People are flocking to these mysterious hills that seem to defy gravity - here's what's actually going on

What goes up must come down, and not the other way around, right?

Wrong. Drive somewhere like Confusion Hill in California or Magnetic Mountain in Canada, put your car in neutral, and watch one of the most widely accepted laws of physics turn on its head. Your car will seem to defy gravity, slowly rolling uphill.

Gravity hills, also known as magnetic hills, mystery spots, and spook hills, have been popping up by the hundreds all over the world. Visitors are flooding to these sites, even paying small fees to experience the eery, seemingly supernatural effects of what has been referred to as "antigravity."

So what's really going on?

There are many possible explanations for what could make an object break one of the sacred laws of science: Mysterious magnetic sources beneath the earth's surface could be slowly pulling you towards them. A glitch in spacetime could cause the laws of physics to unravel into backwards chaos. An army of angry ghosts could be muscling your car to the top of the hill with nothing but their bare ghost hands.

Or maybe it's just an optical illusion.

All of these sites have one thing in common (other than their apparent disregard for gravity): the horizon is either curved or obstructed from view. This is key. Horizons provide us with a very useful reference point when we're trying to judge the slope of a surface. A study published in Psychological Science in 2003 found that false horizon lines can be deceiving to observers perceiving landscapes.

Without a true horizon in sight, objects such as trees and walls - which your eyes use as visual clues to determine perpendicularilty - can play tricks on you. If these objects are leaning slightly, they might make you think you're looking at a downward slope, when in actuality you may simply be looking at a flat (or even uphill!) surface.

As a result, anything you rest upon the surface - whether it's a rubber ball, a stream of water, or a 4,000-pound car - will appear to fight the flow of gravity and travel uphill. And while the thought of ghosts or supernatural forces carrying these objects is tempting, the most likely explanation is that your eyes are just playing tricks on you.