Ian Kluge
In this third part of my review of The Grand Design (Stephen Hawking & Leonard Mlodinow), I’d like to take a closer look at their theory of “model-dependent realism”(42).
This is one of Hawking’s and Mlodinow’s main contributions in The Grand Design. According to this theory:
a physical theory or world-picture is a model (generally of a mathematical nature) and a set of rules that connect the elements of the model to observations. This provides a framework with which to interpret modern science. (43)
In their view “to model-dependent realism it is pointless to ask whether a model is real, only whether it agrees with observation” (46); moreover, if two different models agree with observations, we cannot know which one is “more real than another” (46). This is only wordplay – saying that a “model is real” means precisely that it agrees with observation.
What else could it mean? How can a model “agree with observation” of nature and not be “real” i.e. not correspond to the reality it models? If a model makes testable predictions which are validated, the very fact of validation means something about the model is correct, i.e. corresponds to reality and, therefore, provides real information about nature. Clearly, Hawking and Mlodinow are trying to establish a distinction between ‘agreeing with observation’ and ‘being real’ – but what purpose can such a distinction serve in the pursuit of science? Imagine it being applied in virology: our model correctly predicts the nature and behavior of a deadly virus – but that’s no reason to make a vaccine, since the agreement with the model doesn’t tell us anything real about the virus. Who would accept such reasoning, let alone act on it?
The ultimate, and devastating consequence of accepting this line of thought is that it makes science impossible. Science is no longer a quest for knowledge about the world or nature; it is the quest for knowledge about our theories or models of the world – which is a very different thing. According to model-dependent realism, there is no such thing as scientific knowledge of nature but only knowledge of our own models. And even that is undermined by degeneration into an infinite regress, for when we check a model against our observations, we must also have a model of what constitutes ‘an observation’ and that model requires further observations which in turn must be checked against our model and so on. Furthermore, we cannot even know our own models, because to make a model we have to have a model of models, (and observe whether our model of models agrees with the models we check) and then a model of the model of models and so on ad infinitum.
This catches Hawking and Mlodinow in a logical tangle from which there is no escape: we cannot know nature (as they admit), but neither can we really know what a ‘model’ or an ‘observation’ is. The clear upshot is that science as the quest for knowledge about nature is impossible.
Hence, Hawking’s view covertly carries within it a profound and corrosive skepticism about the possibility of real knowledge about nature. All we can know are our models – and ultimately, as we have seen above, not even those. Moreover, if all knowledge is model-dependent, can we know anything about anything since all we can really know is whether or not our observations agree with our model? It is, after all, “pointless to ask whether a model is real” (46) i.e. whether a model gives knowledge about reality. This skepticism is precisely why Hawking and Mlodinow can undermine the whole concept of progress in science by claiming that the Copernican model is merely more convenient and not more correct than the Ptolemaic model of the solar system. There is no progress because there is no true model or knowledge about nature – only more or less convenient models for whatever our purpose happens to be. That, of course, reduces ‘truth’ to whatever we want it to be.
Next time: Whence “model-dependent realism”?
4 comments
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koinotely
June 17, 2011 at 12:14 pm (UTC -7) Link to this comment
It’s also ironic how Hawking declares philosophy as dead, and then tries to get away with “model-dependent realism” without making reference to results from over half a century ago.
“Though formulated in the mathematical and scientific realms respectively, Lowenheim-Skolem and Duhem-Quine can be thought of as opposite sides of the same model-theoretic coin. Lowenheim-Skolem says that a theory cannot in general distinguish between two different models; for example, any true theory about the numeric relationship of points on a continuous line segment can also be interpreted as a theory of the integers (counting numbers). On the other hand, Duhem-Quine says that two theories cannot in general be distinguished on the basis of any observation statement regarding the universe.”
http://www.megafoundation.org/CTMU/Articles/Theory.html
Yousuf
July 7, 2011 at 2:09 am (UTC -7) Link to this comment
I share Hawking and Mlodinow’s conceptual-view called model-dependent realism. The concept of reality or truth does not apply to models. For this reason, we cannot say that model is true or more real than another model. But it seems natural to do so?
Well, it seems natural to say that arguments are either true or false. In my logic class, we were presented a sound argument and asked to tell whether it is true or false. Most of us answered that the argument was true. Some answered that it was false. If only we had realized that the question was meaningless, in that the concept of truth does not apply to arguments, even though, it seems natural to say so. Similarly, Hawking and Mlodinow reason that the concept of reality or truth does not apply to models themselves. For this reason we cannot ask whether a model is true or not. All we can ask is the practical question: which model is more convenient to use. Their “realism” lacks any metaphysical dimension, so they, unlike the philosophers do not need to justify their position. But they do, however, need to argue why it is that the concept of reality or truth does not apply to arguments. They did not seem to go into detail over here. But philosophers like Rudolf Carnap and Wittgenstein have. The answer lies in rigorous conceptual and logical analysis.
ajatheist
August 29, 2011 at 7:56 am (UTC -7) Link to this comment
Excellent point.
Ian Kluge
July 7, 2011 at 10:20 am (UTC -7) Link to this comment
I won’t repeat my previous arguments about the inadequacy of ‘model-dependent realism’ but rather, will look at another problem related to it. We must ask, ‘Why is one model more convenient to use than another?’ There are 3 obvious possible reasons: (1) convenient because its predictions match what the model says; (2) convenient for us strictly because the math/reasoning is easier; (3) a combination of the two. If (1) and (3) are the case, the model tells us something about reality – otherwise it would not be ‘convenient.’ If reality matches the model’s predictions, something about reality is reflected in the model. Therefore, some models are more convenient because they are more true than others. Furthermore, practical results have metaphysical dimensions or implications. Hawking and Mlodinow pretend not to be interested in these but their conclusions about gravity decisively contradict their claim.
An argument about reality that makes no claims about reality is simply not an argument ‘about’ reality. If science is not about reality, but about convenience of explanation, then there is no reason to be upset with even the most unsophisticated forms of creationism and their denial of evolution.