Flat-Earthers’ Laser Tests are Misleading

Flat-Earthers like to perform the experiment involving lasers to ‘disprove’ Earth’s curvature. If they observe a laser beam from the other side of a lake or an ocean, they would wrongly conclude Earth’s curve does not exist. It was merely a misunderstanding of how lasers work.

A laser beam diverges, and will not be focused to a point very far. A laser emitter with the beam divergence of 1 mRad will have a beamwidth of 10 meters over 10 km. Contrary to what they expected, a laser beam will not stay on the constant height from the surface.

A laser beam is a form of light, and just like every other light, they are affected by atmospheric refraction. In most cases, atmospheric refraction will bend the laser to follow Earth’s curvature up to a point. Some of the laser beams will skirt just above the surface where atmospheric refraction is the highest.

Due to atmospheric refraction, a distant object that appears close to the horizon will look heavily distorted, compressed, and fuzzy. An observer will have difficulty recognizing such a distant object. But a bright laser beam can easily stand out against a darker, blurred background.