New blog

Announcing my new (tentative) blog, Toy Universes.

Blog is shutdown.

All contents will be available as far as there is a host out there in the internet “cloud” making it accessible. I will not delete this blog, so you may be able to access the archives for some time, I guess.

Comments will be shutdown, however.

Thanks and good-bye!

News on Gravity Probe B – Nov. 2009

Read mission status below:

Closing in on Einstein: Frame-Dragging Clearly Visible

News on Garrett Lisi’s E8 theory

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:

http://www.liegroups.org/zuckerman/slides.html

Best,
Garrett

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.

Quantum Gravity quote

A pessimist might say that combining string theory and loop quantum gravity is like combining epicycles and aether.

(John Baez, TWF281)

Connexions

Just learned about this:

Connexions is:

a place to view and share educational material made of small knowledge chunks called modules that can be organized as courses, books, reports, etc. Anyone may view or contribute:

authors create and collaborate
instructors rapidly build and share custom collections
learners find and explore content

This sounds a formidable initiative.

Scientific Philosophy

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”):

****************************************************************************************

Workshop on

Scientific Philosophy: Past and Future

Tuesday 13 April 2010

Tilburg University, The Netherlands

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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

Organizers:

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.

The Potential Nobel

Fellow blogger Clifford from Asymptotia suggests:

How about alternative prizes for this week’s categories? Prizes to work (or authors of the work) that while extremely promising, certainly has not met the promise yet (for which the jury is still out since the work is not done).

Very easy.

The Potential Nobel (physics, literature, peace?) goes to… me.

When I was 17 years-old, I thought I had so much to realize. Today, much older and wiser, I certainly have not yet realized even a small fraction of my earlier envisions. Nor I think I will improve much on that. I have not yet done the work of my life. I do not even know exactly what it is. My opus is pure potential. It will always be. Life is too short. And I am not as clever as I once thought.

I deserve the Potential Nobel prize.

God said “Let Penrose be” and all was wrong

Roger Penrose Says: Physics Is Wrong, From String Theory to Quantum Mechanics.

Nobel Prize Physics 2009 – Results here!

The Nobel Prize in Physics 2009

Charles K. Kao – “for groundbreaking achievements concerning the transmission of light in fibers for optical communication” (1/2 Prize);

AND

Willard S. Boyle and George E. Smith – “for the invention of an imaging semiconductor circuit – the CCD sensor” (1/4 Prize each).

Congratulations!

My non-FQXi Essay

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!

[English][Portuguese] Announcement / Aviso

[English] I have decided to run a separate blog on mathematics for Brazilian students, the Matemática Replay!. This blog [Theorema Egregium] continues with the usual material. Thanks.

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[Português] Eu decidi manter um blog separado sobre matemática para estudantes Brasileiros, o Matemática Replay!. Este blog [Theorema Egregium] continua com o material usual. Obrigada.

[Português] Problemas de Matemática do 2o. Grau

Este “post” dá início (tentativamente) a uma série que irá contemplar problemas de matemática para alunos do 2o. grau (ensino médio brasileiro). O público-alvo é de alunos que estão passando por reais dificuldades em resolver problemas. As soluções serão apresentadas detalhadamente e, em seguida, serão propostos problemas similares.

————
Nos problemas do post de hoje, você precisará ter os conceitos de progressão artimética e de números complexos.
————

Você pode baixar gratuitamente os exercícios no link abaixo:

Problemas de Matemática do 2o. Grau – Como Resolvê-los Passo à Passo – Parte 1
[documento PDF, 3 páginas, 100Kb]

Atenção para Copyright na última página!

AVISO: Agora tenho um blog só de matemática, acesse: Matemática Replay!

Universality of galactic surface densities

You will find an intriguing paper on today’s issue of Nature (subscription required):

Universality of galactic surface densities within one dark halo scale-length by Gentile et al.

Abstract:

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.

First news from quantum gravity school in Corfu

Mathematical physicist John Baez has recently posted his “This Week’s Finds in Mathematical Physics” (Week 280) reporting his impressions of the school. It is a very nice summary and worth reading. See also this thread over at Physics Forums.

[Português] Como resolver problemas de matemática?

Escrevi um tutorial de matemática para alunos do ensino fundamental brasileiro, para o 5o. ano (ou 4a. série, pelo regimento anterior), que pode ser baixado gratuitamente aqui.

Dicas de Matemática: Como resolver problemas?
Autora: Christine Córdula Dantas
Tamanho: 1.3 Mb
Número de páginas: 33

AVISO: Agora tenho um blog só de matemática, acesse: Matemática Replay!

[Português] Tutorial de Eletromagnetismo

Está disponível um tutorial de eletromagnetismo em nível de graduação, escrito em português, gratuitamente no site do arxiv:

http://arxiv.org/abs/0906.2796

Questions and Answers about Perturbative quantum gravity

R. Woodard from the University of Florida will be talking at the International Loop Quantum Gravity Seminar tomorrow (September 22nd). His slides are already available.

See also a previous post.

News from LIGO

An upper limit on the stochastic gravitational-wave background of cosmological origin
The LIGO Scientific Collaboration & The Virgo Collaboration
Nature 460, 990-994 (20 August 2009)

Abstract

A stochastic background of gravitational waves is expected to arise from a superposition of a large number of unresolved gravitational-wave sources of astrophysical and cosmological origin. It should carry unique signatures from the earliest epochs in the evolution of the Universe, inaccessible to standard astrophysical observations. Direct measurements of the amplitude of this background are therefore of fundamental importance for understanding the evolution of the Universe when it was younger than one minute. Here we report limits on the amplitude of the stochastic gravitational-wave background using the data from a two-year science run of the Laser Interferometer Gravitational-wave Observatory (LIGO). Our result constrains the energy density of the stochastic gravitational-wave background normalized by the critical energy density of the Universe, in the frequency band around 100 Hz, to be <6.9 times 10^{-6} at 95% confidence. The data rule out models of early Universe evolution with relatively large equation-of-state parameter, as well as cosmic (super)string models with relatively small string tension that are favoured in some string theory models. This search for the stochastic background improves on the indirect limits from Big Bang nucleosynthesis and cosmic microwave background at 100 Hz.

Update: Now freely available in the arxiv. [0910.5772]

News from Fermi (formerly GLAST)

[Via Backreaction].

[arxiv:0908.1832]

Testing Einstein’s special relativity with Fermi’s short hard gamma-ray burst GRB090510
Authors: Fermi GBM/LAT Collaborations

Abstract: Gamma-ray bursts (GRBs) are the most powerful explosions in the universe and probe physics under extreme conditions. GRBs divide into two classes, of short and long duration, thought to originate from different types of progenitor systems. The physics of their gamma-ray emission is still poorly known, over 40 years after their discovery, but may be probed by their highest-energy photons. Here we report the first detection of high-energy emission from a short GRB with measured redshift, GRB 090510, using the Fermi Gamma-ray Space Telescope. We detect for the first time a GRB prompt spectrum with a significant deviation from the Band function. This can be interpreted as two distinct spectral components, which challenge the prevailing gamma-ray emission mechanism: synchrotron – synchrotron self-Compton. The detection of a 31 GeV photon during the first second sets the highest lower limit on a GRB outflow Lorentz factor, of >1200, suggesting that the outflows powering short GRBs are at least as highly relativistic as those powering long GRBs. Even more importantly, this photon sets limits on a possible linear energy dependence of the propagation speed of photons (Lorentz-invariance violation) requiring for the first time a quantum-gravity mass scale significantly above the Planck mass.

Edit: Discussions are also going on over at Physics Forums.

A Brief Introduction to Loop Quantum Cosmology

A Brief Introduction to Loop Quantum Cosmology [arxiv:0907.5160]
Authors: Guillermo A. Mena Marugan

Abstract: In recent years, Loop Quantum Gravity has emerged as a solid candidate for a nonperturbative quantum theory of General Relativity. It is a background independent theory based on a description of the gravitational field in terms of holonomies and fluxes. In order to discuss its physical implications, a lot of attention has been paid to the application of the quantization techniques of Loop Quantum Gravity to symmetry reduced models with cosmological solutions, a line of research that has been called Loop Quantum Cosmology. We summarize its fundamentals and the main differences with respect to the more conventional quantization approaches employed in cosmology until now. In addition, we comment on the most important results that have been obtained in Loop Quantum Cosmology by analyzing simple homogeneous and isotropic models. These results include the resolution of the classical big-bang singularity, which is replaced by a quantum bounce.

Comments: 15 pages, published in AIP Conference Proceedings, Volume 1130, Geometry and Physics: XVII International Fall Workshop on Geometry and Physics

Einstein on axiomatization of physics

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.

[my italics]

(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?

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 2008 Lectures

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?
Toshihide Maskawa

Nobel Lecture: CP violation and flavor mixing
Makoto Kobayashi

Nobel Lecture: Spontaneous symmetry breaking in particle physics: A case of cross fertilization
Yoichiro Nambu

Recent impact on Jupiter

Steinn Sigurðsson has an interesting post about this recent event over at his blog, Dynamics of Cats.

“New Look” and Twitter

I hope you like the “new look” of Theorema Egregium; notice also that I am “twittering” now– see the side bar. Just experimentally.

Open letter

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.

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Dear Sabine,

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.

Best regards,
Christine
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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.

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Related posts:

Smolin Against the Timeless Multiverse

The Universe

Universes Everywhere

What is science for you? Up to 50 words

What is science – for me

Science is no longer scientific

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.

Christine

PS- This anecdote was inspired by a discussion developed here.

Favorite Prefaces V

Concepts in Solids

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.

Your brain on the edge of chaos

No news to me. I’ve always suspected that. Now, seriously:

Though much of the time it [the brain] runs in an orderly and stable way, every now and again it suddenly and unpredictably lurches into a blizzard of noise.

Neuroscientists have long suspected as much. Only recently, however, have they come up with proof that brains work this way. Now they are trying to work out why. Some believe that near-chaotic states may be crucial to memory, and could explain why some people are smarter than others.

Read whole article by the New Scientist magazine:

Disorderly genius: How chaos drives the brain