Physicists can't just say, "What we do is beyond your comprehension, foolish mortal" ... "if you really understand something in physics you should be able to explain it to your grandmother." ... I was shocked to discover it wasn't true.

This seems inconsistent with the rest of what your post, which argues that you can explain physics to grandmothers or Congressmen, as long as you have the opportunity to iterate back and forth to verify understanding on both sides. While the practical implications of both may be the same ("It's not worth the time to try"), there's a big difference between "not worth doing" and "impossible".

It's like the way someone said that good thinking is to hold two diametrically opposite thoughts at the same time but still continue with whatever we're doing.

When asked to explain in a few words what he had accomplished, Feynman said, "Buddy, if I could tell you in a minute what I had done, it would not be worth the Nobel Prize." Though not exactly it's kind of contradictory to what he said about explaining Physics to your grandmother. He also says he wasn't able to explain what he did to his father.

Feynman said "The first principle is that you must not fool yourself, and you are the easiest person to fool." In a book 'Some time with Feynman', when he talks about working on problems he says you have to fool yourself. It's in a different sense. He says that when you are attacking a formidable problem you may doubt how you'll be able to solve something where others haven't been able to. But then you fool yourself saying you're kind of special and you'll be able to solve and keep working on it.

Usually, what is said taken out of context or only one side of it is taken, as most people want to take things to be either black or white, when most things are in varying shades of gray.

over the course of months

Doubtless. But you may be able to pare it down to something at the same time manageable in a short time and yet neither trite nor vague. I think Feynman did this in the book QED.

There are indeed cases where it does take someone who understands the subject, months of iteration to explain it. But when someone says, "I can't explain it to you," that can either mean:

a) the time to do so is genuinely cost-prohibitive or the listener very stupid

OR

b) the would-be explainer doesn't really understand it and has been operating in a sort of "Chinese room", manipulating symbols without understanding their connection to everything else.

In my experience, a) is the exception, not the rule.

We must not overlook the number one reason something is difficult to explain- that is that what one is trying to explain is nonsense. (this is not specifically directed at anyone posting here)

douglas: I think that counts as a subset of my b), in that if it's nonsense, the would-be explainer doesn't understand it.

Silas- yes, good point, but an important subset in that the person attempting to do the explaining often overlooks it. When was the last time you were having trouble explaining or understanding something and you asked, "Is this just nonsense?"

douglas: Actually, for me that happens quite a bit when on the "having trouble understanding" side, but I'm just cynical like that. For example, I interrogate people in online discussions about the difference in meaning between "Sony's problem was setting the PS3's price point too high" and "Sony's problem was setting the PS3's price too high." (Yes, I know what a price point is, but it doesn't seem to affect their statement.)

OTOH, when on the "having trouble explaining" side, I often do find gaps in my knowledge that force me to concede I don't really understand the topic, in that sense, "overlooking" the possibility it's nonsense.

douglas: Actually, for me that happens quite a bit when on the "having trouble understanding" side, but I'm just cynical like that. For example, I interrogate people in online discussions about the difference in meaning between "Sony's problem was setting the PS3's price point too high" and "Sony's problem was setting the PS3's price too high." (Yes, I know what a price point is, but it doesn't seem to affect their statement.)

OTOH, when on the "having trouble explaining" side, I often do find gaps in my knowledge that force me to concede I don't really understand the topic, in that sense, "overlooking" the possibility it's nonsense.

Silas- I like your example of interrogation. You rabble rouser, and I say that with utmost respect and love. I've had to throw out a couple of deeply cherished beliefs in my time, and it can be brutal. I try to go back to the question, "What does the evidence indicate?", and then I have to be willing to look at evidence that I had neglected because I was to fixed or bias to consider it. I must admit, when I look at the state of the world, I don't have a hard time believing that much of what currently passes as sense is actually nonsense. Ya know?

For the record, Sony's biggest problem is the lack of a killer app for the PS3. When Final Fantasy 13 or Metal Gear Solid 4 are finished, we might just see actual PS3 sales. (Or so I believe, extrapolating from my own behavior; I don't buy a system unless there is a game for it that I want to play.)

I like to think I'm pretty good at explaining things; it is easier to explain when you have back-and-forth feedback than when you're writing a textbook (because when somebody doesn't get something, you can keep throwing words at the topic until something sticks) but sometimes all you have is one shot...

I had a similar run-in when I tried to go through the Cantor Diagonal Argument with a bunch of gifted 13-year-olds. I thought I had them following right through to the end, but when I came to the conclusion, they cried: "But infinity is infinity!"

Not quite as concrete as Bayesian inference, but it's still a difficult concept. Some of those students would probably never think of that lecture again, and some, after some years of ruminating and/or majoring in math, would finally understand what I was getting at. After having that run-in, I actually switched over to teaching conditional probability (in particular, the Mony Hall problem) as my "fun" math lecture.

But you may be able to pare it down to something at the same time manageable in a short time and yet neither trite nor vague. I think Feynman did this in the book QED.

QED was one of my favorite books when I was nine years old. I was shocked when I grew up and read The Feynman Lectures and realized that QED hadn't taught me a single bit of physics.

How do you know QED didn't teach you a single bit of physics?

1. If you assimilated the corresponding bits of the Feynman lectures (or any other physics you encountered along the way) at all more easily for having read QED at age 9, then it did teach you some physics, albeit in a sense hard to quantify.

2. If reading its hand-waving stuff about light taking all possible paths at once increased the probability you'd have assigned to (say) something like the Bohm-Aharonov effect if anyone had thought to ask you how likely you thought it, then it did teach you some physics, even in the "Technical" sense. (Whether more or less than one bit depends on how much that probability increased.)

If having notions like path integrals, phase, and stationary action waved at you unintimidatingly didn't push your thinking about physics in the direction of clearer understanding, then it seems that you were either (1) already implausibly acquainted with them for even an extraordinarily bright 9-year-old, or (2) implausibly impervious to such things for someone capable of reading and enjoying QED. Of course, something could be implausible to me but still true.

I see QED as a bit like stating the axioms of a mathematical theory. You can, in principle, derive the whole theory from the axioms, but in practice it takes generations of ingenuity to come up with the tools to do that. We take courses in mathematics not just to learn the axioms, but also, and primarily, to learn the vast library of tricks that let us do something useful with the axioms.

Similarly, I remember my first or second physics course, either mechanics or electromagnetism. The inside of the cover had, as I recall, all the "axioms", the fundamental laws from which everything could be derived. Those fit inside the cover. But, just as in a mathematical subject, the main body of the subject was the library of tricks that let us actually make specific predictions from those fundamental laws.

Feynman, as I recall, was very up front in QED about what it did and did not contain. He was explicit about it not including the tricks that we would need to learn to apply the fundamental principles to real predictions about real situations.

However, I would not really call the book "vague" or even "hand-waving", any more than I would call the inside cover of my physics textbook "hand-waving" or even "not physics". It was seriously lacking, yes, admittedly so. But not at all in the way that, say, quantum mechanics popularizations typically are. Popularizations include neither the axioms (fundamental laws) of the theory, nor the tricks, but instead are filled with metaphor and impressionistic talk and not a small amount of pop philosophy. Not the same thing at all as QED (I mean QED the book, not the subject of quantum electrodynamics).

You know, I'm starting to suspect you were right the first time.

If I wanted to explain all these marvelous ideas I had, I'd have to go back, and back, and back. I'd have to start with the things I'd figured out before I was even thinking about Artificial Intelligence, the foundations without which nothing else would make sense.

As much as I am enjoying the sequences, I can tell you right now that they are not written in a way that makes them very accessible to the layperson. The Simple Truth is pretty solid, but the rest of the foundations still haven't come into focus for me. I can see the buildings and rooftops, but I still don't feel like I have the foundations.

I am picking up more than enough knowledge and understanding to start filling the gaps myself but I still stop and wonder how tab A fits into slot B. Eventually it clicks and when it does I know how I could have said it to my past self in only a few sentences. But this is an unfair comparison for me to make against you.

The only reason I bring this up is because you seem very interested in explaining your ideas. You are doing great but I don't think you are quite where you want to be yet. I have no problem with the quality of your work but, if you are anything like me, you would have a problem with it if you were given the chance to see it through my eyes. I suspect you would be surprised and say, "Oh, wow, that isn't what I intended at all."

This is why I have been adding my thoughts on the older articles as I read them. I am hoping that that somehow my first exposure can be useful feedback for you. (Well, that and talking about it helps me remember things more accurately.)

In any case, thank you very much for the hard work. I am at 140 of 584 on the list and am looking forward to the rest.

Give students a short intelligence report, have them underline all expressions of uncertainty, then have them express their understanding of the report by writing above each expression of uncertainty the numerical probability they believe was intended by the writer of the report. This is an excellent learning experience, as the differences among students in how they understand the report are typically so great as to be quite memorable.

In one experiment, an intelligence analyst was asked to substitute numerical probability estimates for the verbal qualifiers in one of his own earlier articles. The first statement was: "The cease-fire is holding but could be broken within a week." The analyst said he meant there was about a 30-percent chance the cease-fire would be broken within a week. Another analyst who had helped this analyst prepare the article said she thought there was about an 80-percent chance that the cease-fire would be broken. Yet, when working together on the report, both analysts had believed they were in agreement about what could happen.^141^ Obviously, the analysts had not even communicated effectively with each other, let alone with the readers of their report.

...I personally recall an ongoing debate with a colleague over the bona fides of a very important source. I argued he was probably bona fide. My colleague contended that the source was probably under hostile control. After several months of periodic disagreement, I finally asked my colleague to put a number on it. He said there was at least a 51-percent chance of the source being under hostile control. I said there was at least a 51-percent chance of his being bona fide. Obviously, we agreed that there was a great deal of uncertainty. That stopped our disagreement. The problem was not a major difference of opinion, but the ambiguity of the term probable.

--Heuer, Psychology of Intelligence Analysis, chapter 12 (very good book; recommended)

Richard Feynman once said that if you really understand something in physics you should be able to explain it to your grandmother.  I believed him.

Curiously enough, there is a recording of an interview with him where he argues almost exactly the opposite, namely that he can't explain something in sufficient detail to laypeople because of the long inferential distance.