Feynman’s Lectures: A Survivor’s Guide

A few days ago, I mentioned I felt like writing a new book: a sort of guidebook for amateur physicists like me. I realized that is actually fairly easy to do. I have three very basic papers – one on particles (both light and matter), one on fields, and one on the quantum-mechanical toolbox (amplitude math and all of that). But then there is a lot of nitty-gritty to be written about the technical stuff, of course: self-interference, superconductors, the behavior of semiconductors (as used in transistors), lasers, and so many other things – and all of the math that comes with it. However, for that, I can refer you to Feynman’s three volumes of lectures, of course. In fact, I should: it’s all there. So… Well… That’s it, then. I am done with the QED sector. Here is my summary of it all (links to the papers on Phil Gibbs’ site):

Paper I: Quantum behavior (the abstract should enrage the dark forces)

Paper II: Probability amplitudes (quantum math)

Paper III: The concept of a field (why you should not bother about QFT)

Paper IV: Survivor’s guide to all of the rest (keep smiling)

Paper V: Uncertainty and the geometry of the wavefunction (the final!)

The last paper is interesting because it shows statistical indeterminism is the only real indeterminism. We can, therefore, use Bell’s Theorem to prove our theory is complete: there is no need for hidden variables, so why should we bother about trying to prove or disprove they can or cannot exist?

Jean Louis Van Belle, 21 October 2020

Note: As for the QCD sector, that is a mess. We might have to wait another hundred years or so to see the smoke clear up there. Or, who knows, perhaps some visiting alien(s) will come and give us a decent alternative for the quark hypothesis and quantum field theories. One of my friends thinks so. Perhaps I should trust him more. ūüôā

As for Phil Gibbs, I should really thank him for being one of the smartest people on Earth – and for his site, of course. Brilliant forum. Does what Feynman wanted everyone to do: look at the facts, and think for yourself. ūüôā

Re-writing Feynman’s Lectures?

I have a crazy new idea: a complete re-write of Feynman’s¬†Lectures. It would be fun, wouldn’t it? I would follow the same structure‚ÄĒbut start with Volume III, of course: the lectures on quantum mechanics. We could even re-use some language‚ÄĒalthough we’d need to be careful so as to keep Mr. Michael Gottlieb happy, of course. ūüôā What would you think of the following draft Preface, for example?

The special problem we try to get at with these lectures is to maintain the interest of the very enthusiastic and rather smart people trying to understand physics. They have heard a lot about how interesting and exciting physics is‚ÄĒthe theory of relativity, quantum mechanics, and other modern ideas‚ÄĒand spend many years studying textbooks or following online courses. Many are discouraged because there are really very few grand, new, modern ideas presented to them. The problem is whether or not we can make a course which would save them by maintaining their enthusiasm.

The lectures here are not in any way meant to be a survey course, but are very serious. I thought it would be best to re-write Feynman‚Äôs Lectures to make sure that most of the above-mentioned enthusiastic and smart people would be able to encompass (almost) everything that is in the lectures. ūüôā

This is the link to Feynman’s original Preface, so you can see how my preface compares to his: same-same but¬†very¬†different, they’d say in Asia.¬†ūüôā

[…]

Doesn’t that sound like a nice project? ūüôā

Jean Louis Van Belle, 22 May 2020

Post scriptum: It looks like we made Mr. Gottlieb and/or MIT very unhappy already: the link above does not work for us anymore (see what we get below). That’s very good: it is always nice to start a new publishing project with a little controversy. ūüôā We will have to use the good old paper print edition. We recommend you buy one too, by the way. ūüôā I think they are just a bit over US$100 now. Well worth it!

To put the historical record straight, the reader should note we started this blog before Mr. Gottlieb brought¬†Feynman’s Lectures¬†online. We actually wonder why he would be bothered by us referring to it. That’s what classical textbooks are for, aren’t they? They create common references to agree or disagree with, and why put a book online if you apparently don’t want it to be read or discussed? Noise like this probably means I am doing something right here. ūüôā

Post scriptum 2: Done ! Or, at least, the first chapter is done ! Have a look: here is the link on ResearchGate and this is the link on Phil Gibbs’ site. Please do let me know what you think of it‚ÄĒwhether you like it or not or, more importantly, what logic makes sense and what doesn’t. ūüôā

Gottlieb

Math, physics and reality

Pre-scriptum (dated 26 June 2020): This post did not suffer from the attack by the dark force‚ÄĒwhich is good because I still like it: it is delightfully short but significant. In fact, it could probably serve as the summary of all of my deconstructions of the so-called mysteries in quantum physics‚ÄĒin particular my deconstruction of Feynman’s derivation of the Hamiltonian matrix.

Original post:

This blog has been nice. It doesn’t get an awful lot of traffic (about a thousand visitors a week) but, from time to time, I do get a response or a question that fires me up, if only because it tells me someone is actually¬†reading what I write.

Looking at the site now, I feel like I need to reorganize it completely. It’s just¬†chaos, right? But then that’s what gets me the positive feedback: my readers are in the same boat. We’re trying to make sense of what physicists tell us is reality. The¬†interference model¬†I presented in my previous post is really nice. It has all the ingredients of quantum mechanics, which I would group under two broad categories: uncertainty and duality. Both are related, obviously. I will not talk about the¬†reality¬†of the wavefunction here, because I am biased: I firmly believe the wavefunction represents something real. Why? Because Einstein’s E = m¬∑c2¬†formula tells us so: energy is a two-dimensional oscillation of mass. Two-dimensional, because it’s got¬†twice¬†the energy of the classroom oscillator (think of a mass on a spring). More importantly, the real and imaginary dimension of the oscillation are both real: they’re perpendicular to the direction of motion of the wave-particle. Photon or electron. It doesn’t matter. Of course, we have all of the transformation formulas, but… Well… These are¬†not¬†real: they are only there to accommodate¬†our¬†perspective: the state of the observer.

The distinction between the¬†group¬†and¬†phase¬†velocity of a wave packet is probably the best example of the failure of ordinary words to describe reality: particles are not waves, and waves are not particles. They are both… Well… Both at the same time. To calculate the¬†action¬†along some¬†path, we assume there is some path, and we assume there is some particle following some path. The path and the particle are just figments of our mind. Useful figments of the mind, but… Well… There is no such thing as an infinitesimally small particle, and the concept of some one-dimensional line in spacetime does not make sense either. Or… Well… They do. Because they help¬†us¬†to make sense of the world. Of what¬†is, whatever it is. ūüôā

The mainstream views on the physical significance of the wavefunction are probably best summed up in the Encyclopædia Britannica, which says the wavefunction has no physical significance. Let me quote the relevant extract here:

“The¬†wave function,¬†in quantum mechanics, is a variable quantity that mathematically describes the wave characteristics of a particle. The value of the wave function of a particle at a given point of space and time is related to the likelihood of the particle‚Äôs being there at the time. By analogy with waves such as those of sound, a wave function, designated by the Greek letter psi, ő®, may be thought of as an expression for the amplitude of the particle wave (or de Broglie wave), although for such waves amplitude has no physical significance. The square of the wave function, ő®2, however, does have physical significance: the probability of finding the particle described by a specific wave function ő® at a given point and time is proportional to the value of ő®2.”

Really? First, this is factually wrong: the probability is given by the square of the absolute value of the wave function. These are two very different things:

  1. The square of a complex number is just another complex number:¬†(a¬†+ ib)2¬†= a2¬†+ (ib)2¬†+ 2iab = a2¬†+¬†i2b2¬†+ 2iab = a2¬†‚Äď b2¬†+ 2iab.
  2. In contrast, the square of the absolute value always gives us a real¬†number, to which we assign the mentioned physical interpretation:|a¬†+ ib|2¬†= [‚ąö(a2¬†+ b2)]2¬†=¬†a2¬†+ b2.

But it’s not only position: using the right operators, we can also get probabilities on momentum, energy and other physical variables. Hence, the wavefunction is so much more than what the¬†Encyclop√¶dia Britannica¬†suggests.

More fundamentally, what is written there is philosophically¬†inconsistent.¬†Squaring something – the number itself or its norm –¬†is a mathematical operation. How can a mathematical operation suddenly yield something that has physical significance, if none of the elements it operates on, has any. One cannot just go from the mathematical to the physical space. The mathematical space describes¬†the physical space. Always. In physics, at least. ūüôā

So… Well… There is too much nonsense around. Disgusting. And the¬†Encyclop√¶dia Britannica¬†should not just present the mainstream view. The truth is: the jury is still out, and there are many guys like me. We think the majority view is plain wrong. In this case, at least. ūüôā