Reverse Gravity

Japanese professor Kokichi Sugihara is rather well-known for several utterly mind-breaking optical illusions. I tried to recreate one of his illusions where a marble appears to roll uphill. Here are the results.

It’s a six second long video that I spent three hours trying to make. At least it looks kind of cool.

Process

Though it appears as if the marble is rolling up a slope and going against gravity, that’s not what’s happening. Rather, the angle of the camera and the cuts to the cardboard hide the actual shape of the model.

First, I created a preliminary model to test if I would be able to successfully recreate the illusion in the first place. These are the shapes I used in my attempt. The key part is the arrow-like cardboard cutout. The right side of the arrow is shorter than the left side which allows the shape to look like it’s bent upwards when viewed from an angle. The triangles cut out also help fuel that bent illusion by giving the shape a false sense of depth.

This was the preliminary model when I put all the above pieces together. As you can see, the illusion is partially successful. Though it does look like the cardboard is bent upwards, it still looks incredibly flat. This is most likely because the right side is still too wide. At least though this proved that I was on the right track.

From that first model, I made a second cleaner model. Instead of individual components, I tried to cut it out all at once, including the sides of the model.

Here’s a comparison of the first model and the second model when they’re both flat. For the second model, I shortened the right side of the arrow to be a little less than half of the left side and also increased the length and height of the sides. From here, I just constructed the model again the same way I did for the first model and taped the sides down to a piece of cardboard.

This is what the model looks like from the front. There’s a slight depression along the line at the middle of the model, but it’s only just enough to allow the marbles to roll downwards instead of off the side.

After constructing the model, it was simply a matter of finding the best angle to record a marble to give it the illusion of moving uphill instead of downhill. Et voilà! A marble that rolls against gravity. Newton’s spinning in his grave.

Here’s a video showing the illusion when it’s viewed from different angles. Really the illusion only works when it is viewed from one specific angle, but it’s neat and more than a little trippy to watch the model morph from something that makes logical sense into something that breaks the laws of gravitation. Even when we know what is actually going on, it’s still easy to get caught up in the illusion.

Bonus

Oh, the carnage of all my failed attempts and three hours of caffeine-fueled work. RIP to all the Amazon boxes, you died for a worthy cause.