The Trouble with Quantum Questions: Dialogue III — On Collapse

Characters:

Professor Quillibrace

Mr Blottisham

Miss Elowen Stray

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Blottisham:

I refuse to let this one go.

Quillibrace:

You never do. It’s one of your more endearing qualities.

Blottisham:

Enough evasions. If the wavefunction isn’t a thing, and measurement isn’t a disturbance, then what—precisely—collapses?

Quillibrace:

Your expectations.

Blottisham:

I’m serious.

Quillibrace:

So am I.

Elowen Stray:

Collapse does sound violent. Something falling in on itself.

Blottisham:

Exactly! A rich field of possibilities suddenly reduced to one miserable fact. Surely that’s a loss.

Quillibrace:

Only if you mistake possibility for inventory.

Blottisham:

You can’t just wish away the others. They were there.

Quillibrace:

They were available.

Blottisham:

Which is the same thing!

Quillibrace:

Only if you think availability implies possession.

Elowen Stray:

So nothing disappears?

Quillibrace:

Nothing was ever present as an instance to disappear.

Blottisham:

Then why all this talk of collapse?

Quillibrace:

Because people imagined a thing where there was a constraint.

Blottisham:

You keep saying that as though it absolves everything.

Quillibrace:

It relocates everything.

Blottisham:

Collapse happens at a moment. Everyone agrees on that.

Quillibrace:

Everyone agrees on the grammar of the sentence.

Blottisham:

Don’t start with grammar again.

Quillibrace:

Very well. Let’s start with theatre.

Blottisham:

I fail to see—

Quillibrace:

A play affords many possible performances. On opening night, one is given. Have the others collapsed?

Blottisham:

That’s an analogy.

Quillibrace:

Yes. One with restraint.

Elowen Stray:

The other performances are still possible later.

Quillibrace:

Under different conditions.

Blottisham:

But the quantum case is final! Once measured, the system has a value.

Quillibrace:

For that instance.

Blottisham:

You keep saying that as though it softens the blow.

Quillibrace:

It removes the blow.

Elowen Stray:

So collapse isn’t something that happens to the system…

Quillibrace:

…it’s something that happens to the space of relevance.

Blottisham:

That’s terribly abstract.

Quillibrace:

Reality often is, until we force it into furniture.

Blottisham:

Let me be blunt. Before measurement, there are many possibilities. After measurement, only one remains. That’s collapse.

Quillibrace:

Before measurement, there is no “after” to compare it to.

Blottisham:

You’re dissolving time again.

Quillibrace:

No. I’m placing it where it belongs.

Elowen Stray:

In the instance?

Quillibrace:

Exactly.

Blottisham:

Then collapse has no duration?

Quillibrace:

No more than the present does.

Blottisham:

But physicists argue endlessly about when collapse occurs.

Quillibrace:

Because they are trying to time a category mistake.

Blottisham:

So there is no collapse event?

Quillibrace:

There is an instantiation.

Blottisham:

That’s just your word for it.

Quillibrace:

It’s a word that does less damage.

Elowen Stray:

So what feels like collapse is really the fact that we can no longer speak as if alternatives are open?

Quillibrace:

Yes. Speech tightens.

Blottisham:

That sounds disappointingly linguistic.

Quillibrace:

You introduced language the moment you said “state”.

Blottisham:

So collapse is about description, not reality?

Quillibrace:

It’s about which description can now do work.

Blottisham:

You’re saying nothing ontological changes.

Quillibrace:

Something ontological happens: a possibility becomes actual.

Blottisham:

And the others?

Quillibrace:

Remain possible in the theory—but irrelevant to the instance.

Blottisham:

Irrelevant sounds suspiciously like gone.

Quillibrace:

Irrelevant is kinder—and more accurate.

(A pause.)

Elowen Stray:

So collapse feels dramatic because we were attached to the unrealised possibilities.

Quillibrace:

Yes. We mourn what never happened.

Blottisham:

I do that all the time.

Quillibrace:

You see? Perfectly human. Entirely unnecessary in physics.

Blottisham:

Then the universe doesn’t constantly destroy futures.

Quillibrace:

It simply stops offering them here.

Blottisham:

That’s almost… polite.

Quillibrace:

Reality is impeccably well-mannered.

Elowen Stray:

So the trouble with collapse…

Quillibrace:

…is that we treated actuality as a loss instead of a specification.

Blottisham:

And insisted on asking when the loss occurred.

Quillibrace:

Rather than noticing that nothing was lost at all.

(Silence.)

Blottisham:

I must say, Professor, you’ve made collapse sound rather dull.

Quillibrace:

Dull things rarely keep philosophers awake at night.

Blottisham:

Yet somehow this will.

Quillibrace:

Then it is doing its job.