Re: Tracking

"Wayne Throop" <throopw@xxxxxxxxx> wrote in message
news:1146086904@xxxxxxxxxxxx
: "Logan Kearsley" <chrono.surfer@xxxxxxxxxxx>
: It's made more problematic by the fact that any detectable radiation
: travelling through normal space given off by the FTL drive can't
possibly be
: approaching you faster than the FTL drive is moving away, leading to
: annoying lag in your image of the trail (unless we find someway to
detect
: tachyons, anyway).

Don't see why. Let's say the drive was instantaneous, but there's
a burst of light emitted all along the path. Then you'd immediately see
a spot of light moving away, along the path the ship took. There'd
be no delay, since the ship started close to where you are. And
interestingly, if such a ship moved *towards* you, you'd also see
a spot of light moving away. In the direction it came from. And
if it went past you, you'd have a spot of light moving off in both
directions, and you'd have an interesting time figuring out
which way the ship went.

But it takes finite time for that image to move all the way along the path.
Thus, a delay in seeing where the ship actually is.
The drive doesn't have to be instantaneous, anything that emits light (or
some other signal travelling below or at c) in normal space, while itself
moving faster than light, will exhibit the same behavior of always producing
an image moving away from you, but with different time lags for different
speeds.

Cherenkov radiation would be a nice buzzword for it, but iirc that's
emmitted directionally, towards the direction of travel (more or less,
sort of; actually at an angle, I think). So, if you too can go
FTL, you can move ahead of where you think the ship might have gone,
and see its "wake" of cherenkov radiation. You don't need to get ahead
of where the ship actually is, just ahead of its path by far enough so
that the cherenkov radiation hasn't gotten there yet.

Even that, though, will only tell you where the ship has been, not where
it's going. If you happen to already know by some other method in which
direction the ship was travelling (which I suppose is a prerequisite for
using Cerenkov-type radiation- although Cerenkov radiation involves a
preferred frame, so this can't really be Cerenkov radiation, unless we come
up with some way to define a preferred frame for the drive, and there's no
particular reason that you couldn't assume that the FTL drive happens to
emit something omnidirectionally), and if the ship can't change course in
flight, then you've restricted your search space significantly, at least.

And, of course, you can suppose that a similar "shockwave" effect
exists for gravity, and detect that.

All of these, of course, presume some moderately unlikely things about
the way the ship works. But even in things like the alcubierre drive,
or any sort of "warp" drive, one could suppose there are gravitational
disturbances emitted, more or less in any direction you like.
Just detect those, and Bob's your uncle.

I could imagine some sort of gravitational effect that would track the ships
position instaneously. That's easier for me to imagine than something that
emits sub-light gravitational waves, actually, as doppler shift would seem
to produce waves of imaginary (heh, punny) wavelength without some sort of
preferred frame defined.

Methinks it would be cool to have an SF setting in which that sort of
indefinite tracking, where the image alwasy moves away from you, were the
only option. It neatly avoids the situations in which all danger can be
avoided simply by jumping away, and the situations where running away
doesn't work because you will just be followed, without having to resort to
limited jump-points, frex.

-l.
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Relevant Pages

  • Re: Tracking
    ... travelling through normal space given off by the FTL drive can't possibly be ... a spot of light moving away, along the path the ship took. ... since the ship started close to where you are. ... Cherenkov radiation would be a nice buzzword for it, ...
    (rec.arts.sf.science)
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  • Re: Physics - relativity problem
    ... |I am helping my daughter with her HS physics. ... | while another ship B is also travelling toward Earth at 0.67c from the ... | How fast does ship A approach ship B according to the crew of ship A? ...
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  • Re: Tracking
    ... since the ship started close to where you are. ... If it's travelling at some finite speed, though greater than c, then it _is_ possible to detect which way it's travelling, even if you didn't see its start or stopping point, at least conceivably. ... So you see it at the point of its closest approach, and then you see images of it move away in either direction. ... THe observer will be located at a point Q at a distance h along the y axis: ...
    (rec.arts.sf.science)