To celebrate the centenary of the general theory of relativity we asked physicist David Tong to explain the theory and the equation that expresses it. Watch the video or read the article!

Read about the rocky road to one of Einstein's greatest achievements: the general theory of relativity, which celebrates its centenary this year.

General relativity, Einstein's rise to international stardom, and his legacy.

Why (some) physicists want to modify Einstein's general theory of relativity.

How big is the Universe? Where did it come from and where is it going? Why is it the way it is? These are just some of the questions cosmologists study.

Space is the stage on which physics happens. It's unaffected by what happens in it and it would still be there if everything in it disappeared. This is how we learn to think about space at school. But the idea is as novel as it is out-dated.

A team of physicists have curbed the hope that quantum physics might be squared with common sense. At least if we want to hang on to Einstein's highly respected theory of relativity. Their result concerns what Einstein called "spooky action at a distance" and it may soon be possible to test their prediction in the lab.

The holy grail for 21st century physics is to produce a unified theory of everything that can describe the world at every level, from the tiniest particles to the largest galaxies. Currently the strongest contender for such a theory is something called M-theory. So what is this supposed mother of all theories all about?