Archive for September, 2007

The surprise at the bottom of the infinite quantum well

Thursday, September 20th, 2007

Who remembers the quantum particle trapped in an infinite square well? Ya’ll probably still havin nightmares about it. Turns out there is an interesting new take on this problem that has physicists all a-sea.

For any bods out there who ain’t familiar with it, the simplest problem in any course of quantum mechanics is this: what happens to a quantum particle trapped in a well of a particular width but with infinite sides. The answer is that the probability of finding the particle in any part of the well has a wavelike distribution. This is every physics undergraduate’s shocking introduction to the wave-like behaviour of quantum particles.

It’s straightforward to tackle but start tinkerin’ with this problem and yer get some interesting behaviour. Claude “Acute” Aslangul at the Laboratoire de Physique Theorique de la Matiere Condensee in Paris, asks what happens when you suddenly increase the width of the quantum well.

His answer is that the probability distribution adopts a weird and very un-wavelike pattern and that this pattern is independent of the size of the expansion.

This is a piece o’ good ol’ fashioned physics and here’s a good ol’ fashioned problem for ya: what on Earth is going on here? How can we explain this unwave-like behaviour in physical terms?

Ref: Surprises in the Suddenly-Expanded Infinite Well

“Solar rainstorm” filled the first oceans

Wednesday, September 19th, 2007

Astrogeologists have been a-scratchin their egg-shapes for a good few years now about the origin of the oceans. Where did all that wet stuff come from?

This is how they are workin it out: they look for somewhere else in the solar system that has water with a similar make up and assume ours came from the same place. The thing to look for, say them astroeggs, is the isotopic make up of the water: the ratio of hydrogen to deuterium.

It turns out there are three sources of water in the solar system. Comets carry water which has about twice the ratio of hydrogen to deuterium. Asteroids of the carbonaceous chondrite variety also contain water which has the same ratio as Earth’s oceans. And the solar nebula, the disk of gas and dust from which the solar system formed, has water in which the ratio is 7 times less than on Earth.

On that basis, the answer is obvious: the oceans musta come from chunks of carbonaceous chondrites. The thinkin’ is that these chunks clumped together as the Earth formed, generating heat that evaporated any water they contained. When everything cooled down, this condensed to form the oceans.

Not so fast, cowboy, says Hidenori “Hiddena” Genda at the Tokyo Institute of Technology. He and a buddy have dashed off some impressive analysis of the Earth’s early atmosphere which is thought to have been rich in hydrogen.

Now hydrogen escapes into space more readily than its heavier isotopic cousins which woulda left the atmosphere rich in deuterium. When that happened, deuterium musta been pumped into the oceans, dramatically increasing the ratio of hydrogen to deuterium.

But by how much? Hidden Agenda says that if the oceans came from the solar nebula, this process would have increased the ratio of hydrogen to deuterium in sea water to just what we see today.

This ain’t conclusive but it is compelling. If correct, it means the oceans are the result of a monstrous solar rainstorm that musta left Earth a-rinsed and awash at least 3.8 billion years ago after it passed through a giant cloud of the wet stuff. Kinda biblical, doncha think?

Ref: Origin of the Ocean on the Earth: Early Evolution of Water D/H in a Hydrogen-rich Atmosphere

Sensor fusion improves onboard navigation

Tuesday, September 18th, 2007

Sensor fusion is the tricky task of combining different data streams to give an output that is better than the sum of the parts. Let me tell ya, it ain’t easy. Too often, too much data just confuses things.

So hats off to Cherif “Very” Smaili at The French Institute for Research in Computer Science and Control in Nancy and his mates who have squeezed, merged and melded the data from several sources to improve the way autonomous navigation systems determine where they are.

Anybody who’s ever used GPS knows that at best, it provides intermittent data on position and direction. So Very Smaili has combined GPS information with data from the car’s odometer to give continuous navigation infomation.

If the GPS signal goes down, the onboard computer works out where it is on a digital map using the distance travelled by the car.

Of course, that still leaves some uncertainty should the car come to a junction – there ain’t no way of telling from distance measurements which way the vehicle has gone. So the onboard keeps every possibility open until it can unambiguously work out where it is.

That looks simple and useful, which ain’t a bad combination.

Ref: Multi-Sensor Fusion Method using Dynamic Bayesian Network for Precise Vehicle Localization and Road Matching

And now the earthquake forecaste…

Monday, September 17th, 2007

Ya’ll know there is no way to predict when the Gods plan to set the ground a-tremblin and a-rumblin.

But a group of Italian geophysicists are sayin that the conventional thinkin about earthquakes may need a good shakin itself and that earthquake prediction is not as far fetched as ya’ll thought.

In fact, rumble merchants have long known that certain aspects of earthquake behaviour are highly predictable. For example, earthquakes cluster together in time. So the more recently the ground has been a-rockin and a-rollin, the more likely it is to happen again. And Omori’s law says that the size of aftershocks after a major earthquake decays with time in a predictable way, a relation that has been known for over a hundred years.

So rumble merchants can tell pretty accurately the likelihood of an earthquake in your area. What they can’t tell ya is how big it’s gonna be cos ain’t nobody found a pattern in the distribution of earthquake magnitudes over long time scales.

At least until Eugenio “Red” Lippiello at the University of Naples and pals took a look at the data. They say that a pattern has emerged that allows them to predict the size of the next earthquake with reasonable accuracy. The rule is this: the next earthquake tends to have a magnitude similar but smaller than the previous one. Simple eh!

A bit too simple if you ask me and suspiciously similar to Omori’s law (could they be rediscoverin’ the wheel here?). Earthquake prediction is an emotive topic; it can mean life or death for tens of thousands. So these guys had better be sure of what they’re sayin if they don’t wanna upset an awful lotta people.

Ref: On the Influence of Time and Space Correlations on the Next Earthquake Magnitude

Einstein’s revenge over spooky action at a distance

Sunday, September 16th, 2007

One o’ the most bewilderin’ parts of quantum mechanics is its spooky action at a distance. Einstein couldn’t fathom it and other physicists have been a-puzzlin on it for decades. Today they gotta lil more to fret ‘n’ fuss about.

Alexandre “Napkin” Matzkin at the Universite Joseph-Fourier in Grenoble has found a serious problem with the test that physicists use to measure spooky action at a distance. He says this test is so broad that it can’t tell a photon from a flock o’ parrots. And he’s proved it by showing that certain classical phenomenon pass the test for spooky action at a distance even though there ain’t nothin spooky about them.

The background to this began in 1935 when Einstein and a few pals published details of what they saw as a flaw in quantum mechanics. When two quantum particles become entangled they share the same wavefunction; they are described by the same piece of mathematics. Now separate these particles by, say, the width of the universe and perform a measurement on one of them. According to the mathematics, a measurement on one instantaneously determines the state of the other, regardless of the distance between them. But how does the second particle ‘know’ the first has been measured?

This instantaneous communication, the spooky action at a distance, would be a violation of relatively, says Einstein and his pals. So you quantum bods must be missin’ something somewhere.

But the quantum bods just ignored him. Until 1966 when a physicist at CERN, John Bell, came up with a way of testing for spooky action at a distance. He derived a set of inequalities that if violated in experiment, would prove that spooky action at a distance was occurrin’. Since then, loadsa people have found violations o’ Bell’s inequalities for all kinds a quantum stuff.

What Napkin Matzkin has done is show that it ain’t just quantum stuff that violates the inequalities. He’s gone and found a classical example of ordinary bricks ‘n’ mortar that also violates the inequalities.

That don’t prove that spooky action at a distance ain’t occurrin’ or that quantum mechanics is in some way incomplete (although it might be). It shows that the assumption behind Bell’s inequalities are plain potty and somebody is gonna have to do some serious cogitatin’ n’ considerin’ to sort this out.

Ref: Bell’s Theorem as a Signature of Nonlocality: a Classical Counterexample

Chips ‘n’ chives

Saturday, September 15th, 2007

This week’s highlights from the physics preprint server that didn’t make the arXivblog

A Quantum Matter Transporter

How to Prevent Sonic Booms

A Portrait of Kurt Godel

How Low Viscosity Layers allow Plate Tectonics

Sound Generation by a Turbulent Flow in Musical Instruments

Why P and NP are likely to be different

Beauty and the data beast

Friday, September 14th, 2007

A human lifetime lasts about 3 × 10^9 seconds. The human brain has roughly 10^10 neurons, each with 10^4 synapses on average. Assuming each synapse can store not more than 3 bits, there is still enough capacity to store the lifelong sensory input stream with a rate of roughly 10^5 bits/s, comparable to the demands of a movie with reasonable resolution.

So says Jurgen “Trilby” Schmidhuber, professor of technical robotics at the Technical University of Munich in Germany. How are we to make sense of all this information?

Trilby Schmidhuber’s answer is that our brains look for ways of a-squeezin and a-squashin it: data compression is what them computer bods call it.

Where Trilby sticks his neck out is in equating certain types of compression with particular human experiences. So the experience of compressing the data associated with the symmetries in a human face is what we call beauty. And an unusually large compression breakthrough is what we call a discovery. For example, different apples tend to fall off their trees in similar ways. The discovery of a law underlying the acceleration of all falling apples helps to greatly compress the recorded data, he says.

Ya gotta admire Trilby. Let’s face it, we ain’t gotta clue about the nature of human experience. So any ruminatin’ philosopher has carte blanche to expound any manner of hocus pocus. But at some level, human experience is essentially a phenomenon of information, so maybe it ain’t so crazy to attempt to describe it in this way.

Trouble is, physicists are still a-wondrin and a-speculatin over the nature of information too. So it’s a brave man who wades into the debate over human experience with an argument based on data compression.

Let’s wish him luck, he’s gonna need it.

Ref: Simple Algorithmic Principles of Discovery, Subjective Beauty, Selective Attention, Curiosity & Creativity

Quantum metamaterials: the next generation of superweird stuff

Thursday, September 13th, 2007

Ya’ll heard about metamaterials–that stuff they made invisibility cloaks outta at Duke University last year. It’s mighty strange stuff and it’s about to get a lot weirder in a quantum kinda way.

Metamaterials get their properties from their structure rather than their composition. So chuck a few capacitors, inductors and wires into an eggbox and you gotta material that gives electromagnetic waves some squeezin and a-bendin like nothin’ else on Earth. Metamaterials can bend light backwards, introduce a reverse Doppler shift and turn Cherenkov radiation on its head. But until now they’ve always bin made o’ proper classical bricks n’ mortar.

Now Alexander “Five Fingers” Rakhmanov, currently vacationin’ at the Institute of Physical and Chemical Research (RIKEN) in Japan, says it’s possible to build metamaterials outta quantum building blocks. He and a few pals have come up with a design in which two superconducting rails are connected at regular intervals by tiny superconducting junctions which store a current. These currents (and their direction) can be thought of as bits of quantum information or qubits.

So what ya got here is a line of qubits that can be placed in a quantum superposition.

Now here’s the interestin’ bit. Send an electromagnetic wave down this line and it interacts with superposition of qubits in some mighty fascinatin’ ways. Five Fingers Rakmanov says that by tweaking the qubits, the device can become a photonic crystal with a transparency bandgap that “breathes”, that is changes in size periodically. Or it can behave like an Archimedean Screw which modulates the incident wave and pumps the regions of maximum amplitude along the qubit line at any chosen speed.

That looks like one excitin’ piece o’ kit. Now it’s up to one o’ you guys to rush out ‘n’ build it.

Ref: Quantum Metamaterials: Electromagnetic Waves in a Josephson Qubit Line

The incredible tongue balancing act

Wednesday, September 12th, 2007

About ten years ago, some electrical engineers showed how ya can see with yer tongue. They built an array of electrostimulators and connected it up to a camera. Put the array on your tongue and it provides a pattern of stimulation that matches the pattern of light hittin the camera. This Tongue Display Unit turned out to be almost useful for people with impaired vision.

Now Nicolas “Girls” Guillerme at Laboratoire TIMC-IMAG in Grenoble is usin’ the same ah-dear to improve balance. Instead of an image, the Tongue Display Unit provides feedback about orientation which the wearer can use for balance. Nicolas Girls has already tried out the device on people with their eyes closed and says it helps (although there are so few in the study that there ain’t no tellin whether it’s helpful or not).

Now he wants to see whether it can help diabetics who have lost feeling in their legs and so have trouble balancing. Just don’t ask em to talk with their mouths full.

Ref: A Plantar-pressure Based Tongue-placed Tactile Biofeedback System for Balance Improvement

Google’s virtual telescope

Tuesday, September 11th, 2007

Google ain’t just takin’ over the planet–it’s a-takin’ over the universe. The company created a big splash a couple a weeks ago by adding stars ‘n’ planets to Google Earth. They called it Sky. So now ya’ll can look down on Google Earth and up at Google Sky.

This week, the company outlines its vision for the future of astronomy and Google Sky in a paper on the arXiv and ah don’t mind tellin ya’ll it’s ambitious. Google wants astrobods to use Sky for a-storin and a-sharin their data. Here’s what Ryan “Bantam” Scranton at Google’s gotta say:

Astronomical data is deceptively complex. At
first glance, it is merely the result of pointing a
telescope at the sky and recording what you see.
In reality, however, a scientifically useful description
of a single observation requires knowledge of
when it was taken, from where, over what wavelengths,
in what conditions, covering what area,
and so on.

The goal of Sky is to create a general
framework that will enable users to access images,
catalogs and any associated meta-data across
the full sky in a seamless manner (Szalay & Gray
2001). In short, it can deliver a view of the night
sky across the full electromagnetic
spectrum to a user in an efficient and
scalable manner.

We hope that this step towards the
democratization of science will enable a new era
of visual discovery and science communication.

So Google Sky is set to become a virtual telescope that will allow anybody at any time to view the night sky as seen by the world’s most powerful telescopes. Personally, ah can’t wait.

Ref: Sky in Google Earth: The Next Frontier in Astronomical Data Discovery and Visualization