Most of you have probably heard of the Coriolis effect by now, which makes water drain clockwise in the Southern Hemisphere, and counter-clockwise north of the equator - if only because you watched The Simpsons episode where Bart travels to Australia to find out if it's real or not. 

But online there's still a lot of debate over whether the whole thing is bunk. To get a definitive answer once and for all, Derek from Veritasium and Destin from Smarter Every Day have collaborated on the ultimate video experiment, spanning both hemispheres at once. And they've filmed the whole thing in the Internet's first ever pair of synchronised YouTube videos. Yes, ladies and gentlemen, you're about to watch history being made.

So how do we do this? First of all, the synchronisation only really works on a desktop, as a mobiles won't let you play two YouTube videos at once (I know, I know, and we can land a rover on a comet, right?). But you can get around this by getting together with another science-loving friend and syncing your phones up together to watch the episodes in tandem… or just waiting until you're at home. Trust us, it's worth it. 

To get started, hit play on the Smarter Every Day video on the left, and then wait for Destin to count you in before hitting play on the Veritasium video on the right. A little fine-tuning may be required to make sure you get the videos perfectly in sync, but once you do, you'll see a fantastic tandem experiment conducted simultaneously in the US and Australia. And you'll also get to find out once and for all whether the Coriolis effect is real (and what the hell it actually is).

We don't want to spoil too much, but let's just say the whole thing goes way beyond toilets and into a giant kiddy pool experiment with perfectly controlled variables. And the results… well, they're pretty damn spectacular. This is science vlogging at its very best, folks. 

How to watch:

1. Hit play on the Smarter Every Day video on the left.

2. Wait until Destin counts down to "one" and then hit play on the Veritasium video on the right.

3. Enjoy watching YouTube history in progress.