Quote Originally Posted by Hanna View Post
I remember those scenes from the book and I thought it was one of the silliest aspects of that book. Can anyone explain how that is scientific?
Well, unlike faster-than-light travel, it doesn't blatantly violate known laws of physics; unlike telepathy, it doesn't suppose that there is some "fifth fundamental force" completely unknown to science; unlike the X-Men, it doesn't ridiculously ignore basic principles of how REAL gene mutations work; etc.

But the railgun described by Heinlein is a technically plausible extrapolation of known science. You could, of course, object that such a catapult is totally unrealistic from an economic POV -- in that it would be so enormously expensive to build that it could never pay for itself. You could also foresee that because it might take decades to build something so huge, someone might in the meantime invent a better and cheaper way to get stuff beyond Earth's orbit, thereby making the railgun project obsolete before it was finished!

There is, however, nothing inherently non-scientific or "magical" about the concept, as discussed in this Wikipedia article on Mass drivers.