Essay:Is the sky blue?

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"The sky is blue." It seems obvious. In fact, "Is the sky blue?" is a common rhetorical question that denotes that the answer should obviously be yes. But if we really break apart the saying "the sky is blue", it shows that the answer to this question is not as obvious as it may seem, and there are in fact a lot of problems and hidden assumptions in this statement that seems deceptively simple. In fact, it is a good example to use to examine some of the problems in how humanity processes facts about the universe.

Problems with the statement "the sky is blue"[edit]

This is by no means an exhaustive list:

  • First, there's the problem of what is meant by blue. Some colors referred to as "Sky blue"Wikipedia are actually shades of cyan, so many people would argue the sky is cyan and not blue. The sky's average color is often between cyan and blue, and what point differentiates the two colors is a matter of debate.
  • More importantly, the fact that we consider the sky "blue" is due to the limits of human vision. Our eyes see the sky as blue due to the scattering of blue light in the atmosphere, but violet light gets scattered more in the atmosphere, meaning the sky should be more violet than blue, but due to limits in our vision, we only see the blue. And since the atmosphere scatters all kinds of light, just at different rates, the sky is multicolored in a sense but our eyes only perceive one color at a time.
  • There's also the fact that people who are colorblind do not see all the colors that people with unimpared vision do, and blind people may not have a frame of reference for color at all. "The sky is blue" may be a meaningless statement to these people.
  • And all that is ignoring that humans are sensitive only to the visible light spectrum, and the light that humans can see isn't all that is actually there.
  • Then we get into problems with the word "is". The sky appears blue due to the scattering of light in the atmosphere, but that's not the same thing as saying it is blue — just because a rainbow is visible doesn't mean that it is actually there.
  • There's also the fact that the statement is dependent on your time and location. During sunset, for example, the sky may appear red.
  • Following from that, there's also the fact that this statement only makes sense from a frame of reference on planet Earth — In fact, the statement is more accurately "Earth's sky is blue". The sky on Jupiter looks completely different, and if you were standing on the moon the concept of Earth having a sky would be meaningless (Earth does have an atmosphere, but those are not necessarily the same thing).
  • Then there's the meaning of "sky", which is not a very well-defined term. There are many things which are considered to be part of the sky, like clouds, the sun, the moon, the stars, lightning, auroras, etc., and most of these things are not blue by any typical definition.

Also worth mentioning is the Whorf hypothesis, which suggests that human perceptions of color may be influenced by the language we use to describe color. I won't really lean on this since it's far from being settled science, but there are a few studies that have provided interesting results on the subject. Additionally, all of the above is based on our current understanding of these issues, so it's possible that a future discovery would add more complications to the topic.

So in short, despite "the sky is blue" seeming simple and obvious on the surface, that simple sentence contains a lot of hidden assumptions, and when you look into them the question of whether the sky is blue becomes very complex and without a simple answer.


An interesting thought experiment is to imagine how much of our current understanding of science would be useful to an alien species from a faraway planet. Many of our units of measurement are arbitrary. For example, our standard units of time originate from subdivisions of the Earth's rotation and revolution around the sun, and on a different planet these units of time would make no sense. Numbers are almost always expressed in base-10, not because ten is a physically or mathematically important number but rather because most humans have ten fingers. Even if we try to base our units on universal physical standards, there are still several competing models,Wikipedia and none of them is necessarily less arbitrary than the others. The thing is, this problem is to a certain extent impossible to avoid. You have to start with a frame of reference before you can get anywhere. And the simple fact that we're humans means that there will be some limitations in how we can understand the universe that can't be completely overcome. So this doesn't mean that all of science is invalid due to the assumptions that it requires to function, but it does mean that we have to be aware of the hidden assumptions that are behind every statement, as even if your framework is arbitrary to some extent, it should at least be consistent. "The sky is blue", for instance, has so many inconsistencies in its definitions that it essentially becomes meaningless, while "the light that is scattered by the Earth's atmosphere during the daytime appears blue to most human observers", while also having its own assumptions, is much more consistent in its own framework, and is much more informative and useful as a result.

"If you can't explain it simply, you don't understand it well enough" is a quote often attributed to Albert Einstein, and I quite disagree with this quote, largely because of all of the things I mentioned. "The sky is blue" is a simple explanation, but it does not at all demonstrate any understanding of the sky or the color blue. All of these statements have unstated assumptions in them, and pointing them out makes the explanation seem more complex, but if you cannot point out the assumptions hidden in a statement, then you do not understand that statement well enough. This reminds me of a related issue with the definition of the word "woman", where many people think that because "liberals"/*insert snarl word here* cannot define "woman" in simple terms, that means that they are obviously wrong about what a woman is. One notable example is in Matt Walsh's documentary, where at one point he talks to a gender studies professor who gives a long answer that he mostly skips over, giving the impression that because the answer is long it must be ridiculous. However, saying that a woman is "an adult human female" falls into many of the same traps as "the sky is blue", as all of these words carry hidden assumptions. For example, is female defined by sex chromosomes, genitals, sex hormones, secondary sex charicteristics, or other attributes? Do you need all of these to be female, or only some of these? Is female a completely seperate category from male, are they opposite ends of the same spectrum, or can they potentially overlap? And that's not even getting into things like gender roles, and there are just so many other things to unpack from that definition that I do not have time to list. A good explanation of what a woman is would examine these and many other questions, and you could not reasonably do all this in a single sentence. However, because "adult human female" is easier to communicate and appeals to "common sense", many people consider it a slam dunk answer to the question. This is anti-intellectualism, plain and simple.