Dipen Bhattacharya
A favourite author of mine died recently. His name was Douglas
Adams. He wrote irreverent, but hilarious science fiction stories
satirizing mankind's self-importance. The collection of his stories
came to be known as "The Hitchhiker's Guide to the Galaxy." Douglas
Adams died young, he was only 49, but this article is not about
him. I mentioned Adams because of a quote that appears in
the prologue of his book titled, "Restaurant at the End of the Universe,"
where citizens of the Universe gather to celebrate the
end of time and then return to their respective time zones!
Adams wrote, "There is a theory which states that if ever anyone discovers
exactly what the Universe is for and why it is here, it will instantly
disappear and be replaced by something even more bizarre and inexplicable.
There is another which states that this has already happened."
Notwithstanding Adam's sarcasm, the quote succinctly summarizes
the modern quest to unravel the mysteries of the universe: its possible fiery
origin, its current expanding state and its doomed cold future. In this
process scientists have stumbled on natural phenomena that went against
the common sense and intuition. One can count quantum physics and relativity
among these, but today's story is about the scale of the Universe and
how it can also 'boggle' the mind.
Much of the unraveling of the Universe happened within the past
one hundred years when we gradually came to accept that the scale of the
Universe is simply too big. Even during the early 1900's, we were unaware
of its extent, we thought the Universe was comprised of only one stellar
association that was known as the Milky Way galaxy. Astronomers had seen
quite a few fuzzy nebulous objects in the sky, which, they thought, belonged
to the Milky Way.
But much before that, in 1755, German philosopher Immanuel Kant
published a book called "Universal Natural History and the Theory of
Heavens," where he suggested the possibility that the fuzzy nebulous
object seen through the telescopes could be conglomerations of stars outside
our galaxy. Kant called them "Island Universes." One hundred and sixty five
years later, in 1920, in a famous debate organized by the US National
Academy of Sciences, astronomer Herbert Curtis used the Kantian term
"Island Universe" to assert that the fuzzy spiral nebulae, that astronomers
had been observing for decades, actually reside outside our stellar system.
Soon thereafter, in a series of observations carried out by Edwin Hubble,
it was conclusively proved that those were indeed separate galaxies than
our own. In that decade of 1920, the size of the Universe increased by a
factor of more than hundred.
There was another surprising element to Hubble's observations.
It seemed the other galaxies were hurtling through space, they were running
away from the Milky Way at high speeds. Hubble observed that the further
the galaxy was from us, the faster it was moving away from us. This was
the first evidence of the Big Bang, an initial explosion that caused the
spacetime to expand.
Since Hubble's time astronomers have continuously strived to see
the farthest reaches of our universe. They have discovered gigantic
radio-galaxies, violent quasars, ripples in the distribution of the matter
that were created a few hundred thousand years after the big bang. With
these observations the scale size of the visible Universe increased to
billions of light years.
Compare this with the Ptolemaic conception of the Universe that
prevailed for almost one and a half millenia. Ptolemy's Universe barely
covered the distance to the Sun.
But just when people started getting comfortable with the notion of
the Big Bang and the huge size of the Universe, scientists recognized that the
conditions prevailing right after the Big Bang had to be very special to
match the cosmological observations of the modern day Universe. To
mitigate these inconsistencies in the early 1980's, Alan Guth
and other theoretical physicists developed a model of "Inflationary
Universe." In simple words the model states that when the Universe was
very very young, when it was less than one second old, it went through a
catastrophic inflationary phase. This inflation lasted only a minute fraction
of a second, but within that time the Universe was enlarged more than a
million trillon trillion trillion times. The consequence of this inflation is
that our observable Universe occupies only a tiny fraction of the "total"
Universe. The value of this fraction is model dependent, but for all
practical purposes inflationary theory renders the bigger Universe to be
unknowable.
Since 1980s, astronomers have carried out a series of observations to
verify the inflationary model. Recently, results obtained by a number of
microwave telescopes, flown on balloon platforms in the sky above Antarctica,
seemed to indicate that some sort of inflation did play a role in the early
Universe.
But true to Douglas Adam's saying, scientists have a penchant for
using bizarre notions that often go against everyday common sense. Paul
Steinhard of Princeton University and his colleagues have recently
published papers on an alternative to inflation where Big Bang is defined
as the collision of two Universes. The model is called Ekpyrotic Universe,
the term was borrowed from Greek, ekpyrosis in Greek stands for
"conflagaration" or "cataclysmic fire."
The core of this model lies in an extension of "String Theory"
known as the M-theory. String theory defines the fundamental building blocks
of nature as tiny vibrating strings. In M-theory the Universe has eleven
dimensions. In our Universe, seven of these dimensions are rolled up into
tiny microscopic filament that cannot be perceived with our modern day
observational techniques. In the Ekpyrotic model, two pre-existing
universes, each with four dimensional space-time properties collide within
a five dimensional space-time. The result is the Big Bang and
corresponding fluctuations in the matter density observed in the early
Universe.
But several critics including Andrei Linde, one of the major
proponents of the Inflation Theory, point out that such collision would
produce too much density fluctuation to match our observations of the
Universe. It possibly will take decades to conclusively prove or disprove
these theories, but it is simply astounding to contemplate how far we have
come even within the last hundred years in our pursuit for the scale size of
the Universe. Inflationary or the Ekpyrotic model, negative pressure or
string theory, all point to something beyond our visible Universe, which
might be closed to our exploration for eternity.
Scientists produce extraordinary notions, such as extra dimensions
or creation out of nothing, to explain the Universe. But in the end, just
like the concept of the slowing down of time in Einstein's relativity, we may
find such ideas persuasive. We will then wait for something more bizarre to
catapult us to the next shift in our knowledge paradigm.
June, 2001