From: Anders Sandberg (asa@nada.kth.se)
Date: Sat Jul 12 2003 - 03:51:12 MDT
On Fri, Jul 11, 2003 at 11:48:51PM -0400, Paul Grant wrote:
>
> On Thu, 10 Jul 2003 ABlainey@aol.com wrote:
> It is also true that to get gravity waves one has to manipulate *very*
> large masses.
>
> Me: or shutter a large mass :) like a signal fire :) Why build the fire
> when you can misdirect it using a blanket :)
This assumes there is a way of shutter gravity. It is an old idea in sf
(Cavorite in H.G. Wells _First Men on the Moon_), but when viewed in
general relativity it does not make much sense: gravity is the effect of
curved spacetime, so how do you shutter it in? You would need a way to
prevent the curvature at one point to affect a nearby point which would
require either that you somehow made the Einstein equations stop acting
or introduced a new curvature field in between that did the job - and
that likely involves manipulating absurd amounts of mass and/or exotic
matter again.
> That is *very* expensive relative to the manipulation of photons (which
> effectively have very low masses [based on E = mc^2]).
>
> Me: Depends on how you do it :) no doubt an elegant solution is just
> waiting to be found :) At this point, I wouldn't say its
> impossible, or even improbable :) Just that more data is needed :) In
> any event, it certainly is worth examining, if nothing
> else for the questions it would raise....
So, any ideas for this research program? In what ways can we generate
gravitons (if working within the particle physics framework)?
It seems to me that the ideal method would be to convert one species of
particle into gravitons plus some other species, like how we can get
neutrinos from beta decay. But that likely would require the existence
of some symmetry-breaking current that allowed interaction between the
other three and gravity.
In the GR field framework the issue would be to make strong gravity
waves without having a large energy tensor. Maybe that can happen if one
already has a big (complex) gravitational field where small inputs can
be amplified by tapping energy or curvature already existing in the
system. IMHO this sounds less unlikely than the previous approach, but
still not particularly promising.
> Another really interesting question, which just occurred to me, is:
> does gravity reflect? are their materials which absorb/rebuff gravity...
> or is it all simply a matter of constructive/destructive interference
> sans reflection?
Static gravity fields do not seem to reflect/refract, but there are
indeed some weird goings on for dynamic strong fields. Look at
http://archive.ncsa.uiuc.edu/SCMS/DigLib/text/astro/Gravitational-Wave-Black-Hole-Hobill.html
for example, which shows some nontrivial "refractions" of a gravity
wave.
In general (no no pun intended) you need to learn more about general
relativity in order to say something constructive about gravity. It is
not the simple force we usually assume. Check out the links at
http://math.ucr.edu/home/baez/relativity.html I especially like Greg
Egan's tutorial
http://gregegan.customer.netspace.net.au/FOUNDATIONS/index.html and the
FAQ at http://www2.corepower.com:8080/~relfaq/relativity.html (which has
a nice treatment of the speed of gravity issue)
-- ----------------------------------------------------------------------- Anders Sandberg Towards Ascension! asa@nada.kth.se http://www.nada.kth.se/~asa/ GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y
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