David M. Rountree  

Thursday, 11 December 2008, From the UK "The Independant"
http://www.independent.co.uk/opinion/commentators/bernard-carr-fifth-dimensions-space-bubbles-and-other-facets-of-the-multiverse-1061143.html

The word "universe" literally means everything that exists. But the
history of astronomy might be regarded as a sequence of steps by
which the universe has seemed to get bigger. So what we mean
by "everything" has changed.

Nowadays most cosmologists accept the Big Bang theory – that the
universe started in a state of great compression around 14 billion
years ago. This means that the furthest we can see is the distance
that light has travelled since the Big Bang. This defines the size of
the "observable" universe – but the universe itself could extend much
further than this.

Recent developments in cosmology and particle physics have led to the
even more radical proposal that our universe could be just one of
many – that it is part of a "multiverse", because any mechanism that
can produce our universe could generate others. Some people argue the
universe undergoes cycles of expansion and recollapse, giving
universes spread out in time. Others say that our universe is just
one of many "bubbles" spread out in space. Yet others suggest there
could be universes spread out in a hidden fifth dimension.

A particularly interesting possibility is that the constants of
physics could vary in different universes. If so, the fine tunings
which appear necessary for the emergence of life might not require
a "creator" who designed the universe for our benefit. A key issue
here is whether some fundamental theory will determine all the
constants uniquely. This relates to the question posed by
Einstein: "Did God have any choice when he created the universe?"

But is the "multiverse" a proper scientific proposal or just
philosophy? Despite the growing popularity of the proposal, the idea
is speculative and currently untestable – and it may always remain
so. Astronomers may never be able to observe the other universes with
their telescopes and particle physicists may never be able to detect
the extra dimensions with their accelerators. So, although some
physicists favour the multiverse because it may do away with the need
for a creator, others regard the idea as equally metaphysical. What
is really at stake is the nature of science itself.

Bernard Carr, Professor of Astronomy and Mathematics at Queen Mary,
University of London, spoke at The Royal Astronomical Society earlier
this week