Mind-bending optical illusions are not just found in popular images on the Internet or Tudor paintings, they can also be found when driving around. Gravity hills are one such seemingly impossible feature.
In these locations, gravity seems to stop working properly. You look at the road ahead of you, note you are clearly uphill, and yet a ball will “magically” roll towards you. There is obviously no violation of the laws of physics going on. Instead, our eyes and brains are tricking us, making a road that is physically going downhill appear as if it is going uphill.
The illusion is so good that these locations are often referred to as antigravity hills, spook hills, mystery spots, and for some reason magnetic hills. I guess if the explanation is not obvious, invoking something as non-intuitive as magnets is as good an answer as any other.
The ability of these hills to mess with our perception is quite singular. Researchers have been looking into these locations for some time and think it’s the result of a combination of factors. They found that a key factor is the lack of a visible horizon. The height of the visible horizon is important to assess the slope of a road. If you can see the horizon and you are on a slightly downhill road that it is proceeded, followed, or flanked by a steep downhill road, it will appear that the slight downhill one is going uphill.
This solution comes from a study conducted in 2003 by researchers at the Universities of Padova and Pavia. They tested different scenarios by making physical models, changing certain parameters, and then asking volunteers to work out the type of slope they were looking at.
This is not the only way to have a gravity hill. If the horizon is visible, you can still have the illusion. For that to happen, you need to have a tilted landmass and the road slightly less tilted than the landscape. And voila, the world stops making sense.
Gravity hills are found everywhere in the world. Over 100 such “magical” places are listed online, with 42 of them in the US alone. If you want to experience them for yourself, well you just need to look up the closest one to you.
[H/T: Science Alert]
