Alex Ritson

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.

Wouldn't that be extraordinary?

So what next?

The plan is to have larger telescopes, some in space, to look at dark energy in detail, to get to the bottom of what this mysterious force really is.

The results could tell us not only how the universe will end, but maybe a better idea of how it all began.

Still to come, a Siberian tiger stuns conservationists with her litter.

For a female Amur tiger or Siberian tiger to give birth to five cubs and have them survive as long as these five seem to have survived is pretty remarkable.

In my new family-friendly podcast series, Dead Funny History, historical figures come back to life for just about long enough to argue with me, tell us their life stories, and sometimes get on my nerves.

There's 15 lovely episodes to unwrap, including the life of Ramses the Great, Josephine Baker, and the history of football, plus much, much more.