- 11 days after November 18 is the 333rd day of the year. On that day in 1877, Thomas Edison demonstrates his phonograph for the first time, and we all know how that device was used to pass secret messages via playing music backwards. Don't forget that Thomas Edison was a Freemason and owned the Edison Illuminating Company.

the astronauts put a bunch of mother*&$^ing reflectors on the moon, that's why!

1 - Grab a high-power laser and a light sensor

2 - Point the high-power laser at any of the Lunar Laser Ranging RetroReflectors:
coordinates           degrees N    degrees E
(on the moon -duh)  (latitude )     (longitude)
Apollo 11 LRRR      0.67337      23.47293
Apollo 14   LRRR     -3.64421     -17.47880
Apollo 15   LRRR     26.13333       3.62837

Here, conspiracist friends, is a completely fake and photoshopped picture of an alleged LRRR shot in Hollywood by Stanley Kubrick right before the CIA took him down.

3 - Fire a densely-packed lightbeam at one of these coordinates (with a pulse frequency unique to it so your conspiracist friend cannot pretend it's just space noise).

Another fake long-exposure shot of a laser pointed at the moon to "measure" the "distance" between the "earth" and "the moon"
(we all know this is obviously a mind-control device used by the illuminati to project a hologram of reality upon us)

4 - ?? a couple seconds (you know, because light travels at ~c=~300.000km/sec and the moon is at ~300.000km)

5 - measure light that has been mirrored back to your sensor.

6 - Profit by making your conspiracy theorist ass shut the hell up.

Monkeys don't wonder about if the Earth is flat or round. So at least flatters are smarter than monkeys.

I am interested how you managed to pinpoint those co-ordinates when the earth is spinning at 1000km/s, must be quite tricky
and what was the repeatable experiment you did to confirm the speed of light? or are you just relying on what you have been told (having faith in your scientism)?

https://www.youtube.com/watch?v=vX6tT3dFS78

Why so many words. Just put a plain and simple statement. I've been successfully indoctrinated by the religion of monkey man science to believe it.

Blinded by that science bonus material: https://www.youtube.com/watch?v=SmCE8GhTi-M

EDIT: In a fairy tale of course you can prove spinning ball earth with that science, no doubt. But point is that flat earth reality destroys it and you should wake up.

I wouldn't worry about it too much.  Among most conspiracy theorists, providing evidence contrary to their beliefs will only make their beliefs stronger, and this is usually proportional to how good the counter-evidence is.  If it doesn't make them think the first time, it likely never will.

That being said, they're already paying for their mindset in real life, and how much they pay is proportional to both the time spent and how public they are with it (e.g. are they just sharing their beliefs anonymously, or are they sharing them with friends, family, coworkers, etc.?).  The more they dive into the conspiracy, the more it will take a toll on their social success, financial success, and overall life satisfaction.