Mr Blottisham entered the Common Room carrying a large framed photograph.
Professor Quillibrace looked up.
Miss Stray looked at the photograph.
‘What is that?’
‘Reality.’
Quillibrace regarded it carefully.
‘It appears to be a photograph.’
‘Exactly.’
‘Of what?’
‘Reality.’
‘Whose reality?’
Blottisham frowned.
‘Reality.’
Miss Stray smiled.
‘That seems to settle it.’
‘Thank you.’
Blottisham placed the photograph on the mantelpiece.
‘I've been thinking about scientific realism.’
Quillibrace closed his book.
‘Ah.’
‘A successful scientific theory tells us what the world is really like.’
‘That is one way of putting it.’
‘The equations describe reality.’
‘Yes.’
‘The entities in the theory actually exist.’
‘Sometimes.’
‘The mathematical structure represents the underlying physical world.’
‘Yes.’
Blottisham pointed at the photograph.
‘And eventually, if the theory is good enough, we should be able to say what is actually there.’
Quillibrace looked at the photograph again.
‘Should we?’
‘Obviously.’
‘Why?’
Blottisham looked surprised.
‘Because otherwise what would the theory be telling us?’
‘Perhaps something other than what you have in mind.’
‘Such as?’
‘Relations.’
‘Relations between what?’
‘That is the question.’
Blottisham sat down.
‘You're making this unnecessarily difficult.’
‘That is one of my more consistent virtues.’
Miss Stray laughed.
‘Perhaps we should begin with the picture.’
‘The photograph?’
‘The demand for one.’
Quillibrace nodded.
‘When physics becomes difficult to interpret, we naturally ask for a picture.’
‘Exactly.’
‘What is the electron really?’
‘Yes.’
‘What is the wave function really?’
‘Yes.’
‘What is happening during measurement?’
‘Yes.’
‘What is the particle doing when nobody is looking?’
‘Precisely.’
Quillibrace folded his hands.
‘And what do all these questions assume?’
Blottisham hesitated.
‘That there is an answer.’
‘More specifically?’
‘That there is something there.’
‘Good.’
‘Something physical.’
‘Good.’
‘Doing something.’
‘Excellent.’
Blottisham smiled.
‘You see?’
‘Yes.’
‘Then we're agreed.’
‘Not at all.’
Miss Stray looked at the photograph.
‘Perhaps the problem is that you have smuggled the answer into the question.’
Blottisham stared at her.
‘How?’
‘You ask what the electron is really doing.’
‘Yes.’
‘But that already assumes that the electron is the kind of thing that does things in the familiar sense.’
‘An electron certainly does something.’
‘Perhaps.’
‘It has a trajectory.’
Quillibrace raised an eyebrow.
‘Does it?’
‘Well... not always.’
‘That is the difficulty.’
Blottisham sighed.
‘Quantum mechanics.’
‘Quantum mechanics.’
‘In classical physics, at least, this was easy.’
‘Relatively.’
‘Newton gives us equations of motion.’
‘Yes.’
‘The equations describe bodies moving through space.’
‘Yes.’
‘We can draw the trajectories.’
‘Yes.’
‘The mathematics tells us what happens.’
‘And the picture tells us what is happening.’
Miss Stray nodded.
‘The two reinforce each other.’
‘Exactly.’
Quillibrace stood and took the photograph from the mantelpiece.
‘But quantum mechanics gives us a strange situation.’
‘The equations still work.’
‘Extremely well.’
‘So what's the problem?’
‘We have difficulty turning the equations into a single intuitive physical story.’
Blottisham looked at him.
‘But surely there is a story.’
‘Which one?’
‘The correct one.’
‘And how shall we identify it?’
‘By finding out what the wave function really is.’
Quillibrace smiled.
‘There it is.’
‘What?’
‘The picture department.’
Blottisham frowned.
‘What is wrong with asking what the wave function really is?’
‘Nothing.’
‘Then why are you smiling?’
‘Because the question is more complicated than it sounds.’
Miss Stray spoke.
‘Is the wave function a physical thing?’
‘Yes,’ said Blottisham.
‘Or is it a description of our information?’
‘Perhaps.’
‘Or a catalogue of possibilities?’
‘Perhaps.’
‘Or something physically real in a high-dimensional configuration space?’
‘Possibly.’
‘Does it collapse?’
‘Sometimes.’
‘Never?’
‘Depending on the interpretation.’
‘Does it describe one world?’
‘Yes.’
‘Or many?’
Blottisham looked annoyed.
‘Now you're just being difficult.’
‘I'm merely listing the possibilities.’
‘And there are too many.’
‘That may be the point.’
Quillibrace returned the photograph to the mantelpiece.
‘Notice what has happened.’
‘What?’
‘We began with one theory.’
‘Yes.’
‘One extraordinarily successful mathematical formalism.’
‘Yes.’
‘And immediately obtained several incompatible ontological stories.’
‘Yes.’
‘Yet the empirical predictions can remain the same.’
Blottisham considered this.
‘So the mathematics doesn't tell us which picture to choose.’
‘Not uniquely.’
‘Then perhaps we haven't understood the mathematics.’
‘Or perhaps we have misunderstood what understanding requires.’
There was a pause.
Blottisham looked suspicious.
‘That sounds dangerous.’
‘It often does.’
Miss Stray picked up a piece of chalk from the Common Room fireplace.
‘Perhaps a map would help.’
‘A map?’
She drew a small rectangle on the blackboard.
‘A map is a representation.’
‘Yes.’
‘Is it the landscape?’
‘No.’
‘Does that mean it is arbitrary?’
‘No.’
‘Why not?’
‘Because the landscape constrains it.’
‘Good.’
‘A bad map gets lost.’
‘Exactly.’
Quillibrace nodded.
‘And a good map can be extraordinarily accurate without being a miniature landscape.’
Blottisham looked at the photograph.
‘So the equations are maps.’
‘Not necessarily.’
‘Models, then.’
‘Closer.’
‘But maps tell us about the territory.’
‘Yes.’
‘So scientific theories still tell us about reality.’
‘Certainly.’
‘Then we're back where we started.’
‘Not quite.’
Miss Stray turned from the board.
‘The distinction is between a formal structure that successfully tracks physical phenomena and a literal picture of what reality must be like behind that structure.’
Blottisham was silent.
‘That's rather fine.’
‘It is also important.’
‘So the theory can be true without giving us a picture.’
‘It can tell us something real without uniquely specifying a classical-style inventory of things.’
Blottisham looked pleased.
‘Structural realism.’
Quillibrace glanced at him.
‘You've been reading.’
‘Occasionally.’
‘The basic idea is that science may tell us more securely about the structure of physical reality than about the intrinsic nature of whatever occupies that structure.’
‘Relations rather than things.’
‘More carefully: relations and structural constraints may be what the theory secures most strongly.’
Blottisham frowned.
‘But a structure has to be a structure of something.’
‘Does it?’
‘Surely.’
‘Why?’
‘Because otherwise it's just a structure.’
‘And why is that insufficient?’
Blottisham paused.
‘Because...’
Miss Stray intervened.
‘Perhaps we're still imagining structure as a framework placed around independently existing objects.’
Quillibrace nodded.
‘A relational conception would reverse the emphasis.’
‘How?’
‘Instead of beginning with things and asking how they are related, we might begin with the relations and ask how determinate things emerge within them.’
Blottisham looked at the blackboard.
‘We've been here before.’
‘Indeed.’
‘The thing problem.’
‘The property problem.’
‘The observer problem.’
‘And the future problem.’
Blottisham sighed.
‘You are building a rather large philosophical building.’
Quillibrace smiled.
‘We call it a series.’
Miss Stray laughed.
‘Perhaps the important point is that scientific progress need not be the gradual discovery of a better inventory.’
‘What else could it be?’
‘The discovery of increasingly adequate ways of articulating how physical possibilities are organised.’
Blottisham thought about this.
‘So the theory tells us what can happen.’
‘Among other things.’
‘And what relations constrain what can happen.’
‘Yes.’
‘And probabilities.’
‘Yes.’
‘And transformations.’
‘Yes.’
‘But not necessarily what everything really is underneath it all.’
‘Precisely.’
Blottisham stood.
‘I'm not sure I like that.’
‘You needn't.’
‘Science is supposed to discover reality.’
‘It does.’
‘Then why can't I have a picture of it?’
Quillibrace looked at him.
‘Because the world has not promised to resemble your imagination.’
Miss Stray smiled.
‘Or your photograph.’
Blottisham looked at the framed picture.
‘It is a perfectly respectable photograph.’
‘Of what?’
‘Reality.’
‘Which reality?’
Blottisham sighed.
‘You are both very tiresome.’
Quillibrace sat down again.
‘There is another problem.’
‘Of course there is.’
‘Theories don't merely describe phenomena that were already sitting there waiting to be photographed.’
‘What do you mean?’
‘A theory can change what becomes observable.’
‘How?’
‘New concepts lead to new experiments.’
‘Yes.’
‘New instruments make new phenomena accessible.’
‘Yes.’
‘New mathematical structures allow us to distinguish patterns we could not previously see.’
Miss Stray added:
‘What can be observed depends partly upon the relations through which observation is organised.’
Blottisham looked at her.
‘So the theory changes the observer.’
‘Sometimes.’
‘And the observer changes the theory.’
‘Certainly.’
‘But then we're back to the observer problem.’
‘Yes.’
Blottisham looked increasingly suspicious.
‘You have arranged this.’
‘Arranged what?’
‘The entire afternoon.’
Quillibrace looked innocent.
‘I assure you, I have done almost nothing.’
Miss Stray smiled.
‘Perhaps the theory does not stand outside the world and photograph it.’
‘What does it do, then?’
‘It becomes part of the relation through which the world is investigated.’
Blottisham considered this.
‘You mean the theory is an instrument.’
‘Not merely an instrument.’
‘A way of entering into relations with reality.’
Quillibrace nodded.
‘Better.’
‘But that sounds almost like instrumentalism.’
‘And that would be too easy.’
‘Why?’
‘Because saying that a theory is not a literal picture does not mean that anything goes.’
‘The world still constrains it.’
‘Exactly.’
‘Experiments can still prove it wrong.’
‘Yes.’
‘Its predictions can fail.’
‘Yes.’
‘Its mathematics can't simply be whatever we like.’
‘No.’
‘So reality still pushes back.’
‘Constantly.’
Miss Stray nodded.
‘That resistance is precisely why the theory tells us something real.’
Blottisham looked at the photograph again.
‘Then what is it telling us?’
Quillibrace paused.
‘That is the interesting question.’
‘You don't know.’
‘Not completely.’
‘Then what have we been doing all afternoon?’
‘Improving the question.’
Blottisham groaned.
‘Academics always say that when they don't know the answer.’
‘Sometimes we say it when we have found a better one.’
Miss Stray moved closer to the blackboard.
‘Perhaps the old demand was: “Show me the things that are really there.”’
‘And the new demand?’
‘“Show me the structure of relations, possibilities and constraints that the world permits us to uncover.”’
Blottisham thought about this.
‘That sounds less satisfying.’
‘Why?’
‘There are no things.’
‘There may be things.’
‘But they aren't the whole story.’
‘No.’
‘And there may be no final picture.’
‘Perhaps not.’
‘So what does scientific realism mean now?’
Quillibrace answered carefully.
‘That reality is not whatever our theories happen to say.’
‘Good.’
‘That the world resists our theories.’
‘Good.’
‘That successful theories reveal something about that resistance.’
‘Good.’
‘And that what they reveal need not take the form of a classical inventory of objects with intrinsic properties.’
Blottisham nodded slowly.
‘Reality without the picture.’
‘Perhaps.’
‘That's rather unsettling.’
‘Yes.’
Miss Stray looked at the photograph.
‘But there is something else.’
‘What?’
‘The demand for a final picture may actually make understanding harder.’
‘How?’
‘Because we become so concerned with what the equations are “really describing” that we stop asking what the equations have already forced us to abandon.’
Blottisham was quiet.
Quillibrace continued:
‘Perhaps quantum mechanics does not need to be translated back into classical ontology.’
‘Because classical ontology is the thing that has become inadequate.’
‘Exactly.’
‘So the question isn't “What picture lies behind the equations?”’
‘No.’
‘It's “What kind of reality do the equations require us to think?”’
Miss Stray nodded.
‘Yes.’
Blottisham looked at the photograph for a long time.
Then he took it down.
‘What are you doing?’
‘I think we should remove this.’
‘Why?’
‘It is beginning to give me the wrong idea.’
Quillibrace looked surprised.
‘Progress.’
Blottisham carried the photograph towards the door.
‘Where are you taking it?’
‘To the corridor.’
‘Why?’
‘It can hang there.’
‘Why there?’
‘Because the corridor is not reality.’
Quillibrace considered this.
‘An improvement.’
Blottisham stopped at the door.
‘Although...’
‘Yes?’
‘If the world doesn't come with a final picture...’
‘Yes?’
‘Then perhaps that's rather good.’
Miss Stray smiled.
‘Why?’
Blottisham shrugged.
‘It means we have somewhere to go.’
Quillibrace looked at him.
‘Where?’
Blottisham glanced at the photograph.
‘Into the world.’
And for once, nobody corrected him.
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