Imagine a place so quiet, you can hear your heart beat, your lungs breathe and your stomach digest.The anechoic (meaning echo-free) chamber at Orfield Labs in Minnesota absorbs 99.99% of sound, making it the quietest place in the world, according to the Guinness Book of World Records. To absorb all possible noise, the chamber walls are made from 3ft of sound-proofing fibreglass wedges and insulated steel and concrete, and the floors are covered in a semi-permeable, trampoline-like mesh.While a human can normally hear sounds as low as zero decibels (an average conversation runs at about 30 decibels), the background noise in the anechoic chamber has been measured at -9.4 decibels. This sensory deprivation makes the room extremely disorienting, and people can rarely stay in the dark space for longer than 45 minutes. Without the subtle, but vital auditory feedback that establishes a human’s sense of space, balance and walking become a challenge.The chamber is not just for fun, though. Companies use the chamber to test the sound levels of products, such as washing machines, refrigerators and Harley Davidson motorcycles. NASA uses a similar chamber to perform stress tests on astronauts.Group tours of the labs are available a few times a year and include a brief stop at the anechoic chamber (call the lab for details). But the facility has had so much interest in the 45-minute challenge that the founder Steven Orfield is considering making that option available to the public within the next year, and is working with the Guinness Book of World Records to establish an official record for the longest time spent in an anechoic chamber.The 45-minute challenge will not come cheap, however, as companies renting the space normally pay $300 to $400 an hour, and someone trained from the lab must be able to supervise the participants to ensure their safety.