Time flies when you’re not learning

This short Scientific American article tackles something that’s been on my mind of late:

Why does time seem to speed up with age?

I regularly look back and feel that another year has zoomed by, yet at the same time I can remember stretches of time as a teenager that seemed to go on much much longer. Why is that?

This article posits that

“… our retrospective judgment of time is based on how many new memories we create over a certain period.”

I doubt that it’s something like a numerical counter (“5 new memories over the last hour… check.”). But I could believe that it’s a function of the compressibility of experience. I imagine that repetitive experiences are highly compressible, which is why I can’t individually remember brushing my teeth every day for the last month. But new memories would by construction not be compressible: they represent new information that your brain has opted to preserve at higher fidelity (maybe because they are useful, or surprising, or trauma-inducing).

New memories also capture moments of learning. So those long stretches that bunch up into a sense of time that’s been skipped over… do they also represent periods of non-learning? The horror! Or even worse – learning that has since been forgotten? Well, maybe not; memories aren’t always well anchored in time, so you might retain the information but have forgotten when you learned it. Whew!