I read an interesting piece about even something as seemingly fixed and constant like time can be altered by our own perception. One interesting study was carried out to see the alteration of perception of time. The summary of the study can be read here. In the study, one group of participants were asked to rate the time taken to plunge off a big device, then watch other people do that and rate the time taken for the other people to get to the lower point. The time rated for self-experience was 36% longer, which showed that brain perceives time to be slower when we are undergoing an adrenaline-invoking experiences.
Another way the brain alters the perception of time is called as Chronostasis. The study can be obtained here. It is when you watch the second hand of an analogue watch, it is like it makes its first movement in our observation and then it seems to take a longer time to make a second movement to the next second. I don't really understand the mechanics of the study well, but the explanation is like this: Time appears to be extended a little upon a saccade. A saccade is a quick eye movement. When we observe the first movement of the second hand, and our eye experiences a saccade, the second movement of the second hand seems to take longer in time. Ahh, too many "seconds" and :movements".
There are various other studies that show how our brain can achieve remarkable feats by altering our perception of time. And this is obviously a new and intriguing subject for me. I found this book titled, "The Time Paradox", while browsing the Internet and I think I will make this the to-read-next book. It seems interesting.