"Cardinal Arithmetics is much older than Number Theory. People used to exchange things way before there were numbers. Expressing numbers like 762 is already a sign of a very advanced civilization."

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It's worth remembering that all technology leaves a footprint. For example, our own technology is leaving a footprint in terms of global warming, which could be detected from a long way away. One assumes that a very advanced civilization that has been around maybe millions and millions of years would have an even bigger footprint that might extend beyond its planet to its immediate astronomical environment.

— Paul Davies