136 quotes found
"Although complex, the theory behind the practice of magnetic resonance spectroscopy is based on the fact that, when surrounded by a magnetic field, atomic nuclei may be disrupted by radio frequency waves at specific frequencies, which cause the nuclei to generate signals that can be detected by a radio receiver. These signals can then be converted into meaningful information in the form of spectra, which can subsequently be interpreted to gain information concerning the chemical composition at the region of interest (ROI). Central to the theory behind MRS is the concept of atomic spin, which designates a physical property of subatomic particles. The overall spin of a nucleus is determined by its mass number, the total number of protons and neutrons it contains: an even mass number results in no net spin, whereas an uneven mass number results in a net spin."
"Moreover, even when the chance of a particular event turns out to be extremely small, it is important to resist the idea that that event could not have occurred. Imagine that you own a ticket in a lottery with an extremely large number of tickets—a million, say—and that the lottery is decided by a fundamentally random process, one that has no underlying causal basis by which the outcome will be determined. (You might suppose that each ticket is associated with a specific atomic nucleus of some radioactive element, and that the prize will go to the person whose nucleus decays first.)"
"The great explorer of complex rhythms and meters combined with a totally liberated spirit of dissonance, Edgar Varese dispensed with the term compositionin his works. He called his music “organized sound.” It is completely removed from the world of sounds observable in nature. Even in a score that bears the seemingly descriptive title Ameriques, Varese tends to represent the conceptual Americas as the birthplace of new science, new technology and new sound. His other works bear such scientific titles as Integrals and Hyperprism (a projection of a prism into higher dimensions). His unique score entitled Ionisation is arranged for pitchless percussion instruments and two sirens. The title refers to the disintegration of atomic nuclei."
"But it is possible that certain species of primates are apt to go to pieces under conditions which lead them to effect changes of space-time systems. Such species would only experience a long range of endurance, if they had succeeded in forming a favourable association among primates of different species, such that in this association the tendency to collapse is neutralised by the environment of the association. We can imagine the atomic nucleus as composed of a large number of primates of differing species, and perhaps with many primates of the same species, the whole association being such as to favour stability. An example of such an association is afforded by the association of a positive nucleus with negative electrons to obtain a neutral atom. The neutral atom is thereby shielded from any electric field which would otherwise produce changes in the space time system of the atom."
"In beta decay experiments it is generally some properties of the emitted , the electron and neutrino, that are measured, such as their energy, polarization or angular distribution. ...In beta decay, angular momentum is conserved but it is now known that parity is not conserved. The leptons are emitted in states of indefinite parity."
"Beta decay was…like a dear old friend. There would always be a special place in my heart reserved especially for it."
"It appears that the strong interactions and electromagnetic interactions are invariant with respect to C, P, and T separately, while the weak interactions do not conserve P or C. All experimental results are consistent with the assumption the T invariance holds true for all interactions; consequently, from the CPT theorem, weak interactions must be invariant under CP. One could not, then, determine if the photographed scene were a scene of particles viewed normally, or a scene of antiparticles projected in a mirror."
"The weak force... least fits into our typical picture of what a force should do. ...the categories of 'attractive' and 'repulsive' do not really fit the weak force ... because it has the ability to change particles from one type to another. ...The weak force can change one into another provided they are in the same generation. The electron can be changed into an electron and vice versa, but the electron cannot be turned into the ..."
"In his theory of beta reactivity Fermi introduced a new type of interactions among elementary particles, which today we call "weak interactions". Many new manifestations of weak interactions, which could be interpreted using Fermi's 1933 theory, were found in the following decades. The study of weak interactions has led to surprising discoveries, among which the violation of specular symmetry (known as parity symmetry or P symmetry), and the violation of time reversal symmetry (T symmetry) and of the symmetry between matter and antimatter (CP symmetry)."
"The... weak force... couples to both s and s, and is very short-ranged due to the large rest mass of the messenger quanta involved. Its effective strength is usually many orders of magnitude weaker than electromagnetism, and its action can cause particles to change identity, as when a neutron decays. Unlike the electromagnetic and strong forces, the weak force violates parity conservation."
"For the weak force... universality of coupling strength is not readily apparent. ic weak forces are very different in nature from ic weak processes."
"How can s be produced in the center of the sun and how can they be detected in laboratories here on earth if they are subject neither to the strong force nor to the electromagnetic one? Another force, the so-called weak force, is responsible. The electron neutrino does participate in that interaction, along with the electron."
"The weak force gives rise to reactions... These reactions involve a change of flavor... one version involving the exchange of a positively charged quantum and the other the exchange of a negatively charged quantum. The existence of such quanta was first discussed by some of us in the late 1950s, and they were discovered at CERN twenty-five years later, in experiments that procured a Nobel prize for Carlo Rubbia and Simon van der Meer. The quanta are usually called W + and W -, as they were designated in a celebrated paper by T. D. Lee and C. N. Yang..."
"In 1952... I tried to explain the behavior of the new "strange particles," so called because they were copiously produced as though strongly interacting and yet decayed slowly as though weakly interacting. (Here "slowly" means a half-life of something like a ten billionth of a second... a strongly interacting particle means... a ten trillionth of a second, roughly the time it takes for light to cross such a particle.) ...I thought of assigning these strange particles isotopic spin I = 5/2... But the notion failed to work... I was invited to talk at the Institute for Advanced Study... By a slip of the tongue I said "I = 1" instead... Immediately I stopped dead, realizing I = 1 would do the job. ...But what about the alleged rule that ic strongly interacting particle states had to have values of I like 1/2 or 3/2 or 5/2? ...the rule was merely a superstition... unnecessary baggage that had come along with the useful concept of isotopic spin... [which now] could have wider applications than before. ...[T]he strange particle states differ from more familiar ones such as neutron or proton or s by having at least one s or "strange" quark in place of a u or d quark. Only the weak interaction can convert one flavor of quark into another, and that process happens slowly."
"The strong and weak forces are less familiar because their strength rapidly diminishes over all but subatomic distance scales; they are the s. This is why these two forces were discovered only much more recently. The strong force is responsible for keeping quarks "glued" together inside of protons and neutrons and keeping protons and neutrons tightly crammed together inside atomic nuclei. The weak force is best known for the radioactive decay of substances such as uranium and cobalt."
"In 1933 Enrico Fermi suggested that beta radioactivity, and the manner in which the neutron spontaneously decayed, could be described using a formalism similar to that developed by Dirac for the electromagnetic force, but 10-10 times weaker. With its range of only about 1/1,000th the diameter of the nucleus, it could not play a role in binding the nucleus, but it could affect individual s. The fact that the metastable particles exhibited the same characteristic time of 10-10 second indicated that this weak force acted on many types of particles. ...a 'characteristic time' ...being the time for an interaction across a nucleus 3 fm in diameter; an event taking place in a shorter time [than 10-23 seconds for the strong force] has 'no meaning'. ...For electromagnetic interactions, the strength is 10-3 of the strong force, and so the characteristic time is longer (10-20 [seconds]); this is roughly the time for a photon to cross an atom."
"In addition to transforming a neutron into a proton and vice versa, the weak force was evidently responsible for the decay of a muon into an electron. ...[W]hen the strange particles were found to decay without s it was realized that the force was more complex than had been posited in Fermi's theory of beta decay. Nevertheless, the fact that aspects of the force could be explained by an electromagnetic formalism implied that these forces shared an underlying symmetry."
"The mass of the W and Z prevents the weak force from extending beyond their Compton length (about a hundredth the size of a proton)..."
"[T]he work of a number of theoretical physicists in the 1960s culminated in the electroweak theory that is designed to unify electromagnetism and the weak force... This theory is sometimes called the 'GWS Theory', from... Sheldon Glashow, Steven Weinberg and Abdus Salam... The main feature of the theory is that at extremely high temperatures the electromagnetic and weak forces are two components of a single force, the electroweak force. The symmetry between the two forces would only be apparent at temperatures of trillions of degrees... in the Big Bang. At lower temperatures... electromagnetism remains a long range force, but the weak force takes on the characteristics of... a very weak force that acts over extremely short distances. ...But the theory is dependent on the existence of the Higgs particle..."
"[W]hat shall we say, then, to a nuclear event such as... beta decay... in which a neutron turns into a proton and also shoots out an electron together with an antineutrino? ...Coming from within... is the weak interaction. Not in all nuclei, but certainly in many... the weak interaction sometimes subverts the neutrons and protons bound otherwise so strongly. It takes only a change in flavor. The weak force, with the weak interaction charges as the source, transforms a into an and hence a into a . At the same time, an electron and antineutrino spring loose... The strong force plays no part here, since neither the electron nor the antineutrino carries a strong interaction charge. Electrically neutral, the antineutrino escapes the electromagnetic force as well. ...the weak force ...allows a neutron to decay into a proton, electron, and antineutrino. The four particles all carry weak interaction charges, and their common endowment makes them all actors in a single play."
"s were among the most paradoxical members of the zoo of elementary particles that were discovered after the war. Produced during radioactive decay, they supposedly had neither charge nor mass and they traveled, consequently, at the speed of light. Their only interaction with the world (besides gravity) was by something called the "weak" force, which causes some kinds of radioactive decay. It was so weak that, according to calculations, a typical neutrino could pass through a million miles of water unhindered—stars and planets were transparent to them."
"Antoine-Henri Becquerel discovered radioactivity. Becquerel's discovery preceded J. J. Thomson's... electron by one year. Radioactivity comes in three kinds, called alpha, beta, and gamma. ...only one ...(beta) has to do with the weak interactions. Today we know that the beta rays were actually electrons emitted by neutrons in the nucleus. ...Nothing in QED or QCD explains how a neutron can emit an electron and become a proton. ...Becquerel didn't know ...that another particle flew off... the antiparticle of the ghostly neutrino. ...The neutrino ...doesn't emit photons. It doesn't emit s. This means it [does not experience the respective electromagnetic or s] that electrically charged particles or s experience. The W-boson is key to the neutrino's activities. Not only can the electrons and quarks emit W-bosons—so too can the neutrino. ...[O]ne of the two d-quarks in a neutron can emit a W-boson and become a u-quark, thus turning a neutron into a proton. ...the W-boson is exchanged, where in a QED diagram, the photon would be exchanged. ...weak interactions are very closely related to the electric forces due to photons. ...The W-boson... splits into two particles: an electron and a neutrino "moving backward in time,"... an antineutrino. That's what Becquerel would have seen... had he had a powerful enough microscope."
"The weak force does not seem to hold anything together, only to break it apart. ...we do not observe s of the weak force. ...So the weak force seems a force apart... Interwoven with the surprising story of the weak force has been the story of s, arguably the most intriguing of the fundamental particles. ...the neutrinos provide a unique and valuable mirror on the weak force. ...In the 1920s, and for a while disputed the energy spectrum of electrons emitted in β decay. ...Chadwick demonstrated... that the spectrum was continuous, i.e. the electron could take on a whole range of energies. ...contrary to the single line expected from energy conservation if only... the electron and the nucleus, were involved... Neils Bohr advocated abandoning energy conservation... but in 1930 Wolfgang Pauli daringly proposed an unseen... neutrino... Pauli's intuition... inspired Enrico Fermi in his 'tentative theory of β decay'... to become the basis for ideas of a universal weak force."
"The first intimations that β decay is but one manifestation of some deeper fundamental interaction came during the 1940s from experiments which led to the discovery of the . ...A third charged , the tau, and three neutral neutrinos bring the number of family members to six. In addition there are six corresponding antiparticles. It appears that in any interaction a lepton can be created (or can disappear) only together with an antilepton. This empirical rule of 'lepton conservation'... implies... that it is an antineutrino that accompanies the electron in β decay. ...When the decay or capture of a muon was treated in the same way as β decay in Fermi's theory, the s... appeared remarkably similar. ...The agreement between the coupling constants for β decay, muon decay and muon capture led to the idea of a 'universal Fermi interaction' and... experiments began to reveal more and more new particles with similar weak interactions."
"Why can stars do better than the big bang? ...During the big bang, there were only a few minutes when nuclei could form. Very rare processes, or slow ones, played little role. A case in point is the key process from which the sun derives its energy. In this reaction, two protons collide to produce a deuterium nucleus, a neutrino, and a positron. ...This reaction belongs to the family of weak interactions. ...It remains... a remarkable—and for humanity, remarkably fortunate—circumstance that the central reaction that drives the sun is so rare. It is only this extraordinary rarity that allows the average proton in the sun to last so long, billions of years, even though it is colliding with other protons millions of times a second. ...an entertaining example of Treiman's theorem."
"Once helium burning has occurred... the next possible reaction—carbon burning—is not necessarily slow... This reaction involves ...a strong as opposed to a weak interaction. ...Carbon burning results in magnesium. ...Taking a cross section of a highly evolved star would reveal a system of many layers. The inner layers have been subjected to the largest pressures, thereby forced to the highest temperatures, and burned the furthest; the outermost layers, by contrast, have not burned at all. Thus, as we proceed from outside in, there will be an outermost layer with the initial mix of hydrogen and helium, a layer of mostly helium, a layer of carbon, a layer of magnesium, and so on. ...So we arrive at the picture of a star, in the latest stages of its evolution... now composed of mostly carbon nuclei and other explosive material."
"If grand unified theories are correct, we ought to be able to derive the relative power of the strong, weak, and electromagnetic interactions at accessible energies from their presumed equality at much higher energies. When this is attempted, a wonderful result emerges. ...in the form first calculated by Howard Georgi, Helen Quinn, and Steven Weinberg ...The couplings of strong-interaction gluons decrease, those of the [weak interaction] W bosons stay roughly constant, and those of the [electromagnetic interaction] photons increase at short distances [or high energies]—so they all tend to converge, as desired."
"In the case of the strong interactions, there was a wealth of experimental data, much of it of high precision. Hadronic masses and magnetic moments, nuclear binding energies and transition rates, many things were measured with great accuracy. But the strongly interacting world was so complicated that most of the experimental data was hard to interpret. Only a fraction of the experimental knowledge of strong interactions, such as the scaling behaviour in deep inelastic electron-nucleon scattering, gave simple clues about the underlying quark-gluon world. As a result, experimental clues alone did not suffice."
"The strong force may not unify with the other forces. There’s no evidence for unification in our Universe so far, as proton decay experiments have come up empty. The initial motivation is flimsy here as well: If you put any three curves on a log-log scale and zoom out far enough, they will always look like a triangle where the three lines just barely miss coming together at a single point."
"CND campaigns non-violently to rid the world of nuclear weapons and other weapons of mass destruction and to create genuine security for future generations. CND opposes all nuclear and other weapons of mass destruction: their development, manufacture, testing, deployment and use or threatened use by any country."
"2018 is the 60th anniversary of the Campaign for Nuclear Disarmament, which was founded on the 17th February 1958 at the height of the cold war. CND is planning a number of events — as well as publishing a new book — to mark the 60th year of one of the world's most powerful collective voices against the dangers of nuclear weapons"
"One of the most widely known symbols in the world, in Britain it is recognised as standing for nuclear disarmament – and in particular as the logo of the Campaign for Nuclear Disarmament (CND). In the United States and much of the rest of the world it is known more broadly as the peace symbol. It was designed in 1958 by Gerald Holtom, a professional designer and artist and a graduate of the Royal College of Arts. … The Direct Action Committee had already planned what was to be the first major anti-nuclear march, from London to Aldermaston, where British nuclear weapons were and still are manufactured. It was on that march, over the 1958 Easter weekend that the symbol first appeared in public. Five hundred cardboard lollipops on sticks were produced. Half were black on white and half white on green. Just as the church’s liturgical colours change over Easter, so the colours were to change, “from Winter to Spring, from Death to Life.” Black and white would be displayed on Good Friday and Saturday, green and white on Easter Sunday and Monday."
"The first badges were made by Eric Austin of Kensington CND using white clay with the symbol painted black. Again there was a conscious symbolism. They were distributed with a note explaining that in the event of a nuclear war, these fired pottery badges would be among the few human artifacts to survive the nuclear inferno."
"Although specifically designed for the anti-nuclear movement it has quite deliberately never been copyrighted. No one has to pay or to seek permission before they use it. A symbol of freedom, it is free for all. This of course sometimes leads to its use, or misuse, in circumstances that CND and the peace movement find distasteful. It is also often exploited for commercial, advertising or generally fashion purposes. We can’t stop this happening and have no intention of copyrighting it. All we can do is to ask commercial users if they would like to make a donation. Any money received is used for CND’s peace education and information work."
"I don’t think the Campaign for Nuclear Disarmament has much chance of actually affecting the government. It’s one of the first things you have to face up to. But we do it to keep our self-respect to show to ourselves, each one to himself or herself, that we care. And to let other people, all the lazy, sulky, hopeless ones like you, know that someone cares. We’re trying to shame you into thinking about it, about acting."
"I grew up in the 1980s in the UK, and we had the Campaign for Nuclear Disarmament, all that. People were very, very aware. When I was 13, me and my friends, we were convinced we would die in a nuclear holocaust… What I remember from the '80s is that the fear of nuclear war had receded in favor of fear of environmental destruction. It was almost like we couldn't sustain the fear of it for that long. We have a complicated relationship with our fear. And yes, Putin has been using that doomsday threat and that fear to saber-rattle. It's extremely unnerving."
"The interpretation of these tracks as due to protons, or other heavier nuclei, is ruled out on the basis of range and curvature. Protons or heavier nuclei of the observed curvatures could not have ranges as great as those observed. The specific-ionization is close to that for an electron of the same curvature, hence indicating a positively-charged particle comparable in mass and magnitude of charge with an electron."
"Dear Millikan, I have just received a letter from Rutherford which contains some of Blackett's work which may interest you and Anderson. It is that they have capitulated on the question of positive electrons and agree with Anderson that there are present in large numbers among the tertiary or quartinary (or whatever they are) ionizing particles seen in a Wilson photograph of the effects particles of positive charge and electronic mass. ...I take it that Blackett has collected so many photographs of such tracks as those earlier ones of Anderson that he can no longer resist this devastatingly interesting conclusion. Blackett's photos will come out in P.R.S. (Proceedings of the Royal Society) in March. I have a lecture to deliver."
"The annihilation of positrons with electrons from biological tissues constitutes the basis of Positron Emission Tomography (PET)... widely used in ... [S]ubstances called radiotracers and radiopharmaceuticals are injected into the patient. These are chemical compounds in which one or more atoms have been replaced by short-lived, positron-emitting, radioisotope of elements that are abundant in the body, like Carbon-11... ... Oxygen-15... and Fluor-18... the latter... for the localization and monitoring of tumors... Since these isotopes are short-lived... they must be produced just before being injected... To do this, the corresponding [common] elements are bombarded with protons... from a small accelerator. ...[I]nside the PET scanner ...a series of detector rings ...record the gamma radiation emitted when the positrons are annihilated inside the body. ...[T]he recorded signals are used to make a series of slices that combine to for a 3-D image. ...[T]hey allow doctors to assess the condition of organs and tissues as they can monitor blood flow and many bodily and metabolic processes, including neuronal transmission."
"Kirk: Like Lazarus. Identical, yet both Lazarus. Except one is matter and the other antimatter. If they meet... Spock: Annihilation Jim. Total, complete, absolute annihilation."
"If the Standard Model describes the world successfully, how can there be physics beyond it, such as supersymmetry? There are two reasons. First, the Standard Model does not explain aspects of the study of the large-scale universe, cosmology. For example, the Standard Model cannot explain why the universe is made of matter and not antimatter, nor can it explain what constitutes the of the universe. Supersymmetry suggests explanations for both of these mysteries. Second, the boundaries of physics have been changing. Now scientists ask not only how the world works (which the Standard Model answers) but why it works that way (which the Standard Model cannot answer). Einstein asked "why" earlier in the twentieth century, but only in the past decade or so have the "why" questions become normal scientific research in particle physics rather than philosophical afterthoughts."
"In later years, the advent of a new elementary particle would scarcely ruffle the intellectual sensibilities of the world's physicists; in 1932, Anderson's announcement of the ran into a wall of resistance. If the had resolved many long-standing difficulties of nuclear theory, the positron seemed to complicate matters. It is said that Neils Bohr dismissed Anderson's finding out of hand, and when in the fall of 1932 Millikan discussed the positron in a lecture at the Cavendish, various members of the audience suggested that Anderson had doubtless become tangled in some fundamental interpretive error. But not all of Rutherford's physicists were prepared to ignore Anderson's claims, especially not the resident Cavendish expert on s, Patrick M. S. Blackett."
"The Doctor: Here on Zeta Minor is the boundary between existence as you know it and the other universe which you just don't understand. From the beginning of time it has existed side by side with the known universe. Each is the antithesis of the other. You call it "nothing", a word to cover ignorance. And centuries ago scientists invented another word for it. "Antimatter", they called it. And you, by coming here, have crossed the boundary into that other universe to plunder it. Dangerous."
"It was fortunate that Alan Guth did his work at the same time that another idea came into fashion, which was the theory that we could understand why the universe contains matter and not antimatter in terms of some asymmetry, some favoritism for matter over antimatter in the early universe; it's no good having a scheme that can inflate the universe to enormous dimension of it's not possible to create matter to fill that large universe."
"The new quantum mechanics, when applied to the problem of the structure of the atom with point-charge electrons, does not give results in agreement with experiment. The discrepancies consist of "duplexity" phenomena, the observed number of stationary states for an electron in an atom being twice the number given by the theory. ...It appears that the simplest Hamiltonian for a point-charge electron satisfying the requirements of both relativity and the general transformation theory leads to an explanation of all duplexity phenomena without further assumption."
"The wave equation... refers equally well to an electron with charge e as to one with charge -e. If one considers for definiteness the limiting case of large quantum numbers one would find that some of the solutions of the wave equation are wave packets moving in the way a particle of charge -e would move on the classical theory, while others are wave packets moving in the way a particle of charge e would move classically. ...the electron suddenly changing its charge from -e to e ...has not been observed. The true relativity wave equation should thus be such that its solutions split up into two non-combining sets, referring respectively to the charge -e and the charge e. ...The resulting theory is therefore still only an approximation, but it appears to be good enough to account for all the duplexity phenomena without arbitrary assumptions."
"On August 2, 1932, during the course of photographing cosmic-ray tracks produced in a vertical Wilson chamber (magnetic field of 15,000 gauss) designed in the summer of 1930 by Professor R. A. Millikan and the writer, the tracks... seemed... interpretable only on the basis of the existence in this case of a particle carrying a positive charge but having a mass of the same order of magnitude as that normally possessed by a free negative electron."
"In the course of the next few weeks other photographs were obtained which could be interpreted logically only on the positive-electron basis, and a brief report was then published with due reserve in interpretation in view of the importance and striking nature of the announcement."
"[O]ur equations allow of two kinds of motion for an electron, only one of which corresponds to what we are familiar with. The other corresponds to electrons with a very peculiar motion such that the faster they move, the less energy they have, and one must put energy into them to bring them to rest."
"[W]e find from the theory that if we disturb the electron, we may cause a transition from a positive-energy state of motion to a negative-energy one, so that, even if.. all.. electrons in the world.. started.. in positive-energy states, after a time some... would be in negative-energy states. ...[B]ehaviour of these states in an electromagnetic field shows that they correspond to the motion of an electron with a positive charge ...a . One might... assume that electrons in negative-energy states are just positrons, but ...observed positrons ...do not have negative energies."
"We make use of the exclusion principle of Pauli... there can be only one electron in any state of motion. We... make the assumptions that in the world as we know it, nearly all the states of negative energy for the electrons are occupied... any unoccupied negative-energy state, being a departure from uniformity, is observable and is just a ."
"An unoccupied negative-energy state, or hole... will have a positive energy, since it is a place where there is a shortage of negative energy. A hole is... just like an ordinary particle, and its identification with the ... the most reasonable way of getting over the difficulty of... negative energies..."
"On this view the positron is just a mirror-image of the electron, having exactly the same mass and opposite charge. This has already been roughly confirmed by experiment. The positron should also have similar spin properties to the electron, but this has not yet been confirmed..."
"[W]e should expect an ordinary electron, with positive energy, to be able to drop into... and fill up this hole, the energy being liberated in the form of . This would mean... an electron and a positron annihilate one another. The converse... creation of an electron and a positron from electromagnetic radiation, should also be able to take place. Such... appear to have been found experimentally, and are... being more closely investigated..."
"[I]t is probable that negative protons can exist, since as far as the theory is yet definite, there is a complete and perfect symmetry between positive and negative electric charge, and if this symmetry is really fundamental in nature, it must be possible to reverse the charge on any kind of particle. ...[N]egative protons would... be much harder to produce... since a much larger energy would be required, corresponding to... larger mass."
"We must regard it rather as an accident that the Earth (and presumably the whole solar system), contains a preponderance of negative electrons and positive positrons. It is quite possible that for some of the stars it is the other way about... built up mainly of s and negative protons. ...[T]here may be half the stars of each kind. The two... would both show exactly the same spectra... there would be no way of distinguishing them..."
"It seems probable that the interactions between elementary particles can be completely described by symmetry properties and s and by dimensionless numbers representing interaction strengths. Similarly, we might expect that the elementary particles, as quanta of these interactions, may be described in the same in terms... At the present... however, our description... must also include the , and in some cases, the magnetic moment, although in principle these are probably derivable from interaction strengths and symmetries. ...Symmetries usually result in conservation laws. ...Invariance under space inversion results in ...the conservation of parity. Let us also consider invariance under time reversal, and invariance under charge conjugation, the change of particles to antiparticles."
"Invariance of interactions with respect to space inversion restricts observables to those which do not differentiate between a left-handed and a right-handed coordinate system. Time reversal invariance allows only observables which do not depend on the direction of time, and invariance under charge conjugation restricts observables to those which remain unchanged when all particles are changed to antiparticles."
"Consider a motion picture of a fundamental process, perhaps an elementary particle interaction in the presence of electric and s... If the interactions are invariant under space inversion, it will not be possible... to determine if the film has been reversed in the projector or [equivalently] projected by reflection in a mirror. If... invariant under time reversal, and if entropy is not changed in the process, it will not be possible to tell if the film is run backwards, while if... invariant under charge conjugation, it will not be possible to state whether the picture is that of our universe, or an anti-universe where every particle is replaced by its antiparticle."
"These three invariances are not independent. In the framework of local field theory, invariance under proper leads to the invariance of all interactions under combined operations CPT, where C is the charge conjugation operator, changing particles to antiparticles, P, the parity space inversion operator, changing \overline{r} to -\overline{r}, and T is the time reversal operator, changing t to -t. The equality of the masses and lifetimes of the particles and their antiparticles follows from this theorem."
"The theory of the expanding universe, which presupposes a superdense initial state of matter, apparently excludes the possibility of macroscopic separation of matter from antimatter; it must therefore be assumed that there are no antimatter bodies in nature, i.e., the universe is asymmetrical with respect to the number of particles and antiparticles (С asymmetry). In particular, the absence of antibaryons and the proposed absence of baryonic neutrinos implies a nonzero baryon charge (baryonic asymmetry)."
"We wish to point out a possible explanation of С asymmetry in the hot model of the expanding universe... by making use of effects of CP invariance violation... To explain , we propose in addition an approximate character for the baryon conservation law."
"We can visualize that neutral spinless maximons (or photons) are produced at t < 0 from contracting matter having an excess of antiquarks, that they pass "one through the other" at the instant t = 0 when the density is infinite, and decay with an excess of quarks when t > 0, realizing total of the universe. All the phenomena at t < 0 are assumed in this hypothesis to be CPT reflections of the phenomena at t > 0."
"The strong violation of the baryon charge during the superdense state and the fact that the baryons are stable in practice do not contradict each other. ...The baryon charge is violated if the interaction... is supplemented with a three-boson interaction leading to virtual processes ...we find the decay probability ...The lifetime of the proton turns out to be very large (more than 1050 years), albeit finite."
"After Dirac's publication of the electron wave equation in 1928, many people took up its study."
"I felt that writing this paper on the electron was not so difficult as writing the paper on the physical interpretation."
"It was an imperfection of the theory and I didn't see what could be done about it. It was only later that I got the idea of filling up all the states."
"I felt right at the start that the negative energy electrons would have the same rest mass as the ordinary electrons ...I hoped that there was some lack of symmetry somewhere which would bring in the extra mass for the positively charged ones. I was hoping that in some way the Coulomb interaction might lead to such an extra mass, but I couldn't see how it could be brought about."
"It thus appears that we must abandon the identification of the holes with protons and must find some other interpretation for them. A hole, if there were one [in the world], would be a new kind of particle, unknown to experimental physics, having the same mass and opposite charge to an electron. We may call such a particle an anti-electron. We should not expect to find any of them in Nature, on account of the rapid rate of recombination with electrons, but if they could be produced experimentally in high vacuum they would be quite stable and amenable to observation. An encounter between two hard γ-rays (of energy of at least half a million volts) could lead to the creation simultaneously of an electron and anti-electron. This probability [of the creation of a pair] is negligible, however, with the intensities of γ-rays at present available."
"Then on 2 August 1932 there came along the discovery of the by C. Anderson. ...For Dirac it meant the satisfaction that his equation predicted the situation correctly as he had hoped. His work had also provided the first example in the history of physics where the existence of a new particle was predicted on a purely theoretical basis."
"[C]reation and annihilation concepts antedate quantum mechanics. The concept of annihilation of pairs of oppositely charged, elementary particles... dates from the turn of the twentieth century. It became important in astrophysics about 1924... The annihilating pairs were first positive and negative electrons, later protons and electrons, and finally, starting in 1931, electrons and anti-electrons. ...In Dirac's "hole" theory of 1930... pair annihilation was neither novel nor central. Dirac's object was to deal with a difficulty... that the theory allowed electrons to make transitions to . ...interpreting electrons in states of negative energy as unobservable, and empty negative-energy states, or "holes" as protons. As a by-product, when an electron jumped into a vacant negative-energy state, an electron and a proton disappeared together into radiation. Since pair annihilation was already an accepted concept, this... was admissible."
"Dirac's... paper, "A Theory of Electrons and Protons," makes it clear that his primary purpose was to deal with the negative energy difficulty, and his secondary purpose... was to present a theory of protons. ...[T]he chief novelty ...was the identification of the proton with the absence of the electron, whereas the concept of pair annihilation was not a novelty ...He began by stating the difficulty: relativistic theories of the electron all yield solutions in which the electron has a negative total energy, and quantum mechanical relativistic theories... permit the electron to make transitions from states of positive energy to these states of negative energy. He then argued... that these states, and the transistions to them, cannot be disregarded as nonphysical..."
"Since every particle needed to make up atoms has its antiparticle, it is conceivable... to combine s and s to make ... Then one could use s to make heavier forms of antihydrogen such as antideuterium (an antinucleus containing one antiproton and one antineutron, with a positron in orbit) and anti (one antiproton and two antineutrons)."
"A few hundred heavy nuclei of antideuterium, antitritium, and antihelium-3 have been observed... Sadly, they have been unable to keep these antimatter fragments under control long enough to add positrons and make neutral antiatoms..."
"When a matter particle and its mirror antimatter twin are brought into contact, the two annihilate each other. The mass of both is totally converted into energy. The amount of energy... Einstein's E=mc^2... The annihilation of a gram of matter and antimatter would produce the energy of a 20-kiloton nuclear bomb, the size... dropped on Japan."
"The word "antimatter"... Strictly speaking, it's not... accurate... Antimatter is not "negative matter." It does not have negative mass, or negative spin, or negative (anti-) gravity (...scientists are... running experiments to see if antiprotons have the same kind of gravity as protons). ...One researcher has suggested replacing the... "anti-" with "co-,"... co-matter, co-protons,... Another... suggested... "exo-"... "Exo" in Greek means "outside." Other suggestions... "ob-" (obmatter, obproton) and "contra-" (contramatter and contraproton). None... ever caught on... Hannes Alfven in... Worlds-Antiworlds... said... let's coin a new word for "ordinary" matter... the word koinomatter... after the Greek word koinos, meaning common or well-known. ..."Matter will remain "matter" and "antimatter"... "antimatter"... However... "mirror matter" is the most accurate and unbiased term."
"Mirror matter is, first and foremost, matter. ...[A]ll mirror matter is still matter."
"Schrödinger's theory was not relativistic. It only applied to systems of particles like electrons... moving at low velocities... not close to the speed of light. It... did not take into account the electron's spin. ...Paul Dirac set out to remedy these shortcomings. ...to combine the Schrödinger equations for quantum mechanics, the Einstein equations for special relativity, the Maxwell equations for electromagnetism, and his own non-relativistic equations for the behavior of the electron into a single set of equations. This... described the relativistic quantum behavior of the spinning electron. ...Dirac's solution ...was a startling paper ...In the classical physics of Newton, the energy of a particle always has a positive value. ...Dirac's new equations ...had two possible solutions: an electron with positive energy, or an electron with . ...Dirac discovered that an electron with negative energy passing through a magnetic field would act exactly like an electron with positive energy—if the electron had positive instead of negative charge. To Dirac, this implied that for every particle that existed there was a corresponding mirror-image particle."
"A positron, Feynman has written, can... be thought of as an electron moving backwards in time! An electron doing such... would be indistinguishable from an electron moving with a positive charge. This would also be essentially true for any other mirror matter particle or object."
"An even more bizarre extension of the Feynman model has been suggested by John Wheeler. ...[A]ll the electrons and positrons in the universe are just one single electron seen at different portions of a single long electron path! This... explains why all electrons have exactly the same charge."
"In 1932 Millikan and Anderson were investigating cosmic rays, and they had built a large '... When subatomic particles passed through... they left ghostly vapor trails in the supersaturated air... They placed powerful magnets around it to blanket the interior... with a magnetic field. ...[[Cosmic ray|[C]osmic rays]] ...were bent by the field ...[T]he direction and thickness of the paths... revealed the mass of the particles—and their charge. Anderson... noticed that some of the trails were... like... electrons, but were curved by the magnetic field in the opposite direction. At this point Anderson was not aware of Dirac's prediction ...After nearly a year of effort ...he ...identified ...pair production of electrons and antielectrons from the impact of cosmic rays."
"The first results from the magnet in 1931 and 1932 were dramatic and completely unexpected. An approximately equal number of particles of positive and negative charge were observed, whereas, according to the theories known at the time, one would expect to see only ordinary electrons (all of negative charge). The presence of such an abundance of particles of positive charge was perplexing—something new and mysterious must be ocurring."
"joined me... and I assigned him to the task of continuing the curvature measurements... As more data accumulated... practically all of the low-velocity cases of positive charge were particles... whose mass seemed to be too small to permit their interpretation as s. The alternative explanations... were that these particles were either ordinary electrons (of negative charge) moving upward, or some unknown lightweight particles of positive charge moving downward. In the spirit of scentific conservatism I tended... toward the former... [[Robert Andrews Millikan|[T]he chief]]... repeatedly pointed out that cosmic ray particles travel downward, and not upward, except in extremely rare circumstances, and that these... must be downward-moving protons. This point of view was difficult for me to accept... since in nearly all cases the density of the... tracks... was too low for particles of proton mass. To resolve this apparent paradox, a plate was inserted across the center of the ... [A] fine example was obtained in which a low-energy lightweight particle of positive charge was observed to traverse the plate... This particle came in from the bottom of the chamber, passed through the lead plate and went out near the top of the chamber. ...[I]ts track... was more curved above the plate... this meant it was going slower... therefore, it must have passed through the plate traveling upward."
"I knew it could not have been a proton. Since a proton is 1800 times as heavy as an electron it would have produced a much thicker line [trail]... [I]t could not have been a neutron since neutrons have no electric charge and, therefore, are incapable of producing any kind of line... [T]he line was exactly what would have been produced by an ordinary electron except that electrons had always been found to have a negative electric charge and, therefore, should have turned to the right. This one turned to the left... an electron with a positive charge ...a positive electron!"
"Ionization and curvature measurements clearly showed this particle to have a mass much smaller than... a proton... a mass entirely consistent with an electron. ...[D]espite the strong admonitions of the Chief that upward-moving cosmic ray particles were very rare, this... was an example..."
"In the early 1950s... attention was focused on two new unstable, electrically neutral particles... tau and theta. ...[T]he tau and theta were 'strange'—they carried Gell-Mann's additional charge. They decayed in different ways, and had different parities... [T]he tau and theta had the same mass. ...Chen Ning ('Frank') Yang and , thought it was bizarre for two apparently different particles to have the same mass, and suspected... two faces of the same particle, despite... different parities. ...[They] had to throw overboard ...apparently solid ...assumptions about quantum behaviour: ...[1] it would not be basically altered by left-right mirror reflection... [2] behaviour would not be altered by a mirror that reflected particles as antiparticles and vice-versa... [They] re-examined the evidence for both mirror symmetries, which everyone had assumed ...watertight ...showing that for particle decays this had never been proved conclusively."
"Lee and Yang... suggested that the particle-antiparticle mirror could be flawed. ...[T]wo experiments—by , Leon Lederman and Marcel Weinrich... and by Jerome Friedman and Val Telegdi...—looked at multiple particle transformations in which a pion decays into a , which in turn decays into an electron. ...[These] found that ...[f]or a positively charged pion, the muon's spin points backwards, against its direction of motion. [When t]he antiparticle... a negatively charged pion... decays, the muon emerges with its spin pointing in the direction of its motion. Looking in a mirror that changes particles into antiparticles, the antismoke comes down the chimney."
"For the subnuclear world, the ordinary mirror has to be replaced by an extended mirror that carries out three reflections simultaneously—switching particle to antiparticle and vice-versa, changing left to right and vice-versa, and reversing the . ...[R]espectively C (for charge), P (for parity) and T (for time). The CPT mirror changes Alice into a mirror-image Anti-Alice going backward in time."
"Sakharov looked wryly at the composition of an average cubic metre of Universe. ...a billion quanta of radiation, one proton and no antiprotons. Tracking... to just after the Big Bang... [we] should have had... a billion antiprotons, and a billion and one protons. ...Why the odd proton? ...[A]ntimatter had slipped off the map of the Universe ...Sakharov put forward a three-point explanation."
"[1] Big Bang... particle-antiparticle creation briefly got out of hand, more pairs being created than were reabsorbed back into radiation. ...[T]he present Universe is much larger than a sphere of light rays which started out from the Big Bang... Sometime in the past, the Universe... expanded faster than light... Most of the Universe we have not yet seen, despite traveling at [c]... not yet having had time to reach us. ...In the first fraction of a second... the Universe must have 'inflated' faster than the speed of light and particle-antiparticle pairs were produced faster than they could be reabsorbed."
"[2] ...some mechanism had to tilt the balance in favor of matter. With Cronin and Fitch's... implications for the , Sakharov thought he had... the answer. But was the tiny subnuclear effect... enough..? Probably not... But... [h]eavier quarks, more exotic than strangeness, could show larger effects. Making B particles containing the 'beauty' (...'bottom') quark and manufacturing enough of them to probe the has become a major focus of... research."
"[3] The proton... has to be slightly unstable... Sitting still, the -filled proton would have to disintegrate into electrons and other light particles. ...But ...the level of ...instability needed was so small as to be almost undetectable. ...[E]xperiments are trying to capture this effect..."
"The Big Bang should have been matter-antimatter symmetric. But the visible Universe... shows little sign of this primordial antimatter."
"Paul Dirac, the spiritual father of antimatter, probably did not yet know very much about the Big Bang picture when he gave his Nobel lecture... and suggested that the Universe could contain both matter and antimatter without us knowing... If Dirac were right, the whole Universe should be a uniform mix... overall the two halves of the Universe should balance. Where is this antimatter?"
"Light antiparticles... as s, are common in cosmic rays. However, such... are usually from particle-antiparticle pairs produced... as primary cosmic ray particles collide with atmospheric gas or interstellar dust. ...'Fountains' of positrons... seen... peering into the center of our Galaxy... can be explained by violent cosmic processes spitting out... radiation..."
"Any antimatter stars... [w]hen such... died in explosions, their... antinuclei would have been flung out... But the cosmic rays arriving... have revealed no signs of antimatter heavier than s."
"[P]erhaps matter and antimatter are separated into distinct domains. Maybe... there is... an antidomain. ...Wherever and whenever the boundaries... briefly touched, pieces... would have mutually annihilated to give powerful bursts of... s. As the Universe... cooled these... would have... produced a dim but uniform... signal all over the sky."
"If the initial Universe had contained widely space clusters of matter and antimatter, these would have left their... imprint on the Cosmic Background Radiation. The tiny ripples seen by COBE and other detectors are not compatible with separate domains of matter and antimatter... The Universe we can see looks to have been eternally free of nuclear antimatter."
"It became apparent that in a hot early epoch of the big bang there would exist a fully mixed dense state of matter and antimatter in the form of ic and ic pairs in thermal equilibrium with radiation. As the universe expanded and cooled this situation would result in an almost complete annihilation of both matter and antimatter."
"Antinucleons "freeze out" of thermal equilibrium when the annihilation rate becomes smaller than the expansion rate of the universe. This would have occurred when the temperature of the universe dropped below ∼20 MeV. The predicted freeze out density of both matter and antimatter is only about 4×10-11 of the closure density of the universe..."
"Sakharov showed that three conditions are necessary in order to create the appropriately significant concentration of s in the early universe. They are: • Violation of Baryon Number, B • Violation of C and CP • Conditions in which Thermodynamic Equilibrium does not Hold"
"If CPV is predetermined, then only matter will remain in the present universe. We can refer to this case as a "global" matter-antimatter asymmetry. If... CPV is the result of spontaneous symmetry breaking, domains of positive and negative CPV may result. In the case of spontaneous CPV, the Lagrangian is explicitly CP invariant, but at the symmetry breaking phase transition a CP invariant high temperature vacuum state undergoes a transition to a state where the vacuum solutions break CP either way. This mechanism may be compared to the spontaneous formation of ferromagnetic domains when a piece of unmagnetized iron cools below the critical temperature in the absence of a magnetic field. Although there is no preferred direction of magnetization, individual domains acquire random local directions of magnetization."
"If the CP domain structure is stretched to astronomical size by a subsequent period of moderate inflation, then, following , s may survive as galaxies in some regions of the universe and antibaryons may survive as antigalaxies in other regions. In this case, we have a "local" matter-antimatter asymmetry instead of a global one. ...[i.e.,] a "locally asymmetric domain cosmology (LADC)." Following baryogenesis, the walls of the initially CP symmetric vacuum between the positive and negative CP domains must vanish because they are quite massive and could eventually dominate the evolution of the universe, in conflict with observations."
"Antimatter galaxies will look exactly the same as matter galaxies. This is because the photon is its own antiparticle. However, we can look for other clues. Searches have been made for antimatter in the cosmic radiation and for the indirect traces of cosmic matter-antimatter annihilation in the extragalactic γ-ray background radiation."
"properties can play a crucial role in determining the matter-antimatter asymmetry of the universe if thermal is the correct solution to the problem. Owing to this, the study of Neutrino models goes beyond the mere purpose of generating tiny neutrino masses, and it is natural to incorporate the puzzle of cosmic ."
"One of the most fundamental concepts in the study of physics is the idea of symmetry. Yet, Nature as we know it does not always seem to be perfectly symmetrical. ...[T]he principal theme for this current work is motivated by none other than the apparent between matter and antimatter in the universe. Therefore, along with the appeal of symmetry, a major topic of interest is the mechanism of symmetry breaking or asymmetry creation."
"[I]t is quite fascinating that two seemingly unrelated problems—the tiny masses of light neutrino and the matter-antimatter asymmetry—may be explained by the mere introduction of heavy RH [right-hand] neutrinos to the SM. ...[T]he former may be explained by the Type I seesaw mechanism while thermal leptogenesis provides an attractive solution to the later. This... means that an intricate link between neutrino properties and the baryon asymmetry can be established. Consequently, it has been the purpose of this work to explore the implications of several different neutrino models in the leptogenesis context."
"In the representative models... it has been found that successful leptogenesis is only possible in a very fine-tuned region of the parameter space. Specifically, one must select the f = u case, as well as certain combinations of Dirac and Majorana phases in UPMNS such that a lepton asymmetry can be generated via either resonant of flavoured N2-leptogenesis. Further, it has been shown that although the f = e case can yield a TeV scale RH neutrino, the probability of detecting it at the LHC or a next-generation collider such as the ILC is far too small."
"[W]e investigated the effects of introducing an effective transition electromagnetic dipole moment [EMDM] operator between the LH light and the RH heavy neutrinos. ...As a result, a new scenario for leptogenesis whereby the lepton asymmetry is solely generated by the EMDM-type (instead of the usual Yukawa-mediated) interactions is possible. By exploring the key ingredients leading to , we have shown by explicit computations of the relevant diagrams in a toy model that, in principle, electromagnetic leptogenesis is a viable alternative for creating a lepton asymmetry. ...[T]here is no doubt that transition EMDM interactions between light and heavy neutrinos can have far-reaching consequences in the early universe."
"Sakharov published other papers in cosmology. ...[T]he most far-reaching, innovative, and original... concerned "". "s"... denote collectively not only protons and neutrons but also... unstable particles... created when protons and neutrons collide at extraordinarily high speeds. "Antibaryons"... carry the opposite electrical charge. When baryons and antibaryons collide, they annihilate each other, producing... exotic, unstable particles, such as pi-mesons, which are lighter than baryons, as well as radiation... "quanta"... or photons, which have no mass at all. The "background radiation" cosmologists discovered in the mid-1960s is... a remnant of the... annihilation of baryons and antibaryons... when the universe was created or shortly afterward. Baryons and antibaryons, in other words, are one form of matter and antimatter, respectively; electrons... and their opposite, positrons, are another."
"Sakharov tried to explain why exists... how there came to be a surplus of baryons... The consensus... was that there had to be baryon symmetry when the universe began. But there was no consensus on how symmetry broke down. ...According to Sakharov, for baryon asymmetry... the universe at the quantum level... had to have, in Christopher Korda's words, "an intrinsic ." ...[P]hysicists ...refer to the sequence... Sakharov described as "the Sakharov conditions.""
"Sakharov's conclusion was that ""—the difference between baryons and antibaryons in the universe—was not constant, as most... believed. ...[B]aryons, and in particular protons, can decay, and it was Sakharov's concept of proton decay and how it comes about that proved to be perhaps the most remarkable of all his contributions to cosmology. ...D. S. Chernavski, went as far as to say that, by showing theoretically that the proton can disnintegrate, he revealed "the basis of the universe." Ironically, Sakharov's ideas on the subject did not attract much attention for about a decade. But the development of... gauge theories in the late 1970s sparked new interest... even though proton decay has yet to be confirmed experimentally."
"A nucleus contains two protons and two neutrons. Under suitable circumstances a proton can change into a neutron and emit energy some of which materializes as a positron, similar to what happens in the positron emitters of... medicine."
"The finds itself in the heart of the sun, where there are lots of electrons and is instantly destroyed, turned into s. These try to rush away... but are interrupted by the crowd of electrically charged particles, electrons and protons... [R]epeatedly absorbed by electrons and then emitted with less energy... it will take a hundred thousand years before gamma rays... reach the surface... In doing so the rays lose lots of energy... changing from s to ultra-violet and at last into the rainbow of colours that are visible... So daylight is the result of antimatter being produced in the heart of the sun and, in part, of its annihilation."
"The laws of electricity and magnetism that underlie the existence of bulk matter don't care which bits... carry negative charge, and which... are positive. If we swapped all positives to negative, and all negatives to positive... resulting forces would be the same and the structures they built would... be unchanged. ...[T]o all outward appearances, nothing would appear different. Such a swapping of charges would turn what we know as matter into... antimatter. An anti-atom of would consist of a negative encircled by a positively charged . Paul Dirac... first predicted that such a mirror image of matter should exist."
"[H]ow can an electron with negative electrical charge emerge from the energy in a puff of light, which has no... charge? This is where nature's two forms of matter enter the story. The negatively charged electron has a positively charged form... the . The energy of a photon, a particle of light, becomes trapped in these two complementary pieces of substance. This... can also happen in reverse: an electron and a positron can annihilate one another, their individual energies being taken by the photons that rush from the scene of destruction at the speed of light. The emergence of substance from pure energy... is almost biblical in scope. With antimatter... we make contact with the gods of creation."
"In 1923 ... was investigating s... using a . ...The ...rays would knock electrons out of atoms... whose trails he could see... [I]n addition to knocking electrons out of the gas, they were ejecting them out of the walls of the chamber ...which interfered with the measurements... He... came up with the... idea of sweeping away the unwanted electrons by putting the chamber between the poles of a large magnet. ...[T]he clearer view revealed ...the magnetic forces seemed to make some of the 'electrons' curve 'the wrong way'. Today we know he was seeing s, but... [the] anomalous trails were a distraction from what he was trying to do. ...News about these images spread ...and five years later Skobeltsyn decided to show them at an international conference in Cambridge. ...[N]o one could offer an explanation. It was ironic that [this was]... the same year and... place that Dirac came up with his theoretical prediction of positrons... [A]s no one at the time had any reason to expect... positrons existed, he missed the big prize."
"Blackett had been working with a in Rutherford's group... a chamber that was ready for action every ten seconds or so, and took photos on ordinary film. ...[H]e accumulated ...pictures of trails made by s—a product of radioactive nuclear decays— ...bombarding nitrogen gas in the chamber. ...[I]n 1931 arrived ...His specialty was detecting nuclear radiation using s. ...Their big idea ...put one Geiger counter above a cloud chamber, and another... below. ...By connecting the Geiger counters to a ...a flash of light [and the cinematograph] captured the tracks of the cosmic rays on film. ...They noticed that ...a few tracks that appeared at first sight to be electrons, were ...curved the wrong way in the magnetic field. Blackett talked to Dirac about them... neither aware of the precious truth. ...It was only when they heard of Anderson's discovery that Blackett and Occhialini ...realized what they had."
"[L]uckily... they had more... Many of the pictures showed up to twenty... tracks ...from a copper plate just above the chamber ...roughly half of the particles were negatively charged and the rest positively charged. Blackett and Occhialini realized... the appearance of equal numbers of positrons and electrons must be... the result of s hitting the metal."
"Albert Einstein's equation E = mc^2, implies that energy (E) can be converted into mass (m)—radiation into matter—and Blackett and Ochialini had for the first time demonstrated the creation of matter, and antimatter, from radiation; they had proved that Anderson's new particle was not some weird extraterrestrial interloper."
"An ambitious plan took hold at Berkeley... to build an accelerator that would speed s such that when smashed into a target, there would be enough energy to produce an . ...When energy turns into massive particles they emerge in pairs, a particle... matched with its antiparticle, so the BeVatron was built with enough power to produce an antiproton in conjunction with a proton... Several ideas on how to isolate the antiproton 'needle' from the particle 'haystack' were presented... A small team... of , Emilio Segre, , and won the competition ...their idea worked ...and in 1955 they announced their discovery. One of the other teams led by that had entered the competition also gained success... with the discovery of the in 1957. So thirty years after Dirac['s]... seminal prediction, the basic pieces of the antiworld were in place: , antiproton, and ."
"Since antimatter will destroy any material object, it must be kept in a cage without material walls. The solution... a vacuum that is better than in outer space with magnetic and electric fields that confine the antiparticles, positrons, or antiprotons, as circulating beams. That is in effect what is done at particle physics laboratories such as CERN..."
"Magnetic fields that had been able to focus positrons into stable orbits were unable to control the wild antiprotons... Budker's idea was to pass the antiprotons through clouds of cold electrons. Although electrons are matter and antiprotons are antimatter, they are in no danger to one another: electrons are destroyed by their antiparticle, the positron, while the antiproton is at risk only from protons or neutrons. ...By 1974 Budker... succeeded in making and cooling antiprotons, but not in sufficient numbers to make an intense beam."
"It is just like matter except with a reversal of charges. ...We make it and study it in our laboratories, but find little of it in nature. The laws of physics for antimatter are almost an exact mirror of those for matter."
"For each type of matter particle there is a matching type of antimatter particle. ...[W]e can convert energy from radiation into a matched pair..."
"[T]heories suggest that, at very early times... all possible types of particles and antiparticles, existed equally in a hot, dense, and very uniform . ...[A]s the Universe expanded and cooled... annihilation could still occur whenever a particle met an antiparticle, but the reverse... creation of a particle and an antiparticle, became... rare."
"[H]igh energy laboratories can produce particles with energies similar to those that prevailed in the [very early] Universe... allows us to model the primordial production of small nuclei from collisions starting with s and s, long before stars began to form. Because we know... what energies are required for collisions to take apart... light elements [ less than 11] into... protons and neutrons, we can identify... the time at which the Universe became cold enough that this destruction practically ceased, and... production of elements started in earnest."
"The fate of antimatter to disappear was sealed by the time the Universe was no older than a millionth of a second."
"[T]he mystery of the missing antimatter... What laws of nature, not yet manifest in experiments and not part of our current Standard Model, were active in the early Universe, allowing the observed amount of matter to persist while all antimatter disappeared from the Universe?"
"Perhaps the best-known giant resonance in nuclei is the giant dipole resonance (GDR). The GDR is described in classical hydrodynamics as a class of nuclear motion in which the neutrons and protons within a nucleus move collectively against one another, providing a separation between the centers of mass and charge, thus creating a dipole moment."
"Nuclei interact with the external environment through a number of different fields—electromagnetic, weak and hadronic. The collective excitations induced by these interactions are known as giant resonances. The best known example is the giant dipole resonance, which is stimulated when the electric field of an incident gamma ray exerts a force on the positively charged protons in a nucleus, moving them relative to the uncharged neutrons ... Other giant resonances that have been studied are the monopole, quadrupole and spin-isospin modes of oscillation. The spin-isospin mode involves charge-changing processes, in particular beta decay. The quadrupole and monopole giant resonances are most easily seen with fields that act equally on neutrons and protons, because in these modes the neutrons and protons oscillate in the same mode. The giant resonances are collective oscillations and the various modes of oscillation depend on specific aspects on the nuclear force to sustain them. In the monopole mode, the motion is radial and the frequency depends on the compressibility of the nucleus. In the dipole and spin-isospin resonances, the protons and neutrons are excited out of phase, and the proton-neutron interaction provide the restoring force."
"The spectrum of gamma-radiation emitted by a highly excited nucleus can be calculated in two ways. In the first method the transition probability for gamma emission is related to the photon absorption cross-section by detailed balance. The second method relies on the fact that an excited hot nucleus has thermal fluctuations. In particular it has a fluctuating dipole moment which produces thermal radiation. The two methods are closely related and in both cases the spectrum of the radiation emitted is dominated by the giant dipole resonance. The equivalence of the detailed balance and thermal radiation theories can be demonstrated explicitly for a coupled oscillator model of the giant resonance."
"A powerful method to study the properties of a system is to subject it to a weak external perturbation and to examine its response. For the atomic nucleus subjected to the absorption of a photon or to the scattering of a particle (electron, proton, etc.) the response is ... a function of the energy and linear momentum transferred to the system. ... Up to about 10 MeV the nucleus responds through the excitation of relatively simple states often involving only one or a few particles. In the energy range between 10 and 30 MeV the system response exhibits broad resonances. These are the giant resonances ... Giant resonances correspond to a collective motion involving many if not all the particles in the nucleus. The occurrence of such a collective motion is a common feature of many-body quantum systems. In quantum-mechanical terms the resonance corresponds to a transition between the ground state and the collective state and its strength is described by a transition amplitude. Intuitively it is clear that the strength of the transition will depend on the basic properties of the system such as the number of particles participating in the response and the size of the system. This implies that the total transition strength should be limited by a sum rule which depends 'only' on ground-state properties. If the transition strength of an observed resonance exhausts a major part, say greater than 50%, of the corresponding sum rule we call it a giant resonance."
"Maurice Goldhaber has emphasized that the situation with respect to possible nuclear resonances in (γ,n) or (γ,fission) reactions was quite unclear at the time of George C. Baldwin and G. Stanley Klaiber’s papers on these reactions. ... This was because the rapid rise of their yield to a prominent peak with increasing energy, followed by a slower fall off was then thought to have been due to the competition between the rapidly rising density of nuclear states and the eventual domination of other reaction channels at higher energies. Goldhaber realized, however, that there could be an analogy between a possible collective nuclear resonance and the restrahl resonance (essentially the transverse optical phonon mode) in polar crystals. Goldhaber sought out Teller because of his paper with Russell Lyddane and Robert Sachs, ... relating the restrahl frequency to the asymptotic behavior of the crystal’s dielectric function. Goldhaber and Teller, in their paper together, went on to predict universal, giant photo-nuclear resonances. ..."