Speed of Light
Year of Discovery: 1928
What Is It? The speed at which light travels—a universal constant.
Who Discovered It? Albert Michelson
Why Is This One of the 100 Greatest?
In the late 1800s discovering the true the speed of light had only minor importance because astronomers were the only ones who used this number. (Distances across space are
measured in light-years—how far light travels in one year’s time.) Since their measurements were only approximations anyway, they could accept a 5 percent (or even 10 percent)
error in that value.
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Then Albert Einstein created his famed energy-matter equation, E = mc . Instantly the
speed of light, “c,” became critical to a great many calculations. Discovering its true value
jumped to the highest priority. Light speed became one of the two most important constants
in all physics. A 1 percent error, or even a 0.1 percent error, in “c” was suddenly unacceptably large.
But the problems of discovering the true speed of light—a speed faster than any clock
could measure or other machines could detect—were enormous. Albert Michelson invented
half a dozen new precision devices and, after 50 years of attempts, was the first human to accurately measure light speed. His discovery earned Michelson the first Nobel Prize to be
given to an American physicist.
How Was It Discovered?
This was a discovery that was dependent on the invention of new technology and new
equipment—just as Galileo’s discovery of moons around other planets was dependent on
the invention of the telescope.
In 1928, 74-year-old Albert Michelson struggled to make one last try to accurately
measure the speed of light and discover the true value of “c” in Einstein’s famed equation.
He had designed, financed, and completed a dozen attempts over the previous 50 years.
Michelson was determined this time to measure the speed of light with no more than a 0.001
percent error. That value would finally be accurate enough to support essential nuclear
physics calculations.
Four years earlier, Michelson had turned to the famed gyroscope manufacturer, Elmer
Sperry, to improve upon the equipment available for his measurements. Now in 1928, the
third, and latest, round of equipment improvements was represented by a small octagonal
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