See also https://gwern.net/colder-war
I think the question of interstellar warfare is really tricky. Grand Futures has a whole appendix on this, but the impression I get is that within the distance of a few parsec this is indeed a problem (objects/lasers can be aimed ~okay easily), but over larger scales you're safe because aiming/stochastic motion of large bodies becomes a problem
@niplav Wouldn't heat seeking missiles work better than laser guided at that point? Well, maybe not quite so simplistic, but something that can dynamically alter its course.
@Paradox changing course when you're moving at an appreciable fraction of c is really expensive
@niplav Not if you do it really carefully.
I'm sure there's ramifications in terms of sensor tech that would take some thought I just haven't put into it yet, but it should be more doable that trying to shine a laser on a target a lightyear away.
@Paradox the farther away you are the less you will have to change course, and the slower you are the less energy you will have to spend
But the slower you are the easier it is for someone else to find and evade/redirect your relativistic kill vehicle
Light can't be detected until it actually hits
@niplav Hm. So this'll only work on sub-ftl targets, but imagine there's a sweet spot between, say, 0.1 and 0.99 c, where relativistic effects are greatly reduced, but travel time is still decent. Periodically, you make minor adjustments to your course, so that it's not a sharp change. Eventually you get close enough that the target can't evade your speed.
@Paradox but I'm pretty unsire how this will shake out in the end