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Vaidya-Raychaudhuri Endowment Award Lecture 2023

Dark Matter, Dark Energy and the Cosmic Web

Abstract: The expanding universe consists of galaxies which, far from being randomly distributed, cluster together to form the Cosmic Web. The cosmic web consists of a highly filamentary network of `superclusters’ of galaxies, each of which can contain tens of thousands of galaxies and span hundreds of Megaparsec. Superclusters are separated from each other by vast empty regions of enormous size called Cosmic Voids. The cosmic web is made up of baryons and leptons which constitute stars, the intergalactic medium, etc. Additionally, the web contains copious amounts of non-luminous `dark matter’. Dark matter is non-baryonic in nature and outweighs all the luminous matter in the universe by a factor of nearly ten. The composition of dark matter is presently unknown but it could be in the form of tiny weakly interacting elementary particles or massive black holes. In addition to baryons, leptons, and dark matter the universe also contains a mysterious component called dark energy. Unlike normal forms of matter which have positive pressure, dark energy has a large negative pressure which causes the expansion of the universe to accelerate with time. Dark matter and dark energy together make up 96% of the universe, with only 4% being contained in baryons, leptons, and photons. Numerous models have been advanced to explain the origin of dark energy including Einstein’s famous idea of the cosmological constant, as well as more recent advances such as dynamical dark energy, modified gravity, and extra dimensions. I will attempt to summarize our current understanding of the cosmic web, dark matter, and dark energy and the interplay between them. 

Bio: Varun Sahni is an Emeritus Professor at the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune. He did his BSc at St. Stephens College in Delhi and his MSc and PhD at Moscow State University where he worked under the supervision of distinguished Soviet scientists Prof. Ya.B. Zeldovich and Prof. A.A. Starobinsky. He joined IUCAA in 1991 after working as a post-doctoral fellow in the UK and Canada. He has delivered invited/plenary talks at international conferences held in several countries including the USA, France, UK, Ireland, Germany, Greece, Portugal, Iran, Korea, Japan, Brazil, Estonia, Russia, and India. Prof. Sahni has written over 100 highly cited papers and reviews in leading international journals. He is a fellow of the Indian Academy of Science, the National Academy of Science of India, the Indian National Science Academy (INSA), and The World Academy of Science (TWAS). Prof. Sahni is the recipient of numerous awards including the Shanti Swarup Bhatnagar Award, the Vikram Sarabhai Award, the Homi Jehangir Bhabha medal, and the J.C. Bose national fellowship. Prof. Sahni works in the field of Cosmology with a focus on black holes, the physics of the early universe, gravity waves, the cosmic web, modified gravity & extra dimensions, dark matter, and dark energy.

Looking forward to your participation.

Warm Regards,

Department of Physics

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