What have we learned since Feynman about unsolved problems he mentioned?

[dkotschessaa]

I've learned a great deal through the talks and books (most of which are transcribed talks or interviews) of Richard Feynman. But a lot has happened since then. One thing I've been wanting to do is go back and take note of any time he says "But we don't know such and such yet," or "such and such hasn't been tested." There are also talks he gives on, for example, nanotechnology, a field which was is it's infancy at his time and which he is often credited for starting and which is now a full blown field of study.

I'm wondering if anybody has any thoughts or ideas on some of the questions that were left unanswered in his time that are now answered, or some of the major developments you might have seen since then. Or if you were to dare to revise a Feynman lecture, what might need to be updated?

Approachable topic or too huge? I know there's a lot happening out there.

-DaveKA

 

[Vanadium 50]

Too huge. It's been almost 50 years.

 

[dkotschessaa]

I guess I'm looking for something specific but making it sound too general. I'm not looking for every development that's occurred, but perhaps some of the problems he was interested in or working on or mentioned. What I'll do is go through another lecture and take down a few statements of the kind of things I mean.

-DaveKA

 

[Cleonis]

Or if you were to dare to revise a Feynman lecture, what might need to be updated?

Interesting question.

I cannot think of an example.

For comparison, if lectures about geophysics from some lecturer would be preserved we would not find plate tectonics in them, as it was only in the 60's that a theory of plate tectonics was established.
Plate tectonics is so central to geophysics that any introductory lectures must describe it.
A series of lectures about geophysics would definitely have to be updated.

In physics a lot has been discovered, but I think pretty much all of it has been in the form of pushing the boundaries, exploring more and more terrain. Obviously the periphery has shifted a lot, but I think the homeland remained the same, so to speak.

The Feynman lectures have a particular scope, and I rather expect that within that scope the lectures are not outdated in any way.

 

[Mapes]

Since my background is in mechanics and materials, I skimmed through chapter 30 and a few later chapters.

The first thing I noticed is that Feynman often seems to be "winking" at us in the future. His offhand comments seem prescient. For example, in 38-1 he discusses Poisson's ratio, the familiar ratio between lateral contraction and axial elongation. He parenthetically mentions that "It is reasonable that [Poisson's ratio] should be generally positive, but it is not quite clear that it must be so." (Emphasis in original.) Now, Feynman must have known that's it's not forbidden for a material to expand laterally when stretched axially - despite how unusual that sounds - because Nature only requires Poisson's ratio $\nu$ to be greater than -1 and less than -1/2. (Reason: the bulk modulus $K=E/3(1-2\nu)$, shear modulus $G=E/2(1+\nu)$, and elastic modulus $E$ must all be positive in stable materials.) But it wasn't until decades later that Rod Lakes and other engineers started developing so-called http://en.wikipedia.org/wiki/Auxetics" that have a negative Poisson's ratio.

Many people know how Feynman essentially invented the fields and techniques of microfabrication and MEMS long before the technical capability existed, in his talk "There's plenty of room at the bottom." This Poisson's ratio example is, I think, another great example of Feynman noticing an interesting implication in his time that would be substantially developed in the future.

The second thing I noticed was one possible discrepancy in 30-7. Feynman discusses line dislocations and, in that context, mentions "tin cry," the sound that tin makes when it is quickly deformed. I believe, however, that this sound is now attributed to http://en.wikipedia.org/wiki/Crystal_twinning#Deformation_twins", a different deformation mechanism from dislocation glide, and one that predominates when slip systems for dislocations are scarce (as is the case for HCP tin). A minor point, to be sure, but appropriate for your question about how our knowledge has advanced since Feynman's time.

 

[dkotschessaa]

Excellent, Mapes. That's the kind of thing I was wondering about. Unfortunately I haven't had a chance to go back and look for more specific examples. Since I just started classes that might be a bit ambitious right now.