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One of the most counterintuitive concepts in physics is that all objects fall at the same speed, regardless of mass. equivalence principleThis is a memorable illustration by NASA’s Apollo 15 astronaut David Scott during the moonwalk in 1971.he Dropped A falcon’s wings and a hammer are fired simultaneously via the TV’s live feed, and the two objects collide with the dirt at the same time.
I have long tradition To experimentally test the weak equivalence principle that forms the basis of Albert Einstein’s general theory of relativity. Despite centuries of testing, the equivalence principle has held firm. and now microscope (MICROSatellite pour l’Observation de Principe d’Equivalence) The mission has achieved the most accurate test of the equivalence principle ever. Check Einstein again, Around recent papers It was published in the journal Physical Review Letters. (Additional related papers were published in a special issue of Classical and Quantum Gravity.)
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The 6th-century philosopher John Philoponus was the first to argue that the speed at which an object falls is independent of its weight (mass), and then, about 900 years later, Galileo Galilei had a great influence on it. Galileo allegedly dropped cannonballs of varying masses from Italy’s famous Leaning Tower of Pisa, but the story is probably apocryphal.
Galileo Did it By rolling the ball on an inclined surface, the rolling speed of the ball is greatly reduced, making it easier to measure the acceleration. The balls are similar in size, but the mass is different between iron and wooden balls. Galileo didn’t have an accurate clock, so he reportedly pulsed the movement of the ball. And like Philoponus, he found that no matter what the inclination, the ball would travel with the same acceleration.
Galileo later refined his approach using a pendulum device that measures the period of oscillation of pendulums of different masses but the same length. This was also the method favored by Isaac Newton around 1680, and later by Friedrich Bessel in 1832, both of whom greatly improved the accuracy of their measurements. Newton also realized that this principle extends to celestial bodies, calculating that the Earth and Moon, Jupiter and its satellites, fall toward the Sun at the same speed. The core of the Earth is iron, but the core of the Moon is made mainly of silicates and has a completely different mass.Still NASA’s Laser lunar ranging experiment They confirmed Newton’s calculations: they certainly fall around the Sun at the same speed.
Hungarian physicist Roland Etvös at the end of the 19th century I combined the pendulum approach with torsion balance to create a torsion pendulum and used it to conduct a more accurate test of the equivalence principle. This simple straight bar proved accurate enough to test the equivalence principle more precisely. Torsion balances were also used in subsequent experiments, including an experiment in 1964 using lumps of aluminum and gold as test masses.
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Einstein, in his 1916 paper laying the foundations for his general theory of relativity, cited Etvös’ experiments testing the equivalence principle. But general relativity, while it works quite well on the macroscale, breaks down on the subatomic scale, where the rules of quantum mechanics apply. It would be evidence of a potential new physics that would help combine the two into one grand theory of his.
One way to test equivalence on the quantum scale is to use matter-wave interferometry. This is related to the classic Michelson-Morley experiment, which sought to detect Earth’s motion through a medium called luminous ether, which physicists at the time believed permeated the universe. . Late 19th century, Thomas Young used such an instrument For his famous double-slit experiment, which tests whether light is a particle or a wave, and as we now know, light is both.of The same is true for matter..
Previous experiments using matter-wave interferometry measured the free fall of two isotopes of the same atomic element, but did not expect to detect small differences. In 2014, a team of physicists wondered if there wasn’t enough difference between the compositions to achieve the highest sensitivity.so Isotopes used of different elements, namely rubidium and potassium atoms, in their version of their experiment. The laser pulse ensured that the atoms fell along two separate paths before recombining. This shows that equivalence is still within 1 in 10 million.
