MadSci Network: Physics

Re: Does Graviton Density Relate to How Much Space Is Curved?

Date: Thu Jun 9 15:02:20 2005
Posted By: Steve Nelson, research physicist
Area of science: Physics
ID: 1116805569.Ph

Since you're asking not to have math, we'll back up a bit on this question.
 You can think of gravitation as the exchange of gravitons, just like you
can think of the attraction or repulsion of charged bodies as the exchange
of photons...but there's not even a complete theory of quantum gravitation
in existence yet so we won't discuss the possibility of gravitons (which
have never been observed).  Discussing gravitons simply isn't necessary in
this case.

We'll start with gravitation as simple waves and static fields.  The
concept you mention has been purveyed by science fiction authors before,
Alan Dean Foster comes to mind with something in one of his books called a
KK drive.  Don't recall what KK stood for, but as usual there was a grain
of science in the science fiction author's notion of a spaceflight drive. 
You could indeed focus gravitational waves (not quite the same concept)
from some source along the path of a spaceship and drive it.  The problem
comes in generating these waves and getting them to focus.  Gravitational
waves spread out over distance.  But if some mechanism for producing them
(we're getting beyond the realm of what science knows how to do) and
focusing them was created then it could plausibly stretch spacetime in the
direction that you wanted the spaceship to travel, causing an acceleration.
 Such a mechanism, because of the coupling strength of gravitation, would
most likely involve fast-moving masses at high speeds, it's an open
question as to whether or not you could even get it to work at short range
and whether or not it would be powerful enough to be useful.  But even weak
thrusts over long times/distance (google "solar sail" for recent news of
the development of such a propulsion system) can get you places in space.

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