Matter-Antimatter Asymmetry: Welcome back to "Science For Everyone", ABP Live's weekly science column. Last week, we discussed what dark matter and dark energy are. This week, we discuss what matter and antimatter are, and what a CERN physicist says about the matter-antimatter asymmetry. When the Big Bang happened, matter as well as antimatter was created. It is believed that matter and antimatter must have been created in equal amounts, but eventually, something caused the balance to be tipped.
This is known as the matter-antimatter asymmetry. It is because of this asymmetry that everything we see around us exists.
Check ABP Live's stories published in the weekly science column, "Science For Everyone", here.
Antimatter: All about the counterpart to matter
Antimatter is used to describe the substances composed of subatomic particles that have the same mass as their matter counterparts, but carry opposite electric charge and magnetic moment. The antimatter counterparts to electrons, protons, and neutrons are positions, antiprotons, and antineutrons, and are known as antiparticles.
A positron has the same mass as that of an electron, but carries a positive charge of the same magnitude as that of an electron. Similarly, an antiproton has the same mass as that of a proton, but carries a negative charge of the same magnitude as that of a proton. An antineutron has the same mass as that of a neutron, but carries a magnetic moment opposite in sign to that of a neutron.
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It is not possible for matter and antimatter to co-exist close to each other for more than a fraction of a second because they will collide with each other, following which annihilation will occur. This means that both matter and antimatter will cease to exist. However, large quantities of energy will be released in the form of gamma rays or elementary particles.
Elementary particles are subatomic particles smaller than an atom, and are not made up of a combination of smaller particles. These particles do not have a substructure. In other words, they are the smallest-known building blocks of the universe. Since elementary particles do not have an internal structure, and do not take up space, they are described as zero-dimensional points. There are a total of 10 elementary particles. These are of two types: fermions and bosons. An electron is a fermion, while the Higgs Boson is a boson.
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The ongoing quest to determine the origin of the matter-antimatter asymmetry
Matter and antimatter annihilate upon coming into contact, and disappear in a flash of energy. Despite the fact that the Big Bang should have created equal amounts of matter and antimatter, there is far more matter than antimatter in the universe.
It is this asymmetry that physicists around the world, including those at CERN, are studying. The Antiproton Decelerator at CERN slows down antiprotons to allow physicists to study these particles.
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The Antiproton Decelerator creates antiatoms, and low-energy antiprotons.
Physicists are studying what caused the balance between matter and antimatter to tip, or, in other words, why there is an asymmetry between matter and antimatter.
On the sidelines of an event held at Shiv Nadar School, Gurgaon, ABP Live spoke to Dr Archana Sharma, a senior scientist at the CERN laboratory in Geneva, Switzerland, and asked her about what matter and antimatter are.
Explaining that the collision of matter and antimatter will cause both to disappear into nothingness and energy, Dr Sharma said: “The reverse reaction will be that energy will create matter and antimatter. They have to be equal to conserve energy. Now, when the Big Bang happened, matter was created which is evident from the fact that we are here. The planets, the solar system and galaxies are there. It means that we did not disappear. This means that there is a difference between the matter and antimatter in one way or the other. So, these are particles that are identical to matter. But there is a very slight difference between matter and antimatter, and we are studying that in our experiments.”
She explained that there is a ‘little more’ matter than antimatter. “There is an asymmetry between matter and antimatter. This means that there is a little more matter than antimatter. And this ‘little more’ matter is the universe we see around. This is the asymmetry. We want to study the differences between a particle and its antiparticle. Those are the experiments going on at CERN.”
Dr Sharma also said that physicists are studying the CP Violation, which is the charge and parity violation. “It means that a particle and an antiparticle are identical. They are identical in every way. But when you look in the mirror, and raise your right hand, you see your left hand raised in the reflection. This is a violation. The reflection should also raise its right hand. Similarly, there is an asymmetry between the way particles move and antiparticles move. They have different kinds of spins, and that is the asymmetry we are trying to study.”
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Antimatter: How the concept came into being
The concept of antimatter was introduced to theoretical physics when scientists started studying the duality of positive and negative charges. British physicist Paul Dirac wrote an equation which posed a problem. It was that similar to the way the equation x²=4 has two possible solutions (x=2 and x=–2), Dirac's equation can have two solutions. One of the solutions will be for an electron with positive energy, while the other will be for an electron with negative energy. It was this equation that won Dirac the 1933 Nobel Prize in Physics.
He wrote the equation by combining quantum theory and special relativity, a theory limited to objects that are moving with respect to inertial frames of reference. Special relativity is the origin of Albert Einstein's famous equation, e = mc², which states that mass and energy are interchangeable. The theory of special relativity also states that a material object can approach the speed of light, but never reach it. Einstein's popular equation uses the speed of light to define the relationship between energy and matter. Special relativity not only describes how speed affects mass and space, but also explains the effect of speed on time.
According to CERN, Dirac interpreted from his equation that for every particle, there exists a corresponding antiparticle, which exactly matches the particle, but has an opposite charge. This was an important idea because it made scientists realise the possibility of entire galaxies and universes being made up of antimatter.
Possible reasons behind the matter-antimatter asymmetry
Matter and antimatter particles are always produced as a pair, and during the first fractions of a second of the Big Bang, the hot and dense universe was full of particle-antiparticle pairs that were coming into existence, and going out of existence. However, matter and antimatter were not destroyed together, because had this not been the case, the universe would have contained nothing but leftover energy.
A tiny portion of matter managed to survive, and this is what we see around us today. CERN says that this "tiny portion" is about one particle per billion.
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Not only is the matter-antimatter asymmetry a matter of surprise to physicists, but also the fact that particle physics experiments have revealed that the laws of nature do not apply equally to matter and antimatter.
Spontaneous transformations occur between particles and their antiparticles millions of times per second before they decay. It is believed that there were some oscillating particles in the early universe, a larger quantity of which decayed as matter than as antimatter.
If one compares these oscillating particles to coins spun in exactly the same way, an argument arises that the particles in the early universe should have decayed into equal amounts of matter and antimatter, just as half of the coins will land on heads and the other half on tails.
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But, if one uses a special kind of marble, makes it roll across a table of spinning coins, and allows it to hit most of the coins such that those coins would land on their head, there would be more heads and tails. Similarly, an unknown mechanism in the early universe intervened to make the majority of oscillating particles decay as matter.
Scientists intend to understand the unknown mechanism which caused more matter to be created by studying the differences in the behaviour of matter and antimatter particles produced during high-energy proton collisions at the Large Hadron Collider (LHC) at CERN. If scientists decipher the origin of the matter-antimatter asymmetry, they will better understand why the universe is full of matter.