How "mystery spots" and "gravity hills" work

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How “mystery spots” and “gravity hills” work

All over the US, and in several parts of the world, in rural areas and urban, there are places that locals refer to as either “mystery spots” or “gravity hills”— places where gravity seems to work backwards. But are they really anomalies in gravity? Nope, we’re just gullible. Surprise.

The phenomenon has sparked a lot of ghost stories, from spectral children to Civil War soldiers trying to roll cannons into position. Since the illusion is most noticed on roads near hills, those with a scientific bent nickname it the Magnetic Hill. People think that the hill behind has to have some magnetic property that is influencing their cars. What’s really influencing their cars is good, old-fashioned glitches in human perception.

Remember the joke where a grumpy old-timer tells kids that, in his day, they had to walk to school through the snow, uphill, both ways? That’s not just a joke. People do tend to see inclines as being tilted up more than they seem as tilted down. Researchers at the University of Padova and the University of Pavia found that it’s relatively easy to make people see something as uphill, and hard to make them see it as downhill.

They created a fake landscape out of angled boards. When the middle board was angled slightly downhill, and the boards around it were angled steeply downhill, most people they asked saw the middle board as going uphill. However, when they reversed the experiment, and showed people a slightly uphill stretch between two steeply uphill boards, it was seen as level, and not downhill. When the experimenters went on to test a horizontal board between two downhill stretches it was seen as uphill. When they tested a downhill segment between two uphill boards, it looked level. In other words, there wasn’t anything they could do to make that middle section look downhill to anyone.

And these were just boards. Gravity hills make use of the entire landscape. First, most gravity hills are in places where a straight horizon is obscured in every direction. There isn’t any horizon line to help people get their bearings. Usually the hill in question is a road cut into two uphill segments, but there are hills that are surrounded by downhill slopes. Generally, there are also trees and no buildings in the area. Buildings tend to stay perpendicular to the ground. Most of the time, trees do as well. When it comes to a choice between light and perpendicularity, though, the trees choose light every time. When they lean so that they’re perpendicular to a downhill slope, it looks straight.

When everything, the contrasted slope of the landscape, the angle of the trees, and the inability to check anything against a horizon line, comes together on a slightly downhill slope, it will look uphill to whatever hapless chump happens to be wandering along it. Whenever someone checks with a level, or a GPS system the fun is over. Downhill is downhill. This illusion, though, is one that generally doesn’t fade when you know the trick. So, if you have any mystery spots in your area, do let us know where they are, so we can roll up them.

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