The fifth session was devoted to a relatively new field of gravitational research, the quantum theory of gravitation. The report of D.I. Blokhintsev (Dubna) dealt with fluctuations of the metric, which are especially significant at small distances (of the order of cm). The possibility of the transformation of particle-antiparticle pairs into transverse quanta of the gravitational field, and vice versa, was examined in the report presented by D. D. Ivanenko (MGU). The author suggests that such processes may be of considerable importance in cosmology. An interesting report was read by V. G. Kadyshevskii (MGU), giving a geometrical interpretation of weak interactions.
The study of weak interactions of particles should indicate a new geometry of space-time, with discrete properties at small distances (of the order of cm), in the same way as the general theory of relativity indicates the curvature of space-time as a result of the presence of gravitating masses. The mechanism of gravitational interaction involving the emission of gravitational field quanta, or gravitons, by gravitating bodies was considered by Prof. K. P. Stanyukovich (MVTU), who constructed a theory of gravitational interaction based on the hypothesis of emission and absorption of the actual gravitational field quanta (gravitons). This report provoked a lively debate.
One of the high points of the conference was the session at which experimental verification of the general theory of relativity was discussed. This session was held at the Joint Institute for Nuclear Research in Dubna. A very interesting report, presenting a critical survey of all known observations of the Einsteinian deflection of light rays near the Sun, was read by A. A. Mikhailov, Corresponding Member of the USSR Academy of Sciences.
Corresponding Member of the USSR Academy of Sciences V. L. Ginzburg (Lebedev Institute of Physics) gave a review of the experimental studies of gravitation which are possible using artificial satellites. A basic study entitled "The Possibility of Studying some Relativistic and Cosmological Effects by means of Molecular and Atomic Frequency Standards", which was the work of five collaborators at the Lebedev Institute of Physics (N. G. Basov, O. N. Krokhin, A. N. Oraevskii, G. M. Strakhovskii, and B. M. Chikhachev) was presented by G. M. Strakhovskii. Atomic and molecular frequency standards are known to be extremely precise, due to the use of the natural frequency of spectral lines as a reference. With the help of rockets and artificial satellites, atomic standards can be carried far away from the Earth, which provides a means of measuring reliably the frequency shift produced in a gravitational field. V. B. Braginskii and G. I. Rukman (MGU) presented an interesting report dealing with a projected experiment for detecting gravitational waves under laboratory conditions. The project proposed by colleagues at the Joint Institute for Nuclear Research, namely that an experiment to detect antigravitational properties in antiparticles be carried out, was brought up again and raised considerable interest. A report was also presented by A. A. Bonch Bruevich and Ya. E. Kariss (Leningrad), dealing with the possible existence of anisotropic features of gravitation, and describing an experiment for determining the velocity of propagation of gravity.
The last group of subjects to be considered at the conference concerned the basic problems of gravimetry. The reports presented in connection
with this were: "The Maximum Accuracy of Modern Gravity Measure ments", by P. N. Agaletskii, and "Gravity Observations during a Total Solar Eclipse", by N. P. Grushinskii and M. U. Sagitov (MGU).
A number of the reports discussed the Earth's expansion and the possible connection between this hypothetical phenomenon and gravity, a subject which proved to be rather controversial. The reports which dealt with this were: "The Secular Weakening of Gravity and the Earth's Expansion", by D.D. Ivanenko and M.U. Sagitov (MGU); "Facts in Support of the Expanding-Earth Hypothesis", by V. B. Neiman and I. V. Kirillov; and "Geological Facts Indicating Absence of the Decrease in the Gravitational Constant Assumed by the Jordan-Dirac Hypothesis", by P. N. Kropotkin. Back in the thirties, Dirac and Jordan proposed that the gravitational constant decreases with time. If such were the case, the Earth (as well as any other planet or star) would undergo a gradual expansion. In particular, the fact that some of the continents have matching contours may be explained in this way, provided it is assumed that the Earth was considerably smaller at the beginning of its expansion (4 • years ago), and that its total surface was then equal to the present area of the con tinents. The facts adduced in support of this argument were related to the slowing down of the rotation of the Earth and to the presence of cracks in the terrestrial crust. The discussion of this subject eventually developed into an analysis of geological and biological problems.
It should be noted that of the large number of reports presented at the conference only one (that of V. V. Radzievskii) treated gravitation from the pre-Einsteinian point of view. This approach, moreover, was not received favorably by the participants of the conference.
On 1 July, the last day of the conference, a supplementary session was held, so that reports which had not been presented at the main sessions (due to the overcrowded agenda) could be given. Of these, mention should be made of the report by G. E. Skrotskii (Sverdlovsk), dealing with the effect of the Sun on the rotational properties of an electro magnetic field, and the report by I. I. Kogal'nikova giving a historical survey of the evolution of gravitational concepts.
It is safe to say that the conference was successful and timely, and that it indicated where Soviet gravitational research is up to par in compar ison with work. abroad (the classical theory of gravitation, cosmology) and also where further effort is necessary (the quantum theory of gravita tion and experimental studies). In addition, the conference was helpful in preparing Soviet gravitation physicists for the Fourth International Conference on Gravitation, which was held in Warsaw in July, 1962.
In conclusion, the participants of the conference unanimously adopted the following resolutions: 1) to call a Second Soviet Conference on Gravitation in 1963; 2) to publish all the proceedings of the conference; 3) to establish laboratories for the study of gravitational problems in Moscow and Kazan; and 4) to set up a Soviet Advisory Commission on Gravitational Research, for coordinating and promoting further research in this field.