Lets think this Out! [What's the Matter?]

[peter]

Ok. Let's say we have a universe operating on the same physical laws as ours, but instead of being densely populated with matter there are but two hydrogen atoms, evenly distributed, in the whole damn thing. Now, by the law of Universal gravitational attraction wherein every particle of matter in the universe attracts every other, even across the vastness of the space of their separation, in the frictionless environment in which they find themselves, these two lonely specks of matter will, at a rate determined by the inverse square law, begin to pull themselves together, accelerating all the while until .... what? They reach the speed of light and then collide obliterating themselves into smaller particles or even into pure energy [which is what in the absence of any matter to work on?]. Or do they reach each other before this silly speed is achieved, fall into each others arms and join together in glorious union in the form of an H2 molecule; or, bent by an ever so slight obliqueness in their trajectory, do they fall into an everlasting orbital dance around each other, forever falling together but forever pulling apart to the same degree, so that their much desired conjugation is doomed never to be?

[Vraith]

Ok. Let's say we have a universe operating on the same physical laws as ours,

Hah...how do you get that kind of universe? Ours isn't the size and shape it is because of the laws...it is that way because of the laws interacting with/in relation to all the stuff...
But, ignoring that...it depends. If the two atoms are far apart, and the universe is expanding, [like ours...though that's a serious problem, see above..] the gravity is too weak, they'll just continue getting farther apart. Maybe there is an exact distance where they just hover at the same distance forever, space pushing away, gravity pulling back..
Closer than that, then eventually they'll combine into an h2 molecule.
You'd have to do some math to calculate the velocities they reach...but light-speed seems highly unlikely. [the velocity, again, depends on how far apart they were at the beginning and is dependent on the tiny, tiny mass involved.].
They might have a few [trillions of?] fly-by's in super-elliptical orbit...but eventually they'd pass close and slow enough that they would bond.
They might bond on the very first pass, depending on velocity...
Without something close to light-speed head-on collision, they wouldn't annihilate each other [[and even in that collision...they might fuse to helium??]]---and again, I don't think anything like light-speed is at all likely, but that's a guess without doing a ton of calculating.

[peter]

Good response V, all of which I take on board.........

But actually that post was only the beginning of a much longer affair that got 404'd (no way for you to know that though). Here is the nub of where it was going: it was in essence an question about how the Second Law (which see's the Universes end as a grey spread of totally uniform matter - probably all decayed back to hydrogen again? - and energy, lifeless and static) can be reconciled with the Law of Universal Gravitational Attraction (which would see all of that matter pulling together in the frictionless void of space, thus maintaining the cosmic dance be it however long the Universe lasts). I postulated that the final picture could be that the reason why this second would not happen would be that the matter had settled into a dynamic but static equilibrium, each particle of matter pulled by equal and opposite forces such that no actual inertial change could happen......(but what then of the wrinkles of quantum space - would these not set off the process again - or perhaps even a nudge from the finger of the Primary Cause! ).

[Vraith]

Well...just to give you some more to ponder, not hint at any solutions...
Most cosmological theories that come close to explaining things we see/know require the vacuum to have a minimum, intrinsic energy---the energy is a property of the vacuum/space itself.
AND---the universe is expanding [and most likely accelerating expansion]
AND---it is doing so in at least 3 physical dimensions, so is increasing cubically [to the third power].
SO---the total energy is increasing at that same exponential rate [[more space means, by definition, more energy because all vacuum has a minimum energy]]
Is that energy NEW energy? [[but energy can't be created...]]

Or is the universe not closed [[the energy is coming from elsewhere]].

Final thing...e=mc^2...so, all that "new" energy will have a gravitational effect...and it is [see above] increasing exponentially.

So...the universe is getting bigger, [[and bigger faster all the time]] and more massive/gravid ...and yet becoming heat-deader all the time...
Is this, or is it not, a paradox?

[peter]

Certainly sounds like one to me V.

I read last night that in total, the energy of the Universe is always zero because using the general theory of relativity the energy of the gravitational field is always minus mc squared, exactly balancing the Einsteinian mass energy. Does this sound right to you - I have a conceptual problem with negative energy: what even is that?

[Vraith]

Certainly sounds like one to me V.

I read last night that in total, the energy of the Universe is always zero because using the general theory of relativity the energy of the gravitational field is always minus mc squared, exactly balancing the Einsteinian mass energy. Does this sound right to you - I have a conceptual problem with negative energy: what even is that?

Yea...that's one [and the biggest] way to say that there is no paradox in my example...because the gravitational has the opposite sign, so equals zero total.
But negative energy is weird. Just as weird [at least] as negative distance. You can easily manage it abstractly/mathematically. You can calculate it, reason from/with it, answer some questions using it, even diagram/chart it more or less. But once it is concrete/embodied, it becomes nonsense. Might as well be mimsy borogoves.

[peter]

It appears (to coin a phrase) that not only is the universe weirder than we think it is, it's weirder than we can think it is!

[Cord Hurn]

It appears (to coin a phrase) that not only is the universe weirder than we think it is, it's weirder than we can think it is!

In a way, this is reassuring. We'll never stop finding things to fascinate and intrigue us!

[Hashi Lebwohl]

Or is the universe not closed [[the energy is coming from elsewhere]].

If M-Theory is accurate then the universe we experience is the side-effect of two or more membranes colliding. If those membranes are still colliding then this can account for the extra space/volume/energy which appears to contradict the rule about not creating energy from nothing. Even if extra volume (which contains intrinsic energy) is added, the fact that so much volume is being created compared to the number of stars which currently exist then heat death is still the ultimate end result. Isn't heat death going to take about 10 to 25 trillion years, though. maybe more?

[Avatar]

10 to the power of (10 to the power of 3) years, apparently.

--A