Features Physics World  April 2017
(Shutterstock / Roberts Photography)

Going against the grain

Ploughing your own furrow in fundamental physics is a lonely business, only fit for the most thick-skinned scientists, as Benjamin Skuse reports

Johannes Kepler, Amedeo Avogadro, Ludwig Boltzmann – all made important discoveries that (eventually) extended humanity’s understanding of the world, but died underappreciated. Why? They had come up against the most powerful force in science: consensus.

While a clutch of elite polymaths mainly from Europe and later the US held sway before 1900, today’s consensus is different. Fragmented by disciplines yet global in reach, consensus on any particular question requires the agreement of hundreds or, in the case of issues of global importance, thousands of experts.

Take climate change. In 2013, when John Cook from the Global Change Institute at the University of Queensland, Australia, and co-authors wanted to quantify the consensus on anthropogenic global warming in the scientific literature, they analysed 11,944 climate-science abstracts, finding that 97.1% of those that expressed an opinion on the matter endorsed the consensus position that global warming is a real phenomenon caused by humans (Environ. Res. Lett. 8 031003).

Of the thousands of pro-consensus climate scientists this work represents, one prominent player is Tim Palmer from the University of Oxford, UK. A Royal Society research professor in climate physics, Palmer is most acclaimed for his work on the dynamics and predictability of weather and climate. He has been involved in all five Intergovernmental Panel on Climate Change reports, has co-ordinated two European Union climate projects, and was co-chair of the international scientific steering group of the World Climate Research Programme. It’s safe to say that Palmer is a respected voice among his peers.

Palmer, however, did not start out in climate science. A mathematical physicist by training, he began his research career in fundamental physics, gaining a DPhil in general-relativity theory at Oxford conducted under the watchful gaze of Dennis Sciama. Since then, in his downtime from climate physics, Palmer has continued to pursue his interest in the role of gravity in quantum physics, most notably developing his own fundamental model of quantum entanglement called invariant set theory.

In contrast to his climate-science research, Palmer’s work in fundamental physics challenges conventional wisdom in its field. As we shall see, physicists developing new ideas in fundamental physics face particular challenges, from a lack of peers willing to engage in their work, to their research being scathingly criticized on blogs. The fact that Palmer faces this response – as do other well-respected physicists, who we will shortly hear about – shows that no-one is immune.

Quantum gravity

How to reconcile general relativity with the principles of quantum mechanics – a field known as quantum gravity – is one of the most hotly contested issues in modern physics. The most well-worn approach to the problem is to quantize gravity – to find a theory of the quantum nature of space and time itself. String theory and loop quantum gravity attempt to do this, but they are both complex beasts that fail to adequately unite general relativity with quantum field theory (QFT), despite four decades of research.

How to reconcile general relativity with the principles of quantum mechanics is one of the most hotly contested issues in modern physics

Central to why string theory and loop quantum gravity have not been consigned to the “good idea but doesn’t work” bin is that as a basis to quantize gravity they use QFT, which alongside general relativity is perhaps the greatest achievement of 20th-century physics. QFT has not only never failed a test, but has also fundamentally led to the smartphones, laptops and PCs upon which you may be reading this article.

Although there’s no consensus on a fundamental theory of nature that can explain quantum gravity – because no theories of quantum gravity to date are either consistent or testable – string theory is undoubtedly today’s most popular candidate. String theory has offered new tools in mathematics, as well as powerful methods to generate approximate descriptions of complex systems such as quark–gluon plasmas and condensed-matter systems. Yet fundamental difficulties remain, linked to the prediction of unseen particles without any details of their properties, the non-uniqueness of the scheme for hiding the theory’s extra dimensions, and the lack of connection with experiment.

With such challenges still present, it would be easy to assume string theorists are aching for a completely new theory to work on. But this is not so, as attested by critics like Lee Smolin – a loop quantum gravity proponent at the Perimeter Institute for Theoretical Physics, Canada – in his 2006 book The Trouble with Physics: the Rise of String Theory, the Fall of a Science, and What Comes Next. In Smolin’s view the string theory community is monolithic, with “a tremendous self-confidence” and “disregard for and disinterest in the ideas, opinions and work of experts who are not part of the group”.

So what becomes of those aiming to reconcile general relativity with quantum principles in a different way? Is the string theory community really as dogmatic as Smolin and others have argued?

A fractal universe

Palmer tackles the quantum-gravity conundrum from a new perspective influenced by his climate work, in particular using nonlinear dynamical systems and the beautiful fractal geometries arising from chaos theory. “Pretty much every approach in this area, at least by mainstream physicists, is what I would describe as putting the quantum cart before the gravitational horse,” he explains. “I on the other hand am trying to build a causal, realistic model of quantum entanglement by generalizing the geometry of space–time to include the fractal geometry of state space.”

Complex geometry Tim Palmer’s invariant set theory describes the universe as a deterministic dynamical system evolving on a fractal attractor. Though his background is mathematical physics, he is now primarily a climate scientist, and as such has found this theory has been largely ignored or dismissed. (Shutterstock / Diedie)

First proposed in 2009, Palmer’s invariant set theory has a geometry he claims describes the laws of physics at their most primitive level (arXiv:1605.01051). In essence, invariant set theory pictures the whole universe as a completely deterministic dynamical system evolving on a fractal attractor – a set of points to which state-space trajectories of the underlying dynamical equations are attracted that has a structure that persists under repeated magnification of the set. As participants in this universe, we live in an invariant set of the fractal that contains all physically realistic states of the universe. Key to the idea is that any perturbation making you fall out of this complex fractal set sends you into the unphysical abyss.

In his words: “I have a theory that is deterministic, realistic, so in that sense classical, and everything is constrained by relativity, but is crucially not constrained by the Bell inequalities or any of the panoply of quantum no-go theorems, which if it were would render it inconsistent with experiments.”

Reactions to the theory range from intrigue to pragmatic scepticism – questioning whether the theory is fully formed, which Palmer fully admits it is not – to visceral emotion. “People get very upset as they think that I’m attacking free will,” he says. “But I think this is a subtle issue and if we’re really going to base our ideas of good physics and bad physics on free will, we better have a good definition of what ‘free will’ means.”

Palmer regards this spectrum of opinion as healthy debate, but finding people with whom to slug out the finer details of his theory is difficult, as they are so scarce. “The people I’ve discussed this with are either very interested or they look slightly blankly at me and say ‘well I’m afraid I don’t understand this stuff because I don’t know nonlinear dynamics and p-adic numbers’.” With the theory using terminology more familiar to number theorists than physicists, he finds that many researchers simply don’t have the time to invest in understanding the mathematics underpinning his ideas.

This, combined with the need for more detail and the fact that his most noteworthy work has been in another field, means the default reaction he receives is to simply be ignored. Although Palmer’s research on invariant set theory has been published in well-respected journals and he feels his work has been treated very fairly and openly by the mainstream community, the lack of people willing to listen or able to understand let alone comment on his work has meant he has had to continue developing his ideas in solitude.

Dutch perspectives

Lonely furrow Gerard ‘t Hooft’s cellular automaton theory treats information as a physical quantity so that quantum and classical behaviour are the same. As he is well respected, most criticism of this theory has been constructive. Jonathan McCabe computer-generated this artwork following cellular automata rules. (CC BY 2.0 / Jonathan McCabe)

So is it any easier to present work that goes against the grain if you have a Nobel Prize for Physics or are an established string theorist?

Gerard ‘t Hooft is an internationally acclaimed Dutch theoretical physicist who shared the 1999 Nobel Prize for Physics with Martinus Veltman “for elucidating the quantum structure of electroweak interactions in physics”. Based at Utrecht University in the Netherlands, ‘t Hooft’s scientific contributions to theoretical high-energy physics and QFT have earned him many other awards and honours besides, and he has even had an asteroid named after him. Yet despite such plaudits, he finds himself “ploughing his own lonely furrow” as well when it comes to his physical interpretation of quantum theory and quantum gravity. “A Nobel prize is no guarantee that one’s ideas and results are sheepishly accepted by one’s peers,” he says, adding that this questioning attitude is how things should be in science. ‘t Hooft argues that the universe at some deep level is described by discrete, classical bits. His cellular automaton theory essentially treats information as a physical quantity so that classical and quantum behaviour are the same thing (arXiv:1405.1548).

Meanwhile, one of ‘t Hooft’s former PhD students, Erik Verlinde, at the University of Amsterdam and the Delta Institute for Theoretical Physics, also in Amsterdam, has established himself with valuable contributions to string theory and QFT. His emergent gravity hypothesis suggests gravity is not a fundamental force of nature at all, but a phenomenon that emerges from quantum entanglement, which dictates the structure of space–time (and thus gravity) and its entropy and information content (arXiv:1611.02269).

Extreme gravity Erik Verlinde’s emergent gravity hypothesis suggests that gravity is a phenomenon that emerges from quantum entanglement. He has been both lauded and heavily criticized for this work. (NASA)

A key difference between Palmer’s experience and that of ‘t Hooft and Verlinde is that when the latter write papers challenging conventional wisdom, the media pay attention. Both have been subject to rigorous and sometimes sharp and insulting criticism from former string theorist turned publisher Luboš Motl on his blog The Reference Frame (“childishly wrong”, “mediocre vague paper”) while also being lauded by the press with headlines such as “The future is completely determined” and “The man who’s trying to kill dark matter”, with Dutch outlets even touting Verlinde as the “nieuwe Einstein”.

Does media attention help spread interest in alternative quantum gravity ideas? “I think the media attention helps in getting my work noticed, but it has more drawbacks than benefits,” opines Verlinde. “I actually said to the first Dutch journalist who came to interview me that I did not want hype, since this may make my colleagues uneasy and less willing to seriously study my paper or get involved in follow-up research.”

Both are critical of blogs and websites claiming to democratize science, as Verlinde illuminates: “I am not a fan at all of these sites, since they mix pseudoscience with actual science.” ‘t Hooft agrees: “Unfortunately, these forums are often dominated by people who shout a lot without listening to themselves.”

Where Verlinde and ‘t Hooft have an advantage over Palmer is in their standing in the fundamental-physics community. Using the same language as their peers and having made important contributions to string theory and QFT mean, unlike Palmer’s experience, constructive criticism from the scientific community has not been hard to find. Although requiring a thick skin and complete belief in their theories, often this criticism has led to new and interesting research directions, improving and revising their work.

Yet their hypotheses fly in the face of convention, and Verlinde and ‘t Hooft are driven by the same desire as Palmer, namely to be taken seriously by their peers. “Some people are very dogmatic, few people really follow what I am doing and still fewer agree with me,” says ‘t Hooft. “I am a bit disappointed that there are so few people thinking the way I do.” Verlinde is in the same position, but says he is determined to convince his scientific colleagues that his work is “on the right track”.

Inside the fold

One string theorist who did offer encouraging words about Verlinde’s emergent gravity hypothesis is Mark Van Raamsdonk at the University of British Columbia in Canada. No stranger to resistance from the string theory community himself – receiving rejections and scathing peer reviews in 2009 for a paper that set out his conjecture on the entanglement–gravity relationship – he has since found his ideas have been brought into the fold.

“There are now quite a few conferences per year completely dedicated to these entanglement–gravity connections, and a number of the most distinguished people in the field are focused on this area,” he says. Van Raamsdonk cites the rapid pace of progress, the huge volume of work on the topic and many excellent people to collaborate with as key to allowing him to sharpen and develop his work. For him, being on the right side of the quantum-gravity consensus has been beneficial. And maybe his experience from the other side has let him be more welcoming of alternative hypotheses that could, as his work did, prove to be fruitful.

Although the string theorist majority in quantum gravity is no different from any other scientific community holding sway in a particular field, their hegemony is based on a theory that has yet to resolve the quantum gravity conundrum despite decades of work. Perhaps now is the time to start welcoming alternative ideas in fundamental physics, and to work with those going against the grain.