Wave or corpuscle, such has long been the question. The answer lies in quantum physics and photons, whose surprising behavior always raises new questions…
This article is from the magazine Les Indispensables de Sciences et Avenir n°212 dated January/March 2023.
Today, the researchers of the Kastler-Brossel laboratory of the Collège de France, such as the 2012 Nobel Prize in Physics Serge Haroche, live in full light… except when they are carrying out experiments. The lasers, lenses and mirrors are so sensitive that any stray light would distort the measurements. And yet, it is light that interests these scientists, who here pursue a quest more than 2,500 years old.
“In the “Odyssey”Homer writes that Agamemnon shoots lightning with his eyes”, quotes the physicist. For the Greek poet, it would therefore be the eye that emits light, and not the objects! Almost two millennia later, at the turn of the year 1000, the Arab-Persian scholar Abu Ali ibn Hasan – known in the West as Alhazen – shows that light reaches the back of the eye as it does inside a dark room. Thus, it is objects that emit light, and we capture it either through our vision system or through appropriate instruments.
In the West, the subject of light was not taken up again until the 17th century. René Descartes enacts mathematical laws on refraction in 1637. Twenty years later, the French mathematician Pierre de Fermat states that light goes from one point to another following the trajectory which minimizes its travel time. And in Italy, Galileo tries to measure his speed over a few kilometers, without succeeding. Could it be instantaneous?
It will be up to Olaus Römer, a Danish astronomer at the Paris Observatory, to decide in 1676. Observing the eclipses of Jupiter’s satellite Io which, on leaving the shadow of the planet, reappears ahead or behind what Kepler’s laws predict, it shows that this lag is due to the distance Earth travels as Io orbits the gas giant. Depending on whether our planet is approaching or moving away from it[…]
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