I don’t see anything in physics that won’t allow interstellar trips. The time scales are another matter if you’re talking about sending people.
The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) is technically feasible and has worked in small scale testing both here on earth and on the space station. Its believed that an interstellar trip to Alpha Centauri could be made in around 50 years.
lets be ridiculous and pretend it is possible to go faster than the speed of light. Any man made craft going at that speed hitting something as small as a grain of rice would explode like a nuclear bomb.
Boy, I found this rather visionary site with a discussion from 2008 on VASIMR and the Nuclear Question. Even there an optimistic time is given as 4000 years, and optimistic speeds are given of 1/300 c.
Yeah, and that whole thing about things becoming heavier the faster they go? Well, we’re weightless in space, and I’m sure spaceships are weightless in space, so that whole thing about becoming heavier in space, where there’s no gravity or drag acting upon you...