As you drive down the road leading to Jodrell Bank Observatory, a sign asks visitors to turn off their mobile phones, stating that the Lovell telescope is so powerful it could detect a phone signal on Mars.
Radio telescopes are designed to be incredibly sensitive. To quote the legendary astronomer Carl Sagan, “The total amount of energy from outside the solar system ever received by all the radio telescopes on the planet Earth is less than the energy of a single snowflake striking the ground.”
The total energy now is probably a few snowflakes’ worth, but nevertheless it is