Stardust by John Gribbin, Allen Lane, 拢18.99, ISBN
0713993367
AT THE dawn of the Universe鈥攚ell, three minutes after the big
bang鈥攖he only two chemical elements around were hydrogen and helium. As a
human being, you鈥檒l realise that things have changed. Carbon, oxygen and
nitrogen have been added to the chemical mix that forms our living, watery
bodies, while a clutch more elements produced planet Earth.
Exactly how were these elements made, what determines their proportions, and
what mechanism scattered them? And how has the content of the Universe鈥檚
chemical store cupboard changed with time?
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Today, 99 per cent of the mass of the Universe is still hydrogen and helium.
Astronomers have the annoying habit of referring to all the other elements as
鈥渕etals鈥�. These, chemically combined, make smoke-sized particles in the
envelopes of giant stars鈥攖hat is, stardust.
In his book of the same name, John Gribbin skilfully and engagingly traces
the historical sequence of scientific work on the mystery of the metals. He sets
out the inquiry鈥檚 key steps rather like Sherlock Holmes reading clues.
In the mid-19th century, astronomers had no idea how the Sun could keep
shining for as long as geological and biological evolution seemed to require.
The discovery of radioactivity pointed to the probable energy source. Only in
1919 did Francis Aston鈥檚 experimental skill reveal that a helium atom was less
massive than four hydrogen atoms, pointing to the transmutation of the first two
elements.
In the 1920s astrophysicist Arthur Eddington calculated the physical
conditions in the centres of typical stars: these were just right for
transmutation to take place very slowly.
It took about 30 years for the next step. The combined genius of Geoffrey and
Margaret Burbridge, William Fowler and Fred Hoyle (B2FH as the group was known)
showed how the stellar factory could make elements up to iron and beyond.
Astronomers soon realised not only that stars could produce exotic stardust, but
also that nova and supernova explosions could scatter the dust into space. Then
it could be incorporated into newly forming stars鈥攔ecycling on an
astronomical scale.
The book鈥檚 pace never slackens, and the quest for clues and solutions doesn鈥檛
falter. Gribbin skilfully emphasises what was misunderstood at any moment in the
history, rather than reconstructing a path to today鈥檚 鈥渃orrect鈥� interpretations.
But I was slightly worried that he seems to intimate that astrophysics and
astrobiology today contain fewer misunderstandings than they did in the past. I
am not convinced that we know quite as much about the ubiquitous nature of
intelligent life, or the role of comets for instance, as Gribbin makes out.