They think the known universe is something like 14 billion years old. That could conceivably mean that somewhere out there is a civilization that has been around for 1 billion years.
Our modern civilization on Earth is only about 3000 years old (homo sapiens for 1 million years) — compare that to a civilization that has existed for 1 billion years. We have come a long way technologically in only 3000 years, but just think how advanced a civilization would be that has existed for 1 billion years. Such a civilization would regard us as “advanced” as mere bacteria.
Henry's Views 
Re “We have come a long way technologically in only 3000 years, but just think how advanced a civilization would be that has existed for 1 billion years. Such a civilization would regard us as “advanced” as mere bacteria.”
What you fail to see is that there isn’t and never will be a “civilized humankind” that exists for 1 billion, never mind just 1 million, years because “civilized” humans have an “invisible” deadly disease called a soullessness spectrum disorder — read “The 2 Married Pink Elephants In The Historical Room” … https://www.rolf-hefti.com/covid-19-coronavirus.html
Writers like Asimov have long pointed out that our highly destructive kind will never make it for very long geologically speaking.
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There is this well known formula for computing the number of civilizations in the universe. One element in the formula has the negative factor of the tendency of any civilization to self-destruct (think nuclear weapons in our case or climate change). That one element in the formula drastically reduces the number of possible civilizations in the universe, as it should. But to me, it doesn’t seem unreasonable that there might be civilizations that have tackled this self destructive tendency and so continued to thrive so self destruction becomes a non issue for that small group that have overcome self destruction.
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