Sign up for Brilliant FOR FREE at brilliant.org/minutephysics - the first 200 people get 20% of a premium subscription. This video is about how Russian physicist Aleksandr Fridman corrected Albert Einstein about the expansion of the universe. Einstein thought that general relativity implied that space had to be static and unchanging, but he had made a technical error regarding the differentiation of the metric (in particular, I believe he mistook the determinant of the metric for a scalar rather than a tensor density of weight 2). Friedmann didn't make this differential geometric mistake, and the cosmologies he found from the Einstein Equations were more varied in their properties - they could be expanding, or contracting, or (with the cosmological constant), static. Support MinutePhysics on Patreon! www.patreon.com/minutephysics Link to Patreon Supporters: www.minutephysics.com/supporters/ REFERENCES Alexander Friedmann en.wikipedia.org/wiki/Alexander_Friedmann Einstein Wrongly Criticizes Alexander Friedmann einsteinpapers.press.princeton.edu/vol13-trans/301 Alexander Friedmann Corrects Einstein einsteinpapers.press.princeton.edu/vol13-trans/363 Einstein Admits his Mathematical Mistake einsteinpapers.press.princeton.edu/vol14-trans/77 Interrogating the Legend of Einstein’s “Biggest Blunder” arxiv.org/abs/1804.06768 Cosmological Considerations in the General Theory of Relativity einsteinpapers.press.princeton.edu/vol6-trans/433 On the General Theory of Relativity (Einstein) einsteinpapers.press.princeton.edu/vol6-trans/110 The Field Equations of Gravitation einsteinpapers.press.princeton.edu/vol6-trans/129 The Einstein Field Equations en.wikipedia.org/wiki/Einstein_field_equations Presentation about the Sequence of Events web.mit.edu/8.286/www/slides07/Einstein-and-Friedmann.pdf Tensor Densities: en.wikipedia.org/wiki/Tensor_density MinutePhysics is on twitter - @minutephysics And facebook - facebook.com/minutephysics And Google+ (does anyone use this any more?) - bit.ly/qzEwc6 Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute! Created by Henry Reich

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