New XKCD Forums

Title text: So do you have any plans for z=-0.000000000000045?

So yeah, I had to look this one up. z=0 is the present and a higher number is further in the past, when you're measuring how long ago you're seeing into the past when you look at a distant object, measured using its redshift.

For z<<1, you can just multiply by the age of the universe to get how long she's talking about.