While commercial radio broadcasts began around 100 years ago, these early transmissions used frequencies that were either mopped up by the atmosphere or drowned out by radio emission from the Sun.
In contrast, military radar transmissions set up during the Cold War to detect incoming ballistic missiles have the power and frequency characteristics to be detected over hundreds of light-years – and have already broadcast our existence to any aliens within around 60 light-years of the Earth.
- The thought experiment: What would happen if aliens contacted us?
- How could we talk fluently to aliens?
- How far do we travel through space every day?
- Could we ever detect other universes?