It is reported that Bertrand Russell gave a lecture many years ago about cosmology and astronomy. Opened for comment after he was finished, a woman stood up and scolded him thus: “young man, everyone knows that the earth rests on the back of a turtle.”

Russell responds: “and what is the turtle standing on, ma’am?”

“Young man, it’s turtles all the way down.”

If it is fictional, it is a wonderful fiction.

Pretty nifty trick for a 1970s television. But then, you’d be surprised what becomes possible when Motorola puts “the works in a drawer.”

As you write, when one looks at the available resources the numbers are so huge they approach the limit of infinity. So many stars and planets running so many experiments with elements, molecules, amino acids…

Even if the Goldilocks zone is necessary, there still must be billions of viable planets like ours.

We still don’t know how to jumpstart life given the proper molecular soup, but even if we assume that is inevitable, given the proper ingredients and conditions, there are so many steps to get to us I’m not so sure intelligent life at our level is inevitable. Even on our own planet, where we know life happened, the planet was just fine having all kinds of non-intelligent life for billions of years.

Single celled life first appeared about 4 billion years ago and that was just fine for about 500 million years and it took about 2 billion years to get to sexual reproduction. Was that a one time, fluke mutation or did changing conditions result in an environment where many asexual organisms mutated simultaneously? Then it’s about 500 million more years until we get the first, multicellular life. And even when life evolved incredible diversity, Earth seemed content to house all manner of plant and animal life of all shapes and sizes for hundreds of millions of years without the existence of anything capable of fashioning a shoe, let alone a telescope or rocket ship.

Then, look at what we know about the development of knowledge amongst humans, once we came along. Most cultures were just fine with “stone age” tech. Tribes still exist to this day that live in that fashion. Is agriculture the innovation that leads to “civilization?” If so, would man have developed agriculture if this planet wasn’t tilted so severely (23.8 degrees) on its axis?

And the evolutionary leap required to get bipeds with freed up hands and brains our size seems very precarious. Is there a species where a higher percentage of mothers die in childbirth than humans? And we have to be born a good 12 – 24 months premature with non-hard skulls. Multiple human births (twins, triplets) are rare. 11 – 13 years before we can sexually reproduce. Very risky stuff. Humans in nature are incredibly vulnerable. Nature doesn’t seem to favor intelligence beyond a certain cunning, even at caveman levels.

And, even if all those variable line up to give you an intelligent species with appendages that can manipulate tools, look at the hundreds of thousands of years myriad human tribes existed and did nothing that gets one close to a telescope or rocket ship. The Chinese invented movable type and did nothing with it. The Romans understood steam power. For hundreds of thousands of years horses, oxen, wind and water power were sufficient for human thriving.

It seems that divining the nature of electricity would be essential for a species to engage outside their planet. A lot of very intelligent humans looked at electricity and never learned its nature. Maxwell, Clerk, Volta… a few geniuses made astounding leaps in understanding that allowed others to come behind and use their findings. What if Maxwell had died of cholera, or in an invasion by raiders to his village? Would we still be living with 1700s technology?

It seems elementary to look at the sheer number of potential planets to assume intelligent life at or level, or beyond, must occur myriad times in our Universe. But I think it is easy for us to gloss over the myriad improbable events that must occur to get a species to our level. As I wrote, even when life thrived on this planet, Earth seemed just fine not having any species with our capabilities. Then, once we came along we seemed fine existing without taming electricity, steam or oil, let alone uranium and plutonium.

For what it’s worth, I’ve rarely heard an astronomer argue we’re alone in the universe. But many do think we could alone in the galaxy.