IV. The Future Has Not Happened Yet

Mr Blottisham entered the Common Room carrying a large clock.

Professor Quillibrace looked up.

Miss Stray looked at the clock.

"Why," asked Quillibrace, "are you carrying that?"

"Because I have been thinking about time."

"I was afraid of that."

Blottisham placed the clock on the table.

"The future already exists."

Miss Stray raised an eyebrow.

"Does it?"

"Obviously."

Quillibrace closed his book.

"That is an interesting opening."

"I mean it quite literally."

"Good."

"At this moment, the future is simply what hasn't happened yet."

"That seems contradictory."

"Not at all."

Blottisham pointed at the clock.

"The clock is going forward."

"Yes."

"Every moment has a next moment."

"Yes."

"So the future is already there."

"Where?"

Blottisham hesitated.

"Ahead."

"Where is ahead?"

"Later."

"Where is later?"

Blottisham looked irritated.

"You know perfectly well what I mean."

"Unfortunately, I do."

Miss Stray smiled.

"Perhaps we should start with the physics."

"Thank you."

"In classical mechanics," said Quillibrace, "the state of a physical system at one moment determines its subsequent evolution, given the laws."

"Exactly."

"The future is therefore implicit in the present."

"Exactly."

"If you knew the complete state of the universe..."

"...you could calculate the future."

"At least in principle."

"Yes."

Blottisham looked triumphant.

"There we are."

Quillibrace nodded.

"The Laplacian demon."

"Precisely."

"An intelligence knowing every relevant position and motion, together with the laws of nature, could calculate the entire future."

"Yes."

"And the entire past."

"Yes."

"So the future is already fixed."

"Exactly."

"Even if nobody knows it."

"Exactly."

Quillibrace looked at Miss Stray.

"He has found determinism."

"I noticed."

Blottisham smiled.

"And what is wrong with it?"

"Nothing," said Quillibrace.

Blottisham paused.

"Nothing?"

"Not yet."

He opened his book again.

"Quantum mechanics."

Blottisham groaned.

"I knew you were going to say that."

"Of course."

"Quantum mechanics doesn't change the fact that the future exists."

"Why not?"

"Because uncertainty doesn't mean indeterminacy."

"Explain."

"If I put a red card or a blue card into an envelope, and you don't know which one it is, the card is nevertheless already red or blue."

"Yes."

"So the uncertainty belongs to you."

"Yes."

"Not to reality."

"Yes."

Blottisham sat down.

"Therefore quantum uncertainty is simply ignorance."

Quillibrace regarded him.

"Is it?"

"Yes."

"Why?"

"Because something must actually happen."

"Certainly."

"And therefore the outcome must already be determined."

"Why?"

Blottisham stopped.

Miss Stray watched him.

"Because..."

He frowned.

"If it isn't determined, what determines it?"

Quillibrace smiled.

"Now we're getting somewhere."

Blottisham looked suspicious.

"What?"

"You have just assumed that if an outcome isn't predetermined, nothing could determine it."

"Well..."

"That is not a logical necessity."

"But something must cause it."

"Perhaps."

"And causes determine effects."

"Do they?"

"Usually."

"That isn't the same as saying they determine them uniquely."

Miss Stray leaned forward.

"Perhaps the present constrains what can happen without containing a single already-determined future."

Blottisham looked at her.

"That sounds like cheating."

"Why?"

"Because if there are several possible outcomes, one of them has to happen."

"Yes."

"Then one of them was going to happen."

"Not necessarily."

"What does 'going to happen' mean?"

"The question itself may contain the assumption."

Blottisham looked at Quillibrace.

"You're saying the future isn't there."

"I'm saying we should be careful about what 'there' means."

"That's a philosopher's answer."

"Thank you."

Blottisham stood and began pacing.

"Let's make this simple."

"Please."

"Suppose a quantum system has two possible outcomes."

"Yes."

"One of them occurs."

"Yes."

"So afterwards we can say which one occurred."

"Yes."

"And before the measurement, there were two possibilities."

"Yes."

"Therefore one of them was going to occur."

"No."

Blottisham stopped.

"Why not?"

"Because was going to occur can mean two different things."

"Which are?"

"One: that the outcome was already fixed, but unknown."

"And two?"

"That the outcome belonged to the structured possibilities available to the system, without yet being determined as an actuality."

Blottisham stared at him.

"That's a very fine distinction."

"It is a very important one."

Miss Stray nodded.

"Possibility need not mean ignorance."

Blottisham sat again.

"So what is possibility?"

Quillibrace considered this.

"A structured field of what can happen."

"That sounds vague."

"It is less vague than saying that all possibilities are secretly actual."

Blottisham looked at the clock.

"What happens to the possibilities when one becomes actual?"

"They change."

"Why?"

"Because the world has changed."

Miss Stray spoke.

"That is the important point."

Blottisham turned towards her.

"Suppose a seed grows."

"Yes."

"It becomes a plant."

"Yes."

"The plant has capacities the seed did not exercise."

"Yes."

"Some things are now possible that weren't possible before."

"Yes."

"And some things are no longer possible."

"Yes."

"So actualisation changes possibility."

"Precisely."

Blottisham thought.

"That happens in ordinary life."

"Of course."

"A mutation can change what an organism can become."

"Yes."

"A new invention can make something possible that wasn't possible before."

"Yes."

"A scientific discovery can change what scientists can think."

"Yes."

"So you don't need quantum mechanics."

"No."

"Then why are we discussing it?"

"Because quantum mechanics makes it difficult to maintain the assumption that possibility is merely ignorance of an already-determined actuality."

Blottisham nodded slowly.

"So quantum theory opens a philosophical door."

"Perhaps."

"And you want to walk through it."

"Not necessarily."

"Why not?"

"Because there may be a very large number of philosophers on the other side."

Miss Stray laughed.

Blottisham smiled.

"I think I see the problem."

"Do you?"

"The old picture says there is one future."

"Yes."

"We don't know it."

"Yes."

"But it exists."

"Yes."

"The new picture says..."

He paused.

"There are possibilities."

"Yes."

"And one becomes actual."

"Yes."

"And what becomes actual changes the possibilities."

"Yes."

"So the future isn't a place."

"No."

"It's a field of possibilities."

"Better."

"And it becomes actual."

"Yes."

Blottisham looked uneasy.

"That sounds like the future is genuinely future."

"An alarming conclusion."

"Does physics actually say that?"

Quillibrace shook his head.

"Not quite."

"Then why are we saying it?"

"Because physics has made the question unavoidable."

Miss Stray nodded.

"Quantum mechanics does not settle the metaphysics of time."

"But it unsettles the assumption that the future must already be fully determinate."

"Yes."

Blottisham sat back.

"What about many worlds?"

Quillibrace sighed.

"I knew you would ask."

"If all outcomes occur, then there is no indeterminacy."

"Perhaps."

"All the possibilities are there."

"Yes."

"So the future is still complete."

"In a certain sense."

"Then the old picture survives."

"Possibly."

Blottisham smiled.

"Excellent."

"Don't be too pleased."

"Why?"

"Because you've changed the picture."

"How?"

"In the classical picture there is one actual future."

"Yes."

"In many worlds there is a branching structure of futures."

"Yes."

"So the interpretation has preserved completeness by changing what counts as the actual world."

Blottisham frowned.

"But all the branches exist."

"Perhaps."

"So the possibilities are actual somewhere."

"Yes."

"Then possibility still isn't real possibility."

Miss Stray looked at him.

"Why not?"

"Because if it is already actual, it isn't possibility."

There was a silence.

Quillibrace looked almost pleased.

"That," he said, "is an unexpectedly good objection."

Blottisham smiled.

"I have those occasionally."

"Occasionally."

Miss Stray said:

"The deeper question is whether reality must be complete in the sense of containing every fact that will ever be true."

Blottisham thought about this.

"Why must it?"

"That is precisely the question."

"But surely science wants a complete description."

"Perhaps a complete description of the present."

"Wouldn't that determine the future?"

"Not necessarily."

"Why not?"

"Because prediction and determination are not the same."

Blottisham frowned.

"But if we can predict something..."

"We may predict a probability distribution."

"With astonishing accuracy."

"Yes."

"And then an individual outcome occurs."

"Yes."

"So the theory was right."

"Yes."

"Even though it didn't specify which outcome would occur."

"Exactly."

Blottisham looked at the clock again.

"So physics can predict the structure of possibility without predicting the particular future."

"Precisely."

"That's rather strange."

"Only if you thought prediction meant revelation of a pre-existing actuality."

Blottisham smiled.

"Which I did."

"We noticed."

Miss Stray looked out of the window.

"The future may therefore be constrained without being completely determined."

"By what?"

"The past."

"Yes."

"The present physical state."

"Yes."

"The laws."

"Yes."

"The relations in which things participate."

"Yes."

"But constraint is not necessarily determination."

Blottisham was silent for a while.

Then:

"So the future isn't arbitrary."

"No."

"But it isn't already complete."

"Perhaps."

"It is what can become actual."

"Yes."

"And when something becomes actual..."

"...the possibilities change."

Blottisham nodded.

"Possibility creates possibility."

Quillibrace looked at him.

"That is almost a respectable sentence."

"Almost?"

"I am a professor."

"Ah."

There was another silence.

Blottisham looked at the clock.

"I think I understand."

Quillibrace waited.

"The past is what has happened."

"Yes."

"The present is what is happening."

"Yes."

"And the future is what can happen."

"Better."

"But some things can happen and some can't."

"Yes."

"And some are more probable than others."

"Yes."

"And what happens changes what can happen next."

"Yes."

Blottisham nodded.

"So the world doesn't merely travel along a track."

Miss Stray smiled.

"It may be more like a landscape through which possibilities open and close as the world changes."

Blottisham considered this.

"I prefer the track."

"I suspected you might."

"But the landscape sounds more interesting."

Quillibrace picked up his book.

"That is not a scientific objection."

"No."

"It's a philosophical preference."

"I know."

He looked at the clock.

"Still..."

"Yes?"

"The future really hasn't happened yet."

Quillibrace looked at him.

Miss Stray smiled.

"Not yet."

Blottisham nodded.

"And perhaps that is the point."

He picked up the clock.

"Where are you taking that?"

"Back to my office."

"Why?"

"I need to put it somewhere."

"Where?"

Blottisham paused.

"In the future."

Quillibrace closed his eyes.

Miss Stray laughed.

And for once, nobody corrected him.