In Our Time

Duration: 45 minutes
First broadcast: Thursday 19 April 2007

Melvyn Bragg and guests discuss symmetry. Found in Nature – from snowflakes to butterflies – and in art in the music of Bach and the poems of Pushkin, symmetry is both aesthetically pleasing and an essential tool to understanding our physical world. The Greek philosopher Aristotle described symmetry as one of the greatest forms of beauty to be found in the mathematical sciences, while the French poet Paul Valery went further, declaring; “The universe is built on a plan, the profound symmetry of which is somehow present in the inner structure of our intellect”.

The story of symmetry tracks an extraordinary shift from its role as an aesthetic model – found in the tiles in the Alhambra and Bach’s compositions – to becoming a key tool to understanding how the physical world works. It provides a major breakthrough in mathematics with the development of group theory in the 19th century. And it is the unexpected breakdown of symmetry at sub-atomic level that is so tantalising for contemporary quantum physicists.

So why is symmetry so prevalent and appealing in both art and nature? How does symmetry enable us to grapple with monstrous numbers? And how might symmetry contribute to the elusive Theory of Everything?

With Fay Dowker, Reader in Theoretical Physics at Imperial College, London;
Marcus du Sautoy, Professor of Mathematics at the University of Oxford;
Ian Stewart, Professor of Mathematics at the University of Warwick

http://www.bbc.co.uk/programmes/b00776v8

Duration: 45 minutes
First broadcast: Thursday 29 June 2006

Melvyn Bragg and guests discuss the galaxies. Spread out across the voids of space like spun sugar, but harbouring in their centres super-massive black holes.

Our galaxy is about 100,000 light years across, is shaped like a fried egg and we travel inside it at approximately 220 kilometres per second. The nearest one to us is much smaller and is nicknamed the Sagittarius Dwarf. But the one down the road, called Andromeda, is just as large as ours and, in 10 billion years, we’ll probably crash into it.

Galaxies – the vast islands in space of staggering beauty and even more staggering dimension. But galaxies are not simply there to adorn the universe; they house much of its visible matter and maintain the stars in a constant cycle of creation and destruction.

But why do galaxies exist, how have they evolved and what lies at the centre of a galaxy to make the stars dance round it at such colossal speeds?

With John Gribbin, Visiting Fellow in Astronomy at the University of Sussex; Carolin Crawford, Royal Society University Research Fellow at the Institute of Astronomy at Cambridge; Robert Kennicutt, Plumian Professor of Astronomy and Experimental Philosophy at the University of Cambridge

http://www.bbc.co.uk/programmes/p003c1cn

Duration: 45 minutes
First broadcast: Thursday 03 November 2005

Melvyn Bragg and guests discuss the unique properties of asteroids. They used to be regarded as the ‘vermin of the solar system’, irritating rubble that got in the way of astronomers trying to study more interesting phenomena. It was difficult or even impossible for an observer of asteroids to book time using the world’s best telescopes, because they were regarded as unspectacular objects that could tell us little about the origins of the universe.

However, that has all changed. It is now thought that asteroids are the unused building blocks of planets, ‘pristine material’ that has remained chemically unchanged since the creation of the solar system; a snapshot of matter at the beginning of time. At the moment the Japanese probe Hayabusa is 180 million miles away, pinned to the back of the asteroid Itokawa, attempting to gain our first samples of the chemical composition of an asteroid.

Why did asteroids fail to form planets? How do they differ from their celestial cousins, the comets? And are either of them likely to create another impact on planet Earth?

With Monica Grady, Professor of Planetary and Space Sciences, Open University; Carolin Crawford, Royal Society Research Fellow, University of Cambridge; John Zarnecki, Professor of Space Science, Open University.

http://www.bbc.co.uk/programmes/p003k9kh

Duration: 45 minutes
First broadcast: Thursday 24 November 2005

Melvyn Bragg and guests discuss the search for the Graviton particle. Albert Einstein said “I know why there are so many people who love chopping wood. In this activity one immediately sees the results”. Einstein spent the last thirty years of his life trying to find a theory that would unify electromagnetism with gravity, but success eluded him.

The search is still on for a unifying theory of gravitational force and hopes are pinned on the location of the graviton – a hypothetical elementary particle that transmits the force of gravity. But the graviton is proving hard to find. Indeed, the Large Hadron Collider at CERN still won’t allow us to detect gravitons per se, but might be able to prove their existence in other ways.

The idea of the graviton particle first emerged in the middle of the 20th century, when the notion that particles as mediators of force was taken seriously. Physicists believed that it could be applicable to gravity and by the late 20th century the hunt was truly on for the ultimate theory, a theory of quantum gravity.

So why is the search for the graviton the major goal of theoretical physics? How will the measurement of gravitation waves help prove its existence? And how might the graviton unite the seemingly incompatible theories of general relativity and quantum mechanics?

With Roger Cashmore, Former Research Director at CERN and Principal of Brasenose College, Oxford; Jim Al-Khalili, Professor of Physics at the University of Surrey; Sheila Rowan, Reader in Physics in the Department of Physics and Astronomy at the University of Glasgow

http://www.bbc.co.uk/programmes/p003k9ks

Duration: 45 minutes
First broadcast: Thursday 17 March 2005

Melvyn Bragg and guests discuss ‘dark energy’. Only 5% of our universe is composed of visible matter, stars, planets and people; something called ‘dark matter’ makes up about 25% and an enormous 70% of the universe is pervaded with the mysteriously named ‘dark energy’. It is a recent discovery and may be only a conjecture, but it has been invoked to explain an abiding riddle of the cosmos: if the expansion of the universe is powered by the energy of the Big Bang, then why isn’t the expansion slowing down over time as the initial energy runs down and the attractive force of gravity asserts itself? Scientists had predicted a Big Crunch as the logical opposite of the Big Bang, but far from retracting, the expansion of the universe is actually accelerating…it’s running away with itself.

How do we know that the universe is behaving like this and what’s causing it? If dark energy is the culprit, then what is this elusive, though omnipresent entity?

With Sir Martin Rees, Astronomer Royal and Professor of Cosmology and Astrophysics, Cambridge University; Carolin Crawford, Royal Society University Research Fellow at the Institute of Astronomy, University of Cambridge; Sir Roger Penrose, Emeritus Rouse Ball Professor of Maths at Oxford University.

http://www.bbc.co.uk/programmes/p003k9g5