Share 'Realistic Sci-Fi movies similar to Primer?'

I recently discovered the indie sci-fi movie "Primer" and just love how realistic it is, while still being weird and fictional. So I am on a hunt to find similar movies that are sci-fi as in they are not real, but they are believable and thought provoking. I feel like when I search the sci-fi genre I end up with movies about wacky space aliens or things going "horribly wrong" on another planet. T…