Advent calendar door #22: Meet the mother theory
There's an old Indian story about six blind men who go to visit an elephant. One touches its leg and decides that elephants must be like trees. A second examines its trunk and declares they are like snakes. A third feels its side and concludes they are like walls. You can imagine the rest. Everyone is right yet they are all wrong and it all ends in an argument. Only a major leap of the imagination, inspired by a lot more careful feeling around, could reveal the true nature of the animal that combines so many different characteristics.
In physics such leaps do sometimes occur. And when they do — when seemingly different things are unified under one idea — this represents a great advance in our understanding of how the world works. One of the first examples of such a leap was Newton's realisation, in the 17th century, that the motion of the planets around the Sun and an apple falling to the ground are due to the same thing: the force of gravity. Almost 200 years later James Clerk Maxwell unified electricity and magnetism in his theory of electromagnetism. The drive for unification continued and today we know that there are just three fundamental forces (gravity, the electroweak force and the strong nuclear force) and that there are only twelve basic building blocks of matter (see this Plus article for more information).
But there is a problem. Gravity is described by Einstein's general theory of relativity, which applies to the world at the scale of planets, stars and galaxies. The other two forces are negligible on such large scales. They come into play at the level of atoms and even smaller components of matter. This tiny world, in which gravity usually plays no part, is described by the other great theory to come out of the twentieth century: quantum mechanics.
Both theories do exceptionally well when they are tested against reality. But they are in conflict about the nature of space, or, as Einstein would have it, spacetime. When you combine the two theories you get mathematical results that make no physical sense: they imply that spacetime should tear itself apart (see this Plus article for more information). So the biggest challenge for twenty-first century physics is to come up with a unified theory of quantum gravity, which describes the world at all scales and retains the aspects of general relativity and quantum mechanics that work so well.
A strong contender for such a unifying theory is something called M-theory. The name was invented by the originators of the theory, but nobody seems to know what the M stands for — it could be "mother", "mystery" or even "magic", though it's probably the slightly less enticing "membrane". The Isaac Newton Institute, a mathematical research institute in Cambridge, is currently holding a six-month-long programme, bringing together the leading lights in the field. We went along to meet two of them, David Berman of Queen Mary, University of London, who organises the programme, and Andrew Strominger of Harvard, to find out more about this supposed mother of all theories.
To find out what they told us continue reading this article here.