   
Quantum fluctuations in an inflationary universe sometimes create regions with very
large density (the peaks) and divide the universe into regions with different laws
of physics (shown by different colours). We live in a low-density region. High density
regions expand extremely fast and produce more areas of even higher density. This
starts an eternal chain reaction of self-reproducing universes.
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The
hottest theory of cosmology in the last 20 years is that of cosmic “inflation”–a
burst of force in the very early universe that expanded a dot into almost boundless
space. Professor Andrei Linde of Stanford University, one of the theory’s chief exponents,
explains
Why
do we need a period of inflation in the universe’s early history?
Inflation explains several different things: why the universe is large, why it is
homogeneous, why it looks approximately the same in all directions, why it started
expanding simultaneously. It also explains how galaxies have been formed out of quantum
fluctuations.
Above all, we need to explain why different parts of the universe look approximately
the same. Imagine that the universe just started. At the very earliest time we can
consider [10-43 seconds after creation, called the Planck time], our universe was
a fraction of a centimetre. In this time, light and radiation could only have travelled
a tiny part of this space. So the left side of the universe could not know about
the right, and the middle about neither of them: there was no time for such contact.
Then all of a sudden we have a universe where everything is exactly the same. This
looks like a miracle–something physicists do not expect.
This is where inflation comes to the rescue. In the simplest version of the theory,
inflation starts at the Planck time. Until 10-35 seconds, space would blow up by
the power of 10 to the thousand billion, rather like an elastic membrane stretching
in all possible directions at a speed faster than light to a size much larger than
the universe you now see. Our universe would then be a tiny spot on a huge cosmic
balloon.
Is
there any matter inside this expanding space?
Usually people understand by matter particles that move, collide and build solid
things that we can see. But there are also fields–electromagnetic fields for example.
We do not see the magnetic field of the Earth, but we know that it is there. This
field is also a kind of matter.
Our assumption is that in the early universe, matter was in a very specific form
called a scalar field. We do not see this field–it looks like a vacuum–but if it
exists it may have a lot of energy. In a normal expanding universe the density of
matter decreases, but the scalar field and its energy do not decrease, meaning space
expands faster and for a much longer time. This leads to inflation.
Gradually, however, the scalar field loses energy. It decays and produces normal
particles, and the universe becomes hot as in conventional big bang theory.
But
where did these scalar fields come from?
They
could exist in the universe from the very beginning, just like any other matter.
Those parts of the universe where these fields were small did not experience inflation
and therefore remained very small. But regions of the universe with large scalar
fields have grown up enormously. We live in one such region now.
You
have used the expression “cosmic tree” to describe the true universe. What does this
mean?
Small
fluctuations in the field are necessary for the later formation of galaxies. But
if the fluctuations in this field are large, they could lead to the creation of new
parts of the universe–not just galaxies, but places where the fields have different
values, particles are lighter or heavier, and space and time different as compared
to our part of the universe. These are so far away from us, however, that you will
never have a chance of seeing them.
You
also call this inflation eternal. Does this mean it can happen again?
It may happen at some distance from us now. It might also happen here, though you
are not going to see it because inflation occurs when space is expanding from its
own resources. If inflation happens near you, don’t worry–it’s not going to crush
you. It’s just going to create a baby universe that you will not see.
Twenty years ago, when inflation was invented, it looked like a piece of science
fiction. Gradually it has become the standard cosmological theory, solving many problems
and making important predictions that can be experimentally confirmed. We’ve tried
hard doing something without inflation, but so far nothing else has worked. |
