the Missing Mass", Chris Miller

Dark Matter

 

Intro:

 

 

The thing is that a page full of math might look very "scientific" and impressive, but it is the ultimate conceit to believe all the energy/matter in the universe has already been found and that it falls way short of the critical mass required for a gravitational reversal and a cyclic, Bang/Crunch cosmos. Yet this is what Modest is saying above, complete with all that math to "back it up!

 

BTW, NASA is quite proud of their orbiting "Chandra" observatory and all the new (previously undetected) matter/energy it has been finding and continues to find.

 

What astounds me is that Modest can make the assumptions he does above, dress it all up in a bunch of formulae, and no one but me challenges him.

It was the same on the spacetime thread.... about so many issues, like distances between objects varying with relative perspective, tho the *objective* distances between bodies in our solar system and many beyond are well known and published. But he weasels out of the criticism every time.

I can hardly wait for his maneuver out of this one.

Michael

 

I've grown very tired of your constant attacks on Modest. He has consistently provided evidence, whereas you have shown none. Annoyingly, you continually argue from an appeal to ignorance. You will continue to receive infractions as long as you remain rude and continue to offer claims with no support.

 

A proper way to debate Modest would be something like the following template: "I understand why you believe the universe does not have critical density, but many new sources of matter have been detected such as x, y, and z (with links). When taken together, we can see that these new sources contribute z% to the critical density. If we continue to find new sources at the present rate of a every b years, then we could start to see mass come closer to approaching c in d years."

 

Do you see the difference? I did not insult anyone, I cited sources, and I provided verifiable numbers that support the claim.

 

You must make a similar effort for your posts. Failure to do so will earn you more infractions. It's that simple, your choice.

[modest]

The thing is that a page full of math might look very "scientific" and impressive, but it is the ultimate conceit to believe all the energy/matter in the universe has already been found and that it falls way short of the critical mass required for a gravitational reversal and a cyclic, Bang/Crunch cosmos. Yet this is what Modest is saying above, complete with all that math to "back it up!

 

I'm sorry you didn't understand, but that's really no reason to get upset. The math in my post was never more complicated than multiplication, division, and square root which most middle school algebra students would be able to follow. If you need help understanding any of it then you can surely ask.

 

It is, of course, not true that the derivation I did shows that the content of the universe falls short of the critical density. The derivation finds the value of the critical density which says nothing of the content of the universe. You should see, if you read the post again, that it is separated into two questions. The math part answers the first question.

 

As a matter of measuring the mass content of the universe, you misunderstand what astronomers mean by "finding missing mass" or the "missing mass problem". The fact that this mass is missing means we already know it exists gravitationally. When / if we find it, it will not add to the mass density of the universe. The mass density already contains 5 and 1/2 times as much dark matter as visible matter.

 

Dark matter is already factored into the 26% mass density of the critical density which cosmologists use in the Lamda-CDM model. 4% is known, baryonic matter while the other 22% is unaccounted for. So, finding that unaccounted for mass will not add to the mass density—it will only change unaccounted-for dark matter into accounted-for dark matter.

 

It is not true that the amount of dark matter (and thus the total mass density) is constantly going up. It, in fact, has gone down. Astronomers used to believe, as you do Michael, that the expansion of the universe would slow and reverse. You'll find that model favorably discussed in Hawking's A Brief History of Time. Astronomers set out to measure the "deceleration parameter" which would rather-directly measure the mass content of the universe. What they found care of supernova standard candles was that the expansion of the universe was in fact accelerating. The results have been verified and re-verified because the implications are very profound. It would seem there is some form of dark energy which manifests as negative pressure (either the cosmological constant or quintessence.

 

If this is true (and it sure appears to be) then the universe will not collapse in a big crunch no matter its mass density. If the cosmological constant exists and has any significant value at all then not even a mass density as high as [math]\Omega_M = 4[/math] would cause the universe to collapse. This is explained at the following website (which I often find myself linking :))

 

The second family are the positive cosmological constant models bounded by the green and red lines. These represent universes which expand continuously from R = 0 to infinity. They start from the Einstein-de Sitter point and end at the de Sitter point, i.e a universe with zero matter density and critical density in the cosmological constant. This is because a positive cosmological constant will eventually dominate the total density as it does not fall at all as the universe expands.

 

Solving the Friedman Equation

 

In short, Michael, this issue has a lot of interesting fassets for those interested in exploring them ;)

 

What astounds me is that Modest can make the assumptions he does above, dress it all up in a bunch of formulae, and no one but me challenges him.

 

Speaking of being challenged... I realize now why I have such a good rapport with Coldcreation... mutual respect and a shared love for science. :)

 

~modest

[HydrogenBond]

Is an expansion of space-time equal to an increase in entropy? For the two to be consistent they both in need to increase disorder and absorb energy, such as a red shift, where going from blue to red is equal to energy loss/absorption by entropy.

[modest]

Is an expansion of space-time equal to an increase in entropy? For the two to be consistent they both in need to increase disorder and absorb energy, such as a red shift, where going from blue to red is equal to energy loss/absorption by entropy.

 

No. In the strictest sense expansion itself does not represent an increase in entropy. A Friedmann (expanding) universe is modeled as the adiabatic expansion of a fluid:

The first equation can be derived also from thermodynamical considerations and is equivalent to the first law of thermodynamics, assuming the expansion of the universe is an adiabatic process (which is implicitly assumed in the derivation of the Friedmann-Lemaître-Robertson-Walker metric).

 

Friedmann-Lemaître-Robertson-Walker metric - Wikipedia, the free encyclopedia

 

The change in entropy of an adiabatic process is zero:

entropy changes for reversible, adiabatic processes are it always zero! (See here if you have forgotten why...)

 

Entropy changes

 

The expansion *itself* does not represent an increase in entropy. There are, however, processes in an expanding universe which can and do cause entropy to increase.

 

~modest

[Pluto]

G'day from the land of ozzzzzzz

 

This paper refers to a cyclic process.

 

Interesting reading.

 

[hep-th/0607164] Cosmic Perturbations Through the Cyclic Ages

Cosmic Perturbations Through the Cyclic Ages

 

Authors: Joel K. Erickson, Steven Gratton, Paul J. Steinhardt, Neil Turok

(Submitted on 23 Jul 2006)

 

Abstract: We analyze the evolution of cosmological perturbations in the cyclic model, paying particular attention to their behavior and interplay over multiple cycles. Our key results are: (1) galaxies and large scale structure present in one cycle are generated by the quantum fluctuations in the preceding cycle without interference from perturbations or structure generated in earlier cycles and without interfering with structure generated in later cycles; (2) the ekpyrotic phase, an epoch of gentle contraction with equation of state $wgg 1$ preceding the hot big bang, makes the universe homogeneous, isotropic and flat within any given observer's horizon; and, (3) although the universe is uniform within each observer's horizon, the global structure of the cyclic universe is more complex, owing to the effects of superhorizon length perturbations, and cannot be described in a uniform Friedmann-Robertson-Walker picture. In particular, we show that the ekpyrotic phase is so effective in smoothing, flattening and isotropizing the universe within the horizon that this phase alone suffices to solve the horizon and flatness problems even without an extended period of dark energy domination (a kind of low energy inflation). Instead, the cyclic model rests on a genuinely novel, non-inflationary mechanism (ekpyrotic contraction) for resolving the classic cosmological conundrums.