Scientists are not sure how the brain tracks time. One theory holds that it has a cluster of cells specialized to count off intervals of time; another that a wide array of neural processes act as an internal clock.
On an obvious level, these kinds of findings offer an explanation for why other people’s children seem to grow up so much faster than one’s own. Involved parents are all too well aware of every hiccup, split lip and first step in their own children; whereas, seeing a cousin’s child once every few years, without intervening memories, telescopes the time.
On another level, the research suggests that the brain has more control over its own perception of passing time than people may know. For example, many people have the defeated sense that it was just yesterday that they made last year’s resolutions; the year snapped shut, and they didn’t start writing that novel or attend even one Pilates class. But it is precisely because they didn’t act on their plan that the time seemed to have flown away.
By contrast, the new research suggests, focusing instead on goals or challenges that were in fact engaged during the year — whether or not they were labeled as “resolutions” — gives the brain the opportunity to fill out the past year with memories, and perceived time.
Finally, the mind is perfectly capable of interpreting a fast-forward year, or decade, as something other than a frittering away of opportunities for self-improvement. In another series of experiments published in Psychological Science, psychologists found that when people were tricked into believing that more time had passed than was really the case, they assumed they must have been having more fun. The perception heightened their enjoyment of music and eased their annoyance at doing menial tasks.
(image source: http://www.nytimes.com/imagepages/2010/01/05/science/05mind-1.html)