I. The Thing Problem

The Senior Common Room at St Anselm's was unusually quiet.

Professor Quillibrace was reading.

Mr Blottisham was not reading.

Miss Stray was looking out of the window.

After several minutes, Blottisham closed the book he had not been reading.

"There's something wrong with modern physics."

Quillibrace did not look up.

"Several things, I imagine."

"No, no. Something fundamentally wrong."

"That narrows it down."

Miss Stray turned from the window.

"What have you been reading?"

"Quantum mechanics."

"Ah."

"I don't see why everyone makes such a fuss about it."

Quillibrace lowered his book.

"How fortunate."

"I mean, really. An electron is an electron."

"Is it?"

Blottisham looked at him.

"Obviously."

"What is it?"

"An electron."

Quillibrace waited.

Blottisham waited.

Miss Stray smiled faintly.

"I mean," said Blottisham, "a particle."

"Good."

"With charge."

"Yes."

"Mass."

"Yes."

"And spin."

"Yes."

"And presumably a position."

"Presumably?"

Blottisham frowned.

"Well, it has to be somewhere."

"That," said Quillibrace, "is precisely the sort of statement that becomes interesting in quantum mechanics."

"Interesting?"

"Yes."

"It sounds more like common sense."

"Common sense has a long history of being interesting once physicists stop obeying it."

Blottisham leaned back.

"I still don't see the problem."

Miss Stray spoke quietly.

"Perhaps the problem is not with the electron."

Quillibrace glanced at her.

"Quite."

Blottisham looked from one to the other.

"What, then?"

"Perhaps," said Quillibrace, "the problem is with the word thing."

There was a pause.

Blottisham looked disappointed.

"I thought we were discussing physics."

"We are."

"Then why are we discussing nouns?"

"Because," said Miss Stray, "physics has been using them."

Blottisham considered this.

"Of course it has."

"Very extensively," said Quillibrace.

He closed his book.

"Let us begin at the beginning. A stone has a position. A planet has a mass. An electron has a charge. A particle moves through space and time."

"Quite."

"We measure what things do."

"Yes."

"We discover regularities."

"Yes."

"And we express those regularities mathematically."

"Exactly."

Quillibrace nodded.

"There is nothing obviously philosophical about that."

"Good."

"That is precisely the problem."

Blottisham stared at him.

Miss Stray turned back towards the window.

Quillibrace continued.

"We have become so accustomed to the idea that reality consists of things possessing properties that we no longer notice that it is an idea."

"Because it's true."

"How do you know?"

"Because there are things."

"Such as?"

"The chair."

Quillibrace glanced at the chair.

"An excellent example."

"And the table."

"Another."

"And you."

"I had hoped to avoid that one."

Miss Stray laughed.

Blottisham continued.

"The world exists whether we look at it or not."

"Probably."

"Probably?"

"That is a rather different proposition from saying that the world consists fundamentally of independently existing objects possessing determinate properties."

Blottisham frowned.

"What's the difference?"

Quillibrace looked at Miss Stray.

"Would you like to tell him?"

She shook her head.

"He's enjoying himself."

"I am not."

"Not yet," said Quillibrace.

He stood and walked towards the fireplace.

"For centuries, physics had an extraordinarily successful picture of the world. Objects. Properties. Positions. Momenta. Forces. Interactions. If we knew the relevant quantities and the laws governing them, we could calculate what happened next."

"Exactly."

"The world was an inventory."

"Yes."

"The objects were there."

"Yes."

"The properties were there."

"Yes."

"And the relations told us how the objects behaved."

"Yes."

Quillibrace paused.

"Notice anything?"

Blottisham looked around the room.

"No."

Miss Stray said, "The relations come last."

"Precisely."

Quillibrace resumed his seat.

"The things exist first. Then they enter into relations."

"Well, naturally."

"Why naturally?"

"Because you can't have a relation without things to relate."

Miss Stray turned.

"Can you?"

Blottisham looked at her.

"Obviously."

"Can you describe an entangled quantum state that way?"

Blottisham hesitated.

"Of course."

"Two particles," said Quillibrace.

"Yes."

"Each with its own complete state."

"Yes."

"Which then become entangled."

"Yes."

Quillibrace raised an eyebrow.

"That is one possible way of talking."

"And a perfectly sensible one."

"Is it?"

"Why not?"

"Because the whole point is that the joint state cannot always be reduced to two independently specified states plus something added afterwards."

Blottisham waved a hand.

"That's just because quantum mechanics is complicated."

"Perhaps."

"Or incomplete."

"Perhaps."

"Or we haven't found the hidden variables."

"Perhaps."

"Or there are multiple worlds."

"Perhaps."

Blottisham looked pleased.

"There we are."

"There we are where?"

"We have explanations."

"No."

"No?"

"We have proposals."

"What is the difference?"

"An explanation answers a question. A proposal can merely move it."

Blottisham looked annoyed.

"So what is your question?"

Quillibrace smiled.

"Must reality ultimately consist of independently existing things possessing determinate properties?"

Silence.

Blottisham shifted in his chair.

"Yes."

"Why?"

"Because otherwise what would reality consist of?"

"Relations."

"Relations between what?"

"Ah."

Miss Stray spoke before Quillibrace could.

"Perhaps that is the difficulty."

They both looked at her.

"We keep asking what the things are and then asking how they relate. But perhaps some things are what they are partly because of the relations in which they participate."

Blottisham shook his head.

"That sounds philosophical."

"Yes."

"Which is precisely what we're trying to avoid."

Quillibrace smiled.

"No. It is what we have been trying to avoid."

Blottisham looked suspiciously at him.

"You make it sound as though physics has a philosophy."

"Physics has always had a philosophy."

"I thought philosophy was what philosophers did."

"So did Newton."

Blottisham looked at him.

"Did he?"

"Not exactly."

Miss Stray returned her attention to the window.

"Perhaps that is the difficulty with successful physics. Its philosophical assumptions become invisible."

Quillibrace nodded.

"Precisely."

"We expect things to possess properties."

"Yes."

"We expect those properties to exist independently of measurement."

"Yes."

"We expect separate things to have separate states."

"Yes."

"We expect observation to reveal what is already there."

"Yes."

"And we expect possibility to mean merely what we don't yet know."

Quillibrace looked at her.

"Excellent."

Blottisham looked from one to the other.

"I don't see why any of this matters."

Quillibrace leaned forward.

"Because none of those expectations is a law of nature."

"They seem fairly reasonable."

"So did the rest."

"The rest of what?"

"Classical physics."

Blottisham was silent.

Outside, a bird landed briefly on the window ledge.

Miss Stray watched it.

"Perhaps quantum mechanics has not merely made the world stranger."

Quillibrace said nothing.

"Perhaps," she continued, "it has made our assumptions visible."

Blottisham looked thoughtful.

"And what are we supposed to do about that?"

"Nothing," said Quillibrace.

"Nothing?"

"Not immediately."

"Then what's the point?"

"The point," said Miss Stray, "may be to stop asking how we can make quantum mechanics fit our picture of things."

"And ask?"

She looked back at them.

"What if the picture was never fundamental?"

There was a long silence.

Blottisham stood.

"Well."

Quillibrace waited.

"I think I'll have another cup of tea."

"An admirably cautious response."

Blottisham walked towards the door.

Then he stopped.

"Professor?"

"Yes?"

"If relations are fundamental..."

"Yes?"

"What are they relations between?"

Quillibrace looked at Miss Stray.

Miss Stray looked at the window.

Neither answered.

Blottisham nodded slowly.

"I thought so."

And went to make the tea.