Quantum Mechanics: The Theoretical Minimum

Physics lectures are of three types according to this anecdote of Niels Bohr:“A young man was sent by his own village to a neighboring town to hear a great Rabbi. He was to bring back a report in which all could share. When he returned he told his eagerly awaiting fellow citizens: “The Rabbi spoke three times. The first was brilliant; clear and simple. I understood every word. The second was even better, deep and subtle. I didn’t understand much, but the Rabbi understood it all. The third was by far the finest; a great and unforgettable experience. I understood nothing and the Rabbi himself didn’t understand much either.”Professor Susskind (1) of Stanford University is far ahead of Bohr’s Rabbi – he understands it all. To Susskind “Everything is easy in Quantum mechanics” (2). So easy that he always “destroys his lecture notes to prevent his lectures being the same next time” (3).“Given enough time, with no distractions, you could use [his book (4)] to eventually master Quantum Mechanics” (5). An attractive challenge as the book is only 350 pages.Only 350 pages perhaps, but it assumes you are versed in Classical Mechanics (which you aren’t). Realistically, you need Susskind’s first book (6) plus a preliminary YouTube series of 9 x 1.5 hour lectures on Quantum Entanglement (7). Plus you will need assistance from 10 x 1.5 hour YouTube lectures (8) in parallel with the book. Still a realistic challenge given the results (9).According to Susskind, Quantum Mechanics is much more fundamental that classical physics. “As far as we know quantum mechanics provides an exact description of every physical system” (10). Moreover, “the logic of classical mechanics of Newton is incorrect, the underlying structure is inadequate” (11). Not only should we logically learn quantum mechanics first, it is technically much easier than classical mechanics (12).Susskind lives in a Quantum Mechanical world, the real world, deploring our choice of units that makes Avogadro’s Number (13) and the speed of light (14) ridiculously large and Planck’s Constant (15) ridiculously small. He blames historical chemists who measured things by comparison to the size of their hands. Choosing units appropriate to the sub-atomic scale, such as making Planck’s constant = 1, would make his world feel normal.For those who enjoyed science and mathematics to a reasonable level (16) but who had to follow a career to survive in the world, this is more an opportunity than a challenge. Not that it is not a challenge! It is a mind tingling challenge. A way of familiarizing with the real subject with the actual equations - not a popularization.The fascinating history of Archimedes, Johannes Kepler and Isaac Newton fitting an ellipse to the Mars orbit and concluding with the Law of Gravity is only the half of it. Understand how the mathematics of vectors and matrices are fitted to the real world being Quantum Mechanics. Like Archimedes the French mathematicians Joseph-Louis Lagrange, Siméon Poisson, and the Irish mathematician William Rowan Hamilton were nice enough to magically or inadvertently provide the mathematics a long time prior to make it possible. Why this mathematical physics works no one knows, neither Susskind nor the Rabbi.One moment you feel like like Niels Bohr’s student in his third lecture then you are stunned when Professor Susskind commences a short summing-up by saying, in a matter-of-fact way, that an equation derived in the lecture is called Schrödinger’s equation (17)! Or that the postulates he has been talking about are Dirac’s postulates of Quantum Mechanics formulated in the 1930’s which have never needed to be replaced (18). Or, early on, describes a vector and says that it is Dirac’s notation (19).Finally, Susskind is to be applauded. If this can be done with Quantum Mechanics, it can be done in any subject of Physics or Mathematics or any other area of study. There must be a value in doing this (other than ex-auto workers retraining themselves for jobs at CERN) as the work will inevitably not continue to be publically funded unless tax-payers have some idea what it is.PS: The advantage of a career outside Physics is to know “you always write the minutes before the meeting”. Bohr’s student may finally have understood so little that he was not game to return to his village. As a precaution I have written this travelogue well before completing the trip.(1) Leonard Susskind is the Professor of Theoretical Physics at Stanford University, and director of the Stanford Institute for Theoretical Physics. His Wikipedia entry is a good read in itself.(2) Lecture 9, Quantum Entanglements(3) Lecture 9, Quantum Entanglements(4) Quantum Mechanics – The Theoretical Minimum by Leonard Susskind & Art Friedman. The “minimum” means just what you need to know to proceed to the next level.(5) Science News: quote from back cover of Susskind’s book.(6) The Theoretical Minimum – What you Need to Know to start doing Physics Leonard Susskind and George Hrabovsky.(7) Quantum Entanglements, Susskind, Stanford University, YouTube. It seems that the old unadorned lecture format has stood the test of time with only the whiteboard and marker (when it works) replacing the blackboard and chalk.(8) Modern Physics, Quantum Mechanics, Susskind, Stanford University, YouTube.(9) Well, you did not expect to read 350 pages straight cover to cover and then know Quantum Mechanics, did you? This is a 6 to12 month project – reading, watching YouTube lectures, frantic note taking hoping you might understand it later (the iPad pause button being a luxury unavailable in university lectures), revision, pushing forward, retreating, then finally with your newfound knowledge applying for a job at CERN.(10) Page xix.(11) Lecture 1, Quantum Mechanics(12) Page xx.(13) Avogadro's number, number of units in one mole of any substance (being its molecular weight in grams) ≈ 6×1023.(14) Speed of Light: c ≈ 3×108 m/s.(15) Planck’s Constant: The energy contained in a photon, the smallest possible ‘packet’ of energy in an electromagnetic wave ≈ 6.6x10-34 joule-seconds.(16) Realistically, for those who think they know classical Newtonian Physics and remember studying vectors and matrices, exponentials such as eiθ = cosθ + isinθ and who once knew the expansion of sin(θ + Φ).(17) Lecture 9, Quantum Entanglements(18) Lecture 4, Quantum Mechanics(19) Page 11, Quantum Mechanics – The Theoretical MinimumMalcolm Cameron8 May 2016

In good shape

I've been working through this book. I learned quantum in my undergrad years from the Tannoudji book. It was very dry and I spend most my time trying to figure out what he (Tannoudji) was trying to say, THEN figure out whether I can prove it, etc. Funny how really smart people can create creatively new ways to make stuff more difficult through weird explanations.This is not so with Susskind. Susskind writes like Feynman: clear explanations on complex topics. I assume he's a native english speaker, as his tone is very colloquial and uninimtidating. He assumes the reader knows nothing of quantum and explains things in bit-sized pieces which are easy to digest. He rarely says things like "well OBVIOUSLY this flows from this" (when the things are so obvious).Anyways, the book is a bit unorthodox. It starts off talking about spin states and vector spaces. This is different than the typical quantum books that start off with talking about solving the Schrodinger equation. Which, now that I think about it, isn't really a great place to start. It's a wave equation that's only once-piece of the bigger picture.The result is a book that has a very gradual learning curve.That said, readers still need a bit of math background if they want to get through this book. I'd say at least a decent understanding of complex numbers and matrix algebra are a prerequisite. Both those subjects are thoroughly explained in places online (Khan Academy) for free.SOLUTIONS:I read another reviewer rate the book low because there is a lack of worked out solutions. That I disagree with.Google search "Quantum theoretical minimum solutions" and they will pop up. There are several unofficial sites out there that have answers to the solutions. For instance, google search "the uncertain biscuit quantum" or "chris brittain quantum". The solutions are out there.Also, on that note, the problems in this book are few..but concise and great. Very on-point.Regarding the reviewers who are rating this book low b/c it's too difficult. That's not really a good reason to rate a QUANTUM book low. For two reasons (1) it's a quantum book for christsakes. it is by far the most math-friendly book written on the subject. reading about quantum mechanics without math is not "doing" physics..it's just cataloging knowledge (e.g. stamp collecting), (2) how can you rate a book low if you don't understand it? What are your reviewing parameters?If you have a little complex number knowledge and rudimentary matrix operations (e.g. matrix multiplication, etc.) under your belt, you'll be fine.The Kindle version is fine. That's what I bought (I have a paper copy too). I prefer the kindle version because I can read it on my phone while waiting in line, etc. The equations come out fine (I'm not sure what the other revieweres were complaining about, I'm reading it on my iPhone 5s just fine.)If you know nothing of quantum and want to learn, I highly HIGHLY recommend this book.