Tag Archives: falsifiability

Are predictions an essential part of science?

Theoretical physicist Sabine Hossenfelder recently wrote that that “predictions are over-rated” and that one should instead judge the merits of scientific models “by how much data they have been able to describe well, and how many assumptions were needed for this”, finishing with the suggestion that “the world would be a better place if scientists talked less about predictions and more about explanatory power”.

Others disagreed, including philosopher-of-science Massimo Pigliucci who insists that “it’s the combination of explanatory power and the power of making novel, ideally unexpected, and empirically verifiable predictions” that decides whether a scientific theory is a good one. Neither predictions nor explanatory powers, he adds, are sufficient alone, and “both are necessary” for a good scientific theory.

Popper’s criterion of falsification (the possibility that a theory’s predictions can be empirically refuted) is, of course, one of few elements of the philosophy of science to have attained widespread awareness. But is Popper’s maxim descriptive or prescriptive? If it merely describes what scientists tend to do, then, if scientists came to feel that predictions were not so crucial, would their enterprise still be “science”? Or, if the maxim is prescriptive, such that falsification is a necessary part of the scientific method, then by what authority is that prescription established?

To answer that, let’s turn to Feynman’s well known summation of science:

The first principle is that you must not fool yourself — and you are the easiest person to fool.

Scientists do their best to construct the best and truest model of the world. Pseudoscientists have fooled themselves into a false understanding of the world. And it’s easy to do that, because, given a set of facts, anyone can construct a story that weaves those facts into an overall picture that the story-teller wants to be true. They may need any number of ad hoc explanations, but humans are good at that. It’s easy to sustain the belief that, say, God always answers prayer, if you allow yourself wide flexibility about what the answer looks like, including “God said no this time”.

So both Hossenfelder and Pigliucci are right: a good scientific theory needs to explain the maximum amount of data with the minimum number of ad hoc features. But predictions really are the acid test. If you are making predictions about things where you don’t already know the answer, then your ad hoc explanations will prove useless and sterile. Only an accurate theory — one that correctly describes aspects of the world — will be able to reliably generate predictions that turn out true. This is why making predictions about things you don’t know, and then attempting to verify them, is the gold-standard method that all scientists should adopt when they can, to check whether they have fooled themselves. The telling give-away of the pseudoscientist is their reluctance to submit to that test.

But making predictions that can then be verified may not always be possible. Yes, the scientific method asks that such be done where it can be, but what if we’re talking about topics where the time required or the energy required are not possible? Need we conclude that such topics are beyond the domain of science?

Let’s take a concrete example. Given the finite age of the universe and the finite speed of light (and hence the finite speed at which information can travel from one region of space to another), we can never obtain information about the universe beyond an “observable horizon”, and thus can never empirically verify statements about such a region. Does that mean that any statement about such regions is outside science (perhaps being metaphysical or pseudoscientific)?

A further example concerns attempts to describe the physics of the Planck scale, which is relevant to attempts to find a unified description of the forces of nature, or to understand the origins of the Big Bang, yet which is orders of magnitude beyond our ability to recreate in particle accelerators. Is any such quest pseudoscience? And if it is, how far beyond our current ability to test is it permissible for scientists to construct theories? It would be weird to suggest that a factor 2 is acceptable, but a factor 10 not.

I prefer to fall back on Feynman’s dictum. If we’re discussing topics beyond our ability to test predictions then we need to be extra careful not to fool ourselves, since we won’t have the gold-standard test. But then in science we have to make do with the tools we have; neither cosmologists nor paleontologists can replicate findings in laboratory experiments, yet those fields are still sciences, despite what school textbooks might say about “the scientific method” and the requirement to replicate experiments.

We should see verifying predictions as similar to replicating experiments under laboratory conditions — yes scientists should do it where they can, as being the best ways of minimising self-fooling, but in the end science is pragmatic and often has to make do. Thus there is nothing unscientific about trying to understand aspects of the universe that we cannot directly test, one just has to be extra cautious in the claims one makes. A statement such as: “As far as we know, the universe continues much the same beyond the observable horizon” would seem to be a reasonable feature of a cosmological model, even though it is beyond empirical testing.

So, overall, predictions are not over-rated, but nor are they fully essential. I think this lands me roughly midway between Hossenfelder and Pigliucci.

Science Unlimited, Part One: Pseudoscience

Philosophers Maarten Boudry and Massimo Pigliucci have recently edited a volume of essays on the theme of scientism. The contributions to Science Unlimited? The Challenges of Scientism range from sympathetic to scientism to highly critical.

I’m aiming to write a series of blog posts reviewing the book, organised by major themes, though knowing me the “reviewing” task is likely to play second fiddle to arguing in favour of scientism.

Of course the term “scientism” was invented as a pejorative and so has been used with a range of meanings, many of them strawmen, but from the chapters of the book emerges a fairly coherent account of a “scientism” that many would adopt and defend.

This brand of scientism is a thesis about epistemology, asserting that the ways by which we find things out form a coherent and unified whole, and rejecting the idea that knowledge is divided into distinct domains, each with a different “way of knowing”. The best knowledge and understanding is produced by combining and synthesizing different approaches and disciplines, asserting that they must mesh seamlessly. Continue reading

The cosmological multiverse and falsifiability in science

The cosmological “multiverse” model talks about regions far beyond the observable portion of our universe (set by the finite light-travel distance given the finite time since the Big Bang). Critics thus complain that it is “unfalsifiable”, and so not science. Indeed, philosopher Massimo Pigliucci states that instead: “… the notion of a multiverse should be classed as scientifically-informed metaphysics”.

Sean Carroll has recently posted an article defending the multiverse as scientific (arXiv paper; blog post). We’re discussing here the cosmological multiverse — the term “multiverse” is also used for concepts arising from string theory and from the many-worlds interpretation of quantum mechanics, but the arguments for and against those are rather different. Continue reading

Telling science from pseudoscience and the demarcation problem

demarcPhilosophers of Science have long puzzled over what they call “the” demarcation problem, of how to distinguish science from pseudoscience. In the early 20th Century the Logical Positivists proposed the verification principle, that a statement was meaningful and scientific only if it could be empirically verified. Karl Popper then proposed a similar idea, that a scientific idea is one that can be falsified.

There is a lot of truth in both proposals, but neither can be interpreted too narrowly. The problem is that no statement can be verified or falsified in isolation. Science constructs whole webs of ideas, and it is the whole construct that is then compared to empirical data, to be adjusted and improved as necessary. Further, a statement such as Newton’s law of gravity can never be verified in the general sense, all we can say is that it worked well enough — as part of the wider web of ideas — in the particular instance we tested. Nor is it straightforward to falsify such a law. If our overall model is inconsistent with an observation then we could indeed alter one of the laws; but we might also overcome the inconsistency by altering some other part of the overall model; or we might doubt the reliability of the observations. Continue reading

Applying falsifiability in science

Falsifiability. as famously espoused by Karl Popper, is accepted as a key aspect of science. When a theory is being developed, however, it can be unclear how the theory might be tested, and theoretical science must be given license to pursue ideas that cannot be tested within our current technological capabilities. String theory is an example of this, though ultimately it cannot be accepted as a physical explanation without experimental support.

Further, experimental science is fallible, and thus we do not immediately reject a theory when contradicted by one experimental result, rather the process involves the interplay between experiment and theory. As Arthur Eddington quipped: “No experiment should be believed until it has been confirmed by theory”.

Sean Carroll recently called for the concept of falsifiability to be “retired”, saying that:

The falsifiability criterion gestures toward something true and important about science, but it is a blunt instrument in a situation that calls for subtlety and precision.

Meanwhile, Leonard Susskind has remarked that:

Throughout my long experience as a scientist I have heard un-falsifiability hurled at so many important ideas that I am inclined to think that no idea can have great merit unless it has drawn this criticism.

Continue reading