Nothing happens with antimatter, confirms a new experiment | ET REALITY


Antimatter just lost a little more dynamism.

Physicists know that for every fundamental particle in nature there is an antiparticle: an evil twin of identical mass but endowed with equal and opposite characteristics such as charge and spin.. When these twins meet, they destroy each other and release a flash of energy upon contact.

In science fiction, antiparticles provide the power of warp drives. Some physicists have speculated that antiparticles are 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 to Earth. It turns out that in a gravitational field antiparticles fall just like the rest of us. “The bottom line is that nothing is free and we are not going to be able to levitate using antimatter,” said Joel Fajans of the University of California, Berkeley.

Dr. Fajans was part of an international team known as ALPHA, the Antihydrogen Laser Physics Apparatus collaboration, which is based at CERN and led by Jeffrey Hangst, a particle physicist at Aarhus University in Denmark. Dr. Fajans and his colleagues gathered around 100 hydrogen antiatoms and suspended them in a magnetic field. When the field was slowly reduced, the anti-hydrogen atoms descended like maple leaves in October and at the same rate of downward acceleration, or g-force, as normal atoms: about 32 feet per second per second. They published its result on Wednesday in Nature magazine.

Few physicists were surprised by the result. According to Einstein’s theory of general relativity, all forms of matter and energy respond equally to gravity.

“If you walk the halls of this department and ask physicists, they will all say that this result is not at all surprising.” Jonathan Wurtelesaid a physicist at the University of California, Berkeley, in an announcement issued by the university. It was he who first suggested the experiment to Dr. Fajans a decade ago. “That’s the reality,” Dr. Wurtele said.

“But most of them will also say that the experiment had to be done because you can never be sure,” he added. “The opposite result would have had huge implications.”

In 1928, in one of the most surprising examples of nature following mathematics, physicist Paul Dirac discovered that a quantum mechanical equation describing the electron had two solutions. In one, the electron was negatively charged; This particle is the workhorse of chemistry and electricity. In the other solution, the particle was positively charged.

What was that particle? Dirac thought it was the 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 positive charge and spin. Two years later, Carl Anderson of the California Institute of Technology detected positrons in cosmic ray showers, a discovery that earned him the Nobel Prize in Physics.

And thus the appeal of antimatter was born. Positively charged protons, which dominate atomic nuclei, are accompanied by negatively charged antiprotons. Antielectrons are called positrons. Neutrons, which also reside in atomic nuclei, have antineutrons. The quarks that make up protons have antiquarks, and so on.

In principle, there could be entire antiworlds inhabited by antibeings. The joke goes that if you met your anti-self, that person would extend his left hand to shake, but you’d better not take it or you’d both explode.

For scientists, the excitement of antimatter is not simply adding it to a list of particles with strange names. For them, studying anti-hydrogen atoms is the first step in testing some of the most profound hypotheses about nature, which hold that antimatter should look and behave identically to ordinary matter.

For the past 20 years, scientists in the ALPHA group have been collecting antimatter at CERN, extracting high-energy antiprotons from collisions at the Large Hadron Collider and slowing them down from the speed of light to speeds of a few hundred feet per second and a temperature of about 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 electric fields.

Normal hydrogen, the simplest and most abundant element in the universe, is made up of a positively charged proton accompanied by a negatively charged electron. The ALPHA experiment results in a few atoms of antihydrogen: the nucleus is an antiproton and a positron surrounds it.

In 2002, Dr. Hangst reported that these anti-hydrogen atoms emitted and absorbed light at the same frequencies and wavelengths as normal hydrogen, just as Einstein would have predicted. Since then, many experiments, all indirect, have strongly suggested that antimatter also gravitates normally, Dr. Fajans said. But those experiments have been inconclusive, because gravity is less than one billionth the strength of the electromagnetic fields used to manipulate antiatoms.

In the last experiment, antihydrogen atoms were confined by a magnetic field inside a 10-inch-long metal container. Since, like hydrogen, antihydrogen atoms have a slight magnetic field of their own, they bounce off the walls of this bottle.

The magnetic fields can also be adjusted to counteract gravity and suspend the antihydrogen atoms in the bottle. In the experiment, when the fields were slowly reduced, the atoms finally escaped the field and annihilated in an instant on the walls of the chamber. According to statistical analysis, about 80 percent of these flashes occurred under the camera. This suggests that gravity normally acts to pull antiatoms downward, just as it would with normal matter.

Any violation of the expected symmetry between hydrogen and antihydrogen would have shaken physics to its foundations.

That didn’t happen, Dr. Wurtele said. “This experiment is the first time that a direct measurement of the force of gravity on neutral antimatter has been made,” he said. “It is another step in the development of the field of neutral antimatter science.”

But the result leaves another enigma pending. According to relativity and quantum mechanics (the two conflicting theories that govern 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, with not even a hint of antimatter to be found outside of cosmic ray showers and particle collider collisions. So what happened? Why does the cosmos contain something and not nothing? The issue has been burning for almost a century.

Three years ago, an experiment in Japan with strange particles known as neutrinos reported what could be a clue to the cosmic imbalance. At the Large Hadron Collider, an entire instrument, called LHCb, is dedicated to searching for differences between matter and antimatter that could have tipped the cosmic balance.

When asked if the results of the ALPHA experiment offered any information for the LHCb team, Dr Wurtele said: “Since our answer is consistent with normal gravity, I don’t think it provides any clues, unfortunately.” Which is another way of saying we still don’t know why we’re here.

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