For most of the twentieth century, astronomers assumed the universe's expansion had to be slowing down, tugged on by the gravity of everything inside it. Then, in 1998, two competing teams measured the opposite — the expansion is speeding up — and physics has been trying to explain it ever since. This episode unpacks dark energy, the name we give to whatever is pushing the cosmos apart.

You'll come away understanding how we know the universe is accelerating, why "empty" space might carry energy of its own, and why dark energy is often called the biggest unsolved problem in physics.

Talking Science is sponsored by Kinsoft. Visit www.kinsoft.com.au

Further reading: NASA Science – "Dark Energy, Dark Matter"; ESA – "Euclid mission"; Sean Carroll, The Big ...