Subspace is the cop out that Star Trek uses to get away with things like this. It obeys a very different set of physics to normal space allowing you to travel through it and send messages through it at much faster velocities than possible in normal space. Its been years since I indulged in any Trek technobabble, however if memory serves the "warp" engines create a subspace bubble around the ship, moving it from real space to subspace.
Except ships can still see each other and fire at each other when in warp. Really its a twisted mess. There is also the alternative that it doesnt create a subspace bubble but moves an area of space through the rest of it. The space moves faster than light, not the ship which is inside the space.
Star wars hasnt done any better either. Neither have most of the others. David Webers Honor Harrington series of books took reality as far as it could, ships travel through a subspace but once out they are limited by the speed of light. Really though there are very few fully convincing Sci-Fi series in this area.
I couldnt care less to be honest. I know Sci-Fi shows overlook a lot of basic scientific principles but at the end of the day there is a lot more going on than space ships and laser battles if you take the time to watch and listen. If bending the rules of physics gets us to interesting and relevant storylines and shows we can enjoy then thats fine and dandy by me.
If you start to examine good science fiction too closely then youve completely and wholeheartedly missed the point.
I normally watch them that way too, I watch Heroes and its not worth bothering to examine that for physics issues. Its not until after Ive watched a programme that I usually take belief off suspension and have a look at the issues. I noted those ones during my first viewing of TOS, and it isnt just Star Trek they affect.
Then again I do write my own books, and as far as possible they dont have these problems built in, although there is the possibility I have missed some.
In most of these cases its the writers not knowing physics. Hey, those Sci-Fi junkies dont know the difference so lets give it to them anyway, as long as it looks exciting they wont notice. And in most cases we dont.
I will go as far as saying Star Trek isnt good Sci-Fi any more, it became TV entertainment for the masses. Star Wars wasnt good Sci-Fi either though, just modified WW2 warfare with a bit of swords and sorcery thrown in.
And yes, there is usually a lot more going on, but quite often these areas are as broken as the physics.
Oh, a simple question to finish, if you dont examine Sci-Fi closely, how are you going to know the good from the bad?