At the start of the 20th century, many scientists thought they had learned all there was to know about physics. Surely there were a few unsolved mysteries left, but it seemed like they could all be worked out with better measurements, and slight tweaks to what was already known. The problem was, those mysteries didn’t just go away, and they eventually led to fundamental revolutions in our understanding of nature.

Also, with the discovery of huge, important things, like Relativity and Quantum Mechanics, it might sometimes feel like there are just a few small problems left for physicists to solve. But, our Universe won’t just accept that. Here, SciShow presents 5 of those mysteries that continue to baffle physicists and render their attempts unavailing to this day.