<iframe width="580" height="385" src="https://www.youtube.com/embed/cFo5BjSB_YI?autoplay=1" frameborder="0" allowfullscreen></iframe> <br>Einstein's theory of general relativity is over 100 years old. It's famously weird and complicated, so we've explained it in just five minutes. BBC Earth's Pierangelo ... <br><a href="https://www.youtube.com/watch?v=cFo5BjSB_YI">source</a>