The Reality Detector

The reading room of the Institute was unusually cluttered.

Wires trailed across the carpet. A small metal box sat on the table, covered with switches, dials, and a blinking green light.

Miss Elowen Stray stood beside it, examining the apparatus with cautious curiosity.

“What does it do?” she asked.

Mr Blottisham looked up proudly from a bundle of cables.

“It detects reality.”

Elowen blinked.

“I’m sorry?”

Blottisham gestured grandly toward the device.

“The Reality Detector.”

At that moment Professor Quillibrace entered, carrying his teacup as usual.

He paused.

His eyes moved from the wires, to the box, to the blinking light.

“How encouraging,” he said mildly. “We appear to have made significant progress since breakfast.”

Blottisham beamed.

“I thought you’d be pleased.”

Quillibrace set his cup down carefully.

“And what precisely does the instrument detect?”

“Reality.”

“Yes,” said Quillibrace patiently. “You mentioned that.”

Blottisham tapped the metal casing.

“It settles the question.”

“What question?”

“You know — the big one.”

Elowen looked intrigued.

“The nature of reality?”

“Exactly.”

Quillibrace raised an eyebrow.

“And how does the device accomplish this remarkable feat?”

Blottisham leaned forward.

“Well, quantum physics says that reality behaves very strangely.”

“Indeed it does.”

“Particles are waves. Waves are particles. Observations change the system. Nothing is definite until it’s measured.”

Quillibrace nodded thoughtfully.

“A familiar collection of statements.”

“So,” Blottisham continued, “the big debate is about what reality is really doing underneath all that.”

“And the detector resolves this?”

“Yes.”

“How?”

Blottisham pointed to the blinking light.

“When the light turns green, the system is real.”

Quillibrace looked at the light.

It blinked steadily.

“How reassuring,” he said.

Elowen leaned closer to the box.

“But what exactly is it measuring?”

Blottisham hesitated.

“Well… quantum behaviour.”

“And that tells us what reality is?”

“Of course.”

Quillibrace considered this carefully.

“My dear Blottisham,” he said gently, “may I ask a small question?”

Blottisham sighed.

“You’re about to ruin this, aren’t you?”

“Not at all.”

“Go on then.”

Quillibrace gestured toward the device.

“What, precisely, do you mean by reality?”

Blottisham frowned.

“What do you mean?”

“I mean,” said Quillibrace calmly, “what does the word refer to in this experiment?”

Blottisham looked slightly irritated.

“Reality is… you know… what actually exists.”

Elowen spoke thoughtfully.

“Exists independently of observation?”

“Yes.”

Quillibrace nodded.

“An interesting proposal.”

Blottisham folded his arms.

“What’s wrong with it?”

“Nothing in particular,” said Quillibrace. “Provided we remember that it is a definition.”

Elowen tilted her head.

“You mean there could be other meanings?”

“Quite.”

Blottisham waved a hand.

“But physics is about reality.”

“Physics,” Quillibrace replied gently, “is about constructing models that account for observable phenomena.”

Blottisham stared at him.

“That’s the same thing.”

“Is it?”

Elowen glanced at the blinking light again.

“So the theory tells us how the phenomena behave…”

“Yes.”

“But it doesn’t necessarily tell us what reality is underneath.”

Quillibrace inclined his head.

“A subtle but important distinction.”

Blottisham looked unconvinced.

“But surely there is something underneath.”

“Possibly.”

“And physics should tell us what it is.”

Quillibrace smiled faintly.

“That depends on what one expects a theory to do.”

Elowen considered this.

“So when people argue about interpretations of quantum physics…”

“…they are often arguing about different assumptions concerning reality.”

“Exactly.”

Blottisham gestured impatiently at the device.

“Well that’s what the detector solves.”

Quillibrace looked at the box again.

“And how does it distinguish between these assumptions?”

Blottisham opened his mouth.

Then paused.

“Well… it detects reality.”

Quillibrace waited.

Elowen tried to help.

“But the detector must measure something.”

“Yes.”

“And whatever it measures must already be described by the theory.”

Blottisham’s brow furrowed.

“That sounds right.”

Elowen smiled slowly.

“So the device can only detect phenomena that the theory already predicts.”

Quillibrace raised his teacup.

“A most elegant observation.”

Blottisham looked from the detector to the whiteboard behind him.

Gradually his expression changed.

“So the detector doesn’t actually tell us what reality is.”

“No,” said Quillibrace kindly.

“It just measures behaviour described by the theory.”

“Precisely.”

Blottisham slumped slightly.

“That’s much less dramatic.”

Quillibrace smiled.

“Perhaps.”

Elowen looked thoughtfully at the blinking light.

“So the real question isn’t what reality detector we build.”

“No.”

“It’s what we mean when we say reality.”

Quillibrace nodded.

“My dear Miss Stray, you have identified the essential difficulty.”

Blottisham sighed.

“So the great debate about quantum reality…”

“…may partly be a debate about words.”

Quillibrace’s eyes twinkled.

“My dear Blottisham,” he said gently, “a great many profound debates are.”

The green light continued blinking quietly.

No one was entirely sure what it meant.