EINSTEIN'S VISION 463
considered justified only if it has been shown that according to [the theory] the
momentum transferred by radiation to matter leads to motions as required by
thermodynamics' [El6]. Why is only thermodynamics mentioned; why not rela-
tivity also? Because, I believe, to him relativity was to such an extent the revealed
truth that in his view the phenomenological and provisional quantum theory was
not yet ripe enough, perhaps not yet worthy enough, to be brought into contact
with relativity arguments.
So it was in the days of the old quantum theory. So it remained after quantum
mechanics came along. In the previous section, I noted that Einstein considered
quantum mechanics to be highly successful. I should now be more precise and add
that this opinion of his applied exclusively to nonrelativistic quantum mechanics.
I know from experience how difficult it was to discuss quantum field theory with
him. He did not believe that nonrelativistic quantum mechanics provided a secure
enough basis for relativistic generalizations [E17, E18]. Relativistic quantum field
theory was repugnant to him [Blj. Walter Thirring has written to me of conver-
sations with Einstein in which 'his objections became even stronger when it con-
cerned quantum field theory, and he did not believe in any of its consequences'
[Tl]. Valentin Bargmann has told me that at one time Einstein asked him for a
private survey of quantum field theory, beginning with second quantization. Barg-
mann did so for about a month. Thereafter Einstein's interest waned.
The preceding remarks on quantum field theory refer principally to its special
relativistic version. In the time capsule of Section 2b, I inserted the comment that
to this day the synthesis of quantum theory and general relativity is beset with
conceptual difficulties. Was that what bothered Einstein? It was not, as is best
seen from the closing phrases of his tribute to Maxwell:
'I incline to the belief that physicists will not be permanently satisfied with
... an indirect description of Reality, even if the [quantum] theory can befitted
successfully to the General Relativity postulates [my italics]. They would then
be brought back to the attempt to realize that programme which may suitably
be called Maxwell's: the description of Physical Reality by fields which satisfy
without singularity a set of partial differential equations. [E19]'That programme' is uniquely Einstein's. His main point was that one should not
start out by accepting the quantum postulates as primary rules and then proceed
to fit these rules to general relativity. Instead, he believed one should start with a
classical field theory, a unified field theory, and demand of that theory that the
quantum rules should emerge as constraints imposed by that theory itself.
In the next and final section on the quantum theory, I shall outline how Ein-
stein hoped to achieve this. The question of why he harbored such expectations
brings us to another edge of history. A definitive answer cannot be given. As a
personal opinion, it seems to me that making great discoveries can be accompanied
by trauma, and that the purity of Einstein's relativity theories had a blinding effect
on him. He almost said so himself: To the discoverer ... the constructions of his