A gravity hill is a place where gravity seems to be working against itself; where gravity seems to temporarily not work as it should. There are hundreds of gravity hills around the world and they are characterized as places where a geographical optical illusion has been created.
Gravity Hills: An Optical Illusion
Also known as spook hills, gravity hills are, at their core, an optical illusion. The landscape of an area can make a small downhill slope appear to be going uphill. Cars can be seen rolling uphill against the perceived gradient of the road, stunning drivers and spectators alike. One of the most important feature of a gravity hill is that the horizon line is partially or completely obscured, which blurs viewers’ perception of up and down.
Some gravity hills are reported to not just be optical illusions, but sites of supernatural activity as well. Most of these are local myths and legends, but guides and fans of the local spots swear by their tales.
Where are Gravity Hills Located?
According to researchers, gravity hills tend be located in areas where the stretch of road is relatively short (50-90 m), not too wide, and surrounded by a natural landscape devoid of buildings. These geographical aspects combine to create an optical illusion that gives visitors the impression that a downhill slope is actually uphill.
California, to name just one location of mystery spots and gravity hills, is chock full of anomalies ranging from old mining roads to the Golden Gate Bridge. One particular gravity hill, Mystery Spot in Santa Cruz, has been attracting visitors since the 1930s and is the site of more than a few eerie feelings and misunderstood sightings.
Spook Hill, located in Lake Wales, Florida, is another example of a gravity hill. Spook Hill was listed on the National Register of Historic Places in 2019.
In South Bend, Indiana another gravity hill is the subject of folklore. In 1973 account, Stephen F. Zmyslo submitted a report about a hill outside South Bend, Indiana, where a car in neutral rolls up the hill backwards. Zmyslo noted that the legend claims that a ghost inhabits the location, and that if the motorist applies the brakes, the ghost will push the car up the slope or steal the gasoline.
How Do Gravity Hills Work?
Scientists will point to the facts when observing gravity hills- you can’t see the horizon, the trees are bent in a different manner, the gradient of the road is offset by the geography of the surrounding hills. Our human perceptions are often not enough to discern what is right in front of us; our brains take in so much information and, in the process of filtering some of it out, makes us see things.
The wonder of gravity hills shouldn’t be taken away by science, though. People around the United States and the world continue to marvel at their car parked in neutral rolling up what seems to be a downhill slope. People will pay to stand in line and experience the weirdness surrounding the Mystery Spot in California, while others will marvel at the stream that seems to be flowing uphill.
Bressan, P., Garlaschelli, L., & Barracano, M. (2003). Antigravity hills are visual illusions. Psychological Science, 14(5), 441-449. DOI: 10.1111/1467-9280.02451
Parts of this article have been supplemented with writing by Caitlin Dempsey.