https://www.newscientist.com/article/mg15420814-800-review-the-ultimate-free-lunch/
Review : The ultimate free lunch
By Marcus Chown
The Inflationary Universe by Alan Guth,
Addison-Wesley/Jonathan Cape, £18.99, ISBN 0 224 04448 6
IN 1979, a 32-year-old American physicist called Alan Guth came up with a
crazy idea. If he was right, the Universe was nothing more than a submicroscopic
quantum fluctuation, all the stars and galaxies which crowd space out to the
limits probed by the most powerful telescopes accounted for a mere million
million million millionth of all there was and, in principle, it was possible to
make a universe in the laboratory.
Guth christened his crazy idea “inflation”. And since 1979, there have been
many attempts to explain it to a popular audience, with varying degrees of
success. This latest one, The Inflationary Universe, has the merit of
coming from the horse’s mouth.
Guth invented inflation to solve the “monopole problem” that arises in Grand
Unified Theories (GUTs). These theories attempt to show that the three
nongravitational forces of nature—the electromagnetic force and the strong
and weak nuclear forces—are really aspects of a single “superforce”. GUTs
maintain that the differences between the various kinds of particles in nature
are not fundamental, but a consequence of the way they interact with the more
basic “Higgs field”.
When the Higgs field was symmetric—at the ultra-high energies in the
earliest moments of the big bang—all particles were identical. Only when
the Universe cooled enough to shatter the symmetry were particles endowed with
their distinctive characters.
The monopole problem arises because, on decaying from its symmetric state,
the Higgs field can adopt wildly different directions in neighbouring regions of
space, creating permanent “defects” that behave just like isolated north or
south magnetic poles. According to the calculations of Guth and others, the big
bang should have spawned as many monopoles as protons and neutrons, a result in
spectacular disagreement with observations.
The only way to suppress the creation of monopoles was by delaying the
crucial symmetry-breaking “phase transition” of the Higgs field. Because
regions over which the field could align itself grew with time, the field would
be smoother when the Universe was older. GUT monopoles, the progeny of chaos,
would be scarcer.
The delaying mechanism Guth hit on was supercooling. Just like water, which
can supercool to 40 °C below its normal freezing point before turning to
ice, the Higgs field could have persisted in its high-energy state long after
the time appointed for its symmetry-breaking transition.
Supercooling was perfect for solving the monopole problem. However, its
consequences for cosmology were dramatic. The Universe would be temporarily
suspended in a “false vacuum”, a bizarre state characterised by a huge and
negative pressure.
Einstein’s field equations contain a pressure term which, together with
mass-energy, is responsible for generating gravity. In normal matter, the
pressure term is of no consequence, but it would have been overwhelmingly
important in the supercooled false vacuum. Being negative as well, it would have
generated a repulsive force. Gravity would blow instead of suck, causing the
newborn Universe to inflate enormously.
Most amazingly, as the Universe ballooned in size—from the diameter of
a proton to that of a grapefruit—the negative pressure would conjure
seemingly limitless quantities of energy from the vacuum. It was this energy
that, when the false vacuum finally decayed, would be converted into matter
heated to a blisteringly high temperature that would then expand as the big
bang.
If inflation was correct, here was an explanation for where most of the
matter in the Universe came from, Guth reasoned. It was spirited out of the
vacuum itself, “the ultimate free lunch”.
It was a mind-boggling conclusion. And it was arrived at by an ageing postdoc
facing certain unemployment unless he could come up with something important to
impress his superiors—and fast. Guth succeeded beyond his wildest dreams,
catapulting himself from the edge of academic oblivion to academic superstardom,
where he was fêted by the likes of Stephen Hawking as the youthful creator
of an entire new field of science. The accidents and chance remarks that brought
about this dramatic transformation in Guth’s fortunes are recounted in The
Inflationary Universe, a riveting behind-the-scenes story of science at its
most esoteric frontier.
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