Newsgroups: rec.arts.sf.science Subject: Re: Artificial gravity From: alien@acheron.amigans.gen.nz (Ross Smith) Date: Fri, 20 May 94 23:06:30 GMT+12 Organization: The Boyz from the Dwarf In article <2r20s1$km4@kauri.itd.adelaide.edu.au> kickaha@NEWS_DOMAIN (Sundance Bilson-Thompson) writes: >Anders Sandberg (asa@scaramanga.nada.kth.se) wrote: > >: >If anyone has figures or (preferably) equations relating the density of the >: >fluid, the radius of the loops, angular velocity, and so on, I would be >: >really interested to see them. Will the density be >: >so high that you might >: >just as well use sheets of neutronium? > >: I would also really like to know the actual figures. Its one thing >: playing with the concepts, another to get some figures. > >Anyone? Anyone out there? In one of Robert Forward's papers (the title is "Guidelines to Antigravity" and it was published in 1962 or 63; I don't have the specific reference, but I'm pretty sure it's mentioned in the appendix to _Dragon's Egg_), he describes several ways of producing non-Newtonian gravitational forces. One involves a heavy rotating ring. An object near the centre feels an acceleration with a vertical component pulling it towards the plane of the ring, and a radial component pushing it outwards. The vertical and radial accelerations are: g(z) = - G M w^2 z / c^2 R g(r) = G M w^2 r / 2 c^2 R where M and R are the mass and radius of the ring, w is its angular velocity, r and z are the coordinates of the test body, and G and c have their usual meanings. These formulae only apply for a test body near the origin (r and z both << R). Later he describes "devices based on analogies between electromagnetic and gravitational fields", i.e. the gravitational equivalent of an electromagnet. The one he describes in detail (and I think this is what someone earlier in this thread was thinking of) involves a ring-shaped coil of tubes carrying a heavy, fast-moving fluid (imagine a hosepipe wrapped around a tyre, so it repeatedly passes up through the middle and then down around the outside). This generates a gravitational field through its centre, pointing in the opposite direction to the fluid passing through the centre (downwards in my hosepipe-and-tyre description). The strength of the field is: g(z) = - d ( 4 G N T r^2 ) -- ----------- dt c^2 R^2 where N is the number of turns of the coil, T is the mass flow rate, and R and r are the major and minor radii of the toroidal coil. Notice the time derivative involved: a steady-state flow produces no field at the centre; you need a continuously varying rate of flow (or some other variable in the equation, but flow rate would presumably be the easiest to control). Plugging numbers into these equations shows (as Forward points out in the paper) that any kind of gravity control using general relativity principles requires enormous densities and speeds ("It is obvious that research in the field of gravitation will be very difficult since even the most optimistic calculations indicate that very large devices will be required to create usable gravitational forces."). But he also makes another interesting point: "In studying analogies between electromagnetism and gravitation, it can be seen that one analogous quantity has not been investigated. This is the gravitational equivalent to the magnetic permeability. Electrical power distribution systems depend upon the anomalously large and nonlinear permeability of iron and other magnetic materials. Since all atoms have spin, all materials will have a gravitational permeability which is different from that of free space. Rough calculations show that this difference is very small, but experimental investigation may find materials with anomalously large or nonlinear properties that can be used to enhance time-varying gravitational fields. Also, since the magnetic moment and the inertial moment are combined in an atom, it may be possible to use this property to convert time-varying electromagnetic fields into time-varying gravitational fields. At present, the only way to search for such materials is to intersperse wedges of material between gravitational wave generators and detectors, such as those described by J Weber, and look for a change in amplitude or direction of propagation. The first efforts in this direction have been carried out by the Russian workers Braginsky, Rudenko, and Rukman with negative results." -- Ross Smith (Wanganui, New Zealand) ... alien@acheron.amigans.gen.nz GCS/S d? p c++++ l u-- e- m---(*) s+/++ n--- h+ f g+ w+ t+(-) r+ y? Keeper of the FAQ for rec.aviation.military "Unix has been feverishly evolving for over 20 years, sort of like bacteria in a cesspool, only less attractive." (Unix for Dummies)