Re: Nanotech..Alternate Scenario

Carl Feynman (
Tue, 15 Jul 1997 10:48:44 -0400

At 06:12 PM 7/14/97 -0400, wrote:

>But what about a variation on the Penning Trap?...In a zero-g enviroment
>could not atoms be positioned appropriately via laser beams?...Wouldn't this
>be much easier to build than the other varients?

The problem is that laser beams can only maneuver non-super-cold atoms with
a precision on the order of a wavelength of light, which is 2000 times
larger than an interatomic spacing. The hold provided by the laser beam is
very 'soft'; it doesn't constrain the position of the atom sharply enough to
permit precise assembly in the presence of thermal noise at any temperature
above a millionth of a Kelvin. And below a millionth of a Kelvin, every
atomic bond you form will release enough energy to overheat a billion atoms.
You'll have to wait for them to stop jiggling before you make another bond.
I don't think it would be very efficient. But somebody should try it. It
won't provide a cheap mass-production method, but it might suffice to make
the first assembler.

On these scales gravity is negligible; we won't need zero-g.

Anders writes:
>No, since you need to keep both the building blocks and the object
>under construction floating together. So when you try to push an atom
>in place, the laser will also push at the object; it *might* be
>possible to solve the control problem, but I doubt it.

Actually, the closer an object is in size to a wavelength of light, the
easier it is to push around. For bacteria that are close to one wavelength
across, you can yank them around, hold them in place, etc, with a cheap
desktop laser apparatus. I don't think holding the work-in-progress will be
hard, at least compared to holding the atoms you're adding to it.