Theoretical physics: The emperor's new physics

Journal name:
Nature
Volume:
538,
Pages:
36–37
Date published:
DOI:
doi:10.1038/538036a
Published online

Richard Dawid examines a critique of quantum mechanics, string theory and inflationary cosmology.

Fashion, Faith, and Fantasy in the New Physics of the Universe

Roger Penrose Princeton University Press: 2016. ISBN: 9780691119793

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Illustration by Eoin Ryan

The eminent theoretical physicist Roger Penrose is worried about the current path of physical research. In Fashion, Faith, and Fantasy in the New Physics of the Universe, he argues that the eponymous triad of trends has become overly powerful in contemporary fundamental physics. This core message is delivered in language that demands some mathematical sophistication of the reader. Penrose also discusses some of his own ideas, such as twistor theory — his take on a synthesis of quantum theory and general relativity.

Penrose claims that even well-confirmed theories, such as quantum mechanics, are 'oversold' with respect to their presumptive stability. Quantum physics has had an impressive record of predictive success, ranging from quantum chemistry to elementary particle physics. But it faces a deep conceptual problem. Whereas quantum mechanics has a perfect internal consistency when it describes a system that evolves without being measured, the way in which it represents measurements is not coherently embedded in that description. To Penrose, this indicates that the fundamental principles of quantum mechanics have not yet been found and will rely on the elusive full integration of gravity into quantum physics. He argues that the success of quantum mechanics tends to make physicists insensitive to the theory's conceptual problem and generates an unjustified degree of faith in its basic principles as a solid foundation of physics.

Another source of undue trust in a theory, Penrose asserts, is the physics community's tendency to follow fashion — that is, to settle on one strategy of dealing with a problem before severely testing the theory's empirical predictions. Penrose views string theory (a theory of quantum gravity) as the pre-eminent example.

The final trend in Penrose's triad is fantasy — that is, a wildly speculative idea that goes far beyond what is implied by the known data. Penrose assigns that category to inflationary cosmology, which he argues is treated as an established theory despite a lack of evidence.

Of these three, Penrose's discussion of quantum mechanics ('faith') is the most successful. On the basis of an inspired presentation of quantum mechanics, he makes a case that the theory's enormous scientific success does not remove serious doubts about the finality of its basic principles. His discussions of fantasy and fashion, however, are problematic. He paints an exaggerated picture of their role and systematically underrates the merits of the theories he criticizes.

Fashion and fantasy are presented in separate chapters as independent influences that have become too powerful. But, as Penrose acknowledges, fantasy has always been at the root of new theories. Just think about the atomist speculations that led to the kinetic gas theory in the nineteenth century. For Penrose, the trouble arises when fantasy is given too much credit before a theory is empirically tested. This occurs, he says, when a theory becomes the subject of fashion. In this light, it is difficult to see the independent role of 'fantasy' in Penrose's argument.

Inflationary cosmology is, moreover, not a good illustration of fantasy, even by Penrose's own account. As he acknowledges, recent precision measurements of the cosmic microwave background agree with typical predictions of inflationary cosmology, so it seems difficult now to call it a mere flight of fancy. Penrose presents his important criticism that inflation generically does not explain the low initial entropy of the Universe (although explanations have been suggested in certain models; see S. M. Carroll and J. Chen. https://arxiv.org/abs/hep-th/0410270; 2004). But he presents the case against inflation in a way that hides the independent significance of problems that can be solved by it, such as explaining the homogeneity and flatness of the observed Universe.

There are similar issues with Penrose's claim that fashion is the main reason for string theory's influential position. His analysis of its problems is not up to the task of debunking proponents' physics-based reasons for confidence. Penrose's main complaint about string theory is that it lacks a clear specification of its number of degrees of freedom. He tries to show this in several contexts. However, he tends to omit information that could make the situation less confusing than he takes it to be. For example, he expresses unease about 'gauge–gravity duality', the claim that string theory is empirically equivalent to a quantum field theory in a lower-dimensional space. (If generally valid, that would mean that a string theory in three extended spatial dimensions was empirically equivalent to a quantum field theory in two spatial dimensions.) Such a claim looks startling, because one would naively expect that a three-dimensional theory has more degrees of freedom than a two-dimensional one. Penrose presents this as one of many questionable implications of string theory.

Curiously, however, he presents his case without mentioning that Gerard 't Hooft, who is cited in the book, provided a general understanding of the reduced number of degrees of freedom in quantum gravity without any reference to string theory, before cases of gauge–gravity duality were conjectured in the context of string theory (G. 't Hooft. https://arxiv.org/abs/gr-qc/9310026; 1993). In this light, by generating examples of gauge–gravity duality, string theory does not, as Penrose maintains, make one more prima facie implausible claim, but opens up perspectives for a more thorough understanding of a characteristic of quantum gravity that had already been suggested.

It is always inspiring to read Penrose's uncompromisingly independent perspective on physics. He seems more at home with developing visionary ideas than with detailed criticism of prevalent theories. Unfortunately, this book offers too few of the former and too much of the latter.

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  1. Richard Dawid is a philosopher of science at the University of Stockholm.

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Comments

  1. Report this comment #68791

    Pentcho Valev said:

    If quantum mechanics is "faith", then what is Einstein's relativity? Answer: An absurdity based on the false principle of constancy of the speed of light. That the speed of light is variable, not constant, is obvious. When the initially stationary observer starts moving towards the light source with speed v, the frequency he measures shifts from f=c/L to f'=(c+v)/L (L is the wavelength). This means that either the speed of the light relative to the observer shifts from c to c'=c+v, or the motion of the observer somehow changes the wavelength of the incoming light – from L to L'=Lc/(c+v). The latter scenario is absurd – the motion of the observer is obviously unable to change the wavelength of the incoming light.

    Conclusion: The speed of light is different to differently moving observers (varies with the speed of the observer), in violation of Einstein's relativity.

    Pentcho Valev

  2. Report this comment #68793

    Pentcho Valev said:

    All consequences of Einstein's 1905 false constant-speed-of-light postulate are absurd. One of them, length contraction, implies that unlimitedly long objects can gloriously be trapped inside unlimitedly short containers:

    http://math.ucr.edu/home/baez/physics/Relativity/SR/barn_pole.html "These are the props. You own a barn, 40m long, with automatic doors at either end, that can be opened and closed simultaneously by a switch. You also have a pole, 80m long, which of course won't fit in the barn. [...] So, as the pole passes through the barn, there is an instant when it is completely within the barn. At that instant, you close both doors simultaneously, with your switch. [...] If it does not explode under the strain and it is sufficiently elastic it will come to rest and start to spring back to its natural shape but since it is too big for the barn the other end is now going to crash into the back door and the rod will be trapped in a compressed state inside the barn."

    See, at 7:12 in the video below, how the train is trapped "in a compressed state" inside the tunnel:

    http://www.youtube.com/watch?v=Xrqj88zQZJg "Einstein's Relativistic Train in a Tunnel Paradox: Special Relativity"

    It is not difficult to realize that trapping long objects inside short containers drastically violates the law of conservation of energy. The trapped object, in trying to restore its original volume ("spring back to its natural shape"), would produce an enormous amount of work the energy for which comes from nowhere.

    At 9:01 in the above video Sarah sees the train falling through the hole, and in order to save Einstein's relativity, the authors of the video inform the world that Adam as well sees the train falling through the hole. However Adam can only see this if the train undergoes an absurd disintegration first, as shown at 9:53.

    Clearly we have reductio ad absurdum: An absurd disintegration is required – Adam sees it, Sarah doesn't. Conclusion: The underlying premise, Einstein's 1905 constant-speed-of-light postulate, is false.

    Pentcho Valev

  3. Report this comment #68881

    Maurits Van den Noort said:

    Towards a theory of everything: "The observer's unconscious brain"

    Prof. Maurits van den Noort1*, Prof. Sabina Lim1 & Dr. Peggy Bosch2

    1. Research Group of Pain and Neuroscience, Kyung Hee University, Seoul 130-701, Republic of Korea
    2. Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, 6525 HR Nijmegen, The Netherlands

    We read with great interest the article by Richard Dawid,1 in which the recent book of Roger Penrose1 is critically examined. We agree with Dawid that Penrose focuses more on developing visionary ideas than on providing a detailed criticism of prevalent theories. However, in sharp contrast to Dawid,1 in our opinion, there is nothing wrong with scientists having visionary ideas, on the contrary, nowadays, visionary ideas (and research projects investigating them) are often lacking, in a time where scientists seem to be mostly bothered with achieving long publication lists and keeping their research projects within the economical budget.

    We remember when Penrose published his book entitled, "Shadows of the Mind: A Search for the Missing Science of Consciousness", back in 1994.3 He received a lot of criticism from both physicists and neuroscientists who found that he speculated too much in his book. However, in our opinion, it is too premature to claim that Penrose is wrong. Recently, we have seen discoveries such as: the brain's dark energy,4 default mode networks,5 etc., and colleagues that would have suggested those theories decades ago, would have been laughed at. Neuroscience is a relatively new research field and, therefore, many discoveries are still to be made, possibly proving Penrose?s Orchestrated objective reduction (Orch-OR) hypothesis.6

    Unfortunately, it seems that in his new book, Penrose does not tap the missing link between physics and neuroscience enough,2 because a theory of everything7 should not only fit within the laws of classical and quantum mechanics, but should also fit within the fundamental laws of neuroscience (e.g., for instance, what about the observer's8 (un)conscious brain processing and interaction?). We do not know if Penrose prepares a new book, but if this is the case, our title suggestion would be: "Towards a theory of everything: The observer's unconscious brain".

    *Correspondence to: info@mauritsvandennoort.com

    1. Dawid, R. Theoretical physics: The emperor's new physics. Nature 538, 36-37 (2016).
    2. Penrose, R. Fashion, Faith, and Fantasy in the New Physics of the Universe. (Princeton Univ. Press, 2016).
    3. Penrose, R. Shadows of the Mind: A Search for the Missing Science of Consciousness. (Oxford Univ. Press, 1994).
    4. Raichle, M. E. Neuroscience: The brain's dark energy. Science 314, 1249-1250 (2006).
    5. Raichle, M. E. The brain's default mode network. Annu. Rev. Neurosci. 38, 433-447 (2015).
    6. Hameroff, S., Penrose, R. Consciousness in the universe: a review of the "Orch OR" theory. Phys. Life Rev. 11, 39-78 (2014).
    7. 't Hooft, G. et al. 'A theory of everything' Nature 433, 257-259 (2005).
    8. Schrodinger, E. Die gegenwortige Situation in der Quantenmechanik [The present situation in quantum mechanics]. Naturwissenschaften 23, 807-812 (1935).

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