Alex Ritson

Rather than slowing down, the stars and galaxies were actually accelerating away from each other faster than ever.

A telescope in Arizona tracked the acceleration of 15 million galaxies to learn more about dark energy.

The astronomers involved, such as Professor Ofa Lahav of University College London, were shocked again by what they saw.

Since then, the Royal Astronomical Society has published research from a Korean team led by Professor Yong-Wook Lee of Yonsei University that seems to back this astonishing finding.

No one really knows what dark energy is or why it might be changing, if indeed it is.

But here are three ideas.

Number one, phantom energy.

Now, this is a force that increases as the universe expands.

To such an extent, the stars and galaxies get torn apart.

This idea is called the Big Rip.

Number two, quintessence.

This is a gentler form of energy that also expands the universe, but doesn't result in it being ripped up.

And finally, number three, the universal dark fluid, where there's a single substance that changes from dark matter, invisible particles spread throughout the cosmos, and dark energy.

But then it could be something completely different, involving multiple universes.

Professor Hiranya Perez is from the Institute of Astronomy at the University of Cambridge.

Hundreds of scientific papers have been published on the subject and astronomers are split in what they think is the best explanation, which is no bad thing, according to Professor Robert Massey, who's the Deputy Director of the Royal Astronomical Society.

Who doesn't want to understand how the universe is going to end and how it began?

You know, it's one of those grand questions.

And human beings have always been interested in that, whether you take it from a kind of religious perspective and talking about creation myths and so on, or whether you talk about it from a scientific one.

Having a feel, having an intuitive idea about how it will end, being able to think, OK, this is how things will end in many, many, many billions of years in the future.