From: Anders Sandberg (asa@nada.kth.se)
Date: Tue Jun 10 2003 - 03:30:39 MDT
On Mon, Jun 09, 2003 at 04:16:17PM -0700, Terry W. Colvin wrote:
> Applying propigation of forces math to gravity to determine its "speed"
> seems very silly to me. I'd liken it to someone asking what is the
> velocity of the distance between say London and Manchester!
Yes and no. Fields don't move, but they change from point to point in
spacetime and it is often interesting to know how a change at one point
affects other points. Since that will happen within a future cone from
the point, it makes sense to think of it having a velocity = the amount
of space a disturbance reaches in a given time. Velocity does not make
sense when thinking about a field where nothing new or special happens,
but when it does it tells us something about the causal structure of the
field in spacetime.
In the gravity case things are of course trickier since spacetime is the
field itself.
-- ----------------------------------------------------------------------- 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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