"For the past year or so I've been spending most of my waking hours in a place where light, matter, energy and time obey different laws of physics than those that rule our own universe. Studying the way things move and interact under these alternative laws reveals some familiar behaviour, some strange and eerily beautiful phenomena, and some terrifying risks.

To reach what I will call the Riemannian universe involves nothing more than changing a minus sign to a plus sign in a simple equation that governs the geometry of space-time. And curiously enough, although the consequences sometimes seem bizarre, the basic laws here can be understood more easily and intuitively than those that apply in the real world.

We have known for more than a hundred years that the best way to understand time in our universe is to think of it as combining with the familiar three dimensions of space to form a four-dimensional space-time, which obeys its own distinctive geometrical laws. While Newton saw time as an absolute, universal quantity that marched forward in lock-step at an identical rate for everyone, since Einstein we've realised that the passage of time measures an aspect of our paths through four-dimensional space-time that is very similar to the length of a path in space."

5 out of 5

http://www.gregegan.net/ORTHOGONAL/00/PM.html

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