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“Got a minute?” Cindy asked her teacher, as the three friends entered the room.

Mr. Harrington was reading something on his phone and munching on a carrot. He looked up. “Huh? Oh, sure. What’s up? You kids have a good break?”

“Well, actually,” Bryce started.

“Hush, Bryce,” Madison interrupted. “Nobody cares about your drama.” She turned to address the teacher. “We have a physics question.”

“I have a physics answer!” he replied.

“If a nuclear bomb went off in space, would the radioactive stuff fall down and make people sick?” Cindy asked.

“How far in space?” the teacher asked.

“In orbit. But not like a geosynchronous orbit,” Madison said. “Closer than that.”

He tapped the carrot against his teeth for a moment. “Well there really wouldn’t be any radioactive stuff to fall down,” he said. “You are thinking fallout, like when a bomb goes off on Earth?”

“Exactly,” Cindy said.

“Yeah, so in that case, it’s the dirt that’s the problem. That big mushroom cloud is full of stuff from the ground getting kicked miles up into the air. And that dirt is irradiated, so when it finally comes back down, it’s really dangerous. It radiates alpha particles that mess with biology, causing malfunctions in the way cells operate. That leads to cancer, for example. But up in space, there’s no dirt to irradiate.”

“Oh,” Cindy said.

“Told you,” Bryce said.

Cindy sneered at him and continued, “So it’d be no big deal if a nuke was set off in orbit?”

“Oh, it’d be a big deal. Depending on how high it is, what kind of a device, the yield, it could be catastrophic.”

“Catastrophic?” Madison repeated.

“Yeah.” The teacher put down his carrot and phone, stood, and walked to the whiteboard. Diagramming as he spoke, he explained, “so when a nuclear explosion goes off, it emits gamma radiation.”

“Like the Hulk!” Bryce said.

“Shush,” Madison admonished.

The teacher laughed. “Gamma radiation has a habit of stripping electrons off atoms. What do you call an atom that had an electron removed?” he asked.

“Ion,” Cindy replied. “A cation, since there’s an electron missing, it would have a positive charge.”

“Right! So they call this ionizing radiation. The gamma rays stream down from space and when they hit the atmosphere, they strip the electrons off all the atoms they encounter. Those electrons go shooting down toward Earth at nearly the speed of light.”

“So we get killed by the electrons?” Madison asked.

“No, no. Not you. Your phone,” he explained. “The earth’s magnetic field acts like a guide, so all the electrons in an area move in exactly the same direction. It creates a huge pulse of electricity that hits all at once.”

“Oh!” Bryce said. “An EMP!”

“Right,” the teacher said. “This one is a high-altitude electromagnetic pulse, or an H-EMP. There are various kinds of EMPs, but this one from high altitude is particularly bad, because just one nuclear explosion could destroy any electrical or electronic device over a huge area. Like the whole United States.”

“Just one explosion could do that?” Madison asked.

“Yeah. Just one. And this isn’t just a theory. Back when our country was first developing nuclear weapons, they did experiments to find out what would happen if they blew one up at altitude. I think they used a weather balloon.”

“That’s crazy. What happened?” Cindy asked.

“Radio stations eight hundred miles away in Hawaii got destroyed, I think. The effect was far bigger than they anticipated because they didn’t account for the influence of the earth’s magnetic field. Government scientists have figured out since then there are actually three different effects. The first one happens immediately—that’s when the electrons rain down and ruin all the chips in your phones. Then there’s a second pulse that’s a lot like the effect of lightning. That one isn’t a big deal, since lightning happens all the time. And then there’s a third pulse that acts like a solar flare. That one will take out the grid.”

“Take out the grid?” Madison asked. “What’s that mean?”

“The power lines act like huge antennas and all the energy will end up in the transformers. They’ll all blow up. A solar flare did a huge amount of damage to the Canadian power grid back when I was in college. Took months for them to fix it. It would be like that.”

“Oh my God,” Madison said. “So if someone knew that a nuke in orbit was going to explode, would there be anything they could do to prepare for it? To protect the electronics and the grid?”

“Sure, but not at scale. You can shield electronics. I’m sure the military does. I bet none of their weapons systems would be damaged. But nobody is going to add EMP shielding to a phone or a toaster. It costs too much. And the grid is the grid. I mean, replacing that with something that could stand up to an EMP would cost billions, maybe trillions of dollars.”

“So basically, the lights would be out for months?” Cindy asked.

“Basically,” he replied. “And of course, that would stop transportation, since gas pumps need electricity. And there would be no internet. No phones. It would be like living in the 1800s for a while.”

“People would need a lot of peanut butter,” Bryce said.

Madison looked at him and smiled. “I think we found our answer.”

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