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

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

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.

—

[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.