270 RELATIVITY, THE GENERAL THEORYexclusively devoted to relativity theory and gravitation.* The first international
conference on relativity convened in Bern, in July 1955, three months after his
death. Its purpose was to celebrate the fiftieth anniversary of relativity. Einstein
himself had been invited to attend but had to decline for reasons of health. How-
ever, he had written to the organizers requesting that tribute be paid to Lorentz
and Poincare. Pauli was in charge of the scientific program. Browsing through
the proceedings of the meeting! one will note (how could it be otherwise) that the
subjects dealt with are still relativity in the old style. This conference, now known
as GR04 had 89 participants from 22 countries. It marked the beginning of a
series of international congresses on general relativity and gravitation: GR1 was
held in Chapel Hill, N.C. (1957), GR2 in Royaumont (1959), GR3 in Warsaw
(1962), GR4 in London (1965), GR5 in Tblisi (1968), GR6 in Copenhagen
(1971), GR7 in Tel Aviv (1974), and GR8 in Waterloo, Canada (1977). The
most recent one, GR9, took place in Jena in June 1980. The growth of this field
is demonstrated by the fact that this meeting was attended by about 800 partici-
pants from 53 countries.
What caused this growth and when did it begin? Asked this question, Dennis
Sciama replied: 'The Bern Conference was followed two years later by the Chapel
Hill Conference organized by Bryce de Witt.. .. This was the real beginning in
one sense; that is, it brought together isolated people, showed that they had
reached a common set of problems, and inspired them to continue working. The
"relativity family" was born then. The other, no doubt more important, reason
was the spectacular observational developments in astronomy. This began perhaps
in 1954 when Cygnus A—the second strongest radio source in the sky—was iden-
tified with a distant galaxy. This meant that (a) galaxies a Hubble radius away
could be picked up by radio astronomy (but not optically), (b) the energy needed
to power a radio galaxy (on the synchrotron hypothesis) was the rest mass energy
« 108 solar masses, that is, 10~^3 of a galaxy mass. Then came X-ray sources in
1962, quasars in 1963, the 3°K background in 1965, and pulsars in 1967. The
black hole in Cygnus X-l dates from 1972. Another climax was the Kruskal treat-
ment** of the Schwarzschild solution in 1960, which opened the doors to modern
black hole theory' [S5]. Thus new experimental developments were a main stim-
*The Solvay conferences (which over the years have lost their preeminent status as summit meetings)
did not deal with these subjects until 1958 [M3].
f These were published in 1956 as Supplement 4 of Helvetica Physica Ada.
:|Some call it GR1, not giving the important Chapel Hill meeting a number. Proceedings were pub-
lished in the cases of GRO, GR1 (Rev. Mod. Phys. 29, 351 -546, 1957), GR2 (CNRS Report 1962),
GR3 (Conference Internationale sur les Theories de la Gravitation, Gauthier-Villars, 1964) and
GR7 [S3]. Some of the papers presented at the GR conferences after 1970 are found in the journal
General Relativity and Gravitation.
**Here Sciama refers to the coordinate system introduced independently by Kruskal [Kl] and by
Szekeres [S4]. For details see [M2], Chapter 31.