How did the Universe begin is one of the most profound questions
of all. But to Stephen Hawking, who has perhaps come closer than
anyone to answering it, the question doesn't in fact even exist.
Hawking, who holds Newton's
Lucasian Chair at the University of Cambridge, UK, and his
colleague Thomas Hertog of the European Laboratory for
Particle Physics at CERN in Geneva, Switzerland, are about
to publish a paper claiming that the Universe had no unique
beginning. Instead, they argue, it emerged out of a
profusion of beginnings, the vast majority withered away
without leaving any real imprint on the Universe we know
today. Only a tiny fraction of them blended to make the
current cosmos, Hawking and Hertog claim. According to their
article in Nature:
He and Hawking call their
theory 'top-down' cosmology, because instead of looking
for some fundamental set of initial physical laws under
which our Universe unfolded, it starts 'at the top',
with what we see today, and works backwards to see what
the initial set of possibilities might have been. In
effect, says Hertog, the present 'selects' the past.
Within just a few seconds
after the Big Bang, a single history had already come to
dominate the Universe, he explains. So from the
'classical' viewpoint of big objects such as stars and
galaxies, things happened only one way after that point.
Other 'histories', say, one in which the Earth formed
only 4,000 years ago, have made no significant
contribution to this cosmic evolution.
But in the first instants
of the Big Bang, there existed a superposition of ever
more different versions of the Universe, instead of a
unique history. And most crucially, Hertog says that
"our current Universe has features frozen in from this
early quantum mixture".
In other words, some of
these alternative histories have left their imprint
behind. This is why Hertog and Hawking insist that their
'top-down' cosmology is testable. Hertog says that the
theory predicts the pattern of the variations in
intensity of microwave background radiation, the
afterglow of the Big Bang now imprinted on the sky,
which reveal fluctuations in the fireball of the nascent
Universe. These variations are minute, but space-based
detectors have measured them ever more accurately over
the past several years.
What's fascinating about this
theory is that, by extension, it may be transferable to you
as an individual observers. By applying a stronger variant
of the anthropic principle, one could argue that the cosmos
has structured itself around your very own existence.
That, they insist, is the only possible conclusion if we are
to take quantum physics seriously. "Quantum mechanics
forbids a single history," says Hertog. “Quantum mechanics
forbids a single history.”
The researchers' theory comes
in response to a problem raised by 'string theory', one of
the best hopes for a theory of everything. String theory
permits innumerable different kinds of universe, most of
them very different from the one we inhabit. Some physicists
suspect that an unknown factor will turn up that rules out
most of these universes.
But Hawking and Hertog say that
the countless 'alternative worlds' of string theory may
actually have existed. We should picture the Universe in the
first instants of the Big Bang as a river of all these
possibilities; like a projection of billions of movies
played on top of one another.
Most crucially, Hertog says
that "our current Universe has features frozen in from this
early quantum mixture".
As the two researchers work out
top-down cosmology in more detail, they hope to be able to
calculate the spectrum of these microwave fluctuations and
compare it with observations.
The theory also suggests an
answer to the puzzle of why some of the 'constants of
nature' seem finely tuned to a value that allows life to
evolve. If we start from where we are now, it is obvious
that the current Universe must 'select' those histories that
lead to these conditions. Otherwise we simply wouldn't be
Now, how cool is that!
Posted by Casey Kazan.