Physics books are generally of three kinds: texts for undergraduates, advanced texts for professional researchers, or 'popular science' books with little or no mathematics. This book is none of these. It is not a book for beginners. Nor is it a book addressing any topic at specialist level. It is a book primarily for physicists at post-graduate level, or approaching that level, or for professionals in areas other than their specialism. Above all, it is a book for physics aficionados. This is a term which does not necessarily imply great expertise, but does imply enthusiasm perhaps approaching obsession. Aficionados are people who understand that the serious pursuit of theoretical physics is not something that one chooses to do: it chooses you. This is all very well for those blessed with outstanding brilliance. For the rest of us it can be frustrating to find that desire outstrips ability and that texts at the cutting edge appear accessible only to the blessed few. This is my attempt to redress the balance a little by summarising a few things I think I understand. I hope you may find it useful. Apologies if I have fallen short of my ambition.

What defines the topics addressed? Simply this: I chose those parts of theoretical physics which I consider particularly important or illuminating; the juicy bits, the bits that are cool, the choice cuts. I can guarantee that aficionados will be outraged that I have omitted their favourite bit of theory. I'm sorry, but one must stop somewhere. I hope you enjoy the selection anyway.

Feel free to download the pdf's to the display device of your choice. (Some of the mathematics may be a challenge to read on small hand-held devices).

- Chapter 1: Where Is My Gun?
Schrodinger's cat released at last. It is just silly to imagine a superposition of "aliveness" and "deadness" since being alive is a classical state not a quantum state.

- Chapter 2: Does Decoherence Make Quantum Mechanics Coherent?
What is decoherence? How is decoherence quantified? What are the pointer states? Does decoherence theory elucidate the measurement problem or the emergence of classical behaviour?

- Chapter 3: The Democratic Republic of Free Observers
The physical origin of the Lorentz transformation is the equivalence of inertial observers. Familiarity with 4-vectors and the invariance of the Minkowski metric are apt to make us loose sight of the physical basis of special relativity. Here's a reminder.

- Chapter 4: No Peeking
We are taught that interference effects are destroyed by obtaining "which path" information. This is usually illustrated by specific experimental set-ups. Here it is shown to follow generically from the Hilbert space algebra. If only partial information is obtained does the interference degrade but not completely disappear? Yes.

- Chapter 5: The Gold Standard of Unification
Maxwell's equations and the velocity of light: the first field theory, the first gauge field theory, a gold medal winning example of unification and elucidation of the nature of light; all homage to James Clerk Maxwell.

- Chapter 6: A Watched Pot Never Boils
The quantum Zeno paradox

- Chapter 7: Reflections on Refraction
The laws of reflection and refraction can be derived from the appropriate boundary conditions applied to the wave solutions of Maxwell's equations.

- Chapter 8: The Elitzur-Vaidman Bomb Test
The observability of counterfactuals: in classical physics the fact that something could have happened is totally irrelevant if, in fact, it did not happen - that is, if it is a counterfactual. But in quantum mechanics things are otherwise.

- Chapter 9: So You Think Magnetic Monopoles Do Not Exist?
Well, no, they don't: or do they? Actually it's matter of convention, though a very natural one. The empirical fact is that all particles appear to have the same ratio of charge to magnetic monopole strength.

- Chapter 10: The No-Cloning Theorem
The basis of quantum cryptography, the no-cloning theorem is remarkable for two things: firstly it is so simple to prove in a couple of lines of algebra, and secondly, it was not discovered until as late as 1982.

- Chapter 11: A Free Lunch Called "The Universe"
Key features of the Big Bang are derived in an elementary manner: the critical density, the expansion rate, the time-temperature relation and the cosmic microwave background temperature. The horizon problem and the flatness problem are described.

- Chapter 12: You Can't Outwit the Weirdness
Wheeler's delayed choice interference experiment realised

- Chapter 13: Stationary Action: Is It Minimum?
Is the action minimum or maximum or neither? Since action is defined as the time integral of (KE-PE), and because potential energy is a minimum in the static case, this suggests that the action should be a maximum. But of course it is not (usually). Sometimes texts refer to the Principle of Least Action, but in truth the action is not always a minimum either. What is going on here?

- Chapter 14: The Whole is Less than the Sum of its Parts
The entropy of quantum states and the inequalities it obeys: the quantum weirdness is here manifest in the fact that the information available in a multipartite system can be less than in its parts.

- Chapter 15: The Kepler Problem
You may have thought there was nothing more to be said about the Newtonian two body problem, or Kepler problem. Here the general solution to the orbital shape of the Kepler problem is derived via the Runge-Lenz vector. If the solutions are conic sections, what exactly is the cone?

- Chapter 16: Entangled Interference
Resolution of the conundrum that interference phenomena using entangled particles appear to present the opportunity for faster-than-light communication. Refutation of the lazy assertion that entangled particles are not subject to interference phenomena.

- Chapter 17: Going Round in Circles
How to calculate motion with respect to a rotating coordinate system; derivation of the centrifugal and Coriolis forces; are they fictitious? Is gravity? The Foucault pendulum; Why is the behaviour of gyroscopes counter-intuitive? How to demonstrate antigravity to the unwary.

- Chapter 18: Delayed Quantum Erasure
The weirdness maxes out. What is quantum erasure? What is delayed erasure and does it challenge causality? (No)

- Chapter 19: The Classical Definition of Temperature and the Efficiency of Heat Engines
Why the various definitions of temperature are the same; The elegance of classical thermodynamics; The derivation of the maximum efficiency of a heat engine; The importance of functions of state.

- Chapter 20: It's Teleportation, Jim, but Not as We Know It
Quantum teleportation: What it is and what it is not. What has to be transported conventionally through space, and why it does not provide a means of faster-than-light communication.

- Chapter 21: Big Bang Nucleosynthesis
The first few minutes: the shifting balance of protons and neutrons and the escape into the helium sanctuary; the light element abundance of the universe.

- Chapter 22: How the Magic is Lost
An illustration of decoherence

- Chapter 23: Cosmic Geometry: FLRW Spacetimes
Space and time in general relativistic cosmology; FLRW spacetimes; positive and negative curvature and whether the universe is finite or infinite; the critical density revisited; the cosmological constant and implications for universal expansion.

- Chapter 24: How the Magic is Retained
If the environmental interaction energy is small compared with the spacing of the system's eigen-energies then decoherence selects the energy eigenstates. An initial energy eigenstate, and its attendant spatial delocalisation, is then proof against the ravages of decoherence.

- Chapter 25: Spontaneous Order through Gravitational Collapse
How do orderly structures arise spontaneously given that the universe starts in a chaotic state? Why does this not violate the second law of thermodynamics?

- Chapter 26: Why Are Big Things Classical?
Why does decoherence tend to happen very rapidly for objects with large numbers of degrees of freedom? Provisional: there is much in this Chapter which still needs checking or completing

- Chapter 27: Noether’s Theorem and the Origin of Spin
Conservation laws are the cornerstones of physics. That the conservation laws are a mathematical result of symmetries is one of the most fundamental features of modern physics. The quantities which are conserved as a result of the Poincare symmetries of Minkowski spacetime are derived here. Amongst other things this puts spin in its proper context. Provisional: there is much in this Chapter which still needs checking or completing

- Chapter 28: Sins of Intention
Can a Null Measurement Collapse the Wavepacket? (Yes).

- Chapter 29: The Remnant of a Shadow
The optical theorem relates the total scattering cross section to the imaginary part of the forward scattering amplitude. How can the forward amplitude contain enough information to specify an integral over all scattering angles? This used to mystify me. Here I de-mystify it.

- Chapter 30: The Unavoidable Weirdness
The infamous Einstein, Podolsky and Rosen gedanken experiment; hidden variables and Bell’s inequality; experimental support for the completeness of quantum mechanics, i.e., that there are no hidden variables.

- Chapter 31: If the Universe is Expanding Why Can I Never Find a Parking Space?
No, it's not because your car is getting bigger too.

- Chapter 32: Angular Momentum Eigenstates
How the angular momentum eigenvalues and the corresponding states are derived by purely algebraic methods.

- Chapter 33: Entanglement
The origin and quantification of quantum weirdness: entanglement, the resource for quantum technologies.

- Chapter 34: Causality and Analyticity
The relationship between causality and analyticity; its implications for the propagation of electromagnetic waves in dispersive media; dispersion relations and their relevance in particle physics.

- Chapter 35: The Algebraic Hydrogen Atom
The energy levels of the non-relativistic hydrogen atom can be derived without solving for the associated states by making use of the Runge-Lenz vector which also facilitates the solution to the classical Kepler problem. Provisional: this Chapter still needs checking and completing

- Chapter 36: The Static Casimir Effect
Place a pair of parallel conducting plates sufficiently near each other and a force of attraction is generated. This is the Casimir effect (though possibly augmented by Van de Waals forces). The Casimir effect is often cited as evidence that zero point energy is real, because the force can be derived from the zero point energy of quantum fields in the vacuum state.

- Chapter 37: The Relativistic Hydrogen Atom: Peculiarities of the Dirac Ground State
The ground state of the electron in a hydrogen atom has an orbital angular momentum quantum number of zero, so there is no electric current, right? Wrong! New at 4/1/14

- Chapter 38: Molecular Tunnelling?
Can covalently bonded molecules pass through each other by quantum tunnelling? No - but the reason why provides a nice exercise. The conclusion is important because it eliminates a cheap solution to the protein folding problem.

- Chapter 39: Quantum Pencil Balancing
In classical physics the idea of a pencil perfectly balanced on its tip, but also subject to precisely no disturbance, merely presents a problem which is indeterminate by definition. Remarkably, in quantum mechanics, the problem of how long such an ideal balance will persist has a definite answer - 5 seconds. COMING SOON

- Chapter 40: Pitfalls of Popularisation
Popularisers of physics have a tough job. We must allow them considerable latitude as regards strict accuracy. Rigour is often the enemy of comprehensibility. Nevertheless it is instructive to examine some sins that have been committed.COMING SOON

- Chapter 41: Waves Making Tracks
Tracks in cloud chambers or bubble chambers give every impression that the agency causing them is particle-like. But actually the wave description is also consistent with these linear tracks.

- Chapter 42: The McGlinn-O'Raifeartaigh Theorem
If an internal symmetry commutes with the homogeneous Lorentz group then it commutes with the whole Poincare group. The implication is that there is no easy, purely group-theoretical, route to deriving the hadronic mass spectrum. This Chapter still needs the algebra checking

- Chapter 43: The Relativity of Particles and Hawking Radiation
Relativity teaches that distance, duration, energy and gravitation are all relative to the state of motion of the observer. But surely the number of particles different observers see must be the same? No, not so. The Fulling-Davies-Unruh effect is discussed and used as a poor man's approach to the Hawking radiance of black holes. The generic lesson is that the presence or absence of particles is relative to the observer's state of motion, and hence to the spacetime geometry and the gravitational field.

- Chapter 44: The Uncertainty Principle
Derivation of the uncertainty inequality from a non-zero commutator; how the uncertainty principle has become less central in Quantum Mechanics than it was.

- Chapter 45: Superdense Coding
How much classical information can one Qubit convey? (2 bits, amazingly) COMING SOON

- Chapter 46: The Standard Model of Particle Physics and QCD
The standard model could hardly be left out, though whether it is a "choice cut" or a bit of a mess is another matter. For a long time progress in physics was synonymous with increasing elegance and simplicity. The full electroweak-QCD Lagrangian, not to mention extracting predictions from it, is not exactly simple. new at June 2014

- Chapter 47: The Physical Limits of Information and Computation
Information must have a physical manifestation, and computation is always a physical process. Consequently physics imposes limits on the quantity of information and the speed of computation possible with finite resources.

- Chapter 48: The Higgs Mechanism and the Hadronic Mass Spectrum
Since I wrote the first version of this preview, the Nobel has been awarded for the Higgs mechanism. Does the Higgs mechanism really explain the origin of all mass, as media physicists keep saying? No, it does not, and this false impression is important enough to merit a short chapter of its own. It also serves to motivate a discussion of the determination of the low mass hadronic spectra from QCD via lattice gauge theory, one of the icons of modern physics. But what a pity it cannot be done on the back of an envelope with a bit of algebra.COMING SOON

- Chapter 49: The Running Couplings
Renormalisation of field theories imbues the effective coupling constants with a dependence upon the energy scale, i.e., they are not really constants. Measurements of the electromagnetic fine structure 'constant' at various energies compare well with the log expansion expected from renormalisation theory. This is another of the icons of modern physics. COMING SOON

- Chapter 50: Big Things Behaving Quantum Mechanically
Chapter 26 has rationalised why big things tend to be classical. However this is not a hard and fast necessity - just a general trend: there are exceptions, and the exceptions provide the most interesting phenomena. Here some of the exceptions are discussed: superconductivity, superfluids, Bose-Einstein condensates, interference experiments with large molecules (viruses?) and the entangling of macroscopic diamonds. COMING SOON

- Chapter 51: Cosmic Geometry: Times, Distances and Redshifts
The cosmological redshift and its relation to times and distances; how various measures of cosmological distances can be defined and evaluated; calculating the age of the Universe from the cosmological parameters.

- Chapter 52: Does a Uniformly Accelerating Charge Radiate?
You might think that the question of the electromagnetic radiation emitted by a uniformly accelerating charge would be simple book work, presenting no problems of principle. You would be wrong. This problem is notorious.

- Chapter 53: Dynamic Casimir Effect: Radiation from an oscillating 1D barrier?
COMING SOON

- Chapter 54: Berry phase
COMING SOON

- Chapter 55: Where is the Charge in the Kerr-Newman Solution?
The charge is zero, or divergent, or non-zero and finite depending how you measure it. But in the latter case it consists of two spatially separated parts of opposite sign which partly cancel.This Chapter still needs the algebra checking

- Chapter 56: The Power Spectrum of the CMB
Both the Big Bang theory and inflation theory have other significant successes. However one of the most impressive successes is the quite detailed prediction of the structure in the power spectrum of the cosmic microwave background. This is the third of our icons of modern physics. So the universe really did spring from a quantum fluctuation - did it? COMING SOON

- Chapter 57: The Total Mass-Energy of the Universe
Gravitational energy is a slippery fish and cannot be pinned down. Consequently the question of the total universal mass-energy appears irresolvable unless there is somewhere 'outside' the universe in which to stand to do the measurement. Nevertheless there is a perennial temptation to regard the total mass-energy as zero, since this makes creation ex nihilo consistent with the principle of conservation.

- Chapter 58: The Total Entropy of the Universe and Where It Is
In which components of the universe does most entropy reside? By how much has structure formation reduced the entropy of baryonic matter? Three salient size scales of black holes are defined and turn out to be the same.

- Chapter 59: Why Space is 3D
With all this talk of Kaluza-Klein theories and strings and M-branes in 10 or 11 dimensions it may seem perverse to be defending 3D space as essential. OK, but I like being perverse. And, of course, ordinary everyday space IS 3D, darn it. COMING SOON

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