From Aristotle to Hiroshima
sunny morning in the city of Hiroshima, tea was being made in
offices, children were being bundled off to school and a lonely,
propeller-driven plane buzzed unnoticed through the sky above.
When the atom bomb fell, the furious, boiling ball of fire killed some
one hundred thousand human beings at once. The city centre
disappeared, rivers and criss-crossing canals were vaporized and
buildings were blown apart for miles. Pedestrians walking across a
distant bridge were suddenly sooty silhouettes on scarred concrete.
Many more who at first survived the initial blast soon died horribly as
their flesh peeled from their bones, and their organs were eaten away
by the radiation.
The atom bombs dropped on Hiroshima and Nagasaki, like those
still poised and ready in missile silos around the world today, stand as
emblems of the power – of the depth and the danger – of our new
ideas about space and time. The basic theory of the bombs is given by
Albert Einstein’s famous equation that says that ordinary matter can
be converted into tremendous explosions of pure force and energy.
The following chapters will trace Einstein’s surprisingly simple
theories, showing how new ideas about time led to new ideas about
energy, and give instructions for constructing an atomic bomb. But
here we should pause to contemplate the power of ideas, the
possibility that seemingly idle questions may have far-reaching
Modern answers to the two questions above mix great tragedy and
great beauty, and are known as the “philosophy of space and time”.
This subject has played a central role in European philosophy since
the time of the ancient Greeks. It is sometimes traditional to divide
philosophy – the “love of wisdom” – into three branches according to
the three leading questions:
- What is there? What exists? What is reality composed of? Does it
include atoms, space, ghosts, souls, Beauty, God?
- What can we know? Which sorts of knowledge are reliable? Canwe trust our senses? Who should we believe? What is truth?
- What should we do? What is good or evil? Is our aim successful
survival or saving our souls? Should we tell lies? Should we be
guided by reason or emotion, or both?
For each question, the corresponding branch of philosophy is:
- Metaphysics – the study of reality
- Epistemology – the study of knowledge
- Ethics – the study of good and evil, of values
The philosophy of space and time is part of metaphysics. Some people
mistakenly think that the word “metaphysics” means “after or beyond
physical science”, but the word is really an historical accident.
Historians explain that Aristotle (384–322BCE) wrote many books,
which were kept in a chest after his death in 322BCE. A later editor
bound them together into volumes and gave each volume a title. One
dealt with “Physics”, and was so entitled. The next dealt with more
basic questions but had no title. It came to be called “the book that
came after the one entitled Physics”, and this name, “After-the-
Physics” or “Metaphysics” (“meta” being Greek for “after”), has
stuck through the ages. Aristotle would have probably preferred to
call it “First Philosophy”, simply because it dealt with the most basic
and general questions that could be asked. It was thus a deeper
continuation of physics, not a separate subject.
This is important because the philosophy of space and time deals
with many ideas that are part of modern physical science: it is not
“after” or “beyond” physics. Here, there is no dividing line between
philosophy and science.
In fact, the division between philosophy and science may have been
a temporary aberration. A little history will help explain this. What
we call “science” in the modern sense grew from a small movement in
the 1600s led by a few philosophers, aristocrats and mechanics. At
that time the new vogue in studies of nature was simply known as
“philosophy”. Only some two centuries later, when the trend had
caught on and attracted many investigators, was a need felt for some
new name for the discipline. “Science” slowly came to have the sense
of a study of nature that emphasized experiment and mathematics.
The word “scientist” was not coined until 1863.
These new terms signalled a novel and peculiar split between
philosophy and the emergent “science”; suddenly there were two
disciplines and two communities of thinkers, where before there had been one loose community of philosophers. Crudely put, the
philosophers withdrew from experimenting and observing the world
while scientists tried to restrict themselves to measurement,
calculation and deduction. Philosophers thought in their armchairs:
scientists looked through their telescopes and microscopes. The split
widened so much in the twentieth century that some people
complained that Europe had “two cultures”: the humanities were
separate and isolated from the sciences.
There are now healthy signs that this split is healing, and the
philosophy of space and time is one area where philosophy and
science are converging and overlapping again. After all, both are
studying the same world. One reason for this convergence is an
extraordinary and unexpected crisis in our understanding of space
and time. Physicists had been optimistic that Einstein’s theories were
both correct and fundamental. Now there is a widespread sense that,
although his theories make many correct predictions, they are
somehow wrong and mistaken. Just as Einstein overthrew earlier
physics, we may now be on the verge of a new revolution. The new
problems are so surprising and so deep that ambitious philosophers
have invaded physics and thoughtful physicists have begun raising
broad and searching metaphysical questions again. The quantum
theory of matter, the new theory of gravitation (“quantum gravity”),
astronomy and attempts at unified theories of physics are all throwing
up challenges to our understanding of space and time. These are deep
enough to be called philosophical.
It is an exciting moment to study the philosophy of space and time.
We possess deep and beautiful theories that seem right and illuminat-
ing, and make many verifiable predictions. We also know now that
they are not fundamentally correct, but we do not understand why.
We do not understand how to proceed.