The Accelerating Universe by Mario Livio, John Wiley, $27.95, ISBN
047132969X
TIME and time again, when a theory that physicists judge to be beautiful
squares up to one considered ugly, the beautiful one invariably triumphs. Why?
In his thought-provoking book, The Accelerating Universe, astronomer
Mario Livio attempts an answer.
Livio straddles two worlds. A self-confessed 鈥渁rt fanatic鈥�, he is also the
head of science programmes at the Space Telescope Science Institute in
Baltimore, Maryland, which controls NASA鈥檚 Hubble Space Telescope. He is
uniquely qualified to tackle this question, as he explores what constitutes
beauty in the worlds of art and science.
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Livio argues that all beautiful scientific theories possess three essential
attributes: symmetry, simplicity and an adherence to the generalised Copernican
principle.
Symmetry is the property of remaining the same under certain transformations.
In physics, this requires that fundamental laws are the same today as they were
last week, the same around Alpha Centauri as they are on Earth, and so on. As
for simplicity, this is the requirement that physics replaces many questions
with a few, basic equations.
Livio鈥檚 third requirement for a beautiful theory is that it should adhere to
the principle of mediocrity鈥攁 bit disheartening for those in pursuit of
beauty. More commonly known as the generalised Copernican principle, this simply
states that the best theories are those that do not require the observer to live
in a special place in the Universe or at a special time in history in order to
be true.
Now we come to the nub of Livio鈥檚 engaging book and the reason for its title.
Beauty, in Livio鈥檚 words, is 鈥渋n distress鈥�. In 1998, physicist Saul Perlmutter
and his colleagues at the Lawrence Berkeley Laboratory in California discovered
that, contrary to all their expectations, the expansion of the Universe is not
slowing under the braking effect of gravity, but speeding up. Most of the energy
content of the Universe is apparently not contained in matter, nor even in
invisible 鈥渄ark鈥� matter, but in empty space. And this empty space is driving the
galaxies apart at an accelerating rate.
Why the distress? Well, the repulsive force of empty space, as encapsulated
in the so-called cosmological constant, turns out to be smaller than that
predicted by theory by a highly embarrassing 1 followed by 123 zeros. The
reaction of many physicists on hearing of this discovery was much the same as
Isidor Rabi鈥檚 on hearing of the discovery of the muon, the heavy cousin of the
electron: 鈥淲ho ordered that?鈥�
Desperate situations require desperate remedies. Steven Weinberg, winner of
the Nobel Prize for Physics, may be well-known for his hope that there exists a
鈥渇inal theory鈥濃�攁 framework in which everything from the mass of the
electron to the strength of gravity is pinned down by mathematical
self-consistency. Even he, however, has had to resort to the 鈥渁nthropic
principle鈥� to explain the repulsion of empty space. This says the cosmological
constant is the magnitude it is because if it were any bigger or smaller, it
would have hindered the formation of galaxies and stars鈥攁nd the existence
of human observers. Weinberg and Livio agree that appealing to the anthropic
principle is highly unsatisfactory.
So has beauty died in physics? Livio thinks not. On the face of it, he
admits, we appear to live in a messy Universe composed of about 5 per cent
ordinary matter, 25 per cent cold and hot dark matter and 70 per cent mysterious
鈥渄ark energy鈥� of empty space. He points out that this hotchpotch hides the fact
that the Universe has exactly the 鈥渃ritical density鈥� required by the theory of
inflation, which solves two of the outstanding puzzles of cosmology: why the
Universe is homogenous, that is, why matter is spread uniformly through space,
and why the Universe is 鈥渇lat鈥�, that is, at the critical density.
Livio likens the situation to that of Kepler鈥檚 discovery that the planets
moved in messy, elliptical orbits rather than beautiful, circular orbits. Now we
realise the superior beauty beneath鈥攖he hand of the inverse-square law of
universal gravity. In the same way, Livio鈥檚 fervent hope is that the repulsion
of empty space turns out not to be an ugly duckling, but a beautiful swan. Let鈥檚
hope he is right.