The Trouble with Quantum Questions: Dialogue VI — On Wave–Particle Duality

Characters:

Professor Quillibrace

Mr Blottisham

Miss Elowen Stray

---

Blottisham:

This one is unforgivable.

Quillibrace:

Good morning to you too.

Blottisham:

A thing cannot be both a wave and a particle.

Quillibrace:

An admirable commitment to furniture.

Elowen Stray:

It does feel like cheating. One minute ripples, the next pellets.

Blottisham:

Exactly! Choose a side!

Quillibrace:

The universe did. You keep changing the question.

Blottisham:

Don’t be sly. Experiments show wave behaviour and particle behaviour.

Quillibrace:

They show different behaviours under different experimental cuts.

Blottisham:

That’s evasion again.

Quillibrace:

That’s repetition. We’ve been here before.

Elowen Stray:

So it’s not duality in the thing?

Quillibrace:

It is duality in description.

Blottisham:

Ah. So the particle is innocent, and the physicists are confused.

Quillibrace:

Largely, yes.

Blottisham:

But surely the entity must be something.

Quillibrace:

It is what the cut makes it.

Blottisham:

You’re saying the experiment determines the nature of the thing?

Quillibrace:

No. I’m saying the experiment determines which question gets answered.

Elowen Stray:

That’s subtler.

Blottisham:

It’s infuriating.

Quillibrace:

Infuriation is often the first sign of category error.

Blottisham:

If it’s a wave, it should spread. If it’s a particle, it should localise.

Quillibrace:

And if it’s a description awaiting instantiation, it will do neither until asked properly.

Blottisham:

You make it sound passive.

Quillibrace:

I make it sound conditional.

Elowen Stray:

So wave and particle aren’t properties?

Quillibrace:

They are modes of construal.

Blottisham:

Construal again. Everything is construal with you.

Quillibrace:

Everything meaningful is.

Blottisham:

Then why does the interference pattern disappear when we measure position?

Quillibrace:

Because you have replaced a question about distribution with a question about localisation.

Blottisham:

So the wave vanishes?

Quillibrace:

No wave was ever there.

Blottisham:

That’s outrageous.

Quillibrace:

So was thinking it was a little ocean.

Elowen Stray:

Then what interferes?

Quillibrace:

The admissible outcomes under the constraints of the experiment.

Blottisham:

That sounds bureaucratic.

Quillibrace:

Nature is very orderly.

Blottisham:

You’re telling me there is no underlying picture at all.

Quillibrace:

I’m telling you pictures come after cuts, not before.

Blottisham:

But classical physics gave us pictures!

Quillibrace:

Classical physics dealt in systems that tolerated premature picturing.

Elowen Stray:

So quantum theory punishes impatience?

Quillibrace:

Firmly.

Blottisham:

Then wave–particle duality is a failure of imagination.

Quillibrace:

It is a failure of restraint.

Blottisham:

You mean we should stop asking what it really is?

Quillibrace:

At least until you can say relative to which cut.

Elowen Stray:

So the same system can be wave-like or particle-like, depending on how it’s engaged?

Quillibrace:

Yes. Without contradiction.

Blottisham:

I hate that word.

Quillibrace:

Most contradictions evaporate when you stop demanding exclusivity where none was promised.

Blottisham:

Then duality isn’t a deep mystery?

Quillibrace:

It’s a pedagogical scar.

Elowen Stray:

From forcing old categories onto new phenomena?

Quillibrace:

Exactly.

Blottisham:

So the trouble with wave–particle duality…

Quillibrace:

…is that we mistook incompatible descriptions for incompatible realities.

Blottisham:

And insisted the universe pick one.

Quillibrace:

When it had already picked coherence.

(A pause.)

Blottisham:

Very well. I withdraw my demand for a verdict.

Quillibrace:

Progress.

Blottisham:

But I reserve the right to sulk.

Quillibrace:

That, at least, is a classical behaviour.