[Physics FAQ] - [Copyright]

Updated May 1998 by PEG.

Original by Philip Gibbs 1996.





I know a place where things seem to roll uphill. How does it work?

Sometimes you may find or hear of a mysterious place where objects can apparently roll uphill. This is a remarkably common illusion that is found in numerous locations around the world. Usually it is a stretch of road in a hilly area where the level horizon is obscured. Objects such as trees and walls that normally provide visual clues to the true vertical, may be leaning slightly. This creates an optical illusion, making a slight downhill look like an uphill slope. Objects may appear to roll uphill. Sometimes rivers even seem to flow against gravity.

Spots where the illusion is especially powerful often become tourist attractions. Tour guides may claim that the effect is a mystery, that it is due to magnetic or gravitational anomalies, or even that it is a paranormal phenomenon that science cannot explain. This is not true of course. Natural anomalies can only be detected with sensitive equipment and cannot account for these places, but science can easily explain them as optical illusions.

There are several things that enable us to sense which way is up. The balance mechanism in our inner ears is one system we have, but visual clues are also important and can be overriding. If the horizon cannot be seen or is not level, then we may be fooled by objects that we expect to be vertical but that really are not. False perspective might also play a role. If trees in a line get larger or smaller with distance, our sense of perspective is thrown off. Objects far away may seem smaller or larger than they really are.

People often overestimate the steepness of a slope. If you are standing on a slope of 1° it will seem like a slope of 5°, and if you stand on a slope of 5° it may seem like you are on a slope of 30°. Because of this effect, the anti-gravity illusion can seem stronger than it should be—even though you know the cause.

Even when the true cause is understood, it can be difficult to believe. In some cases the sea horizon is partly visible and it seems incredible that the effect can be an illusion. If you think there is a magnetic anomaly, just use two plumb lines, one made of iron and one of stone. They will hang at different angles if a strong magnetic field is acting horizontally. In fact magnetic anomalies are never that strong, and are never the cause.

But it is not always easy to demonstrate that a slope that appears to go uphill is really going downhill. Plumb lines and spirit levels cannot be relied on if you think there is a gravitational anomaly. If the slope runs parallel to a sea view, it will be possible to compare a plumb line with the horizon; otherwise, the only reliable way of determining the true horizontal is by careful surveying. A good topographical map of the area may show which way the land is really sloping, and the results will confirm the illusion. Gravitational anomalies are always very small. In any case, how would you ever notice a gravitational anomaly?—after all, your sense of balance would be affected equally to how objects would be affected. The anomaly would not be apparent unless there was a clear view of the sea behind the slope, which there never is.

A search on the web turns up a surprising number of examples of this illusion. Most are natural, while others have been constructed in theme parks. Below is an incomplete list of some natural ones. Many thanks to those who have sent more site details for this list. Do check locations are correct before making a long journey and remember that it may be dangerous or illegal to stop or reverse your car on slip roads and bends!

Mystery Spot Road , off Branciforte Drive, Santa Cruz, CA, USA. A spot 50 m in diameter in the redwoods of the Santa Cruz Mountains.

, off Branciforte Drive, Santa Cruz, CA, USA. A spot 50 m in diameter in the redwoods of the Santa Cruz Mountains. Mystery Spot , Putney Road, Benzie County, Michigan, USA.

, Putney Road, Benzie County, Michigan, USA. Gravity Hill , Northwest Baltimore County, USA, along a public road running through the Soldier's Delight environmental area.

, Northwest Baltimore County, USA, along a public road running through the Soldier's Delight environmental area. Gravity Hill , Mooresville, Southwest Indianapolis, USA. Located off SR 42 on the south side of Mooresville.

, Mooresville, Southwest Indianapolis, USA. Located off SR 42 on the south side of Mooresville. Gravity Road , Ewing Road exit ramp off Route 208, Franklin Lakes, USA.

, Ewing Road exit ramp off Route 208, Franklin Lakes, USA. Mystery Hill , Blowing Rock, Highway 321, Carolina, USA.

, Blowing Rock, Highway 321, Carolina, USA. Confusion Hill , Idelwild Park, Ligonier, Pennsylvania, USA.

, Idelwild Park, Ligonier, Pennsylvania, USA. Gravity Hill , off State Route 96 just south of New Paris, Bedford County, Pennsylvania, USA.

, off State Route 96 just south of New Paris, Bedford County, Pennsylvania, USA. Gravity Hill near White's Hill, just south of Rennick Road on County Truck U, south of Shullsburg, in LaFayette County, Wisconsin, USA.

near White's Hill, just south of Rennick Road on County Truck U, south of Shullsburg, in LaFayette County, Wisconsin, USA. Oregon Vortex , near Gold Hill, Grant's Pass, Oregon, USA.

, near Gold Hill, Grant's Pass, Oregon, USA. Spook Hill , North Wales Drive, North Avenue, Lake Wales, Florida, USA.

, North Wales Drive, North Avenue, Lake Wales, Florida, USA. Spook Hill , Gapland Road just outside Burkittsville, Gapland (Frederick County), Maryland, USA.

, Gapland Road just outside Burkittsville, Gapland (Frederick County), Maryland, USA. Magnetic Hill , near Neepawa in Manitoba, Canada.

, near Neepawa in Manitoba, Canada. Magnetic Hill , just off the Trans Canada highway, Moncton, New Brunswick, Canada.

, just off the Trans Canada highway, Moncton, New Brunswick, Canada. Gravity Hill , on McKee Road just before Ledgeview Golf Course in Abbotsford, British Columbia, Canada.

, on McKee Road just before Ledgeview Golf Course in Abbotsford, British Columbia, Canada. Electric Brae , on the A719, near Croy Bay, South of Ayr, Ayeshire, Scotland.

, on the A719, near Croy Bay, South of Ayr, Ayeshire, Scotland. Anti-Gravity Hill , Straws Lane Road, Wood-End, near Hanging Rock, Victoria, Australia.

, Straws Lane Road, Wood-End, near Hanging Rock, Victoria, Australia. Morgan Lewis Hill , St Andrew, Barbados.

, St Andrew, Barbados. Hill South of Rome , in Colli Albani, near Frascati, Italy.

, in Colli Albani, near Frascati, Italy. Malveira da Serra , on N247 coast road west of Lisbon, Portugal.

, on N247 coast road west of Lisbon, Portugal. Mount Penteli , on a road to Mount Penteli, Athens, Greece.

, on a road to Mount Penteli, Athens, Greece. Mount Halla , on the 1.100 highway a few miles south of the airport, near Mount Halla, on the island of Cheju Do, South Korea.

, on the 1.100 highway a few miles south of the airport, near Mount Halla, on the island of Cheju Do, South Korea. Magnetic Hill, on the Pekina Bypass Road just south of Orroroo, about 300 km north of Adelaide, Australia. (Note from the editor, 2016: I recently visited this spot and as the sign suggested, I parked my car in neutral, handbrake off, along the road. I also did the same thing at a right angle to the road's direction. The sign said the car would move, but my car didn't move at all. Being relatively new, perhaps it doesn't have enough iron in it? Admittedly the road is unsealed and thus not easy for a car to roll on at the best of times; but it has always been unsealed.)

References:

"Skeptical Inquirer", Vol 16, No. 1, 1991; an article about the illusion at Spook Hill.

"Seeing Is Believing? Haunted Shacks, Mystery Spots, and Other Delightful Phenomena" by Chris Banta.