If you stand in it for long enough, you start to hear your heartbeat. A ringing in your ears becomes deafening. When you move, your bones make a grinding noise. Eventually you lose your balance, because the absolute lack of reverberation sabotages your spatial awareness. In this room at Microsoft’s headquarters in Redmond, Washington, all sound from the outside world is locked out and any sound produced inside is stopped cold. It’s called an ‘anechoic’ chamber, because it creates no echo at all — which makes the sound of clapping hands downright eerie. The background noise in the room is so low that it approaches the lowest threshold theorized by mathematicians, the absolute zero of sound — the next step down is a vacuum, or the absence of sound. This is the world’s quietest place.