Primer(2004) directed by Shane Carruth

This user review from IMDB says it better than I can:

"For much of the film I sat watching open-mouthed, half smiling at the film for reasons I am still trying to understand. Perhaps it was the fearless choice to stick to its own voice, to avoid watering it down by appealing to the wider audience. Perhaps I was amazed at the economy of this film (not just the reported budget, either); at how it so effortlessly dances around the pitfalls inherent with this almost universally misplayed genre. What an interesting film!

There's a breathtakingly light touch with details and subtlety. In fact the film contains and is defined by many aspects deliberately avoided in "sci-fi movies", namely, the surface banality inherent in much of engineering or innovation. In the real world this is characterized simply by hard work, testing and analysis and not visually dynamic at every turn. How they've made this aspect fascinating is a testament to the well-tuned ear and eye of the filmmaker. Listening to these characters talk, you feel relieved that there is none of the nonsense typically associated with sci-fi films: no buxom models or chisel-faced bodybuilders arguing passionately about trivialities while secretly accomplished in physics. This is intelligent fiction about real people engaged in science and engineering who stumble onto something extraordinary. Perhaps thats why it feels so fresh."