Antimatter
Antimatter is the collective name for antiparticles and everything is made up of them, as is the "normal " matter of "normal" particles. Antimatter may take the form of atoms and molecules that bound systems of positrons, antiprotons and possibly anti- neutrons.
In the observable world antimatter is very short-lived, because the encounter of a particle-antiparticle pair, the two destroy each other under release of energy in an annihilation reaction.
Some light antiparticles are ubiquitous in nature, but the atoms or molecules of antimatter come, if known, of course not before.
Conceptual history
1898 used the physicist Arthur Schuster the term antimatter in two letters to Nature for the first time. He speculated about all the star systems of antimatter, which would be of our matter by observing indistinguishable. Even before that Karl Pearson in 1892 and William Hicks spoke in the 1880s, the possibility of " negative matter ".
The hypotheses of Schuster was given by the work of Paul Dirac in 1928 a foundation. This was prepared on the basis of the work of Wolfgang Pauli called the Dirac equation, a relativistic, ie based on the special theory of relativity wave equation first order to describe the electron. On the basis of this equation, Dirac predicted the existence of the positron as antiparticle to the electron advance. Put simply, there is the so-called Dirac representation of quantum field theory, the vacuum from a brimming Dirac sea of electrons. A arisen by electron-positron pair creation pair consists of the electron, by excitation (ie energy) has been taken out of this Dirac sea, and left behind a "hole" that represents the positron. Today, according to the Feynman - Stückelberg interpretation of the negative energy states are interpreted as creation operators for antiparticles of positive energy, so that the Dirac sea has become unnecessary.
Antimatter on Earth
Antiparticles and antimatter atoms can be produced in pair formation reactions using particle accelerators. With a substantially smaller outlay positrons can be obtained by producing beta -plus- active radionuclides. This positron radiation has important applications in medicine.
The first antimatter particles, the positron, was proved by Carl David Anderson in cosmic rays in 1932. Also antimuons are generated by cosmic rays when they penetrate into the Earth's atmosphere.
A working group under Walter Oelert from Forschungszentrum Jülich in 1995 as first pointed at the Low Energy Antiproton Ring ( LEAR ) at CERN some antihydrogen atoms by so bound systems of an antiproton and a positron. In the following two years, researchers repeated at Fermilab in the U.S. the experiment.
The end of 2009 were discovered by the Fermi Space Telescope surprisingly positrons during a lightning storm; the telescope should really only be used to search for gamma radiation.
2010 38 antihydrogen atoms were detected at CERN in the Alpha Project, which were captured for 172 milliseconds in a magnetic trap. However, much larger amounts are needed for a spectroscopic investigation.
In April 2011, we succeeded at CERN, almost 17 minutes to capture 309 antihydrogen atoms at a temperature of about one Kelvin, that is 5800 times as long as in November 2010. This is commonly evaluated by researchers at CERN and commentators as a major breakthrough, the new opportunities to explore the properties of antimatter. This involves, for example, possible violations of symmetries in particle physics. This relates to the question of why more matter was created after the Big Bang than antimatter.
The heaviest antimatter nucleus observed was also produced in April 2011 at the Relativistic Heavy Ion Collider anti - 4He.
Speculation about energy use
The destruction ( annihilation) is stored as a ground for the pairing energy is released again. In the electron-positron annihilation this occurs as electromagnetic radiation, in the case of heavy particles ( proton-antiproton ) partly in the form of other particles with high kinetic energy. The entire mass of the particle-antiparticle pair is implemented and not only, as in nuclear fission and nuclear fusion, a small fraction (see mass defect ). The Annihilation of a given mass of 50 % 50 % matter antimatter would so much more energy release than the reaction of an equal mass of fusion reactor fuel. For example, the annihilation of a hydrogen atom would provide with an anti- hydrogen atom the energy of 1.88 GeV; the fusion of a deuterium nucleus with a tritium nucleus, however, provides only 17.6 MeV. The Antimaterieannihilation sets here so about 100 times as much energy as free as nuclear fusion.
Because of this high storage efficiency for energy has been thinking about uses of antimatter ( in the form of positrons) for weapons purposes.
In the space has been discussed several times about the possible benefits for propulsion systems. Scientists at Pennsylvania State University studied the projects AIMStar and ICAN -II in the 1990s, theoretical concepts.
So far there is not a realistic approach, prepared as sufficient amounts of antimatter could be stored and transported.
As a source of energy antimatter artificially generated will never be used: For the generation always at least as much energy is required, such as the destruction is again released. For technical reasons, moreover, the efficiency of production would be less than 100%.
Antimatter in the Universe
The previous experiments and theories arise largely identical behavior of matter and antimatter (see CP violation ). Thus, after the hot and dense initial state of the universe ( Big Bang ) matter and antimatter were created in approximately equal amounts and again, " annihilated " and shortly afterwards was Annihilation.
On the other hand, show all previous observations in the cosmos only the "normal " matter. You must be the remains of a small imbalance at the beginning of the universe. Earlier speculation that the universe is in other filled in some areas with matter, antimatter, are now considered unlikely. There was as yet no annihilation radiation, which should occur at the border areas, proven. The direct search for anti - helium atoms, which took place in 1998 with an Alpha Magnetic Spectrometer aboard a space shuttle, showed in the cosmic radiation no evidence of antimatter. A total of about 3 million helium atoms were detected, but underneath was not a single anti-nuclear.
The comparison of model calculations in the framework of the Big Bang theory and astronomical data ( primordial nucleosynthesis, WMAP ) suggests that the ratio of matter and antimatter almost 1 was initially. A tiny imbalance - about 1 particles surplus to 1 billion particle-antiparticle pairs - meant that a residue of matter was left over which is detectable in our universe today. This imbalance of matter and antimatter is one of the conditions for the stability of the universe, and thus also for life on Earth. On closer balance of matter and antimatter would have been completely converted into radiation in the course of cooling of the universe.
The reason for this imbalance is one of the great mysteries of elementary particle physics and cosmology; it is believed that only unifying theories ( for example, string theory, M - theory, supersymmetry ) will explain this unequal distribution satisfactorily. One of the prerequisites for a preponderance of matter is the CP violation (see baryogenesis ). This was first with kaons in the 1960s discovered ( Cronin, Fitch). In the 1990s, 200 million B- meson anti-B meson pairs were generated at SLAC in the U.S. and examines how these break down again. In the evaluation, it was found that the B- mesons is about twice less often in a pion and a kaon decay than their antiparticles. The previously examined Kaonensystem the difference was 4 to one million.
Antimatter in the science fiction
Antimatter comes in many novels and movies, where their physical properties may differ from the real. In the world of Star Trek, a matter -antimatter reaction serves as an energy source for the fictional warp drive to accelerate to faster than light and also as a weapon. In the pulp novel series Perry Rhodan antimatter was used to radiate gravitational shock waves and so to convey a message. In the novel, Angels & Demons by Dan Brown Scientists at the CERN visible amounts of the substance have made .