Dark radiation in big bang cosmology

Keeping Science in Darkness

Sometimes the existence of a new ‘particle’ in physics has been proposed long before it was discovered by an experimentalist in a lab experiment. Some examples of this are the anti-electron (positron) proposed by Paul Dirac in 1927 and discovered in 1932; the neutron, predicted by Ernest Rutherford in 1920, and discovered by James Chadwick in 1932; the pi meson discovered by C. F. Powell’s group in 1947 but predicted by Hideki Yukawa in 1935; and in 2012 a particle was detected exhibiting most of the predicted characteristics of the Higgs boson, which was predicted by Peter Higgs and five others in 1964.  For their prediction, Peter Higgs and François Englert, were awarded the Nobel Prize in Physics in 2013.

In astrophysics such a new ‘particle’ could be the planet Neptune. Its existence was mathematically predicted by Urbain Le Verrier before it was directly observed in 1846 by Johann Gottfried Galle at the Berlin Observatory. (There was some dispute over credit as John Couch Adams from Cambridge had separately made predictions on the position of the planet.)

Those predictions, which led to successful outcomes, were based on the established laws of nature; for Neptune it was Newton’s gravitational theory, and for particle physics, the newly developing quantum theory. Continue reading