Why is antimatter important to scientists

But other antimatter sources are even closer to home. For example, bananas produce antimatter, releasing one positron—the antimatter equivalent of an electron—about every 75 minutes. This occurs because bananas contain a small amount of potassium, a naturally occurring isotope of potassium.

As potassium decays, it occasionally spits out a positron in the process. Our bodies also contain potassium, which means positrons are being emitted from you, too. Antimatter annihilates immediately on contact with matter, so these antimatter particles are very short-lived.

Antimatter-matter annihilations have the potential to release a huge amount of energy. A gram of antimatter could produce an explosion the size of a nuclear bomb.

However, humans have produced only a minuscule amount of antimatter. Those made at CERN amount to about 1 nanogram. The problem lies in the efficiency and cost of antimatter production and storage. Making 1 gram of antimatter would require approximately 25 million billion kilowatt-hours of energy and cost over a million billion dollars.

To study antimatter, you need to prevent it from annihilating with matter. Scientists have created ways to do just that. Charged antimatter particles such as positrons and antiprotons can be held in devices called Penning traps. These are comparable to tiny accelerators. Inside, particles spiral around as the magnetic and electric fields keep them from colliding with the walls of the trap. Because they have no charge, these particles cannot be confined by electric fields.

Instead, they are held in Ioffe traps, which work by creating a region of space where the magnetic field gets larger in all directions. This meant that colliding particles no longer had enough energy to create electron-positron pairs. Electrons and positrons are annihilated into photons, or particles of light. Photons react strongly with electrons in plasma and therefore freeze out relatively late.

The antimatter evolution stage that has been the most difficult to explain is baryogenesis, or the creation of composite charged particles. Composite charged particles are subatomic particles that are made up of two or more elementary particles, like nucleons protons and neutrons. Baryogenesis is the stage where there is believed to be an imbalance with particle-antiparticle annihilation. This is called matter-antimatter asymmetry. The Standard Model alone does not explain what would cause the differential decoupling between matter and antimatter.

Theoretically, there are specific conditions that allow this asymmetry to occur, also known as the Sakharov conditions. To construct a consistent theory of baryon-antibaryon asymmetry, one needs to satisfy the Sakharov conditions.

These conditions are required for baryon asymmetry but do not explain its magnitude. A baryon, such as a proton or a neutron, is a composite particle made of three quarks. Antibaryons are made of three antiquarks.

The baryon number is the difference between the number of baryons and the number of antibaryons in a particle interaction. In a scenario or state where the universe is symmetric, the baryon number is conserved. CP symmetry is the conservation of charge conjugation and parity in particle interactions.

Charge conjugation flips the particle charge in question, meaning every existing particle has a corresponding antiparticle.

If a particle interaction is CP conserving, the interaction looks the same when the direction of particle velocities is flipped and the charge is inverted. In the case of baryon asymmetry, there is an obvious CP violation as the charge conjugation of matter overabundance should also mean antimatter overabundance, which is not observed. In the existing Standard Model, CP violation is possible in weak interactions.

This is important as it proves that a CP violation can occur in the system of baryogenesis. However, the mechanism in the Standard Model falls orders of magnitude short in trying to explain baryon asymmetry to the extent observed in the universe. Extensions beyond the Standard Model are therefore put into place to account for other factors that may induce a CP violation during baryogenesis.

Thermal equilibrium means that every collection of particles in a given system has the same average temperature, while the relative abundance remains the same. The baryon asymmetry is dependent on a process that does not occur in thermal equilibrium. This means that matter and antimatter would have to behave differently at some temperature, or that they would have to interact differently with the system at some temperature. It also means that matter would have to leave the system at a different time and temperature than antimatter did, thereby creating different abundances of matter and antimatter.

To understand why the matter-antimatter asymmetry exists, evidence as to why matter and antimatter are not symmetric, both in theory and in observation, must be explored.

Matter-antimatter annihilation produces large amounts of high-energy photons which are detected easily. Sensors would detect a much larger number of photons if antimatter was in greater abundance. Any non-negligible amounts of antimatter would not have been able to survive for this long without undergoing annihilation. If there were any significant amount of antimatter, it would annihilate the matter particles of the interstellar medium.

Any large celestial object made of antimatter would undergo annihilation quickly. The observed annihilations place constraints on the antimatter fraction ratio of surviving antimatter to matter to less than 10 Theoretically, one can try and account for a symmetric universe through the same means arrived at in an asymmetric one, by considering a theory for a matter-antimatter symmetric universe. At cooler temperatures during cosmological history, the time scale of nucleon and antinucleon interaction is shorter than that of universe expansion.

At one point, the abundance of nucleon-antinucleon pairs would become so little that they would practically cease to annihilate. However, the relic abundance of nucleon-antinucleon pairs predicted at this point would fall nine orders of magnitude short a factor of 10 9 of the observed nucleon abundance. As a result of the low density of nucleons, primordial nucleosynthesis stage of the Big Bang during which protons and neutrons were created would be limited, and hence, most of what would be left after the nucleon and antinucleon freeze-out are protons and electrons.

Any collapsed structures, such as stars or galaxies, are unlikely to form. Since the asymmetry between matter and antimatter is present, one can now explore the theoretical building blocks necessary to account for this phenomenon. The Standard Model includes the discovered and theorized fundamental particles in the universe. Some aspects of Sakharov conditions are part of the Standard model, such as CP violation, but out of the thermal equilibrium processes.

However, even with these features, the degree to which baryon asymmetry is observed is not achieved. In supersymmetry, every Standard Model particle has a fundamental particle, a super-partner with the same quantum numbers except for their spin, or intrinsic angular momentum. Because there are more particles through which CP violation can occur, the magnitude of CP violation increases.

This results in the production of sufficient baryon asymmetry. Something must have happened to tip the balance. One of the greatest challenges in physics is to figure out what happened to the antimatter, or why we see an asymmetry between matter and antimatter. Antimatter particles share the same mass as their matter counterparts, but qualities such as electric charge are opposite. The positively charged positron, for example, is the antiparticle to the negatively charged electron.

Matter and antimatter particles are always produced as a pair and, if they come in contact, annihilate one another, leaving behind pure energy. During the first fractions of a second of the Big Bang , the hot and dense universe was buzzing with particle-antiparticle pairs popping in and out of existence. If matter and antimatter are created and destroyed together, it seems the universe should contain nothing but leftover energy.

Does antimatter fall toward the Earth at the same rate as ordinary matter, or does it behave differently? This has been difficult to determine given the fact that the affects of gravity can be difficult to measure on gaseous particles. But at ultra cold temperatures, like absolute zero, these particles behave a little more like a liquid than a gas. If symmetry holds true, the antihydrogen atoms should fall upwards, but most mainstream physicists believe this will not happen; they believe the antihydrogen will fall.

But demonstrating that these symmetries are broken will result in a very exciting fundamental revision of our ideas about physics, affecting not only particle physics but also our understanding of gravity and relativity and maybe even Bizarro World. Who knows what will be discovered? Reference: C. Baker, et al, Laser cooling of antihydrogen atoms , Nature