Bye-bye to the universe, hello to the multiverse

WHAT is the universe made of? The ancient Greeks conceived of the "atom" but today's physicists talk of smaller particles - quarks and electrons, neutrinos, Higgs bosons and photons.

Understand them - and the forces that hold everything together - and we might finally get a handle on what makes it all tick.

The trouble is, the more we drill down into the subatomic world, the more complexity we find. Perhaps, according to a leading theoretical physicist, we do not live in a world of particles and forces at all - but of pure mathematics.

Max Tegmark, professor of physics at the Massachusetts Institute of Technology, claims that at the heart of everything are numbers. On one level this is uncontroversial; the whole point of physics is that we can use mathematics to describe the world around us.

But Tegmark goes further. His mathematical universe hypothesis states that not only does maths describe the world we live in, it is the world we live in.

"If you grant that both space and everything in space is mathematical," he said, "then it begins to sound less insane that everything is mathematical."

Tegmark, a tall, affable Swede, is one of the rock gods of cosmology, a select group of thinkers who are using their mathematical prowess to tear up all our cherished notions about the universe.

He and others believe that the universe is far grander and stranger than science has been willing to admit.

When I meet him in a swanky London bar, the conversation soon conjures a Narnia-like vision of parallel worlds, infinite space and places where an identical me and an identical him are having the same interview in an identical bar, but on a planet (10 10 ) 123 light years away.

The philosopher-kings of the 21st century are unafraid to speculate on the wildest shores of physics.

Said Tegmark: "We are not talking about vague philosophical notions but about mathematical theories. It is not my job to tell the universe how it should be."

Classical cosmology contends that the universe is basically what you see when you stare up at the night sky. We live in a huge sphere of expanding space about 90billion light years across that contains maybe half a trillion galaxies.

Impressive, but a mere gnat on an elephant's back compared to the multiverse, the name given to the concept that states that there must be far, far more "stuff" out there than even our best telescopes can see, or ever will be able to see.

Leading physicists such as Tegmark, Brian Greene, of Columbia University, and Astronomer Royal Lord Rees are fully signed-up multiversers.

Some evidence for the multiverse comes from observation.

Since the Big Bang 13.8billion years ago, there has been plenty of time for space to look very different in various directions - huge clusters of galaxies in one direction, vast voids in another - but it does not.

The best explanation is that the early universe underwent a period of unimaginably fast expansion, called inflation.

If there was a period of rapid expansion - a faster-than-light stretching of the fabric of space-time - in the first quadrillionths of a second after the Big Bang, regions of space now tens of billions of light years apart could then have been connected.

Last month a team of scientists announced that their telescope at the South Pole, Bicep 2, had probably discovered gravitational waves - a discovery that would not only back up our models of the Big Bang but provide strong evidence for inflation and the reality of the multiverse.

Recent discoveries such as this suggest that space might have inflated to an infinite extent after the Big Bang. Physicists believe that the inflationary process was capable of creating matter as well as space, in similarly infinite quantities.

In which case, go far enough and you will see an exact "repeat" of the stars and galaxies we see around us, including another planet Earth and another you - and worlds where Elvis lives, where Hitler won World War 2, and where strange creatures like unicorns graze.

"To get rid of that conclusion," Tegmark says, "either inflation is wrong . or space is in fact not infinitely stretchy."

Tegmark's universe of gyrating numbers, of equations coming to life, is one of bizarre possibilities and incomprehensible scale. But his most shocking argument is about the role of humans.

Said Tegmark: "All those galaxies only became beautiful 400 years ago when someone saw them for the first time. If we humans wipe ourselves out, then the entire universe becomes a huge waste of space."

He believes that we are probably the only life form cognisant of "our universe", and that if we do not destroy ourselves we could colonise the cosmos.

If that is true, we are the meaning of life, the universe and everything, and ours is the most significant century in nearly 14billion years.