If we ever detect an Extraterrestrial Civilization (ETC) and start communicating with them, the messages could take years, decades, or even centuries to travel back and forth.

We face a challenging 49-minute long delay just communicating with the Juno spacecraft orbiting Jupiter, and that's well within our Solar System. Communicating with an ETC that's hundreds of light-years away or even further is a daunting task.

It's even worse if we're sending probes.

Imagine if a robotic probe arrived in our Solar System, sent by an ETC. They detected us and sent their probe to introduce themselves and learn more about us. We would be shocked, and the event would change civilization's trajectory forever.

Imagine we waited for another one, and imagine that we had to wait centuries. Generations of humans would live and die, we would've learned all we could from the probe, and it would sit in a museum somewhere.

As humanity waited for the next probe, the scientific community would publish a flood of papers on the probe and what might happen next. A whole new field of study would be born. Politicians would stake entire careers on the issue, and opinion-piece writers, artists, and musicians would have a field day. Scams would appear, and cults might spring up.

 Then imagine our sensors detect another incoming probe from the same place as the previous one. Imagine our surprise when we receive it, retrieve it, and begin to study it, only to find that it's not as advanced as the previous one and contains older information and messages than the first one. Its technology would be less advanced, and it would be more primitive.
 

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