Courtesy
of Courtesy Kansas State University and World Science
staff
Part of a graphical depiction of the molecular vibrations.
(Courtesy Max Planck Inst. for
Nuclear Physics)
Physicists say they’ve
recorded tiny vibrations of individual
molecules, that could be called sounds—depending
on how you define sound—and put them in audible
form.
The resulting bell-like tones can be heard here.
But the study went much further.
The vibrations in their original form, scientists said,
are too fast and small to hear, but otherwise fit the
physical description of what makes a sound: they can produce
similar vibrations in neighboing molecules, which
do the same to their neighbors, and so forth, spreading
the oscillations outward.
That’s
enough to meet some dictionary definitions of sound, though
others apply the word only to what can be heard.
Audible sound consists of the same sorts of vibrations,
but much bigger and slower, and affecting trillions of
molecules, so they can move the eardrums.
Uwe Thumm, one of the researchers, said he prefers not
to call the effects of a single molecule’s vibration
“sound.” But “that’s a matter
of what you define as ‘sound,’” he added.
There’s no firm line between audible and inaudible:
different animals are sensitive to very different vibration
characteristics, though it’s safe to say none can
hear a molecule.
Making a molecule’s vibrations audible, however,
is just a matter of playing them back much, much slower
and louder, researchers said.
To imagine what one molecule might sound like if you could
hear it, picture the smallest bell you can: it would make
a tiny, high-pitched ping. Now, try to conceive of a tone
unimaginably smaller and higher. To convert this from
a fantasy into something you can really hear would require
doing what the researchers did: replaying a recording
very slowly to lower the pitch—like a 45-rpm record
being played at 33-rpm—and of course with a volume
boost.
To make original the “sound” itself, Thumm,
of Kansas State University, and colleagues struck hydrogen
atoms with short, intense laser pulses. They then scaled
the vibration speeds, or frequencies, down to about 1,000
Hertz, for a human-audible pitch.
But they went much further: they also analyzed the vibrations
almost as music, to determine how the molecule, composed
of mainly of two core particles called protons, reacted
to the pulses. “The laser pulse either makes the
molecules vibrate more violently or blows them apart,”
Thumm said, which is unsurprising because protons are
linked by smaller particles, electrons, that act as a
spring. The protons, banged with a pulse, oscillate back
and forth.
While this may be easy to picture on a large scale, Thumm
said particles act differently at the subatomic, or quantum
level. This means determining the protons’ locations
after being hit isn’t easy.
It’s similar in a way to what happens if you drop
a marble in a bathtub, he said: looking at the circular
ripples, one can at first tell where the marble was dropped.
But when those ripples bounce off the tub’s sides,
the wave pattern changes shape, and it becomes harder
to tell where the marble fell. Thumm said the same thing
happens to the protons not within seconds, but in about
60 billionths of a millionth of a second.
After this, you lose track of the distance between the
protons, Thumm said. “All you can say is that they
have a certain likelihood of being at a certain distance.
This is in agreement with the bathtub experiment: Seconds
after the marble was dropped, you can’t tell where
exactly it plunged in.”
But things work still differently at the quantum level.
The researchers said they were surprised to find that
waiting about 10 times longer after the original hit,
the proton-proton distance again becomes definite. “We
call this a revival of the original motion,” Thumm
said. “It’s not going to happen in the bathtub,
but it happens at the quantum level.”
Thumm and colleagues analyzed molecular motions by breaking
them into their various frequencies, or vibration speeds.
Different frequencies are what create different pitches
in music. The molecular frequencies could thus be analyzed
as if they were musical chords.
This study—based on experiments at the Max Planck
Institute for Nuclear Physics in Heidelberg, Germany—bore
out the picture of “revival” of motion, Thumm
said. And happily, he added, this also confirmed predictions
he published in 2003 with the institute’s Bernold
Feuerstein. The agreement “was almost perfect and
exceeded our expectations,” Thumm said.
One can literally “listen to the vibrations and
hear the ‘revival,’” Thumm said.
Thumm said researchers hope to be able to do the same
thing for more complex molecules like water or methane.
Just as a C Major chord sounds different from a D minor
chord, Thumm said other molecules also would have their
own unique sound. The study, published in the Oct.
10 issue of the research journal Physical Review Letters,
could also help investigators in the goal of applying
lasers to steer chemical reactions, Thumm said.
MORE
INFORMATION
This article first appeared
in the World Science News on February 6, 2008. Their website
can be found at www.world-science.net
Music without words means leaving behind the mind. And leaving behind the mind is meditation.
Meditation returns you to the source. And the source of all is sound. — Kabir
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