Sophisanmus,
TrashMan is absolutely right: the main achievement of the recent few centuries is the *method* of peer-review, as much as the results themselves.
As for physical law being relative...or an "approximation". Let me give you an example. Gravitational constant, "g", 9.81 m/s/s, is a damn good approximation. Sure, it comes from a more complicated equation that involves earth's radius, and, techincally, if you jump two feet in the air the value of "g" is corrected. That is, correction on the order of 0.6 m to a constant that is 6,360,000 m. Not to mention 1/ R^2, so another 7 orders of magnitude, but who cares, right? So, the correction is so tiny, that even the difference between see level and airplane altitude is pretty hard to observe. Yes, it is an approximation. Will it ever make any difference in your life? Nope.
And then there is something like conservation of momentum or energy. You know the T-shirt: "speed limit 300,000 km/sec - it's not just a good advice, it's the LAW" ? Those laws are fixed. Nothing "approximate" or "relative" about them. These laws are observed everywhere in this universe, completely and fully.
As to applying the laws to sci-fi... In my personal preference, the concepts should not offend common sense, i.e. not violate the basic physical law in a fundamental way. For example, no armor, alien or human, can violate conservation of momentum. I.e. a small, light alien, hit with a sledgehammer, should fly. He may be OK when he lands, being alien and all that, but fly he must.
Just my $0.02