From: Robert J. Bradbury (bradbury@www.aeiveos.com)
Date: Fri Aug 27 1999 - 19:54:57 MDT
On Fri, 27 Aug 1999 hal@finney.org wrote:
>
> This passage does illustrate one of the technical flaws in the book,
> which is that the people see by light rays. In fact, from what I have
> read, it is not practical to focus light with a microscopic eye, and
> in fact organisms of that size do not use vision. Presumably nanotech
> devices will follow the same rules, and rely on touch and "taste"
> (chemical sensors) to navigate and sense their environment.
They do rely on "touch", they can also rely on sound (ultrasonic)
sonar which works quite well. I think you may want to re-examine
some of use of light however. In biology there is a lot of use
of confocal and I think some use of near-field microscopy. As
I understand it, these do not have the same restrictions as
vision that requires "focusing" light rays. Clearly the "eyes"
of the explorers shrunk to that degree would not work normally.
Perhaps one of our physicists would like to comment on the
restrictions of these methods.
There is a small discussion of the use of light for laser communications
in Nanomedicine. This summer I went round-n-round with Robert Freitas,
my father (a laser physicist) and eventually a BU astronomer about the
problem of the absorption or emission of a frequency of light by an
emitter/absorber that is smaller than the wavelength. The topic
is an important for both communication in vivo as well as because
the change in the black-body curves between "dust" and "macro-scale"
emitters is the feature pointed out by Kardashev required to distinguish
Dust-envoloped stars from Dyson Shells (a feature very near to my heart!).
Robert finally won the absorption argument when he pointed out that
a single chlorophyll molecule has a size much less than the wavelength
of the light it absorbs. The BU astronomer gave me a reasonable
explanation about the dust emission [if anyone wants it I can send
it to them].
> This is 5 million miles
> per hour at the scale of the ship! Asimov does not really discuss the
> difficulties of navigating among cells jostling about at this speed,
> but he does realize that there is a paradox here. Red cells and other
> residents of the blood bump into the walls and each other without damage,
> but we know that bumping things at five million mph will cause great
> damage.
Robert F. has a a fairly extensive discussion of navigation problems
in NM, especially vis-a-vis the different flow rates depending on
distances from the artery walls. It turns out that this issue
plays an important role on the sizes and shapes nanobots can have.
>
> But from the point of view of a hypothetical nanomedical device, this
> artistic device must be discarded. The nanomachine would not be any
> less robust than the cells surrounding it, and indeed if made of rock
> as proposed, it should be much stronger. Further, the appropriate time
> scale for its actions will be on the order of tenths of microseconds.
Actually you would be surprised at the strengths of some of the materials
in your body. There is an extensive table of these in NM. The time
scales vary over a very wide range depending on a nanobots purpose.
Robert
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