Cosmology is a way to answer the two fundamental questions: what is the origin and structure of the
Universe, as a whole? Historically, all the civilizations tried to answer these questions, based on their
knowledge on the surrounding world. The discovery of the telescope and its application into astronomy
triggered a revolutionary change in our view on the surrounding world. Following Newton it became
widely accepted that the Universe is infinite, static and distributed with matter homogeneously, on large
scale. This view had two basic flaws: Olbers paradox (why the night sky is dark), and the Seeliger
paradox (the homogeneous Universe is gravitationally indefinite). The first half of the 20th century
experienced revolutionary changes in this field, theoretically and observationally. The theoretical frame-
work was established by Einstein due to the General Relativity, while the observational one by Hubble
discovering the effect named after him. These revolutionary changes had no impact on the astronomy in
Hungary. Some changes started, however, in Hungary at the end of the 50th. Paál, György started his
pioneering work on the observational cosmology in Konkoly Observatory. His first significant result was
the discovery of a local inhomogeneity, a supercluster, in the region of about 300 Mpc around our
Galaxy. He rediscovered the dark matter in the clusters of galaxies dynamically solving the problem of
time scale needed to reach the equilibrium configuration after the Big Bang. He and his colleagues
predicted the existence of the dark energy and gave an estimation of Omega_Lambda = 0.667 differing only 3% from
the recent value obtained by the Planck satellite (Omega_Lambda = 0.686).
The talk is devoted to the anniversary of his death 25 years ago (22.03.1992).
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