The book addresses the layman reader and does not require a prior knowledge of Mathematics or a previous exposure in quantum theory. The reader can comprehend the book following the reasoning of the authors and is not necessary to understand whatever Mathematics appear in the text - limited anyway with the exception of the epilogue which is optional and which does include quite a bit of Algebra. The authors explain that the sole reason for the presence of Mathematics in the text is for the interested reader not to rely on the authority of the authors but to have available the mathematical underpinning. The book, however, is not an easy reading the remarkable writing ability of the authors notwithstanding.
The authors follow a natural sequence and a step by step approach. They present the phenomena that puzzled physicists in the latter part of the nineteenth century which eventually led them to abandon the deterministic Newtonian world and adopt the counterintuitive, arcane, esoteric and probabilistic quantum theory which, however, predicts experimental results with amazing accuracy. The authors consider sequentially a single quantum particle, atom, clusters of atoms, which lead to both the covalent bond and Chemistry and the development of the transistor, the most remarkable ivention in the last hundred years and based on quantum theory;they then consider particle interaction and quantum field theory, the elusive Higgs boson and its significance in the origin of mass. An optional epilogue concerns the computation of the maximum mass of a white dwarf.
The phenomena which puzzled physicists in the second half of the nineteenth century were their inability to obtain the exact relationship between the distribution of wavelengths emitted by hot objects and their temperature and radioactive decay which run counter to the perceived stability of atoms.
The word quantum is due to Max Planck who in a stroke of genius in 1900 realized that the 'black body radiation' problem could only be explained if light is emitted in quanta that is discrete packages.
The coup de grace for Newton's theory was given as a result of a series of experiments in the 1920's. Until then it was accepted that light as shown by Maxwell were emitted via electromagnetic waves. In a series of experiments from 1923 to 1925 Arthur Compton and his co-workers succeeded in bouncing the quanta of light off electrons. In 1926 the light quanta were christened 'photons'. The evidence was icontrovertible - light behaves both as a wave and as a particle. That signalled the end of classical physics and the beginning of quantum theory. There is also the double-slit experiment with electrons conducted by Davisson and Germer at Bell laboratories in 1927 displaying an inteference pattern and in this way demonstrating the particle-wave duality of the electrons.
A quantum particle is a single particle that is in many places at once;we refer to these counterintuitive, spread-out yet-point-like particles as quantum particles. The field associated with the particle is called the wavefunction;the Erwin Schrodinger equation of the wavefunction describes how it changes as time passes. The famous Heisenberg Uncertainty Principle states that it is impossible to know with accuracy both the position of a particle and its momentum;the precise statement is that the product of the uncertainty in the position of a particle and its momentum will be roughly equal to Planck's constant. The de Broglie equation states that the potential equals the Planck constant divided by the wavelength. This is interesting because it relates the potential associated with a particle and wavelength which is associated with waves. The de Broglie equation constituted a huge conceptual leap. In his original paper, he wrote that a 'fictituous associated wave' should be assigned to all particles, including electrons, and that a stream of electrons passing through a slit 'should show diffraction phenomena'. In 1923 this was theoretical speculation, because Davisson and Germer did not observe an inteference pattern using beams of electrons until 1927.
The simplest atom comprise the positively charged proton which is a qvantum colossus compared with the tiny and negatively charged electron and is electrically neutral. It is also a virtually vast empty space. The problem faced by early workers was that as electrons orbit around the nucleus emit light and in the process lose energy and spiral inwards on an inevitable collision course with the proton. This does not happen and we should explain why. The reason is that electrons inside atoms occupy states of definite energy, known as stationary states. It is possible for an electron to make the transition from one energy state to another with the concurent emission/absorption of a photon. The emission of photons in this way makes tangible the energy states in an atom, we see the characteristic colour of atomic emissions. One of the fascinating aspects of our quantum universe is the Pauli Exclusion Principle in that only two electrons can occupy each available energy level. Freeman Dyson and Andrew Lenard in 1967 showed that matter can only be stable if electrons obey the Pauli Exclusion Principle.
The contemplation of atomic clusters will lead us to chemical bonding and the transistor. There is a preference for two atoms with half-filled bands to stick together as a result of sharing the electrons between them known as covalent bond. Covalent bond is the basis of Chemistry and results in the creation of molecules from water to DNA.
Due to space limitations I shall not enter into the basis of the transistor apart from mentioning that it is deeply quantum but shall present some staggering figures. To-day, every year the world manufactures over 10 in the 18th power transistors, which is one hundred times more than the sum total of all the world's grains of rice consumed every year by the world's seven billion residents. The transistor has a continuing tranformative impact on our lives with application in Science, Medicine, and telecommunications. Your mobile phone has one billion transistors.
The nature of the interaction between particles is the domain of quantum field theory. The first and best studied quantum field theory is quantum electrodynamics, or QED. QED is the theory that explains how electrically charged particles, like electrons and protons interact with each other and with light (photons). It is capable of explaining all natural phenomena with the exception of gravity and nuclear phenomena. QED does not explain the 'strong nuclear' processes that bind quarks together inside protons and neutrons or the 'weak nuclear' processes that keep our Sun burning. Th W and Z particles madiate the weak force while the gluons mediate the strong force. We do not have yet a quantum theory of gravity.
The authors opted to conclude the book with the computation of the maximum mass of a 'white dwarf' amounting to 1.4 solar masses as a tribute to the scientific method, quantum theory, and the human intellect. The calculation was first performed by Subrahmanyan Chandrasekhar in 1930 and relies on an understanding of nuclear physics, of quantum physics, and of Einstein's Theory of Special Relativity. It depends on Planck's constant, the speed of light, Newton's gravitational constant, and the mass of proton.
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