We live in a universe where there is a lot of matter and, by and large, there is no antimatter at all. Two of our readers want to know what antimatter is, and a physicist gives them an answer to this question.
Antimatter. From this word breathes fascinating books and films in which villains get to explosives from antimatter or spaceships travel on such fuel.
But what is this substance - what is, in essence, antimatter?
The readers of Wiedenskub would like to know this very much. They have read some of the many articles we have published about physicists' experiments with antimatter, but they would love to know more.
First, we must clarify that physicists' antimatter should not be confused with those antibodies that are known to us from biology and medicine. There antibodies (also called immunoglobulins) are special protein compounds, part of the body's defense against diseases. They can bind to foreign molecules and thus protect the body from microorganisms and viruses.
But here we will not talk about them. We contacted a scientist from the world of physics: Nikolaj Zinner, a lecturer at the Department of Physics and Astronomy at Aarhus University, will be happy to tell us about antimatter.
Substance with opposite charge
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“All those particles that, as we know, are in nature, everything that our world consists of, exist in variants with the opposite charge. This is antimatter,”says Nikolai Sinner.
“Antimatter looks exactly the same and has the same mass as ordinary matter, but it has exactly the opposite charge. For example, positively charged positrons have negatively charged electrons. Positrons are antiparticles of electrons."
So there is nothing fundamentally unusual about antimatter. It is just a substance with an opposite charge relative to the substance in the environment of which we are usually found. But why there is so little of it is just a mystery, and we will return to this later.
“In everyday life we do not encounter antimatter, but it appears in many situations, for example, during radioactive decay, under the influence of cosmic radiation and in accelerators. It just disappears very quickly again. When a positron meets an electron, the result is pure energy in the form of two high-energy light particles - quanta.
Disappears in a flash of light
“Here is an electron and a positron, they have opposite charges, so they attract. They can get very close to each other, and when this happens, they merge and form two photons. This is a consequence of the laws of nature, - says Nikolai Sinner. "The mass of two particles is converted into energy in the form of two particles - quanta of gamma radiation."
“If you had a lot of antimatter, and you allowed it to come into contact with ordinary matter, you would cause a very powerful reaction. And vice versa: energy can be converted into matter and antimatter, and this happens in particle accelerators."
Used in medical scanners
It is this phenomenon, when the meeting of matter and antimatter leads to their disappearance and the release of energy, is probably the first thing that fascinates the authors of science fiction.
For example, antimatter plays an important role in Dan Brown's Angels and Demons, and in Star Trek, interstellar ships run on antimatter.
But in the real world, antimatter has a more peaceful application.
The antimatter in the form of positrons from the decay of radioactive materials is used in hospitals in PET (positron emission tomography) scanners, which can take pictures of internal organs and detect unhealthy processes in them.
“So antimatter isn't all that mystical. This is a part of nature that we enjoy using,”says Nikolai Sinner.
We also expose ourselves to antimatter by eating bananas. They contain potassium, which is slightly radioactive and releases positrons when it decays. About every 75 minutes, a banana emits a positron, which quickly collides with an electron, and they turn into two gamma photons.
But all this is absolutely not dangerous. To get a dose of radiation that corresponds to what we get when taking an X-ray, we will have to consume several hundred bananas.
It was predicted even before the discovery
You can better understand what antimatter is if you look at the history of its discovery. Interestingly, the existence of antimatter was predicted even before it was discovered.
In the 1920s, it turned out that a new theory called quantum mechanics was perfect for describing the smallest particles of matter - atoms and elementary particles. But it was not so easy to combine quantum mechanics with the second great theory of the 20th century, the theory of relativity.
The young British physicist Paul Dirac rushed to solve this problem and managed to derive an equation that combines quantum mechanics with special relativity.
With the help of this equation, it became possible to describe the motion of an electron, even if its speed approached the speed of light.
But the equation prepared a surprise. He had two solutions, just like the equation "x² = 4": x = 2 and x = -2 ". That is, it could describe not only the well-known electron, but also another particle - an electron with negative energy.
Discovered in Wilson's cell
Then they knew nothing about particles with negative energy, and Paul Dirac interpreted his discovery as follows: there can exist a particle that is exactly the same as an electron, with the exception of the opposite charge.
If the electron has a negative charge, then there must be a corresponding particle with a positive charge. According to calculations, the same rule should apply to all elementary particles, that is, in general, all the particles that make up the world.
And so the hunt for the anti-electron began. American physicist Carl Anderson used a fog camera (aka Wilson's camera) to detect traces of particles from space that have the same mass as an electron, but with the opposite charge.
This is how Dirac's antielectron was discovered, which was named positron - short for "positive electron". From that moment on, step by step, new antiparticles were discovered.
The universe was pure energy in the beginning
Dirac suggested that distant stars - perhaps half of all we see in the sky - may be composed of antimatter, not matter. This follows, for example, from his speech, which he gave while accepting the Nobel Prize in Physics in 1933.
But today we know that everything in the universe consists only of matter, and not of antimatter. And this is really mysterious, because at the beginning of the existence of the universe there should have been approximately the same amount of both, Nikolai Sinner explains.
“If we start to rewind the development of the universe, the energy will become more and more. The density will increase, the temperature will rise. Finally, everything will turn into pure energy - energy-carrying or force particles like photons. This was the beginning of the universe, according to our most common cosmological theories."
“And if we again go forward from this point of reference, then at some point the energy will have to start converting into matter. It is perfectly possible to create matter from pure energy, but in this case you get as much antimatter as matter. That's the problem - you would expect the same amount of both."
“There must be some law of nature that is responsible for the fact that today there is more matter than antimatter. And nothing more can be said about this imbalance. And so this asymmetry could be explained."
Neutrinos will help solve the riddle
The big question is where in the laws of nature one should look for the reason for the victory of matter over antimatter. Physicists are trying to figure this out through experiments.
At the CERN Research Center in Switzerland, antimatter is produced and held in magnetic fields, and through a series of antihydrogen experiments, physicists are trying to find an answer to the question of whether matter and antimatter are exact mirror images of each other.
Perhaps there is still a small difference between them, with the exception of charge, and this difference will help explain why there is so much matter in the universe relative to antimatter.
Managed to create antihelium
Since antimatter is very rare and quickly disappears when it encounters a substance, there are no molecules of antimatter in nature, and only its smallest molecules can be created.
In 2011, American scientists managed to create antihelium. There were no larger atoms.
We at Wiedenskab wrote a lot about these experiments, which so far demonstrate that antimatter behaves in exactly the same way as matter, which, for example, is described in the article “Aarhus Scientist Carried Out the Most Accurate Antihydrogen Measurements in History”. And, perhaps, solving this riddle will help us find elementary particles called neutrinos. We wrote about this in the article "Ice experiment will reveal the secret of matter."
“We can hope that we will find the answer in the neutrino, because we already know that it behaves strangely. There are many gaps in physics here, so it would be wise to start digging here,”says Nikolai Sinner.
Antimatter itself is not all that mystical, but physicists have not yet figured out why there is so much more matter than antimatter in the universe today. They are working on this issue.
Henrik Bendix