Stephen Hawking's explosive new theory
Date: Sunday, June 29th, 2008 (CST )
Topic: Cosmology & Astronomy
 Prof Stephen Hawking has come up with a new idea to explain why the Big Bang of creation led to the vast cosmos that we can see today. Astronomers can deduce that the early universe expanded at a mind-boggling rate because regions separated by vast distances have similar background temperatures. They have proposed a process of rapid expansion of neighbouring regions, with similar cosmic properties, to explain this growth spurt which they call inflation.
But that left a deeper mystery: why did inflation occur in the first place? Now New Scientist reports that an answer has been proposed by Prof Stephen Hawking of Cambridge University, working with Prof Thomas Hertog of the Astroparticle and Cosmology Laboratory in Paris.
Prof Hawking is best known for his attempts to combine theories of the very small, quantum theory, and that of gravity and the very big, general relativity, into a new theory, called quantum gravity. Quantum mechanics is awash with strange ideas and can shed new light on inflation, which came in the wake of when the universe itself was around the size of an atom.
By quantum
lore, when a particle of light travels from A to B, it does not take
one path but explores every one simultaneously, with the more direct
routes being used more heavily.
This is called a sum over histories and Prof Hawking and Prof Hertog propose the same thing for the cosmos.
In this theory, the early
universe can be described by a mathematical object called a wave
function and, in a similar way to the light particle, the team proposed
two years ago that this means that there was no unique origin to the
cosmos: instead the wave function of the universe embraced a multitude
of means to develop.
This is very counter
intuitive: they argued the universe began in just about every way
imaginable (and perhaps even some that are not). Out of this profusion
of beginnings, like a blend of a God’s eye view of every conceivable
kind of creation, the vast majority of the baby universes withered away
to leave the mature cosmos that we can see today.
But, like any new idea,
there were problems. The professors found that they could not explain
the rapid expansion - inflation - of the universe, evidence of which is
left behind all around us in what is called the cosmic microwave
background, in effect the echo of the big bang, a relic of creation
that can be measured with experiments on balloons and on space probes.
Now, in a paper in Physical
Review Letters with Prof James Hartle of the University of California,
Santa Barbara, they realised that their earlier estimates of inflation
were wrong because they had not fully thought through the connection
between, on the one hand, their theoretical predictions and, on the
other, our observations of the echo.
At first, they found that
the most probable history of the cosmos had only undergone "a little
bit of inflation at the beginning, contradicting the observations,"
said Prof Hertog. Now, after a correction to take account of how the
data we have on inflation is based on only a view of a limited volume
of the universe, they find that the wave function does indeed predict a
long period of inflation.
"This proposal, with volume
weighting, can explain why the universe inflated," Prof Hawking tells
New Scientist. By taking into account that we have a parochial view of
the cosmos, the team has come up with a radical new take on cosmology.
Most models of the universe
are bottom-up, that is, you start from well-defined initial conditions
of the Big Bang and work forward. However, Prof Hertog and Prof Hawking
say that we do not and cannot know the initial conditions present at
the beginning of the universe. Instead, we only know the final state -
the one we are in now.
Their idea is therefore to
start with the conditions we observe today - like the fact that at
large scales one does not need to adopt quantum lore to explain how the
universe (it behaves classically, as scientists say) - and work
backwards in time to determine what the initial conditions might have
looked like.
In this way, they argue the
universe did not have just one unique beginning and history but a
multitude of different ones and that it has experienced them all.
The new theory is also
attractive because it fits in with string theory - the most popular
candidate for a "theory of everything."
String theory allows the
existence of an" unimaginable multitude of different types of universes
in addition to our own," but it does not provide a selection criterion
among these and hence no explanation for why our universe is, the way
it is", says Prof Hertog.
"For this, one needs a theory of the wave function of the universe."
And now the world of
cosmology has one. The next step is to find specific predictions that
can be put to the test, to validate this new view of how the cosmos
came into being.
Copyright: Telegraph
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