Without specific numbers and calculating chance of life like ours to occur I don't see how you can confidently make such claims. It could very well be the case that even for a universe this large, it was a statistical anomaly for it to have life. Maybe out of 1000 similar universes only 1 would happen to have life. How can you tell the odds so confidently?

Maybe even out of 1,000,000,000 of similar universes only 1 would actually happen to have life. It's similar with planets. If you only know of 1 planet within 1B to have life, how can you tell the odds are not low enough to have 1 universe out of 1B to have life?

This could be an awesome example of survivorship bias to assume because there's life here, there must be life elsewhere in the universe too. We only have experience with a planet where there's life, so we are innately biased to think that it might be more frequent occurrence than it really is.

Other than arguing that the infiniteness of the universe somehow indubitably lends credence to the emergence of some convergent sentience, could you or anyone point to something a bit more rigorous (such as the paper your parent comment linked to)?

We are aware of the evolution of one sapience in the universe. What argument do you provide that suggests this is such a mind bogglingly unique occurrence that it cannot have happened anywhere else in the universe's volume of over 400,000Gly^3 at any time during its age of 13.8 Gyr?

In other words, the fact that it has happened at least once very strongly suggests it has happened more than once.

"In other words, the fact that it has happened at least once very strongly suggests it has happened more than once."

No, it doesn't at all.

Maybe just the opposite.

The universe is mind-bogglingly large, but it's also really, really empty, and really, rally sparse. The numbers games starts to dwindle very quickly in terms of all the ingredients necessary.

And the Fermi paradox helps provide crudely indirect evidence.

If there was any validity at all to the 'common life theory' - then it would have started long ago and probably spread everywhere to the point wherein there would probably be ample evidence.

In the 'common life' scenario, it should be rare/impossible to find life that's disconnected from other life scenarios.

There's a decent chance we are alone.

I guess I disagree with the basis of the argument that it happened once, it has to have happened another time. I don't think a single instance of very unique set of circumstances is the basis of a pattern.

I don't think the argument is that it "has to have happened another time". The argument is that if it is possible to happen once, it's likely to have happened more than once, the "existence heuristic." It proves only that it might be worth looking, unless perhaps further research indicates that we on earth are not, in fact, intelligent life, and then the likelihood of intelligent life elsewhere in the universe falls off dramatically.