Stars will disappear, the sun will go out and then the Earth and our bodies will be ripped into pieces.

This 'Big Rip' might be the way our universe ends and it may happen "on literally a human time scale", Nobel laureate Brian Schmidt said.

At a public talk by the Australian Astronomical Observatory in Sydney, Professor Schmidt - a joint winner of the 2011 Nobel prize for physics - described how our universe is rapidly expanding.

The expansion will eventually force our neighbouring galaxy - Andromeda Spiral - to merge with our Milky Way in about three billion years, Professor Schmidt said.

While it sounds messy, the space between our stars means it will be less like a train wreck and more like two swarms of bees coming together, he said.

Nevertheless, it will irrecoverably alter our view from Earth.

"We will see stars, but we will look out into an empty universe," he said.

Professor Schmidt said only 4.5 per cent of the universe is made up of things we can see - atoms, while the rest is invisible.

Dark matter makes up 24 per cent and dark energy the remaining 72 per cent.

Once this dark energy takes over, it will cause more space to expand, creating more dark energy, "which can then push harder against gravity, creating even more space".

"The creation of space eventually can happen even more quickly than light can travel."

This could lead to one of the "craziest theoretical ideas" and one of Professor Schmidt's favourites - the 'Big Rip'.

"You will see the stars in the sky start disappearing as they accelerate beyond the speed of light.

"Then one day the sun will go out.

"Then, not too long after, you and the Earth will be ripped into pieces."

Or it could end in a less dramatic fashion.

Either way, Professor Schmidt said, unless dark energy suddenly disappears very quickly, the universe it seems is fated to expand and fade away.

- AAP