What strikes me most about this thread, with its frequent emphasis on what's "really" possible, is that once you assume "warp" space travel (i.e. as in the SE IV game), 21st Century science goes out the window. Perhaps it would be more productive* to speculate how the "warp" travel already built into the game can explain other game features. Example: For in-system travel, why not replace Newtonian acceleration/deceleration, with its inconvenient mass/energy/velocity/fuel limitations, by a continuous "micro-warp" drive with constant velocity (very convenient) and whatever limitations you like? BTW, this is somewhat similar to the "stutterwarp" in the Traveller role-playing game, which is based on, yes, REAL science, i.e. [begin handwaving] quantum tunneling [end handwaving].
Or take the "Alderson Drive" in the Niven/Pournelle novel "The Mote in God's Eye". The "warp points" in this fictional universe arise from an as-yet-undiscovered "fifth force". Presumably the discovery of this new force would lead to a whole new branch of physics and many practical applications, but to my knowledge the authors made no use of this technology beyond interstellar travel. If so, then I'd say they missed a good opportunity.
Back to SE IV. You want "shields"? No problem! Apply the same game technology used for interstellar travel to generate a "warp field" around your ship that "warps" incoming matter/energy harmlessly AROUND the vessel! Now for game/story purposes you may want limits on how much "incoming" can be deflected (leaky shields) or you may want "incoming" to "use up" shield/warp energy (consumable shields). Your weapons can be modified shield projectors that create a long thin warp field (as opposed to a short fat shield) along which you can fling projectiles, photons, anti-protons, etc. toward enemy vessels. Since warp fields defy "conventional" physics your "beams" don't scatter and efficiency is so amazingly high that minimal cooling is required.
Just as the first lasers led to multiple practical applications in telecom, weaponry, medicine, computers, chemistry, physics, etc. I would expect a fictional scientific breakthrough to affect many aspects of a scifi story.
*by the phrase "be more productive" I mean "waste time more efficiently"
