According to legend, the astronomer and physicist Galileo Galilei (1564-1642) discovered the fundamental nature of falling bodies by dropping cannonballs of different weights from the top of the Tower of Pisa, while an assistant observed the moment the projectiles hit the ground. Still according to this story, it was by observing that the cannonballs arrived at the ground at the same time, regardless of their mass, that Galileo discovered gravitational acceleration, which is independent of the mass of objects in free fall.
This story is probably false, if only because it is very difficult to judge with the naked eye when two objects moving at high speed in free fall reach the ground and, therefore, to make a precise quantitative study. In all likelihood, Galileo would have instead used long inclined planes on which he rolled balls of different masses to measure their rate of acceleration and make his great discovery.
Regardless, an international team of physicists – including a good number of Canadian researchers – recently carried out an experiment comparable in every way to that of the Tower of Pisa, which sought to find out if atoms antimatter were subjected to the gravitational attraction of the Earth in the same way as atoms of matter.
Will these antiatoms fall in the same direction and accelerate in the same way as atoms of matter? Will they go in another direction (up?) or will they accelerate at a different pace? Needless to say, the answers to these questions could have important consequences for our current physical theories and our understanding of the great universal forces, starting with gravity…
Recall that antimatter particles have the same characteristics as matter particles, except that their electric charge (and certain other fundamental characteristics, such as spin) are of opposite sign: the antiparticle of the electron, the positron, has the same mass as the electron, but is positively charged, while the electron is negatively charged. Same thing for the antiproton, similar to a proton, but with a negative charge.
When an antimatter particle comes into contact with its material counterpart, the two particles disintegrate by converting the sum of their masses into energy (E = mc2) in the form of gamma rays. The Universe as we know it is entirely made up of matter, which to this day constitutes a great mystery, since the laws of quantum mechanics applied to the phenomenon of the Big Bang predict the production of both types of matter in equal quantities…
The propensity of matter and antimatter to annihilate at the slightest contact explains why it is extremely difficult to manipulate antimatter in the laboratory. Fortunately, magnetic confinement systems allowed the team led by Danish researcher EK Anderson to keep antihydrogen atoms suspended in a vacuum long enough to be able to judge the direction of their fall in the Earth’s gravitational field.
Their instrument, called ALPHA-g, was built in the laboratories of the TRIUMF Institute in British Columbia before being shipped to the European Organization for Nuclear Research (formerly known as the European Council for Nuclear Research). nuclear research, CERN) on the Franco-Swiss border. This is where the experiment, the results of which the researchers published in the journal Nature on September 27, took place.
Good news, the antiparticles fall in the “good” direction, which already allows us to say that there does not seem to be an “antigravity” which would be associated with the antiparticles. The mass of the latter is therefore “attracted” by the mass of the Earth in the same way as ordinary matter.
It remains to be seen whether antiparticles accelerate at the same rate as ordinary matter in the Earth’s gravitational field, i.e. around 9.8 m/s.2. Given the very low mass of these antiatoms, measuring their acceleration remains an enormous challenge, which the researchers intend to meet as they continue to refine their experimental setup.