Universe Today | Astronomy without a Telescope | 24 July 2010
A Larger Estimate of the Entropy of the UniverseIt all started so full of promise. All at once, our universe burst upon the scene, but much of that initial burst quickly dissipated into background neutrinos and photons – and ever since, pretty much everything our universe has ever done has just dissipated more energy. So, despite the occasional enthusiastic outburst of supernovae and other celestial extravagances, it's becoming increasingly apparent that our universe is getting on a bit.
The second law of thermodynamics (the one about entropy) demands that everything goes to pot over time – since anything that happens is an opportunity for energy to be dissipated.
The universe is full of energy and should always remain so, but that energy can only make something interesting happen if there is a degree of thermal disequilibrium. ...
This is roughly the idea behind increasing entropy. Everything of note that happens in the universe involves a transfer of energy and at each such transfer some energy is lost from that system. So, following the second law to its logical conclusion, you eventually end up with a universe in thermal equilibrium with itself. At that point, there are no disequilibrium gradients left to drive energy transfer – ... nothing else of note will ever happen again – a state known as heat death.
It's true that the early universe was initially in thermal equilibrium, but there was also lots of gravitational potential energy. So, matter (both light and dark) 'clumped' – creating lots of thermal disequilibrium – and from there all sorts of interesting things were able to happen. But gravity's ability to contribute useful work to the universe also has its limits.
- arXiv.org > astro-ph > arXiv:0909.3983 > 22 Sep 2009 (v1), 25 Jan 2010 (v3)
