What is the Universe Expanding Into?
In the late 1920’s, Belgian physicist Georges Lemaître and American astronomer Edwin Hubble independently discovered evidence for the expansion of the universe. They found the further away a distant galaxy is, the greater its light is shifted to a lower frequency (redshifted). Why? Because the expansion of the universe causes light emitted by a galaxy to stretch in frequency on its way to Earth.
Based on this galaxy distance/redshift evidence, Einstein finally withdrew his objections to an expanding universe and eliminated the cosmological constant from his equations. In his autobiography, physicist George Gamow — a former student of Alexander Friedmann — said Einstein told him the cosmological constant was “the biggest blunder of his life.”
If the universe is expanding, what is it expanding into? We commonly think of space as rigid — that the distance between any two points in space is fixed.
General relativity tells us this is not so. Space is flexible, it can warp or bend or stretch. So our universe is not expanding into anything. It is space itself or the distance between points in space which is increasing or expanding over time. Wild, huh!
More precisely, it is the space between clusters of galaxies which is expanding. Within galaxy clusters, gravity overcomes and stops the expansion. So space within our solar system, within our galaxy is not expanding. Thus we are not expanding (ignoring the bag of potato chips and chocolate chip cookies I just wolfed down).
A Too Short Life
Belenkiy writes that the “seminal contributions (of Alexander Friedmann) have been widely misrepresented and undervalued.” Perhaps one reason was Friedmann’s relative isolation from the West during the Communist era. Another was his untimely demise.
Alexander Friedmann died on September 16, 1925 from typhoid fever. He was thirty-seven years old. His wife Natasha gave birth to his only son a few months later. He never lived to see the Lemaître/Hubble evidence for the expansion of the universe. Nor did he live to learn of British physicist Arthur Eddington’s proof that Einstein’s static universe solution is unstable.
In 1927, an excited Lemaître told Einstein of his own more limited dynamic solutions of general relativity. Einstein in turn introduced him to Friedmann’s papers. Four years later Lemaître proposed what we now call the big bang. Supported by a number of independent observations, this landmark theory tells us our universe began in a singularity and has been expanding ever since – an idea first proposed as theoretically possible by Alexander Friedmann.
Belenkiy, Ari. Alexander Friedmann and the Origins of Modern Cosmology. (2012). Physics Today. Vol. 65, no. 10, pp. 38-43. Accessed October 31, 2012.
Mastin, Luke. Alexander Friedmann (1888 – 1925). (2009). Accessed October 31, 2012.
Tropp, E. A., Frenkel, V. Y., Chernin, A. D. Alexander A. Friedmann: The Man Who Made the Universe Expand. (1993). Cambridge U. Press, London.
Dziuba, Andy. Alexander Friedman, The Inventor of the Big Bang. (2011). Accessed October 31, 2012.
Gamow, George. My World Line; an Informal Autobiography. (1970). Viking Press, New York.