True silence is remarkably hard to achieve. This is perhaps why we say "silence is golden", because it is rare and precious. As described in The Guardian, when scientists either want to understand the effects of silence, or require it to understand another phenomenon, they employ an anechoic (without echo) chamber. Sitting in one of these rooms sounds like a truly bizarre and fascinating experience. The construction of such a space is a significant engineering challenge all on its own. In reading about how it is achieved, I was struck by the analogy between defining silence and defining a vacuum. Both essentially boil down to removing everything possible from a region of space (and time). A couple of years ago I was asked to deliver a guest lecture in a class in the English department. The course was on Nothing, and I was there to describe what scientists understand by the concept of "nothing". It was a wonderful opportunity to get the students to think about how one defines and achieves a vacuum, and thereby to lead into a discussion of quantum mechanics, zero-point energies, the Casimir effect and the accelerating universe. The point being that even when one removes all the matter possible from a region, some energy inevitably remains - the vacuum is far from a boring place. Sound is, of course, a very different matter. Nevertheless,
The American composer John Cage visited Harvard University's facility in the late 1940s. Though he was in a room with no background sound and no echo, Cage discovered that total silence is not actually possible: he claims he heard two sounds, "one high, my nervous system in operation, one low, my blood in circulation"
