The great silence: Just 4 in 10k galaxies may host intelligent aliens

You’ll need a lot of energy for complex life. The list of things that can naturally provide enough without having extremely-hostile side effects is pretty much limited to stars, and then only if you get really lucky in a whole bunch of ways.

Then you need to turn that into chemical energy to actually do anything with it.

That’s gonna turn useful chemicals from the environment into waste you can no longer use. If you’re lucky the waste is chemically useful, and if something can evolve to use it, maybe it can turn it back into what you need (happened with oxygen). If the waste isn’t useful, you better hope your planet’s recycling it somehow. Ideally with some kind system that adjusts with a feedback-loop so it doesn’t limit your growth too much.

Our one example sure looks extremely fragile, in that if you mess with any of several things a little bit, you might still get life, but it’ll cyclically wipe itself out, or never be able to harvest enough energy to support complex life, or any number of other problems that end in not seeing intelligence arise.

That said, if, say in a billion years, we survive as a race, and still haven't met anyone, then some of those drake choices are very different than we imagine them -- and we must have somehow gotten really lucky, or there is something else very strange going on. Regardless, it would likely be pretty bad news to a single-planet lifeform to meet us at that point, or at least tectonic, depending on how altruistic society as a whole would be at the time of the meeting.

Earth is home to just one species who've developed wireless communication, and we don't broadcast across astronomical distances if we can help it these days.

If someone sent you raw radio data, what's it modulated by? Frequency? Phase? Amplitude? A combination of the three? Is it multiplexed with other data? And then, if you magically figure that out, it's not even in a language you speak? If it's even a spoken language!

Good luck haha.

Perhaps we just missed the signals?

Let's ponder some timescales. The Earth has been around ~4.5 billion years, life began a half billion to a billion years later. It wasn't until about 2 million years ago that the species that was to evolve into modern humans started to use fire. That's 3.498 billion years or so of life before what we might considered civilization.

Humans first started using radio about 125 years ago. An instant in cosmic timescales. Powerful broadcast radio signals first showed up in 1930s. We are already starting to transition to lower power point-to-point wireless transmission. That means our radio waves are become far less detectable at stellar distances. Give it another 25 or 50 years and humans might well have gone silent, for all practical purposes, to hypothetical aliens.

To have another advanced civilization arise both within detection distance of Earth and in an overlapping instant of time where we might detect each other? The odds are unfathomably tiny.

Furthermore it also makes no sense to just scream in all directions so you will use highly directed microwave beam or laser. If you are not in the path of such communication, you will hear silence.

For example, once upon a time "tool use" was considered a unique capability of humans, and from that was derived definitions of intelligence, etc. Well, turns out lots of other animals use tools, at least under that original, somewhat simplistic definition. But what's the significance of that fact--that other animals use tools? Does it mean they're also intelligent, just like humans? People have argued as much, but the "tool use" test was basically pulled out of someone's butt to begin with; the fact we all agree other animals use tools, now, doesn't actually imply much of anything.

People draw conclusions where none can be drawn. And people establish presumptions and definitions to fit their preferred conclusions.