Theemile wrote:And we also have to realize that the relative size of ship at a distance is going to be very, very small, so it is not going to occlude much - only massive computer support (which of course does exist) is going to be able to perceive any of it.
I mentioned this point of reference a year or 2 ago. One day I looked up and saw a Plane overhead and the math quickly ran through my head, and I came up with the following:
Occluding a star is also particularly unlikely. It does happen: a 100-m ship's hammerhead at 10 million km distance has an angle of .1 / 10^7 = 10^(-8) radians. A G2 star like our Sun at 10 light-years has an angle of 1.47 * 10^(-8) radians. If this ship passed in front of this star, it would occlude 68% of the star. If the ship is not straight-on or the star is any smaller or further away, the occlusion is likely to be total.
So you'd see the star blink. Stars don't blink in space.
The problem with this situation is that the chance that you're occluding any visible star is negligible at any appreciable distance and, even if you do, the time of occlusion is also very minimal. I haven't calculated this, but I guess we're talking about, at worst, a one in a billion chance of occlusion that lasts about a nanosecond. The only case where the occlusion is likely and long-lasting is the stupid case: traveling in a straight line towards a stationary enemy. This just doesn't happen.
So, you see, my problem is not that the nanites exist and do a job. It's that they seem to be necessary in the first place.
If the background object is not punctual, but has a visible area, like a nebula or one of the nearby galaxies, then you'd see a dark point moving across its face. It's possible that a warship has sensors scanning for that, since the number of background nebulae and galaxies is finite, so it might as well dedicate sensor and computer time to it. Though at the same time, the lurker knows where those objects are and would avoid the likely routes where it might be detected.