Ralph Asher Alpher - Big Bang Nucleosynthesis Theory

Big Bang Nucleosynthesis Theory

Alpher's dissertation in 1948 dealt with a subject that came to be known as Big Bang nucleosynthesis. The Big Bang is a term coined initially in derision by Fred Hoyle on BBC Radio in 1950 to describe the cosmological model of the universe as expanding into its current state from a primordial condition of enormous density and temperature. Nucleosynthesis is the explanation of how more complex elements are created out of simple elements in the moments following the Big Bang. Right after the Big Bang, when the temperature was extremely high, if any nuclear particles such as neutrons and protons, became bound together (being held together by the attractive nuclear force) they would be immediately broken apart by the high energy photons (quanta of light) present in high density. In other words, at this extremely high temperature, the photons' kinetic energy would overwhelm the binding energy of the strong nuclear force. For example, if a proton and a neutron became bound together (forming deuterium), it would be immediately broken apart by a high energy photon. However, as time progressed, the universe expanded and cooled and the average energy of the photons decreased. At some point, roughly one second after the Big Bang, the attractive force of nuclear attraction would begin to win out over the lower energy photons and neutrons and protons would begin to form stable deuterium nuclei. As the universe continued to expand and cool, additional nuclear particles would bind with these light nuclei, building up heavier elements such as helium, etc. Alpher argued that the Big Bang would create hydrogen, helium and heavier elements in the correct proportions to explain their abundance in the early universe. Alpher and Gamow's theory originally proposed that all atomic nuclei are produced by the successive capture of neutrons, one mass unit at a time. However, later study challenged the universality of the successive capture theory since no element was found to have a stable isotope with an atomic mass of five or eight, hindering the production of elements beyond helium. Since this dissertation was (correctly) perceived to be ground-breaking, over 300 people attended the dissertation defense, including the Press, and articles about his predictions and a Herblock cartoon appeared in major newspapers. This was quite unusual for a doctoral dissertation.

Later the same year, collaborating with Robert Herman, Alpher predicted the temperature of the residual radiation (known as cosmic background radiation) resulting from the hypothesized Big Bang. However, Alpher's predictions concerning the cosmic background radiation were more or less forgotten and they were rediscovered by Robert Dicke and Yakov Zel'dovich in the early 1960s. The existence of the cosmic background radiation and its temperature were measured experimentally in 1964 by two physicists working for Bell Laboratories in New Jersey, Arno Penzias and Robert Wilson, who were awarded the Nobel prize in physics for this work in 1978.

Although his name appears on the paper, Hans Bethe had no direct part in the development of the theory, although he later worked on related topics; Gamow added his name to make the seminal paper's title a pun on "Alpha-Beta-Gamma", the first three letters of the Greek alphabet. Thus, Alpher's independent dissertation was first published on April 1, 1948 in the Physical Review with three authors. The humor engendered by the prodigious Gamow may at times have obscured the critical role Alpher played in developing the theory. This seminal paper was based on his dissertation (defended shortly thereafter). Other scientists who read the paper may have erroneously assumed that Gamow and Bethe had been the primary contributors. With the award of the 2005 National Medal of Science, Alpher's original contributions (nucleosynthesis and the cosmic microwave background radiation predicition) to the modern big bang theory are beginning to receive due recognition. Neil deGrasse Tyson was instrumental in a NSF committee recommendation (personal communication to Dr. Victor S. Alpher, July 26, 2007).

Alpher and Robert Herman were awarded the Henry Draper Medal from the National Academy of Sciences in 1993. They were also awarded the Magellanic Premium of the American Philosophical Society in 1975, the Georges Vanderlinden Physics prize of the Belgian Academy of Sciences, as well as significant awards of the New York Academy of Sciences and the Franklin Institute of Philadelphia. Two Nobel Prizes in physics have been awarded for empirical work related to the cosmic background radiation — in 1978 to Arno Penzias and Robert Wilson and in 2006 to John Mather and George Smoot. Alpher and Herman (the latter, posthumously) published their own account of their work in cosmology in 2001, Genesis of the Big Bang (Oxford University Press). He was elected a Fellow of the American Academy of Arts and Sciences in 1986. In 2005 Alpher was awarded the National Medal of Science. The citation for the award reads "For his unprecedented work in the areas of nucleosynthesis, for the prediction that universe expansion leaves behind background radiation, and for providing the model for the Big Bang theory." The medal was presented to his son Dr. Victor S. Alpher on July 27, 2007 by President George W. Bush, as his father could not travel to receive the award. Ralph Alpher died following an extended illness on August 12, 2007. He had been in failing health since falling and breaking his hip in February 2007.