Nikifor Todorov/

WATCH: Why the Speed of Light Is NOT About Light

More like speed of causality.

8 JUL 2016

The Universe is pretty nuts when you think about it. All that matter zooming around space, colliding into each other and aggregating into greater things like planets and asteroids, unfathomable black holes swallowing everything at the centre of a galaxy, while star systems are hurtling towards the edges at speeds we can't explain.

And yet, in all this hustle and bustle, for whatever reason, everything in the Universe appears to keeps to a very strict speed limit: 299,792 km/sec (186,282 mps).


Why this speed in particular? That's the absolute fastest that a light particle - or photon - can travel in a vacuum. That's the speed of light, and everything in the Universe must adhere to it, according to our current understanding of the laws of physics.

And yet, that statement isn't exactly correct, as the episode of Space Time above explains, because it's backwards.

The Universe DNGAF about your rules, or your light. The speed limit that everything in the Universe must adhere to - the universal constant - is about something much deeper. As Matt explains, the speed of light should really be called the speed of causality.

You can think of causality in relation to a concept known as the spacetime interval, which states that causal connections are the only order of events that all observers, from wherever they're positioned in the Universe, can agree on.

But why does causality have to have a speed limit, and why does light get to determine that limit?


To understand that, we need to look at two things that have been crucial to our current understanding of the laws of physics: Galileo's principle of relativity - which was the precursor to Einstein's theory of relativity - and Maxwell's equations.

Set out by physicist and mathematician James Clerk Maxwell, Maxwell's equations would form the foundation of classical electrodynamics, and cast doubt on the robustness of Galilean relativity.

Now here's where the video gets really good, because in order to reconcile what's going on with relativity and Maxwell's equations, we get to talk about a pony on roller skates, and an electric monkey on a skateboard.

When all that madness is said and done (our new favourite phrase is "total monkey speed"), we come to the conclusion that electromagnetic forces hold clues about the fundamental interplay between space, time, and velocity, says Matt, and this cannot hold if your maths relies on an infinite speed of light.

But how does all that fit together, and why do you need a specific limit of light speed to hold it all in place? I'll let the episode of Space Time above explain all that, and get ready to feel very confused, and then very smart by the end of it, because this stuff is complicated, but incredibly awesome. Science is always worth the brain-hurt.

And for more on causality, check out the video below:

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