Is entropy opposite of gravity?

[onix]

If all of the universe's mass accumulates to pure energy, heat & entropy, does gravity bring it back to a single point to start the big bang process all over again?

 

[Matthias99]

Well, since gravity is (or at least appears to be) a property of objects with mass, converting all the mass in the universe to energy would result in zero gravitational attraction. At least that's what I would think.

 

[thereaderrabbit]

Matthias- I'm under the impression that all forms of energy are associated with mass in some manner. Potential energy certainly is (by the form you choose to store it), kinetic energy by definition is directly associated with a mass, electricity and light can be quantified as particles (with the properties of a wave too!)...

Onix- I like the question I think it's a little misguided, but does raise a good point.

Basic thermodynamics states that the entropy of the universe can only grow or be maintained as a function of time, wouldn't gravity (in the form of a force pulling the universe into a single point? i.e. counteracting the Big Bang) then be struggling against this (when looking at timescales on the order of the age of the universe)?

 

[CycloWizard]

nm

 

[ludl]

The question this thread starts with is THE question.
Is Universe expanding to a limit or not.
So far none has made an answer.

 

[DrPizza]

Originally posted by: ludl
The question this thread starts with is THE question.
Is Universe expanding to a limit or not.
So far none has made an answer.

IIRC, it's been looked at quite a bit lately. The startling result is that the expansion of the universe is accelerating! Regardless, it's pretty much accepted now that the universe is going to grow without limit. (No "big crunch" at the end - no Restaurant at the end of the Universe)

 

[DrPizza]

Originally posted by: Matthias99
Well, since gravity is (or at least appears to be) a property of objects with mass, converting all the mass in the universe to energy would result in zero gravitational attraction. At least that's what I would think.

You know... that brings up one of the big questions I've had that hasn't been answered for me yet. (I've never actually asked it though before this time... just pondered it.)

An electron has mass, therefore a gravitational field. Ditto for a positron. Smack them into each other resulting in annihilation of both and a release of energy (gamma rays?). Where does the gravity go?

 

[DrPizza]

Perhaps I should refine my question:

In a supercollider collision between a particle and an antiparticle, new massive particles (more mass than the original two particles combined) may be created (which generally decay very quickly). For example, the collision/annihilation can result in a pair of Tau-Leptons each with about 3500 times the mass of the original electron or positron. Of course, each Tau-Lepton decays very quickly into one or more particles.

If we had a super-super-super (add in a bunch more super's... )sensitive gravitational detector, would it record the gravitational force of attraction from the particles increasing, then decreasing?

 

[Matthias99]

Matthias- I'm under the impression that all forms of energy are associated with mass in some manner. Potential energy certainly is (by the form you choose to store it), kinetic energy by definition is directly associated with a mass, electricity and light can be quantified as particles (with the properties of a wave too!)...

Electromagnetic radiation has no (rest) mass -- I thought this meant it did not create any gravitational pull, but I will say my understanding in this area is very limited.

Originally posted by: DrPizza

Originally posted by: Matthias99
Well, since gravity is (or at least appears to be) a property of objects with mass, converting all the mass in the universe to energy would result in zero gravitational attraction. At least that's what I would think.

You know... that brings up one of the big questions I've had that hasn't been answered for me yet. (I've never actually asked it though before this time... just pondered it.)

An electron has mass, therefore a gravitational field. Ditto for a positron. Smack them into each other resulting in annihilation of both and a release of energy (gamma rays?). Where does the gravity go?

It seems (to me, anyway; I'm not a physicist) that gravity is a property of space-time, rather than an interaction directly between the particles. Presumably the process of annihilating the particles slightly reduces the 'curvature' of local space, which has a side effect of reducing the effective gravitational pull being felt by other matter in the area.

What I'm taking this from is mostly Einstein's 'bowling-ball-on-a-bed' analogy -- putting a heavy object on a flexible surface (like the top of a bed) distorts the surface, which (depending on your perspective) looks like an attractive force between the objects, even though there is no force directly transmitted between them. Removing one object only directly affects the distortion of the surface, although the effect is 'felt' by the other objects on the surface.

 

[thereaderrabbit]

Here is a good read that brushes up against our topic: http://www.newscientist.com/channel/space/mg18524911.600

-Reader

 

[onix]

Originally posted by: thereaderrabbit
Here is a good read that brushes up against our topic: http://www.newscientist.com/channel/space/mg18524911.600

-Reader

I liked the read.

Gravity is mysterious, almost as much as entropy. Why togetherness, why disorder? There must be some mathematical conundrum that cannot be answered without some relationship here. What does string theory have to say?

 

[silverpig]

Originally posted by: Matthias99
Well, since gravity is (or at least appears to be) a property of objects with mass, converting all the mass in the universe to energy would result in zero gravitational attraction. At least that's what I would think.

Actually it's exactly the opposite. A radiation filled universe has more self gravitation than a matter filled universe.

The universe was at one time dominated by radiation and it expanded relatively slowly. As that radiation cooled and its energy density dropped (it goes as 1/r^4... very quickly), matter came to dominate the dynamics of the universe. However, not too long ago on cosmological scales, matter ceased to dominate (goes as 1/r^3), and the dark energy/cosmological constant/vacuum energy came to dominate the dynamics of the universe.

Gravity is the curvature of space as described by Einstein's field equation G(mu)(nu) = 8 Pi T(mu)(nu) where T(mu)(nu) is the stress-energy tensor. Basically, it's a description of the amount of "stuff" in a certain part of space. That stuff can be energy, matter, cosmological constant, anything really.