Dyson sphere

A depiction of a hypothetical Dyson swarm surrounding a star

Hydrogen-induced cracking (HIC) [ clarification needed ]

In 1974, the Arecibo Observatory was used to send the first known intentional radio message transmission into space

01The 1974 Arecibo Message was aimed at globular cluster M13 — 25,000 light-years away, arrival date roughly 26,974 AD.
02Stephen Hawking publicly warned that contacting aliens could be analogous to Native Americans meeting Columbus — and we know how that ended.
03METI International transmitted 'Sonar' toward GJ 273, a nearby star, in 2017 without any international consensus or oversight body approving it.

Temperature map of the cosmic microwave background measured by the Planck spacecraft

01The pigeons roosting inside the horn antenna were trapped and relocated twice before the engineers accepted the hiss was cosmic.
02Penzias and Wilson won the 1978 Nobel Prize in Physics — accidentally, while testing satellite communication equipment.
03Princeton cosmologist Robert Dicke had been building a detector specifically to find this radiation; Penzias called him first, and Dicke told his team: 'We've been scooped.'

Freeman Dyson proposed in 1960 that a civilization running out of energy would dismantle its own planets to build a shell around its star, capturing every photon. We should look for the heat.