‘Earth has no curvature, I can’t see it!’ – Flat Earth Debunked, Part 1.

You may have heard of the ‘Flat Earth‘ theory. And you may have even frequented forums and talked to those who believe in it. Having done so myself, I found the experience quite hostile, with members quick to fiercely defend their position. These include a ‘lack of visual curvature.’

And with all the ridicule that they suffer, I can see why. If I was constantly hounded by anonymous trolls I would do the same.

But ‘Flat Earthers’ aren’t illiterate or ignorant, their ranks include academics, highly trained professionals and, crucially, people just like you and me.

curvature flat earth debunk

The concept of a ‘Flat Earth’ is not a new one, but has enjoyed a resurgence. Image courtesy of Flickr.

So we must ask, why are some people convinced? What is the evidence, and how do they think? We have already briefly touched on how inaccurate and loaded information can trick even the most savvy, so what’s the deal here?

We will travel through science, and delve into individual and cultural psychology to explain this phenomenon. And having run a small poll myself*, a good 12% of people answering would deserve the time taken to do so.


So I felt that instead of insulting or dismissing them, we could investigate the central arguments of the theory. And then put those points up for discussion, encouraging debate over division.

Today it’s;

‘I cannot see the curvature, so the earth must be flat’

The Problem Of Curvature

Take a step outside and review the horizon. It is very unlikely that you will see a curve, and up to certain heights, this will remain a constant. But above this height, a small curvature will become apparent, as if hidden from view.

Why? The answer lies in a combination of physics, biology,  a ‘common sense‘ fallacy and finally, something called ‘confirmation bias.’

So as academic Ben Goldacre is often paraphrased ‘I think you will find that it’s bit more complicated than that.’

Curvature And The Science Of Sight

Firstly, let us consider physics and biology,  principally how we ‘see things.’ To make a complex subject simple, let’s imagine light as a straight ray of information. Light reflected off a surface will enter our eyes (if it is within our field of view,) and activate ‘photoreceptor‘ cells in the back of the eye.

These ‘rods and cones‘ then code the information, send it across our optic nerves to our visual processing areas, and our brain creates an approximate image.


curvature eye flat earth

The human eye is good at some things and poor at others. And this is due to the environmental demands placed on its evolution. Image courtesy of Flickr (Fabian Schuster.)

Human vision is not perfect, but adapted through evolution to be efficient enough to aid in our survival. We are good at focussing in things right in front of us, better at seeing movement in the dark, and relatively poor at spotting things at distance.

The reasons for this are many, but put generally it is because our ancestors were protected by these traits, or were not affected by some failures.

So why is this relevant here? The simple answer is there has been no demand to appreciate a curvature over the short time and distances our eyes have evolved to address.

You do not need to see the curvature of the earth over thousands of miles to throw a spear at an animal 10 meters away, and since evolution is naturally conservative, there would be no reason to evolve this ability. Nature would prioritise useful information, like nearby predators.


evolution threat curvature

A sabre-tooth tiger becomes a threat at short distances, so our eyes are equipped to spot nearby threats. Image courtesy of Flickr.

An Evolutionary ‘Failing’

The failure of the human eye to see such a curvature is both an inability to recognise detail at distance (i.e the fractional degree of curvature on the horizon,) and to have a wide enough field of view at lower altitudes to appreciate changes at great distances.

As you get higher up however, the field of view is able to accommodate larger areas (as they are ‘smaller’ relative  to your vision,) and able to discriminate this curvature because the distances involved become less restrictive.

And very simply, we cannot see the curve at ground level because our eyes aren’t actually able to do so. It’s a limit of evolution, not evidence of ‘flatness.’

The failure of the ‘I cannot see the curvature’ argument is actually three-fold.

It encapsulates three fallacies, the first an error in information availability (i.e our eyes cannot appreciate curvature.)

The second is something called ‘a common sense fallacy’ and is perfectly explained by the statement ‘If I can see it, I believe it.’

And the third is ‘confirmation bias’, or more bluntly ‘I see what I want to see.’

Curvature and Common Sense

A common sense argument (appeal to common sense) asserts that what appears ‘common sense must be true’ as based on senses and basic interpretation. Alternatively, what may trick our senses or contradict a simple interpretation ‘is false’ (although at that point we are also entertaining an argument from incredulity.)

The fallacy lies in the difference between the truth and our natural limitations to recognise it, or in the case of the flat earth, even perceive it.

For just one example, let us consider a common optical illusion, ‘The Cafe Wall.‘ Here our eyes see angular lines that do not exist, and this is due to exposing a failure in the way our brains process information. It can be summarised as follows:

  1. I can see angular lines

  2. I trust my eyes

  3. There are angular lines

This is just one example of a common sense fallacy, but the ‘absence curvature of the earth’ is another;

  1. I cannot see a curve on the horizon

  2. I trust my eyes

  3. The earth must be flat

A more logical interpretation accounting for the limits of biology and the fallacy would be;

  1. I cannot see a curve on the horizon

  2. I am neither high up enough or possess the power of magnification or field of vision to appreciate any curvature at this juncture

  3. This is reasonable as my eyes are limited beyond the evolutionary precepts of their development

  4. I cannot conclude that the earth is flat, so I must review other evidence.

Curvature And Confirmation Bias

Finally, a confirmation bias exists when one wishes to confirm their a priori assumption regardless of the evidence. Or ‘I want to believe it, so I believe it no matter what.’

Often people will dismiss contradictory evidence (cognitive dissonance) or twist it to fit their narrative. We are all guilty of this, and I will use an example common in the western world;

  • Belief : Father Christmas is real.

  • Observation: There are presents, the cookies are gone and the living room smells of whisky.

  • Conclusion: Father Christmas bought presents, ate the cookies and probably deserves a DUI.

As hyperbolic as this example is, it points out just how illogical confirmation bias is. So let’s address the subject at hand;

  • Belief: The Earth is Flat

  • Observation: I cannot see a curve

  • Conclusion: The Earth is flat

Wheres a more logical approach would include the uncertainty inherent in the observations and role of bias;

  • Belief: The Earth is Flat

  • Observation: I cannot see a curve

  • Consideration: I may not be able to see a curve, there is good reason for this. Also, there are numerous images of a spherical earth.

  • Conclusion: I cannot conclude the earth is flat, so I must review other evidence.

Conclusion – A Lesson In Limitation

So now we have debunked the myth, it is worth noting that this is not a simple mistake. To reconsider that ‘the earth is flat’ because ‘you cannot see the curvature’ both means knowing the limitations of our vision, and the nature of logical fallacies.

And what’s more, we all make these mistakes, and it often takes some convincing to trust the evidence outside of your own experience. So next time someone tells you that ‘I cannot see the curve’ you can simply say:

‘I cannot see the curve from this vantage point ether, no-one could. Our eyes are not evolved to spot such a tiny curve at the distances we regularly encounter. It is clear from optical illusions that our eyes are not perfect, and that our brains can be deceived. I assure you that if you were to look again from high enough, you could see the curve in the same way that recognising an optical illusion undermines the trick’

And if they want more convincing, direct them here.

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The opinions in this article are those of Dr Janaway alone and do not necessarily represent those of his affiliates. Image courtesy of CDC Global (Flickr.)

Author’s note

The more I research and discuss these issues, the more I realise that we could all be just as convinced given a difference in where and when we encountered the source information. And comparing ‘Flat Earth’ to other widely held beliefs, such as ‘Aliens exist in Area 51’ or ‘Prayers Save Lives’, it is clear that many believe in things that others would immediately dismiss.

But we must ask ourselves whether that belief is justified given the framework of the believers view, and for ‘Prayers Save Lives’ at least, a belief in an all powerful God would preclude the assertion. The same is true of ‘If I can see it, I can believe it.’

Personally, I believe that it is in all of our favour to engage in respectful discussion, because we have all believed in things that we cannot prove objectively, either in the past or even now. Discussion over division, reason over ridicule and evidence over evangelism.

*The poll mentioned is just one example of many addressing the same subject. It is a low power poll, and likely biased toward those would organically be interested in the subject and limited by the scope of my social media influence. I encourage you to run the same poll.

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  • Mike
    Posted on June 14, 2018 at 4:35 pm

    Dude, this is a strawman. Maybe there are some FE’ers who think this way, but for the most part, people do not think that our inability to see the curvature proves that the earth is flat. People just wonder why there is no visual evidence for the curvature beyond the pictures supposedly taken from space.

    If the earth truly had a curve, we could observe it using digital photography and computer equipment. A person should be able to stand on a high point and take a picture of the horizon, then take it home and observe the curve by magnifying the image, but I am not aware of anyone doing this. Can you do this?

    You’re probably just a shill here to waste people’s time or confuse the minds of the simple. Either way, if you can’t demonstrate the curve using digital photography than you have no leg to stand on.


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