Utter darkness

DW: What exactly are the researchers from the European Southern Observatory talking about when they're saying that the Universe is dying?

Jochen Liske: What they mean by that is that there are fewer and fewer stars around to shine. Stars need fuel to shine and to burn. A star essentially does nuclear fusion at its center, and for this nuclear fusion it needs fuel. What is happening is that the universe is chomping through the available fuel, so that the rate at which new stars can be born is declining quite steeply and the net amount of stars is actually decreasing. And that means that the total amount of light produced by stars is also decreasing. Over time, the universe will turn from a reasonably bright lit place into a darker and darker place and eventually, it'll be completely dark.

Is there a time-frame for this? Can we say how many billion years the patient has left before it will be dead?

Not exactly. That's unfortunately where the analogy kind of breaks down a little bit. The universe isn't so much dying, with a specific time of death in the future. It's declining, and this is happening over a very long time - we're talking billions of years here. If anyone is still out there in ten billion years, peering out into the universe with technology similar to what we have today, there will still be something left to see, just not very much. All the galaxies will have dimmed quite a bit. But there is no specific point at which death occurs.

The universe will be a much darker place than it is today. It's not like the universe will stop existing, there'll still be galaxies around. It'll be a place full of dead stars.

So we can't really wonder what comes after "the universe has died?"

Exactly. There's no one point in time where the universe is completely different before and after. It's rather the ratio of living stars to dead stars that is changing. It's actually a little like the demographic change going on in Germany - there are more old people than young people and eventually you have more people dying than are being born - and the exact same thing is happening with stars.

Jochen Liske is a professor of observational astronomy at Hamburg University. Before that, he worked at the European Southern Observatory (ESO) in Garching, southern Germany.