Einstein’s Unfinished Symphony: Listening to the sounds of space-time
by Marcia Bartusiak, Joseph Henry Press, ÂŁ17.95, ISBN 0309069874
FANCY a gamble of the grandest kind? At the California Institute of
Technology there’s a corridor in which hangs a row of 10 framed letters. Each is
a bet between an eminent physicist and Kip Thorne, occupant of an office on the
corridor. Thorne is one of the world’s leading experts on Einstein’s theory of
general relativity, but he’s modest enough to admit that on one topic he has
unfailingly backed the wrong horse.
Back in 1978, Thorne bet the Italian physicist Bruno Bertotti a slap-up
dinner that gravitational waves—the ripples in the fabric of space and
time that Einstein predicted should permeate the cosmos—would be detected
within 10 years. A decade later Thorne had to pay up. By then, he had a similar
bet running with the Princeton astrophysicist Jeremiah Ostriker, wagering a case
of wine that gravitational waves would be found by 1 January 2000. Thorne lost
that one, too.
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The ever-optimistic Thorne is apparently now looking for takers for yet
another bet over when this last great prediction of Einstein’s theory will be
confirmed. Anyone wondering whether Thorne will be a three-time loser should
read Marcia Bartusiak’s account of the long, hard and sometimes bitter attempt
to tune in to what she calls Einstein’s “unfinished symphony”.
Even by the notoriously demanding standards of general relativity, the search
for gravitational waves is a mind-boggling challenge. Confirmation of the two
most famous predictions of general relativity—the precession of Mercury’s
orbit, and the bending of starlight by the Sun—seems a doddle in
comparison. The shift in Mercury’s orbit is a thumping great 0.0001 degrees per
year, while the Sun bends starlight by an angle equivalent to a pencil seen from
merely a kilometre away.
In contrast, the most powerful sources of gravitational waves in the cosmos
are predicted to distort our bit of space-time by around 1 part in 1021. Think
of that pencil again: roughly speaking, the distortion is the equivalent of a
pencil’s-width change in the diameter of our whole Galaxy. Oh yes, and such
events probably take place just a few times a century in our neck of the cosmic
woods. If you’re lucky.
As Bartusiak makes clear, there are many scientists who do feel lucky. They
are taking part in a worldwide effort to pin down the first unequivocal evidence
for the existence of gravitational waves. This is much more than just a vastly
expensive exercise in tying up scientific loose ends, says Bartusiak.
Gravitational waves, she points out, carry gravity around the cosmos just as
photons carry electromagnetism. And just as optical telescopes collecting
photons of light have revolutionised our understanding of the visible Universe,
so would a gravitational wave detector transform our understanding of events as
yet beyond our reach— including the big bang itself.
It is an impressive aim, and one that has persuaded the US National Science
Foundation to part with well over $300 million to help fund the device at
the centre of Bartusiak’s account—the Laser Interferometer Gravitational
Wave Observatory (LIGO). Consisting of two sets of L-shaped, evacuated vacuum
tubes with each arm 5 kilometres long, LIGO is now being assembled in Louisiana
and Washington. Once it’s completed, laser beams will be squirted down the tubes
and bounced off mirrors. The slightest change in the beams will be analysed for
the telltale signs of a gravitational wave distorting the space-time through
which the beams travel.
Bartusiak does a grand job of highlighting the challenges involved in this
staggeringly demanding project. Vacuum tubes pumped down to a trillionth of an
atmospheric pressure; mirrors polished so smooth that if they were magnified to
the size of the Earth, the largest bump in the surface would be just an inch
high; and magnetic control systems that can move those mirrors by less than the
width of an atomic nucleus.
She also has a gift for apt metaphors, talking evocatively of LIGO being able
to detect the “cymbal crashes” of exploding stars, the “drumbeat” of a swiftly
spinning pulsar and the “glissando” of two black holes merging into one
another.
Best of all, Bartusiak gives a sense of the ebb and flow of confidence among
scientists trying to hunt down gravitational waves, including the debacle over
the claims of the brilliant pioneer of gravitational wave research, Joseph Weber
of the University of Maryland. During the late 1960s, his team announced the
detection of more than a dozen gravitational wave events using detectors
consisting of huge metal bars. The trouble was, no one else could confirm them.
Bartusiak describes how arguments over the reality or otherwise of the events
became so heated that the chairman of one physics meeting had to intervene to
prevent Weber and one of his critics from slugging each other. Her account of
the rise and fall of Weber’s claims should be read by anyone who thinks the
scientific community pours its vitriol only on outsiders.
Where I found her book less good is that she fails to give a really clear
explanation of just how the designers of LIGO and its ilk can hope to detect
such tiny effects. I for one still cannot understand why the random jolts of
quantum uncertainty don’t wash out the feeble wobbles of space-time they are
looking for.
More baffling than quantum uncertainty itself is how the gravitational wave
hunters have managed to extract these vast sums of taxpayers’ money for so
strange a project. For, believe it or not, the existence of gravitational waves
was confirmed back in the 1980s by studies of two pulsars orbiting each other.
Their behaviour bore out Einstein’s predictions to within 0.5 per cent and a
Nobel prize was handed out to Russel Hulse and Joseph Taylor in 1993. No
scientist seriously doubts that gravitational waves exist.
So, as far as I can tell, governments have handed a small group of scientists
hundreds of millions of dollars to build vast devices that have only a slim
chance of detecting a phenomenon we already know exists. Of course, LIGO will be
a useful test bed for the technology of detecting gravitational waves, and will
become dramatically more sensitive as that technology improves. But the huge
amounts already spent are almost certainly just a down payment on something much
bigger.
In the end, I came away from Bartusiak’s nicely judged account of this
awe-inspiring project feeling that as long as researchers still devote their
lives to such long shots, and governments continue to fund them, there is still
hope for the scientific enterprise.