It has units after all: meters per second. Related: The genius of Albert Einstein: his life, theories and impact on science And so, the speed of light became an important cornerstone of modern physics.īut still, why that number, with that value, and not some other random number? Why did nature pick that one and no other? What's going on? That's because all massless particles are able to travel at this speed, and since light is massless, it can travel at that speed. It's just some number, but it turns out that Maxwell had already calculated this number and discovered it without even knowing it. Of course, this conversion rate, this fundamental constant that unifies space and time, doesn't know what an electromagnetic wave is, and it doesn't even really care. What's the exchange rate? Einstein found that there was a single constant, a certain speed, that could tell us how much space was equivalent to how much time, and vice versa.Įinstein's theories didn't say what that number was, but then he applied special relativity to the old equations of Maxwell and found that this conversion rate is exactly the speed of light. In other words, we need to know how much one meter of space, for example, is worth in time. There needed to be some sort of glue, some connection that allowed us to translate between movement in space and movement in time. So how could they possibly be on the same footing? They appear to be two completely different things. A meter or a foot is very different than a second or a year. But as we all know, space is very different than time. With his special theory of relativity, Einstein realized the true connection between time and space, a unified fabric known as space-time. Ergo, light is made of electromagnetic waves and it travels at that speed, because that is exactly how quickly waves of electricity and magnetism travel through space.Īnd this was all well and good until Einstein came along a few decades later and realized that the speed of light had nothing to do with light at all. This allows waves of electricity to create waves of magnetism, which go on to make waves of electricity and back and forth and back and forth, leapfrogging over each other, capable of traveling through space.Īnd when he went to calculate the speed of these so-called electromagnetic waves, Maxwell got the same number that scientists had been measuring as the speed of light for centuries. Laying the groundwork for what we now understand to be the electromagnetic force, in those equations he discovered that changing electric fields can create magnetic fields, and vice versa. Maxwell had been playing around with the then-poorly-understood phenomena of electricity and magnetism when he discovered a single unified picture that could explain all the disparate observations. That's when the physicist James Clerk Maxwell accidentally invented light. Continued measurements over the course of the next few centuries solidified the measurement of the speed of light, but it wasn't until the mid-1800s when things really started to come together.
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