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In 276BC a Greek man named Eratosthenes arranged for people to put a couple of sticks in the ground 500 miles apart and measure the angle at which their shadows were projected on the ground at the same time. The shadows made different angles and this would be impossible if the Earth was flat. If you stand near the shore you can watch ships sail over the horizon and watch as they disappear around the curve of the Earth. There are photos of the Earth from orbit in which it looks spherical. There are many more observations that can only be explained by the Earth being approximately spherical. This raises a problem: why are there people who say the Earth is flat? I'm going to use flat Earth theories as an example because very few people will object and it doesn't require a lot of explanation to see why flat Earth theories are wrong.
There are many other ideas that can be refuted by observation or by other arguments that have no known criticisms but which people nevertheless hold. How can it be the case that people hold such ideas?
There is another problem that is related although you mig
ht think it isn't. A person doesn't invent or maintain ideas because they are justified because justification is impossible. So how can we describe how a person adopts and maintains his ideas? Instead of justification a person produces variations on his ideas in response to problems and then selects among those variations. Knowledge is created by an evolutionary process. What are the units on which this process operates?
A gene is a unit of information that can be genetically transmitted: it can be copied from one generation to the next without changing. Cultural information can also be transmitted without changing. For example, the plays of William Shakespeare have been copied for centuries without being changed. Song lyrics are copied without being changed, both in video and audio on the internet and in cover versions. By analogy with genes, Richard Dawkins defined the term **meme** to denote a culturally transmissable unit of information.
A meme is copied as a result of the behaviour of people who experience it. A good novel may be copied because people read it, like it and recommend it to their friends. But there are also smaller units of cultural information such as gestures, practices like wiping your bum with toilet paper after you defecate, catchphrases and walking.
A gene is copied by machinery that is set up to copy it exactly. A meme is not copied in that way as pointed out by David Deutsch in "The Beginning of Infinity", Chapter 11. Rather, a person enacts some behaviour and another person copies it by guessing about how and why the behaviour was enacted. For example, a person might guess that others wear shoes to protect their feet from damage and hear a rhyme about how to tie shoelaces:
Bunny ears, bunny ears, playing by a tree.
Criss-crossed the tree, trying to catch me.
Bunny ears, bunny ears, jumped into the hole,
popped out the other side beautiful and bold.
That rhyme is itself a meme that people transmit to help children learn how to tie shoelaces.
The shoelace tying meme solves a problem of how to keep shoes on your feet. This helps people to move around and to solve many problems such as how to get to work, or go shopping, or go to meet friends. Those problems lead to further problems that people want to solve, like how to perform tasks at work, or what to buy at the shop, or what to do with their friends.
Some memes solve a problem by stopping the problem solving process. Sometimes a teenager will kill himself for various reasons like academic failure, sexual rejection and so on. This solves the problem of the teenager feeling bad about those failures but it stops him from solving any further problems.
David Deutsch called memes that lead to more problem solving **rational memes** and those that stop problem solving **antirational memes**.
Rational memes have to persuade people to hold them by solving problems and by opening up the possibility of solving further problems. Solid state physics solves problems by explaining the structure of solid materials. This gives people the opportunity to solve new problems, like using solid state physics to help fabricate chips used for computers.
Antirational memes have to convince their holders to adopt them and to refrain from criticising them. Flat Earthers often claim the scientific establishment is corrupt and so people shouldn't listen to scientific criticisms of flat Earth theories. This doesn't make much sense because if scientists were corrupt shills for the globe it shouldn't be too difficult to refute their ideas. The only effect of urging people not to engage with advocates of the standard theory of the Earth is to shield flat Earth from criticism. The same is true for other claims that you shouldn't engage with critics of some theory or ideology. For example, trying to censor flat Earth content or other antiscience content runs the risk of creating or reinforcing a tendency to treat scientists and scientific institutions as infallible. There are many examples of scientists' fallibility and even of them acting in a corrupt or cruel manner. For example, doctors decided to leave syphilis untreated in a group of black Americans despite the availability of cheap and effective treatments. Scientists and doctors are people and people act in stupid and bad ways, so we should expect that scientists and doctors will sometimes do stupid and bad things and should look out for such problems.
People who hold antirational memes will deny that they are antirational and will provide examples of people arguing over the relevant ideas. But in general those people can't state the opposing position correctly or work out its consequences. Nor can they state correctly the criticisms of their position let alone refute them. For example, flat Earth believers don't understand and can't refute the standard position on why boats disappear when they sail over the horizon:
Clinging to an idea in the face of repeated failures to be able to state the opposing position is a sign that something is badly wrong in how a person is thinking about that topic.
Anyone who is reading this should not imagine that they are immune to antirational memes. Nor should they imagine that I am immune to them. You should be looking out for problems with your worldview and you should be extremely suspicious if you start behaving in any of the ways described above on any topic. If the above gives you a twinge of intellectual conscience in how you think about some topic you should investigate that instead of suppressing it.