Cars run out of petrol, stars run out of fuel and galaxies collapse into black holes. As they do, the universe and everything in it is gradually running down. But how run down is it? Researchers from The Australian National University have found that the universe is 30 times more run down than previously thought.

PhD student Chas Egan and Dr Charley Lineweaver from the ANU Research School of Astronomy and Astrophysics have computed the entropy of the universe. Scientists compute entropy to find out how efficient an engine is or how much work can be extracted from a fuel or how run down and disordered a system is. Using new data on the number and size of black holes they found that the universe contains 30 times more entropy than earlier estimates.

"We considered all contributions to the entropy of the observable universe: stars, star light, the cosmic microwave background. We even made an estimate of the entropy of dark matter. But it's the entropy of super-massive black holes that dominates the entropy of the universe. When we used the new data on the number and size of super-massive black holes, we found that the entropy of the observable universe is about 30 times larger than previous calculations," said Mr Egan.

"Contrary to common opinion, the maintenance of all the complicated structures we see around us -- galaxies, stars, hurricanes and kangaroos -- have the net effect of increasing the disorder and entropy of the universe. But to be fair, their contributions are negligible compared to the entropy of super-massive black holes," added Dr Lineweaver.

The researchers' results have important implications for terrestrial and extraterrestrial life. "The universe started out in a low entropy state and, in accordance with the second law of thermodynamics, the entropy has been increasing ever since," Mr Egan said. "This is important because the amount of energy available to life in the universe, including terrestrial life, depends on the entropy of the universe. We'd like to know how much energy will be available to life forms anywhere in the universe, and where this energy is. The first step in this procedure is to determine the entropy of the universe. That is what we did."

Dr Lineweaver said that the next step in the research is to out how close we are to maximum entropy, how much entropy is being produced and how much time we have left before the universe and all life in it dies in the inevitable heat death.