Last Updated on August 20, 2026 by Rob Cashman

“Don’t look at the light. You might not be able to see where we are going.”

“I am going to take you on a ‘rollercoaster ride’ about light. But as you ‘ride the waves’ of this interaction, at each peak, drop, or curve, I want you to keep asking yourself, “are we still speaking about light?” And if your answer is “yes we are,” then ask yourself, “what if this whole ride never was talking about light at all?”

In our previous article entitled, “Why Do Monsters Only Come Out At Night?” we spoke about the way our human eyes understand the world around, and how our visual system changes its mechanism based on whether we are seeing that object in daylight, in darkness, or at dusk or dawn. The premise of the article was “why is it that we only see monsters at night,” but the actual message is that our perception of the world changes when both external factors (daylight vs. darkness) [and internal factors (the cones or rods we use, and how we experience our world)] change the playing field that we think we are living in. So the conclusion there that ‘monsters only appear to come out at night’ is really an observation that our experience of the world is altered by forces or variables that we are not aware even have an impact upon us. So too with light; welcome aboard. Fasten your seatbelts.

Perception #1: What we experience when we see an object is not simply the object itself; it is the result of an interaction involving the object.

SIGNPOST: We are no longer focusing on an object or a thing (a car, its color, light); we are focusing on the interaction between then.

In the monsters article, we described how our eyes don’t actually see color; the brain translates what we see and interprets what we see into the colors of the objects in our world that we perceive. We also observed that object appearing to us as red, blue, or some other color, does not necessarily mean that this color is simply “inside” the object (or a proper description of that object’s color, as it actually ‘is’).

Rather, when we see color on an object, we are seeing the result of an interaction. Light encounters an object. The materials that comprise that object interacts with that light in particular ways (thinking about materials science here, where various materials interact with others in predictable ways). Some wavelengths interacting with an object might be absorbed more strongly than others. Other wavelengths might be reflected or scattered toward us. When our visual system processes the light from that object that reaches our eyes, it gives rise to the experience we call color.

Perception #2: Sometimes the interaction we believe we are seeing might not reveal other interactions that are beyond our ability to see.

SIGNPOST: Even if we describe the interaction (e.g., in order to understand the object,) we might only be seeing our own involvement in that interaction. We might not be seeing the actual interaction itself (we might see a reflected wavelength that we interpret as ‘red’, but that might not be the only interaction happening between light and the car.

When we look at a ‘red’ object, we are not simply discovering an intrinsic property of ‘redness’ in the object. The actual interaction is more complicated. The pigments and materials comprising the car (whether steel, plastic, or whatever materials cars are made of) absorb some wavelengths more strongly than others, while other wavelengths are reflected or scattered back toward us. The particular distribution of light that reaches our eyes is then interpreted by our visual system as a particular color.

[Even how we perceive that object changes depending on whether it is daylight or nighttime, and whether and how the car interacts with light outside of the ‘slim’ visible spectrum of colors that we can see, e.g., infrared light, ultraviolet light, microwaves, etc. is a possibly a topic for a future article.]

That means that what we see might often be descriptive of our experience of an interaction (light + us), but we still might not be seeing the intended interaction (light + car) to describe the object itself.

Observing color alone cannot a complete description of an object, nor does it describe the complete interaction either. The light that hits the car, and the light that gets refracted to us is not the same light, and the interaction between the light and the car is not the same interaction as the wavelength of light as it enters our eyes. Because just like our visual systems can produce the perception of the same ‘red’ color in multiple ways, our brains can interpret ‘red’ from different combinations of wavelengths.

So us seeing a ‘red’ color might does not mean that the car reflected only that wavelength and absorbed all other wavelengths of light. The color we observe is merely observing one piece of information about the way that the reflected light interacts with us. What we infer about the car based on how it interacted with the light is a separate interaction.

Instead of asking, “What color is the car?” we can ask, “What interactions of light happen between the light, the car, and me?” That is a much more informative question.

And that raises a much more interesting question:

Perhaps we might never reach the object we intend to observe by attempting to observe it through an infinite set of interactions and causes. It is easier to say that once we discover that what we perceive can be evidence about something we cannot directly see, color becomes merely one variable that we can use to understand what a thing is.

SIGNPOST: I just switched from things that we can see (car, reflected light, color) to things that we cannot see (we can observe what interactions happen between something and us, but we cannot see the interactions that happen between, i.e., light and the car, before the light was reflected to us.

NEXT we will shift from ‘direct perception’ to ‘indirect perception’.

What We See—and What We Don’t See

There is another interesting way to think about this.

Direct Perception: When we see a red car, we see the light that reaches our eyes, and our brains conclude, “the car is red.” But the light that reaches us is only part of the story.

Indirect Perception: Through our experience of color, we can also infer that other wavelengths of light have also interacted with the material differently. Some have been absorbed. Others may have been scattered or reflected in directions that never bring them to our eyes.

So our perception gives us information about what happened to the light. Through this, we are learning about the object indirectly. What we experience when we observe properties are not the properties themselves; we see the consequences of what happens when other things interact with them.

SIGNPOST: I just moved us from direct perception to indirect perception, and then we just switched from observing interactions of light on Earth to interactions of light in Space.

I also just switched from discussing wavelengths of light as it relates to the color of an object to wavelengths of light (as a spectrum) as it relates identifying the properties and measuring movement of objects in Space.

Perception #3: Sometimes the interactions between light and objects in Space can teach us indirectly about the properties and movement of those objects.

The idea that “we learn about objects indirectly,” is not merely a philosophical idea. Modern science makes extraordinary use of exactly this principle. Scientists do not have to open up a distant star to determine what it is made of; they can examine the light coming from it.

When that light is separated into its component wavelengths, the resulting spectrum contains patterns that reveal information about the matter through which the light has traveled, or from which it has originated. Particular elements and molecules interact with particular wavelengths in characteristic ways. Those patterns can therefore reveal chemical composition, temperature, density, motion, and other physical properties.

This is the basic idea behind spectroscopy. The spectrum is not the object; it is information produced by the object’s interaction with electromagnetic radiation. And from that information, we can infer properties of the object that our eyes could never directly see.

Perception #4: Sometimes we can observe the shift in the frequency or wavelength of light and/or sound to determine whether something in our line of sight is moving closer to us or away from us.

SIGNPOST: Just as there are wavelengths of light in Space, there are wavelengths of sound on Earth, Whether in Space or on the ground, Doppler shifts in the wavelength or frequency also help determine movement.

This is why astronomers can determine whether a comet is moving towards us or away from us. NASA explains that when an astronomical object in our line of sight moves toward us, its spectral lines shift toward shorter wavelengths (blue); when it moves away, they shift toward longer wavelengths (red). Without looking at the object’s motion directly, by calculating the amount of the shift, astronomers are able to calculate the relative velocity of the object.

We get a similar effect when an ambulance speeds past us. As it passes by us at high speeds, the sound of the siren it emits experiences a ‘doppler shift‘. As it moves towards us, the siren sounds higher in pitch, and when it moves away from us, it sounds as if the pitch of the siren shifts downwards.

[Even though Doppler shifts occur differently in these two examples, we can still ask what else can we extrapolate from understanding one that we don’t yet know about the other?]

The Doppler effect gives us another example of the same broader principle, although through a different mechanism: While sound waves are not light waves, the acoustic wavelengths carry information not only about what emitted it (here, the siren), but also about how that source is moving relative to us.

But how far can we take that idea?

What Is the “Nature” of an Object?

This is where the question becomes more difficult. If I can study the way a material interacts with light and learn about its chemical composition, temperature, structure, or other physical properties, have I learned its “nature”? Perhaps.

But what do we mean by its “nature”? If by ‘nature,’ we mean its chemical composition, physical structure, or measurable properties, then science has already demonstrated that interactions can reveal an extraordinary amount.

SIGNPOST: We are no longer speaking about science (but we will ‘return to the light’ soon). We have shifted from asking if we can determine the properties of an object to the ‘nature’ that we can infer about that object from our observation. Quick warning — I will be playing with words here, because the ‘nature’ of a thing could be its behavior, or more philosophically, what it is meant to be.

But what it we apply the definition of “nature” as being the way it behaves, we can make broader observations which can also be scientifically accurate. If the ‘nature’ of a thing is broadened to include the way it behaves, the way it responds to its environment (the interactions it has with those it interacts with), or the effect it has on other things, or the role or ‘function’ it plays within a larger system, this deepens the analysis.

We would not claim that observing a wavelength of light allows us to infer a hidden moral judgment about an object. We would also not go so far as to claim that physics can reveal some mystical or esoteric essence simply by looking at the color that it appears to us. Rather, our question is more of a modest—and perhaps more interesting—question:

“Perhaps we can explore this with a little illumination! Gentlemen.” – Phantom of the Opera

Light gives us one particularly beautiful example.

SIGNPOST: Next we begin to explore interactions between light and objects in Space, such as the Sun and a theoretical object – a ‘blackbody.’ Also shifting the analysis from discussing direct vs. indirect evidence to positive evidence (what is there) versus negative evidence (what is missing).

What Does the Sun Tell Us About Itself?

Consider the Sun.

To our eyes, the Sun appears extraordinarily bright—often appearing white, although from Earth’s surface it can take on a yellowish appearance depending on atmospheric conditions and the circumstances in which we observe it.

But if we separate sunlight into its component wavelengths, we discover something much more complicated than the simple “yellow ball” we see in the sky.

The Sun emits electromagnetic radiation across an enormous range of wavelengths, including the wavelengths that make up the visible spectrum. When a broad mixture of visible wavelengths from the Sun reaches our eyes together, we generally perceive it as ‘white’ light. But we can learn something about a thing not merely from what the Sun reveals, but also from what is missing.

Perception #5: Sometimes we can perceive what an object is by observing what is missing.

The measurable light that we receive from the Sun’s contains a ‘fingerprint’ of sorts. If we spread that light out into a spectrum—a kind of ‘rainbow’ produced by separating its different wavelengths—we find very thin dark lines running through it. NASA describes that these lines represent wavelengths of light that are missing or greatly reduced, for example, because cooler gases in the Sun’s outer atmosphere absorb particular wavelengths of light.

Atoms and ions have characteristic sets of spectral lines associated with their allowed transitions, producing distinctive and observable patterns [with the proper machinery, e.g., with spectroscopy]. The National Institute of Standards and Technology (NIST) even keeps an active database of these ‘fingerprints’ in their Atomic Spectra Database.

By comparing the patterns in the Sun’s light with patterns measured from elements here on Earth, scientists have been able to determine which elements are present in the Sun. This is how helium was identified in the Sun’s spectrum (as a ‘fingerprint’) before it was ever discovered on Earth. (It is also why the name of this element comes from Helios, the Greek word for Sun).

In other words, the Sun is telling us something about itself through the way its light interacts with matter. The light coming from the Sun is not merely illumination. It gives us information that we can use to make inferences.

And this brings us to the strange thought that caused me to write this article. Notice how every object I am about to discuss is connected through interactions involving radiation.

– The Paradox of the Black Sun –

Suppose we temporarily forget what we already know about the physics of the Sun. Imagine that we encountered an extremely luminous object (here on Earth) without knowing what it is. We observe that it appears white. We realize that it would be a dumb idea to touch it.

SIGNPOST: Pay close attention in this section to language; we are about to distinguish ‘calling something black’ from characteristics of the ‘presence or absence of illumination’ (light) that would properly describe why something would ‘appear as black’. And NO, we will not be asserting that the Sun is actually black (but we will make a fascinating comparison between the Sun and a real theoretical ‘blackbody’).

Next we will be shifting in language from light as it would form a spectrum (above) to light as it relates to radiation emitted from an body in space.

We observe that this extremely luminous object sends enormous quantities of radiation outward. We observe that everything around it becomes illuminated because of that radiation. What would we conclude about the object?

We might say that its defining characteristic appears to be that it continuously radiates energy outward, and it reveals other things by illuminating them. But even if the Sun metaphorically emitted ALL of its light, to an observer [blinded by the light], we wouldn’t describe the Sun itself as black-colored. Even to a philosopher imagining that the Sun radiates infinitely (leaving nothing of itself), we couldn’t describe it as ‘black’ as in, ‘devoid of light’.

SIGNPOST: 1) ‘black’ as a color; 2) ‘black’ as a description (devoid of light); next, 3) ‘black’ as a title of a thing.

But here the language becomes almost paradoxical. A black hole is not ‘black‘ because this is its color; rather, it is called “black” because its event horizon prevents light from escaping outward from within it. . So to an observer right outside the black hole’s horizon, to him, the black hole would appear as black because it does not emit visit light that would reveal a surface.

SIGNPOST: Comparing the Sun to a “blackbody,“ was the most evocative and interesting part of this article. A Sun is not a blackbody, but it raised questions of whether it was the scientific community. Watch for the distinction between emitting light and absorbing light. Also pay attention to the use of the word radiation that is also emitted and/or absorbed.

The Sun is not exactly a ‘Blackbody’

Science also has a concept called a blackbody, not because it is theorized to be a ‘black-looking object’. A ideal blackbody is described as ‘black’ because it absorbs 100% of the electromagnetic radiation that falls on it. Like the black hole, from an observer’s perspective, a blackbody that is not hot enough to glow visibly would appear ‘black’ because if we shined visible light on it, it would absorb that light rather than reflect it back to our eyes.

But absorbing light and emitting light are two very different things. A blackbody can absorb radiation while also emitting radiation of its own. The amount and type of radiation it emits depends on its temperature. The hotter the blackbody becomes, the more energy it radiates outward; and the wavelengths of some of that radiation become shorter. Heat up a blackbody enough, and it will eventually start to glow visibly.

Heat a blackbody to the temperature of the Sun (about 5,800K), and its emitted radiation would have the spectrum remarkably similar to the Sun’s overall spectrum.

SIGNPOST: Experience the crescendo. We just came to a point where we have described something as having a black color, we have described how something would appear black because of the absense of light, we have called something black as part of its name, but we also discussed these in terms of their interactions and their relationships with light, and radiation. We then took all of these, introduced something called a ‘blackbody’, and then showed how its light spectrum is very similar to the Sun’s light spectrum. But then we ‘pull out the rug’; we shift away from the suggestion we all want to make, and we change tracks one last time to return us home.

The Sun is not literally a perfect blackbody. Its radiation contains absorption lines and other features that an ideal blackbody would not have. But the overall pattern of the Sun’s emitted radiation is remarkably close to that of a blackbody at about 5,800 K. That makes the blackbody a useful model for understanding the way the Sun radiates energy.

But what something does by emitting radiation (Sun), and what it does by absorbing radiation (blackbody) are two different kinds of interaction.

In a broader sense, this distinction matters because we also learn about the Sun by observing its interactions with the other parts of the solar system. The radiation reaching us on Earth is not the Sun itself; but from it, we can we can observe what the Sun is doing. And once again, by observing the energy it sends outward, we can learn about the Sun not by observing it directly, but by observing what it does.

Perception #6: We can learn what an object is by observing what it does.

This is the idea I find most interesting, not for the reasons I am about to describe, but for the implications that I am purposefully NOT going to describe (maybe in another universe, I might have decided differently.)

Philosophers often believe that to understand something, they must somehow discover its hidden ‘essence’. They want to know ‘what the thing really is‘. But perhaps that is not always how knowledge works.

Perhaps the best way to learn what something is by observing how it interacts in relationship to something else.

• A material encounters light. We observe what happens. From that interaction, we infer properties of the material.
  
  
• A star emits radiation. We analyze that radiation. From it, we infer the star’s composition, temperature, motion, and physical conditions.
  
  
• A planet passes in front of a star. We observe how the star’s light changes. From those changes, we can infer properties of the planet’s atmosphere.

Again and again, the thing we want to understand is not observed directly; we merely observe an interaction, and from that interaction, we work backward toward an understanding of the thing itself.

That suggests a broader principle:

Light provides an unusually clear example because light is constantly interacting with the physical world around us. Objects absorb it. Reflect it. Scatter it. Transmit it. Emit it. And each of those interactions carries information that we can use to understand it.

Could this be how knowledge works more generally?

If the Sun is not exactly a blackbody, then what is it?

Imagine what scientists did when they observed that the radiation signature of the Sun was almost identical the the radiation signature that would come from a blackbody at the same temperature. The observation was not of the Sun itself, but its light.

Then they must have made the connection that at hot temperatures, both an ideal blackbody and the actual Sun emit radiation. But there is something that the blackbody does that that would have create the paradox of the Black Sun that I described above; a blackbody absorbs 100% of all electromagnetic radiation that hits its surface. Imagine what their next question was.

It is the behavior of an object that teaches not only what it interacts with, but what it is.

Raising the Stakes: From the Sun to its Rays

As we close this article, we close it not with a bang, but with an explosion in scope.

FINAL SIGNPOST: Until now, we have been asking an epistemological question: How can we know something by observing what it does? Now, as we move from the Sun to its rays, I want to ask an ontological question: What kind of thing is the thing we are observing—and what happens when that thing has no independent existence apart from its source?

This takes us beyond the scientific analysis we have been using and into a different kind of question about existence.

Chassidus offers an ontological way of thinking about this: the rays of the Sun have no independent existence of their own apart from their source.. “Turn off the Sun, and the rays disappear.” But while the rays of the Sun don’t have independent existence of their own, when the Sun radiates energy, light, and warmth, its rays carry that energy outward to every corner of the universe a ray can reach.

The individual rays of the Sun do not create or radiate energy, light, or warmth on their own. Thus, from observing their behavior, we can learn more not about a ray of light, but systems of illumination.

But what might we learn if we observe a class of dependent actors through their relationships to their source?

What if, instead of studying a single ray, we studied the behavior of rays as a class of dependent actors? Could the patterns we discover tell us something about the system that produces them?

I don’t know. And maybe that is a good place to begin. Maybe simply by changing the question, we can uncover insights that extend far beyond light.