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==The Brans-Dicke Theory of Gravitation==

==The Brans-Dicke Theory of Gravitation==

While Dicke accepted [[Theory of Relativity|Relativity]], both special and general, he believed that plain General Relativity did not fully explain gravity.  Along with his former student Carl Brans, he formulated the Brans-Dicke theory, which includes a scalar field in addition to the tensor field defined by general relativity.  This "scalar-tensor theory" (as opposed to plain relativity, which is just a "tensor theory") included a scalar field, usually denoted ω, which, when assigned a certain value, they believed matched experimental data better.  (When ω is set to infinity, the Brans-Dicke theory becomes equivalent to plain General Relativity.)  Brans and Dicke suggested a value of about 5.  The observable differences between Brans-Dicke and general relativity are extremely tiny.

While Dicke accepted [[Theory of Relativity|Relativity]], both special and general, he believed that plain General Relativity did not fully explain gravity.  Along with his former student Carl Brans, he formulated the Brans-Dicke theory, which includes a scalar field in addition to the tensor field defined by general relativity.  This "scalar-tensor theory" (as opposed to plain relativity, which is just a "tensor theory") included a scalar field, usually denoted &omega;, which, when assigned a certain value, they believed matched experimental data better.  (When &omega; is set to infinity, the Brans-Dicke theory becomes equivalent to plain General Relativity.)  Brans and Dicke suggested a value of about 5.  The observable differences between Brans-Dicke and general relativity are extremely tiny, but the Mariner and Cassini spacecraft (below) clearly detected this<ref name="exper1">http://content.time.com/time/magazine/article/0,9171,943324,00.html This is currently behind a "paywall".  Before that, the theme of the full article was the demise of Brans-Dicke, and it explained that the Mariner measurements supported plain relativity and refuted Brans-Dicke.</ref> <ref name="exper2">http://www.jpl.nasa.gov/releases/70s/release_1970_0566.html</ref> <ref name="exper3">[https://books.google.com/books?id=9ZuP9JQzc00C&pg=PA157&lpg=PA157&dq=brans-dicke%2Bmariner&source=bl&ots=Y2jhf2OjcU&sig=C8qWD1E5ukCe_5DiKObCiWjAEKg&hl=en&sa=X&ei=cCw9VcfBE8HksASynoHICw&ved=0CDkQ6AEwBQ#v=onepage&q=brans-dicke%2Bmariner&f=false The Rise and Fall of the Brans-Dicke Theory]</ref>.

Dicke was instrumental in proposing extremely sensitive tests of General Relativity.  Modern measurements of the various tests, specifically from Mariner 6 spacecraft in 1969, and the Cassini spacecraft in 2004, show that plain Einsteinian relativity, not the Brans-Dicke theory, agrees with observation.<ref>http://content.time.com/time/magazine/article/0,9171,943324,00.html</ref> <ref>http://www.jpl.nasa.gov/releases/70s/release_1970_0566.html</ref> <ref>[https://books.google.com/books?id=9ZuP9JQzc00C&pg=PA157&lpg=PA157&dq=brans-dicke%2Bmariner&source=bl&ots=Y2jhf2OjcU&sig=C8qWD1E5ukCe_5DiKObCiWjAEKg&hl=en&sa=X&ei=cCw9VcfBE8HksASynoHICw&ved=0CDkQ6AEwBQ#v=onepage&q=brans-dicke%2Bmariner&f=false The Rise and Fall of the Brans-Dicke Theory]</ref>  Nevertheless, interest in the Brans-Dicke formulation has recently revived, in the context of dark matter / dark energy investigations.

Dicke was instrumental in proposing extremely sensitive tests of General Relativity.  Modern measurements of the various tests, specifically from the Mariner 6 spacecraft in 1969 and the Cassini spacecraft in 2004, show that plain Einsteinian relativity, not the Brans-Dicke theory, agrees with observation<ref name="exper1"/> <ref name="exper2"/> <ref name="exper3"/>. Nevertheless, interest in the Brans-Dicke formulation has recently revived, in the context of dark matter / dark energy investigations.

==Biography==

==Biography==

Dicke was born on May 6, 1916 in St. Louis, [[Montana]]. He received a bachelor’s degree from Princeton University in 1939, as well as a doctorate from the University of Rochester in 1941. In the same year he became a staff scientist at the radiation laboratory of MIT. In 1975 he was appointed Albert Einstein professor of science and nine years later he became emeritus professor.<ref>http://www.britannica.com/EBchecked/topic/162137/Robert-H-Dicke</ref>

Dicke was born on May 6, 1916 in St. Louis, [[Montana]]. He received a bachelor’s degree from Princeton University in 1939, as well as a doctorate from the University of Rochester in 1941. In the same year he became a staff scientist at the radiation laboratory of MIT. In 1975 he was appointed Albert Einstein professor of science and nine years later he became emeritus professor.<ref>http://www.britannica.com/EBchecked/topic/162137/Robert-H-Dicke</ref>

Dicke's work was closely related to that of Arno Penzias and Robert Wilson, who first measured the [[cosmic background radiation]], though Dicke was the theorist who explained it<ref>http://www.nps.gov/history/history/online_books/butowsky5/astro4k.htm and http://www.astrosociety.org/pubs/mercury/9404/dicke.html</ref>.  The 1978 [[Nobel Prize]] for Physics was awarded to Penzias and Wilson, but not Dicke, for this work.  Some people think that this was unfair, and that Dicke should also have won the Nobel Prize for any of his many other achievements also (such as his laser work).

Dicke's work was closely related to that of Arno Penzias and Robert Wilson, who first measured the [[cosmic background radiation]], though Dicke was the theorist who explained it<ref>http://www.astrosociety.org/pubs/mercury/9404/dicke.html</ref>.  The 1978 [[Nobel Prize]] for Physics was awarded to Penzias and Wilson, but not Dicke, for this work.  Some people think that this was unfair, and that Dicke should also have won the Nobel Prize for any of his many other achievements also (such as his laser work).

== References ==

== References ==