Archive for September, 2007

Bobs ‘n’ bits

Sunday, September 30th, 2007

Other highlights from the physics preprint server this week

Is our Sun a Singleton?

Two Distinct Logical Types of Network Control in Gene Expression Profile

Spinflation for Preschoolers

Kinetic Exchange Models for Income and Wealth Distributions

How photons can escape into extra dimensions

New Insights into Traffic Dynamics

Why the first stars could have been filaments

Saturday, September 29th, 2007

Star formation in the early universe ain’t particularly well understood. Why should a pristine cloud of dust suddenly collapse to form a star?

One theory is that clumps of dark matter create gravitational wells into which the dust clouds collapse (although why dark matter should be clumpy and not smooth is anybody’s guess).

But Liang “Ang Li” Gao at Durham University in the UK says that in some theories dark matter might equally be drawn into filaments. In which case the first stars would have formed as filaments rather than spheres. So they’d look like giant lightbulbs hanging in the cocktail lounge of space.

Ref: Lighting the Universe with Filaments

Halting the horrible kilogram shrink

Friday, September 28th, 2007

The kilogram is a-shrinkin’ and ain’t nobody sure why. The problem is the way it is defined: the mass of a lump o’ metal stored in a vault in Paris. That’s no good cos a few atoms rub off each time it is picked up and others seem to fall off even when it ain’t picked up. In the last few years, it’s lost about the mass of a grain of sand.

Ain’t there a better way to define the kilogram? There sure is and shortage of em either. In November the world’s heavyweight experts are meeting in Paris to select the best definition by a vote or a toss of a coin or by some other method they ain’t told us about.

So between now and then expect to see plenty of elbowin’ n’ jostlin as the various definitions jockey for position. This week it’s the turn of Ronald “McDonald” Fox and Theodore “Over-the” Hill at Georgia Tech in Atlanta to pitch their definition.

They reckon that best way to define a kilogram is to fix the value of Avogadro’s constant, the number of atoms in 12 grams of carbon-12, at 84446886^3. That would make one gram exactly equal to the mass of 18 x 14074481^3 atoms of carbon-12.

It’s a good try but ain’t nobody gonna be happy with that definition. Why use carbon-12 and not silicon which is the current darling of most heavyweights in physics? And why rely on countin’ when you can define a kilogram in terms of its equivalent energy, thereby linking it via relativity to another fundamental: the Planck constant?

It’s all shapin up nicely for one helluva mudwrestle in Paris in November. All we need is a unit of hellraisin so we can work out the winner.

Ref: A Better Definition of the Kilogram

Galactic rings: the smoking gun for modified gravity

Thursday, September 27th, 2007

For a while now, them star gazers have been banging heads over the nature o’ gravity.

Here’s the problem: when you look at the way galaxies are a-spinnin and a-spiralin, there just ain’t enough gravity to hold em together. So either there is some hidden mass putting its gravitational shoulder to the wheel: the so-called dark matter. Or there’s something wrong with the 1/r^2 rule at large distances and gravity is stronger than we think at these scales.

In 1981, Mordehai “Mouse” Milgrom modified gravity to cope with this problem in a theory called MOdified Newtonian Dynamics or MOND. It says that gravity is a little stronger over galactic distances and this is what stops spinning galaxies from tearin’ themselves apart.

But the theory makes some strange predictions too. For example, it says that some galaxies should look as if they are surrounded by a ring of dark matter.

Earlier this year, the Hubble Space telescope found exactly that — a ring of dark matter around the galaxy cluster Cl 0024+17, which lies 5 billion light years from Earth. What astrogawpers actually saw were distorted images of galaxies behind Cl 0024+17 caused by the mass of Cl 0024+17 bendin’ light as it passed by, a phenomenon called gravitational lensing. The astrobods used these distortions to infer the distribution of mass around Cl 0024+17 and concluded it must have a ring of dark matter even though they ain’t actually seen a ring of any kind.

So Mouse Milgrom is a-shoutin and a-ravin from the roof tops: this is exactly what his theory predicts. Could it be enough to prove MOND once and for all?

Probably not. Gravitational lensing data is notoriously difficult to interpret so the work is by no means done and dusted. But even if it’s right, one swallow, don’t a summer make. He’s gonna need a lot more evidence before his ideas become mainstream.

Ref: : Rings and Shells of “Dark Matter” as MOND Artifacts

Public transport: the cities most vulnerable to attack

Wednesday, September 26th, 2007

Public transport networks are easy targets for terrorist attacks: anybody in London, Tokyo or Madrid will tell ya that. So Christian “Furbie” von Ferber at Coventry University in the UK and his buddies have decided to model a few of ‘em from the point of view of network theory and find out how vulnerable they are to various kinds of attack.

Public transport networks have many small world features. For example, it’s easy to get from one point in a city to another with only a few changes in transport. Now small world networks are known to be robust under random attack but particularly vulnerable against specific organised attacks.

So Furbie von Ferber has worked out how various systems break down when stations or connections between them are removed according to predetermined rules. So this ain’t a measure of how easy it is to attack the transport system but how well the buses ‘n’ trains run after an attack (and let’s face it, in my ‘hood they don’t run too good at the best o’ times).
Here’s the list of cities he’s chosen to model: Berlin, Dallas, Dusseldorf, Hamburg, Hong Kong, Istanbul, London, Los Angeles, Moscow, Paris, Rome, Sao Paulo, Sydney and Taipei.

Strangely, no room for Madrid or Tokyo, both of which have suffered serious attacks on their transport systems.

Turns out that Paris and Hong Kong look the most robust and Dallas (do they have public transport in Dallas?) looks the most vulnerable: shout BOO and it’ll grind to a halt.

What Furbie von Ferber fails to do is say what Dallas has gotta do to strengthen its network. Of course, that wouldn’t be in any way related to the potential for consultancy fees from this work ;)

Ref: Attack Vulnerability of Public Transport Networks

The world’s first visible light invisibility cloak

Tuesday, September 25th, 2007

Last year, the world went bonkers when scientists at Duke University in North Carolina unveiled the world’s first invisibility cloak. There weren’t no let up in the wall-to-wall media coverage it generate. And impressive though it was, what many reporters forgot to mention was that the cloak works only for microwaves at a single frequency and only in two dimensions.

So if yer happen to be a sandwich flat alien with microwave radar dishes for eyes then this cloak mighta fooled ya.

Now Igor “Smelly knees” Smolyaninov and buddies at the University of Maryland in College Park, have built the world’s first invisibility cloak that works at optical frequencies. The cloak is based on a design by Vladimir Shalaev from Purdue University who dreamt up a new method building invisibility cloaks that gets around some of the limitations that otherwise prevent them working at optical frequencies.

And of course, there are a few catches this time too. This cloak also works only in two dimensions, when the light is polarised in a particular way and over a scale of only a few micrometers. But from acrons to oak trees grow.

So if yer happento be a sandwich flat alien the size of a grain of pollen wearing polaroid sun glasses, this is the invisibility cloak for you.

What’s amazing, though, is the speed with which these eggheads are a-buildin and a-developin this technology. It ain’t no more than a handful of years since people said that optical invisibility cloaks ain’t possible, even in theory. Even the optimists were sayin only last year that it’d be 10 to 15 years before we see optical versions. So hats off to the Smelly Knees of Smolyaninov.

Ref: Electromagnetic Cloaking in the Visible Frequency Range

Einstein and the greatest scientific fraud of the 20th century

Monday, September 24th, 2007







Einstein swallowed it hook, line and sinker.


Poor old Einstein! But I know ya’ll will forgive him



How do black holes move?

Sunday, September 23rd, 2007

There’s more to that question than meets the eye.  Black holes ain’t like nothing else in the Universe, havin’ all kinds  strange quantum properties as well as some curious gravitational ones too. So when it comes to cruisin’ the cosmos, do black holes move like classical objects such as stars or like quantum objects such as photons?

Carol “Kilo” Herzeneberg, some kinda freelance scientist in Chicago, has done some calculatin’ n’ computin’ and come up with an answer.  She reckons that big black holes move-to-the-groove like stars and small black holes get-down-to-the-beat like photons. And the threshold between these behaviours occurs for a black hole about the size of a nucleon.

That might sound lil but a black hole that size would have mass of about 2 trillion kilograms (2 x 10^12 kg). That’s about the mass of Wyoming, which is about as close as you can get to a black hole on Earth.

Here’s something  for Kilo Herzenberg to Gedanken about: how many of these things are a-floatin’ and a-driftin’ round the cosmos and what’s the probability of one of them popping into existence anywhere near Earth in my life time?

Ref: How do Black Holes Move, as Quantum Objects or as Classical Objects?

Bits ‘n’ pieces

Saturday, September 22nd, 2007

The best of the rest from the physics preprint server

Analysing Google’s PageRank Algorithm

Designing Molecular Motors: a Beginner’s Guide

Seeking a Solution of the Pioneer Anomaly

Sims and music makers

Friday, September 21st, 2007








Any other suggestions?
