“You’re not going to find anything down there,” Dr. Price explained. “There’s no such thing as a negative radio frequency. You can represent them mathematically, sure, but there’s no real world analogue. A wave observed forward or backward in time is physically identical.”

Those words didn’t seem to have any effect on her student, however, who continued turning the knob on her device counterclockwise. “Well, you and I might know that, but does the radio?”

“What do you mean?”

“We care about what does and doesn’t exist, but the radio doesn’t have any idea.”

She laughed. “Well, what do you think it’s going to do with those frequencies? Imagine a signal to play for you?”

“You never know.”

“I can’t believe what some of you kids come up with.” She shook her head. How do freshmen like this not drown during their morning shower? “A machine like that doesn’t have the capacity to creatively interpret data like a human does. Think about, for instance, the way you see shapes in clouds, or hear the ocean in seashells. Your brain is wired to find complex patterns in noise. Now, think about what happens when you tune a television to a dead channel. Do you see the difference?”

“I do,” she replied. “At least, when it comes to extremely unimaginative televisions.”

“I don’t-“ she gripped her forehead in frustration. “I don’t see what would be different about your radio.”

“Well, for one thing, I put its batteries in backwards. That’s something you wouldn’t be able to see.”

Seriously? “Anything else?”

“Nah, one thing at a time. I have to maintain experimental control, after all.”

“Well, you have fun with that. I have to go teach another class,” she lied. “I’ll be back in a few hours.”

Dr. Price did eventually return, although more than a few hours later, hoping that it would be late enough to have the lab to herself. When she opened the door, however, she found that her student was still inside, now mostly naked, and gripping the same radio to her chest. Its speakers were oozing a steady stream of muffled white noise directly into her exposed skin. She turned her head slowly towards her instructor, revealing dime-wide pupils and a toothbare grin. “You made it back just in time,” she spoke. “They’re about to play my song.”

Negative frequencies have meaning in a world where then comes before if.

When it comes to electronics, negative frequencies allow for the existence of electric ghosts.