FUNDAMENTAL BUILDING BLOCKS 313
This is a 2-dimensional slice of a
6-dimensional mathematical structure
called a Calabi-Yau manifold. It is
suggested that string theory’s six
hidden dimensions may take this form.Despite its current limitations,
M-theory has proved a huge
inspiration to various fields of
physics and cosmology. Black hole
singularities can be interpreted
as string phenomena, as can the
early stages of the Big Bang. One
intriguing upshot of M-theory is the
“cyclic universe” model proposed
by cosmologists such as Neil Turok
and Paul Steinhardt. In this theory,
our universe is just one of many
separate branes separated from
each other by minute distances in
11-dimensional space-time, and
drifting minutely in relation to one
another on trillion-year time scales.
Collisions between branes, it has
been argued, could result in huge
releases of energy and trigger new
Big Bangs.
Theories of everything
M-theory has been proposed as a
possible “Theory of Everything”—
a means of uniting the quantum
field theories that successfully
describe electromagnetism and
the weak and strong nuclear forces
with the description of gravity
provided by Einstein’s general
theory of relativity. Hitherto, a
quantum description of gravitation
has remained elusive. Gravity
appears to be radically different
in nature from the other three
forces. These three forces all act
between individual particles but
only on relatively small scales,
while gravity is insignificant except
when huge numbers of particles
conglomerate, but acts across
enormous distances. One possible
explanation of gravity’s unusual
behavior is that its influence at the
quantum level may “leak out”
into the higher dimensions, so that
only a small fraction is perceived
within the familiar dimensions of
our universe.
String theory is not the
only candidate for a Theory of
Everything. Loop quantum gravity
(LQG) was developed by Lee
Smolin and Carlo Rovelli from
the late 1980s. In this theory, theIf string theory is a mistake,
it’s not a trivial mistake. It’s a
deep mistake and therefore
kind of worthy.
Lee Smolinquantized properties of particles
arise not from their stringlike
nature, but rather from the small-
scale structure of space-time itself,
which is quantized into tiny loops.
LQG and its various developments
offer several intriguing advantages
over string theory, removing the
need for additional dimensions, and
it has been applied successfully
to several major cosmological
problems. However, the case for
either string particles or looped
space-time as the “Theory of
Everything” remains inconclusive. ■