Seven-Colored Light

Friends who have studied physics should all know.

The refractive index of visible light in different environments varies, such as glass, air, water, etc.

These things have a unified conceptual name: medium.

Now, as the theoretical research of optics has gradually become standardized, many junior high school students will also understand a principle:

Light can propagate in a medium, but the propagation of light itself does not require a medium.

But don't forget, Little Ox is in 1665, a time when optical research was still in its infancy.

Therefore, for Young Newton to have thought of the possibility of the seven colors of light having different effects in different media based on just a few words from Xu Yun, and in less than half a minute, it was an absolutely extraordinary performance.

Indeed.

Little Ox at this time did not yet know that light itself is a boson and does not need any fermions to propagate—in this era, the pinnacle theory of optics regarding refraction was a mathematically equivalent form derived by Snell, and it was unknown to anyone before his death.

It would not be publicly known as the famous Snell's Law until Huygens and others reviewed his manuscript in 1678.

Before that, it had only been derived in an equivalent form by Descartes in his "Dioptrics."

And there's also a confusing account within this that no one can clearly ascertain the truth of, leading to them still sharing the honor of discovering the law of refraction of light.

Therefore, although Little Ox's statement subconsciously encompassed the speculation that visible light could not propagate through a certain 'environment,' this was completely understandable—to be honest, just thinking of the first part was already amazing!

Then, looking at the small cluster of colorful light on the ground, Little Ox suddenly thought of something else.

After thinking for a few seconds, he asked Xu Yun:

"Fat Fish, since sunlight can be dispersed into seven beams of colored light, are these seven colors different lights?

Also, theoretically, these seven beams of light should be able to be recombined into a single beam of white light, right?"

Xu Yun twitched the corner of his mouth. Well, with just one sentence, he hit two critical points again.

However, by this time, he had gradually adapted to the monstrous thinking ability of this ancestor, so he quickly adjusted his mindset and said:

"Sorry, Mr. Newton, I only know the answer to the latter question—as long as the conditions are right, the seven colors of light can be recombined into a beam of white light."

Little Ox's interest was piqued, and his eyes darted around:

"Fat Fish, you just said that a prism can also verify the phenomenon of dispersion?"

"That's right, and the effect of a prism is much better than that of a lens."

Little Ox nodded slightly, but soon his brow furrowed again:

"A prism. These are easy to find in London; you can buy one at any street-corner optician's shop, but here in Woolsthorpe..."

Seeing Little Ox frowning, Xu Yun seemed to magically take a prism out of his pocket:

"Mr. Newton, what is this?"

Little Ox took it and looked:

"Huh? How do you have a prism?"

Xu Yun smiled without saying a word.

The price of prisms as trinkets in later generations had dropped to a ridiculously low level, and many people liked to buy them as keychains or even necklace pendants. Xu Yun had taken an optics course last semester and casually bought a prism pendant to string onto his keychain.

More than ten minutes later.

A table about one meter in diameter, a prism, and a black wooden board were successively placed next to a water tank.

Then Xu Yun set up the prism, skillfully adjusted the angle, and gave Little Ox an OK gesture.

After a moment.

A long strip of spectrum indeed appeared on the cardboard behind the prism, and it was much clearer than the previous one.

Seeing this, Xu Yun retreated to the side, deliberately not making any comments, wanting to see how far this youthful version of his ancestor could go without any hints.

Little Ox paced over to the table and bent down to examine the spectrum carefully.

Then, after hesitating for a few seconds, he picked up a piece of black cardboard.

He cut a circular hole in it and placed it outside the prism, in the direction from which the light was coming.

Most of the sunlight was blocked by the cardboard, and only a circular beam of light passed through the small hole and shone in, and then...

A long strip of spectrum still formed.

Seeing this, Little Ox let out a soft "Huh."

Perhaps it was because he wanted to share his thoughts, but he suddenly looked at Xu Yun again:

"Fat Fish, have you heard of Mr. Descartes' theory?"

Xu Yun nodded and said:

"Of course, I've heard of it. I even visited the University of Poitiers once.

Mr. Descartes believed that the color of light comes from the medium between the luminous body and the human eye, and is unrelated to the light source.

The color of light is not an inherent characteristic of the light itself, and he also proposed the theory of light path transformation."

"That's well said, but look here."

Little Ox held a piece of cardboard in one hand and pointed to the projected long strip of spectrum with the other.

"According to Mr. Snell's equivalent formula and Mr. Descartes' theory, a circular light beam should form a circular or elliptical spot after passing through a prism.

But after dispersion, the seven colors of light form a long strip spectrum.

Could it be that...

Mr. Descartes' theory has a problem?"

After speaking, Little Ox thought for a moment. Without waiting for Xu Yun to respond, he picked up the cardboard and scissors again and made a smaller hole.

He placed this piece of cardboard behind the first prism. This way, using this round hole, he could capture any light beam from the colored light band. (Little Ox had drawn this device himself back then, DOI: 10.1098/rsta.2014.0213, by Little Ox himself. Those interested can take a look, he's truly a soul artist.)

Then Little Ox beckoned Xu Yun over, signaling him to come forward.

"Fat Fish, I'll report the data, and you'll record it."

Xu Yun's pupils contracted slightly, knowing that Little Ox was step by step approaching his ultimate "net." However, his expression remained unchanged.

"Okay, Mr. Newton."

Afterward, the two of them, one holding paper and pen, the other began to calculate the angles.

"Red light, incident angle i60°, deflection angle β32.2°"

"Orange light, incident angle i60°, deflection angle β37.4°"

"Incident angle i60°, deflection angle β38.7°"

20 minutes later, four sets of 28 data points were recorded.

Different colors of light have different refractive indices in optical glass. The deeper reason involves relative magnetic permeability μr and relative dielectric constant εr. These two constants require calculation using Maxwell's equations in the medium, then establishing an intuitive model for the interaction between matter and light, deriving the equation of motion through linear dissipative forces, and finally solving for its steady state using complex methods, and so on.

However, considering it hasn't been released yet and it's inconvenient to PUA the readers. Cough, due to the complexity of the content, everyone just needs to understand the relevant conclusions from a macroscopic perspective.

After all, Little Ox's era didn't have Maxwell's equations, right?

"Violet light 1.532, Blue 1.528, Green 1.519, Yellow 1.517, Orange 1.514, Red 1.513"

Looking at the fixed set of data in front of him, Little Ox couldn't help but take a deep breath.

It was obvious.

The refractive indices of different colored lights were different and remained constant; the properties of these seven colors of light were different.

From this, one conclusion could be drawn:

White light is indeed not a pure light; it is composed of different lights.

And this represented that

he was perhaps one step closer to the truth of the world.

At the same time.

Little Ox looked at the light that had split into seven and yet was unified as one. Something suddenly occurred to him.

His chest heaved a few times, and he quickly ran back into the house.