I was today years old when I learned that "light years" is actually relative to time on Earth 🤯— Steven Tey (@steventey) June 11, 2023
E.g. if you're traveling at 99.99% the speed of light to a star that's 4 light years away, it would take you just 3 weeks.
But to your loved ones on Earth, those 3 weeks = 4 years. pic.twitter.com/aMxNqdLswK
See also this article about time in Harper's Magazine. I feel like the more I learn about time the less I know.
Aside: I feel like there is an awesome pop culture book to be written about relativity and quantum mechanics that makes it accessible for people like me; or maybe it exists and I haven't found it yet?