In Our Time

Melvyn Bragg and his guests discuss absolute zero, the lowest conceivable temperature. In the early eighteenth century the French physicist Guillaume Amontons suggested that temperature had a lower limit. The subject of low temperature became a fertile field of research in the nineteenth century, and today we know that this limit – known as absolute zero – is approximately minus 273 degrees Celsius. It is impossible to produce a temperature exactly equal to absolute zero, but today scientists have come to within a billionth of a degree. At such low temperatures physicists have discovered a number of strange new phenomena including superfluids, liquids capable of climbing a vertical surface.

With:

Simon Schaffer
Professor of the History of Science at the University of Cambridge

Stephen Blundell
Professor of Physics at the University of Oxford

Nicola Wilkin
Lecturer in Theoretical Physics at the University of Birmingham

Producer: Thomas Morris

http://www.bbc.co.uk/programmes/b01r113g

Duration: 43 minutes
First broadcast: Thursday 16 May 2013

Melvyn Bragg and his guests discuss cosmic rays. In 1912 the physicist Victor Hess discovered that the Earth is under constant bombardment from radiation coming from outside our atmosphere. These so-called cosmic rays have been known to cause damage to satellites and electronic devices on Earth, but most are absorbed by our atmosphere. The study of cosmic rays and their effects has led to major breakthroughs in particle physics. But today physicists are still trying to establish where these highly energetic subatomic particles come from.

With:
Carolin Crawford
Gresham Professor of Astronomy and a member of the Institute of Astronomy at the University of Cambridge

Alan Watson
Emeritus Professor of Physics at the University of Leeds

Tim Greenshaw
Professor of Physics at the University of Liverpool.

http://www.bbc.co.uk/programmes/b01sdnkg

Duration: 45 minutes

First broadcast: Thursday 14 April 2011

Melvyn Bragg and his guests discuss the neutrino.

In 1930 the physicist Wolfgang Pauli proposed the existence of an as-yet undiscovered subatomic particle. He also bet his colleagues a case of champagne that it would never be detected. He lost his bet when in 1956 the particle, now known as the neutrino, was first observed in an American nuclear reactor.

Neutrinos are some of the most mysterious particles in the Universe. The Sun produces trillions of them every second, and they constantly bombard the Earth and everything on it. Neutrinos can pass through solid rock, and even stars, at almost the speed of light without being impeded, and are almost impossible to detect. Today, experiments involving neutrinos are providing insights into the nature of matter, the contents of the Universe and the processes deep inside stars.

With:
Frank Close
Professor of Physics at Exeter College at the University of Oxford

Susan Cartwright
Senior Lecturer in Particle Physics and Astrophysics at the University of Sheffield

David Wark
Professor of Particle Physics at Imperial College, London, and the Rutherford Appleton Laboratory.

http://www.bbc.co.uk/programmes/b0106tjc

Duration: 45 minutes
First broadcast: Thursday 03 March 2011

Melvyn Bragg and his guests discuss the age of the Universe.

Since the 18th century, when scientists first realised that the Universe had existed for more than a few thousand years, cosmologists have debated its likely age. The discovery that the Universe was expanding allowed the first informed estimates of its age to be made by the great astronomer Edwin Hubble in the early decades of the twentieth century. Hubble’s estimate of the rate at which the Universe is expanding, the so-called Hubble Constant, has been progressively improved.

Today cosmologists have a variety of other methods for ageing the Universe, most recently the detailed measurements of cosmic microwave background radiation – the afterglow of the Big Bang – made in the last decade. And all these methods seem to agree on one thing: the Universe has existed for around 13.75 billion years.

With:
Martin Rees
Astronomer Royal and Emeritus Professor of Cosmology and Astrophysics at the University of Cambridge

Carolin Crawford
Member of the Institute of Astronomy and Fellow of Emmanuel College at the University of Cambridge

Carlos Frenk
Director of the Institute for Computational Cosmology at the University of Durham.

http://www.bbc.co.uk/programmes/b00yz3gy

Duration: 45 minutes
First broadcast: Thursday 06 May 2010

The Cool Universe is the name astronomers give to the matter between the stars.

These great clouds of dust and gas are not hot enough to be detected by optical telescopes.

But over the last few decades, they have increasingly become the focus of infrared telescopy.

Astronomers had long encountered dark, apparently starless patches in the night sky.

When they discovered that these were actually areas obscured by dust, they found a way to see through these vexing barriers, using infrared telescopes, to the light beyond.

However, more recently, the dust itself has become a source of fascination.

The picture now being revealed by infrared astronomy is of a universe that is dynamic.

In this dynamic universe, matter is recycled – and so the dust and gas of the Cool Universe play a vital role.

They are the material from which the stars are created, and into which they finally disintegrate, enriching the reservoir of cool matter from which new stars will eventually be formed.

As a result of the new research, we are now beginning to see first-hand the way our planet was formed when the solar system was born.

With:
Carolin Crawford
Member of the Institute of Astronomy, and Fellow of Emmanuel College, at the University of Cambridge

Paul Murdin
Visiting Professor of Astronomy at Liverpool John Moores University’s Astronomy Research Institute

Michael Rowan-Robinson
Professor of Astrophysics at Imperial College, London

http://www.bbc.co.uk/programmes/b00s7b6r