The Five Ages of the Universe by Fred Adams and Greg Laughlin, The Free
Press, 拢18.99/$25, ISBN 0684854228
REPORTS of the death of the Universe are much exaggerated. Yes, one day in
the far future the Sun will be a chilly cinder, its very protons decaying away
unimaginably slowly. But consider what 鈥渢he far future鈥� means. The sky is due to
go dark 1013 or 1014 years from now鈥攁nd that margin of estimate alone is
about 10 000 times the current age of our Universe. There is, you could say,
plenty of time at the end.
In The Five Ages of the Universe, Greg Laughlin and Fred Adams
journey through these unimaginable expanses of time. At one point, we are
fast-forwarded to the year 101600鈥攖hat鈥檚 the year 1, followed by 1600
zeroes. Taking pity on their readers, Adams and Laughlin define the year 105 as
the fifth 鈥渃osmological decade鈥�, the year 1050 as the 50th, and so on. Armed
with this shorthand, which is convenient so long as you forget the
non-logarithmic meaning of 鈥渄ecade鈥�, it is at least possible to pretend that we
have tamed the future.
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Hardly a page goes by without the authors painting a picture of some new and
totally bizarre cosmic landscape of the far future. But be warned: a PhD is
needed to understand many of the explanations. Adams and Laughlin are both
astrophysicists鈥擜dams at the University of Michigan Ann Arbor and Laughlin
at the University of California at Berkeley鈥攁nd much of the book
represents their own cutting edge research.
Predicting the long-term future of the Universe is nothing new鈥擣reeman
Dyson and Martin Rees first attempted a detailed picture back in the 1960s. But
physics and cosmology have made enormous strides since, and Adams and Laughlin
have managed to put together a coherent scenario. Their framing device helps:
they divide the history of the Universe into 鈥渇ive ages鈥�, each defined by the
type of astronomical objects that predominated at that time.
The first age鈥攁nd the least interesting, because it has been covered in
so many other books鈥攊s the Primordial Era. It stretches from 鈥渃osmological
decade鈥� 鈭�50 to 5鈥攖hat is, from 10-43 seconds after the Big Bang to the
year 100 000. This is the era of 鈥渋nflation鈥�, the divergence of the forces of
Nature, the triumph of matter over antimatter and the forging of the light
elements from hydrogen in a 10-minute orgy of 鈥渘ucleosynthesis鈥�. It comes to an
end with the condensation of the first atoms, freeing matter from the tyranny of
radiation so that the stuff of the Universe can begin to congeal into the first
stars and galaxies.
Blazing down
The Stelliferous Era鈥攖he age of stars鈥攊s our era. Living as we do
in the 10th cosmological decade, we are still in the blazing dawn of the
Universe when the most profligate stars set the heavens afire, squandering their
nuclear fuel.
But it is the meek that will inherit the Universe, say Adams and Laughlin.
More than 70 per cent of stars are 鈥淩ed dwarfs鈥� that are too dim to be visible.
But like misers who hoard their resources, these stellar embers will be around
when spend-spend-spend stars are long gone. In fact, because red dwarfs burn all
their hydrogen fuel rather than, like the Sun, just the hydrogen in their cores,
some will still be around well into the 14th cosmological decade.
But what of this future? Adams and Laughlin emphasise repeatedly that as
longer and longer vistas of time open up, events that are more and more unlikely
become important. Take stellar collisions. Stars in our Milky Way are like sand
grains separated by kilometres of empty space. Collisions are so unlikely that a
star lives for 100 trillion years, on average, before it hits another star. But
on timescales of 100 trillion years or more, such a collision becomes a
certainty. The Milky Way will gradually 鈥渆vaporate鈥� as red dwarfs ricochet off
each other into intergalactic space.
And after the hydrogen is all used up? The party keeps on going. The third
age, the Degenerate Era, will be dominated by white dwarfs, the super-dense
relics of burnt-out stars, and brown dwarfs, objects that never got hot enough
to become stars in the first place. Adams and Laughlin subscribe to the idea
that a significant part of the Universe鈥檚 invisible or 鈥渄ark鈥� mass consists of
as-yet-undiscovered weakly-interacting massive particles (WIMPs). These will,
they say, gather in the cores of dwarf stars. There, very slowly, different
flavours of WIMP will collide and annihilate, warming the dwarfs to a chilly 63
degrees kelvin.
In the 35th cosmological decade, when the annihilation of dark matter is a
distant memory, they foresee yet another fuel coming into its own: the decay of
protons into, say, pions and positrons. Stars will be powered by their own
disintegration鈥攁 process that in human terms translates as eating yourself
to keep warm.
As the decades roll on, the successive stellar fuel sources become more and
more measly. Stars which in their youth burned at tens of thousands of degrees
will in their ultra-old age glow at only a few tens of degrees, and then at
fractions of a degree. Events will slow down remorselessly as the energy
differentials that drive interesting phenomena in physics become smaller and
smaller. But the future is not boring. While processes in the Universe slow
down, the time available for things to happen grows with each 鈥渃osmological
decade鈥�: interesting things continue to unfold.
Interesting things like life. It was Dyson who first postulated that all life
needs is structure, not biochemistry. Adams and Laughlin regard life as
possible, even probable, in the complex atmospheres of white dwarfs, which are
rich in heavy elements. And in the Black Hole Era鈥� the fourth and
penultimate age of the Universe鈥攑erhaps life will be made out of strings
of black holes. With so little energy about, conversations could take trillions
of trillions of years. Such life structures might have the same number of
thoughts in a million gelid years as we have in three score and ten. But time is
no problem: black holes will be around until the 100th cosmological decade.
Shiny new toy
The sheer chutzpah of physicists is amazing. Not content to speculate on the
first 10-43 seconds of the Universe, they believe they can map out鈥攁t
least roughly鈥攖he next 10100 years and beyond. But the point is not that
we are sure the future will turn out the way Adams and Laughlin say. Rather,
it鈥檚 that in 1999, for the first time, we have in our hands a self-consistent
model of physics and cosmology.
Of course, self-consistency does not necessarily imply correctness. However,
like children handed a new and exciting toy, we would be mad not to see what it
can do. Adams and Laughlin have cranked the shiny new machinery of physics.
They have taken us on the ultimate journey through space and time, probing
for鈥攁nd finding鈥攖he limits of our understanding.
Even at the cold, dark end they find hope. They raise the possibility of a
Universe spontaneously 鈥渢unnelling鈥� into a lower-energy state of the quantum
vacuum, wiping the slate of physics clean and starting afresh with a new
Universe, new laws and new possibilities. It鈥檚 a vision that defies all the
odds, and proves again that science is stranger than science fiction, and that
the Universe may continue to surprise for eternity.