Antimatter is just a little less lively.
Physicists know that every fundamental particle in nature has an antiparticle. These are evil twins with identical masses but equal and opposite properties such as charge and spin.. When these twins meet, they obliterate each other and emit a flash of energy upon contact.
In science fiction, antiparticles provide the power for warp drive. Some physicists have speculated that antiparticles may be repelled by gravity or even travel backwards in time.
A new experiment at CERN, the European Center for Nuclear Research, brings some of that speculation back to Earth. It turns out that in a gravitational field, antiparticles fall just like we do. “The bottom line is there’s no such thing as a free lunch, and you can’t use antimatter to levitate,” said Joel Fajans of the University of California, Berkeley.
Dr. Fajans was part of an international team known as ALPHA (Antihydrogen Laser Physics Apparatus Collaboration). The team is based at his CERN and led by particle physicist Jeffrey Hangst from Aarhus University in Denmark. Dr. Fajans and his colleagues collected about 10,000 antiatomic hydrogen atoms and suspended them in a magnetic field. As the magnetic field slowly descended, the antihydrogen atoms cascaded down, like maple leaves in October, with the same downward acceleration (G force) as normal atoms. That’s about 32 feet per second.They are The results were announced on Wednesday Published in Nature magazine.
Few physicists were surprised by this result. According to Einstein’s theory of general relativity, all forms of matter and energy respond equally to gravity.
“If you walk down the halls of this department and ask any physicist, they will all tell you that this result is not at all surprising.” Jonathan Warteresaid a physicist at the University of California, Berkeley, in a statement from the university. It was he who first proposed this experiment to Dr. Fajans 10 years ago. “That’s the reality,” Dr. Wartere says.
“But most of them will also say they had to experiment because they weren’t sure,” he added. “If it had been the other way around, it would have had a huge impact.”
Alice’s world through the looking glass
In 1928, in one of the most surprising examples of nature after mathematics, physicist Paul Dirac discovered that the quantum mechanical equations describing electrons had two solutions. One is that the electrons were negatively charged. This particle is the workhorse of chemistry and electricity. In other solutions, the particles were positively charged.
What were those particles? Dirac thought it was a proton, but J. Robert Oppenheimer, later of atomic bomb fame, suggested it was an entirely new particle: a positron, identical to an electron but with a positive charge and spin. did. Two years later, Karl Anderson of the California Institute of Technology detected positrons from cosmic ray showers, a discovery for which he received the Nobel Prize in Physics.
And so the temptation of antimatter was born. The positively charged protons that dominate the nucleus are matched by the negatively charged antiprotons. Antielectrons are called positrons. Neutrons also exist in atomic nuclei and have antineutrons. Antiquarks and other quarks that make up protons exist.
In principle, there could be entire anti-worlds inhabited by anti-beings. The joke is that if you meet your anti, he’ll stick out his left hand and shake your hand, but you better not take it or you’ll both explode.
For scientists, the thrill of antimatter isn’t just being added to a list of particles with strange names. For them, studying antihydrogen atoms is the first step toward testing one of nature’s deepest assumptions: that antimatter should look and behave like ordinary matter.
For the past 20 years, ALPHA group scientists have been collecting antimatter at CERN, sucking up high-energy antiprotons from collisions at the Large Hadron Collider and slowing them from the speed of light to speeds and temperatures of hundreds of feet per second. I did. Approximately 15 degrees above absolute zero. The antiprotons are then mixed with a cloud of antielectrons or positrons produced by the decay of radioactive sodium in a so-called mixing trap controlled by an electric field.
Ordinary hydrogen, the simplest and most abundant element in the universe, consists of positively charged protons and negatively charged electrons. The ALPHA experiment results in the production of some antihydrogen atoms. The nucleus of an atom is an antiproton, surrounded by positrons.
In 2002, Dr. Hungst reported that these antihydrogen atoms emit and absorb light at the same frequencies and wavelengths as normal hydrogen, just as Einstein predicted. Since then, a number of experiments have strongly suggested, although all indirectly, that antimatter also has normal gravity, Fajans said. However, these experiments were inconclusive because gravity is less than a trillionth of the strength of the electromagnetic field used to manipulate antiatoms.
anti-message in a bottle
In the latest experiment, antihydrogen atoms were trapped inside a 10-inch-long metal container by a magnetic field. Like hydrogen, antihydrogen atoms have their own slight magnetic field, so they reflect off the walls of this bottle.
The magnetic field can also be adjusted to suspend antihydrogen atoms in the bottle against gravity. In the experiment, when the magnetic field was slowly lowered, the atoms eventually escaped from the field and instantly disappeared on the walls of the room. Statistical analysis showed that approximately 80% of these flashes occurred below the chamber. This suggests that gravity acts in a direction that pulls antiatoms downward, just as it does in normal matter.
Breaking the expected symmetry between hydrogen and antihydrogen would fundamentally shake up physics.
That didn’t happen, Dr. Wartere said. “This experiment is the first time that direct measurements of gravity on neutral antimatter have been made,” he said. “This is another step in advancing the field of neutral antimatter science.”
But as a result, a new puzzle is imposed. According to the theory of relativity and quantum mechanics (two competing theories governing the universe), the Big Bang should have created equal amounts of matter and antimatter, which should have annihilated each other long ago.
However, our universe is all matter, and apart from cosmic ray showers and collisions from particle colliders, there is not the slightest amount of antimatter. what happened? Why is there something in the universe instead of nothing? This question has been burning for almost a century already.
Three years ago, researchers in Japan reported that experiments using strange particles known as neutrinos could provide clues to the imbalances in the universe. At the Large Hadron Collider, an entire instrument called LHCb is dedicated to looking for differences between matter and antimatter that could upset the balance of the universe.
Asked whether the results of the ALPHA experiment had given the LHCb team any insight, Dr. Wartere said: “Our answer is consistent with normal gravity, so I don’t think it can give us any hints, unfortunately. ” he said. This translates to saying we still don’t know why we’re here.