Light moves at 186,000 miles per second - almost 671 million miles per hour. That’s so fast it’s hard to picture. In a single second, a beam of light could circle the entire Earth seven and a half times. It travels from the Sun to Earth in about 8 minutes, even though the distance is 93 million miles.
Einstein’s theory of relativity says that this isn’t just fast - it’s the universe’s absolute speed limit. Nothing with mass can ever reach the speed of light. As things accelerate, they need more and more energy, and an object with mass would need infinite energy to actually hit lightspeed. Only things without mass - photons of light, gravitational waves - can travel at that speed.
This has wild consequences. Time runs slower when you move fast. If you could somehow travel at 99% of light speed for a year, only a year would pass for you - but on Earth, decades would have gone by. Light is so fundamental that the entire structure of space and time is built around it.
