Astronomy and Astrophysics - An Introductory Survey, A lecture series by Prof. G. Srinivasan - Lecture 37 - The Accelerating Universe

AstroPHYSICS with Srini (https://www.youtube.com/@astrophysicswithsrini1094) The newly launched youtube channel of Prof. Srinivasan. WATCH it, SUBSCRIBE to it, and bring it to the attention of your friends! And here is why. The present course of introductory lectures will end with the 41st lecture. There are many topics in basic physics, as well as astrophysics, that you encountered in this course that deserves a 'revisit'. Prof. Srinivasan plans to make new videos on these topics and upload them to this channel. This will start to happen after the last lecture of this series has been released. Meanwhile, this channel is up. Currently, the PLAYLIST contains the 40 lectures that he delivered at the International Centre for Theoretical Sciences, a few years ago. You are welcome to contact Prof. Srinivasan at [email protected] if you have suggestions for topics, or if you have questions. -------------------------------------------------------------------------------- In the late 1990s, observation of distant supernovae established the fact that the Universe is, contrary to expectations, actually accelerating. Measurements of cosmic microwave background also strongly indicate that the Universe does not have large-scale curvature. The obvious conclusion drawn from these is that only about 30% of the energy density of the Universe comes from baryonic matter that we are familiar with. The rest, that is 70% of the energy density of the Universe, must come from vacuum energy, metaphorically called as the `dark energy'. ABOUT THE LECTURE A surprising and startling discovery was made around the year 2,000 – the universe is not only expanding, but the expansion is accelerating! In the first half of this lecture, I describe how this great discovery was made. If the expansion is ‘accelerating’ then it implies two things, (i) There must be a cosmic repulsion, and (ii) This cosmic repulsion must be dominating over the attractive gravity in the present epoch. What could this ‘cosmic repulsion’ or ‘repulsive gravity’ be due to? In the second part of this lecture, I describe the present state of our understanding of this deep and intriguing question. ABOUT THE LECTURE SERIES This lecture series is organized by the Astronomical Society of India as a part of its Golden Jubilee celebrations. Aimed at undergraduate and graduate students, this series of talks by renowned astrophysicist and teacher, Prof G. Srinivasan, starts from the first principles of Physics and builds up the subject rigorously to the present state of our understanding. Series website: https://astron-soc.in/srini-ana The website hosts a question bank as well as a list of suggested reading for each lecture (prepared by Dr. Sushan Konar) ABOUT THE SPEAKER Professor G. Srinivasan In a research career spanning more than five decades, his interests have spanned many aspects of physics and astrophysics. He is a passionate teacher and has authored two outstanding Astronomy texts titled ‘What Are The Stars?’ and ‘Can Stars Find Peace?’ He is a Past President of the Astronomical Society of India, and a Past President of the Division on Space and High Energy Astrophysics of the International Astronomical Union. In his distinguished career he has worked at the University of Chicago, USA; the IBM Research Laboratory in Zurich, Switzerland; Chalmers University of Technology, Goteborg, Sweden; the Cavendish Laboratory, University of Cambridge, England and the Raman Research Institute, Bengaluru Follow us on social media at https://twitter.com/asipoec https://www.facebook.com/asi.poec/ This series is also supported by the IAU OAE Centre in India https://twitter.com/astro4edu_India https://www.facebook.com/OAE-Center-India-105698322030674