350 THE LATER JOURNEYnone of his doing* that a page of his manuscript appeared on the front page of
The New York Times under the heading 'New Einstein theory gives a master key
to the universe' [N5]. He refused to see reporters and asked Helen Dukas to relay
this message to them: 'Come back and see me in twenty years' [N6]. Three years
later, Einstein's science made the front page one last time. He had rewritten his
appendix for the fourth edition, and his equations (Eq. 17.61) appeared in the
Times under the heading 'Einstein offers new theory to unify law of the cosmos'
[N7].
'It is a wonderful feeling to recognize the unifying features of a complex of
phenomena which present themselves as quite unconnected to the direct experi-
ence of the senses' [E82]. So Einstein had written to Grossmann, in 1901, after
completing his very first paper on statistical physics. This wonderful feeling sus-
tained him through a life devoted to science. It kept him engaged, forever lucid.
Nor did he ever lose his sense of scientific balance. The final words on unified
field theory should be his own:
The skeptic will say, 'It may well be true that this system of equations is rea-
sonable from a logical standpoint, but this does not prove that it corresponds to
nature.' You are right, dear skeptic. Experience alone can decide on truth.
[E83]17f. A Postscript to Unification, a Prelude to Quantum Theory
The unification of forces is now widely recognized to be one of the most important
tasks in physics, perhaps the most important one. It would have made little dif-
ference to Einstein if he had taken note of the fact—as he could have—that there
are other forces in nature than gravitation and electromagnetism. The time for
unification had not yet come.
Pauli, familiar with and at one time active in unified field theory, used to play
Mephisto to Einstein's Faust. He was fond of saying that men shall not join what
God has torn asunder, a remark which, as it turned out, was more witty than
wise. In the 1970s, unification achieved its first indubitable successes. Electro-
magnetism has been joined not to gravitation but to the weak interactions.
Attempts to join these two forces to the strong interactions have led to promising
but not as yet conclusive schemes known as grand unified theories.
The unification of gravitation with the other known fundamental forces remains
now as much of a dream as it was in Einstein's day. It is just barely possible that
supergravity** may have something to do with this supreme union and may end
our ignorance, so often justly lamented by Einstein, about T^.
*The Princeton University Press displayed the manuscript at an AAAS meeting in New York City.
**For an authoritative account of the status of supergravity, see [Zlj.