Researchers at Trent University have found a way to reach back in time and listen to ancient civilizations in their most public and private moments.
This startling breakthrough comes shortly after researchers at MIT learned how to "hear" through soundproof glass by using high speed, high resolution video cameras and sophisticated computer algorithms. The camera was pointed at an everyday object on the other side of the glass, in this case a bag of potato chips. Any sound in the room, like a conversation, causes everything in the room to vibrate ever so slightly. By processing the high speed, high resolution video of the chip bag with sophisticated MIT developed software, researchers could eavesdrop on a private conversation, even through soundproof glass.
In collaboration with their colleagues at MIT, Trent researchers used an electron microscope and sophisticated software to detect and interpret "frozen" vibrations in just about anything that was once wet and then dried. Things like stucco, cement, paint, even mud. It's a lot like how a vinyl record is made. While The resin is warm and soft, a needle that vibrates to music transfers the vibrations (sound) to the resin, which then hardens, thus holding the sound forever. Of course in this case there was no needle to conveniently transfer sound. So Trent researchers used an electron microscope to scan for molecular disruptions that could be attributed to sound vibrations. Using the record analogy, they were looking for those telltale etchings in the so-called groove of a so-called record.
Finally researchers had their eureka moment by comparing reference paint samples that were created in a silent sound proof room, to paint samples that were created to Bob Marley's Legalize It.
According to lead researcher Paul Otonbee, "The sound was a little hazy and we only got a small sample but it was enough. We succeeded! The trick to getting a longer recording time is to find a sample that dried slowly. If you think of paint, the last part to dry is usually the bottom layer while the top layer, exposed to the air, dries first. So you carefully analyze your sample knowing that you're going to have a recording that spans the entire drying time, you just need to understand how to get it. We've had great results with cement and stucco and paint."
Interestingly, Paul points out these three things were all in use in Caesar's Rome. Paul's team has just returned from a trip to Rome and the Vatican City. "I'm sorry I cannot speak about what we did, we're under a non-disclosure agreement with the Roman and Vatican authorities. But I can tell you that archeologists have recently discovered that it was common practice in ancient Rome, in places like the Coliseum and such, to paint live scenes during major events. Just like a scribe would write down events with words, painters would do the same with paint on wet stucco. In the ancient Coliseum, these frescos were painted next to the Emperor's booth. It is also believed that any important public event, like a trial or civil debate would be painted for public record, sort of like a court drawing today. These frescos were then copied to velum and displayed in various locations throughout the empire. They would have projected the image of Rome, its power, its good governance, and, in the case of the Coliseum depictions, important lessons about bravery and the terrifying consequences of rebellion. One of the most amazing things to me is that these frescos were just painted over at the next event. They just laid down a new bed of stucco and went to it."
But it's the public debates that interest Paul the most. "When Ceasar was addressing the Senate, what did he actually say? Did he say 'I came, I saw, I conquered' What did he tell the Senators about his achievements? What did his voice sound like?" When Jesus stood in judgement before Pontius Pilate, was there a painter in the room? Reputedly Pilate was an egotistical man who wanted nothing to do with the crucifixion of Christ. So what better way to 'wash his hands of it' than to show it in a painting?" Paul estimates that the drying time for most of these frescos would have been 2 to 4 hours, "that's a long recording" he says with a smile.
When asked how one would go about extracting and analyzing such a sample Paul intimates that "you would need a team of specialists. Archeologists to find the frescos. Specialized x-ray equipment to determine how many paintings exist in a plaster wall slab. And once you have a reasonable image of each painting, you need the help of Roman scholars to determine what the scene depicts. There's usually a caption in each painting so that helps.
Once we are confident that we know what we are dealing with, we take core samples. Then we use an electron microscope to identify, in the core sample, the precise beginning and end point of each fresco. One core sample can contain hundreds of unique frescos. We look for subtle variations in the chemistry of each unique fresco layer. We do this with a mass spectrometer and by using an electron microscope to reveal signature patterns that occur each time a fresh layer of plaster is put on top of a dry layer. To get sound from one layer, you have to know exactly, to the micron, its beginning and end position in the core sample. Once we improve our techniques, we likely won't need to know the exact beginning and end location; we'll just analyze and it should be obvious, as though we were playing back a tape recording.
Now the fun part begins. You need to understand how long it took for your layer to dry so that you can understand how dense or loosely packed is your recording. A typical fresco is between 2 and 4 millimeters thick. Faster drying compounds will have a shorter recording time and slower drying compounds will have more recording time. If you get it wrong your analysis could yield white noise or nothing at all. To help determine the drying times we go back to the analysis gleaned from the electron microscope and the mass spectrometer to create reference samples that are chemically identical. We conducted a number of experiments and are pretty confident that the average drying time was between 2 to 4 hours. Of course we can only guess at environmental factors like the temperature and relative humidity of the day, and these things have a huge impact on drying time.
The best we can really do is come up with a range of drying times. The problem with that is that even within a relatively tight range, say from 3 hours to 3 hours 10 minutes, there are a mind-boggling number of possibilities to analyze. Given that we are looking for virtually undetectable perturbations in the chemical arrangement of plaster, we need to narrow our search area as much as we can. Or so we thought. That's where connections with the MIT super computing group saved the day. The team at MIT helped tweak our software and provided access to their computing resources. MIT computers probably reduced our analytics time, for one sample, from days to minutes.
The first time we lifted sound from a non-lab made sample, i.e., a sample gathered from the field, we were euphoric! The software has this funny user interface that looks like someone is turning an old radio dial. Well we sat around watching that silly dial spin around and around. Then it started to slow down, then it stopped. We all jumped out of our seats. But then the dial went in reverse. Everyone let out a sigh and I though the software had a bug. And then, finally, we heard it. Outside of getting married and the birth of my son, I have never been happier or more shocked.
I cannot tell you exactly what we heard due to our non-disclosure agreement, however I can say that there are audible human and animal noises. There were identifiable musical instruments and what appears to have been a single male voice delivering some sort of a public address. I wish I could say more but you can appreciate the gravity of this discovery."