It's official. The universe is dying.

[Alex K]

http://www.msn.com/en-au/news/world/the-...spartandhp

Without applause or encore, the lights are going out across the universe, as old stars die faster than new ones are born to replace them.

Astronomers described the slow death of the cosmos in fresh detail on Monday after training some of the world’s most powerful telescopes on a vast region of space.

They analysed starlight from more than 220,000 distant galaxies and found that the universe has lost about half of its twinkle over the past two billion years. It will lose far more in the next two billion.

“The universe is curling up on the sofa and becoming a couch potato,” said Joe Liske, an astronomer at the European Southern Observatory in Garching, Germany, who took part in the study.

But where does all the energy go?

Ok, so, energy conservation is a funny thing ina changing spacetime. Naively, energy is not conserved. Boru's sand analogy is true for matter at rest (i.e. rest energy E=mc2) with respect to the cosmic rest frame, which simply gets more dilute while the amount stays the same. It is not true for kinetic energy, the extreme example being light which has no rest mass. In addition to being diluted, it gets redshifted, thus actually losing energy. A photon that got sent by a star billions of years ago will now carry less energy because it is redder. The CMB photons have lost a factor of 1100 of energy since they started their journey. In general relativity, his violation of energy conservation can be seen immediately from the equations because the usual conservation law gets an additional modification from curved space (somewhat simplified, it is actually the so-called connection which is not the same as curvature). A conserved quantity can nevertheless be constructed when one assigns an energy to the curvature of spacetime itself. In this case, one gets a conserved energy where during the expansion, energy leaks out from the contents of the universe into the geometry.