|Title||Khalatnikov, Isaak Markovich: certificate of election to the Royal Society|
|Description||Certificate of Candidate for Election to Foreign Membership. Citation typed |
|Citation||Khalatnikov is distinguished for his important contributions to two different branches of theoretical physics: first to our understanding of quantum liquids and liquid helium in particular, and then to general relativity and cosmology. Apart from these personal contributions (detailed below), he has, as Director of the famous Landau Institute, been an important influence in the development of Soviet theoretical physics.|
As regards his work on quantum liquids he has made outstanding contributions to our theoretical understanding of superfluidity in liquid 4He and in 3He- 4He mixtures. He was responsible for the correct formulation of the two-fluid hydrodynamic equations that describe the macroscopic behaviour of these systems, a task that included the development of a proper description of some very complex dissipative and non-linear effects; and he developed into a highly sophisticated and detailed theory the idea, due originally to Landau, that the normal fluid can be described in terms of a gas of weakly-interacting excitations.
His work on general relativity and cosmology began with a famous paper he wrote with E M Lifshitz in 1963. In the first part of the paper, they reviewed and extended Lifshitz's pioneering 1946 paper on small perturbations of a Friedmann cosmological model. This is still the standard treatment of the subject, and the accepted explanation of how small departures from homogeneity and isotropy in the early universe would have grown as the universe expanded, until they became large enough to cause the formation of galaxies and stars.
In the second part of the paper, Lifshitz and Khalatnikov raised the question of whether the equations of general relativity predict that spacetime will come to an end at a singularity, either in the past or the future. The Friedmann cosmological models with physically reasonable matter all begin with a Big Bang singularity, in which the whole universe is compressed into a single point. Some of the Friedmann models also end with a Big Crunch singularity, in which the whole universe recollapsed to a single point. Lifshitz and Khalatnikov argued however that the Friedmann models were very symmetric solutions, and that this did not tell one anything about general solutions without symmetries, and with the full number of degrees of freedom. They concluded that such general solutions would not contain singularities. However, later work by Khalatnikov and Belinski showed not only that general solutions could have singularitites, but also indicated how the universe would behave near a singularity.
More recently, Khalatnikov has considered statistical properties of cosmological solutions of the Einstein equations. He has also shown that nearly all cosmological solutions with a massive scalar field have a period of exponential or inflationary expansion. Such inflation in the early stages could account for many otherwise unexplained features of the universe today.
Fellows associated with this archive
|NA4207||Khalatnikov; Isaak Markovich (1919 - 2021)||1919 - 2021|