Assignment 5

the Discovery of Expanding Universe

         Everyone knows Edwin Hubble discover the evidence that the universe is expanding at a faster speed. However, he is not the person who set up the model shows the universe is expanding. Alexander Friedman, a Russian cosmologist and mathematician, is the 1st person who applied Einsteins' equation and found that the universe is expanding.

Russian Mathematician and cosmologist Alexander Alexandrovich Friedmann. Image by Qwerk

          Alexander Alexandrovich Friedman wan born on 16 June 1888 in Saint Petersburg, Russia. His father was a ballet dancer and his mother was a planist. He was an excellent student in high school. He began studying mathematics from 1906 to 1910 at saint Petersburg state university. He was appointed the position in the Aerological Observatory in 1913 and got his master's degree in pure and applied mathematics in 1914. He went to Leipzig to study with Vilhelm Bjerknes, the leading theoretical meteorologist of the time. When the World War 1 broke out, Friedman volunteered to serve with the Russian air force as a technical expert and as a bomber pilot, he went to the Central Aeronautical Station but it was disbanded after 1917 Russian Revolution. He worked as a theoretical mechanics professor at Perm University from 1918-1920. Friedman back to Saint Petersburg in 1920 because the Red Army occupied Perm and civil war. He had several works at that time: a teacher of mathematics and mechanics at Petrograd University, a professor of physics and mathematics at Petrograd Polytechnic Institute, and as a researcher at the Petrograd Institute of Railway Engineering, the Navy Academy and the Optical Institute.(1)
         Scientists at that time thought our universe was static and eternal. Einstein hold that opinion too. In 1917 Einstein adjusted his field equations to model just such a static universe. He added the repulsive force of a cosmological constant to model just such a static universe. However, Friedman didn't know such change. He became familiar with Albert Einsteins' General Theory of Relativity. In 1922, Friedman published a set of remarkable solutions to Einstein's equations. He introduced a new universe model at that time,  a dynamic universe can change its size overtime. In fact, Friedman introduced the expression "expanding universe'. One of his solution even point out that the cosmos began in a singularity-an infinitesimally small point. The model had an expansion rate which increased overtime. These characteristics of his model all has been proved right through observation in the future.

Per the Friedmann equations, the geometry of the universe is determined by its overall mass/energy density. If equal to the critical density, Ω0 the universe has zero curvature (flat configuration). If less than critical, the universe has negative curvature (open configuration). If greater than critical, the universe has positive curvature (closed configuration). Image credit: NASA/GSFC (2)

        But, Einstein didn't believe such a result while Friedman wrote a letter showing his works. Einstein calling Friedman's non-stationary world 'suspicious'. Friedman immediately sent another letter to Einstein in which detailing his work and calculation. After reading the letter, Einstein wrote in the journal:
"...my criticism...was based on an error in my calculations. I consider that Mr. Friedmann's results are correct and shed new light."(2)
       In 1923 and 1924, Friedman travelled through Europe, discussing his areas of research with other scientists, particularly in German, Norway and the Netherlands. Then he returned to Saint Petersburg( named Leningrad at that time), where he was given the job of director of the Main Geophysical Observatory in Leningrad. In July 1925, Friedman attended a record-setting balloon flight, reaching an evaluation of 7400 meters. However, 2 months after this experiment, Friedman died from typhoid fever in September 25, 1925, at the young age of 37.(1)
       Friedman's model of universe has 3 types. The first one is called closed universe, in this type, the universe begins with a Big Bang and continue expanding. But after a long enough time, the mutual gravitational attraction of all the matter slows the expansion to a stop. The universe then starts to fall in on itself, replaying the expansion in reverse direction. Finally all the matter collapse back to a singularity, in what physicist John Wheeler likes to call the Big Crunch.

Close Universe: The Big Bang's momentum is offset by gravity, producing a Big Crunch. (3)

       The second one is called open universe, in which there is not enough matter to stop the expansion of universe in which the universe will expand forever, eventually all stars go out and the whold universe became dark and cold. The third one is called flat universe, the universe will expand forever but the speed at which the galaxies separate will eventually reach zero.(3)

Open Universe: There is not enough matter to stop the universe from expanding forever. (4)

Flat Universe: Expansion slows until the rate approaches zero. (3)

       As Friedman being the director of the Main Geophysical Observatory in Leningrad in 1924. George Gamow studied after him. Gamow gaining his PhD from the university of Leningrad in 1928.

George Gamow, Professor, University of Colorado (5)

He was invited to Niels Bohr's Institute for Theoretical Physics at the University of Copenhagen in Germany from 1928 to 1931, with a break in 1929 to work with Ernest Rutherford at the Cavendish Laboratory, Cambridge. Gamow backed to the USSR but after a short time he decided to flee Russia due to an increased oppression by Stalin. He successfully escaped while attending the 1933 Solvay Conference for Physicists in Brussels, Belgium. Gamow and his family moved to United States in 1934, and Gamow began working as Professor of Physics at George Washington University in Washington DC. In 1948, Gamow and his student Ralph Alpher produced a paper entitled "The Origin of Chemical Elements", which outlined how the present levels of hydrogen and helium in the universe could be largely explained by reactions occurred  during the Big Bang. This lent theoretical
support to the Big Bang theory. Gamow also estimate the strength of residual cosmic microwave background radiation in this paper. Gamow died on August 19, 1968 due to his excessive drinking habit, at age 64.(4)

References:

(1) Luke Mastin, Important Scientists: Alexander Friedmann (1888-1925), 2009. The Physics of the             Universe,   http://www.physicsoftheuniverse.com/scientists_friedmann.html

(2) Mark Edgall, Alexander Friedmann: Unsung Hero of Modern Cosmology, October 31, 2012. decoded Science, http://www.decodedscience.com/alexander-friedmann-unsung-hero-of-modern-cosmology/19423

(3) Friedmann Universe, PBS Organization,  http://www.pbs.org/wnet/hawking/universes/html/univ_fried.html

(4) Luke Mastin, Important Scientists: George Gamow (1904-1968), 2009. The Physics of the Universe,  http://www.physicsoftheuniverse.com/scientists_gamow.html

(5) The Distinguished Life and Career of George Gamow. Department of Physics, University of Colorado Boulder, http://phys.colorado.edu/public-outreach/distinguished-life-and-career-george-gamow