Dang it! I can’t find the cite.
They’ve actually done experiments where they took a kid and an adult and stuck them in a room with no clocks. At the end of however long of time, when they asked the subjects how much time had passed, the kids always estimated a longer period of time while the adults would always guess a shorter period of time.
This is something I’ve given a fair amount of thought to and I think it’s a combination of factors, most of which have been mentioned above. One of this is that a given unit of time is a less significant portion of one’s life over time. So it makes sense that 5 years seems like an eternity as a child, since it’s pretty much one’s whole life, seems like a really long time as a teen or young adult, and doesn’t seem all that long when one is old.
Another part is relative to events. When one is really young, things are always new and changing. But as one gets older, things start to settle into routine. Any given day doesn’t seem all that much shorter, but the work week seems to fly by. A lot of that is just because there aren’t any particularly distinguishing events over the course of an average week. Having fewer interesting events leaves less to be remembered, so it seems shorter.
One thing that does seem interesting, though, is how the same amount of time can seem both really long and really short. Trying to think about things that happened say two or three years ago, at least for me, can make for some interesting comparisons. For instance, I remember a particular movie that came out about that long ago, and it seems fairly recent because I didn’t see many movies between that one and the last few months. I also remember dating a girl then, and it seems quite a while ago, because I was fairly actively dating and had several other dates between then. So thinking about them independently, they seem to be quite a bit of time apart, like I dated her maybe 3-4 years ago and the movie is maybe a year and a half old, and yet, I saw that movie with her. So, it can lead to some interesting contradictions in remembering time.
Very good article (New Yorker) profiling David Eagleman, whose research addresses this question directly. Among other interesting bits, he believes that time perception is indeed influenced by repetitive experience, as discussed upthread.
I was just talking about perception of time with my coworker last night, and we came to a certain agreement. Basically, working 4 weeks on a boat, and having 4 weeks off at a time, makes time go by REALLY fast. I think it has to do with the fact that, on the day I come back to the boat from my 4 weeks off, it feels familiar, and in a way, feels like I never even left. It kind of feels to me that I am on the boat year round. But, at the same time, when I am home and enjoying my off time, it also kind of feels like that’s where I always am, for the whole year. Of course, I’m really only ever in either of those places for half the year, or 6 times total. And when you split things up and say “wow I only go out to the boat 6 times in a year?” it really doesn’t feel like very long at all. It gets so predictable and repetitive, that time just zooms by. My coworker has been out here with me for a year now, and it still feels like to both of us that he “just” started working out here.
This meshes with my personal thoughts - I really noticed this when I was on vacation recently for two weeks. New experiences (or at least substantially different from everyday) made it feel like an incredibly long time compared to my usual routine. A Saturday spent running around Paris, seeing sights and so on, felt far longer subjectively than hanging out in my own apartment playing a videogame that I’ve played over and over.
One thing is that when you’re young, especially in school, you can date specific events to a particular year. Along the lines of “that song came out while I was driving, but before college, so 1996”. Later events, not so much. General timeframes, like mid-2000s, sure, but something like 2005 specifically? Not usually.
This leads me to thinking that it’s partly the frequent changes in environment/experience we go through when we’re young. A new schedule in school every year, new friends, moving apartments all the time in our early 20s, all this makes time more specific, so it doesn’t blur together, so it feels longer.