Announcing my new (tentative) blog, Toy Universes.
Archive for the Science Category
Lisi posted this yesterday over at Physics Forums; I reproduce here:
Hello PF folk.
If you believe the Dirac equation in curved spacetime, and you believe Spin(10) grand unification, then a Spin(3,11) GraviGUT, acting on one generation of fermions as a 64 spinor, seems… inevitable.
Also, it’s pretty.
And it’s up to you whether or not to take seriously or not the observation that this whole structure fits in E8. Personally, I take it seriously. Slides are up for a talk I gave at Yale:
I am not certain whether it addresses Distler’s previous objections (as I am not certain whether the issue was even settled at that time– see here and here, which goes as far as I could follow. More (older) personal opinions can be found here, here and here in reverse chronological order).
Edit: I forgot to add. I do find the theory beautiful and interesting. I hope it can be properly tested.
Edit: Here are further links that are relevant to this post.
There is no “Theory of Everything” inside E8 by Jacques Distler and Skip Garibaldi.
Here is Distler’s blog entry on his paper.
There was a discussion of Distler and Garibaldi’s paper at Physics Forums some time ago.
There was also a discussion at n-Category Café some time ago.
From the PhilPhys – Philosophy of Physics Mail Group, I received this (and I share the same thoughts on its rationale — “philosophical theses and arguments should be just as clear and precise as scientific ones”):
Tuesday 13 April 2010
Tilburg University, The Netherlands
Various philosophers of the past – and many philosophers of today – believe that there can be real progress in philosophy and that such progress is facilitated crucially by a close interaction between philosophy and the sciences. “Scientific Philosophy” maintains that philosophical theses and arguments should be just as clear and precise as scientific ones; philosophers ought to build theories and models much as scientists do; and the application of mathematical methods as well as input from empirical studies are often necessary in order to gain new insights into old philosophical questions and to progress to new and deeper ones. This workshop will address what Scientific Philosophy is all about, what it has in common with science and where it might diverge from it, what we can learn from its historical successes and failures, and, most importantly, how we should assess its future prospects.
The invited speakers include:
Michael Friedman, Stanford
Christopher Hitchcock, Caltech
Volker Peckhaus, Paderborn
Stephan Hartmann, Tilburg
Hannes Leitgeb, Bristol
Jan Sprenger, Tilburg
There’ll be three to four slots for contributed papers. If you are interested in presenting something, please send an extended abstract of up to 1500 words to TiLPS@uvt.nl by 15 January 2010. Decisions will be made by 1 February 2010.
There is no registration fee. However, participants have to register by sending an email to TiLPS@uvt.nl by 15 March 2010.
The workshop takes place on the day before the conference “The Future of Philosophy of Science”. Check.
Roger Penrose Says: Physics Is Wrong, From String Theory to Quantum Mechanics.
Yes, this is true. I have just written my non-FQXi Essay, in the sense that I have not submitted it to the presently running edition, now featuring the theme “What’s Ultimately Possible in Physics?”.
You may be wondering why I have not submitted it. After consideration, I have found some reasons, but let me tell you only the short one: I concluded that it is undignified to compete for a prize on speculation.
But I have written my short essay anyway. It took me only a couple of hours, and I must point out that it is not a scientific work, nor a philosophical work. It is a speculative work. But this fact does not mean that it is not a serious speculative work.
So here it is, in case you are interested:
Title: When Response Nullifies
Author: Christine Córdula Dantas
3 pages, 72 Kb, pdf format
Update 05 Oct 2009: A few typos, corrections, stylistic improvements and additions were made. Please replace previous version with the current one. Other corrections are welcomed. Thanks!
You will find an intriguing paper on today’s issue of Nature (subscription required):
It was recently discovered that the mean dark matter surface density within one dark halo scale-length (the radius within which the volume density profile of dark matter remains approximately flat) is constant across a wide range of galaxies. This scaling relation holds for galaxies spanning a luminosity range of 14 magnitudes and the whole Hubble sequence. Here we report that the luminous matter surface density is also constant within one scale-length of the dark halo. This means that the gravitational acceleration generated by the luminous component in galaxies is always the same at this radius. Although the total luminous-to-dark matter ratio is not constant, within one halo scale-length it is constant. Our finding can be interpreted as a close correlation between the enclosed surface densities of luminous and dark matter in galaxies.
See also the Editor’s Summary.
As noted by the authors:
A large central luminous density thus implies a large core radius, and in turn a small central dark matter density. This precise balance must be the result of some unknown, fine-tuned process in galaxy formation, because it is a priori difficult to envisage how such relations between dark and baryonic galaxy parameters can be achieved across galaxies that have experienced significantly different evolutionary histories, including numbers of mergers, baryon cooling or feedback from supernova-driven winds.
Update: I thought it would be interesting to point to a previous work of mine and collaborators (back from 2003) which shows that the central dark matter halo densities for a large data sample ranging from dwarf ellipticals to clusters of galaxies, based on the application of the two-component virial theorem (2VT) to these systems, do not show universality. Only the abstract is available:
Title: The case against scale-invariant central halo densities: implications for the self-interacting dark matter scenarios in the context of the two-component virial theorem
Authors: Ribeiro, A. L. B.; Dantas, C. C.; Capelato, H. V.; Carvalho, R. R.
Publication: Boletim da Sociedade Astronômica Brasileira (ISSN 0101-3440), vol.23, no.1, p. 163-163
I will attempt to find the poster PDF and make it opportunely available here.
More on the 2VT can be found here:
Title: The Two-Component Virial Theorem and the Physical Properties of Stellar Systems
Authors: Dantas, Christine C.; Ribeiro, André L. B.; Capelato, Hugo V.; de Carvalho, Reinaldo R.
Publication: The Astrophysical Journal, Volume 528, Issue 1, pp. L5-L8.
Update 2: Interesting discussions here.
Here is the Einstein’s quote that I have previously promissed to post:
If, then, it is true that the axiomatic basis of theoretical physics cannot be extracted from experience but must be freely invented, can we ever hope to find the right way? Nay, more, has this right way any existence outside our illusions? Can we hope to be guided safely by experience at all when there exist theories (such as classical mechanics) which to a large extent do justice to experience, without getting to the root of the matter? I answer without hesitation that there is, in my opinion, a right way, and that we are capable of finding it. Our experience hitherto justifies us in believing that nature is the realization of the simplest conceivable mathematical ideas. I am convinced that we can discover by means of pure mathematical constructions the concepts and the laws connecting them with each other, which furnish the key to the understanding of natural phenomena. Experience may suggest the appropriate mathematical concepts, but they most certainly cannot be deduced from it. Experience remains, of course, the sole criterion of the physical utility of a mathematical construction. But the creative principle resides in mathematics. In a certain sense, therefore I hold it true that pure thought can grasp reality, as the ancients dreamed.
(Einstein, 1954, Ideas and Opinions, quoted from Schweber, “Einstein and Oppenheimer: the meaning of genius”)
I think the above quote by Einstein is remarkable is several ways, specially the privileged role of creativity and freedom of the human mind expressed in mathematical language, but at the same time the recognition of experience as the sole criterion of the physical utility of such mathematical constructions.
(The above quote, according to Schweber, was an observation by Einstein on Hilbert’s program of axiomatization of physics.)
How Far Are We from the Quantum Theory of Gravity? [arxiv:0907.4238]
R. P. Woodard (University of Florida)
Abstract: I give a pedagogical explanation of what it is about quantization that makes general relativity go from being a nearly perfect classical theory to a very problematic quantum one. I also explain why some quantization of gravity is unavoidable, why quantum field theories have divergences, why the divergences of quantum general relativity are worse than those of the other forces, what physicists think this means and what they might do with a consistent theory of quantum gravity if they had one. Finally, I discuss the quantum gravitational data that have recently become available from cosmology.
Comments: 106 page review article solicited by Reports on Progress in Physics
Nobel Lectures from the 2008 winners have been recently published in Reviews of Modern Physics and are freely available:
Nobel Lecture: What does CP violation tell us?
Nobel Lecture: CP violation and flavor mixing
Nobel Lecture: Spontaneous symmetry breaking in particle physics: A case of cross fertilization
I make here publically available my letter to Sabine (Backreaction) concerning ou recent exchange of comments over at her blog. I will not post her letter because it was personally addressed to me. However, since my letter was general enough, and perhaps elucidative enough, here it is.
Thanks for your email. I think that it is quite possible that I have not expressed myself the best possible way. My comments were an attempt at a criticism on the topics based on those that you have mentioned in your post, which I had assumed to be representative of the conference. All I want to say is that I do not care what people want to work on, but I am tired to see professional scientists working on non-scientific issues (viz., those which the scientific method is not applied) as scientific. I consider this very non-ehtical and a dis-service to the public.
Theory must provide a means to experimental verification (in principle, at least), if not, you have an unproven hypothesis. Some people at the frontier of physics are not taking care of this very important concept and elevate their unproven hypotheses to principles of truth, from which they base all their subsequent work. We cannot rely on our subjective judgements to consider some theory acceptable or not: this is why the scientific method exists as a pillar for science.
I think FQXi is perfect as a funding agency for non-mainstream, alternative approaches, which nevertheless are perfectly scientific. Also, philosophical themes (which is a completely different class of discipline, with its own epistemological rules). However, it appears that this question is not clear enough.
I am glad to learn that your work was well received. I hope that you have understood that my criticism was not aimed at your work on phenomenology, which is evidently scientific enough.
EDIT: Sabine writes that “most of them [the projects] eventually won’t lead anywhere – that being the nature of the business”. The problem is not that some projects lead nowhere, but that any non-scientific project leads nowhere by construction. If one’s work is based on an unproven hypothesis which is elevated to a principle of truth, from which all subsequent work is based, then it is highly probable that it will indeed lead nowhere. Or the conclusions will be most probably false.
She also insists that I point to specific projects that I consider non-scientific. As I already emphasized, my comments were based on the themes that she highlighted on her post, not on the program, which was not made avaliable on the FQXi site at the time of the postings. In any case, I leave the excercise to the reader to apply the scientific method and find out the answer by him/herself.
Dear Traveller of the Future,
If for some reason this set of electronic ramblings reach you, I salute you.
But my salute is embeded in deep sorrow. I have just realized that I am a living testimony of the end of science — a human activity arduously conceived during centuries in order to objectively probe nature into her deepest substrate: a triumph of the human mind.
For some reason, many people engaged into such a dignified activity slowly gave up on the arduous road, and chose the easiest paths, which unfortunately often lead to the swampy terrain of incertitude and ignorance.
Although there are still many advancements, specially technical ones, there is Death waiting at the frontier.
Science is no longer scientific!
Best wishes to you, Traveller of the Future, to whom the idea of what was gained and what was lost may never be perceived, but I still hope that the starlight inspire your soul, somehow.
PS- This anecdote was inspired by a discussion developed here.
P. W. Anderson
I reread Concepts in Solids with both pride and embarrassment. Pride, both because it was this set of lectures which inspired Brian Josephson to invent his effect — not every book can point to the precise Nobel prize it inspired — and because l did, in a very brief space, manage to touch some of the key topics which are still not adequately covered in your average solid state theory book. For instance, it is shocking that the main texts used in this country still do not touch on the Mott transition or the “Magnetic State.” I was aiming at conceptual, not mechanical physics, and I hope I got there.
Embarrassment, because after all, there has been 30 years of physics since then. For instance, I note that I guessed absolutely wrong in dismissing tight-binding theory out of hand: it has not yet totally coine into its own but it is, in my present opinion, the right way to think about most bonding in solids. I am not ashamed of skipping localization – only Mott was interested in it, and neither of us yet knew where to go next. I was prescient about broken symmetry — as Josephson realized — but left out phase transitions, as I myself noted.
Nonetheless, I believe that the average student will still be harmed less by this book than by any number of other books I should not name, and I welcome the reissuance.
Finally, an interesting paper on dark energy.
Cosmographic analysis of dark energy [http://arxiv.org/abs/0906.5407]
Authors: Matt Visser (Victoria University of Wellington), Celine Cattoen (Victoria University of Wellington)
Abstract: The Hubble relation between distance and redshift is a purely cosmographic relation that depends only on the symmetries of a FLRW spacetime, but does not intrinsically make any dynamical assumptions. This suggests that it should be possible to estimate the parameters defining the Hubble relation without making any dynamical assumptions. To test this idea, we perform a number of inter-related cosmographic fits to the legacy05 and gold06 supernova datasets, paying careful attention to the systematic uncertainties. Based on this supernova data, the “preponderance of evidence” certainly suggests an accelerating universe. However we would argue that (unless one uses additional dynamical and observational information, and makes additional theoretical assumptions) this conclusion is not currently supported “beyond reasonable doubt”. As part of the analysis we develop two particularly transparent graphical representations of the redshift-distance relation — representations in which acceleration versus deceleration reduces to the question of whether the relevant graph slopes up or down.
There is a new article by Lee Smolin at Physicsworld.com, “The unique universe“, where he exposes his metaphysical position on the multiverse and the notion of time as fundamental, not emergent.
My thoughts are close to Smolin on those issues, see my previous post on the multiverse here:
and, in a funny side, my cartoon here:
Concerning the question whether time is fundamental or not, my philosophical position is that it is fundamental, although there is a facet of it which can be made artificially emergent. See my essay on concurrent time here .
Classical Mathematical Physics: Dynamical Systems and Field Theories
by Walter Thirring [son of Hans Thirring, who was the co-discoverer of the Lense-Thirring frame effect in general relativity]
(Preface to the second edition).
Since the first edition already contained plenty of material for a one-semester course, new material was added only when some of the original could be dropped or simplified. (…) This involved not only the use of more refined mathematical tools, but also a reevaluation of the word fundamental. What was earlier dismissed as a grubby calculation is now seen as the consequence of a deep principle. Even Kepler’s laws, which determine the radii of the planetary orbits, and which used to be passed over in silence as mystical nonsense, seem to point the way to a truth unattainable by superficial observation: The ratios of the radii of Platonic solids to the radii of inscribed Platonic solids are irrational, but satisfy algebraic equations of lower order. These irrational numbers are precisely the ones that are the least well approximated by rationals, and orbits with radii having these ratios are the most robust against each other’s perturbations, since they are the least affected by resonance effects.
Interesting results coming from Gravity Probe B, including a better understanding of the discrepancies between the four gyroscopes, leading to better data on geodetic effect and frame dragging effect in all four gyroscopes.
Also, a complete document “Gravity Probe B Science Results—NASA Final Report” is now available from their site.
[Via PhilPhys - Philosophy of Physics Mail Group]
The London School of Economics and Political Science announces that this year’s Lakatos Award, of £10,000 for an outstanding contribution to the philosophy of science, goes to:
Richard Healey (University of Arizona), for his book Gauging What’s Real: The Conceptual Foundations of Contemporary Gauge Theories (Oxford University Press, 2007).
He will visit LSE to receive the Award and give the Award Public Lecture during summer term, 2009.
Gauge theories have provided our most successful representations of the fundamental forces of Nature. How though do such representations work to tell us what kind of world our gauge theories reveal to us? Professor Healey’s book describes the representations provided by gauge theories in both classical and quantum physics. He argues that evidence for classical gauge theories of forces (other than gravity) gives us reason to believe that loops rather than points are the locations of fundamental properties. As well as exploring the prospects of extending this conclusion to the quantum gauge theories of the Standard Model of elementary particle physics, the book assesses the difficulties faced by attempts to base such ontological conclusions on the success of these theories.
The Lakatos Award is given for an outstanding contribution to the philosophy of science, widely interpreted, in the form of a book published in English during the previous five years. It was made possible by a generous endowment from the Latsis Foundation. The Award is in memory of the former LSE professor, Imre Lakatos, and is administered by an international Management Committee organised from the LSE.
The Committee, chaired by John Worrall, decides the outcome of the Award competition on the advice of an international, independent and anonymous panel of Selectors.
An interesting interview with Carver Mead, author of the (unconventional) Collective Electrodynamics: Quantum Foundations of Electromagnetism.
THE SCIENCE AND PHILOSOPHY OF UNCONVENTIONAL COMPUTING (SPUC09)
Cambridge (UK), March 23-25, 2009
SECOND CALL FOR PAPERS
We welcome submissions on topics normally classified under ‘natural computing’ or ‘unconventional computing’ or ‘hypercomputing’ including (but not restricted to) quantum computing, relativistic computing, biology-based computing, analogue computing, and also submissions on the philosophical implications of these new fields for topics including (but again not restricted to) philosophy of mind, philosophy of mathematics, the Church-Turing thesis.
Each presentation should last no more than 30 minutes; a further 10 minutes will be allowed for discussion.
Those wishing to make a presentation should submit by email a 250-word abstract of their paper to Mark Hogarth (email@example.com); enquiries to the same.
Registration fee (yet to be fixed) will be around £100.
Student bursaries are available.
Conference website: http://web.mac.com/mhogarth/Site/SPUC_Conference.html
Mark Hogarth (Cambridge, UK)
CONFIRMED INVITED SPEAKERS
Selmer Brinsjord (New York, USA))
Jeff Barrett (Irvine, USA)
Philip Welch (Bristol, UK)
Tim Button (Harvard, USA)
Cristian Calude (Auckland, New Zealand))
István Németi (Budapest, Hungry)
Benjamin Wells (San Francisco, USA)
Hajnal Andréka (Budapest, Hungry)
Apostolos Syropoulos (Xanthi, Greece)
Susan Stepney (York, UK)
Bruce MacLennan (Tennessee, USA)
Peter Kugel (Boston, USA)
Mark Sprevak (Cambridge, UK)
Selim Akl (Kingston, Canada)
José Félix Costa (Swansea, UK)
Mike Stannett (Sheffield, UK)
John Tucker (Swansea, UK)
Barry Cooper (Leeds, UK)
Sponsored by EPSRC through HyperNet (the Hypercomputation Research Network, EP/E064183/1)
I am writing to ask for your assistance in drawing the attention of exceptional, highly motivated students to the Perimeter Scholars International (PSI) program.
PSI is an innovative, Masters level course designed to prepare students for cutting-edge research in theoretical physics. It provides a broad overview, allowing students to choose their preferred specialisation, and extensive tuition in formulating and solving interesting problems.
The due date for applications is February 1st: applications received after this date may still be considered but only as long as places remain available.
A number of outstanding lecturers have already signed up to teach, including for example Yakir Aharonov, Phil Anderson, Matt Choptuik, Nima Arkani-Hamed, John Cardy, Ruth Gregory, Michael Peskin, Sid Redner, Xiao-Gang Wen, and a number of Perimeter Institute research faculty. They will be supported by full-time tutors dedicated to the course.
All accepted students will be fully supported.
For further details, see www.perimeterscholars.org.
Thank you in advance for helping us to make this exciting opportunity known as widely as possible.
With my best wishes,
Perimeter Institute for Theoretical Physics
Waterloo, Ontario, Canada
This appears to be an interesting news coming from the ARCADE 2 experiment. I quote from their recent paper “Interpretation of the Extragalactic Radio Background”, M. Seiffert et al. 2008, ApJ, submitted (available here):
We have presented evidence for isotropic radio emission detected by ARCADE 2 beyond what can be explained by Galactic emission and the unresolved emission from the known population of discrete sources. The excess emission is consistent with a power law, with an index of −2.56, which is significantly flatter that what might be expected from an unidentified population of faint, diffuse, steep spectrum (index ∼ −2.7) radio sources associated with star-forming galaxies. We have also examined and placed limits on two classes of spectral distortions to the CMB. Such distortions are not supported by the data and cannot explain the excess emission (…)
We conclude that the three most important sources of error, Galactic emission, instrumental systematic errors, and radio emission from the faint end of the distribution of known sources, are unlikely to be sufficient to explain the excess emission presented here.
Two of the authors are Brazilian colleagues working at the Astrophysics Division at INPE (National Institute for Space Research, Brazil).
[Via Peter Woit]
I have submitted an essay to the FQXi competition. If you are interested in reading it, click here.
Title: On the Nature of Time – Or Why Does Nature Abhor Deadlocks?
This essay aims at introducing a novel point of view on the nature of time, inspired by a synthesis of three seemingly unrelated concepts: Bergson’s notion of duration, Dijkstra’s notion of concurrency, and Mach’s notion of inertia.
Edit (June 9th 2009): Apparently, the essays on the nature of time are no longer available at the FQXi site. I have made a very few small corrections and modifications in my essay and a new version is available here (pdf file).