Gravity hill

A gravity hill, also known as a magnetic hill, mystery hill, mystery spot, gravity road, or anti-gravity hill, is a place where the layout of the surrounding land produces an optical illusion, making a slight downhill slope appear to be an uphill slope. Thus, a car left out of gear will appear to be rolling uphill against gravity.^[1]

The slope of gravity hills is an optical illusion,^[2] although sites are often accompanied by claims that magnetic or supernatural forces are at work. The most important factor contributing to the illusion is a completely or mostly obstructed horizon. Without a horizon, it becomes difficult for a person to judge the slope of a surface, as a reliable reference is missing. Objects which one would normally assume to be more or less perpendicular to the ground, such as trees, may be leaning, offsetting the visual reference.^[3]

A 2003 study looked into how the absence of a horizon can skew the perspective on gravity hills, by recreating a number of antigravity places in the lab to see how volunteers would react. As a conclusion, researchers from Universities of Padova and Pavia in Italy found that without a true horizon in sight, the human brain could be tricked by common landmarks such as trees and signs.^[4]

The illusion is similar to the Ames room, in which objects can also appear to roll against gravity.

The opposite phenomenon—an uphill road that appears flat—is known in

• List of gravity hills
• The Crooked House – a building with an internal gravity hill optical illusion.

References

External links

Wikimedia Commons has media related to Gravity hills.

• Dunning, Brian (January 11, 2011). "Skeptoid #240: Mystery Spots". Skeptoid.