What exactly is "science fiction"? Is it the same as "fantasy" fiction? Does it necessarily need to be structured based on hard science? In my humble opinion, science fiction is based upon scientific facts and our current understanding of scientific theories. As more scientific data is gathered, we expand our knowledge base, adapt theory and develop new hypotheses. Science is by definition empiric; that means it is a work in progress, to learn from experiments conducted to explore a concept while limiting extraneous variables, so that the experimental tests are independently reproducible by others. That's hard science. But our body of scientific knowledge is not set in stone, it must evolve to encompass new observations and new mathematical discoveries across many scientific disciplines to uncover the whole truth. And we are not there yet.
Science fiction, speculative fiction and fantasy fiction writers imagine new things, synthesize new concepts and construct entirely new worlds by extrapolating from our society's scientific discoveries of the moment. That's what makes science fiction and fantasy fiction so fresh - it's free to imagine what might be! Just because something doesn't exist in OUR dimension or at this particular electromagnetic, gravitational, or space-time frequency doesn't mean it doesn't exist. Somewhere. Out there.