Here's another theory - you know... one of those ones that random thoughts lead to, but you have no way of proving to yourself, let alone anyone else. It's about the perception of the passage of time.
Everyone says the years seem to go past quicker now than they used to. So either time is really speeding up (which I understand is actually possible) or our perception of it is changing. I reckon that you perceive time in relation to the amount you have already lived. So, for instance, when I was 6 it always seemed FOREVER until next Christmas. SOOOO far away. But now I can't believe it's the 1st August - Christmas was, like, yesterday wasn't it?
But when I was six, the proportional time from one Christmas to the next was 1/6 of my life. Now I'm 34. So a year then felt like 34 divided by 6 years now: 5.67 years. I think that sounds about right. How can we ever prove this?
While we're on the subject of time, I have another. You know sometimes when you look at your watch the first second seems to last a lot longer than any subsequent second. You think your watch has stopped. I think I know why this happens.
One of the main things your brain has to do is to keep you out of danger. So whenever you change your field of view, your brain has to reassess the whole picture for new danger. This involves lots of calculations every time you change your field of view. If your perception of time is related to the number of calculations your brain is doing per second, then time could appear to be slower after changing you view. I have used this to make unpleasant things (time on a rowing machine) appear to go faster, by deliberately not changin my field of view. Sadly I'm not sure it had a huge effect. However, I have seen experiemtns on TV where peoples brains respond quicker under the aeffect of adrenaline. I wonder if it's the same thing?