Einstein's Biggest Blunder

Heather Couper presents a narrative history of astronomy.

In 1915, Albert Einstein found that he had to introduce a new factor into his equations of gravity to prevent the stars from falling in on one another. He called it the cosmological constant. But then, astronomers discovered that the light from galaxies was stretched in a way that could only be explained if the galaxies were flying apart from each other and the universe was expanding.

A recent twist to this tale came in the year 2000, when estimates of the rate of the expansion revealed that the most distant galaxies are accelerating. The only way to explain this was by a force called dark energy - in effect, a cosmological constant.

Readers are Timothy West, Robin Sebastian, Julian Rhind-Tutt and John Palmer.