14 October 2005
The inflationary theory for
the Big Bang has taken hold in recent years, and is now well-enshrined as
mainstream cosmology. This theory explains both the uniformity of the
universe (on the largest scale) and also the reason why there are galaxies
and stars on a smaller scale.
The theory goes like this:
In the first microsecond, the universe was an enormously hot gas of
particles (plasma). Then a strange thing happened (to say the least). The
kind of physics that governed the universe was changing as the temperature
rapidly cooled, and we got to a temperature where gravity became briefly
repulsive, and blew the universe up so that the entire visible universe
(billions of light years) grew almost instantaneously from a region the size
of a (present day) atom!
This is not a fairy tale –
or at least, there are a lot of very smart people in the world who are
taking it seriously.
That plasma before the BB
may have been quite lumpy, but the lumps were bigger than a present-day
atom. That’s why, so the story goes, we see the same kinds of galaxies and
quasars when we look out as far as we can see (billions of light years) to
the East, or billions of light years to the West. They all grew from
the same "atom".
But why are there galaxies
and stars at all? The theory is that this atom-sized lump that became the
universe wasn’t completely uniform because of quantum mechanics. QM makes
everything lumpy, but only a tiny bit. Inflation made these smallest of all
lumps into hotter and cooler spots in the universe, and the cooler regions
didn’t expand so fast, so they ultimately settled out into galaxies and
stars. The rest is history.
The bottom line is that
physicists today are hoping to learn something about the quantum structure
of space and time on the tiniest scale (10-33 cm, or a millionth of a
billionth of a billionth the size of a present-day atom) by studying (statistically)
the biggest structures in the sky - which are the hot and cold spots in the Cosmic
this week in the American Scientist