Here's something simple to think about (not).
Think about "now." Too late, it's already become "then."
"Now" on the sun takes 8 minutes to get to Earth. It still looks like a "now." But it's a then.
When a mosquito bites you "now," it takes a teeny amount of time for that "now" to reach your brain.
If two people, one 6 feet tall, the other five feet tall are bit at the same instant by two mosquitoes, the "ouch" takes longer to travel to the taller person's brain than the shorter person's brain. There's hardly a difference, but it's different enough to make two different "nows."
That's what he's talking about.
You can think about this for a long time.
Want to keep this list going?
Send me your "now" thoughts in the comments below.
xkcd is a webcomic created by Randall Munroe. The comic's tagline describes it as "a webcomic of romance, sarcasm, math, and language."