Over the past five years, the mysterious tale of dark matter has been taken yet another bizarre twist. Just as cosmologists decided that the Universe is full of a strange invisible matter, they then realised that space was even weirder than they had thought.

After a full census of all the galaxies visible in the Universe, astronomers calculated that their total mass (including their hidden dark matter) only made up about one-third of the critical density needed to satisfy the best current theory about the early Universe [known as inflation].

At first, cosmologists thought that inflation must be wrong. But then further data from measurements of the cosmic microwave background showed that the total density of the Universe did add up to this special critical density, so inflation could be reinstated and another solution had to be found. So even after their best attempts to renovate our cosmic home, most of the Universe still remained elusive.

The problem is that this new component seems even stranger than dark matter. Not only is it invisible just like dark matter, but it must have a repulsive force, otherwise it would get sucked into galaxies and affect their motion. So this mysterious stuff has been labeled 'dark energy' and is a kind of cosmic antigravity force that counteracts the attractive force of gravity. This means that instead of the expansion of the Universe slowing down, in fact, it is speeding up. Recent measurements of distant supernovae agreed with this conclusion, finding that the Universe was indeed expanding with increasing pace.

Interestingly, this had already been foreseen in a botched sum. But this wasn't the sloppy homework of a spotty student, this was a calculation by Albert Einstein no less! It was 1917 and he was trying to reduce the dynamics of the whole Universe into a set of mathematical formulae. His results insinuated that the Universe was expanding. However like the vast majority of people at the time, Einstein assumed that the Universe was static. So to stop his model Universe from growing, he invented a number he called the 'cosmological constant' to insert into his equations, restoring the safe, steady nature of his static Universe.

After Edwin Hubble found that the Universe was indeed expanding, Einstein quickly retracted this number, calling it his 'biggest blunder'. But he needn't have been so hasty because now, nearly 80 years later, it has been reinstated to account for this mysterious dark energy that is overtaking gravity. These new findings are helping cosmologists look into the future and foresee the destiny of the whole Universe.

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