Professor Quillibrace had almost finished his morning tea when Mr Blottisham entered carrying a polished wooden case.
Professor Quillibrace looked at it with immediate suspicion.
"What have you brought today?"
"Billiard balls."
Professor Quillibrace slowly put down his teacup.
"I see."
"No, Professor."
Blottisham smiled cheerfully.
"I don't think you do."
Miss Stray entered behind him.
"Oh dear."
"You recognise the expression?"
asked Professor Quillibrace.
"The wooden case."
"Yes."
"It usually means Mr Blottisham has purchased something in the interests of science."
Blottisham opened the case with great satisfaction.
Inside were a dozen brilliantly polished billiard balls.
"There."
Professor Quillibrace sighed.
"I suppose these are electrons."
"No."
"No?"
"They're billiard balls."
Professor Quillibrace looked mildly relieved.
"Oh."
"They're going to become electrons."
The relief disappeared.
Miss Stray quietly poured herself some tea.
"I have found," she remarked,
"that this generally improves the experience."
Blottisham arranged the balls carefully across the billiard table that occupied one corner of the Common Room.
Nobody could remember why the college possessed a billiard table.
Professor Quillibrace suspected it had something to do with the nineteenth century.
"There."
said Blottisham proudly.
"What exactly are we demonstrating?"
"Particle physics."
"With snooker?"
"Billiards."
"My apologies."
Blottisham picked up the cue.
"Physicists used to describe particles as tiny billiard balls."
"They sometimes did."
"So..."
He tapped one gently.
"...they should collide."
"They do."
"They should bounce."
"In certain circumstances."
"They should possess surfaces."
Professor Quillibrace hesitated.
"Well..."
"They should roll."
"No."
"They should spin."
Professor Quillibrace brightened.
"Yes."
Blottisham looked delighted.
"Aha!"
"I knew it!"
"They spin."
"They possess something we call spin."
"So they really are spinning?"
Professor Quillibrace became very still.
"No."
"But..."
"It is called spin."
"Because..."
"It resembles..."
"...not really."
Miss Stray looked sympathetically at Professor Quillibrace.
"It has been one of those mornings."
Blottisham looked down at the billiard balls.
"If electrons are tiny balls..."
"They are not."
"...how smooth are they?"
"They are not smooth."
"How rough?"
"They are not rough."
"Then what are they?"
Professor Quillibrace looked thoughtfully at the ceiling.
"One sometimes wonders whether language has apologised sufficiently."
Miss Stray smiled.
"I suspect it has not."
Blottisham was still examining the balls.
"They must have a surface."
"Not in the ordinary sense."
"An inside?"
"Not in the ordinary sense."
"An outside?"
"No."
"So..."
Blottisham frowned.
"...where do they keep themselves?"
The room became silent.
Professor Quillibrace looked as though he had suddenly developed a deep interest in the fireplace.
Finally Miss Stray spoke.
"I think Mr Blottisham has arrived at the edge of the metaphor."
Professor Quillibrace nodded gratefully.
"The billiard-ball picture works rather well..."
"...until one asks billiard-ball questions."
Blottisham looked genuinely puzzled.
"But surely that is how one tests a metaphor."
Professor Quillibrace stopped.
He considered the question for several moments.
"Actually..."
"...yes."
The discussion continued.
Blottisham struck one ball gently.
It rolled across the table and struck another.
"There."
"Momentum."
"Quite."
"But..."
He looked puzzled again.
"Do electrons make that satisfying clicking noise?"
Professor Quillibrace laughed despite himself.
"No."
"Pity."
"It is."
Miss Stray looked at the moving balls.
"They are excellent for visualising collisions."
Professor Quillibrace nodded.
"Indeed."
"But they also encourage us to imagine tiny hard objects."
"Which eventually becomes misleading."
"Precisely."
Blottisham stopped another ball with his finger.
"I think I understand."
Professor Quillibrace looked hopeful.
"The metaphor opens the door."
"Yes."
"But if one insists on walking further..."
"...one eventually arrives in the billiard room."
Miss Stray laughed.
"A remarkably elegant summary."
The clock struck four.
Blottisham carefully packed away the billiard balls.
"I have one final question."
Professor Quillibrace smiled wearily.
"I thought you might."
"If particles aren't really little balls..."
"No."
"...why did physicists call them particles?"
Professor Quillibrace was silent for a long time.
Finally he answered.
"Because every generation must begin somewhere."
Miss Stray nodded.
"And because every new idea must first borrow an old language."
Professor Quillibrace smiled.
"Until it gradually teaches us why that language was never quite enough."
As Blottisham closed the wooden case, he looked thoughtful.
"So today's experiment has failed."
Professor Quillibrace shook his head.
"No."
"It has done exactly what a good experiment should do."
"It has?"
"It has shown us where the model stops."
Blottisham looked pleased.
"I do enjoy experiments with successful failures."
Miss Stray smiled.
"I suspect science does too."
They left the billiard room together.
The polished balls remained in their velvet-lined case.
Perfectly round.
Wonderfully tangible.
Entirely unsuited to being electrons.
And yet, for one delightful afternoon, they had helped three colleagues discover precisely why physicists had once imagined them that way—and why they eventually had to imagine something else.
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