I, as many people in science communication,
am fascinated with flat earthers. Here you have a group of people steadfastly
rejecting evidence that’s right in their face. Today, I want to tell you why I nevertheless
think flat earthers are neither stupid nor anti-scientific. Most of them, anyway. More importantly, I also want to explain why
you should not be embarrassed if you can’t remember how we know that the earth is round. But first I have to tell you what flat earthers
actually believe and how they got there. The most popular flat earth model is that
of a disk where the North pole is in the middle and the south pole is an ice wall on the edge
of the disk. But not all flat earthers sign up to this. An alternative is the so-called bipolar model
where both poles are on the disk, surrounded by water that’s held by a rim of something,
maybe ice or rocks. And a minority of flat earthers believe that
earth is really an infinite plane. They mostly agree though that gravity does
not exist, and that the observations we normally attribute to gravity come instead from the
upward acceleration of the flat earth. As a consequence, the apparent gravitational
acceleration is the same everywhere on earth. I explained last week that this is in conflict
with evidence – we know that the gravitational acceleration is most definitely not the same
everywhere on earth. The idea that gravity is due to upward acceleration
also causes other problems. For example, you have to assume that the moon
and the sun accelerate along with the flat earth so we don’t just run into them. That’s an ad-hoc assumption which disfavors
the flat earth hypothesis against models where the orbits of the moon and the sun can be
calculated from the gravitational law. But that’s not the only problem. You also have to get the moon and the sun
to somehow circle around over the disk to explain day and night and the phases of the
moon. To get the day-night cycle to be noticeable,
you have to shrink the sun and move it closer to the earth. You also have to somehow get the radiation
of the sun to be directional. That’s many more ad hoc assumption. But even with those assumptions, the size
of the sun will change during the day more than we observe. And no one has ever successfully predicted
solar eclipses on a flat earth, or calculated the observed motions of the planets. The bottom line is: it’s not easy to improve
on today’s scientific standard. It was for good reasons that the hypothesis
of a flat earth was abandoned more than two thousand years ago. Some people suggested to me that flat earthers
do not actually believe the earth is flat, they are just mocking people who take scientific
evidence on trust. And that, let us to be honest, is something
we all do to some extent every now and then. And it is probably the case that some flat
earthers are indeed just pretending. But I find it exceedingly implausible they
are all just faking it. To begin with, they would all have to be excellent
actors. Just look at some of the videos on YouTube. Also, they’re putting quite some time and,
in some cases, money behind their conviction. And that’s while most of them full well
know coming out as flat earther will make others doubt their sanity. All that makes it unlikely they are just in
for the fun. Now, you may want to discard flat earthers
as conspiracy theorists, which some fraction of them arguably are. But I think that would be somewhat unfair
to most of them. To understand why, it helps to have a look
at the history of the flat earth society. The flat earth society goes back to an Englishman
by name Samuel Rowbotham, who lived in the 19th century. He was a medical doctor who believed he had
proved that the earth is flat and then complained for the rest of his life that the supposed
scientific authorities ignored him. He referred to his methodology as “Zeteticism”
after the Greek word zeteo, “to seek”. By “Zeteticism” he meant an extreme version
of the philosophy of empiricism. Rowbotham’s philosophy, which is still the
philosophy of flat earthers today, is that if you want to understand nature, you should
only rely on information from your own senses. You can for example read on the website of
the flat earth society: “The world looks flat, the bottoms of clouds
are flat, the movement of the Sun; these are all examples of your senses telling you that
we do not live on a spherical heliocentric world. This is using what’s called an empirical
approach, or an approach that relies on information from your senses. “
That flat earthers insist on evidence from your own senses only really is key to understanding
their problem; I will come back to this. But first, let me tell you the rest of their
history. After Rowbotham’s death in 1884, the flat
earth idea was carried forward by another British guy, Samuel Shenton, who once explained
to a journalist: “No man knows the ultimate shape of the earth, but that portion we life
on is definitely flat. No one will ever know what the whole complexity
is like, I suppose, because it goes beyond his sphere of observation, investigation and
comprehension.” Again, note the emphasis on personally collected
evidence. In 1954, Shenton created the International
Flat Earth Society. Few people cared. He died in 1971. After his death, the Flat Earth Society was
taken over by the US-American Charles Johnson. But even after the advent of the internet,
flat earthers did not attract much attention. Johnson died in 2001, at which point the flat
Earth society had 3500 or so members. The job then fell to another American, Daniel
Shenton, who is not related to the earlier Shenton but whose logic falls right in line. He said in an interview with the Guardian
in 2010: “I don't think there is solid proof. I'm not intentionally being stubborn about
it, but I feel our senses tell us these things, and it would take an extraordinarily level
of evidence to counteract those. How many people have actually investigated
it? Have you?” Shenton had the idea to set up a wiki page
for the flat earth community. Still no one cared. But in 2016, everything changed. What happened in 2016 is that a few devout
flat earthers put up videos, here, on YouTube. And that really got things going, by way of
recruiting new believers. These videos have meanwhile been watched by
millions of people. And that had consequences: In a 2018 poll
in the United States, two percent of the respondents said they believe the earth is flat, while
another 7 percent are not quite sure. Reliable numbers are hard to come by, but
we are meanwhile probably talking about more than ten-thousand people in the developed
world who reject science that was settled by the middle ages. Let that sink in for a moment. How does someone end up rejecting something
as scientifically well-established as the fact that the earth is round? There is not only one reason, of course. Some flat earthers find the idea is appealing
for religious reasons, others are of the crowd who think NASA is evil, space a fake, and
the moon landing didn’t happen. But mostly it’s because they think they
are merely being rational skeptics. They have not themselves been able to prove
the earth is round, so they believe they are only reasonable when they request evidence. CNN for example reports from a flat earth
conference: “Like most of the speakers at the event
CNN spoke to, he was convinced after he decided he couldn’t prove the Earth’s roundness.” I want to leave aside here that, of course,
you cannot strictly speaking prove any empirical fact; you can only prove mathematical identities,
so more precisely we should speak of seeking evidence that disfavors the hypothesis that
the earth is flat. Of which there is plenty, starting with the
historical evidence about how stellar constellations shift if you travel, how the length of shadows
changes, to Newton’s 1/R^2 force law that is the law for a sphere, not a disk, not to
mention Einstein and gravitational redshift and the perihelion precession of mercury, and so on, and
so forth. The problem that flat earthers have is that
they cannot do most of these observations themselves. So if you buy the idea that it’s only your
personally collected evidence that you should accept, then it seems you cannot refute the
idea that the earth is flat, and so flat earthers philosophy forbids them to accept
scientific fact. Needless to say, if you want to hold on to
your convictions it helps if you refuse to do observations that could speak against them. There are actually many ways to convince yourself
that the earth is round which are not that technically difficult. Buy a telescope and try to explain the motions
of the moons of Jupiter, for example. So what’s wrong with flat earther’s attitude? Isn’t it asking for evidence exactly what
rational thinkers should do? Sure, evidence is key to scientific progress,
but flat earthers’ philosophical approach by which they reject certain types of evidence
is inconsistent and, ultimately, logically wrong. See, the only evidence anyone ever has of
anything is evidence you collect with your own senses. Except, as Descartes pointed out, evidence
of your own ability to think, but this is not relevant here. Relevant is that the distinction which flat
earthers are trying to draw between different types of evidence does not exist. All evidence you have is sensory input. If you hear an explanation of someone else’s
experiment, if you read a paper laying out someone else’s argument, that’s your own
sensory input. A distinction which does exist, however, is
that some of our sensory input requires very little decoding, while some requires a lot. Flat earthers’ problem is that they refuse
to decode difficult sensory input. A good example for the need to decode sensory
input by conscious thought are optical illusions. Your brain tries to interpret visual input
in ways that sometimes gives a misleading result as in this example. You almost certainly think square A is darker
than square B. It is not. To understand your sensory input correctly
you need to draw on other information, in this case your knowledge about optical illusions. Your brain interprets this image as if it
was a natural, 3-dimensional scene, and therefore calculates back to the original color of the
squares taking into account what appears to be a shadow. This is the wrong interpretation if you want
to know the actual color of pixels on the screen. The lesson is, if you do not think about your
sensory input, if you do not properly decode it, you arrive at a wrong conclusion. Flat earthers similarly arrive at the wrong
conclusion by failing to decode evidence, indeed by simply ignoring a lot of evidence
that their own senses deliver. This is evidence about how society and science
works. Whether we are scientists or not, we all constantly
use this evidence to navigate life. And I am sure flat earthers are no exception. Just consider going to the supermarket and
buying canned soup. Do you have evidence that what’s in the
can is edible? Probably not. For one, the can’s closed. And if you are anything like me, you probably
have no idea how or where or by whom it was produced. Why then are you not afraid of eating canned
soup? Isn’t this entirely irrational? No, because you do have evidence that canned
soup is edible. You know how the legal system in your country
works, you know that there are regulations on what can be sold as food in a supermarket,
you know that if what’s in that can was harmful to you, then a lot of people along
the food chain would be punished for their mistake, and they don’t want that. Your trust in canned food is an entirely reasonable
inference from evidence, evidence that you collected with your own sense, because what
else could you possibly have collected it with? Now let’s come back to flat earthers. Most of you don’t have a physics degree
and chances are that after learning in school how we know the earth is round you didn’t
think much about it ever again. By and large you are probably confident it’s
correct because what you learned in school was plausible, and you know it is widely taught
to children, and you know that your government strives to give children in your country a
scientifically accurate education. So you have good reason to think the knowledge
you were taught is backed by solid scientific evidence. There is no appealing to authority here. You have totally yourself collected all this
evidence about how society works. You have also yourself collected lots of evidence
that science works. Any airplane, any laptop, any pair of glasses
is evidence that science works. It’s evidence that the system works. It’s evidence for how the whole world works. So, if you cannot recall just what experiments
demonstrate that the earth is not flat, or if you cannot immediately figure out what’s
wrong with flat earther’s arguments, there’s no shame in rejecting their claims, because
your rejection is based on evidence, evidence that science works. What’s wrong is that flat earthers’ claim
they are leading a scientific argument. But there is no scientific argument about
whether the earth is flat. This argument was settled long ago. Instead, flat earthers’ argument is about
whether you should trust evidence that other people have collected before you. And it’s an important argument because this
trust is essential for society and science to progress. The only alternative we have is that each
and every one of us has to start over from scratch with birth. You see, flat earthers would eventually figure
out the earth is round. But it might take them a thousand years until
they’ve reinvented modern science. This is why I think scientists should take
flat earthers’ philosophical problem seriously. It’s a problem that any scientifically advanced
society must address. It is not possible for each and every one
of us to redo all experiments in the history of science. It therefore becomes increasingly important
that scientists provide evidence for how science works, so that people who cannot follow the
research itself can instead rely on evidence that the system produces correct and useful
descriptions of nature. To me, therefore, flat earthers, are a warning
sign that scientists should take seriously. The more difficult scientific experiments
and arguments are to follow for non-experts, the more care we must take to explain how
we lead those arguments. Thanks for hearing me out, see you next week.
This is a 2-year-old video that I think every flat Earther should be made to watch. It's not dismissive of their views, and explains why it's a somewhat reasonable trap to fall into.
She goes over the history of the epistemological roots of flat earth "science" and explains why what seems reasonable "I don't trust what I don't get from my own senses," is in real terms, not even possible, much less rational.