If I experience many new things during a short period of time, let's say a week or a weekend, it sometimes feel like it happened months ago when I reflect on the experience shortly after.

Last summer, this phenomenon yet occured when me and my wife whent on a short trip outside town, and coming back it felt like days had passed when in fact we had just been away for something like 5–7 hours.

So, a popular saying says that time goes fast when having fun. For me, the combination of fun and experience new things tend to slow things down. This summer trip got me curious, and a search led me to an article on The Huffington Post called "This Simple Mental Trick Can Slow Down Time" that explained why I had felt the way I felt.

Most of us know the feeling well: As we grow up and fill our days with more busyness, time seems to fly by faster and faster. Of course, we know that time is moving at the same rate as it did during childhood, when lazy summer days seemed to stretch on infinitely. But what's changed is our perception of time. According to neuroscientific research recently highlighted by Inc. Magazine, how the brain perceives time passing determines whether our days feel luxuriously long, or short and harried -- and it's something that we have a certain level of control over. By paying attention and actively noticing new things, we can slow time down.

And in this clip, "The Speed of Life" presented by Derek Muller from the YouTube channel Veritasium, an experiment with repetitive images (at the 3:45 minute mark) supports the theory mentioned above:

H/t Holy Kaw.