Re: Hard Sci-fi?

>> 1. imagined technology
>>      example: the FTL in Contact
>>
>> 2. imagined progress in scientific knowledge:
>>      example: bacteria are discovered on Mars
>>
>> 3. imagined scientific theories
>>      example: a working theory of quantum gravity
>>
>> 4. scientific mistakes
>>      example: the FTL in Star Wars
>>
>> What distinguishes category 4 from the others is that it violates the
>> correspondence principle, which states that a new scientific theory has
>> to be consistent with older ones, within the realm of applicability of
>> the older ones, because otherwise the new theory would be contradicted
>> by the experiments that the older ones were based on.
> 
> What's the difference between the two FTL technologies you mention?

The FTL in Star Wars violates relativity in blatant and obvious ways,
like getting the energy scales wrong. Heck, even the STL in Star Wars
violates classical mechanics, and violates it within the realm of
applicability of classical mechanics. E.g.,  we have spaceships
traveling across solar systems in a matter of hours, which means they're
going at speeds of at least ~10^7 m/s. This is small enough compared to
c that relativistic effects are small, and we're within the domain of
applicability of classical mechanics (with an error of <~1%). Classical
mechanics says that at this speed, a spaceship with a mass of 10^7 kg
has an energy of about 10^21 J, which is about the same as the total
megatonnage of the world's nuclear arsenal. That means that every
decent-sized spaceship in the movie is an awesome weapon of mass
destruction, if you simply crash it into a planet. You don't
need a Death Star. The reason the energy scales are totally wrong is
that George Lucas planned the battle scenes of the movie by watching
old WWII footage.

 > It's often impossible to determine whether a certain technology is 
possible
 > or plausible, because we most ofter don't get any details at all.
 > Technobabble doesn't count in my book!

I guess it depends on what you mean by "possible." My definition of
hard SF would be that it has to be possible in the sense that it
doesn't violate those laws of physics that have already been thoroughly
verified within their realm of applicability. The FTL in Contact is
"possible" in this sense. Of course just because a certain technology
doesn't violate the laws of physics, that doesn't mean that it's
practical, plausible, likely, ...