All posts by Blake Stacey

Currently (Re)reading

I noticed this one when it first hit the arXivotubes a while back; now that it’s been officially published, it caught my eye again.

G. Rozhnova and A. Nunes, “Population dynamics on random networks: simulations and analytical models” Eur. Phys. J. B 74, 2 (2010): 235–42. arXiv:0907.0335.

Abstract: We study the phase diagram of the standard pair approximation equations for two different models in population dynamics, the susceptible-infective-recovered-susceptible model of infection spread and a predator-prey interaction model, on a network of homogeneous degree [tex]k[/tex]. These models have similar phase diagrams and represent two classes of systems for which noisy oscillations, still largely unexplained, are observed in nature. We show that for a certain range of the parameter [tex]k[/tex] both models exhibit an oscillatory phase in a region of parameter space that corresponds to weak driving. This oscillatory phase, however, disappears when [tex]k[/tex] is large. For [tex]k=3, 4[/tex], we compare the phase diagram of the standard pair approximation equations of both models with the results of simulations on regular random graphs of the same degree. We show that for parameter values in the oscillatory phase, and even for large system sizes, the simulations either die out or exhibit damped oscillations, depending on the initial conditions. We discuss this failure of the standard pair approximation model to capture even the qualitative behavior of the simulations on large regular random graphs and the relevance of the oscillatory phase in the pair approximation diagrams to explain the cycling behavior found in real populations.

Calloo! Callay!

My copy of Quantum Mechanics and Path Integrals by Feynman and Hibbs just arrived! If, say, David Griffiths’ textbook epitomizes the ordinary “vernacular” treatment of quantum mechanics, QMaPI is a classic unorthodox approach. Intended for students who already have a bit of background in the subject, it builds up the Lagrangian alternative to the Hamiltonian method, a highly useful idea when one goes on to study field theory, string theory or advanced statistical physics.

For years, this book was only available in beat-up old library copies and illegal DJVU files from Lithuania, but now, Dover has brought forth a new edition. I’m not certain on this, but it appears as if the book was so heavily pre-ordered that Amazon.com sold out of it the day it became available for purchase.

EDIT TO ADD: One erratum — on p. 364, Thorber should be Thornber.

Because the World Needs Nightmares

You know what the Scientifick Blogohedron needs more of? Well, besides introductions to basic subjects, so that we can be more than chatterbots reacting to whatever news story incenses us the most?

Gosh, you people are demanding.

No, I’m talking about nightmare fuel!

And as only children’s television can deliver. You remember Square One TV, right? It came on PBS in the afternoons, after Reading Rainbow and before Where in the World is Carmen Sandiego?. Like every other aspect of my generation’s formative years, it can be relived via the video tubes. Our lives have already been uploaded: the Singularity came and went, and we were all too busy arguing to notice.

Looking back, Reimy the Estimator Girl was fairly cute, and the “Angle Dance” is somewhat frightening in that in-1983-this-was-the-future way, but one bit of sheer irrational terror stands out. I refer, of course, to the mask which Reg E. Cathey wears in the title role of “Archimedes”:

LYRICS WITH LINKY GOODNESS:

Archimedes!
Archimedes!
A mathematician and scientist
Born in 287 BC
He lived in the city of Syracuse
On the island of Sicily

He said he could move the world
If he only had a place to stand
A fulcrum and a lever long
And the strength of an average man

He solved the problems of his days
Using math in amazing ways
His great work lives on today
Archimedes!
Archimedes!
Continue reading Because the World Needs Nightmares

Colony Collapse Disorder

Bug Girl takes on a recent paper which claimed to find evidence that cell phones have it in for beehives. The punchline:

This paper (which for a student research paper would be questionable) should not have been in a journal. It definitely should not have postulated a connection to Colony Collapse Disorder.
And it should never have made the levels of press exposure that it did.

Read the rest at her blag.

To Seek A Newer World, Etc.

Science After Sunclipse has moved to a new home with a more cheerful colour scheme, http://scienceblogs.com/sunclipse/.

Really, there’s not much more to say than that. They asked; I said I could only move if they upgraded their software to allow equation support; they said an upgrade was in the works; eventually, I decided to get situated over there so that somebody who knows how the software is meant to be used is around to get it going. These things don’t happen until somebody pushes. Like Dad always said, the bitchy wheel gets the grease.

Oh, and I figured I should profit, even if only a tiny bit, from any traffic which goes to the Carnival of Elitist Bastards.

Calling All Elitist Bastards

It lacks ten days until the next Carnival of Elitist Bastards. The fourth instalment of this more-august-by-the-minute institution will be hosted here, at Science After Sunclipse, on the thirtieth of August. Entries for consideration should be sent to elitistbastardscarnival at gmail dot com by the twenty-ninth. If you’ve got writing which exalts the intellect; which details the life of sophistication and subtlety; which illustrates, by example, the pleasure and virtue of knowledge justly won — eh bien, alors, this carnival is for you.

INCIDENTALLY, if you’re looking for something to uplift your spirit, I have just been informed that the TV series Cosmos (1980) is available for sale on iTunes. I don’t have iTunes, so I can’t tell you much more than that.

Interlude, with Cat

Want to know why I never get anything done? It’s not just because I find myself volunteered to write a one-act musical entitled Harry Crocker and the Plot of Holes. It’s also because Sean Carroll linked to a whole bunch of physics blogs, mine included, thereby obligating me to read through all their archives, and in the backblog of High Energy Mayhem I found a pointer to a talk by Krishna Rajagopal (my professor for third-term quantum — small world) on applying gauge/gravity duality to strongly coupled liquids like RHIC’s quark-gluon soups and cold fermionic atoms tuned to a Feshbach resonance. It still counts as “work” if the videos I’m watching online are about science, right? Look, if you use the “Flash presentation” option, it plays the video in one box and shows the slides in another! (Seriously, that’s a simple idea which is a very cool thing.)

Anyway, while I stuff my head with ideas I barely have the background to understand, and while I’m revising a paper so that it (superficially) meets PNAS standards, and while I try to re-learn the kinetic theory I forgot after that exam a few years back. . . Here’s a cat!

\"Extra credit\"? Professor Cat is amused.

(This one is for Zeno, and was recaptioned from here.)

Right Skill, Right Time

OK, first of all, let me say that there exist few better ways to procrastinate than reading an essay on time management. Terry Tao has lots of suggestions; following a fraction of them would probably make me a better human being. One item, though, is worth special attention:

It also makes good sense to invest a serious amount of time and effort into learning any skill that you are likely to use repeatedly in the future. A good example in mathematics is LaTeX: if you plan to write a lot of papers, it makes sense to go beyond the bare minimum of skill needed to jerry-rig whatever you need to write your paper, and go out and seriously learn how to make tables, figures, arrays, etc. Recently I’ve been playing with using prerecorded macros to type out a standard block of LaTeX code (e.g. \begin{theorem} … \end{theorem} \begin{proof} … \end{proof}) in a few keystrokes; the actual time saved per instance is probably minimal, but it presumably adds up over time, and in any event feels like you’re being efficient, which is good for morale (which becomes important when writing a long paper).

The risk is that you might end up a freak like me: after you’ve defined a few macros for moments and cumulants and partial derivatives, you get bitten by a radioactive backslash key and start typing all your class notes in LaTeX while the professor is lecturing. That aside, thinking about the proper time to learn these “accessory skills” puts me in the mood for a rant. (Well, what doesn’t?)

MIT did an exasperating thing with its undergraduate physics programme shortly before my time. The way I heard the story, they’d been afraid of losing students to other majors, so they dumbed down the sophomore-year classes (virtually excising Lagrangian mechanics, for example). We were left with a “waves and vibrations” class which was rather a junk drawer of different examples; a quantum-mechanics course which lacked guts and thus forsook glory; a decent introduction to statistical mechanics; and a relativity class which, hamstrung by fear of sophistication, also suffered because it lacked a singing Max Tegmark.
Continue reading Right Skill, Right Time

Monday BPSDB: Null Physics

BPSDBA fellow named Terry Witt has been advertising his self-published book, Our Undiscovered Universe, in places like Discover magazine and Scientific American. Unfortunately, the ad pages aren’t exactly peer-reviewed, or even cross-checked with a nearby grad student; being businesses, magazines naturally care about revenue. Upon examination, Our Undiscovered Universe turns out to be brimming over with crank physics and general nonsense. Ben Monreal, who was one of the intimidatingly smart people in the lab where I did my undergrad thesis, has weighed Witt’s “Null Physics” and found it wanting; his review of Our Undiscovered Universe is quite a good read.

Witt’s book starts with pseudomathematics before moving on to pseudophysics. As Ben explains,

Chapter 1 is where Witt lays out a series of “proofs” derived from what he calls the “Null Axiom”. That axiom is: “Existence sums to nonexistence” (pg. 28)—something that Witt calls self-evident after a page of invalid set theory. The central mistake, if I had to identify one, is the claim that “X does not exist” is the same as “everything except X exists”. This is utter baloney, whether in formal logic or in set theory or in daily experience.

Actually, as the book unfolds, Witt doesn’t appear to use this dead-in-the-water non-axiom for anything. He does, however, pile on more pseudomathematics:

Chapter 3 contains such gems as Theorem 3.1: “The Existence of Any Half of the Universe is Equal to the Nonexistence of the Other Half” (pg. 66) and Theorem 3.9: “The Time Required for Light to Traverse the Universe is Eternity, infinity/c” (pg. 72). I am not making this up. Witt throws around “infinity” as though it were an ordinary real number; he multiplies and divides by it, etc., with normal algebraic cancellation. This is complete nonsense; there are two centuries of mathematical thought figuring out the mathematical properties of infinity, and Witt’s approach is valid in exactly none of them. (Witt later explained on his online forum—currently disabled—that he’s reinvented all of the mathematics associated with “infinity”. His reasoning, if that’s what you call it, was that his new definition jibed with a grand idea about math being dependent on nature; it was an argument from incredulity.)

When Witt does finally get around to physics, five chapters into the book, he doesn’t do any better.
Continue reading Monday BPSDB: Null Physics

Quantum Woo, Part N

BPSDBTime for a little BPSDB! The redoubtable Ben Goldacre has the dirt on Bill Nelson’s “QXCI machine,” a device for “bioenergetic health auditing,” a medical procedure well-known among specialists as an essential step in the surgical removal of cash from wallets. Best of all, though, is what QXCI stands for: Quantum Xrroid Consciousness Interface. Now, quantum physics has jack to do with consciousness, but more importantly, “quantum xrroid” just sounds. . . painful. Like a blood boil growing inside your X, if you know what I mean.

Maybe a “quantum xrroid” means that your X is in a superposition of inflamed and not inflamed and only settles on one or the other option when your doctor examines it.

(Incidentally, I met the redoubtable Ben Goldacre in Vegas a few weeks ago — and thereby would hang a tale, if he weren’t still hoarding the photo evidence.)

Currently Reading

Random fun items currently floating up through the arXivotubes include the following. Exercise: find the shortest science-fiction story which can connect all these e-prints, visiting each node only once.

Robert H. Brandenberger, “String Gas Cosmology” (arXiv:0808.0746).

String gas cosmology is a string theory-based approach to early universe cosmology which is based on making use of robust features of string theory such as the existence of new states and new symmetries. A first goal of string gas cosmology is to understand how string theory can effect the earliest moments of cosmology before the effective field theory approach which underlies standard and inflationary cosmology becomes valid. String gas cosmology may also provide an alternative to the current standard paradigm of cosmology, the inflationary universe scenario. Here, the current status of string gas cosmology is reviewed.

Dimitri Skliros, Mark Hindmarsh, “Large Radius Hagedorn Regime in String Gas Cosmology” (arXiv:0712.1254, to be published in Phys. Rev. D).
Continue reading Currently Reading