To encourage U.S. travelers to use their facilities, various U.S. airports have installed Wi-Fi systems that allow travelers to use cellphones and tablets to access the Internet and e-mail accounts. Several airlines had set up their own wireless communication systems to process passenger tickets and to track luggage before the airports had installed their Wi-Fi systems. When the airport Wi-Fi systems started operating, their radio signals interfered with some of the airlines’ wireless communications systems, causing ticketing and baggage data transmissions to be garbled or blocked. At the same time, transmissions from the airlines’ wireless systems had the same effect on the airports’ Wi-Fi systems. Under the airlines’ contract with the airports, the airports had the right to use the frequencies on which conflicts had arisen. Thus, the airlines had to incur the costs to recalibrate or replace their systems entirely to eliminate wavelength “pollution” created by competing systems.

Why is it that an external cost would be created if transmissions from a company’s Wi-Fi system garbled the signals of the wireless computer networks in a nearby residential neighborhood?