Wednesday, January 21, 2015

Making Invisible Fields Visible

Illustration showing movement of air through various rooms,
from Lectures on Ventilation (1869) by Lewis W. Leeds.
Image via Wikimedia Commons.
I used to teach physics to arts students and geophysics to environment science students. One of the mathematical concepts which was a challenge to convey was that of the field. In broad terms, it's rather simple really. A field is simply something which is defined at all points in space. A temperature field in a room is a scalar field; that means there is simply a value for temperature, a number you could measure, at any point (distance north from the corner, distance east from the corner and height off the floor) in the room. A vector field is the same thing, but at every point there is an amplitude and a direction. Add a fan or simply ventilation to the room and you can measure airflow at any point; this is a vector field. The illustration gives you an immediate sense of both the temperature and air flow field in a room - illustration as early data visualization.

Berenice Abbott (1898 - 1991) created brilliant
black and white science photographic illustrations like this one

Scifi loves the idea of a force field; this is a vector field descripting a force, like for instance, gravity, at all points in space. You can't see these fields; they are invisible - but they are (hopefully) easy to imagine. You may remember seeing a simple demonstration of magnetic field lines: iron fillings around a bar magnet, tracing out loops from pole to pole. Such a simple experiment is shown - complete with extra electrically conductive metal key - in Berenice Abbott's photo.

Our own Earth has a magnetic field of course, and it is really not that different from that of a bar magnet. Certainly, to first order as physicists say, you can imagine our earth with magnetic field lines from pole to pole tracing loops similar to those in the photo in a full three dimensions. The main complication to this picture is the sun, and way the solar wind intereacts with the Earth's magnetic field.

"Lines of Force and Equipotential Surfaces in a diametral section of a spherical Surface in which the superficial density is a harmonic of the first degree" from A Treatise on Electricity an Magnetism, James Clerk Maxwell, 1873

Schematic diagram of how the Sun interacts with the Earth's magnetic
field (curtesy of the USGS). The solar wind distorts the field basically
compacting the field in on the sunward side creating a bowshock and 
blowing a long 'magnetotail' outward on the night side of the Earth.
Geophysicists use the way these fields interact to probe our planet. We
can all enjoy the beauty of the auroras caused by this interaction. Solar 
storms can also interfer with radio communications, damage GPS and 
other satellites, and even cause electrical blackouts. 

I love the creative, eerie and entrancing take of Semiconductor (the duo of Ruth Jarman and Joe Gerhardt) take in their short film 'Magnetic Movie'. They let NASA space scientists talk about magnetic field lines, and then animate the Space Science Laboratories at UC Berkeley employing very low frequency radio audio recordings (3 Hz to 30 kHz) as an input for their animated embellishments. They are taking poetic license with reality, but somehow expressing more than we might, if we could literally reveal these invisible fields.

Magnetic Movie from Semiconductor on Vimeo.

They write,
The secret lives of invisible magnetic fields are revealed as chaotic ever-changing geometries . All action takes place around NASA's Space Sciences Laboratories, UC Berkeley, to recordings of space scientists describing their discoveries. Actual VLF audio recordings control the evolution of the fields as they delve into our inaudible surroundings, revealing recurrent ‘whistlers' produced by fleeting electrons . Are we observing a series of scientific experiments, the universe in flux, or a documentary of a fictional world?

Perhaps a little more literal, is another artistic work by Semiconductor, which strives to make the invisible geomagnetic field visible. In '20 Hz' they employ data gathered by CARISMA (the Canadian Array for Realtime Investigations of Magnetic Activity, the magnetometer element of the Geospace Observatory Canada project, operated by U of Alberta) of a geomagnetic storm in the Earth's upper atmosphere - data recorded at the frequency of 20 Hertz (of course). They 'play' the data as the audio track and use the data to generate the visuals.

20 Hz from Semiconductor on Vimeo.

They write,

20 Hz observes a geo-magnetic storm occurring in the Earth's upper atmosphere. Working with data collected from the CARISMA radio array and interpreted as audio, we hear tweeting and rumbles caused by incoming solar wind, captured at the frequency of 20 Hertz. Generated directly by the sound, tangible and sculptural forms emerge suggestive of scientific visualisations. As different frequencies interact both visually and aurally, complex patterns emerge to create interference phenomena that probe the limits of our perception.

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