From: Anders Sandberg (asa@nada.kth.se)
Date: Sat Jul 12 2003 - 04:02:52 MDT
On Fri, Jul 11, 2003 at 08:35:01PM -0400, ABlainey@aol.com wrote:
> In a message dated 12/07/2003 01:20:55 GMT Daylight Time, asa@nada.kth.se
> writes:
>
>
> > In general it seems that the speed of gravity disturbances is very close
> > to the speed of light. It might be interesting to imagine a universe
> > where this was not true. What about a world where gravity was as slow as
> > the speed of sound?
> >
>
> Can you clarify what you imagine this world would be like. To me I can't
> really see that the propogation speed would make any observable difference as the
> effective force levels would still be the same in any region.
For a static field in such a "slow gravity" universe nothing would
change. But imagine sending out Voyager towards Jupiter. At first it
experiences the weak tug towards the place where Jupiter was a long time
ago, and is accelerated that way. As it approaches the region where
Jupiter is, the acceleration will change direction and move towards the
current position, and as Voyager continues beyond it will shift back
towards an old position.
Even worse, Jupiter is actually moving "supersonically" in this setting!
If Voyager is approaching from straight ahead of the planet it will not
experience any gravitational field since Jupiter is moving faster than
the information about where it is is spreading through the gravity
field. So on one side of Jupiter you would actually be weightless! On
the other side all the information is present and you get normal
gravity. And you get a discontinous bow shock where you go from no
gravity to a mix of several accelerations pointing towards many former
positions (likely just causing an inward accleration into the shock
cone).
A universe with this kind of enormously slow gravity would be very
different. Gravitational radiation would be intense, likely making all
orbits unstable - everything would spiral together. Jupiter would slow
down even more simply by ejecting matter ahead of its motion (since the
atmosphere on the front side would not "know" that there was a planet
beneath). Gravity shockwaves would crisscross the universe, acting as
great navigational hazards.
Hmm, sounds almost like the typical pulp sf world.
-- ----------------------------------------------------------------------- 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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