# How to Show Relativity Must be True

/It's been a tough day, and there's a lot of work out there that needs to be done. I needed a bit of mental breathing space, and so I decided to do something that I enjoy: writing about physics. In particular, I thought I'd explain why special relativity MUST be true. That is, why it MUST be the case that objects must appear contracted in length if they are moving relative to you (you can of course also demonstrate that time ticks differently for objects moving at different speeds, but I won't prove that here).

As a physicist, I get emails from people who get very upset that something as counterintuitive as special relativity is how the Universe works. They give lots of arguments about why things couldn't or shouldn't work that way. But, it turns out they do. More importantly, it turns out that you can pretty easily show that, in order for electromagnetism to work, special relativity is the only option. This is why Einstein's paper on special relativity is titled "On the Electrodynamics of Moving Bodies."

Since electromagnetism is the underpinning of all our modern technology, we understand it really well. And none of it works without relativity. Let's see how.

The result is very counterintuitive. But the logic is actually very simple: either electromagnetism doesn't work or special relativity is true. Lengths must contract otherwise some people would see a charge repelled from a wire and others would not, and that's not logically possible. So: length contracts (and if you examine the situation in more detail, you can show that this implies time dilates).