Saturday, 25 June 2011

Particle physics wind chime


Continuing our theme of sonification, particle physicist Matt Bellis is one of a group of scientists who have created a novel way of transforming particle detectors into musical instruments. The Particle Physics Windchime is a computer application that takes particle physics data, such as particle type, momentum, distance from a fixed point, and other datasets, and turns it into sound. First conceived at the Science Hack Day in San Francisco in 2010 by Bellis and fellow scientist, David Harris, the Windchime is currently sonifying data from BABAR, a high energy physics experiment located at SLAC National Accelerator Laboratory in California.

In creating their instrument, Bellis and his collaborators were inspired by the way that wind chimes work. Their chime is played by the particles passing through it, just like wind through a wind chime. "Think of it," Bellis said in a recent interview with SLAC, "the wind itself makes no sound. You hear the wind if it rustles the leaves in a tree. The motion of the wind itself doesn't necessarily make a sound. The wind has to interact with something to make noise." In the same way, "When you have these particles that pass through the detector, they send it ringing, resonating."

Bellis emphasises that sonifying data in this way can help lead to important new scientific insights: "I wanted to create the Particle Physics Windchime partly because I wanted to see if there's something new we can learn from the data. Is there something I can hear in the data that I can't see or that a computer can't pick up? Will it add to an intuitive understanding of the data?"

The Particle Physics Windchime is by no means the only project that sonifies particle physics data in order to understand it in new ways. The LHC Sound Project has been converting data from the ATLAS experiment at CERN for the last two years.

Run by Lily Asquith, Richard Dobson, Archer Endrich and Alabama 3 percussionist, Sir Eddie Real, the project is helping scientists see data from the LHC in different ways. The scientists and composers have notes in several interviews how musical the data appears to be:

"We can hear clear structures in the sound, almost as if they had been composed. They seem to tell a little story all to themselves. They're so dynamic and shifting all the time, it does sound like a lot of the music that you hear in contemporary composition," Richard Dobson (in an interview with the BBC, June 2010).



A history of the universe in sound


Our Particle Decelerator correspondent gives a TED talk on the story of the history of the universe by listening. It's punctuated by three anecdotes which show how accidental encounters with strange noises, taught us some of the most important things we know about space ...

Whilst the talk refers to "sounds from space", it is important to emphasise that stars and planets are not directly audible. Sound waves can not propagate in the vacuum of space. However, it is possible for radio waves emitted from celestial bodies to be heard by using radio technology.

The talk recalls the early history of the science of radio astronomy. Before astronomy was computerised, radio astronomers would monitor radio telescopes by listening. In our solar system, the Sun is the strongest source of radio waves, so it's the most powerful transmitter in our radio sky. Jupiter also sends us strong, and beautifully varied, radio signals. And radio astronomers also detect radio waves from far-flung celestial bodies in the distant universe, and simple audification techniques allow us to hear these signals.


Saturday, 4 June 2011

Uncertainty isn't what it used to be


One of the central planks of quantum mechanics was this week called into question in a new take on the classic two-slit experiment.

One of the central notions in quantum mechanics is that light and matter can behave as both particle and wave. The principle of "complementarity" has always been understood to prevent the observation of both behaviours simultaneously. However, new research published in Science on 2 June, suggests that physicists at the University of Toronto and Griffith University in Brisbane have for the first time observed both behaviours at the same time.

In Thomas Young's 19th century "two-slit experiment", light is passed through two tiny holes and is then viewed on a screen. The two beams interfere with each other, forming a diffraction pattern, as if the light were made of waves. If one of the slits is blocked, the light can be seen as a single beam on the screen, as if light were made of particles. The two-slit experiment shows that, depending on how it's measured, a photon will act like either a particle or a wave, but never both.

Aephraim Steinberg of the University of Toronto and Sacha Kocsis of Griffith recreated this experiment, easily observing the interference pattern indicative of the wave nature of light. But significantly, they were also able measure the path of the particles of light.

Science reporter, Adrian Cho elaborates on the importance of their new research:
"For decades, [the] experiment has served as physicists' canonical example of the uncertainty principle: the law of nature that says you can't know both where a subatomic particle is and how fast it is moving, and thus can't trace its trajectory. But now physicists have tweaked that classic experiment to show that they can follow the average path taken by many particles."

Steinberg and his team allowed photons to pass through a calcite crystal which gave each photon a small deviation in its path. By measuring the light patterns on a camera, the team was able to deduce what paths the photons had taken. They clearly saw the interference pattern which infers the wave nature of light, but surprisingly they also could see from which slits the photons had come from, a telltale sign of the particle nature of light.

Marlan Scully, a quantum physicist at Texas University, commented:

"It's a beautiful series of measurements by an excellent group, the likes of which I've not seen before.",

"This paper is probably the first that has really put this weak measurement idea into a real experimental realisation." He said that the work would - inevitably - raise philosophical issues as well. "The exact way to think about what they're doing will be researched for some time, and the weak measurement concept itself will be a matter of controversy"

Professor Steinberg commented, "I feel like we're starting to pull back a veil on what nature really is".