[extropy-chat] Re: An Error in Nanosystems!

[Hal Finney]

Chris Phoenix writes:

> Which is easier to believe: that Drexler is an idiot who doesn't know 
> what "relatively prime" means, or that he was thinking faster than he 
> was writing and meant to say that *one-half* of the bearing (3 vs 7) 
> represented a relatively prime combination?

I wouldn't say that someone was an idiot just for making this mistake.
Maybe this text originally referred to an earlier version of the design,
where the numbers actually were relatively prime, and when the design
got changed, nobody noticed that the phrasing was now inaccurate.
The point is that the guy can make mistakes, just like anybody else.

> If the whole bearing were 
> relatively prime, it would wobble as the region of alignment traveled 
> around the axis.  If there are two opposing regions of alignment, it 
> won't wobble--but that requires that the numbers be mutually divisible by 2.

I don't know about that: see figure 10.19, which has 6 inside and
11 outside, relatively prime.  Drexler discusses this bearing in some
detail in 10.4.7e, and he doesn't say anything about wobble (although he
is worried about possible reconstruction of the inside piece).  It was
while I was reading about this bearing that I was led to figure 1.1,
the improved version.

Or see
http://groups.google.com/groups?start=10&hl=en&lr=&ie=UTF-8&oe=UTF-8&group=sci.nanotech&selm=Jul.26.00.00.42.1993.27440%40planchet.rutgers.edu&rnum=20 ,
a Usenet posting by me in 1993, in which I refer to some Extropians list
debate which Drexler got involved with(!), in which he recommended
analyzing a bearing with 19 and 27 units in the inner and outer rings.

> BTW, do you have the hardcover Nanosystems?  My softcover version has a 
> different caption: "Note the six-fold symmetry of the shaft and 
> fourteen-fold symmetry of the surrounding ring; with a least common 
> multiple of 42, this combination yields..."

No, I didn't even know there was a hardcover version.  I bought the
book shortly after it came out and I have a first printing, I believe
(evidenced by the "10 9 8 7 6 5 4 3 2 1" on the bottom of the copyright
page).

But I am genuinely amazed to learn that Drexler is changing and revising
the book with subsequent printings!  I had never heard this before.  What
else has changed between my version and the most recent one?  Is there a
list anywhere?  Don't people like me who bought an early version deserve
to know about what other material Drexler may have revised?

It is common practice in the academic community to publish an error list
that provides this information.  Silently revising the book to erase
errors is not enough for those who are relying on earlier versions.
I would hate to think that Drexler is hiding the fact that his book had
errors in order to promote that absurd and counterproductive myth that
it is perfect!  For an important and foundational book like Nanosystems,
not providing errata is a lapse which should be corrected.

Hal