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Time, Space and Philosophy by Christopher Ray, Routledge, pp 268, £8.99
pbk

It is no coincidence that the two most successful theories of physics
ever devised – general relativity and quantum theory – are riddled with
apparent paradoxes and open to contradictory philosophical interpretations.
This is because they deal with the ultimate concepts: time, space and the
fundamental constituents of matter and radiation. These concepts have been
the subject matter of philosophical inquiry for centuries, and we should
not let our obsession with 20th-century technology blind us to the fact
that we still do not have answers to the oldest and most basic of philosophical
questions.

Christopher Ray poses all the eternal brain-teasers, together with some
of the more speculative questions, in Time, Space and Philosophy. Beginning
with Zeno’s paradoxes and the problems of the apparent infinite divisibility
of space, he goes on to discuss the concepts of time, space and motion as
advanced by Isaac Newton, Gottfried Leibniz, George Berkeley, Ernst Mach
and Albert Einstein. He describes the various possible solutions of Einstein’s
gravitational field equations of 1916, culminating in our current world
picture with its cosmological conundrums: the big bang, inflation, black
holes and cosmic censorship.

Ray moves easily and competently through this material. Although his
book appears to be directed towards students taking courses in the philosophy
of science or metaphysics, it is accessible also to science students interested
in the philosophical dimension. For the general reader, the book is perhaps
too detailed only in a few areas.

One of the major problems with Einstein’s general theory of relativity
is that it provides no internal guide to ‘acceptable’ solutions of the field
equations. The theoretician is therefore left free to shape the Universe
to meet his or her own desires or prejudices. Einstein fudged his own solution
by introducing a ‘cosmological constant’, whose only purpose was to yield
a universe more acceptable to him. He later called this his ‘greatest mistake’.
Observations of the Universe imply that such a constant has a value that
is effectively zero.

And yet, Ray argues that the cosmological constant ‘enriches the theoretical
context’ of general relativity, claiming that assertions as to its ad hoc
character are ‘neither accurate nor helpful’. From the viewpoint of the
philosopher, the attractiveness of general relativity is lessened if the
constant is dismissed from the theory. There would, for example, be no room
for Kurt Godel’s solutions of the field equations which allow the possibility
of time travel and backwards causation. Without the constant, the philosopher’s
ability to speculate would certainly be greatly reduced.

Within the last few decades, quantum theory’s more outrageous predictions
have been subjected to stringent experimental tests. The theory has survived
these tests, albeit at the expense of our ability to comprehend the nature
of physical reality at the quantum level. However, except for a few observational
tests on the perihelion of Mercury and the bending of starlight by the Sun,
it has been very difficult to devise and carry out tests of general relativity.
This situation may change in 1998 with NASA’s Gravity Probe B, a satellite
mission to detect the predicted distortion of space-time in the vicinity
of the Earth.

However these experiments turn out, the basic philosophical questions
will undoubtedly remain unanswered, even if some idle speculation is shown
to be misguided or irrelevant. Until such time as experiment puts us on
empirically firmer ground, Ray’s book serves as a good guide to the very
wide range of philosophical questions concerning our conceptions of time
and space.

Jim Baggott is a freelance science writer. His new book, The Meaning
of Quantum Theory, will be published early this year by Oxford University
Press.