String theory under fire

Brian Greene and Tasneem Zehra Husain questioned by Roger Penrose and Eric Weinstein

On the third day of HowTheLightGetsIn, the Arena was buzzing with those brave souls wishing to see the clash of titans over string theory. An extraordinary panel: Nobel Laureate Roger Penrose, pioneering string theorist Tasneem Zehra Husain, Polymath Mathematical Physicist Eric Weinstein and the ground-breaking string theorist Brian Greene. The panelists gathered at HTLGI to debate the trouble with String Theory, theory or framework, community or oligarchy, a beautiful theory or one detached from reality.

String theory, heralded as a potential theory of everything, has dominated theoretical physics for over thirty years, with more scientific papers arising from it than any other theory. But critics argue the theory has held undue influence and proclaimed that it is an error to pursue it. String theory proposes 11 dimensions and a vast landscape of possible universes without any evidence. Moreover, a theory of everything has not been forthcoming, and predictions of supersymmetry particles have not been confirmed.

The distinguished panel came together to discuss whether it’s time to move on from string theory, recognise that the search for supersymmetry has failed, and seek alternative accounts of the universe supported by observation and experiment. Penrose and Weinstein argue we should see it’s mathematics, without any connection to the physical world, as little more than fantasy. Whereas Greene and Husain state that the continued power and allure of string theory is justified by its potential to unify our understanding of the universe once and for all.


Presumably given that scientists themselves want to be correct they will pursue ideas they think will lead them to the truth


Roger Penrose kicks off the debate by arguing that whilst initially intrigued by this theory in the 1980s its need for 26 dimensions including time was too far at odds with the obvious fact that we live in a 4-dimensional world that includes time. Whether or not you think this is a powerful enough objection, much of the world has turned out to be more mysterious than we first imagined, Penrose has a more powerful objection. The theory is driven by mathematics, “which is not an objection by itself” he argues, “as most of what I do is driven by mathematics.” Rather he put forward that if it’s meant to be a theory about the world it should make predictions which can be tested. But it seems that it is mostly, if not entirely, about the mathematics.

Professor Brian Greene offers his take, that the question we face doesn’t really grip onto what scientists are doing. We can’t pronounce how science should move on from this or that question. Scientists should choose what they find exciting. We should let people work on whatever they want as long as it gets results that inspire further research. If the work is fruitful, and it leads to future developments means then it should be pursued. A powerful argument for pluralism and to let scientists do that for which they are trained. Brian ends with the powerful argument, “leave it to the marketplace of ideas where scientists vote with the most precious resource that they have: their time.”

The question of whether it’s time to move on from the dominance of string theory in our account of the universe is put to our third panellist Tasneem Zehra Husain. Husain, taking the defensive line of her chosen field, reports that the maths is still talking to them. That scientists are in a self-correcting system wherein theorists are left to follow the ideas which lead to new notions and theories based on what speaks to them. And presumably given that scientists themselves want to be correct they will pursue ideas they think will lead them to the truth. Furthermore, she argues that String theory has had only 40 years and yet still leads us to effective new ideas. The equations are speaking to us, and we should not stop listening. It seems to be leading us to a robust mathematical framework which tells us more and more about the world.

These powerful arguments, for letting the science lead, are echoed by Weinstein. But that doesn’t stop him from criticising String Theory for a far worse crime. Weinstein argues that although voting with time is ideally how the world should work, much like a pizza parlour slashing their rival's tyres, the political economy of science has pushed everything towards string theory. It has dominated the field; it has pushed out many brilliant scientists and researchers due to the enormous funding and political moves of string theorists and their work. A put up or shut up mentality is levelled at critics of string theory and oppositional attitude, which Weinstein argues is not reciprocated for the string theorists. They get away with far more mathematical speculation without empirical considerations.

Having levelled this criticism the panel moves on to the two defining questions which are at the centre of this debate. Is the dominance of string theory due to its effectiveness, despite the lack of empirical justification, and is the community of string theorists one which has begun to act as both referee and player? These two questions get at the trouble with string theory, the lack of results besides mathematical proofs and the overarching dominance it has both in the minds of others and as a symptom of its early success.

Penrose and Weinstein question the validity of the connection between the mathematical framework that string theory proposes and the empirical evidence it has gathered. The amount being nil. Greene and Husain refute that “String theory will be testable, but the energy scales are too high to test at the moment.” Greene goes further by saying, “I’m not interested in spending my time on a theory which is wrong.” He builds on this arguing that it's not the theory's fault but the theorists fault that we do not understand or aren’t yet able to get empirical evidence for its results. Unfortunately, as Husain puts it, “it is incredibly difficult and the calculations and conditions have to be precise as we have learnt in the study of particle physics at CERN and elsewhere”.


“If Einstein hadn’t discovered general relativity, it would have emerged out of string theory.”


Penrose again raises the concern that the field of string theory seems to be a mathematical theory which tells us about linera algerbra and simplifies some calculations. It simplifies but in the wrong direction, it’s a theory which has distracted from dealing with an explanation off why quantum mechanics works. The implication then being that what it could tell us about the physical world is limited. Greene shoots back that it is the only theory which is able to show the results of Black Hole evaporation, which Penrose and Steven Hawking developed so many years ago. He pushes back further arguing that it is the only theory which is able to tell us about the unification of Quantum mechanics and General relativity. A claim which if any loop quantum gravity theorists were on the panel would have disputed. However, the claim is still an important part of the defense of the theory.

Weinstein, taking a measured line between criticism of Greene, who he claims is the best example of a string theorist from the early days of the theory, and a defence against Penrose’s dismissal of its explanatory powers. Rather he takes string theorists to task for not engaging with the work of colleagues outside of the community. He challenges the string theorists with whether they have looked at the work of Peter Woit and others. A theory he disagrees with, and he has his own alternate theory which he has “put up”, but theories that could replace String Theory which are worthy of discussion. And ones which could be studied. He receives push back from Weinstein who argues that if he can take the 45 minutes to begin to get to grips with Woit’s theory then Greene as the smarter man could do this.

Finally, the panel moves to the question of simplicity. The beauty of the theory is a large part of what they take be its success. The host, Katie Robertson, put this to Penrose . He tackles this assumption by saying that string theory is an ugly theory. Rather than offering simplicity and beauty rather it demands that we should accept a range of other dimensions which we do not have the ability to experimentally understand. Furthermore, the line that there is not enough energy to excite these dimensions is flawed. The power of the beginning of the universe is accessible via supercolliders, so why is this not enough to excite and show experimentally what is going on with string theory’s claims. Greene ardently disagrees. The power of string theory is that, working from the quantum, general relativity emerges out of the mathematics. “If Einstein hadn’t discovered general relativity, it would have emerged out of string theory.” That, he argues, is a sign of its beauty.

Weinstein pushes back with his own beautiful metaphor. “A baby is beautiful, a giraffe is beautiful. It is possibly beautiful that cutting the head of a giraffe and attaching it to the body of a baby” this is what he thinks of the work that has been done previously. Both Penrose and Greene, in his estimation, have these beautiful mathematical theories at a certain level but the string theorists wants to pull them together in an ugly way. The energy level demanded is also ugly. His alternative proposal being that we should have conferences all over the world to look at all the theories which have been proposed as counters. And look to see whether a more beautiful theory emerges naturally.

Husain concludes the discussion by arguing that there is still much work to do. She is not opposed to looking at alternatives. But that it is still the early days of the field, and we should wait to see what advances are made before we try and move people away from their interests in the field.

The debate raised many interesting questions about the nature of theories and the power and importance of experimental and mathematical confirmation. However, a path forward seems to lie in a mixed position. Perhaps Weinstein’s endorsement to look for alternatives is exactly what we need. The future of the field is certainly muddled, and string theory doesn’t have the dominant position it once held. But until we have a more successful and empirically verified version, the question remains open whether we should move on from the troubled string theory.

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