"I can imagine an intelligent society without high tech. "

I can too, but it's highly, HIGHLY, unlikely. Unless they developed high-tech and THEN decided against it.

Then there's the microbial kind or even reptiles, et al... WHO KNOWS... we don't yet.

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I believe that there was life (yep even intelligent life) in the universe before us and are now extinct as well as there being intelligent life forms now and even microbial or even in the form of fossils in some cases, we just have not encountered them yet.

Our universe is HUGE (never mind those 'tiny'-on the contrary- images that our Hubble telescope found - North and Southern hemisphere - HDF-North; NDF- South.) as well as old.

Just keep in mind what 'sentient' means. Some may be with us now and are out of reach and some may be long gone. They may be/have been intelligent, sentient/technological, or not.

We have not encountered them yet or proven that they're not there at all. Our universe is huge as well as older than we are. (Good grief, they/we even know that our Milky Way galaxy has had a collision or two in it's life time).

FWIW & MHO