Antimatter Falls Down
Posted by on Thursday, September 28, 2023 Under: Particle Physics
Today it was announced that antimatter falls down.
That might sound trivial, but it is an interesting an important result in our understanding of particle physics and the laws of nature.
Everything that we see around us, and most of what we see in space, is formed of matter. However just over ninety years ago, physicists discovered that every known type of matter particle in nature is paired with another type of particle, known as antimatter. And whenever matter is created or destroyed, the same amount of antimatter must be similarly created or destroyed.
We know that antimatter particles have the same properties as ordinary matter - specifically the same mass, and the same magnitude of electric charge (but with opposite sign). However one question remained - will antimatter be attracted by gravitation as ordinary matter is, or will it be repelled. And today that question seems to have been answered.
In a groundbreaking paper unveiled in the prestigious journal Nature, the ALPHA collaboration based at CERN's Antimatter Factory has just unveiled a fascinating result: atoms of antihydrogen formed in the lab, comprising a positron swirling around an antiproton, descend to Earth in a manner akin to their ordinary matter counterparts. Antimatter interacts with gravitational fields in the same way as ordinary matter does.
(Gravity, the force of attraction between objects with mass, stands as one of the four fundamental forces of nature, albeit the feeblest. Antihydrogen atoms, being electrically neutral and robust constituents of antimatter, present themselves as ideal subjects for scrutinizing how antimatter interacts with gravity.)
The ingenious methodology employed by the ALPHA collaboration involves harnessing negatively charged antiprotons, generated and decelerated in the Antimatter Factory's AD and ELENA apparatus, and coupling them with positively charged positrons sourced from the decay of sodium-22 nuclei. These neutral antimatter atoms can then be captured in a magnetic trap, shielding them from annihilation with any regular matter that might be present.
While previous efforts primarily focused on spectroscopic inquiries within the ALPHA-2 instrument, employing laser or microwave radiation to probe the internal structure of antihydrogen atoms, the ALPHA team also developed a vertical contraption christened ALPHA-g. It welcomed its inaugural antiprotons in 2018 and was put into service in 2021. This setup enables the measurement of vertical positions where antihydrogen atoms annihilate upon the deactivation of the trap's magnetic field, allowing the atoms to escape.
This is precisely the experiment undertaken by the ALPHA researchers in their latest inquiry, building on a proof-of-concept endeavor with the original ALPHA configuration in 2013. They confined clusters of roughly 100 antihydrogen atoms, one cluster at a time, and then delicately liberated the atoms over a span of 20 seconds by gradually reducing the current in the top and bottom magnets of the trap. Computational simulations of the ALPHA-g setup indicated that, for regular matter, this process would result in approximately 20% of the atoms exiting from the top of the trap and 80% from the bottom, a distinction induced by the gravitational pull. By aggregating outcomes from seven such trials, the ALPHA team confirmed that the proportions of anti-atoms exiting from the top and bottom aligned with the predictions of the simulations.
And so in the end, antimatter interacts with gravity in the exact same way as ordinary matter does. This is what we expected, and matches up with the predictions of the best theories that we currently have, but it is still a critical part of scientific advancement to verify such results with precise experiments.
And that is exactly what the ALPHA team has achieved today with this most interesting new result.
That might sound trivial, but it is an interesting an important result in our understanding of particle physics and the laws of nature.
Everything that we see around us, and most of what we see in space, is formed of matter. However just over ninety years ago, physicists discovered that every known type of matter particle in nature is paired with another type of particle, known as antimatter. And whenever matter is created or destroyed, the same amount of antimatter must be similarly created or destroyed.
We know that antimatter particles have the same properties as ordinary matter - specifically the same mass, and the same magnitude of electric charge (but with opposite sign). However one question remained - will antimatter be attracted by gravitation as ordinary matter is, or will it be repelled. And today that question seems to have been answered.
In a groundbreaking paper unveiled in the prestigious journal Nature, the ALPHA collaboration based at CERN's Antimatter Factory has just unveiled a fascinating result: atoms of antihydrogen formed in the lab, comprising a positron swirling around an antiproton, descend to Earth in a manner akin to their ordinary matter counterparts. Antimatter interacts with gravitational fields in the same way as ordinary matter does.
(Gravity, the force of attraction between objects with mass, stands as one of the four fundamental forces of nature, albeit the feeblest. Antihydrogen atoms, being electrically neutral and robust constituents of antimatter, present themselves as ideal subjects for scrutinizing how antimatter interacts with gravity.)
The ingenious methodology employed by the ALPHA collaboration involves harnessing negatively charged antiprotons, generated and decelerated in the Antimatter Factory's AD and ELENA apparatus, and coupling them with positively charged positrons sourced from the decay of sodium-22 nuclei. These neutral antimatter atoms can then be captured in a magnetic trap, shielding them from annihilation with any regular matter that might be present.
While previous efforts primarily focused on spectroscopic inquiries within the ALPHA-2 instrument, employing laser or microwave radiation to probe the internal structure of antihydrogen atoms, the ALPHA team also developed a vertical contraption christened ALPHA-g. It welcomed its inaugural antiprotons in 2018 and was put into service in 2021. This setup enables the measurement of vertical positions where antihydrogen atoms annihilate upon the deactivation of the trap's magnetic field, allowing the atoms to escape.
This is precisely the experiment undertaken by the ALPHA researchers in their latest inquiry, building on a proof-of-concept endeavor with the original ALPHA configuration in 2013. They confined clusters of roughly 100 antihydrogen atoms, one cluster at a time, and then delicately liberated the atoms over a span of 20 seconds by gradually reducing the current in the top and bottom magnets of the trap. Computational simulations of the ALPHA-g setup indicated that, for regular matter, this process would result in approximately 20% of the atoms exiting from the top of the trap and 80% from the bottom, a distinction induced by the gravitational pull. By aggregating outcomes from seven such trials, the ALPHA team confirmed that the proportions of anti-atoms exiting from the top and bottom aligned with the predictions of the simulations.
And so in the end, antimatter interacts with gravity in the exact same way as ordinary matter does. This is what we expected, and matches up with the predictions of the best theories that we currently have, but it is still a critical part of scientific advancement to verify such results with precise experiments.
And that is exactly what the ALPHA team has achieved today with this most interesting new result.
In : Particle Physics
I am a theoretical physicist & mathematician, with training in electronics, programming, robotics, and a number of other related fields.
