The Senior Common Room had been discussing reality for nearly an hour.
This was considered by Professor Quillibrace to be a dangerous amount of time.
"Reality," he observed, "has a tendency to become less cooperative the longer one examines it."
Mr Blottisham entered carrying a notebook.
"I have a question."
Professor Quillibrace smiled.
"Excellent."
"Why?"
"Because after three weeks of discussing physics, you have finally arrived at the most useful opening sentence."
Miss Stray looked up from her book.
"What is the question?"
Blottisham sat down.
"What exactly is a particle?"
Professor Quillibrace looked pleased.
"Ah."
"That seems like a simple question."
"Those are often the most dangerous."
Blottisham opened his notebook.
"I thought a particle was a very small thing."
"Yes."
"Like a tiny object."
"Yes."
"Just too small to see."
"That is certainly how the word encourages us to think."
"But?"
Professor Quillibrace walked to the blackboard.
He wrote:
PARTICLE
"The word itself carries assumptions."
"Such as?"
He wrote:
1. It is a thing.
"Yes."
2. It has an identity.
"Yes."
3. It occupies a location.
"Yes."
4. It possesses properties.
"Yes."
Blottisham nodded.
"That sounds reasonable."
"It does."
"So what's the problem?"
Professor Quillibrace turned.
"The problem is that quantum physics repeatedly asks us to reconsider all four."
Miss Stray smiled.
"And yet the word remains."
"Why?"
"Because replacing a familiar metaphor is not easy."
Blottisham looked puzzled.
"But if the metaphor no longer works..."
"Yes?"
"Why keep it?"
Professor Quillibrace smiled.
"An excellent question."
He wrote:
ELECTRON
"Imagine an electron."
"Yes."
"What image appears?"
"A tiny sphere."
"Naturally."
"Something moving around."
"Naturally."
"But that image belongs to classical physics."
"Before quantum mechanics?"
"Yes."
"In quantum theory, the electron behaves differently."
"How?"
"Sometimes like a particle."
"Yes."
"Sometimes like a wave."
"Yes."
Blottisham looked pleased.
"Ah. So it is both."
"That is the usual phrase."
"Is it correct?"
Professor Quillibrace paused.
"It is useful."
"That sounds like a politician's answer."
"It is a physicist's answer."
Miss Stray laughed.
"The difficulty," she said,
"is that 'particle' and 'wave' are both inherited metaphors."
Blottisham looked between them.
"So neither is the thing itself?"
"Perhaps."
"Then what is the thing itself?"
Silence.
Professor Quillibrace sat down.
"That question may assume too much."
"What do you mean?"
"Perhaps we are asking nature to provide an answer in categories that belong to us."
Blottisham frowned.
"You mean the universe doesn't know about particles?"
"Precisely."
"It doesn't?"
"No more than a river knows it is a river."
Miss Stray smiled.
"The names are ours."
"Yes."
"The patterns are discovered."
"Yes."
"But the categories..."
"Are human ways of organising experience."
Blottisham looked at the notebook.
"So a particle might not be a little thing."
"Correct."
"But it is still something."
"Perhaps."
"Perhaps?"
"That word is doing considerable work."
The room became quiet.
Miss Stray looked towards the window.
"Maybe physics has gradually moved away from asking, 'What things exist?'"
"Towards?"
"'What structures and relationships exist?'"
Professor Quillibrace nodded.
"That is a very modern way of thinking."
Blottisham looked thoughtful.
"So instead of objects first..."
"Yes?"
"...relations first?"
"Possibly."
"That sounds rather strange."
"Only because we are accustomed to objects being fundamental."
"But perhaps objects are what appear when relationships become stable."
Professor Quillibrace looked at him.
A pause.
"That..."
he said carefully,
"...is an unexpectedly sophisticated observation."
Blottisham smiled.
"I've been reading."
"Ah."
"Badly?"
"Not necessarily."
Miss Stray laughed.
"But there is something important here."
"What?"
"If our basic metaphor changes..."
"Yes?"
"Our whole picture of reality changes."
Professor Quillibrace pointed to the blackboard.
"For centuries, physics imagined reality as a collection of things."
"Objects."
"Yes."
"Then it began to imagine reality as fields."
"Yes."
"And interactions."
"Yes."
"So the question becomes..."
He wrote:
WHAT IS FUNDAMENTAL?
Blottisham looked at the words.
"Things?"
"Perhaps."
"Fields?"
"Perhaps."
"Information?"
Professor Quillibrace glanced at Miss Stray.
"That is a question for another afternoon."
The clock struck five.
As they gathered their books, Blottisham looked once more at the word on the board.
"Particle."
"Yes?"
"It seems strange now."
"Good."
"Good?"
"Strangeness is often the beginning of understanding."
Miss Stray smiled.
"The moment a familiar word becomes unfamiliar again..."
"Yes?"
"...we have started thinking."
Professor Quillibrace erased everything except the title.
He left one word behind:
THING
Blottisham looked at it.
"Is that the question?"
"No."
"Then what is?"
Professor Quillibrace picked up his coat.
"Whether reality is made of things..."
He paused.
"...or whether things are how reality appears to us."
The room fell silent.
The blackboard remained.
The question remained.
And somewhere beneath all the mathematics, one of the oldest philosophical questions had quietly returned.
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