Flat-Earthers’ laser tests are misleading. They pointed the laser from near the surface toward a distant observer. If the observer sees the beam, they conclude Earth is flat. It was a misunderstanding about laser & how atmospheric refraction affects it.
A laser beam diverges and will not stay focused forever. With a beam divergence of 1 mRad, the laser will have a beam width of 10 m over 10 km. It means the observer at 10 km away in the middle of the beam can change their height by 5 m and still be able to see the direct laser beam.
Lasers are just a form of light. Atmospheric refraction can bend it following Earth’s curvature, like any other form of light. By pointing the laser parallel to the surface, some beams will skirt just above the surface where atmospheric refraction is the highest, deflecting the beam to be visible beyond the curvature.
To the observer, the area very close above the horizon will appear distorted, fuzzy & compressed. It can be difficult to recognize the shape of an object. But a bright, nondescript laser beam can stand out against a dark background.
Therefore, just because a laser beam is visible over a considerable distance, it does not mean Earth is flat. The aforementioned characteristics of laser beams and Earth’s atmosphere cause the beam to be visible.
- Beam divergence – Wikipedia
- What is realistically the least possible beam divergence of a laser? – Quora
- Why Flat Earth Laser Tests are Misleading – Metabunk
- Lake Balaton Laser experiment to determine the curvature of the Earth, if any. – Metabunk
- flat Earth FAIL – Why ALL flat Earth laser experiments beyond the land-water horizon are inconclusive and worthless – Flat Earth Lunacy