Re: Tracking
- From: Erik Max Francis <max@xxxxxxxxxxx>
- Date: Wed, 26 Apr 2006 17:42:28 -0700
Logan Kearsley wrote:
I'm not entirely sure which 'he' you're referring to, so I'll respond for
both the cases of Wayne Throop and Major Oz. Pay attention to which ever one
is appropriate.
I was responding to your response to Wayne, so I was referring to Wayne.
WT: Even so, since the image is always of a ship moving away from you, you
can't tell what direction the ship is moving in unless you know at least one
of where it started or where it ends up.
See my reply to Wayne; for non-instantaneous travel, it _is_ possible to tell in which direction the ship is travelling, even if it passes by you and you didn't see it start or stop. The position of the first image you detect will not be at the point of closest approach; it will lag behind it. That will tell you in which direction the ship is travelling. (If you're looking at a horizontal track and you see the first light of the ship to the left of its closest approach, then you know it's travelling left to right.)
MO: That wasn't specified. The original post just said 'tracking'. In my
idiolect, that encompasses figuring out where it's going / has ended up, not
just in which direction it went.
The original post talked about a chase where the one pursued turns on his FTL drive, and the pursuer wants to know where he's going. That certainly means that the starting position is known.
If he said nothing but _track_ then you might have a point, but the story he set up clearly indicates that the starting position is known.
That's why I didn't say 'gravitational waves'. Just some unspecified
gravitational effect. We've already broken the universe by assuming an
unspecified form of FTL; what's to stop this particular unspecified form of
FTL from producing instantaneous changes to the gravitational field at a
distance? It may be less physically plausible, but at least its easier for
me to wrap my brain around than imaginary wavelengths are.
Well I mentioned gravitational waves only as an example. Gravitational waves aren't responsible for transmitting the effects of gravity any more than real photons are responsible for transmitting the effects of electromagnetism.
The whole point here is trying to reconcile something that is not known to be possible with what we do know; obviously he could have made up anything he wanted ("Pixie Dust") but he was asking to find something that didn't sound too ridiculous.
The universe itself doesn't rule out faster-than-light travel, we just have plenty of good reasons to conclude that it's very likely not possible. Since you're talking about the Alcubierre drive later -- which is a solution to the Einstein field equations of general relativity -- that kind of proves the point. "Breaking the universe" is probably overstating it; even if there is faster-than-light travel, that doesn't mean that our existing theories of gravitation are therefore wrong.
--
Erik Max Francis && max@xxxxxxxxxxx && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
Why do we give ourselves away / 'Till only emptiness remains
-- Chante Moore
.
- References:
- Tracking
- From: MajorOz
- Re: Tracking
- From: Logan Kearsley
- Re: Tracking
- From: Wayne Throop
- Re: Tracking
- From: Logan Kearsley
- Re: Tracking
- From: Erik Max Francis
- Re: Tracking
- From: Logan Kearsley
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