A fragment I saved and shared in a thread: the description of a SETI-style detection at the Very Large Array in New Mexico. A narrow-band signal at the neutral hydrogen frequency (1420 MHz), tracked for 10 hours across the sky, made of 292,380 pulses in two amplitudes, with a repeating structure framing a “central” section of 256,507 pulses.
That structure (a message that announces itself by repeating its own header) is the classic first-contact thought experiment, the one Carl Sagan built Contact around: the aliens don’t send words, they send unmistakable mathematics.
The original text I saved was a third-party excerpt, so this note is a summary rather than a copy.