Measuring the speed of light
Prof Alan Davies, University of Hertfordshire
‘E = mc2, Einstein’s famous equation. To calculate the energy we need to know c, the speed of light. Most early observers thought that light was transmitted instantaneously i.e. with infinite speed. Galileo was the first to attempt to measure the finite value.
He was hopelessly wrong, but it started a story which we shall follow in this lecture. We shall start with the first reasonably accurate measurement by Ole Rømer using astronomical observations and follow with Hippolyte Fizeau’s first terrestrial measurement.
We then move on to twentieth century techniques. Finally, we shall see its importance in the new definition of the SI metre.
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