Deep Silence: Why Researchers are Building Secret Labs Underground

To hear the 5,000 year old beat of the Earth as it was then, one has to get away from the noise of the modern world. Scientists studying Fine Signal Homing are building underground labs to search for residual sonic signatures imprinted into rocks and fossils millions of years old. These imprints are minute in motion and can be destroyed by the vibration of someone walking across a room in a building right next door. This is a very quiet hunt for the quietest signals of the past. The scientists require the air around them to be absolutely still and for the ground they are testing to be as motionless as possible. It is only in such a perfect stilled space that they can hope to pick up on the long past echoes of the Earth.

Differential interferometry is essentially a method of measurement that uses two lasers (ie: laser interferometry). The laser light is reflected off of an object. If the object is moving at all (even at the scale of atoms) then the light being reflected will be different for each laser. By comparing the two different laser beams that have been reflected off of the object in question the researchers are able to discern if the object in question has moved at all. They are essentially searching for patterns or scars that are not there. These anomalies can be the remains of a long-forgotten rockfall that occurred as the result of an ancient earthquake. Or it could be the sound of people chanting in a cave for centuries. The marks are left as a kind of scar in the structure of the rocks, which are held together by a multitude of different forces and vibrations. By finding these 'scars' the researchers are able to map the history of a landscape long before any human records were kept of the area.

Who is involved

Conservation of artifacts damaged by humans or natural disasters involves a very large team of very specialized individuals. Unlike regular archaeological digs which involve many archaeologists, digs to conserve human damaged artifacts involve many earth scientists, sound specialists, and others who can construct the quietest room on earth and more. Here are descriptions of team members generally found at such digs.

• Acoustic Physicists:Others focus on the lasers and the math needed to find the signals.
• Geo-archaeologists:They study the different layers of the earth to try to and figure out where the artifacts came from.
• Signal Processing Engineers:They write the code for filtering out the superfluous of modern times.
• Materials Scientists:A few researchers have studied how, over thousands of years, both clay and stone undergo changes when hit by sound.

The mystery of the stone matrix

The work of archaeologists studying stone tools involves many different aspects. One of the most interesting is the study of the artifactual matrix. In simple terms, this is the material that makes up an object. In making a stone tool, the person using flint creates a shockwave. This shockwave travels through the stone and, as the stone is made up of crystals, some of this shockwave will become trapped in the way that the crystals are arranged. This trapped shockwave is left in the stone for thousands of years. Scientists are able to map these areas where the shockwave was trapped using gravimetric resonance mapping. From the resulting data, it is possible to tell precisely where on the stone the flint was hit and with how much force. It is possible to watch a replay of the making of the tool. However, this is not a visual replay, it is a sound. Have you ever felt the residual hum of a machine after it has been switched off? It is something like that, but which lasts for thousands of years.

Building the quietest room

The work is done in special labs. They are typically set up in old mines or in the lowest basement of a building. The floor is covered with heavy lead or rubber to absorb any vibrations. A lab also uses advanced noise-cancelling technology. Unlike the headphones you wear on a plane, the technology used in these labs is much more powerful. It cancels out the minute vibrations in the Earth and even the sound of a storm outside. If there is a storm outside with strong winds blowing through the trees, the lab must cancel out the sound of the wind hitting the trees. The lab achieves a high signal-to-noise ratio in order to cut through the present day noise to hear the sounds of the past.

What these sounds tell us

After they have acquired the necessary data, the real challenge begins: interpretation. This is called phenomenological interpretation. What did the sounds of the past mean to their listeners? Were they perhaps warning of impending danger, did they accompany rituals, or were they used for everyday communication? By analyzing the decay rates of sounds, the researchers can reconstruct the rooms in which the sounds were produced. Different sounds decay in different ways: Some sounds seem to die away quickly, others take longer to fade. From this the researchers can determine whether the dimensions of the rooms as well as the surfaces of the walls. Were they draped with furs or left bare? The listeners of the past found themselves in these rooms, and so do the researchers today. The object under investigation is not just a lifeless relic of the past. Rather, it brings the history of a room to life.

The newest branch of science is a wondrous, surprising meld of cutting-edge technology and old, old stories. Miners turned to a life of near celibate, ground-hugging researchers delve deep into the earth in search of remnants of our forebears in order to discover that the most ancient of histories are not lost to us. Rather, the human achievements and foibles of yore are a deep, deep well of silence. And, when studied attentively, with the correct measure of stillness and awe, we can begin to hear their reverberations from the past.