Light
Simple but holds everything together
At some point last month, I started thinking about light more deeply. And I concluded that light is a beautiful thing, and depending on whom you ask, they'll tell you different things.
For me, the speed of light in vacuum is so exact, and nothing in the universe directly explains why it has the value it does. It's about 3 × 10 ^8 m/s. If you try to travel faster than that as an object with mass, relativity shows that the energy required approaches infinity, making it physically impossible to reach or exceed that speed.
The number itself sets a limit for what can be causally connected in our universe. Nothing with mass can travel faster than light. And to conceptually think about travelling at that speed, a quick look at Einstein's equation E = mc^2 shows that even if the mass is extremely small but still greater than zero, the energy needed to accelerate it to light speed would be enormous.**1
Another thing about light that fascinates me is that it's the bedrock of the internet. Undersea fibre optic cables that connect the world rely on light to move an enormous amount of data across long distances. The cell tower you see isn't the full picture. Only the distance between us and the base stations relies on radio waves. The data from the base stations travels as light pulses through fibre back to the network nodes.
If I had asked myself what light is about eight years ago, I'm sure the only thing in my head would have been that it's just an electromagnetic wave.
Another remarkable thing is that light doesn't need a medium—it can travel through a vacuum. The Michelson-Morley interferometer experiment helped establish this, and as a consequence, the speed of light is constant for all observers, regardless of their motion.**2
When you think long enough about light, you start to sense that it's more than just a physical quantity with a number attached to it. It's the boundary of what's possible and the quiet rule that shapes how we experience time and distance.
I think it's one of the most beautiful ideas we've discovered, and the closest thing we have to a universal language.
**1 My original thought was that the energy doesn't exist in our universe. But then I started thinking of the Kardashev scale, and I'm imagining what could be unlocked at Type III civilization level.
**2 This was fascinating to me because special relativity shows how other properties like time and distance aren't constant for everyone, yet the speed of light is.