The GBT is highly sensitive and can detect radio waves emitted milliseconds after the birth of the universe. But when a signal has travelled so far, from so long ago, it can easily be drowned out.

"The telescope has the sensitivity equivalent to a billionth of a billionth of a millionth of a watt… the energy given off by a single snowflake hitting the ground," says business manager Mike Holstine. "Anything man-made would overwhelm that signal."

Not only are there no mobile phones, there are no baby monitors, microwave ovens or wireless doorbells.