Physics Frontiers Index

Podcast Home

Posted Shows:

1. G4V: The Gravitational 4-Vector Formulation of Gravity
(Recorded: 10/8/2016) (Published: 10/31/2017)  [video]
2. The de Broglie-Bohm Interpretation of Quantum Mechanics
(Recorded: 10/15/2016) (Published: 11/15/2017)  [video]
3. Graviteoelectromagnetism
(Recorded: 10/22/2016) (Published: 12/6/2017)  [video]
4. Phononics
(Recorded: 11/5/2016) (Published: 1/4/2017)
5. Pilot Wave Hydrodynamics
(Recorded: 11/20/2016) (Published: 1/20/2017)
6. General Relativity for the Experimentalist
(Recorded: 11/26/2016) (Published: 2/14/2017)
7. Virtual Gravitational Dipoles
(Recorded: 12/3/2016) (Published: 3/14/2017)
8. Vacuum Fluctuations and the Casimir Effect
(Recorded: 12/10/2016) (Published: 4/27/2017)
9. f(R) Theories of Gravity
(Recorded: 12/17/2016) (Published: 6/2/2017)
10. Requirements for Gravitational Theories
(Recorded: 1/15/2017) (Published: 6/30/2017)
11. Photonic Molecules and Optical Circuits
(Recorded: 1/21/2017) (Published: 7/16/2017)
12. A Gravitational Arrow of Time
(Recorded: 1/28/2017) (Published: 8/20/2017)
13. Exotic Photon Trajectories in Quantum Mechanics
(Recorded: 2/4/2017) (Published: 9/14/2017)
14. Stochastic Electrodynamics
(Recorded: 2/11/2017) (Published: 10/4/2017)
15. Five Proven Methods of Levitation
(Recorded: 3/5/2017) (Published: 10/21/2017)
16. Stochastic Resonance Energy Harvesting
(Recorded: 3/11/2017) (Published: 11/6/2017)
17. The Physics of Time Travel
(Recorded: 4/2/2017) (Published: 11/23/2017)
18. The 2T Physics of Itzhak Bars
(Recorded: 4/8/2017) (Published: 12/6/2017)
19. Exoplanets. [Lost track]
(Recorded: 4/15/2017)
20. Time Crystals
(Recorded: 4/22/2017) (Published: 12/21/2017)
21. The Origin of Inertia
(Recorded: 4/29/2017) (Published: 1/10/2018)
22. Weyl Quasiparticles
(Recorded: 5/7/2017) (Published: 1/18/2018)
23. Dark Energy
(Recorded: 5/20/2017) (Published: 2/8/2018)
24. The Island of Stability
(Recorded: 5/27/2017) (Published: 2/23/2018)
25. Gravitational Field Propulsion
(Recorded: 6/11/2017) (Published: 3/15/2018)
26. Antimatter Production at a Potential Boundary
(Recorded: 6/17/2017) (Published: 3/25/2018)
27. The Gravitational Equivalence Principles
(Recorded: 9/10/2017) (Published: 4/14/2018)
28. The Quantum Vacuum and the Casimir Effect
(Recorded: 9/16/2017) (Published: 4/24/2018)
29. Gravitational Alternatives to Dark Energy
(Recorded: 10/15/2017) (Published: 5/14/2018)
30. Consistent Histories Interpretation of Quantum Mechanics
(Recorded: 10/29/2017) (Pubished: 5/24/2018)
31. The Parameterized Post-Newtonian Framework
(Recorded: 11/12/2017) (Published: 6/8/2018)
32. Tunneling Time
(Recorded: 11/25/2017) (Published: 7/6/2018)
33. Retrocausality
(Recorded: 3/3/2018) (Published: 7/25/2018)
34. CPT Symmetry and Gravitation
(Recorded: 3/28/2018) (Published: 8/10/2018)
35. The String Theory Landscape
(Recorded: 5/12/2018) (Published: 9/21/2018)
36. The Electromagnetic Stress Tensor in Metamaterials
(Recorded: 5/26/2018) (Published: 10/14/2018)
37. The Einstein-Cartan Theory Torsion Field Theory
(Recorded: 6/10/2018) (Published: 10/29/2018)
38. Why is Space-Time Four Dimensional?
(Recorded: 9/8/2018) (Published: 11/25/2018)
39. Negative Effective Mass
(Recorded: 9/29/2018) (Published: 12/9/2018)
40. The Octonions
(Recorded: 10/20/2018) (Published: 12/23/2018)
41. The Chameleon Field
(Recorded: 11/3/2018) (Published: 2/24/2019)
42. Entropic Gravity
(Recorded: 4/4/2019) (Published: 5/3/2019)
43. The Positive Energy Theorem
(Recorded: 12/9/2017) (Published: 6/6/2019)
44. Spooky Action at a Distance
(Recorded: 5/2/2019) (Published: 7/15/2019)
45. Loop Quantum Gravity
(Recorded: 6/13/2019) (Published: 8/16/2019)
46. Wigner's Friend
(Recorded: 7/18/2019) (Published: 9/21/2019)
47. Bimetric Gravity
(Recorded: 8/15/2019) (Published: 11/23/2019)
48. Graviton-Photon Oscillations
(Recorded: 9/13/2019) (Published: 1/19/2020)
49. The Unruh Effect
(Recorded: 10/31/2019) (Published: 4/4/2020)
50. X17
(Recorded: 12/6/2019) (Published: 5/3/2020)
51. Gravitational Wave Astronomy
(Recorded: 3/19/2020) (Published: 6/9/2020)
52. Sterile Neutrinos
(Recorded: 4/24/2020) (Published: 7/7/2020)
53. Electromagnetic-Gravitational Repulsion
(Recorded: 5/21/2020) (Published: 8/16/2020)
54. The ANITA Experiment
(Recorded: 6/4/2020) (Publishted: 10/18/2020)
55. Multiversality
(Recorded: 6/25/2020) (Published: 12/6/2020)
56. The Anomalous Magnetic Moment of the Muon
(Recorded: 7/23/2020) (Published: 4/1/2021)
57. Qunatum Effects and Gravitational Waves
(Recorded: 10/1/2020) (Published: 5/2/2021)
58. The Higgs Portal
(Recorded: 11/9/2020) (Published: 6/7/2020)
59. The Hubble Crisis
(Recorded: 1/7/2021) (Published: 7/25/2021)
60. Physical Warp Drives
(Recorded: 3/25/2021) (Published: 9/12/2021)
61. Dark Stars
(Recorded: 6/10/2021) (Released: 10/31/2021)
62. Deformed Special Relativity
(Recorded: 2021/08/08) (Released: 2/13/2022)
63. Gleason's Theorem with Blake C. Stacey
(Recorded: 1/18/2022) (Published: 3/20/2022) [ Video ]
64. Born's Rule with Blake C. Stacey
(Recorded: 1/18/2022) (Released: 4/24/2022) [Video] [Extra]
65. Time and Causality with Michal Eckstein [Video]
(recorded: 3/21/2022) (Released: 5/20/2022)
66. The Limits of Gravitation with James Owen Weatherall
(Recorded: 5/19/2022) (Released:6/26/2022) [Video][Extra]
67. Optical Gravity with Matthew Edwards
(7/20/2022) (8/14/2022) [Extra]
68. Quantum Resource Theories with Gilad Gour
(08/04/2022) (09/25/2022)
69. The Flavor Puzzle with Joe Davighi
(08/23/2022) (11/20/2022)
70. Path Integrals and Entanglement with Kenneth Wharton
(11/8/2022) (12/18/2022)
71. Inflation and the Primordial Graviton Background with Sunny Vagnozzi
(12/1/2022) (2/19/2023)
72. Born's Rule and Quantum Gravity with Antony Valentini
(03/03/2023) (2023/04/23)
73. Quantum Money with Jiahui Liu
(03/28/2023) (06/18/2023)
74. Stochastic Thermodynamics with David Wolpert
(05/10/2023) (07/09/2023)
75. Which Theories Have a Measurement Problem? with Nick Ormrod and Vilasini Venkatesh
(07/17/2023) (08/20/2023)
76. Undecidability and Theories of Everything with Claus Kiefer
(08/07/2023) (01/28/2024)
77. Maxwellian Ratchets with Alex Jurgens
(12/18/2023) (2024/03/31)
78. Quantum Machine Learning with Bruna Shinohara
(02/16/2024) (05/31/2024)

Coming Soon (in editing):


Decoherent Histories and Many Worlds with Philipp Strasberg

Upcoming Shows (recorded and unedited):



Scheduled Recordings:


Delayed


Ideas:

XX. Superdeterminism
XX. Time Reversal Violations
XX. Quantum Mechanics and Closed Timelike Curves




Podcast Home

Suggested Shows for Physics Frontiers

This post is a list of topics Randy and I have discussed, and is intended to be kept up to date in what should be an easily found spot so that I don't lose any more lists of possible show topics.

Please feel free to comment about topics you'd like to see discussed, especially if you have a reference for them.  Priority goes to references in refereed publications.

Also please feel free to suggest ways to narrow down or split the topics; many of these are too broad, especially when following a show format focuses on discussing one or two scientific papers.

Before suggesting a topic, make sure that we haven't already discussed it in the index. But, if there's something from the show that you'd like to hear more about, we're also willing to revisit topics, similar topics, and aspects of topics.

Possible topics:

Gravitation

Ghosts 1

Galileon 1

de Sitter Unvierse
Chameleon Fields 1 2
Bimetric Theories of Gravity
The Parameterized Post-Newtonian Framework
Post-Post-Newtonian Physics
Black Holes and Hawking Radiation
Mass, Gravitational Binding Energy, and Nuclear Mass Defect
massive gravity 1
Cosmological Constant 1
Gravitational Waves
More Experimental Evidence in Gravitation – Hafele Keating Exp., Precession of Perihelion of Mercury, Deflection of Starlight, time dilation, gravitational waves, frame dragging, etc (don't think we did enough on this one; some topics need more elaboration) Tests of Lorentz Invariance 1 2

Gravity Probe B and Gravitomagnetism 1 
Dark Energy Survey results 1
Unruh's Law
Bekenstein's Law
Bekenstein's Bound
Dark Matter 1
Inhomogeneous Cosmology 1
k-moufage 1 2
Unruh Effect

Quantum Mechanics

Consistent Histories Interpretation  (Griffiths, Omnes)
Multiple Worlds 1

Process Quantum Theory (David Finkelstein)

Nonlinear Schrodinger Equations and Wavefunction Collapse (still a thing?)

Rosenfeld Universe

Wheeler-Feynman Absorber Theory
Higgs Stuff

Wigner function and Weyl transforms –  transition from QM to classical
Double slit experiments with superconductors
Standard Model: What's Next? 1  (The squarkless gluiNO)
Stochastic Electrodynamics (time and quanta and GR) 1 2 3
Asymptotic Freedom
Quantum Gravity Oscillations

Vacuum

Mass for the Graviton 1

Space-Time Vacuum (specific theories?  which?)

Twistors ala Penrose 1 2
Superstring/Brane stuff (More specific?)
Non-commutative Geometry [Alain Connes] 1 2
Loop Quantum Gravity 1 2
Links between Loop Quantum Gravity and String Theory 1
Spin Networks 1
Holographic Principle  1 2 
Emergent Gravity (verlinde) 1
Qubits in Space 1
Consistent Histories and Relativity (Topos) (Christopher Isham) 1 2 3 4



Materials Physics

Bose-Einstein Condensation of Quasi-Particles
Massless Dirac Fermions (on the verge of exciton condensation)
Excitons in general.
Metamaterials (too broad)

Spin States in Quantum Fluid Analogy (analogy to what?)

Sonoluminescence and Sonofusion
Fusion Power
Superparamagentism
Thermionic Energy Harvesting

Uncategorized

Buesard-Poliwell Reactor (wuzzis?)

From Podomatic Comment:  Paul Corkum did a lecture entitled " a molecule takes a selfie". This was a lecture discussing his work with attosecond lasers. I'm not sure if you're familiar with this topic. It was fascinating in many respects. One being a new way of creating quantum computers. He only touched on that possibility during the lecture. 



People to Investigate:
Raphael Sorkin


Linder:

• Matters of time directionality in gravitation theory
• Theoretical basis for a solution to the cosmic coincidence problem

Hossenfelder:

• Phenomenological Quantum Gravity
  
• The Minimal Length and Large Extra Dimensions
  
• Running Coupling with Minimal Length
  

[Last Updated 7/24/2019]


Posted Shows

Speakable and Unspeakable in Quantum Mechanics by J.S. Bell

John S Bell is well known because of his development of what is known as Bell’s theorem – a proof showing that quantum entanglement means that local causality does not exist. This book, Speakable and Unspeakable in Quantum Mechanics, is a collection of 24 technical and semi-technical papers written by Bell on that topic. Bell’s outlook is partially physical and partially philosophical, making these papers quite interesting reading. At this point I would say it’s incredibly well-written and accessible, but I remember trying to read this as an undergraduate in the 90’s (when there were only 22 papers; I picked this one up because I lost the old one in a postdoc-postdoc transition) and having quite a lot of trouble with it.   Many of the papers seem to be addressed to philosophers, whereas others are standard physics papers. But most of them lay in the no man’s land between theoretical physics and the philosophy of science.

Many of Bell’s concerns run throughout the book, with slight variations from paper to paper. One of them is the incoherence of quantum mechanics:

So long as wave packet reduction is an essential component [of quantum mechanics], so long as we don’t know exactly how and when it takes over for the Schrödinger equation, we do not have an exact and unambiguous formulation of our most fundamental theory.

And that cannot stand. In order to have a reasonably scientific quantum theory, you should be able to express exactly when the wavefunction collapses. This is for several reasons, but what Bell really wants to know is this: if I measure the magnetic moment of an electron in a magnetic field, when does the electron decide which Sz state it is in (up or down)? Here are some options, which aren’t all of them:

• Does it do so when I turn on the static magnetic field?
• Does it do so when the microwave detection field reaches it?
• Does it do so when the response is felt by the field?
• Does it do so when the inductive current is generated in the pick-up coil?
• Does it do so when the microwave current passes through the diode detector?
• Does it do so when the detector is read by the multimeter?
• Does it do so after the multimeter output is analyzed by the computer?
• Does it do so when the analysis is displayed on the screen?
• Does it do so when the graduate student save the data?
• Does it do so when the Ph.D. looks at the charts?
• Does it do so when the paper is submitted or accepted?
• Does it do so when the paper is printed or earns an award? 

The Ph.D. gag was Bell’s favorite sarcastic line in these papers (judging by the number of re-uses), which were drawn from publications like Reviews of Modern Physics, Foundations of Physics, and so on, as well as invited lectures and symposia and book chapters. The important thing is that “measurement,” resulting in the collapse of the wavefunction, is an essential part of quantum theory, but it is not well defined theoretically. In Bell’s words:

The Landau-Lifshitz formulation…when applied with good taste and discretion is adequate for all practical purposes,” but it is “still ambiguous in principle about exactly when and exactly how the collapse occurs…”

 This is the same problem that led Schrödinger to torture analogical cats late at night in obscure journals.* Furthermore, Bell feels that “highly idealized ‘measurements’ should be replaced by an interaction of continuous, if variable, character.” This is essentially the thing that Aharonov explores in the book that started PhysicsFM off, Quantum Paradoxes.

Bell returns again and again to the Einstein-Poldosky-Rosen paradox (EPR, in case I use it again), its reformulation by Bohm into a more physical experiment, and finally, the Aspect Experiment which was the first practical test of the EPR paradox (the introduction to the new edition was written by Alain Aspect himself). The Aspect Experiment really turned Bell’s Theorem into an experiment, but Bell’s theorem was one that elucidated the true importance of what had been an almost forgotten result by Bohm – for the practical reason that no one could figure out how to do the experiment with 1950’s technology. The experiment took entangled photons (rather than electrons in Bohm’s experiment) and looked at their correlations. If you are looking at just up vs. down, clockwise vs. counterclockwise, and so on, then the correlations are fairly simple and come directly from conservation laws. However, when you tilt the detectors with respect to each other, the classical and quantum predictions diverge in such a way that an inspired and talented experimental physicist can tickle out the subtle differences. And when he did that experiment, Alain Aspect fount that quantum mechanics won and Bell’s theorem implied that local causality** was lost.

And at that point, “the concept of ‘reality’ [became] an embarrassing one for many physicists,” according to Bell.

Much of the book also discusses the interpretation of quantum mechanics. Bell looks at interpretations differently than most. In “Six Possible Worlds of Quantum Mechanics,” Bell categorizes theories into a 3 x 2 matrix. Bell’s three main categories are a no-nonsense measurement-based approach that doesn’t attempt to understand what is happening between measurements, that the wavefunction collapse is a real thing that happens to the quantum system and changes it, and that there are two or more subsystems in any quantum system that account for wave-particle duality (hidden variables). The “x2” breaks three interpretation into unromantic and romantic pairs. The romantic dual makes the interpretation interesting without adding any true meaning.

Thus, you have this practical approach being paired with the Bohrian Copenhagen interpretation where the universe holds complimentary views, macroscopic and microscopic, simultaneously. The collapse interpretation is paired with a Wignerian dualistic interpretation where it is the act of intelligent observation that collapses the wave function. The de Broglie-Bohm hidden variable interpretation is paired with Everett’s multiversal interpretation where each possible way in which something can happen does happen – just in another universe.

This is a very different view of Everett. Specifically, Bell’s interpretation of the many-worlds interpretation is to say that the many-worlds part is inessential. It is comforting, he says, to cosmologists (because it allows them to ignore the collapse of the universal wavefunction), but the additional “worlds” don’t add any new physics or understanding of what is happening. So, he says, if you strip the romantic multiverse from Everett, you have a (possibly different) nonlinear hidden variable theory than conjured by Bohm. I’ve never seen anyone else say that. To everyone else the many-worlds of the many-worlds interpretation are the point.

The most annoying gripe Bell makes is to continually harp on his theory of “Be-ables,” which would be a subset of quantum mechanical observables with certain properties that make things less weird. I don’t think it helps so much as he thinks, and it certainly wasn’t clear what the different was, other than terminology, the in the first half-dozen papers he mentioned them in.

In sum, I very much like this book. It is wonderfully written, physically insightful, and historically important. Many of the points, especially those from lectures, are very much Bell’s own thoughts and just his own thoughts that no one else thinks (beables), but even there he is trying to make points about the unsuitability of quantum theory without refinements that tell us what several of these mathematical objects that we use refer to in the physical world.

* Well, not really obscure. But still.

** “Local causality” might seem to be a strange combination of words, but it is what we normally think of as causality. First, if P causes Q, then P occurs before Q. Second, if P causes Q, it should be close enough to affect Q by special relativity. That is P is close enough to Q that light can travel from P to Q. It really is what you’d think about as causality in relativity theory.

Quantum Mechanics and the Particles of Nature by Anthony Sudbery

Quantum Mechanics and the Particles of Nature: an outline for mathematicians by Anthony Sudbery has been one of my favorite books on quantum mechanics since I was an undergraduate. This is despite the fact that I probably haven't read it from cover-to-cover ever in my life. It has, however, been a book that I have returned to again and again when looking at quantum mechanics.

The book is a curious amalgam of physics and mathematics. The meat of the book, chapters 2-4, 6 and 7, are formally sound, mathematical beasts proceeding axiomatically though their various topics and become highly algebraic, in the modern sense. Chapter 3, on "Quantum Dynamics" introduces Lie algebras and symmetry groups (SU(2) and all that), and Sudbery never looks back. Most of the book proceeds with a pattern of: (1) description of the physics, (2) a theorem that encapsulates the description, and (3) a rigorous proof of the theorem. This is incredibly abstract for an introduction to the subject -- unless you're an undergraduate mathematics student, which this work was designed for. Sudbery is not trying to teach solution techniques, but rather to express how the artifice of quantum mechanics fits together logically, and this is often as much the province of applied mathematics as it is theoretical physics. I don't know the demarcation between the two, you'll have to get an applied mathematician and a theoretical physicist that are working on similar subjects to draw the line for you.

[It is designed for the British student, not the American one. I went through many undergraduate textbooks from England that I found extraordinarily good that were far too dense for any of my students. This of course may not be true for all colleges, but it was my experience.]

I have a few advantages over the usual reader for a book like this: (1) I survived my graduate Quantum Mechanics courses, (2) I have a degree in "theoretical mathematics" (as opposed to applied mathematics), so I am familiar with proofs and the axiomatic style and have even taken a modern algebra course, (3) I have taught both 300-level modern physics, materials science, and nanotechnology courses to undergraduates, all of which include a reasonable amount of quantum mechanics (even if very basic), and of course, (4) I talk about these sorts of things on a podcast. SO the going this time was easy, even if it is a book that I've owned for twenty-five years.

I originally found this book in the college bookstore -- we had an extraordinary college bookstore when I was an undergrad -- and immediately fell in love with it upon reading the first chapter. I'm sure I got through the next two and the fifth, but I don't know how much of the others. The first chapter, "Particle and Forces" is as lucid a description of particle physics as I've ever read, and it's a description that stayed with me even after I forgot where it came from. I found it so clear and memorable that I thought it came from a popular book, and when in the 2000s I was looking for it, I kept looking in old Scientific American books (Particles and Forces: at the heart of the matter, it think it was; it seems to have disappeared) and Polkinghorne's The Quantum World (which hasn't disappeared, and I'd replace if it did) and similar books that I'd read a little bit earlier or later. I did not go back to a textbook that I was working in my spare time and didn't actually finish. The reason why I wanted to find it again is that I'd attempted this book before I took a quantum mechanics course, and it left a lasting impression on how I thought about the subject. I finally found out that this was the book I had been looking for, off and on, for ten years when I pulled it out to help me prepare lectures for modern physics when I taught it.

But the thing that brought me back to this book most of all was chapter 5, "Quantum Metaphysics." This talks about the quantum theory of measurement, The de Broglie-Bohm Interpretation of Quantum Mechanics and Quantum Interpretations in a rigorous way. Even as an undergraduate, I found this chapter entrancing. When I took a philosophy course on (philosophical) cosmology, I used this general approach to discuss how the various interpretations of probability relate to the interpretations of quantum mechanics (which not think is a lot harder than I thought it was then). You can get an idea about how clear this chapter is if you listen to Randy and I talk about section 5.5 as the intermission in our discussion of Aharanov and Rohrlich's Quantum Paradoxes. It is a touchstone that I come back to every time I think about how to think about quantum mechanics.

That said, I had some rough going with the problems in this book. One reason is that so many of them are proofs, and a problem I've always had with proofs is determining whether or not I've really justified every step. Too often I worry that this or that step is for a special case and isn't extensible to other cases, and so on -- and I'm not as lucky as a student because I don't have a red pen man to tell me what I did wrong or reassure me that I did it right (students may disagree about the desirability of the red pen men). Another is that I think Sudbery expects you to have actually learned things in a mathematics course, meaning that I have to reconstruct the methods for the more application-oriented problems. This makes the problems especially valuable, and I find myself writing up multi-page analyses of what I did to solve a problem to remind myself what I did -- something I haven't done since my graduate work.

The chapters in between these two, 2-4, dealing with "Quantum Statics", "Quantum Dynamics", and "Some Quantum Systems" are all equally rewarding, giving a mathematical picture of the basic ideas of quantum mechanics. The last two chapters are more difficult. "Quantum Numbers" and "Quantum Field Theory" go a little beyond what is presented in most undergraduate courses. They talk about isospin and hypercharge, the weak and strong forces, and grand unification. All very interesting stuff that satisfy the "particles of nature" part of the title more than the "quantum mechanics. The integration of abstract algebra, matrix mechanics, and differential equations is complete here, and if you let your guard down reading about quantum metaphysics, it will bit you in the ass. It did me. I had a harder time with these two chapters than Cohen's An Introduction to Hilbert Space and Quantum Logic (available at Walmart , apparently), which I read a few years ago. I won't look it up to see how many years ago because I don't want to get depressed.

So again, if you're looking for a memorable book on quantum mechanics, one that you'll grow into, pick up Anthony Sudbery's Quantum Mechanics and the Particles of Nature. Even if it did cost me two weeks wages when I was working at the drug store, I never regretted picking this gem up.

Sleeping Beauties in Theoretical Physics: 26 Surprising Insights by Thanu Padmanahhan:

Thanu Padmanahhan's book, Sleeping Beauties in Theoretical Physics is a great find.  It's reasonably accessible for a technical tome on theoretical physics, it has an interesting framework that makes the connections between chapters on very different subjects coherent, and it covers a number of interesting topics, including ones that I'd thought I'd have references to in other books but my knowledge of them must have come from papers.

The feature that Padmanabhan uses to categorize physics is similar to the one used by Griffiths in his Introduction to Electrodynamics:  a cube has eight vertices, and each of these vertices is a type of physical theory.  Each of the eight vertices has one of three Boolean values: gravitation, relativity, and quantum.  If the effect is accounted for, the value is on, if not, it's off.  The vertex where they are all off is Newtonian Mechanics (without gravity) and the far vertex is a Theory of Everything (or somesuch, he calls it something else). Turning gravity off is like setting the gravitational constant equal to zero, turning relativity off is like setting the speed of light to infinity, and turning quantum mechanics off is like setting Planck's constant equal to zero.

So, I could make a list of the different vertices:

(0,0,0) Newtonian Mechanics
(1,0,0) Newtonian Gravity
(0,1,0) Special Relativity
(0,0,1) Qunatum Mechanics
(1,1,0) General Relativity
(1,0,1) Gravitational Quantum Mechanics
(0,1,1) Quantum Field Theory
(1,1,1) Theory of Everything

The most interesting statement in the introductory chapter is that GQM is a theoretically unpopular zone, and very poorly developed, despite being one step away from the TOE and possibly holding clues to it (or, I assume it would, even if it's boring to the high-powered mathematical physics wizards).

Sleeping Beauties touches on most of these topics  (perhaps being short on the TOEs), showing up with some interesting takes on different phenomena, many of which I knew (rainbows and mirages, Thomas precession), many of which I didn't realize (the connection between Thomas precession and the Foucault pendulum), and many I had never touched on in my life (gravitational bending of the electric field).  The twenty-six chapters have at least twenty-five topics and are each worthy of attention, especially those where he's making connections either between the vertices of his scheme or between subjects that seem disparate (but really aren't).

But, it's not for people who avoid mathematics.

The very first chapter of content, "The Emergence of Classical Physics," is an example of this.  It tries to show how minimization principles in classical physics are explained by the limit of quantum mechanics.  This uses Wigner functions to show that the action is the phase of the quantum mechanical wave function, and so classical particles follow trajectories that follow paths where the wave function's phases isn't cancelled out by neighboring paths (just like in Feynman's QED: The Strange Theory of Light and Matter). Obviously, if you're not up on the quantum mechanics or the calculus of variations, you might not see why this is so awesome.  Speaking of QED,  chapter 17, "If Quantum Mechanics is the Paraxial Optics, Then..." does something similar by applying the results of chapter 16's investigation of the transformation from wave optics to ray optics to discuss how quantum particles move in quantum field theory.  Including why you must include trajectories for your particles that go backward in time.  It's all the same process.

That is probably the most obvious recurring theme in the book: by understanding how a theory can be derived from a more fundamental theory, mysterious things like minimization principles can be made to make sense.  That is, if you know how to turn off one of the switches, then you can better understand why things occur in the lower level theories -- and where those theories might lead you astray.

I therefore heartily recommend this book, and hope you both read and like it, but it does require an investment in mathematics to realize its physical returns.

["I therefore heartily recommend..." Looks like I've been writing too many recommendation letters, again.]

Screwing Up on Quantum Computing

Well, I screwed that up.

In the next Physics Frontiers podcast, recorded about six months ago (approx. 1/27), Randy and I talked about photonics and quantum computing. The papers we read were very interesting and we had a good time talking about them, although we got a little bit confused (as my memory serves me, I believe that happens in the next episode as well). During the episode I went off on three digressions that I probably shouldn't have: science fiction, quantum computing, and economics and politics. I cut out all of the economics and politics bits (again). I left in the quantum computing, and that's what this is about.

I first read a journal article and had discussions with reasonably technical people about quantum computing in the 90's, before 1998 and after 1995 based on the people I was talking to. The whole idea that someone could construct an algorithm for a computer of a type that didn't exist yet really intrigued me at that point, and since one of my majors was "theoretical mathematics" (I think that's what the track name for all that abstract algebra and number theory stuff was at that school), figuring things about like how to factor large numbers very quickly was interesting to me. The applications to cryptography, not so much. But, the state of the art at that time was a sheet of paper and a proof, so my marginal interest in the subject didn't really go anywhere.

I've occasionally looked in on quantum computing from time to time since then. I've read a couple of technical books on the subject, for example, and I'll read articles about it when I actually have time to crack open one or two the Science and Nature magazines that clutter up my office. So, although I'm certainly not an expert (I'm not an expert about anything we talk about on Physics Frontiers), I certainly didn't think anything really astounding had happened. I was pretty sure a couple of people had put together a small number of qubits in one or the other of the ultracold settings.

I had no idea that Google and IBM had them up and running.

That's what my phone told me today, about lunchtime.

I think that I had heard that quantum computer simulators existed, and so some of my comments were just thoughtless ("people who design algorithms for computers that don't exist and then mathematically prove they'll run correctly" or something like that), but the fact that IBM has a 17 bit quantum processor up and running and they're giving people beta access with an SDK for Python makes some of my comments laughable. And of course, Google's up to the same thing.

It's amazing how fast these things are developing.

Oh well. The episode's already short, so I won't edit anything more out. You can just hear me babble from the past about things in the future.

Now, how can I get into that IBM beta?

List of Requirements for Gravitational Theories

Here it is without fanfare. If you have any questions about any part of it, please comment in the comments:


-------------------------------

To be theoretically consistent and compatible with experiment, a theory of gravitation must:

1. Predict correct cosmological dynamics
1. Big bang nucleosynthesis
2. Produce the correct evolution of cosmological perturbations
1. Cosmic microwave background
2. Large scale structure
3. Have the correct weak-field limits
1. Reproduces Newtonian Mechanics
2. Predicts post-Newtonian experiments in weak field
3. Produces stable solutions
1. Matter-side instabilities (Dolgov-Kawasaki)
1. Ground states should be highly symmetric
2. Gravity-side instabilities
1. Stable de Sitter solutions
3. Stability of the first loop in quantum gravity
4. Stability in the face of inhomogeneous but isotropic perturbations
5. Black hole nucleation
4. Not contain any ghost fields
5. Admit a well-posed Cauchy problem
6. Reasonable theory of gravity waves