And what are gravitational waves?

What's the mysterious stuff that makes up 70% of our Universe?

With online socialising and alternative realities like Second Life it may seem as if reality has become a whole lot bigger over the last few years. In one branch of theoretical physics, though, things seem to be going the other way. String theorists have been developing the idea that the space and time we inhabit, including ourselves, might be nothing more than an illusion, a hologram conjured up by a reality which lacks a crucial feature of the world as we perceive it: the third dimension. Plus talks to Juan Maldacena to find out more.

The mathematical maps in theoretical physics have been highly successful in guiding our understanding of the universe at the largest and smallest scales. Linking these two scales together is one of the golden goals of theoretical physics. But, at the very edges of our understanding of these fields, one of the most controversial areas of physics lies where these maps merge: the cosmological constant problem.

Are the unchanging features of the Universe really unchanging?

One of science's biggest prizes awarded for research into strings and knots

Cambridge celebrates 25 years since the first very early Universe workshop

One of the many strange ideas from quantum mechanics is that space isn't continuous but consists of tiny chunks. Ordinary geometry is useless when it comes to dealing with such a space, but algebra makes it possible to come up with a model of spacetime that might do the trick. And it can all be tested by a satellite. Shahn Majid met up with Plus to explain.

Nurturing the future of observational cosmology

There might not be a Nobel Prize for mathematics, but maths is at the heart of the 2006 Nobel Prizes.

Was Einstein right?

Scientists have for the first time measured the speed of gravity and tested Einstein's assumption - or have they?