Chapter 153: The Alpha Particle Scattering Experiment

The morning sun had yet to fully climb over the window sill in Horace’s manor when a piercing scream shattered the tranquility.

“I’m not going! Absolutely not! That integration formula isn’t derived yet, you can’t do this to me!”

The study’s doorframe was being held in a death grip.

Horace was spread-eagled against the door, his ten fingers clawing at the seams, completely devoid of the dignity of a Ninth Circle Archmage, looking for all the world like a primary school student trying to finish his homework on the last day of vacation.

Eleonora stood in the hallway, holding a steaming cup of black tea. She wore a casual beige long dress, her hair casually tied back.

She smiled gently, the fine lines at the corners of her eyes smoothing out, like the most pleasant breeze in spring.

“Horace~”

She called out softly.

Horace shuddered, his grip on the doorframe visibly loosening.

“My dear, it’s just a small experiment.”

Eleonora took two steps closer, bringing the black tea to his lips.

“A sample of the derivative of that newly discovered radioactive element—now called ‘Radium’—just arrived.

I need someone good at arithmetic to help me record the data. And you know, no one is more precise with numbers than you.”

Horace eyed the tea warily, then looked at Eleonora’s harmless, smiling face.

“Just recording?”

“Of course.” Eleonora blinked. “And, I’ve prepared your favorite cherry pie. Freshly baked.”

Horace swallowed hard. He waged a fierce, one-second-long internal battle between solving his conjecture and the cherry pie, ultimately succumbing to the protests from his stomach.

“…Only for half an hour.” Horace let go of the doorframe and took the tea. “And I want a double portion of pie.”

“Deal.”

The smile on Eleonora’s face grew even brighter. She took her husband’s arm and headed towards the high-spec alchemy laboratory in the basement.

Although he had grumbled about not wanting to move, once he was in the laboratory, Horace quickly got into the zone.

It was a sealed room built entirely of anti-magic metal. In the center of the room stood a complex apparatus, its main body a sealed, lead vacuum box.

“This is the verification experiment you were talking about?”

Horace circled the apparatus, pointing to the tiny nozzle. “Using those… ‘alpha particles’ to bombard gold foil?”

“Correct.”

Eleonora was adjusting the array, calibrating the positioning of the zinc sulfide fluorescent screen used for detection. “What Lia said at the dining table that day has been on my mind.”

“She said your plum pudding was no good?”

Horace pulled a quill from his pocket and drew a circle on his recording slate.

“She said…”

Eleonora’s hand paused as she recalled the seemingly casual yet certain look in Lia’s eyes. “‘What if the bullet bounced back?'”

Horace scoffed, spinning the quill between his fingertips.

“In your model, the inside of an atom is diffuse positive charge. And what are alpha particles? They’re positively charged heavy cannonballs.

What else can happen when you fire a cannonball at a cloud of mist, or a mushy pudding, besides it passing through? Don’t tell me the pudding can bounce the cannonball back?”

“That’s what I thought too.”

Eleonora activated the source’s excitation array.

Inside the lead box, the small, precious sample of radioactive material began to emit a stream of high-energy particles, invisible to the naked eye.

These particles were collimated by a narrow slit, forming an extremely fine beam.

It shot straight towards the center, at a piece of gold foil far thinner than a cicada’s wing.

If Eleonora’s model was correct, the vast majority of these particles would pass directly through the gold foil and strike the fluorescent screen behind it.

Even if they were deflected by the repulsive force of the positive charge, the angle would be very small, like a stone’s path altering slightly when thrown into water.

“Lights out,” Eleonora ordered.

The laboratory plunged into darkness. Only the faint glow from Horace’s recording slate and the fluorescent screen behind the gold foil remained.

Pop.

A point of light appeared on the fluorescent screen.

Pop, pop.

The dots of light appeared one after another, as dense as fireflies on a summer night.

Horace yawned and began to record on his slate: “All penetrated. Deflection angles all within 1 degree. No surprises. I told you Lia was worrying for nothing. A child’s intuition can be wrong sometimes.”

Eleonora stood in the darkness, staring at the flashing points of light.

Everything was perfect. Perfectly in line with her ‘Plum Pudding’ model.

The inside of an atom was indeed empty, or rather, soft.

But.

Lia’s “what if” kept spinning in her head.

“Horace,” Eleonora said suddenly.

“Hmm? Are we done recording? I’m going to eat my pie.”

“Move the detection screen.”

“Move it where?”

“Move it to the front.”

The sound of a chair scraping came from the darkness, followed by Horace’s incredulous complaint:

“The front? You mean the side facing the light?

That’s the direction the particles are coming from! What do you expect to see?

Particles hitting it and turning back? That violates the conservation of momentum! Unless there’s a solid iron lump hidden in the gold foil!”

“Let’s just do it for the sake of rigor.”

Eleonora’s voice was soft, but it carried a persistence Horace couldn’t refuse. “Science requires ruling out all impossibilities, for example…”

Horace grumbled as he manipulated the mechanical arm, slowly moving the fluorescent screen to the front of the gold foil, on the same side as the particle source.

In this position, theoretically, there should be dead silence.

Because no particle could defy the common sense of physics and bounce back after hitting a soft “pudding.”

It was like firing a machine gun at a thin sheet of paper; the bullets would never ricochet back and hit you.

The laboratory was so quiet that only the humming of magic could be heard.

A minute passed.

The fluorescent screen was pitch black.

Horace grunted smugly. “See, I told you…”

Pop.

In the darkness, a single point of faint green light abruptly flared up in a place it absolutely shouldn’t have.

Horace’s voice died in his throat.

He rubbed his eyes.

“Did… did something just light up?”

“Shut up,” Eleonora’s voice was tense. “Watch.”

Silence descended again.

A few more minutes passed, just as Horace was thinking it had been a hallucination.

Pop.

Another one.

This one was extremely clear.

Just to the side and front of the gold foil, an alpha particle was violently deflected back at a large angle of nearly 150 degrees, striking the fluorescent screen and kicking up a tiny but dazzling spark of light.

Pop.

Though rare, though faint.

Over the next ten minutes, the fluorescent screen, which represented the impossible, lit up more than a dozen times.

The quill in Horace’s hand fell to the floor.

In the quiet laboratory, the soft sound was deafening.

“This is unreasonable…”

The great mathematician’s voice was dry. He lunged towards the screen, his nose almost touching it.

“An alpha particle’s mass is over 7000 times that of an electron, and its speed is twenty thousand kilometers per second.

To make something like that turn around, it must have collided with something much more massive and with an absurdly high charge density.”

He began to scribble furiously on his recording slate.

“A uniformly distributed fluid could never provide this kind of repulsive force. To bounce this ‘cannonball’ back, all the positive charge must…” Horace stopped.

He turned his head to look at Eleonora.

By the faint light of the instruments, he saw that his wife’s face was pale, but her eyes were burning with a fanatical light.

“Be concentrated together,” Eleonora finished his sentence.

She held out her hand and sketched a tiny point in the air.

“Not pudding…”

“Not a fluid.”

“The atom… is empty.”

Eleonora’s voice trembled with the excitement of glimpsing a corner of the truth.

“The vast majority of its mass and all of its positive charge are curled up in a tiny, tiny point at the center. So small that we couldn’t observe it before.”

“Only when an alpha particle is extremely lucky and hits this hard core head-on is it deflected back.”

“All the other particles just pass through this void.”

Horace felt his scalp tingle.

He looked at the fluorescent screen, which was still flashing occasionally.

Each flash was a microscopic ‘cannonball’ roaring, telling them: You were wrong.

“Lia…” Horace picked up the pen from the floor. “How did she know?”

“She didn’t know.”

Eleonora shook her head. She walked to the experiment table, her fingers stroking the gold foil. “She’s just bolder than we are. She dared to imagine the most impossible possibility.”

“That pudding model is scrap paper now.”

Horace gave a bitter smile. “My heavens, if this gets published, the entire atomic theory system will explode. Everyone has always thought the world was solid, and now you’re telling them that most of it is actually empty?”

Eleonora’s eyes were deep. “If the positive charge is concentrated in the center, and the electrons are outside… then why don’t the electrons fall in? Opposite charges attract, that’s an ironclad law.”

“Unless they’re moving.” Horace reacted instantly, his intuition making him grasp the key point. “Centrifugal force. Like planets orbiting the sun.”

Just then, the gold foil, under continuous particle bombardment, finally gave way and a small hole appeared.

The experiment was forced to a halt.

The lights came back on.

Horace slumped into his chair, looking at the data he had just recorded.

Even if it was only a one-in-a-few-thousand probability, the fact that particles had bounced back had already shown him the direction of the truth.

“Still want cherry pie?” Eleonora asked.

Horace was stunned for a moment, then glanced at the record sheet.

“No.”

He slapped the paper on the table. “I need to calculate just how small that nucleus is. Now that I know the scattering angle, I can deduce its scattering cross-section.”

He grabbed a stack of blank parchment. The old man who had been clamoring for a break just moments ago was now as energetic as an apprentice who had just drunk a potion of vigor.

“Coulomb’s Law… conservation of momentum… conservation of energy…”

The tip of his pen flew across the paper, making a scratching sound.

Eleonora stood by quietly, watching her husband work.

“I’ve got a rough range!”

Horace suddenly looked up, holding a sheet full of formulas.

“That nucleus… the radius of that nucleus is only about one hundred-thousandth of the atomic radius!”

“One hundred-thousandth…” Eleonora gasped.

“If you compare an atom to a great cathedral…”

“…that nucleus is probably only the size of a fly.”

“And the rest of the space is completely empty, with only a few tiny electrons flying around.”

“This is the truth of matter.”

“A void.”

“An absolute void.”

Eleonora turned and walked out, even forgetting to turn off the instruments.

“I have to tell Lia. No, I have to go find her directly.”

“Wait!” Horace called after her.

“What?”

“Take me with you.”

Horace clutched the calculation sheet, his beard trembling.

“This planetary model has a huge mathematical flaw! If the electrons orbit the nucleus, then according to Maxwell’s equations, an accelerating charged particle will radiate electromagnetic waves, lose energy, and eventually spiral into the nucleus!”

“The atom will collapse! The world will be destroyed!”

Horace shouted, “This model is a dead end in classical physics!”

Eleonora stopped in her tracks.

She looked back at her husband with a playful glint in her eyes.

“You’ve discovered it too?”

“Nonsense! This is the most basic deduction!”

“Then take a guess.”

Eleonora smiled. “That little girl who had us do this experiment, do you think she knows it’s a dead end?”

Horace’s mouth fell open.

“She… she knows?”

“She definitely knows.”

Eleonora pushed open the door, and a cold morning breeze rushed in, dispersing the stuffiness of the lab.

“She smashed the wall, letting us see the ruins inside. And now she’s just standing on those ruins, watching us.”

“Waiting for us to beg her to rebuild this grand edifice.”

Eleonora lifted her skirt and hurried up the stairs.

“Let’s go, Horace.”

“I want to ask her, if the world isn’t going to be destroyed, how exactly are the electrons supposed to fly?”

Horace stood frozen for two seconds, then shot up, grabbing his coat and chasing after her.

“Wait for me! And bring the cherry pie! That Lia girl likes sweets. Maybe if she eats it and is happy, she’ll torture my brain cells a little less!”

The manor door was slammed shut.

Two streaks of light shot into the sky, heading straight for the Tower of Truth in the Royal Capital.

(TN: I remember learning about this experiment back in 6 or 7th grade, let’s see when they’ll reach Bohr’s model)