The Trouble with Quantum Questions: Dialogue IV — On Superposition

Characters:

Professor Quillibrace

Mr Blottisham

Miss Elowen Stray

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Blottisham:

I’ve prepared myself for this one.

Quillibrace:

That already worries me.

Blottisham:

Superposition. Two states at once. Even you can’t wriggle out of that.

Quillibrace:

I’ve never wriggled in my life.

Elowen Stray:

It does sound straightforward. The particle is here and there.

Blottisham:

Exactly! At last, something delightfully paradoxical.

Quillibrace:

Paradoxes are usually bookkeeping errors with excellent publicity.

Blottisham:

There it is. The wriggle.

Quillibrace:

No. The receipt.

Blottisham:

Look—before measurement, the system is in a superposition of states. After measurement, it has one. That’s what the equations say.

Quillibrace:

The equations say what is admissible, not what is furnished.

Blottisham:

You really do enjoy ruining the furniture.

Quillibrace:

Only the imaginary pieces.

Elowen Stray:

So when we say “two states at once”, what’s wrong with that?

Quillibrace:

The “two”. And the “at once”. And the “states”.

Blottisham:

You’ve crossed the line into pedantry.

Quillibrace:

Pedantry is precision without purpose. This has a purpose.

Blottisham:

Fine. Explain superposition without subtraction.

Quillibrace:

Very well. Superposition is not multiplicity in reality; it is openness in specification.

Blottisham:

That’s not an explanation. That’s a slogan.

Quillibrace:

Then let’s try another. Superposition is the refusal of the theory to commit early.

Elowen Stray:

So nothing is actually doubled?

Quillibrace:

Nothing is instantiated twice, no.

Blottisham:

But the system contains multiple possibilities!

Quillibrace:

Contains is doing far too much work.

Blottisham:

They must be somewhere.

Quillibrace:

They are nowhere. They are allowable.

Blottisham:

You’re making possibility sound ghostly.

Quillibrace:

You keep trying to give it a body.

Elowen Stray:

Is superposition then just ignorance?

Quillibrace:

No. Ignorance presupposes a fact you lack. Superposition presupposes no such fact.

Blottisham:

That’s slippery.

Quillibrace:

That’s disciplined.

Blottisham:

When I toss a coin, it’s either heads or tails, even if I don’t know which.

Quillibrace:

Yes. And that’s precisely why coin tosses are not quantum systems.

Elowen Stray:

So before measurement, there isn’t a hidden answer?

Quillibrace:

There is no answer yet.

Blottisham:

Yet again you deny reality its privacy.

Quillibrace:

I deny it unnecessary secrets.

Blottisham:

Then what is superposition?

Quillibrace:

It is the theory speaking in the plural where the world has not yet spoken at all.

Elowen Stray:

So the plural belongs to the description?

Quillibrace:

To the constraint on description.

Blottisham:

Constraint sounds terribly limiting for something meant to be mysterious.

Quillibrace:

Mystery thrives on looseness. Physics does not.

Blottisham:

But the particle interferes with itself! Surely that means it’s in two places.

Quillibrace:

It means the conditions permit patterns that cannot be decomposed into single-path stories.

Blottisham:

That was evasive.

Quillibrace:

That was careful.

Elowen Stray:

So superposition isn’t a crowd inside the particle?

Quillibrace:

No more than a menu is a crowd inside a restaurant.

Blottisham:

You and your metaphors.

Quillibrace:

You and your counting.

Blottisham:

Then what collapses in superposition?

Quillibrace:

Nothing collapses in superposition. Superposition is what remains when collapse has not yet occurred.

Blottisham:

So it’s a waiting room?

Quillibrace:

No. Waiting implies time. This is logical openness, not temporal delay.

Elowen Stray:

So the system isn’t undecided.

Quillibrace:

The system is uncommitted.

Blottisham:

You make it sound like a shy guest.

Quillibrace:

It is a well-behaved theory.

(A pause.)

Blottisham:

Let me try again. Is the particle in two states at once?

Quillibrace:

No.

Blottisham:

Is it in one?

Quillibrace:

Not yet.

Blottisham:

Then where is it?

Quillibrace:

Wherever the instance places it.

Blottisham:

Which hasn’t happened.

Quillibrace:

Correct.

Blottisham:

So superposition is… nothing?

Quillibrace:

Superposition is the disciplined refusal to pretend something has happened when it hasn’t.

Elowen Stray:

That feels oddly reassuring.

Blottisham:

It feels like cheating.

Quillibrace:

Only if you wanted drama.

Blottisham:

I always want drama.

Quillibrace:

Physics is under no obligation to oblige you.

Blottisham:

Then the trouble with superposition…

Quillibrace:

…is that we mistook openness for multiplicity.

Elowen Stray:

And imagined crowds where there were only conditions.

Blottisham:

I suppose that does make it quieter.

Quillibrace:

Reality is often quieter than its metaphors.

(Silence.)

Blottisham:

Very well. I withdraw one particle from my imaginary menagerie.

Quillibrace:

A promising start.