If you’ve ever taken an extended, curvy driving tour through mountainous, rural America – Hatfield and McCoy country or deeply forested Oregon, perhaps – you might have encountered a sign much like this one:
Known as gravity hills, mystery hills, magnetic hills, mystery spots, and a slew of other catchy names, these locations are part Americana tourist trap, part carnival funhouse. For a slight fee, you can watch your car roll uphill while in neutral or see balls roll up inclines.
Unlike some attractions, the purveyors at a gravity hill actually can deliver these promises. But how does it work?
According to many owners, an automobile disobeying the laws of gravity stems from supernatural, magical, or unexplained phenomena. Some claim ancient, Indigenous curses or ghosts cause peculiarities; some tout leylines deep within the earth that exert magnetic power over a vortex; others claim gravity itself breaks down anomalously at their mystery location.
And, yes, some proclaim the locations receive help from out of this world.
If rolling uphill sounds dubious to you, consider the case of the gravity hill in Lewisberry, Pennsylvania.
There, a group of ghost children, doomed to the afterlife after a bus accident, push cars up the incline at the spot of their demise:
Strangely, another group of ghost children, who perished in a school bus, push cars up a gravity hill in Altadena, California, as well.
From a sample size of two, it seems all those who believe these spots to be the cause of leylines, gravitational anomalies, or ancient curses are simply wrong. It’s the ghost children.
As you can see from the videos above, this phenomenon actually is real. Vehicles do seem to roll up grades. Short of ghost children, what is happening in these situations?
If you watched the second video above, you know the answer: optical illusions.
The mystery lies in the layout of the gravity hill. For our sense of up and down, we subconsciously rely on the horizon. On gravity hills, the natural horizon is almost always hidden or obscured. This lack of our natural plane allows for some downhill slopes to appear to be going uphill, thanks to the topography of the entire system. Without our usual frame of reference, other objects that we associate with specific orientations, such as trees or houses, might fool us into believing the entire system is slanted in a way that it is not. For example, we usually see trees growing straight up, perpendicular to the ground. However, trees can grow at angles. If we cannot see the horizon, we might assume a tree is pointing straight up, when it’s actually slanted in comparison to the horizon.
Watch the two videos above again.
In the Pennsylvania video, you can see the actual horizon is obscured. Instead, we see an artificial horizon comprised of the road with which the hill intersects. Take a look at that road. You can see it is also topping a hill. Further, the trees do not grow straight. At the beginning of the video, the car seemingly sits on a downslope, though it likely appears that way through a matter of perspective. In reality, that stretch could be flat. All these factors combine to make it look as if the section near the stop sign goes upward toward the location of the car at the start of the video. If one could zoom out from the locale, the true nature of the hill would reveal itself to be a downslope.
Similarly, in the California footage, the true horizon is hidden by the mountain as the car approaches, throwing off our sense of equilibrium. Then, when the camera moves to a side view, our horizon becomes the undulating hill, which hides the true slant of the road.
In 2003, researchers at the Universities of Padova and Pavia in Italy studied how the lack of a horizon can impact a human’s perspective and sense of equilibrium. Although these optical illusions can occur naturally, the researchers created scenarios in a lab that mimicked those of gravity hills. They discovered they could fool viewers with the simple placement of signs or trees.
This video gives a nice wide view of a gravity hill and how we can be tricked into thinking slopes point in a direction they actually do not:
While we’ve focused on cars rolling uphill, the opposite phenomenon can also occur, as evidenced in the preceding video. In bicycle racing, they call these stretches “false flats.” These spans often happen during protracted climbs. To a rider, a section might appear to be flat, especially in relation to the previous gradient. However, the flats are actually still uphill, creating psychological hardships for the rider, hoping for a break but getting an upslope.
So, the next time you drive by the Oregon Vortex or any other gravity hill, remember a couple of things. Our eyes can deceive us; take the wide view. And, if you think it might have been aliens causing the antigravity anomaly, it was actually ghost children. Guaranteed.
Further Reading and Exploration
Antigravity Hills are Visual Illusions – Psychological Science
These Gravity-Defying Hills Are One of The Strangest Natural Phenomena We’ve Seen – Science Alert
I know a place where things seem to roll uphill. How does it work? – University of California Riverside
List of gravity hills – Wikipedia