Orion said nothing. His brow knotted tight.
Manhattan he knew. An island off America's east coast, the Muggle financial center, part of New York.
MACUSA, the Magical Congress of the United States, Woolworth Building, all in the same area.
British Pure-blood families didn't pay much attention to American magical politics, but basic geography wasn't beyond them. The Blacks had holdings on the European continent; they weren't entirely ignorant of what lay across the water.
But the Manhattan Project?
What project?
He searched his memory. Nothing.
The wizarding world had little cause to associate with Manhattan. MACUSA had operated out of New York for over two hundred years, and occasionally news drifted over about legislative adjustments or elections.
But those were American wizards' affairs. Nothing to do with Britain.
He shook his head slowly, puzzlement in his expression. "Never heard of it."
Regulus nodded. He leaned back a fraction, and his tone flattened to something measured. "In 1945, Muggles built a weapon."
Orion watched him. Didn't interrupt.
"They found something," Regulus said, keeping the pace unhurried, the language plain. "Countless times smaller than a grain of sand. The deepest layer of matter's structure. It took Muggles decades to work out what it even looked like."
He continued. "They discovered that if you fired something even smaller into it, the thing would split apart. When it split, it threw out more of those smaller pieces, along with an enormous amount of energy. Those ejected pieces would slam into the matter around them, and that matter would split too, throwing out still more, releasing still more energy."
His eyes held Orion's. "One triggers the next, one splits the next, forming a chain. The chain runs on its own. Once it starts, it doesn't stop."
Orion listened in silence. He understood.
Regulus's description was blunt, stripped of jargon, free of the Muggle terminology that would have lost him.
"They called it the Manhattan Project," Regulus said. "A few thousand of the smartest people the Muggle world could produce, gathered from across the globe, locked away in a stretch of desert for three years. These weren't ordinary people. They were the absolute pinnacle of their field, across the entire Muggle world. They called their discipline physics, the study of the rules governing all things. Every single one of them was the foremost mind in their area."
Orion's mouth twitched at the corner, but he stayed silent.
Three years. A few thousand of the smartest Muggles. Doing one thing.
His view of Muggles in general aligned with most Pure-blood wizards'.
A species without magic, naturally inferior in a wizard's eyes. No explanation needed. The way giants looked at Gnomes, the way Dragons looked at Puffskeins.
But he wasn't the kind of Pure-blood supremacist who was blind to the point of stupidity.
In his younger years, he'd leafed through a few Muggle texts, and they'd given him a rough understanding of one thing.
Within the Muggle population, the vast majority were unremarkable. The difference between them and livestock was clothing and speech.
But the ones at the very top, the handful who were genuinely thinking, the depth and sharpness of their thought could match the best minds in the wizarding world.
Admitting that didn't diminish him. Those Muggles who had driven a single pursuit to its absolute limit, he acknowledged their intelligence.
Anyone who pushed a craft to its furthest edge, wizard or Muggle, deserved to be taken seriously.
Regulus's voice continued. "In three years, they built three of these weapons. The first was test-detonated in the desert."
Something lit behind his eyes. "At the moment of detonation, the temperature at the center exceeded the surface of the sun. Sand within a radius of several kilometers melted outright, fused into glass. The shockwave expanded from the center, flattening everything too slow to escape. A mushroom-shaped cloud punched tens of thousands of meters into the sky, visible from dozens of kilometers away."
Orion's fingers tightened against the desktop.
Temperature exceeding the sun's surface. Sand turned to glass. Several kilometers leveled.
His mind ran the conversions.
The maximum kill radius of explosive spells was perhaps a few dozen meters. Flame spells covered even less.
Fiendfyre didn't operate by radius; it burned wherever it spread. But it needed time to crawl, not an instant.
Several kilometers.
No spell he knew of, including the lost Magic, could accomplish that.
"The second one," Regulus said, his voice uninflected, "was dropped on a city. Hiroshima"
He held up a single finger. "That day, over a hundred thousand people died. In the months that followed, tens of thousands more. Burns, radiation sickness, starvation. One city. Two hundred thousand people. One weapon. Gone."
Orion's brow was clenched so tight the lines had gone white. His breathing had slowed.
He thought of the Ministry of Magic's war archives, the records of another medieval war magic effect.
An entire army swallowed in an instant by black fog. Castle walls crumbling in seconds. Spells requiring dozens of wizards acting in concert, capable of turning the tide of a battle.
But those were legends. The records were vague, the effects magnified by centuries of retelling, the truth long since unrecoverable.
And those demanded coordinated casting by dozens, preparation time, specific astronomical and geographical conditions.
What Regulus was describing: one weapon, one instant, hundreds of thousands.
"The third, three days later, was dropped on Nagasaki." Regulus's voice didn't pause. "Another seventy or eighty thousand dead. Days later, the Muggle war ended."
The study went quiet. A pop from the hearth.
Orion said nothing.
Regulus was silent for a moment too, then continued.
"Muggles don't have magic. What they found was a different path. They took a form of matter and broke it down to the deepest level, smaller than sand, smaller than dust, down to where it couldn't be broken any further. And they discovered that at that scale, matter had force locked inside it. Locked for billions of years, since the day this planet was born. They cracked it open and let it tear itself apart."
He raised a hand, fingertip pointing loosely toward the hearth.
"The method was to fire something even smaller into it. One triggers the next, the chain starts, runs on its own. All they provided was the first impact. The rest, matter completed by itself. From detonation to conclusion, less than a second."
He lowered his hand and looked at Orion.
"Thirty years have passed. They've built them bigger and bigger, more and more. The current Muggle stockpile is roughly fifty thousand. Some are individually dozens of times more powerful than the one that hit Hiroshima. Enough to scour the Earth's surface several times over."
The silence from Orion stretched long.
Regulus didn't speak either. He leaned back and waited.
A flame jumped in the hearth.
Orion wasn't unaware that Muggles could wage war.
He knew they had massive conflicts, knew the last one to engulf the entire Muggle world had been only thirty years ago.
Knew that Grindelwald had exploited the chaos of that war to advance his vision of the greater good.
1945. Grindelwald fell to Dumbledore. The same year, the Muggle war ended.
The wizarding world knew something of that war. Knew it had been brutal. Knew many had died.
But he hadn't known that Muggle weapons had advanced to this degree.
There had been rumors that year, something about Muggles dropping something on an island, obliterating a city.
But Pure-blood circles never paid attention to Muggle affairs. Heard and forgotten. No one dug deeper.
He hadn't thought much of it either.
Now, hearing Regulus lay it out with numbers, details, temperatures, ranges, it was no longer rumor.
Hundreds of thousands of lives. In any wizarding war, that was an impossible figure.
The Killing Curse killed one at a time. The Cruciatus Curse tortured one at a time. Fiendfyre needed time to spread. Plague curses needed vectors to propagate.
Wizards had countless ways to kill, but every one came with a cost.
This thing. One weapon, one second, hundreds of thousands, a city erased.
But panic didn't touch him, let alone fear. He was the Head of House Black. He'd seen too much to be shaken by a fact.
One green flash for one life, one weapon for one city. The outcome was death either way. The difference in scale wouldn't make him lose composure.
He pulled his thoughts back and began assessing with cold logic.
This weapon's destructive power eclipsed any spell. No point debating that. But a wizard's strength didn't lie there. The advantage wizards held over Muggles had never been firepower.
Muggle-Repelling Charms blanketed every corner of the magical world.
From Diagon Alley to Hogwarts, from Quidditch pitches to every Pure-blood estate, Muggles could walk right up to them and see nothing, suddenly remembering urgent business elsewhere, turning on their heels and leaving.
Anti-mapping enchantments ensured magical structures never appeared on Muggle maps. They couldn't capture so much as a photograph, from the sky, from the ground, from the water. Impossible.
Apparition meant any wizard under attack could vanish in an instant. The strike hadn't landed and the target was already gone.
The Fidelius Charm was more absolute still. A secret sealed inside a single soul. Unless the Secret-Keeper spoke it aloud, no method, no magic, no torture could extract the location.
12 Grimmauld Place was hidden exactly that way. The street numbers jumped from eleven to thirteen. The house between them had evaporated from the world's memory.
Muggle weapons needed a target's location to strike.
They couldn't find the entrance to the wizarding world. Couldn't discover a single wizard village. With what would they deliver that weapon?
At what?
To Muggles, wizards didn't exist. You couldn't hit a target that wasn't there.
Fifty thousand, enough to scour the Earth several times over. Let them scour it. The only ones dying would be Muggles.
So this weapon, when it came down to it, was someone else's problem. Impressive, but irrelevant to the wizarding world.
Orion ran through these thoughts, then stopped.
Something clicked.
He looked at Regulus.
Regulus wouldn't sit in this study, spend this much time, to lecture him about a Muggle weapon that had nothing to do with the magical world.
So the point wasn't how formidable Muggles were. It certainly wasn't to peddle some theory about the Muggle threat.
He was talking about the Disintegration Curse.
The Manhattan Project. Muggle weapons. The Disintegration Curse. A swelling curse.
Orion's back left the chair.
He'd been thinking about Muggles this whole time. Muggle weapons couldn't reach wizards because wizards could hide.
But what if Regulus turned it on wizards?
The Fidelius Charm could conceal a house. It couldn't conceal a city.
Muggle-Repelling Charms only worked on Muggles. Anti-mapping enchantments blocked Muggle maps and cameras.
If a wizard could produce destruction on that scale, all they needed was to know what general area you were in, then erase the entire area...
The house under the Fidelius Charm would still stand. But everything within three kilometers of it would be vapor, the soil beneath the foundations fused to glass. Where would you hide?
Orion's breathing was heavier than before.
If the Disintegration Curse could reach that level, then every calm, rational conclusion he'd drawn about wizarding advantages, applied to a wizard-versus-wizard scenario, had to be thrown out.
He stared at Regulus, gaze burning, voice no longer steady. "Can you do it? The Disintegration Curse?"
Regulus met his father's eyes and shook his head. "No. A few thresholds short."
Orion blinked. He settled slowly back against the chair and let out a breath.
He realized he'd lost his composure. A Head of House Black, unable to sit still over a hypothesis. That wasn't like him.
But if it were true, what would it mean?
War between wizards had always been wizard against wizard, spell against spell. A conflict involving a hundred was already considered large-scale.
Grindelwald at the height of his power, with thousands under his command, had thrown all of magical Europe into turmoil and earned the title of the greatest wizarding war in centuries.
Yet from start to finish, Grindelwald had never destroyed a city.
If a wizard could replicate that weapon's effect. One wizard, one spell, one city...
He forced the thought down.
Not being able to do it was the normal state of things.
That weapon had taken a few thousand of the Muggle world's brightest minds, locked together for three years, to produce. He didn't know the specifics of the process, but he could imagine the staggering resources involved.
Regulus was thirteen. He'd already reached a point most wizards couldn't touch. If on top of that he could achieve this level outright, talent wouldn't be the word for it anymore.
Then another realization surfaced. Regulus had said he couldn't do it, but there'd been a second half to the sentence.
A few thresholds short.
That wasn't can't.
Where there were thresholds, there was direction. Where there was direction, there was a path.