Spurious Realism

Dr Jonathan rougier

I’d like to share the transcript of a short presentation I gave recently, at a session called All About The Model at the Battle of Ideas organised by the Institute of Ideas at the Barbican on the 19-20 Oct, 2013.  It concerns what I term ‘spurious realism’.  If you read on I should make it clear that I have no reason to distrust vulcanologists!  But I was searching for a strongly visual example.

Here is the transcript, lightly edited.

Models are abstractions.  Their purpose is to organise the knowledge and the judgements that we have about the systems that we study.  When you are looking at model output, you are looking at a representation of the knowledge and the judgements of the modeller.  Now in the domain where the modeller is the expert, his knowledge and his judgements are probably a lot more reliable than yours or mine.  So we have no reason, a priori, to distrust the output that we get from carefully considered scientific models constructed by domain experts.

However, the there is one aspect of the modelling process which always causes me some concern, and alarm — what I will call ‘spurious realism’.  Suppose that we went to Hollywood and we asked them to construct a simulation of a large volcanic eruption.  There is no doubt that what we would get back would be spectacular, and you and I would probably be completely convinced that this was a real volcanic eruption.  And the reason, of course, is that Hollywood knows what you and I — non-experts — think that a volcanic eruption should look like.  However, it would probably be unconvincing to a vulcanologist, and it wouldn’t be a good platform for making predictions.

Instead, we might have gone to an vulcanologist, with access to a state of the art code for simulating volcanic eruptions, and asked him to construct a simulation of a large volcanic eruption.  When he came back with the model output and showed us what he had done we would see immediately that it was not realistic.  We would see, for example, that spatially the domain had been pixelated into rectangles. That time didn’t progress smoothly, but was jerky.  That the colour scheme was completely false — he might, for example, have used a blue to red to white colour scheme as a heat map.  That the eruption itself had very few degrees of freedom.  We would be in no doubt at all that what we were seeing was an artifact — this would be completely clear to us just by looking at the model output.

So if a vulcanologist had come to us with a simulation that looked a bit Hollywood — that looked a bit realistic — we ought to suspect that what he has done is cosmetically post-processed the output.  But what he’s really done, and this is the concerning issue, is he’s removed from the model output those visual clues that reminded us that we are dealing with an artifact, and which should have cautioned us against putting too much trust in the model output.

So the point I’d like to make about spurious realism is that when you are dealing with scientific models of complex systems, like environmental systems, it’s almost paradoxical, but my view is the more realistic looking is the model output — the more Hollywood if you like — the more cautious we ought to be in trusting the judgement of the modeller who constructed it.