Just before this BBC podcast gets underway, here's something you may not know.

My name's Linda Davies and I Commission Podcasts for BBC Sounds.

As you'd expect, at the BBC we make podcasts of the very highest quality featuring the most knowledgeable experts and genuinely engaging voices.

What you may not know is that the BBC makes podcasts about all kinds of things like pop stars,

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Hello early in the 20th century physicists were alarmed at the realization that the smallest things in the universe don't obey the laws described by Newton's theory of gravity.

Ripe apples fall from trees and the moon orbits the earth in thrall to its gravitational pull and Newton had been God.

But there's no such force of gravity at work in the world of very small things.

It seems there's one set of rules for the realm of everyday objects and a very different set of laws for the quantum world where tiny

particles actually form the building blocks of all those larger things.

It doesn't appear to make sense.

Physicists decided there must be another theory, a much larger theory,

that unites, incorporates and finally make sense of these divided realms, and this has been the

holy grail of physics ever since.

Last year we explored string theory on this program, but one of my guests today is researching

what he believes is a much stronger contender for the title of Theory of Everything.

He is Lee Smolin, author of Three Roads to Quantum Gravity, and Professor of Physics at the

Center for Gravitational Physics and Geometry at Pennsylvania State University.

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