### Has there ever been a paradigm shift?

Friday, December 6th, 2013

Yes, once!

Paradigm and paradigm shift are so over used and misused that the world would benefit if they were simply banned.  Originally Thomas Kuhn (1922–1996) in his 1962 book, The Structure of Scientific Revolutions, used the word paradigm to refer to the set of practices that define a scientific discipline at any particular period of time. A paradigm shift is when the entire structure of a field changes, not when someone simply uses a different mathematical formulation. Perhaps it is just grandiosity, everyone thinking their latest idea is earth shaking (or paradigm shifting), but the idea has been so debased that almost any change is called a paradigm shift, down to level of changing the color of ones socks.

The archetypal example, and I would suggest the only real example in the natural and physical sciences, is the paradigm shift from Aristotelian to Newtonian physics. This was not just a change in physics from the perfect motion is circular to an object either is at rest or moves at a constant velocity, unless acted upon by an external force but a change in how knowledge is defined and acquired. There is more here than a different description of motion; the very concept of what is important has changed. In Newtonian physics there is no place for perfect motion but only rules to describe how objects actually behave. Newtonian physics was driven by observation. Newton, himself, went further and claimed his results were derived from observation. While Aristotelian physics is broadly consistent with observation it is driven more by abstract concepts like perfection.  Aristotle (384 BCE – 322 BCE) would most likely have considered Galileo Galilei’s (1564 – 1642) careful experiments beneath him.  Socrates (c. 469 BC – 399 BC) certainly would have. Their epistemology was not based on careful observation.

While there have been major changes in the physical sciences since Newton, they do not reach the threshold needed to call them a paradigm shifts since they are all within the paradigm defined by the scientific method. I would suggest Kuhn was misled by the Aristotle-Newton example where, indeed, the two approaches are incommensurate: What constitutes a reasonable explanation is simply different for the two men. But would the same be true with Michael Faraday (1791 – 1867) and Niels Bohr (1885–1962) who were chronologically on opposite sides of the quantum mechanics cataclysm?  One could easily imagine Faraday, transported in time, having a fruitful discussion with Bohr. While the quantum revolution was indeed cataclysmic, changing mankind’s basic understanding of how the universe worked, it was based on the same concept of knowledge as Newtonian physics. You make models based on observations and validate them through testable predictions.  The pre-cataclysmic scientists understood the need for change due to failed predictions, even if, like Albert Einstein (1879 – 1955) or Erwin Schrödinger (1887 – 1961), they found quantum mechanics repugnant. The phenomenology was too powerful to ignore.

Sir Karl Popper (1902 – 1994) provided another ingredients missed by Kuhn, the idea that science advances by the bold new hypothesis, not by deducing models from observation. The Bohr model of the atom was a bold hypothesis not a paradigm shift, a bold hypothesis refined by other scientists and tested in the crucible of careful observation. I would also suggest that Kuhn did not understand the role of simplicity in making scientific models unique. It is true that one can always make an old model agree with past observations by making it more complex[1]. This process frequently has the side effect of reducing the old models ability to make predictions. It is to remedy these problems that a bold new hypothesis is needed. But to be successful, the bold new hypothesis should be simpler than the modified version of the original model and more crucially must make testable predictions that are confirmed by observation. But even then, it is not a paradigm shift; just a verified bold new hypothesis.

Despite the nay-saying, Kuhn’s ideas did advance the understanding of the scientific method. In particular, it was a good antidote to the logical positivists who wanted to eliminate the role of the model or what Kuhn called the paradigm altogether. Kuhn made the point that is the framework that gives meaning to observations. Combined with Popper’s insights, Kuhn’s ideas paved the way for a fairly comprehensive understanding of the scientific method.

But back to the overused word paradigm, it would be nice if we could turn back the clock and restrict the term paradigm shift to those changes where the before and after are truly incommensurate; where there is no common ground to decide which is better. Or if you like, the demarcation criteria for a paradigm shift is that the before and after are incommensurate[2]. That would rule out the change of sock color from being a paradigm shift. However, we cannot turn back the clock so I will go back to my first suggestion that the word be banned.

[1] This is known as the Duhem-Quine thesis.

[2] There are probably paradigm shifts, even in the restricted meaning of the word, if we go outside science. The French revolution could be considered a paradigm shift in the relation between the populace and the state.

### Higgs skeptic

Thursday, September 8th, 2011

As the net closes in on the Higgs boson, and we get closer to discovery or complete elimination I suddenly realized that I’m running out of time on this particular blog post. You see, unlike most of my colleagues I don’t actually think that the Higgs boson exists, and that’s a shock to some! Why would someone who doesn’t think the Higgs exists work at CERN at a time when the Higgs boson is the focus of the media frenzy whenever CERN appears in the news?

Recent Higgs exclusion from ATLAS (P. MeridLiani, Physics in Collision 2011)

I’ve come across many physicists who almost unthinkingly assume the Higgs boson exists, or that it simply must exist because our theories say so, even going as far as to say at a lunch at the American Physical Society meeting “We’re going to discover the Higgs boson at CERN or Tevatron in the next couple of years, and that’s the most exciting thing at the moment.” What a dangerous attitude!

First of all, there are plenty of other exciting results which are coming out of other areas of particles physics. For example there’s the mysterious X(3872) and its friends from the world of charmonium physics which could overturn our understanding of the quark model. Or the recent tantalizing dark matter results which show us for the first time a glimpse of the dark sector, that makes up about 95% of the universe around us. Now, having a belief in the Higgs boson one way or the other doesn’t stop these results being fascinating or important, but having a “mass” hysteria about the Higgs boson could mean that we don’t give these discoveries the attention they deserve.

This also raises the question about public perception and news coverage- why have one story repeated over and over, instead of dozens of diverse stories in the news? A lot of this comes from the strategies adopted by the high energy physics community. Studies have been performed that ask the public what they like to hear about when they see physics in the news, and they usually want to know about our origins and the “big” questions. So it’s no surprise that we focus on the Higgs boson and keep hearing phrases like “Just after the big bang.”

Moving away from the media frenzy we come to the other reason to be wary. If the Higgs boson exists and nothing else is found at the LHC then the Standard Model will be vindicated and our worldview will not be shaken. We could declare victory, pop champagne corks and bask in the glory of one of the most successful scientific edifices in history. Unfortunately that’s what happened just over a century ago, when Lord Kelvin declared “There is nothing new to be discovered in physics now.” While he was busy finding his sixth decimal places, special relativity and quantum mechanics came along and overturned all of physics, in an unprecedented paradigm shift. Given the hints we have at the moment, from the dark sector, the muon’s gyromagnetic ratio and a few other areas we mustn’t get complacent, and we certainly shouldn’t expect to vindicate any particular model.

The Michelson-Morley interferometer

We’re certainly more prepared for a paradigm shift than we were in 1900, but we’re also falling into the same traps. Back then people were concerned the aether, a mysterious substance that made light behave itself. The problem went like this: light travels at the same speed, no matter how fast you travel when you measure it. Since light is a wave, and every wave we know about travels in some medium, there must be some medium that the light travels through. This medium was the aether and it filled all of space, with a uniform density. It was perfectly rigid to light, forcing light to always have the same speed, but perfectly transparent to matter, so that solid objects could pass through it without hindrance. It was a pretty good hypothesis for Victorian era physics, and about the best they could come up with. Unfortunately, what was needed was a totally new idea and a totally new framework on which to build the theories of the new century. We find ourselves in a similar situation today. The Higgs field is a triumph of quantum field theory, using the most advanced theories of our time and building on the success of decades of research. But then the Higgs field has similar properties to the aether, it’s a perfect, isotropic field filling the universe. It interacts with everything, but it’s surprisingly difficult to see, no matter how hard we look. If we don’t see the Higgs boson, but instead see something else then we could be in for another glorious revolution in physics, and the quantum field theories could seem like quaint approximations of a bygone era.

But the most important reason I don’t believe the Higgs boson exists is simply lack of evidence. There has not been a single scrap of evidence to suggest that the Higgs boson exists, and like Feynman says “It doesn’t matter how beautiful your theory is, it doesn’t matter how smart you are. If it doesn’t agree with experiment, it’s wrong” and at the end of the day, reality has the final say in whether our theory is correct or not. Until then we need to be agnostic about the Higgs boson, and not let it cloud our thinking.

The days of the Higgs bosons searches are coming to an end. If we find it there will be celebrations everywhere (and yes, I’ll join in, I’ll be very happy if it’s discovered!) If not then we’ll be back to the drawing board, and there will be a whole suite of new (and old) models that can keep us busy for decades. A few years ago I put my money where my mouth is. I bet a friend $20 that we would not find the Higgs by 2020, and he enthusiastically snapped up the deal. As the final months of the search sail by, I find myself asking, would I be happier with a Higgs discovery, or$20? Either I pay $20 and get a Higgs boson (a much more attractive proposition than the multi-billion dollar price tag that comes with the LHC!) or I take my$20 and spend it on a few coffees or beers as I ponder where physics will go next. I’m spoiled for choice!