The Role of Gravity

[OSHMUNNIES]

I'm sure this question (or something similar) has been addressed in a previous thread before, but since I don't really feel like searching for it (and I know you all will LOVE answering it) I'm going to ask anyway.

Given that every particle in the universe attracts every other particle in the universe with a force proportional to the same gravitational constant, why do so many independent collections of mass (planets, stars, galaxies, etc.) exist at all? Shouldn't we have a completely isotropic universe instead?

I realize that mass and distance between objects plays an important role, but...I don't even know what I'm asking anymore...help me out.

[Cap'n Refsmmat]

The force is also proportional to the distance -- or rather, it decreases with the distance squared.

 

This means that when objects clump, they tend to start forming bigger clumps, rather than spreading out.

[OSHMUNNIES]

Makes sense, but why should any two objects "clump" to begin with? Would this be due to other forces (electric, magnetic, etc.), or just random, chaotic subatomic activity? I suppose now I'm asking about the initial conditions of the universe (aren't I?). In other words, was there ever a state of complete isotropy of matter and energy (the singularity?)? If so, what caused its transition into chaos? If not, why the hell not? Am I in over my head?

 

(I know I'm rambling, I'm cramming for a physics exam and some of this stuff is pretty thought-provoking!)

[Mr Skeptic]

If matter were perfectly perfectly distributed it would not clump, but even the slightest fluctuations would lead to local differences and clumping.

[ajb]

You are talking about galaxy seeding, that is what mechanism coursed the otherwise homogeneous and isotropic distribution of matter to start to clump?

 

The best answer to date is to be found in the standard model of cosmology, that is the Lambda CDM model. In the early universe there was a period of rapid expansion known as inflation. Without any details, you can describe this mechanism via a single scalar field called the inflaton field. (There are many different models here, but for now all we need is one field and we won't need to know much about that ).

 

The classical dynamics of this field allow for the inflation. In fact, this situation is very general and it is difficult at present to find the details of such a field.

 

Now, it is believed that the tiny fluctuations in the distribution of matter were initiated by quantum fluctuations in the inflaton field. These tiny fluctuations have left their mark in the CMBR and as far as I know quantum fluctuations in the inflaton field gives good agreement with what is seen.

 

It is also possible that it was not the inflaton field, but some other field that is responsible. This field is known as the curvaton. It is not responsible for inflation, just the matter density distributions.

[StringJunky]

Makes sense, but why should any two objects "clump" to begin with? Would this be due to other forces (electric, magnetic, etc.), or just random, chaotic subatomic activity? I suppose now I'm asking about the initial conditions of the universe (aren't I?). In other words, was there ever a state of complete isotropy of matter and energy (the singularity?)? If so, what caused its transition into chaos? If not, why the hell not? Am I in over my head?

 

(I know I'm rambling, I'm cramming for a physics exam and some of this stuff is pretty thought-provoking!)

 

You might find this CDM Model stills and animation interesting:

 

http://cosmicweb.uchicago.edu/filaments.html

[rigney]

Another aspect. What if our universe is entropic and maintaining balance through its constant vectorial reach and systematic circular pattern systems, in a continuum?

Just a thought.

[pioneer]

The best answer to date is to be found in the standard model of cosmology, that is the Lambda CDM model. In the early universe there was a period of rapid expansion known as inflation. Without any details, you can describe this mechanism via a single scalar field called the inflaton field. (There are many different models here, but for now all we need is one field and we won't need to know much about that ).

 

Another consideration is connected to the relationship between entropy and relativity. As space-time expands, entropy will increase.

 

One simple way to help explain this is to compare entropy in a stationary reference to a moving reference. In this scenario, we have two identical machines that produce widgets, with each machine creating defects (entropy) at the average rate of 1 per 1000 widgets. Since time has slowed in the moving reference, and since times moves faster in the stationary reference, if we compare the two machines side by side, the one in the expanded reference will generate more widgets and entropy. Or expanded space-time allows more entropy.

 

As such, with the primordial singularity initially in highly contracted space-time, and the period of inflation, quickly expanding space-time, entropy is on the rise, with the original uniform field increasing entropy, forming discontinuities to reflect the entropy rise of the inflation. This is why we get so many galaxies and stars forming so early in the universe; space-time inflation expansion increases entropy.

 

To increase entropy we need to add energy. That means that expanding space-time needs energy. This is logical since it needs to overcome the force of universal gravity, which takes energy.

 

The inflation period needed an energy source to expand space-time and increase entropy. This suggests a phase change within the field that releases the energy needed for the inflation, which expands space-time increasing entropy for the defects, causing matter to clump due to gravity, which lowers local entropy, releasing entropy energy for further expansion of space-time. We still have the galaxies contracting toward black holes, lowering entropy, as the universe expands.

[rigney]

Pioneer, while I appreciate your input, you were head and shoulder over my thoughts. I'm sitting here wondering just what to say next? Since I've never learned to interpolate fourteen billion years, I can only express my wonder. Perhaps after reading your reply fifteen or twenty times, I may absorb just enough to get out of this stupid funk of mine.

Let me mull your reply over for a while. Thanks, rigney

[DrDNA]

 

To increase entropy we need to add energy. That means that expanding space-time needs energy. This is logical since it needs to overcome the force of universal gravity, which takes energy.

 

that's a cool trick.

[rigney]

After the dust settles, just what is gravity? While many equations have been laid down explaining it, beginning with Newton; it is still only theoretical? Even the word graviton is make-believe. What we have defined as gravity absolutely works to perfection, probably better than the (other three forces combined?) but its physical presence is still unproven and unknown. Perhaps it isn't physical at all, but possibly made up of several other properties?

Edited May 29, 2010 by rigney

[Nano]

After the dust settles, just what is gravity?

 

It's funny that the "standard model" is thought to be the most successful description of how all particles and forces interact, but still whenever you ask quantum mechanics about gravity, they're goin' : "Hmm, oh yea, gravity. I'd forgotten about that..uuh, something to do with gravitons"

 

As you understand, I am no professor, and have not the slightest idea what gravity is on a basic level, except an exchange of gravitons. I'm still waiting for someone to explain it though. I think Einsteins GR is the most elegant theory, but that's only me. I guess someone with more knowledge have to fill in the facts and give us the solutions to the mysteries of gravity.