X FOREWORD
not so reliable. One must bear in mind that although Einstein was an able
mathematician, his profound natural gifts lay in physics not mathematics. This
comes through particularly in the section of the book on general relativity, where
Einstein's struggles are described, starting with his appreciation in 1907 of the
fundamenal role of the equivalence principle and ending with his final field
equations in 1915. In place of the sureness that Einstein exhibited in his earlier
work, now there is vacillation: he is continually saying that he believes that he has
found the final form of the theory, only to retract in a few months' time and to
present a quite different scheme with equal confidence.
This is not to belittle Einstein's supreme achievement, however. On the contrary,
the discovery of general relativity shines out as all the more remarkable, and it
speaks even more strongly of the sureness of Einstein's physical instincts when one
realizes how uncomfortable Einstein actually was with the mathematics. In his
work on unified field theories, which occupied him throughout the final twenty
years of his life, Einstein's vacillation is apparent to an even greater degree. He was
now in an area where guidance needed to come through mathematics rather than
through physics, so the sureness of Einstein's touch was no longer to be found.
Finally, there is the issue of Einstein's refusal to accept, fully, the quantum
theory, as that subject had been gradually developed by others during the course
of Einstein's life. Is this also an indication of a failing of Einstein's judgement, as
his years advanced, or of a lack of appreciation of the elegance of its mathematical
structure? I do not think so. It must be said that some of Einstein's objections to
quantum theory have not really stood the test of time—most notably that it was
"unreasonable" that the theory should possess strange non-local aspects (puzzling
features that Einstein correctly pointed out). Yet, his most fundamental criticism
does, I believe, remain valid. This objection is that the theory seems not to present
us with any fully objective picture of physical reality. Here, I would myself certainly
side with Einstein (and with certain other key figures in the development of the
theory, notably Schrodinger and Dirac) in the belief that quantum theory is not
yet complete.
But why should we still trust the views of a man whose instincts were fashioned
by the physics of over one hundred years ago? Surely Einstein's initial insights into
the quantum structure of things were simply overtaken by the impressively
successful theories of younger men. Why should we go along with Einstein's
"nineteenth-century" view of an objective physical reality when modern quantum
theory seems to be presenting us with a more subjective picture? Whatever one's
beliefs may be on this matter, Einstein's extraordinary record tells us that his views
are always worthy of the greatest respect. To understand what his views actually
were, you cannot do better than to read on...
ROGER PENROSE
Oxford
June 2005