The Evidence of Absence was a replica military surveillance blimp launched above a residential neighbourhood in London.

Currently deployed in Iraq and Afghanistan, these helium-filled behemoths have been considered for use by border control forces in the U.K. and U.S., and as part of an early warning sensor system over Washington D.C. ostensibly designed to detect a cruise missile attack -- though civil liberties organisations have been quick to note their potential for civilian surveillance.

The title refers to a remark by former Secretary of Defense Donald Rumsfeld concerning the search for Saddam Hussein’s alleged weapons of mass destruction: “The absence of evidence is not evidence of absence.” 

The Evidence of Absence, 2015.  Replica military surveillance blimp over London.