Soviet astrophysicist, originally a specialist in nuclear
physics. His cosmological theories led to more accurate determinations
of the abundance of helium in older stars.
Zel'dovich was born in Minsk, studied at Leningrad (now St Petersburg),
and in 1931 began work at the Soviet Academy of Sciences. During World
War II he contributed research towards the war effort. He later worked
at the Institute of Cosmic Research at the Space Research Institute
of the Soviet Academy of Sciences in Moscow.
During the 1930s, Zel'dovich was involved in a research programme aimed
at discovering the mechanism of oxidation of nitrogen during an explosion.
He also wrote about the chemical reactions of explosions, the subsequent
generation of shockwaves, and the related subjects of gas dynamics and
Zel'dovich participated in early work on the mechanism of fission during
the radioactive decay of uranium. In the 1950s he developed an interest
in cosmology and in such subjects as quark annihilation and neutrino
detection. In 1967 he proposed that in its initial stages the universe
was uniform in all directions, but that as it has expanded, this isotropy