Between the lines: multiverse special

Physics World, May 19, 2011http://physicsworld.com/cws/article/indepth/45846#art-many

A trio of books about the idea of the multiverse


Multiverses on parade

               The Hidden Reality, Brian Grrene
               Allen Lane/Knopf (2011)
               £25.00/$29.95hb 384pp

A universe with infinite spatial extent will contain infinitely many
mini-universes. An infinite number of these mini-universes will be
exactly like our own. Welcome to the mind-blowing nature of infinity –
and the sometimes equally mind-blowing nature of the multiverse, which
is a common theme among the books in this month's column. First up is
Brian Greene's The Hidden Reality, which explores nine variations on
the multiverse theme. Of these, the type of multiverse that arises as
a consequence of infinite space – Greene calls it the "quilted
multiverse" because regions of space will repeat like patterns in a
quilt – is actually one of the easiest to comprehend. From then on,
things get both more complicated and more interesting, as Greene leads
the reader through cosmic inflation, string theory and the "many
worlds" interpretation of quantum mechanics. Greene's tour of
multiverses also takes in some even more exotic territory, as he
considers the possibility that our distant descendents could one day
create simulated universes – or that we are living in one such
simulation (as in the film The Matrix). All of this is, of course,
extremely speculative, and large swathes of it seem fated to remain
that way forever. Yet those who believe – not unreasonably – that
multiverse theories have more in common with religion or philosophy
than they do with science should still give Greene's book a chance.
The chapter on "Science and the multiverse", in particular, explores
the many criticisms of multiverse theories in a sensitive and
thoughtful way. Sceptical readers will find they can appreciate
Greene's logic and candour, even if they ultimately decide to disagree
with him.

For physicsworld.com's interview with Brian Greene, go to:http://physicsworld.com/cws/article/indepth/45854

Many universes, many quotations

               The Book of Universes, John Barrow
               Bodley Head (2011),  £20.00 368pp

In contrast to Greene's book, which focuses on the most up-to-date
views on multiverse theories, John Barrow's The Book of Universes
takes a more historical approach. By beginning with the universe
according to Aristotle and other Greek philosophers, and continuing
through Copernicus, Kant and Laplace into the modern era, Barrow makes
an important point: our concept of the universe has expanded
tremendously over the years, so it is unsurprising that scientists are
now seeking to extend it still further. The downside of this leisurely
tour, however, is that the book takes an awfully long time to get
going. After 100 pages, we have only just reached Einstein and the
20th century.

The pace does pick up later in the book, with a good chapter on
"post-modern universes" that covers, among other things, Barrow's own
research on the possibility that the speed of light was not constant
in the early universe. However, even here the narrative is repeatedly
interrupted, because either the author or his publisher thought it was
a good idea to chuck in at least one quotation every six paragraphs or
so. We do not normally discourage witty comments from scientists, but
The Book of Universes contains so many that they actually get in the
way. Worse, for every quote that reveals a deeper truth – such as
Chaim Weizmann's comment that "Einstein explained his theory to me
every day and on my arrival I was fully convinced that he understood
it" – there seem to be at least two that have made it into the book
simply because they are vaguely amusing. Whoever was responsible for
filling the book with them should have heeded the words of crime
novelist Dorothy L Sayers, who once wrote that "A facility for
quotation covers the absence of original thought." (And the reviewer
is quoting!)


A sceptical overview

               Higher Speculations: Grand Theories and Failed Revolutions in
Physics and Cosmology
               Helge Kragh, Oxford University Press (2011) £35.00/$63.00hb 408pp

A little over a century ago, some British mathematicians and
physicists thought they had uncovered the theory of everything.
According to their theory, the fundamental particles of nature were
actually composed of different types of vortices, swirling in a
perfect, frictionless fluid. This theory was beautiful, elegant and
coherent. As late as 1903, the American physicist Albert Michelson
declared that it "ought to be true, even if it is not". Vortex theory
could also explain – in a way that traditional theories of solid atoms
could not – the existence of lines in the spectra of chemical
elements: clearly, the lines represented different modes of vibration
in the vortex atom. Of course, no-one now believes in vortex atoms,
but as Helge Kragh explains in Higher Speculations: Grand Theories and
Failed Revolutions in Physics and Cosmology, the rise and fall of
vortex theory makes a useful cautionary tale for modern
theory-of-everything enthusiasts. Kragh, a historian of science, is
interested in how such explanations arose, why they failed and whether
any parallels can be drawn with modern theories – including those that
incorporate some version of a multiverse. Much of the book's second
half is devoted to teasing out the links between theories of the
multiverse, string theory and the anthropic principle; Kragh defines
the latter as "an attempt to deduce non-trivial consequences about
nature from the consideration that what we observe must be compatible
with our existence". These three concepts have quite separate
historical origins, Kragh observes, yet since the mid-1980s some
elements of them have merged. His scholarly book offers a sceptical
but largely impartial overview of the multiverse and related
speculation.