Today we are blessed with two extraordinarily successful theories of physics. The first is Albert Einstein's general theory of relativity, which describes the large-scale behaviour of matter in a curved spacetime. This theory is the basis for the standard model of big bang cosmology. The discovery of gravitational waves at the LIGO observatory in the US (and then Virgo, in Italy) is only the most recent of this theory's many triumphs.
The second is quantum mechanics. This theory describes the
properties and behaviour of matter and radiation at their smallest
scales. It is the basis for the standard model of particle physics,
which builds up all the visible constituents of the universe out of
collections of quarks, electrons and force-carrying particles such
as photons. The discovery of the Higgs boson at CERN in Geneva is
only the most recent of this theory's many triumphs.
But, while they are both highly successful, these two structures
leave a lot of important questions unanswered. They are also based
on two different interpretations of space and time, and are
therefore fundamentally incompatible. We have two descriptions but,
as far as we know, we've only ever had one universe. What we need
is a quantum theory of gravity.
Approaches to formulating such a theory have primarily followed two
paths. One leads to String Theory, which has for long been
fashionable, and about which much has been written. But String
Theory has become mired in problems. In this book, Jim Baggott
describes "the road less travelled": an approach which takes
relativity as its starting point, and leads to a structure called
Loop Quantum Gravity. Baggott tells the story through the careers
and pioneering work of two of the theory's most prominent
contributors, Lee Smolin and Carlo Rovelli. Combining clear
discussions of both quantum theory and general relativity, this
book offers one of the first efforts to explain the new quantum
theory of space and time.