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0.3 x 10~3

-10~7

-2 x 10-7

In fact, these calculations were the first to be published on the early evolution of the universe that took account of the tritium channel, and thus they attracted attention. They resulted in the composition of the prestellar matter of the universe in Table 4.2.

The abundances are expressed as a percentage of the mass. Following Zel'dovich, I took the total mass density in all types of relativistic particles to be four times the mass density in electromagnetic radiation. In my computations the mass density in nucleons is much smaller. In the first column of the table, pi is the mass density in nucleons at a conveniently chosen temperature for the calculation, T1 = 4.3 x 108K. If p1 = 10-6gcm-3, the case in the middle row in the table, and the present baryon mass density is 10-30gcm-3, the present temperature in this model is about 4K.

Zel'dovich's assignment was completed. According to his idea, my paper should "work" in favor of the "cold" model published by him in Atomic Energy, and should argue against Gamow's "hot" model. Thus my paper concludes

The theory of a "hot" state for prestellar matter fails, then, to yield a correct composition for the medium from which first-generation stars formed: for p1 < 10~6 g/cm3, several percent of deuterium is obtained, in conflict with observation [9], while for pi > 10~6 g/cm3, too high a He4 content is found.

The reference is to Zel'dovich (1963b).

After the discovery of the CMBR (at temperature close to what would be implied by the middle row of the table) this conclusion lost its significance and became the only drawback of the paper. This is why, even after 1965, Zel'dovich (1966), Sakharov, Peebles (1971), Sciama (1971, p. 169), and others mentioned and quoted my paper as an additional illustration of the efficiency of Gamow's "Primeval Fireball." Thus in his paper Symmetry of the Universe Sakharov (1968, p. 85) wrote

One of the typical conclusions of the Primeval Fireball is the formation of a sufficient amount of helium as a result of thermonuclear reactions (up to 33% of mass, according to the calculations by Fermi and Turkevich USA) in the early prestellar stages of the expansion of the universe. It is interesting that those results were not published, since they involved the data on thermonuclear reactions with tritium, which were considered confidential at that time (the fifties). In succeeding years those calculations were reproduced by Smirnov (USSR) and Peebles (USA).

To be just, let me mention that during the work on the paper I realized the significance of the value of the He4 :p mass fraction as a parameter that might be compared with the observations, and thus could influence the choice of the model of the universe. After the discovery of the CMBR in 1965 the situation was enriched: there appeared to be a chance to compare the value of the temperature of the expanding universe, calculated in the framework of Gamow's model, with its observable magnitude. But it was not that simple, since even six years later Peebles (1971, p. 127) wrote

The close agreement of the Gamow-Alpher-Herman temperature of the residual radiation from the "Ylem" with the effective temperature T0 = 2.7 K of the modern candidate for the "Primeval Fireball" is an impressive result, but unfortunately it is somewhat delicate for use as an argument in support of the Primeval Fireball hypothesis.

Yakov Zel'dovich strongly believed in his hypothesis. Naturally his paper in Atomic Energy appeared in the special issue in commemoration of Igor Kurchatov. Zel'dovich was an inexhaustible source of enthralling tasks in fresh arrangement.

Sakharov, who published at least two papers in the framework of Zel'dovich's model, was interested in the idea of the "cold" model as well. He emphasized in his Memoirs (Sakharov 1990, p. 246) that this work provided "a kind of psychological 'warmup' that made possible my subsequent papers of the 1960s."

When the CMBR was discovered, the "cold" model in its original form collapsed. However, it is a fact that Zel'dovich devoted himself not only to the development of the "cold" model, but also to the general physics of the relativistic big bang cosmology, and thus was right on the crest of the thrilling fundamental research and one step away from the triumph. At the time he was out of favor with fortune, and decisive progress fell to others' share.

According to Lev Altshuler,3 Yakov Zel'dovich felt this keenly: "One day he stopped by our place. He was entirely dispirited. He said that from the point of view of general physical considerations he had every reason to adduce his hypothesis of the 'cold' Universe. But indeed, he said, 'if the Universe were hot there should be relict cosmic microwave background radiation!

3 Lev Vladimirovich Altshuler (1913—2003) was a veteran of the Soviet atomic project.

And I should have explained to experimentalists what they should observe and how'."

On March 3, 1984, Zel'dovich wrote in his autobiographical afterword (Zel'dovich 1985, p. 445; English translation in Sunyaev 2004, p. 352)

At the beginning of my astrophysical activity, I was bothered by habits acquired in the course of my applied activities. An astrophysicist should pose the questions: how is nature constructed? What observations provide the possibility of elucidating this? However, I formulated the problem more like this: how would it be best to construct the universe, or a pulsar, in order to satisfy given technical conditions - forgive me, I meant to say direct observations? This is how the idea of a cold universe arose, and my idea of a pulsar as a white dwarf in a state of strong radial oscillations. As justification for these ideas, I can only say that I was never stubborn about my errors. Apparently, on the whole, my activity - scientific and propagandistic - has been useful.

Serving to truths of science, he has acknowledged defeat with dignity. And having acknowledged it he advocated with all his passion the epoch-making significance of the discovery of the CMBR for the concept of the evolution of the universe.

I remember him immediately doing brilliant reports on this advance in overcrowded auditoriums of the Institute for Physical Problems, on the International Conference on blast waves in plasma, which took place in Novosibirsk Akademgorodok in 1967, speaking to mathematicians and attracting their attention to cosmological problems. He soon published a review, The "Hot" Model of the Universe in the journal Uspekhi Fizich-eskikh Nauk (Zel'dovich 1966). There he referred to the discovery of the CMBR as a result of paramount importance for astronomy.

And again there was an increasing stream of publications!

Yakov Zel'dovich was one of the creators of the first Soviet atomic bomb. The successful test of it on August 29, 1949, liquidated the atomic monopoly of the USA. Zel'dovich contributed a lot to atomic defense subjects for the Soviet Union. He originated the physical basis of the internal ballistics of solid fuel missiles. He passed down more than a vast scientific heritage: he gave rise to schools of thought in chemical physics, hydrodynamics, combustion theory, nuclear physics, elementary particle physics and astrophysics.

Tsukerman and Azarkh (1994, p. 144) emphasized that

What always struck one about Zel'dovich was his indefatigable scientific energy, his lively interest in everything new, his extraordinary versatility, and his intuition ... Zel'dovich's influence on his students and colleagues was striking. Thanks to him they often discovered within themselves capacities for creative work which might otherwise have gone partially, or even totally, unrealized ... Zel'dovich was ... a man of absolute honesty, self-critical, willing to recognize when he was wrong and others were right ... When he succeeded in doing something substantial or overcoming a methodological difficulty through some elegant manoeuvre, his joy was child-like.

When the CMBR was discovered it opened new directions for research in cosmology. It was through Zel'dovich's leadership that physicists in the Soviet Union were ready to do research in these new directions in much the same way as their colleagues in the USA. I have described the many aspects of his leadership elsewhere (commencing on page 103 in Sunyaev 2004); here I mention a brief summary.

No doubt a central example is his organization of the Sarov "youth" seminar dedicated to astrophysical and cosmological problems. Having left Sarov for Moscow he immediately assembled a new collective of young devotees under the same banner. Nowadays Zel'dovich's alumni and progeny are well-known experts in their branches of science and work not only in Russia but also in other countries. In his seminars, and in all his activities, he was an enemy of scientific inertia: he purveyed "hot news" from the most broad variety of branches of physics and from the physical societies of the country. According to the apt statement of Victor Adamskii, Yakov Zel'dovich never "held his knowledge and ideas inside: he splashed them out soon." As Zel'dovich said of himself, in science he was attracted not so much to the cascade of discoveries already made, but rather to the evident, wide incompleteness of a theory. During contacts with him there always appeared a pleasant sensation of a touch with the front line of research, at the very edge of it, where not so much solution as an avalanche of questions dominates. He never parted with his small slide rule, which he wielded masterly, and with a thick writing-pad where he performed his calculations. He never lost the chance to discuss scientific problems he was interested in with a visitor. It was thanks to him that his collaborators and colleagues experienced the delight, were within arm's reach from the wonder of discovery, of the CMBR; it happened in our sight. As every generously gifted person, he was simple, "regular," and convenient, but not always and not for everybody. While recalling this exceptional person one realizes that time will swallow up the details and particular streaks and will keep his true and majestic scale.

In conclusion let me offer the following thought.

Penzias and Wilson (1965a) rehabilitated the "Primeval Fireball" hypothesis of Gamow, when they discovered isotropic noise with a temperature of about 3 K. By that time P. J. E. Peebles together with R. H. Dicke, P. G. Roll and D. T. Wilkinson, who already were purposefully looking for the CMBR, shortly realized and explained what their luckier colleagues had observed.

So, the unexpected "noise" in a supersensitive horn antenna resulted in an outstanding discovery, which was awarded with the Nobel Prize. It was basically akin to the discovery of spontaneous fission of uranium by Georgiy Flerov and Konstantin Petrzhak, who also fought against the "background" in their supersensitive ionization chamber in the late 1930s.

Those common things for astrophysicists and nuclear physicists and the correspondingly interdisciplinary similarity were neither unique nor accidental. They are much more meaningful. If one recalls the 1930s, one can see how generously and unexpectedly these two areas supplied each other.

Lev Landau published three papers: On the Theory of Stars (Landau 1932), Internal Temperature of Stars (Gamow and Landau 1933), and On the Origin of Stellar Energy (Landau 1937).

Hans Bethe (1939) discovered (independently of other authors) the proton-proton and carbon-nitrogen cycles of thermonuclear reactions which are the sources of energy for stars on the main sequence. He won a Nobel Prize for that work 30 years later. It was the first Nobel Prize in astrophysics.

Oppenheimer and Volkoff (1939) performed the first computation of the structure of a neutron star, and Oppenheimer and Snyder (1939) predicted the existence of black holes.

In 1939 to 1940 Yakov Zel'dovich and Yuliy Khariton published three papers, which became the basis for the modern physics of nuclear reactors and energetics.

And what were the results?

Oppenheimer became the head of the research laboratory in Los Alamos, where the American atomic bomb was built, and Bethe became the head theorist of the group.

The picture was similar in the Soviet Union. Yu. Khariton was appointed supervisor for the Soviet atomic bomb project in Sarov, the Russian nuclear center, and Ya. Zel'dovich was the head theorist. G. Flerov and L. Landau were direct members of the atomic project.

It is not surprising, if one recalls the beginning of my story.

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