Grass is green. Mom said so, playground friends too, and teachers in school confirmed it as well. And it’s still true, at least according to our newest technologies[1]:
Me: What color is grass?
ChatGPT 4o: Grass is typically green, varying in shades from light to dark green. The green color comes from chlorophyll, a pigment in the plant cells that is essential for photosynthesis.
Except, of course, it isn’t. At least, it’s not a characteristic of the grass itself. Since Alhazen (965-1040 CE)[2] we know that the perception of colors is created in our minds, triggered by light being reflected from objects and then entering our eyes. The spectrum of colors is explained by different wavelengths of light, as Newton found out later (with prisms and all of that).
Still, we talk about colors as if they were characteristics of the objects themselves. Why? Probably because it’s easier. Your mom just wants to yell “Don’t forget to buy red apples!”, not “Don’t forget to buy apples that, when light gets reflected on them, causes your brain to create the perception of what we call red!” It’s too much of a mouthful and not practical. Just buy those damn red apples; got it?
When Subjectivity Theory claims that matter is also created in our minds (in the OPIP book, as well as in blog posts like Objective vs. Subjective Worldviews) the analogy with colors is invoked again and again. That’s because it fits so well—not only the basic idea of something being created in our minds, but also in many other details. The analogy can be taken quite far, and this post explores this further.
Imagine you traveled back to a time when everyone agreed that colors are a characteristic of objects themselves. How easy do you think it would be to convince people that we create it in our minds? You’re right—it would have been a tough job. But let’s not stop there; we need to understand why exactly it would have been so difficult.
First, there’s social pressure. Everybody knows that the grass is green, and you don’t want to be that weird lunatic who is obviously insane. We live in a society, and you must play by the rules. Of course, you can try to break the rules; if you’re lucky, you’ll only be the outsider who everybody laughs about. If you’re less lucky, you’ll share the fate of people like Giordano Bruno who, for challenging the geocentric model (Earth at the center of the universe), was burned at the stake. “Ouch.”
Social pressures don’t have to be that drastic; they can be subtle too. If you perceive grass as gray, but you hear everyone describing the grass as green, then you adjust accordingly. You’re thinking, “Not sure what I was thinking; everybody says the grass is green, so it’s got to be green.” (We then also try to convince ourselves by thinking things like, “It’s just replacing “ay” with “een,” so it’s not that bad.”[3]) If you hear something often enough, you start believing it. As often, it all comes down to psychology.
Despite all the social pressures and group psychology, let’s assume you’re of the highly stubborn kind and keep insisting that the grass doesn’t have any color in itself. Society then just starts ignoring you. That’s another way to get rid of disagreements—by dismissing them. Full agreement is restored. Simple.
In summary, once beliefs are established in society, they are hard to overturn. But we already knew that. How did we get to those beliefs in the first place? The idea that colors are a characteristic of objects themselves comes from the concept of agreements. You look at the grass, it looks green, and if Jimmy looks at the grass, he says it’s also green. You both agree, making you conclude that grass is green for everybody. If it doesn’t matter who’s looking at it, it must be a characteristic of the grass itself. And why do you agree that the grass is green? It’s because you and Jimmy are quite alike: you share 99.9% of your genes. You’re built in the same way and make up the color of the grass (“reality”) in the same way.
The concept of agreement isn’t only external. It happens within us too. We look at the grass at point A, perceive it as green, then look at it again at points B and C, it’s still green, and infer that it must be permanently green (also at times D, E, and F, when we’re not looking). And once we establish that rule, we believe it is further corroborated every time we look at the grass. But this is a thinking mistake; we can look at the grass a million times, and it will appear green a million times, but that doesn’t change the fact that we make it up every time.
Another reason agreements happen is when we perceive something different, but we’re not aware of it. How do I know exactly that what I call green you don’t perceive as yellow? It’s hard to tell. Even if you did perceive grass as (what I call) yellow, it could be that we both walk through our entire lives agreeing that the grass is green, without realizing that our perceptions are distinctly different. Agreements always occur only on a certain level; if we dig deeper, we may find disagreements, and thereby erode our belief in an objective world.
Each of the factors above can be so strong that they make disagreements unlikely. And if they occur in combination, there is almost no escape from agreeing. This is all very counterintuitive. In our daily lives, the challenge is usually the opposite: finding agreements—such as which TV channel to watch, which car to buy, which salary to agree on. However, the counterintuitiveness isn’t surprising; that’s what makes it so hard to find the solutions. Once we know what the challenge is, we’re halfway there. Identifying the challenge is the challenge (see “What’s the Problem?”).
If finding disagreements is the challenge, then how can we show someone who believes that green is a characteristic of the grass itself (let’s give that person the highly imaginative name Greene[4]) that sometimes, it’s not green? That may change their views. Which examples can we state to convince Greene?
Attempt 1: Grass is White in Winter
When it’s cold and frosty, grass can appear white.
However, Greene might object that we’re looking at the frost, not the grass itself.
Attempt 2: Yellow Grass in Hyde Park
Contrary to common belief, the sun does sometimes shine in England. During some phases, it even shines so much so that grass turns yellow, as observed during the 2018 heatwave.
However, Greene will object that this has changed the grass itself. The new color is still a characteristic of the grass; it only changed from green to yellow. Therefore, our examples must not involve altering the nature of the grass itself.
Attempt 3: Smokin’ It
If you take some of the grass and smoke it, the rest of the grass may change its color due to hallucinations. Without touching the grass (the part we didn’t smoke), it changed its color, thereby showing that the crucial part is how we process the light coming from the grass in our brains.
However, Greene will object that it’s exactly as we said: they’re hallucinations. Hallucinations distort our perception of the world, so we don’t see how it “really” is. Hence, this line of reasoning also doesn’t get us anywhere.
Attempt 4: Color Blindness
Now we come up with a watertight argument: not everybody can see green. Approximately 8% of men and 0.5% of women of Northern European descent are red-green colorblind, preventing them from seeing the grass as green.[5] That must be proof that color is subjective and created in our minds. Take that, Greene.
However, Greene may simply respond that the red-green color blindness is caused by the absence or malfunctioning of the green cone photoreceptors in the retina (which is true). In other words, there’s simply something wrong with colorblind people. They cannot perceive how reality really is.
Attempt 5: Grass at Dusk and Dawn
Well played, Greene. But what about the following: in the early morning or late in the evening, grass may have different colors. At dawn, the light is often soft and golden, casting a warm hue over the grass, while at dusk, the light can be more reddish or pinkish due to the setting sun.
That doesn’t shake Greene. The conditions we described are not the norm and simply distort our perception of the true color of the grass. This could be caused by many factors, such as the changing light itself, our eyes adjusting to different lighting conditions, or plenty of other things.
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The bottom line is: arguing with Greene is no fun. Can we still win the battle? Possibly, but for that, we may need to bring out the heavy guns…
If our everyday examples don’t do the deed, we can try turning to extremes: scenarios we don’t usually experience. Paradoxically, those often make things clearer. One such example could be with respect to speed. If we look at the grass, and then move our head back quickly—very quickly, such as at 25% the speed of light—then grass will appear red due to the Doppler effect.
Similarly, moving our head back at 12% of the speed of light will make the grass appear orange, and at 6%, yellow. In the same (but opposite) way, if we move our heads toward the grass, we’ll first see light blue (15% speed of light), indigo (21%), and violet (31%). In other words, by moving our heads back and forth, the color of the grass will keep changing through all the colors of the rainbow.
While this is a nice phenomenon, it has the unfortunate drawback of causing a severe level of dizziness. Therefore, we come up with a solution: instead of flipping our heads back and forth, we jump on a rocket ship that is traveling away from Greene’s grass (who stays on Earth) at 25% the speed of light, making their grass appear red to us constantly—without any dizziness. At that point, Greene will have to agree that the color of the grass depends on the observer’s reference frame, getting them one step closer to admitting the subjectivity of colors.
[Incidentally, high speeds aren’t the only example of an extreme that would have such effects. If we traveled to a massively massive object such as a black hole, the light emitted from the grass would be redshifted as well. (If you’re scared of black holes’ tendencies to suck you in and spaghettify you, a neutron star would do the job too.) Then we could see red grass without any movement. But high speeds are more fun, so let’s get back to that…]
To give Greene something to look at too, we took a bushel of grass on our rocket ship as well. Greene will also see our grass as red, as the grass is moving away at 25% the speed of light. It only matters how quickly the grass, and the observer, are moving away relative to each other. The question who is “actually moving” becomes irrelevant (and, as it’s irrelevant, raises the question of whether absolute movement “exists” at all, at least in this case).[6]
After traveling in space for a while, we start to feel lonely, and get tired of seeing Greene’s grass in red. So, we decide to come back to Earth. As we turn, Greene’s grass will change to orange, yellow, light green, dark green (darker than Greene sees it; sometimes, the grass is greener on the other side), blue, indigo, and violet. And what colors will our grass have to Greene? The color changes will be identical, however—and that’s what breaks the symmetry—they will only occur much later to Greene. When we turn, we see the changes instantly, as the light required to experience it (that has been emitted from Greene’s grass) has already been travelling in the meantime and hits our eyes instantly as we turn. Our grasses’ light (the new light emitted after the turn), however, first needs to travel all the way back to Earth, so it takes time for Greene to experience the same effect. Once it does hit Greene’s eyes, he will see it blue-shifted as well, and even more so (as we’re traveling in the direction of the light), but this doesn’t compensate for the long time Greene didn’t see any changes. In other words, when we compare which colors we saw, and for how long, we’ll find that we experienced more blue-shift overall than Greene did.
At this point, the initiated physicist will see a parallel to the twin paradox. However, it’s more than a parallel; the two phenomena are fundamentally deeply connected. The illustration with the Doppler effect isn’t a superficial, easy-to-understand picture that gives the average person a first, but essentially simplified and inaccurate, idea of what’s going on. The (relativistic) Doppler effect can be used to calculate time dilation and what the different twins observe (as shown well in this animation) to the billionth decimal place.[7]
But let’s take a step back. Why should those two scenarios be deeply connected? In the twin paradox, we’re talking about clocks and time dilation. In the above example, it’s about grass and seeing different colors. To explore this, we should first establish what a clock is. At its core, a clock is a device that is tracking some form of movement. The perception of a color also involves movement (light rays entering our eyes and our brains processing this information), and hence implies the elapse of time according to our interpretation. The movements that occur may not be as reliably periodic as in the case of a conventional clock, making timekeeping less accurate, but at the most basic level, the same things occur. In that sense, everything is a clock—provided it moves.
Another reason why we may have difficulties recognizing the two scenarios as similar is that we may still hold the notion that clocks measure an objective time. After all, isn’t that what we do with measurements? We take a device that (objectively) measures something. It takes us a while to wrap our heads around the fact that clocks don’t measure something abstract and objective, but they basically measure themselves. The idea that clocks measure something objective comes again from agreements. For example, Earth spinning around its own axis can be seen as a clock (one revolution measuring one day), agreeing with the quartz clock that tracks a different type of movement but agreeing with the Earth as clock in that the number of revolutions always stays the same. The idea that time is subjective isn’t new to physics of course; relativity theory states exactly that. It only stops short in terms of the interpretation of what it means about the nature of the world, as mentioned below.
What can we learn from the thought experiment with the colors? First, it may clear up some confusions that are present today in the physics community. For example, there is an ongoing discussion on whether the explanations must include acceleration and deceleration, or general relativity, to resolve the twin paradox.[8] The example with the colors suggests that those additional concepts are not needed.
However, does the thought experiment with the colors reveal something even more fundamental about our world?
Let’s extend the original thought experiment as follows: after we’ve traveled away from Earth for a while, Greene pulls out another bushel of grass we didn’t know about. What color does this grass have (to us) before the light reaches our eyes? The answer is straightforward: it doesn’t have any color. It’s neither green, nor red, nor blue. And even if we knew that it is going to be either green, red, or blue, it would still not make sense to describe it as being in a “superposition” of those states.[9] Our brains haven’t created the color yet, so it simply doesn’t exist. Talking about colors before they are perceived is nonsensical.
The example of light and colors pertains to our sense of vision. It probably doesn’t need to be emphasized that the same applies to all other senses too. No matter how loud, smelly, tasty, or slimy the grass is that Greene pulls out, we cannot attribute any of those characteristics to the grass before they have been perceived. And as those senses are all we have to infer what we call “existence,” the question becomes how much sense there is in the concept of existence before perception.[10] In the words of John Archibald Wheeler, the renowned American physicist: “No phenomenon is a phenomenon until it is an observed phenomenon.”
An obvious objection might be that the grass is still there, we just don’t know about it yet. However, an equally obvious rebuttal is: how do you know it’s there? Similar to quantum mechanics, you cannot exclude yourself from the experiment. This would only make sense in an objective world. Essentially, it’s like saying, “Assuming the objective worldview, the subjective worldview is incorrect.” While this is a logically valid statement, you cannot prove something if you start with it as assumption.
Another objection might be that it seems too strange to postulate that in the billions of years before sentient beings existed, there shouldn’t have been any matter because matter is created in our minds. How, then, did we come about? First, if you agree that before conscious beings existed, there were no colors for billions of years, this should bring you one step closer to accepting the same for matter. Second, as mentioned before, Subjectivity Theory doesn’t rule out an objective world; it just makes it a bit less clear what this outside world is. The conclusion is only that the world turns out to be different than we initially thought, as it happened so often in the history of science. Perhaps matter is the result of a more fundamental objective reality that we don’t yet understand, similar to how colors are created by the underlying reality of different wavelengths of light.
Several interpretations in quantum mechanics, including the most widely accepted[11], emphasize the significant role of the observer, with some even highlighting the importance of subjectivity.[12] Relativity theory states that it all depends on which perspective to take—what could be more subjective than that? If we want to unify theories, we should look for common ground. Subjectivity is a strong candidate for this common ground. Many parts are already on the table; the challenge now is to find the right interpretation. We only need to take the final step. Admittedly, while this might be a small step for logic, it is a huge step for human psychology.
To read more about the principles of progress in physics and Subjectivity Theory, get the OPIP book.
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[1] In light of the rapid developments in the AI space, this article will likely not age well if it refers to ChatGPT-4o as the “newest technology,” so let’s correct this to “one of the newest, publicly accessible AI technologies as of June 8, 2024.”
[2] While Alhazen (Ibn al-Haytham) made significant contributions to the understanding of light and color perception in his Book of Optics (c. 1011-1021), it is worth noting that earlier philosophers and scientists also explored these ideas. Ancient Greek philosopher Democritus (c. 460 – c. 370 BCE) suggested that color is not an inherent property of objects but arises from the interaction between objects and observers. However, it was Alhazen who first studied light and vision with a rigorously empirical and methodical approach.
[3] For British people it’s even easier as they only need to replace “y” with “en.”
[4] Greene can indeed be a first name. For example, Greene Vardiman Black (1836–1915) was one of the founders of modern dentistry in the United States. Greene Washington Caldwell (1806–1864) was an American politician who served as a U.S. Representative from North Carolina. Talking about politics and political correctness, it should be noted that the implied rigidity and limitations in thinking associated with the name “Greene” in this post are not meant to allude to any real-life individuals. Any resemblance to current politicians is purely coincidental.
[5] To be precise, only individuals with deuteranopia, a specific and less common type of red-green color blindness, cannot see any green. Those with other types, such as deuteranomaly, can see green and red but have difficulty distinguishing between certain shades of these colors. And while we’re being precise, the medically correct term for color blindness is ‘color vision deficiency’ (CVD).
[6] Of course, this isn’t a new insight. Movement is always relative, as captured in the principle of relativity that was articulated by Galileo and later expanded upon by Einstein (and even Newton, who introduced the concepts of absolute space and time, acknowledged that the laws of motion are consistent across inertial frames, meaning that whether you are at rest or moving at a constant velocity, the same physical laws apply). However, there is value in re-deriving such laws and making them understandable on an intuitive level. Also, the idea that something irrelevant may be regarded as “non-existing” can be a useful concept for gaining new insights, as discussed in the OPIP book.
[7] It’s not only accurate to the billionth decimal place, but to whatever point we calculate it, which can be much further. The precise way to say it is that the Doppler effect allows an exact calculation of the effect. However, due to the inflationary and inexact use of the word “exact” in common language (often describing situations as exactly the same that aren’t) it has lost some of its expressive power. Hence, by using high numbers as illustrations, it reminds us how exact the true exact really is.
[8] For example, see the quotes in the section “Disagreement among Physicists” on Philosopher’s View. This disagreement exists and is real; it cannot be negated by those who believe they know the answer and that there shouldn’t be any disagreement, which is an entirely different statement. The fact that there is still disagreement among respected physicists about the correct solution to the twin paradox even after around 100 years since it was conceived (with some claiming there is no solution at all) may indicate that there is room for further clarifications, which may pave the way for new insights.
[9] This now bridges into the peculiar realm of quantum mechanics. Regardless of the correctness of the concepts discussed here, any new comprehensive theories will need to account for the unusual phenomena observed in both the macroscopic and microscopic worlds. Also see Reality on Rotating Discs.
[10] It’s interesting to observe that most people would agree with statements such as “No brains, no color. No brains, no sound. No brains, no odors or tastes.” However, when it comes to existence, which we purely derive from our senses, it is considered to have a life on its own.
[11] For the popularity of the Copenhagen Interpretation, see Schlosshauer, M. et al. (2013): „A Snapshot Of Foundational Attitudes Toward Quantum Mechanics” (Studies in History and Philosophy of Science).
[12] While the Copenhagen Interpretation assigns a crucial role to the observer, it leaves open what constitutes an observer (not implying the need for consciousness), and at which point in the process a measurement is made. This “measurement problem” is one of the key open questions in quantum physics today. However, some interpretations, such as the von Neumann-Wigner interpretation, directly assign subjectivity a crucial role.
