From: sl25@cus.cam.ac.uk (Steve Linton)
Subject: Re: Anybody? Anybody? Class?
Organization: U of Cambridge, England
Date: Tue, 26 Jan 1993 12:21:44 GMT

In article <1k1sg9INNj6n@shelley.u.washington.edu>, dayne@byron.u.washington.edu (Dayne Miller) writes:
|> Can anyone help with the following questions?
|> 
|> 1) What is the theoretical maximum density for information storage? In other
|> words, using nanotech/quantum effects/whatever, could we get as dense as one
|> bit per atom/molecule of the storage medium? More dense? Less? And how would 
|> the info be stored; magnetically, holographically, or otherwise?

In theory you can certainly do one atom per bit, though I don't know how you'd
read/write it. For example: consider a diamond, each atom represents a 1 if it's
carbon 13 and a 0 if it's carbon 12. 

|> 
|> 2) Is there an approximate value for the tensile/compressional/torsional
|> strengths of General Products monomolecular hull material (from Niven's Known
|> Space) other than "effectively infinite"?

No

|> 
|> 3) Years ago I heard about some U.S. Navy/DARPA feasability study concerning
|> the possibility of using neutrinos to provide communication with submarines.
|> Whatever became of that?

I never heard of it. The idea strikes me as implausible. Neutrinos at low and
moderate energies are very hard to detect, while high energy ones would be
stopped (or slowed) by the intervening rock.

|> 
|> 4) In Dan Simmons' _Fall of Hyperion_, he makes reference to "coherent
|> electron beams" ("CEBs", or "CEEBs", or something like that). Is this a
|> weapon grounded in anything we have or are developing today?

Coherence is fairly irrelevant to a beam weapon, all you want is the beam not to
spread. Electron beam weapons are being studied, but seem unsuitable for use in
an atmosphere or a planetary magnetic field.

|> 
|> 5) Again from Niven: What *is* the theoretical minimum tensile strength of
|> scrith (Ringworld foundation material)?

This is easy to compute, based on the rotational stresses and reasonable
assumptions for the weight of the soil and atmosphere. I can't remeber the answer
but it's fairly enormous. I think scrith has to be able to support about 10^11 m
of itself at 1G. That is a constant cross-section scrith rope hanging in a
uniform 1G would be 100 million kilometers long before it snapped. 

A check on this (well, a check on Niven) could be obtained by modelling the
impact of an asteroid, and comparing it with the specification of Fist-of-God
mountain.

|> 
|> 6) More Niven yet: Is there any theoretical way in which to "temporarily
|> neutralize the charge of the electron" in a manner similar to that of the
|> Slaver disintegrator (and the proton as well, as in the Wunderland
|> Treatymaker)? Maybe some aspect of superstring theory of which I am unaware?
|> (Yes, that covers a *LOT* of territory.)

No, roughly speaking. Charge is conserved. You might be able to fire a beam of
neutral weak current carriers (Z0 is it?) carefully tuned to strip the charge
away leaving neutrinos in the atoms and a continuing beam of W- particles, but
the power you would need would make it much easier to blow the target up some
other way.

|> 
|> 7) Lasers consist of coherent, parallel quanta of energy emission. How perfect
|> is the parallelism? In other words, how much spread will occur over, say, one
|> light year in a perfect vaccuum? Or perhaps more importantly, how much spread
|> (and scatter) can be expected over a given distance (AU, light year, light 
|> minute, solar radius, whatever) given the mean density of solar and/or inter-
|> stellar medium?
|> 

Apart from scattering, the spread depends on the aperture of the laser, and the
wavelength of the light. In "The Flight of the Dragonfly" Robert L. Forward has
an optical laser with a 300km aperture focussed onto a 1000km target at 6 light
years. The final focussing lens of the laser is many AU from the actual power
source.


|> 8) How feasible is David Brin's idea of using "refrigerator lasers" to cool
|> objects in space? Is the idea dependant upon high-temperature superconductors
|> (of heat, not necessarily electricity)? Or would any highly-efficient heat pump
|> work?
|> 

Any highly efficient heat pump will work. The point of the laser is simply that
it enables you to lose heat from the high-temperature end of the system without
either losing mass or having a physical radiator in thermal contact with the sun.
The greater the temperature difference (more exactly ratio) between the hot and
cold ends of the system the more efficient your heat-pump needs to be.


	Steve Linton
Newsgroups: rec.arts.sf.science