(Was it just me or does the topic line of this thread read like some "Discount Cialis" spam in your email box?)
I agree and disagree with the points above at the same time. For instance, "Apes of Angels" is certainly true of Hard SF, but 2300 isn't that hard of SF.
1)
Flagrant violations of physics as we know will be few. Usually one or two. Extremely realistic SF may have none at all. 2320 has one violation for the sake of FTL travel.
2)
No Force/Psi/Magic. No Jedi Knights, no Psi Corps, no "Earth Goddess" archetype (hot) women with empathic abilities.
3)
Nobody brings a knife to a gunfight. Nor do they bring lightsabers or cutlasses. They may have sonic stunners or similar exotic weaponry, but just because some people are members of the SCA doesn't mean that in the year 40,000 people will be fighting with glowing swords and chainsaw battleaxes.
4)
Few Handwavium Solutions. Hard Sci-Fi tends to be partially about the implications of technology with an emphasis that there is a price to be paid for the benefits of anything, especially technology. There Ain't No Such Thing As A Free Lunch. You won't have magic thrust plates to lift starships cheaply and cleanly into orbit, instead you have rockets, slingshots, and orbital elevators. You don't have artificial gravity to keep filming costs down. Ships use centrifuge type arrangements to simulate gravity or go without and deal with the associated issues in other ways. Industry produces pollution of some sort. It may not necessarily be the byproducts we're familiar with today (the future may not necessarily have 55-gallon drums dumped in waterways or coal smog), but there will be other problems, just as ugly and pressing, that people will have to deal with.
5)
The Future Is "Aliens" not "Star Wars." You don't have cheap plentiful fusion power for levitating cities, 3000 ton tanks with Iridium armor, and so on. Instead, hard sci-fi tends to have a gritty, industrialized feel to it. Instead of spotlessly clean glass cities inhabited by tall beautiful in shimmery tunics and lucite sandals, there'll be garbage in the streets, graffiti on the walls, and homeless people. Ships have carbon scoring and are dinged and dented. Exploration vehicles are heavily built and have fenders, rollcages, and look like they've been rebuilt and jury-rigged to function. You can still find switchboxes, bundles of cables sticking out from behind wall panels. Cutting edge technology tends to be heavy, expensive, and fragile.
6)
Fewer Fantasy Archetypes. Hard Sci-Fi generally tries to stay away from fantasy archetypes. You don't have elves and dwarves or entire cultures/races that overemphasize the same narrow ranges of human traits as elves and dwarves just because the author played a lot of D&D and can't get away from his or her love of such archetypes. For instance:
6a)
A humanocentric world. The stories of good hard sf are about humans. They might be genetically engineered so they hardly look like humans, or they might pretty similar to us. The societies they live in may be radically different from our own, or they may be quite similar. If you have players who think that humans are boring and would rather play elves or talking cartoon animals, there's going to be issues.
6b)
The Human Experience is not necessarily universalizable. Aliens don't just fulfill some required archetype of the human mind just because we'd like one. Indeed, we may decide they're intelligent but come to realize we can't have meaningful communication with them beyond the most basic of concepts because they're so different from us. They're not boogeymen who are brutal, militaristic, and have an inexplicable lust for human women whom they'll put into metal bikinis and make dance for them at the first opportunity. Nor are they are our "star brothers" (or "star goddesses") who are wise, far-seeing, live in harmony with the universe, love pyramids, and see us as foolish children (I guess you could add that they certainly don't look like Caucasian humans with blond hair and blue eyes). In neither case do they vote conservative or liberal just because that's how the GM thinks the world should work.
Originally posted by Employee 2-4601:
Is there a form of FTL which is even remotely hard scifi, or is it a handy handwave for easy interstellar gaming?
It might not be necessary.
For instance, consider two key advances made: relativistic star travel (like some significant percentage of lightspeed) and anagathics technology. If the average human lifespan stretches out to 300 (or even 500), and age 200 becomes the new 30 years old, then a 10 year round trip from here to Alpha Centauri might not be so onerous to people left behind.
There would certainly be ramifications. There probably wouldn't be an interstellar government. The effects of such longevity as well as the "Forever War"/"Urashima Taro"/"a night in the faerie circle" type effects of being "disconnected from time" by dropping out of communication for so decades while going from star to star would be something to remember as well.
But exploring the ramifications of technology is a big part of hard sci-fi.
Only slightly belatedly 
