The **Orthogonal series** is a sci-fi trilogy by Greg Egan, composed of *The Clockwork Rocket*, *The Eternal Flame*, and *The Arrows of Time*. It is an example of how you can simultaneously be hard sci-fi and violate the laws of physics.

Let's talk about geometry. The Pythagorean theorem tells you a² + b² = c², relating two possible paths you can take through space. Taking a different path increases the distance you need to travel.

Note I said *space*. What about paths through time? Well, as it turns out, the Pythagorean theorem for time is a² **-** b² = c². That is, taking a "longer" path *reduces* time. If you've ever heard of how travelling near the speed of light causes your personal time to be shorter, this is the formalization of why.

What does this have to with a sci-fi novel? Simple.

What if Pythagorean theorem for time was a² + b² = c², just like space? Orthogonal is about such a universe.

This changes physics. There's no universal speed limit. Different wavelengths of light travel at different speeds. Emitting photons causes your energy to *increase*. And that's only the beginning.

Orthogonal is an exploration of an alternate world. The plot is lacking, but the joy comes from the world. Go read it.