11/09/2024

Folha: 'Who created the Theory of Relativity?'

Reduction of Marcelo Viana's column in Folha de S. Paulo

In 1905, his "annus mirabilis" (miraculous year), the German physicist Albert Einstein (1879–1955) published four absolutely extraordinary scientific papers. Among them, "On the Electrodynamics of Moving Bodies" founded the Theory of (special) Relativity, one of the most revolutionary advances in the history of science.

The theory rests on two central ideas: the laws of physics are the same for all observers in uniform motion (principle of relativity); the speed of light in a vacuum is the same for all observers, regardless of their motion relative to the light source.

The consequences are counterintuitive. Events that are simultaneous for one observer may not be so for another. Moving clocks measure time more slowly, and objects appear shorter in the direction they are moving. Nothing in the Universe moves faster than light. Mass and energy are equivalent concepts, related by the famous equation E= ^mc²

But how much of it was actually new?

In 1887, American physicists Albert Michelson (1852–1931) and Edward Morley (1838–1923) attempted to measure the absolute motion of the Earth relative to the "ether" that supposedly filled all of space. They tried and failed.

Aiming to explain the results of Michelson and Morley, in 1895 the Dutchman Hendrik Lorentz (1853–1928) introduced a set of formulas relating the observations of two observers in motion.

This work attracted the attention of the French mathematician Henri Poincaré (1854–1912), who, in the same year, published the first version of the principle of relativity: "it is impossible to determine absolute motion relative to the ether: all we can measure is the relative motion between two bodies".

Poincaré improved Lorentz's work while giving him full credit. "Poincaré, on the contrary, obtained a perfect invariance of the equations of electrodynamics and formulated the 'principle of relativity,' terms which he was the first to use. Let us add that, while in this way correcting the imperfections of my work, he never criticized me for them," wrote Lorentz.

In June 1905—the same month Einstein submitted his article for publication—Poincaré published "On the Dynamics of the Electron," a five-page paper in which he clearly formulated his principle of relativity. "The impossibility of experimentally demonstrating the Earth's motion seems to be a general law of nature. We are therefore led to accept this law, which we call the 'principle of relativity,' and apply it without restriction."

For almost all intents and purposes, Poincaré's contribution was forgotten, and Einstein received full credit for the new theory. Which, incidentally, he would generalize a decade later when creating the Theory of General Relativity, incorporating the phenomenon of gravitation. This state of affairs seems fair: to the modern scholar, Einstein's formulation of relativity appears superior.

To read the full text, visit the newspaper's website.