Extremely small and incredibly fast, muons offer amazing proof of special relativity

Cosmic rays are constantly raining down on our planet. Their collisions with the Earth’s upper atmosphere create an endless, invisible – and, thankfully for us, harmless – particle shower on its surface. One byproduct of these collisions is the creation of extraordinarily short-lived particles known as muons that, rather curiously, seem to exist for much longer when moving towards the planet than when created by scientists working in the lab. This whiteboard animation from MinutePhysics explains how this apparent inconsistency is caused by a phenomenon known as time dilation, and, by extension, provides one of the simplest and most repeatable demonstrations of special relativity available to us.