h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Any closed system is supposed to be going towards a state of disorder. This would include the universe itself. On a short term level I think I can visualize this. However if you were to play time backwards, what would the ordered state of the universe be like right after The Big Bang? What would make that big cloud of hydrogen ordered in any way, since I assume it would not have some crystalline structure. Is it merely about how as the universe expands, the atoms within it has more states and positions to be in?

well right after the big bang you'd not have atoms or hydrogen or such normal stuff. We're not yet sure what you would have but some sort of parent particles I guess. As the energy levels get higher so you get the more exotic particles. Maybe at the very start all there is is energy in a highly ordered form that we can't understand yet.

There is also a question mark (albeit a small one) over whether our universe really is a closed system.

>Is it merely about how as the universe expands, the atoms within it has more states and positions to be in?<

I would say that's more or less spot on.

Entropy (the 'amount' of disorder) is often defined in science as a function of the number of degrees of freedom of a system. The smaller a system then the less entropy it has since everything is pressed together and has less room for manoeuvre and hence fewer degrees of freedom.

Creating atoms and molecules out of the primeval matter would actually reduce the entropy of those particles themselves but there would be a large rise in entropy associated with release of other particles such as photons and neutrinos which are released as by-products when particles combine to form larger ones.

So the increased 'disorder' would manifest itself by combination of 'fundamental' particles such as quarks and leptons to form larger particles associated with massive energy releases as they bond in the form of a radiation of neutrinos, photons and other by-products. This would also necessitate an expansion in volume which in itself, (as you said yourself) would increase the degrees of freedom associated with the system.

The higher order of the primeval universe would therefore seem to me to be the reverse of this process. A lot fewer photon, neutrinos etc, a lot less volume...

Hope that ramble made sense...

more so than mine did

That sounds a bit disappointing really. It also makes me wonder how the entropy is, if the universe does a Big Crunch.

it looks like god has swept up after himself and tucked his PJs in the top of his bed