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In half a billion years our sun will start the end of its life cycle and boil away all oceans on earth. So life as we know it will end then. But intelligent life probably won't take so long to evolve again and we have several species today who have enormous potential if they only manage to evolve usage of tools somehow. We are where we are today to a large part because of our prehensile extremities.

I think you might be off by an order of magnitude. The sun is expected to begin the death process (and therefore swell into a red giant) in 5 billion years, not 500 million years.

Why isn't at least one species expanding across the cosmos though? The light speed limit isn't really much of a hurdle for cosmic timescales.

The guy on cool worlds YouTube channel (Department of Astronomy, Colombia) has argued that we're still in the early days. The conditions for intelligent life in the galaxy hasn't been around for that long.

Maybe interstellar colonization is just never gonna be worth it?

We could already colonize Antarctica, or the sea-- those are easier to reach, supply and colonize than other planets, but we are not trying.

Most of our past exploration/settling efforts happened because there was some gain to be had; it seems quite plausible (if somewhat bleak) to me that interstellar travel could just remain pointlessly expensive regardless of technological progress.

> We could already colonize Antarctica, or the sea-- those are easier to reach, supply and colonize than other planets, but we are not trying.

On the other hand - we were and still are present on the Antarctica, have a permanent base on the South Pole etc.

Perhaps there is, but once again it would have to be visible from our light cone in order for us to even be capable of detecting it. Even with a civilization of 100,000 or even a million years that's still tiny and highly unlikely to happen within a timeframe that intersects with our small window of awareness.

And even if these aliens have cracked FTL travel, who's ever going to find our little planet on the ass end of some mediocre galaxy, with an EM emissions bubble that has only covered 100 light years so far? Needle in a haystack.

Hmm, let's say there's 100 billion stars in our galaxy and one billion habitable planets. Assuming we are average, half, or 500 million have civilizations older than ours. We could assume some sort of distribution where we could say 10% are older than a million years. So 50 million civilizations older than a million years in the milky way. In a million years moving at 0.1c you move 100,000 light years, or across the whole galaxy.

They could have been here already before modern humans even existed.

Seeing how it took earth 4 billion years to figure out how to get inhabitants to set foot on another stellar body the rise of intelligence may be the unlikely event here.

Perhaps it's much more likely to have happened elsewhere in the galaxy 4 more billion years from now. If I remember correctly, stars with our particular properties haven't been around for too long.

I recommend looking into cool worlds lab since you seem to like inferring from the numbers.

We've set foot on only 1 other stellar body.

Luna is sort of made from the Earth. And it's so close that Earth has a stronger pull on it than Sun.

So we have set foot on another stellar body, sure. But we also... kind of haven't.

And then we had to retreat from it anyway. Homo sapiens, hunter champions, arrived at an uninhabited body and were outmatched.

Way to go, smartest species we know of. You've done jack shit.

It may simply not be worth it. Outside of sheer curiosity, there are two reasons I can think of to leave your own solar system. One is overcoming resource scarcity. But interstellar space is extremely hostile to anything that isn't a cloud of dust and there are no resources available for thousands if not millions of years. If you've developed technology already to overcome the need for resources and are hardened to endure conditions for that span of time, you may overcome the resource limits of your own solar system anyway.

The second reason is to escape the death of your own sun. That takes long enough that far fewer lifeforms would be expected to even face that challenge compared to resource scarcity. If you manage to sustain a high-level civilization that can overcome resource scarcity and conquer the challenges of interstellar travel for the billions of years it takes a star to die, maybe you can simply prevent that death by technological means we could not possibly foresee or understand?

Those are hand-wavy answers, but this is sort of the problem. We're imagining near god-like beings here and asking why they don't behave the way humans have historically behaved with respect to exploring and colonizing remote parts of our own planet. The analogy breaks down at some point and we have no idea what beings capable of that kind of thing would even want to do.

Even our best sci-fi imagines answers that are pulled out of imaginary asses but frankly no less plausible than anything else anyone here will come up with. The builders of the expanse series expanded to a few hundred systems but then simply didn't need to expand any further. They figured out how to stop fusion and star-aging and tapped into energy sources from other universes (then got killed off anyway, but seemingly would not have kept expanding). The monolith aliens of the space odyssey series evolved into a non-material form that was actually here the whole time but we had no means of detecting them.

> using Cambrian explosion as a benchmark

I think that's wrong. And thinking of it like that provides another possibility:

The dinosaur era was a local maximum that couldn't develop human-like intelligence and technology. Then around 65 million years ago, Earth got "reset" and broke us out of the local maximum. Only after that did life have a chance to develop in a different direction and end up as us.

Seems at least possible to me that life is quite abundant, but local maximums that can't develop intelligence/technology might be more common than we think and it's easy to get stuck there. Earth just got lucky.

Conversely, it can be amazingly rare to break out of these local maxima.

For instance, it took 60 million years from the first trees until the appearance of the right fungi able to decompose the lignin in wood. (Coal deposits arose because trees from the Carboniferous Period had nothing to make them rot). If you think about it, that's a very long time for a very small amount of evolution.

Equally, as I understand it, all life on Earth has a common ancestor, and therefore a single origin. So life only started here once. And therefore is exceedingly rare.

Extending your logic (which is convincing), we, too, could be a local maximum and a form that is relatively low on the “cosmic intelligence scale”, if there is such a thing and if it is linear-ish.