When something happens, the volume of space full of things that it could cause expands over time. The surface expands at the speed of light. I wrote a web toy, Lightcone (which is the name of this shape), to play with this idea.

It gives you a constantly updating list of all the stars that have been enveloped by your own personal lightcone. That is, when you were born, that was reflected in light which left the Earth. News of your birth is travelling away from the Earth, and at any given moment we can see which stars the news is passing.

In this particular screenshot of my list, the news of my birth is about to pass Zeta Tucanae. It counts down: 6 months, 5 months, 4 months, then, you know, 6 weeks, 5 weeks, 4 days, 3 days. 3 hours, 2 hours, 1 hour, and then… your light passes it, you could have – in theory – affected this star, and it’s inside your lightcone.

Ticking these stars off now somehow feels more meaningful to my than my birthday. Years are pretty arbitrary, and long periods to count. I can’t really conceive of them. But these stars come along every few months, which is a more human scale. Plus they’re huge! Seriously big balls of burning stuff. That feels very real. I make a note, in a lot of my projects, of what star I’m passing at the time. When I wrote Mind Hacks it was a star called “p. Eridani,” and I mentioned it in the introduction. Now those are the only words I can read in the translations.

Matt Webb, S&W, posted 2006-04-06 (talk on 2006-02-23)