On 6/25/2012 1:14 AM, Invisible wrote:
> Then we usually have things like cloaking (rather difficult in a cold,
> dark vacuum), tractor beams (how would that work?), teleporters (um...)
> and so forth.
>
Not really. You are not trying to cloak the stuff that isn't there, just 
the stuff that is, which includes light, EM, and possibly your own 
signals. Interestingly, one of the recent Star Wars books did it right, 
in that cloaks, as we can do them, don't just leave the thing inside 
invisible, they render everything inside unable to see out, so there was 
a whole fleet, sitting and waiting, for a scout to finally slip in at 
their coordinates and say, "Ok, time to move", in the mean time, they 
all sat in the, literal, complete dark, looking at a black wall, with no 
idea what was going on outside.

As for tractor beams. The problem is, as mentioned, distance. Gravity 
can't be adjusted, yet, magnetism can, but has a short range, and 
doesn't work on non-metals, so you have some issues making it work. The 
biggest one is compensating for masses. Two ships of equal size would be 
pulled "towards" each other, unless one of them was intentionally 
thrusting away, to compensate. Surprisingly, a lot of Sci-Fi shows, and 
books, get this right. Others, just ignore it. None of them, in general, 
actually violate the rule, they just fail to explain that the "pulling" 
ship is either way larger, so relatively unaffected by mass, already 
traveling in the same direction, so only accelerating a bit in that same 
direction, or, most likely, reducing its speed/thrusting the opposite 
direction, to compensate.

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