Flat earthers are a thing in 2020.  Here is a simple do at home proof it is round given a large enough area of apparently flat land. Take a tripod like one would use for a camera and mount a laser pointer on it.  Lasers have the feature of being very well collimated, so their light does not die out in the same way as that from an ordinary light.   Point it at a paper target, attached to a car, and mark where the light falls.  It can help to point a camera at the paper target and record as this happens.

 Drive, you will have to drive to get far enough away, 10 miles straight away from the laser source.  Note the position of the laser dot.  The dot will have gotten bigger, but the center of the dot can be identified.  Drive another ten miles away, then again note the position of the center of the laser dot. Atmospheric effects may cause the dot to shimmer a bit but if you keep everything lined up you’ll still see it.  

The center of the dot will stay in precisely the same place.

OR

The center of the dot will appear to have risen some distance.

To do this experiment requires a very large area of apparently flat land.  Here in the Americas there are very large salt flats which should be large enough such as Salar de Uyuni in South America or the Bonneville Salt Flats in the United States of America.

If the first observation is made, then the Earth is flat. 

If the second observation is made, then the Earth is round.   

The Earth is VERY large, so it takes a laser level of precision to observe it from the ground.  After this open your mind to the fact that the Earth is round and scientist aren’t liars out to deceive people.

Elitism: Why Round Earth Arguments from Scientist Often Fail to Convince.

The problem with the arguments above is that to flat earthers who do not believe space is real all of them fail.  They presuppose a belief that outer space exists. They need a proof that does not presuppose that at all.  They then proceed to denigrate flat earthers which is not how to get people to agree you are right.

In case anyone wonders, I of course believe in space.  I am a theoretical astrophysicist. My whole life is dedicated to thinking about astronomical and astrophysical phenomena in relation to the fundamental laws of nature. I have a master’s degree and a remarkably interesting story on why I don’t have a doctorate (It wasn’t my grades).  I work on a project that will put a gravitational wave observing satellite system into space, the Laser Interferometer Space Antenna, LISA.  So, I can say the following about the above three people as colleagues in at least a broad sense of the word.

They come off a bit elitist.  Imagine if I started my proposed experiment by talking about how I am from a tiny suburb of Chicago which has had two astronauts grow up in it.   “How dare you”.  Then talked about my credentials.  Then proposed my experiment. How would that come off to a flat earth believer who thinks space is a hoax?   

DeGrasse Tyson touches on this aspect of the “debate” a little.  This is not really a “debate” this is one set of people speaking facts and another speaking thing that are clearly counterfactual.  That said people being people to convince people facts just aren’t enough. They just aren’t.

Misguided Theism: Why Flat Earthers Believe The Earth Is Flat.

A lot of flat Earth discourse is based in a very American interpretation of the King James bible.  Many born again Evangelical Christians who think the Earth is flat also think that the King James Bible, and only the King James Bible, is the literal word of Jesus Christ.  Not any other translation, not even the earlier copies in Hebrew or Aramaic which Jesus actually spoke in. 

I invite such believers, not to convert or anything, but do look at the clear proof and solid evidence and to reflect on just on sentence from the Quran. “Al-ḥamdu l-illāhi rabbi l-ʿālamīn” “Praise be to God, Lord of the Worlds”. 

If a fully Christian centric argument is all you’ll believe here’s an argument rooted in the bible showing that it does not imply a flat Earth either.

Embrace heliocentrism and abandon the somewhat sacrilegious anthropocentrism that places our world as special.  Accept our place as just one tiny grain of sand in all of creation.   Just one planet that God would have created and populated with life.

What could be more pro-life than to believe that the universe is vast, expansive, and full of it?

Accepting the Earth is round after looking at your own simple experiment, and at all the evidence is accepting the true greatness of God.

Rejecting the Earth is round. Limiting creation to a region of finite extent enclosed in a “firmament” is to limit God based on our own human limitations.

Correction: The dot would appear to rise not drop. The laser shot parallel to the surface of the Earth, will, if the Earth is round appear to rise up as the paper target is moved farther from it. From the perspective of a person standing by the laser the paper target would appear to drop.