[sailingparrot]

Note that I personally don't have a set opinion on this subject. I am only trying to respond to OP's question of why some people would think this is a possiblity. But I like to play devil's advocate so:

> Or other societies realized widely broadcasting noise is bad for whatever reason.

> Or maybe broadcasting widely resulted is a case study for getting your civilization invaded, so they avoided it it or only send signals as strong as they need to be

Every other society realized it at the same time? Which would imply every other society is roughly born at the same time, which sounds unlikely. So some of them (like us) should not yet have discovered the danger of broadcasting signals.

> Or maybe it's so consistently and universally done that we simple see it as cosmic background radiation.

I don't think you can possibly mistake the CMB with some artifical radio signals coming from point sources.

> Or maybe something like quantum entanglement someday makes wave transmissions for communication seem as backwards as smoke signals

Definitely a possibility, but again, that would assume some kind of synchronicity between all other societies (no one is still figuring out quantum communication). But since radio signals are hard to pickup at a long range, it's possible. But we also haven't seen any other traces of civilizations: probes, dyson spheres etc.

[nobody9999]

>Every other society realized it at the same time? Which would imply every other society is roughly born at the same time, which sounds unlikely. So some of them (like us) should not yet have discovered the danger of broadcasting signals.

And I'll play Devil's Advocate to your Devil's Advocate. :)

It's entirely possible that there have been other technological civilizations over the past 13.7 or so billion years. That's a long time. As such, any civilization that stopped broadcasting in our direction, if they ever did so in the first place, any more than 100,000 or so years ago, would be completely undetectable to us -- ever.

What's more, as was pointed out in another comment, we haven't been looking for such signals for long (~60 years) and haven't surveyed anything close to the entire galaxy.

I guess the most accurate thing we can say would be that we haven't detected another technological civilization within 60 light years or so in the few places we've looked.

Given the lack of data, the Drake equation[0] is less a predictive device than a way to categorize our ignorance.

The Fermi Paradox[1] and its "where is everybody?" question is more in line with what I perceive to be your point.

Given that we haven't looked very hard for very long (as I mention above) in an enormous galaxy that's existed for billions of years, it seems to be in a similar position as any predictions from the Drake equation.

It's interesting to speculate, but without enough data, speculation is all it is.

[0] https://en.wikipedia.org/wiki/Drake_equation

[1] https://en.wikipedia.org/wiki/Fermi_paradox

[sailingparrot]

> It's entirely possible that there have been other technological civilizations over the past 13.7 or so billion years. That's a long time. As such, any civilization that stopped broadcasting in our direction, if they ever did so in the first place, any more than 100,000 or so years ago, would be completely undetectable to us -- ever.

But this is assuming radio signals are the only way we could detect a civilization, what about probes (von neuman or regular), dyson spheres etc. ?

> I guess the most accurate thing we can say would be that we haven't detected another technological civilization within 60 light years or so in the few places we've looked

The signals we received in the last 60 years come from the entire observable universe (it's how we define the observable universe), not just from a 60 ly radius. But the furthest the signal comes from the hardest it is to detect (or the strongest it would have to be to be detectable).

> It's interesting to speculate, but without enough data, speculation is all it is.

I certainly hope that everyone is aware that is pure speculation ;)

[nobody9999]

>The signals we received in the last 60 years come from the entire observable universe (it's how we define the observable universe), not just from a 60 ly radius. But the furthest the signal comes from the hardest it is to detect (or the strongest it would have to be to be detectable).

A fair point. I should have been more specific and limited my statement: "we haven't detected another technological civilization, currently broadcasting electromagnetic signals in our direction, within 60 light years or so in the few places we've looked."

However, that doesn't mean such civilizations don't exist, nor does the fact that we haven't detected any such signals at any distance, or any other indications of such civilizations, extant or not.

[sailingparrot]

> I should have been more specific and limited my statement: "we haven't detected another technological civilization, currently broadcasting electromagnetic signals in our direction, within 60 light years or so in the few places we've looked."

Why restrict yourself to those 60 light years? We haven't heard about any other civilizations in the entire observable even if their transmission happened a long time ago and they may be extinct by now.

It's only true in the other direction: only a civilization less that 60 ly away could possibly have detected our radio signals so far.

[fiblye]

> But this is assuming radio signals are the only way we could detect a civilization, what about probes (von neuman or regular), dyson spheres etc. ?

That’s trying to find a needle in a universe sized haystack, and we’ve only just started digging. Concluding that there’s probably not a needle when we’ve only just started digging our hands in is premature.

[sailingparrot]

> That’s trying to find a needle in a universe sized haystack

But that is the whole point of the fermi paradox. Given the staggering numbers of planets in our galaxy/universe, and given the staggering age of the universe (when compared to our history), it should not be like trying to find a needle in a haystack.

If it is, then that means life is extremly rare, which already answers part of the question.

[fiblye]

That comes with the big assumption that in basically any given corner of the universe, civilizations in galaxies billions of light years away are pumping out radio signals strong enough to be detected from earth.

How likely is it that by the time humanity would be a space faring society that we’d be pumping turbo charged radio signals that are easily distinguished from noise when doing a quick sweep? How likely is it that societies are using radio signals or something similar for a long period of time, and not simply using some better method that humans have yet to discover?

[sailingparrot]

No, the assumption is because our solar system and earth are not particularly old, if life is commonplace, then there are civilizations that should be billions of years older than us. Imagine where we would be (assuming we don't simply destroy ourselves in the next 50 years) with a billion more year of technological progress? We should be all over the galaxy, colonizing left and right, sending probes everywhere, creating dyson sphere like structures that would be easily detectable from afar etc. And that is just one civilization on an single planet out of 100 billions planets in our galaxy.

Of course everything is just speculation, for every hypothesis on one side of the argument you can find 2 hypothesis from the other side that counter it. But the point is, to go back to the original question, that the right answer is definitely not obvious and if someone's opinion is that we are alone, or at least that life is very rare, it's not completly crazy.

[halfdan]

Even if it's as rare as one in a billion we'd still have to map billions of suns, their planets and actually look for it. Other than SETI I don't know any really serious, concerted efforts to looks for other signals of life.

Even the discovery here was somewhat random and required someone to start digging through recorded data.

[krapp]

>Given that we haven't looked very hard for very long (as I mention above) in an enormous galaxy that's existed for billions of years, it seems to be in a similar position as any predictions from the Drake equation.

Also remember the search space isn't even just a single galaxy, it's the entire observable universe with a hundred billion galaxies, give or take.

[WrtCdEvrydy]

> Every other society realized it at the same time? Which would imply every other society is roughly born at the same time, which sounds unlikely. So some of them (like us) should not yet have discovered the danger of broadcasting signals.

Yeah, that's the Dark Forest book in effect.

If you broadcast, other civilizations could attempt to destroy you, so most civilizations find some way to dampen transmissions or limit them somehow.

[sailingparrot]

> Yeah, that's the Dark Forest book in effect.

Precisely, and in the Dark Forest book we (humans) did indeed detect radio signals from other civilization very early after we built the radio telescopes capable of doing so. So the fermi paradox is not present in this alternate reality.

In our reality we haven't detected anything yet, hence the paradox.

[guerrilla]

> Definitely a possibility, but again, that would assume some kind of synchronicity between all other societies

Does this not happen with eyes, limbs and especially blood which have evolved independently many times? Maybe whatever the reason is is actually quasi-inevitable and we're missing the few that fall outside of that evolution for some unrelated reasons.