0224042068

MARCUS CHOWN’s new book unravels what is perhaps the greatest detective story

in the history of science: the origin of the atoms. The word “unravel” is

particularly apt, as The Magic Furnace really tells two intertwined

stories.

The first is how scientists isolated the elements and unlocked the secrets of

the atom. The second is a story of enlightenment: how we came to understand that

the light elements originated in the big bang and were only transformed into the

heavier elements during the life and death of stars.

It was the Greek Democritus who first suggested, in around 430 BC, that

matter consists of an assembly of grains that cannot be subdivided and so are

“uncuttable”. Hence the name he gave them: atomos.

Early this century, however, physicists such as Ernest Rutherford showed that

even the atom could be split, which eventually led to an understanding of the

structure of the elements. But how had they been created? Why were some

elements, such as carbon, common while others were very rare? The answer lay in

the stars.

As it became apparent that the Earth was several billion years old,

physicists worried about how the Sun had managed to sustain its output of energy

for such a vast length of time. The discovery of radioactivity, they realised,

could perhaps provide the answer.

Helium, a by-product of radioactive decay, had even been discovered in the

Sun’s atmosphere. Surely this was proof that the Sun was radioactive? But though

the Sun’s spectrum showed the presence of many stable elements, only minuscule

amounts of radioactive elements such as uranium and thorium were found. Nuclear

fission was rejected.

The answer came when it was realised that the Sun’s energy could be provided

by nuclear fusion as lighter elements were transformed into heavier ones. But

the process is tortuous, and it was not until the mid-1950s that astrophysicists

such as Fred Hoyle were able to work out the many steps in the complex chain of

events.

Hoyle even predicted a specific property of the carbon nucleus on the basis

that without it carbon would be very rare and life could not exist! As Chown

points out, it was perhaps a great injustice that Hoyle was never awarded the

Nobel Prize for this work.

The story was not yet finished. There is at least ten times as much helium in

the Universe as could have been made in the stars. The discovery of the

radiation left over from the fireball of creation confirmed the big bang origin

of the Universe. It was then that the excess helium had been created.

One of the problems with science writing, in that the precise statement of a

concept can get in the way of the flow of the narrative. Chown has dealt with

this admirably, by providing footnotes to clarify or fill out the main text.

Another appealing aspect is the way in which we are given character sketches

of the many scientists involved. For example, we are told that Robert Bunsen, of

Bunsen burner fame, spent much of his time in a fog of offensive vapours, which

did little for his sex appeal. He never married, perhaps as a result. But he

must have had some charm, as the wife of a prominent chemist is quoted as

saying: “First I would like to wash him, and then I would like to kiss him!”

Even if you know the basics of this story, you will profit from Chown’s

insight into the subject. And if you don’t, you will find this a clear

introduction to a fascinating area of physics and astronomy.

Chown is to be congratulated on a beautifully crafted book. Like his previous

work, Afterglow of Creation, it will surely be a strong candidate for

future science book prizes.

FEW areas of research have attracted as much public and media interest as
that covered by Ken Croswell in Planet Quest—the long and
sometimes tortuous path that has finally led to the discovery of planets
orbiting other suns. Our fascination with this find is, of course, down to the
widespread belief that planets and their satellites are the most likely setting
for the evolution of life. This is an integral part of the story that Croswell
skilfully unfolds.

We are first given a thorough grounding in the science of our own Solar
System, and reminded how its other planets were discovered. The abortive
searches for Vulcan, which was believed to be closer to the Sun than Mercury,
and Planet X, thought by some to exist beyond the orbit of Pluto, are included
to help make us aware of the pitfalls that can occur along the way. We learn how
the giant Jupiter protects the inner planets of our Solar System from the vast
majority of cometary impacts, and so may allow periods of calm long enough for
life to evolve.

The heart of this book is naturally about the first discoveries of planets
around distant stars. Croswell presents this fascinating story very well. He
often quotes those directly involved in the search, allowing us to share their
feelings as hopes were dashed or tentative discoveries confirmed.

An apt analogy to convey the fundamental problem of detecting extrasolar
planets is that it is like trying to observe a glow-worm sitting on the rim of a
searchlight. Astronomers are thus forced to use indirect methods to infer the
presence of a planetary system.

Two such methods have emerged so far. Both depend on the fact that a planet
and its star move in orbits around their common centre of gravity. The star will
have a cyclic motion as well as its linear movement through space. The cyclic
movement can manifest itself in two ways. First, the star will follow an
oscillating path that may be detected by astrometric techniques, involving very
precise positional measurements taken over many years. Second, its spectral
lines will show small periodic changes in wavelength due to the Doppler
effect.

The astrometric method has a long history— indeed, the “wobble” of
Sirius was observed in 1844, and its white dwarf companion star confirmed in
1925. But planets are far smaller than stars. The deviations they cause in
stars’ paths are far smaller than those caused by the more massive white dwarf
star, making reliable detection exceedingly difficult. Investigators have
claimed detection of several planets using this technique, most notably two that
were supposedly in orbit around nearby Barnard’s star. None of these claims has
stood the test of time. Accurate measurements of very small changes are also
needed for the Doppler method. Here, tiny shifts in the position of lines in a
star’s spectrum are the target, but the accuracy of the measurements is limited,
and this method will not pick out planets much smaller than Jupiter.

Success, Croswell tells us, finally came from a completely unexpected
direction, as astronomers observing stars similar to our Sun were refining their
techniques.

A neutron star is the remnant of a supernova—a giant star whose life
ends in a massive explosion. The core of the supernova, with a mass somewhat
greater than the Sun’s, has collapsed down to a diameter of just 20 kilometres
or so. The collapse causes it to spin rapidly, and as it rotates it emits beams
of radiation that sweep across space. From Earth, we observe these as regular
pulses of light or radio waves—hence the name “pulsar” for this type of
star. Their actual periods are so precise that minute changes in the observed
period, caused by the effects of even a small companion planet, can be
detected.

Croswell tells us how Alex Wolszczan and Dale Frail discovered a family of
three planets around pulsar B1257+12. The innermost is just under half the mass
of Mercury, with the outer two around three to four Earth masses and located at
distances from the pulsar that are similar to Mercury’s distance from our
Sun.

Planets in orbit around pulsars would be places highly inhospitable to life
as we know it, as they are swept by beams of gamma rays many times a second.
Perhaps this is why these first extrasolar planets have elicited a rather
lukewarm response from other planetary researchers, many of whom are driven by
the search for the grail of extraterrestrial life. For them, only planets in
orbit around stars like our Sun are really interesting. It should not be
forgotten, however, that the pulsar technique is the only one to have shown that
planets of masses similar to the Earth’s do exist. It will be a long time before
it will be possible to detect planets of this mass ranged around normal
stars.

The first planet around a Sun-like star has, however, finally been found. At
Geneva Observatory, Michel Mayor and Didier Queloz use a Doppler technique
capable of detecting Jupiter-sized planets. In September 1994, they first
observed 51 Pegasi, a star in the constellation Pegasus. By December it was
obvious that something strange was occurring, and further measurements showed
that the motion of the star varied periodically—every 4.2 days. The size
of the variation implied a planet with around half the mass of Jupiter, but
circling the star at a distance of only five solar diameters. Such a weird
planet worried them. Not until the following October were they confident enough
to announce its discovery.

At this time in California, Geoffrey Marcey and R. Paul Butler had already
built an even more sensitive system, but one that required considerable
computational effort to produce results. Partly because of this, their search
had not revealed any planets up to that point.

Within a few days of learning of the new planet’s discovery from Geneva,
however, Marcey and Butler were able to confirm its presence and were soon to
discover further planets whose signatures had lain buried within their
observational data. Though most of these planets, like the one orbiting 51
Pegasi, were very close to their parent star, one—discovered in orbit
around 47 Ursae Majoris—has a mass around three times that of Jupiter, and
is twice as distant from its star as our Earth is from the Sun. So for the first
time a solar system like ours was beginning to be revealed.

These techniques are not sensitive enough to reveal Earth-like planets, but
Croswell consoles us by describing how techniques such as adaptive optics and
infrared interferometry may be able to do so in the future. It is even possible
that, by spectral analysis of their atmospheres, we might detect the presence of
ozone, an excellent marker for the presence of oxygen, which could indicate a
life-bearing planet.

Croswell ends this excellent book with a 50-page section containing a
glossary of scientific terms used, and notes linked to each chapter. These give
references to an exhaustive bibliography of papers stretching as far back as
1860. This section is just one indication of the detailed research Croswell has
put into his book, making it a joy for any student of the subject. I find it
hard to see how anyone could have done a better job in bringing this exciting
field to the general reader.

In the summer of 1940, during some of the most desperate days of the Second World War, when a German invasion of Britain was expected within weeks, a young Welshman set out on a crucial journey to the US. He was escorting a metal deed box containing virtually all of Britain’s military secrets. By far the most important was a prototype of the resonant-cavity magnetron, the key to building high-power short-wavelength radars.

Britain’s own resources were stretched to the limit and help was needed to manufacture the magnetrons and develop the radars. As a result, the Americans set up the top-secret Radiation Laboratory and enlisted many of their most brilliant scientists to work on converting the British invention into a potent weapon.

So begins Robert Buderi’s masterly book. Having set the scene, he then takes us back to the mid-1930s to describe the early days of radar and the development of the Chain Home early warning radar system. This later allowed Britain’s fighter aircraft to intercept enemy planes efficiently and so made a significant contribution to winning the Battle of Britain. Much of The Invention that Changed the World charts radar’s subsequent development in Britain and in the US. Buderi shows how airborne radar played a key role in the winning of the Battle of the Atlantic by detecting U-boats, and also enabled Allied bombers to locate targets deep within Europe. Buderi also gives us an insight into the parallel development of the German Freya and Würzburg radars and the successful efforts to locate and destroy them in the run-up to D-day.

One of the Radiation Laboratory’s key developments was an anti-aircraft radar that controlled gun batteries via a “predictor” which took account of the time of flight of the shells and the aircraft’s course. Equipped with proximity fused shells, the batteries succeeded in downing many of the V-1 flying bombs before they reached London.

Having read the first half of this nearly 500-page book, the reader will be in no doubt that if the atomic bomb ended the war, radar won it. The story could have perhaps ended here, with the disbandment of the Radiation Laboratory and the dispersal of scientists back to their universities, armed with new techniques with which to continue their research. Instead, Buderi goes on to show just how many major discoveries of the postwar years arose out of wartime radar research.

Radars had, on occasion, been plagued by mysterious echoes and swamped by interference for which there was no obvious cause. At the end of the war, small groups in Britain and Australia began to investigate these anomalies. The echoes proved to have come from the ionised trails left by meteors as they arced across the sky; the interference appeared to be associated with the Sun. Sunspots turned out to be the cause of this interference, but it was soon discovered that there were other discrete sources of radio emissions in the heavens. As a result radio astronomy was born. Other researchers used their knowledge of radar to make other discoveries, such as nuclear magnetic resonance, the transistor and maser.

With the advent of the Cold War, the Americans realised that they needed something like the Radiation Laboratory to develop early-warning systems against long-range bombers and intercontinental ballistic missiles. The Lincoln Laboratory was set up and Buderi demonstrates how it developed SAGE, the first integrated air defence system, and giant radars to warn of missile attack. These radars were also used to study the planets, giving a precise scale to the Solar System-vital if spacecraft were to travel across it-and penetrating the thick clouds of Venus.

Buderi cannot be praised too highly for producing a scholarly and superbly researched book which is also enjoyable to read. He gives a real feeling of the lives of the dedicated scientists and engineers as they struggled to meet almost impossible deadlines. How their work led to many major discoveries following the war is an equally compelling story.