It’s not hard to spend hours upon hours reaching the deepest depths of videos over on YouTube, and I think we can all admit that we’ve found things on YouTube we could have never imagined even existed. Over the years, the amount of content people watch each day has grown more and more, and today YouTube has revealed that users are now watching over 1 billion hours of video each day…

The company says in a blog post that it reached this milestone at some point last year, and as WSJ notes, it represents a ten-fold increase from the same total back in 2012. Putting that in perspective, Google says 1 billion hours is equivalent to well over 100,000 years, the same amount of time it takes for a beam of light to make it from one side of the Milky Way to the other.

A few years back, we made a big decision at YouTube. While everyone seemed focused on how many views a video got, we thought the amount of time someone spent watching a video was a better way to understand whether a viewer really enjoyed it. It wasn’t an easy call, but we thought it would help us make YouTube a more engaging place for creators and fans. And last year, we hit a big milestone on that journey: people around the world are now watching a billion hours of YouTube’s incredible content every single day!

While many would attribute this to the sheer amount of content and the ever-growing quality of it (which surely helps, at least in part), YouTube has another answer: personalization algorithms.

Once you’ve spent some time watching video on YouTube, you’ll notice that the recommendations alongside the video tend to find videos that you enjoy, even if those videos aren’t directly related to what you’ve been watching. The Wall Street Journal points out that this is thanks to a partnership between YouTube and the Google Brain team, which have worked together to filter out “single-use” videos (those which you aren’t really interested in, but happen to watch from time to time).