Why Trust a Theory? Reconsidering Scientific Methodology in Light of Modern Physics

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Monday (7 December)

09:30 - 09:50 Opening (Watch online)
09:50 - 10:30 David Gross: What is a Theory? (Watch online)
10:30 - 11:10 Carlo Rovelli: Has Theoretical Fundamental Physics become Sterile? (Watch online)
11:10 - 11:35 Coffee Break
11:35 - 12:15 Richard Dawid: Non-empirical Confirmation (Watch online)
12:15 - 12:55 Massimo Pigliucci: Post-empirical Physics, Falsificationism, and the Public Perception of Science (Watch online)
12:55 - 14:35 Lunch
14:35 - 15:15 Radin Dardashti: Physics without Experiments? (Watch online)
15:15 - 15:55 Helge Kragh: Fundamental Theories and Epistemic Shifts: Can History of Science serve as a Guide? (Watch online)
15:55 - 16:35 Peter Achinstein: Scientific Speculation (Watch online)
16:35 - 17:00 Coffee Break
17:00 - 18:30 Panel I (Host: Stephan Hartmann): Why Trust a Theory? (Watch online)

Tuesday (8 December)

09:30 - 10:10 Björn Malte Schäfer: Dark Gravity, Dark Fluids, and Dark Statistics (Watch online)
10:10 - 10:50 Chris Smeenk: Gaining Access (Watch online)
10:50 - 11:20 Coffee Break
11:20 - 12:00 Gordon Kane: String/M-Theories about our World are Testable in the Traditional Physics Way (Watch online)
12:00 - 12:40 Joseph Silk: The Limits of Cosmology, Post-Planck (Watch online)
12:40 - 14:30 Lunch
14:30 - 15:10 Fernando Quevedo: Achievements and Challenges for String
 (Watch online)
15:10 - 15:50 Chris Wüthrich: Considering the Role of Information Theory in
Fundamental Physics
 (Watch online)
15:50 - 16:30 Viatcheslav Mukhanov: Is the Quantum Origin of Galaxies Falsifiable? (Watch online)
16:30 - 17:00 Coffee Break
17:00 - 18:30 Panel II (Host: Johanna Erdmenger): How far do we get with Empirical Data? (Watch online)
19:15 Dinner (Cafe Reitschule)

Wednesday (9 December)

09:30 - 10:10 George Ellis: Limits in testing the Multiverse (Watch online)
10:10 - 10:50 Joseph Polchinski: String Theory to the Rescue (Watch online)
10:50 - 11:20 Coffee Break
11:20 - 12:00 Elena Castellani: Scientific Methodology: A View from Early String Theory (Watch online)
12:00 - 12:40 Dieter Lüst: Aspects of Quantum Gravity (Watch online)
12:40 - 14:30 Lunch
14:30 - 15:10 Sabine Hossenfelder: Lost in Math (Watch online)
15:10 - 15:50 Karim Thebault: What can we learn from Analogue Experiments? (Watch online)
15:50 - 16:30 Georgi Dvali: Secret Quantum Lives of Black Holes and Dark Energy (Watch online)
16:30 - 17:00 Coffee Break
17:00 - 18:30 Panel III (Host: Daniele Oriti): Has Physics changed? – and should it? (Watch online)


Peter Achinstein: Scientific Speculation

Throughout the history of science controversies have emerged regarding the legitimacy of speculating in science. Three very strong views about the general practice of speculating have emerged: One, very conservative, says “never do it, or at least never publish it.” It is the official doctrine of Isaac Newton: “hypotheses have no place in experimental philosophy.” (Of course, he violated his official doctrine on several occasions). Another, more moderate position is the official doctrine of hypothetico-deductivists such as Whewell, Popper, and Hempel: speculate freely but verify before publishing. The third, the most liberal, is suggested by Feyerabend’s principle of proliferation: speculate like mad, and publish, even when you have no idea how to test your speculations.

In my talk I want to reject all three of these views. They are too simple-minded. Some speculations are good ones, some not so good. I will ask how a speculation is to be evaluated. In the process of doing so, I will consider two historically important speculations: James Clerk Maxwell’s kinetic theory speculations from 1860 to 1875, and a speculation that has been put forward by some string theorists, as well as by others, viz. that there is a “theory of everything” (whether or not it is string theory). The first, I will argue, deserves praise, the second does not.top

Elena Castellani: Scientific Methodology: A View from Early String Theory

Looking at the developments of quantum field theory and string theory since their very beginnings, it does not seem that the methodology in fundamental physics has changed. The same strategies are applied in theory building and assessment. The methodology leading to the string idea and its successive developments is the same one we can find in many fundamental developments in theoretical physics. These have been crowned with successful empirical confirmation (sometimes, after a number of years): starting with the history of the positron to arrive at the Higgs particle.top

Radin Dardashti: Physics without Experiments?

Most of the fundamental theories in modern physics are relevant at energy scales or length scales where empirical access is currently hard to obtain. Accounts of theory assessment within the philosophy of science literature are, however, usually concerned with the relation between the theory and the empirical data they predict. So these “traditional” approaches seem not to allow for theory assessment in these cases. Recently, Richard Dawid has developed an account of non-empirical theory assessment, which uses evidence not entailed by the theory to assess the theory. In this talk I present a problem-oriented perspective on these issues, which allows to better assess the possibilities and limitations of non-empirical theory assessment.top

Richard Dawid: Non-empirical Confirmation

The talk will analyse reasons for the high degree of trust many physicists have developed in empirically unconfirmed theories. An extension of the concept of theory confirmation (to be called “non-empirical confirmation”) will be suggested that allows for confirmation by observations that are not predicted by the theory in question. The last part of the talk will address a number of worries that have been raised with respect to this approach.top

David Gross: What is a Theory?


Georgi Dvali: Secret Quantum Lives of Black Holes and Dark Energy


George Ellis: Limits in testing the Multiverse

Our ability to test cosmological models is severely constrained by visual horizons on the one hand, and physical horizons (limits on testing physical theories) on the other. Various arguments have been given to get round these limitations. I will argue that these amount to philosophical choices, which may or may not correspond to physical reality, and hence resulting claims do not amount to established scientific results. This holds in particular to a variety of claims of physical existence of infinities of galaxies, universes, or beings like ourselves in a multiverse. We need a strong philosophical stance to distinguish which of these claims should indeed be regarded as proven science,and which not.top

Sabine Hossenfelder: Lost in Math

I will speak about the role of social and cognitive biases in hypotheses pre-selection, and reflect on the rationale behind the concepts of naturalness, simplicity and beauty.top

Gordon Kane: String/M-Theories about our World are Testable in the Traditional Physics Way

Some physicists hope to use string/M-theory to try to construct a comprehensive underlying theory of our physical world – a final theory. A quantum theory of gravity must be formulated in 10 dimensions, so obviously testing it requires projecting it onto our 4D world (called “compactification”). Most string theorists study theories, not phenomena, and are not much interested in testing theories about our world. Compactified theories generically have many realistic features that provide tests, such as gravity, Yang-Mills forces like the Standard Model ones, chiral fermions, softly broken supersymmetry, Higgs physics, families, and hierarchical fermion masses. String phenomenologists have also formulated a number of explicit tests for compactified theories. I give examples of tests from compactified M-theory (involving Higgs physics, superpartners at LHC, electric dipole moments, and more). Theoretical technologies, and experimental technologies and facilities, have both improved steadily in recent years so tests have already occurred for some of the examples and are underway for more. All tests of theories in physics have always depended on assumptions and approximate calculations, and tests of string/M-theories do too. It is clear that compactified theories exist that can describe worlds like ours, and it is clear that even if a multiverse were real it does not prevent us from finding comprehensive compactified theories very much like one that might describe our world.top

Helge Kragh: Fundamental Theories and Epistemic Shifts: Can History of Science serve as a Guide?

Epistemic standards and methodologies of science inevitably reflect the successes and failures of the past. In this sense, they are in part of a historical nature. Moreover, the commonly accepted methodological criteria have to some extent changed over time. Faced with the problem of theories that cannot be tested empirically, perhaps not even in principle, it may be useful to look back in time to situations of a somewhat similar kind. Roughly speaking, previous suggestions of non-empirical testing have not fared well through the long history of science. Ambitious and fundamental theories of this kind have generally been failures, some of them grander than others. So, is there any reason to believe that they will not remain so in the future? Can we infer from history that empirical testability is a sine qua non for what we know as science? Not quite, for it is far from obvious that older scientific theories can be meaningfully compared to modern string theory or multiverse physics. History of science is at best an ambiguous guide to present and future problems, yet it does provide reasons for scepticism with regard to current suggestions of drastic epistemic shifts which essentially amounts to a new “definition” of science. top

Dieter Lüst: Aspects of Quantum Gravity



Viatcheslav Mukhanov: Is the Quantum Origin of Galaxies falsifiable?


Massimo Pigliucci: Post-empirical Physics, Falsificationism, and the Public Perception of Science

Trouble, as explicitly hinted at in the title of a recent book by Lee Smolin, has been brewing for a while within the fundamental physics community. Ideas such as string theory and the multiverse have been both vehemently defended as sound science and widely criticized for being “not even wrong,” in the title of another book, by Peter Woit. Recently, George Ellis and Joe Silk have written a prominent op-ed piece in Nature, inviting their colleagues to defend the very integrity of physics. To which cosmologist Sean Carroll has responded that physics doesn’t need "the falsifiability police,” referring to the famous (and often misunderstood or badly applied) concept introduced by Karl Popper to demarcate science from pseudoscience. The debate isn’t just “for the heart and soul” of physics, it has spilled onto social media, newspapers and public radio. What is at stake is the public credibility of physics in particular and of science more generally — especially in an era of widespread science denial (of evolution and anthropogenic climate change) and rampant pseudoscience (antivax movement). Since philosophers of science have been invoked by both sides, it is time to take a look at the “physics wars” from a detached philosophical perspective, in my case informed also by my former career as an evolutionary biologist, a field that has peculiar similarities with what is going on in fundamental physics, both in terms of strong internal disputes and of perception by a significant portion of the general public.top

Joseph Polchinski: String Theory to the Rescue

The search for a theory of quantum gravity faces two great challenges: the incredibly small scale of the Planck length and time, and the possibility that the observed constants of nature are in part the result of random processes. A priori, one might have expected these obstacles to be insuperable. However, clues from observed physics, and the discovery of string theory, raise the hope that the unification of quantum mechanics and general relativity is within reach.top

Fernando Quevedo: Achievements and Challenges for String Phenomenology/Cosmology

An overview is given on the efforts for string theorists to make contact with low-energy physics and cosmological observations. The main challenges for the future will be addressed.top

Carlo Rovelli: Has Theoretical Fundamental Physics become Sterile?

Fundamental physics has changed from a field capable of spectacular successful predictions (electromagnetic waves, black holes, antiparticles, just to name a few...) to a depressing sequence of failed predictions: low-energy supersymmetry being the most recent and burning. Why? I will consider the possibility that the last generation of theoretical physicists has modified the practice of scientific method. Unproductively.top

Björn Malte Schäfer: Dark Gravity, Dark Fluids, and Dark Statistics

Observational cosmology has the purpose of investigating gravity on large scales through the observation of the expansion dynamics of the Universe on one side and through cosmic structure formation on the other. In my talk I will go through the arguments why these observations are able to constrain models of gravity, what constraints there are independent from the assumptions of a certain model, how cosmology switches from being statistics to systematics dominated, and what precision and accuracy need to be archived by future surveys. Lastly, I’ll describe the process of statistical inference, errors, priors and fundamental limits in cosmology.top

Joseph Silk: The Limits of Cosmology, Post-Planck

I will discuss how one might follow up on the Planck satellite which has given us a remarkable confirmation to high precision of what has become known as the “standard model of cosmology.” This model is purely phenomenological and establishes a robust framework around which a number of fundamental issues remain unresolved. In order to make further progress, what is our optimal choice of future strategy?top

Chris Smeenk: Gaining Access

Theories allow us to use accessible data to answer questions about other domains. In the initial stages of inquiry, a theory is often accepted based on its promise for extending our epistemic reach in this sense. Using theory to gain access to unobserverable phenomena poses an obvious risk of circularity: the theory specifies dependencies that hold between data and the target phenomena, and the data provide evidence when interpreted in light of the theory. How does the successful use of the theory to gain access support the theory itself? Demanding strong evidence at the outset, to even accept a theory as a starting point for inquiry, would be counter-productive. Detailed evidence for the theory can best be obtained by exploiting the theory in ongoing research. I will argue that physicists have often “trusted a theory” in this sense, despite relatively weak initial evidence. Borrowing the Cold War slogan, we should “trust” a theory in the sense of accepting it to gain access to new phenomena, provided that we can “verify” it by stringent tests in ongoing research. The crucial question regards whether the fundamental assumptions of the theory can be subjected to further tests. These tests are needed to justify taking a theory to capture the fundamental quantities and physical laws, rather than being merely compatible with a given body of data. I will argue that there are two distinctive obstacles to testing contemporary theories (such as inflationary cosmology): (1) lack of sufficient theoretical constraints (“anything goes”); (2) lack of independent observational and experimental access. The second point reflects our practical limitations. I take the first point, however, as grounds for doubting that the ideas under consideration qualify as a “theory” in the sense of earlier physical theories.top

Karim Thebault: What can we learn from Analogue Experiments?

In 1981 Unruh proposed that fluid mechanical experiments could be used to probe key aspects of the quantum phenomenology of black holes. In particular, he claimed that an analogue to Hawking radiation could be created within a fluid mechanical 'dumb hole'. Since then an entire sub-field of 'analogue gravity' has been created. In 2014 Steinhauer reported the experimental observation of Hawking radiation within a Bose-Einstein condensate dumb hole. What can we learn from such analogue experiments? In particular, can they provide confirmation of novel phenomena such as black hole Hawking radiation?top

Chris Wüthrich: Considering the Role of Information Theory in Fundamental Physics

Information theory presupposes the notion of an epistemic agent, such as a scientist or an idealized human. Despite that, information theory is increasingly invoked by physicists concerned with fundamental physics, physics at very high energies, or generally with the physics of situations in which even idealized epistemic agents cannot exist. In this talk, I shall try to determine the extent to which the application of information theory in those contexts is legitimate. I will illustrate my considerations using the case of black hole thermodynamics and Bekenstein's celebrated argument for his formula for the entropy of black holes. This example is particularly pertinent to the current workshop because it is widely accepted as 'empirical data' in notoriously deprived quantum gravity, even though the laws of black hole thermodynamics have so far evaded direct empirical confirmation.