Nostalgia is a very strange feeling. It is probably the best depiction of bittersweet out there. Nostalgia can make people happy, it brings up fond memories and reminds people of easier days. Nostalgia can also be sad because it comes with the harsh realization that those days are long gone and things have changed a whole lot. Time is an odd concept; there is no stopping it, but everyone can learn to appreciate it for what it does to the world.

It might seem like a weird concept since everyone is still experiencing the 2000s, but 2000s nostalgia is a very real thing. 2000s kids are 24 at the oldest, which means many things from their own childhoods have changed over the past couple of decades. The 2000s have been a rollercoaster so far, and it's only going to get weirder. It is interesting to see just how much things have changed even since the early 2000s, which is not that long ago, relatively.

Take a look back at some of the things that started this century off on an interesting foot. Here are 25 images to remember and think about while realizing how quickly time goes by.