Matter From Antimatter

Dr. S. S. VERMA; Department of Physics, S.L.I.E.T., Longowal; Distt.-Sangrur (Punjab)-148 106

2017-09-26 07:49:34



The big bang should have created equal amounts of matter and antimatter in the early universe. But today, everything we see from the smallest life forms on Earth to the largest stellar objects is made almost entirely of matter. Comparatively, there is not much antimatter to be found. 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 matter/antimatter asymmetry. If matter and antimatter are created and destroyed together, it seems the universe should contain nothing but leftover energy. Nevertheless, a tiny portion of matter – about one particle per billion – managed to survive. This is what we see today. In the preceding few decades, scientists have learned from particle physics experiments that the laws of nature do not apply equally to matter and antimatter.

They are keen to discover the reasons why. Researchers have observed particles spontaneously transforming, or oscillating, into their antiparticles at a rate of millions of times per second before decaying. Some unknown entity intervening in this process in the early universe could have caused oscillating particles to decay as matter more often than they decayed as antimatter. Scientists could find hints as to what this process might be by studying the subtle differences in the behaviour of matter and antimatter particles created in high-energy proton collisions at the Large Hadron Collider (LHC). Studying this imbalance could help scientists paint a clearer picture of why our universe is matter-filled.

Material is the basic component to our material world. We always thrive hard to have more and more desired material.  Scientifically, matter and antimatter are always being generated on earth in equal proportions (i.e., matter and antimatter symmetry). However, being unstable, antimatter remains in energy form and cannot be seen by human beings. Indian mythology is full of stories claiming the powers of great people (rishimuni’s) to generate matter from antimatter from air/surroundings making use of great mystical power attained by them through long mediation and reciting of some mantras/hymens. With the development of technology on the growth of science, this route whose results/outcomes cannot be generalized and repeated on demand has thus not been approved, recognized and so followed by scientific community. Science community no doubt desire to make use of plenty of antimatter available all around us in different applications like energy generation, as a source of fuel etc. The methods proposed on the basis of science and technologies in this regard along with the pandora of possible uses are being briefly summarized in the present article.


In particle physics, antimatter is a material composed of antiparticles, which have the same mass as particles of ordinary matter but opposite charges, as well as other particle properties such as lepton and baryon numbers. Collisions between particles and antiparticles lead to the annihilation of both, giving rise to variable proportions of intense photons (gamma rays), neutrinos, and less massive particle–antiparticle pairs. The total consequence of annihilation is a release of energy available for work, proportional to the total matter and antimatter mass, in accord with the mass–energy equivalence equation, E = mc2. Antiparticles bind with each other to form antimatter, just as ordinary particles bind to form normal matter. For example, a positron (the antiparticle of the electron) and an antiproton (the antiparticle of the proton) can form an anti hydrogen atom. Physical principles indicate that complex antimatter atomic nuclei are possible, as well as anti-atoms corresponding to the known chemical elements. Studies of cosmic rays have identified both positrons and antiprotons, presumably produced by collisions between particles of ordinary matter.


Characteristics of 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 anti-particle 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. Antimatter in the form of anti-atoms is one of the most difficult materials to produce. Antimatter in the form of individual anti-particles, however, is commonly produced by particle accelerators and in some types of radioactive decay. The nuclei of anti-helium (both helium-3 and helium-4) have been artificially produced with difficulty. These are the most complex anti-nuclei so far observed.


Antimatter all around us: Small amounts of antimatter constantly rain down on the Earth in the form of cosmic rays, energetic particles from space. These antimatter particles reach our atmosphere at a rate ranging from less than one per square meter to more than 100 per square meter. Scientists have also seen evidence of antimatter production above thunderstorms. Some antimatter sources are even closer to home e.g., 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-40, a naturally occurring isotope of potassium. As potassium-40 decays, it occasionally spits out a positron in the process. Our bodies also contain potassium-40, which means positrons are being emitted from you, too. Antimatter annihilates immediately on contact with matter, so these antimatter particles are very short-lived.


Matter-Antimatter asymmetry: Antimatter should have annihilated all of the matter in the universe after the big bang. According to theory, the big bang should have created matter and antimatter in equal amounts. When matter and antimatter meet, they annihilate, leaving nothing but energy behind. So in principle, none of us should exist. But we do. And as far as physicists can tell, it’s only because, in the end, there was one extra matter particle for every billion matter-antimatter pairs. Physicists are hard at work trying to explain this asymmetry.


Artificially created antimatter: Humans so far have produced only a minuscule amount of antimatter. All of the antiprotons created at Fermilab’s Tevatron particle accelerator add up to only 15 nanograms. Those made at CERN amount to about 1 nanogram. At DESY in Germany, approximately 2 nanograms of positrons have been produced to date. If all the antimatter ever made by humans were annihilated at once, the energy produced wouldn’t even be enough to boil a cup of tea. 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.


Antimatter trap: 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. But Penning traps won’t work on neutral particles such as antihydrogen. 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. The particle gets stuck in the area with the weakest magnetic field, much like a marble rolling around the bottom of a bowl. Earth’s magnetic field can also act as a sort of antimatter trap. Antiprotons have been found in zones around the Earth called Van Allen radiation belts.


Possible applications of antimatter

Medical: PET (positron emission tomography) uses positrons to produce high-resolution images of the body. Positron-emitting radioactive isotopes (like the ones found in bananas) are attached to chemical substances such as glucose that are used naturally by the body. These are injected into the bloodstream, where they are naturally broken down, releasing positrons that meet electrons in the body and annihilate. The annihilations produce gamma rays that are used to construct images. Scientists on CERN’s ACE project have studied antimatter as a potential candidate for cancer therapy. Physicians have already discovered that they can target tumors with beams of particles that will release their energy only after safely passing through healthy tissue. Using antiprotons adds an extra burst of energy. The technique was found to be effective in hamster cells, but researchers have yet to conduct studies in human cells.


Fuel: isolated and stored anti-matter could be used as a fuel for interplanetary or interstellar travel as part of an antimatter catalyzed nuclear pulse propulsion or other antimatter rocketry, such as the redshift rocket. Since the energy density of antimatter is higher than that of conventional fuels, an antimatter-fueled spacecraft would have a higher thrust-to-weight ratio than a conventional spacecraft. For a simple comparison, if matter–antimatter collisions resulted only in photon emission, the entire rest mass of the particles would be converted to kinetic energy. The energy per unit mass (9×1016J/kg) is about 10 orders of magnitude greater than chemical energies, and about 3 orders of magnitude greater than the nuclear potential energy that can be liberated, today, using nuclear fission (about 200 MeV per fission reaction or 8×1013J/kg), and about 2 orders of magnitude greater than the best possible results expected from fusion (about 6.3×1014J/kg for the proton–proton chain). The reaction of 1 kg of antimatter with 1 kg of matter would produce 1.8×1017 J (180 petajoules) of energy (by the mass–energy equivalence formula, E = mc2), or the rough equivalent of 43 megatons of TNT – slightly less than the yield of the 27,000 kg Tsar Bomb, the largest thermonuclear weapon ever detonated. Matter-antimatter annihilation propulsion is proposed to be a future fuel for faster-than-light travel.


Weapons: antimatter has been considered as a trigger mechanism for nuclear weapons. A major obstacle is the difficulty of producing antimatter in large enough quantities, and there is no evidence that it will ever be feasible. However, the U.S. Air Force funded studies of the physics of antimatter in the Cold War, and began considering its possible use in weapons, not just as a trigger, but as the explosive itself.


The possibility of antimatter first surfaced in equations formulated by British theoretical physicist Paul Dirac in 1928 - four years before American experimenter Carl Anderson found positrons in cosmic rays. So far physicists have managed to make mirror-image hydrogen, electron-positron pairings called positronium, and helium with an antimatter twist. One of the experiments at CERN has observed D-mesons ‘flipping’ between matter and antimatter. There is currently no technology available to mass-produce or collect antimatter in the volume needed for its applications. However, a small number of researchers have conducted simulation studies on propulsion and storage. One day, if we can figure out a way to create or collect large amounts of antimatter, their studies might help antimatter-propelled interstellar travel become a reality.