Possible answer: First nearly every civilization that mastered, say, radio, did it millions of years ago. Second, nearly every such civilization long ago found much better means of communications than we know about. Third, they realize that trying to communicate via radio is silly and use much better means we don't know about. Net, they are out there and communicating, but we don't hear them and they don't hear us or bother with us. To hear us, they would have to be within 100 light years, and that's not far enough to cover many candidate planets.
That is my preferred explanation as well. A caveman would not notice a WiFi signal even if it was blasting right through the cave; he would probably be looking for smoke signals or something.
Also, a huge intelligence gap makes communication uninteresting. e.g. we know a little bit about how ants communicate via pheromones, but we're not trying to send "messages" to them; what would it possibly be useful to say?
> First nearly every civilization that mastered, say, radio, did it millions of years ago
So then we'd expect to receive signals from civilizations that are a few million light years away. Yet we don't see those signals.
We're too young a civilization to be spotted by other life forms (as you said, they'd have to be within a 100 light years or so). But when we look at space in any direction it looks dead. Just background radiation.
A point in my guess is that an old civilization won't be trying to use radio to communicate with us and will be using something better than radio we don't know about. Next, for communications over 1000 light years with just radio, there can be some issues of signal to noise ratio!
Sure, we can see a star 1000 light years away, a galaxy 1 billion light years away, and a quasar 10 billion light years away, but a signal from a planet over 1000 light years away? Besides, 1000 light years may not be far enough to cover many planets transmitting. Our galaxy is, what, 100,000 light years across? So, just for our galaxy, might want to think about distances of 50,000 light years or so. The nearest ordinary galaxy is the one in Andromeda, and that's about 1.5 million light years away.
Those are long distances for a radio signal from a planet.
"A point in my guess is that an old civilization won't be trying to use radio to communicate with us and will be using something better than radio we don't know about."
While a popular conjecture in this recurring debate, over the decades we've built up an awful lot of evidence that there really is no better mechanism for distance communication than electromagnetic radiation. We're running out of places for such putatively better mechanisms to hide.
I dislike this line of argument in the modern time, because it conflates two discussions, "what we scientifically know about the universe", and "could conceivable be true even though we have no evidence for our conjectures". While the second may be superficially more fun, it's ultimately a waste of time for any sort of serious discussion because you can hypothesize anything you want. It's content-free, despite the haze of words you can throw up. The first is much more interesting, and while 50 years ago one could still hypothesize better communication mechanisms, I think the argument when used in a serious discussion is out of date. We can name some non-EM communication mechanisms (neutrino beams, for instance), but they all suck horribly by comparison.
That we don't know everything is scientifically rock solid!
Your point is mostly that the stuff we don't know is bad science; I agree.
Still, this thread is to try to answer the question, where is ET?
Historically it would have been better to assume that there was stuff unknown that was better as an explanation than the stuff we did know, going WAY back: The Earth is a ball riding on the back of a turtle? We understood balls and turtles but not gravity of spheres! The earth is a ball held up by Hercules? Similar. To keep the sun moving across the sky we have to pour blood on this special rock? The planets are from wheels rolling in wheels? The stars are light coming through holes in ths sky? The sun is a fire based on coal? The Milky Way is all of the universe? The universe is expanding so there are just three cases, (1) keep expanding but more and more slowly, (2) stop expanding and reach 'steady state', (3) quit expanding and contract into a big crunch. It was ALL wrong! And in all cases the right answer was from things we didn't know yet!
For "We're running out of places for such putatively better mechanisms to hide". Ah, it's always been such! Where was Newton going to look for a solution to the orbit of Mercury? Where was Newton going to look for why he couldn't make gold with chemical reactions? The big bang seems to have things moving faster than the speed of light; where to look? We're not getting the right flow rate of neutrinos from the sun; where to look? Essentially all life on earth is just from DNA; so where to look for the reason there is no other mechanism?
But just now we have at least two biggie places to look: Dark matter and dark energy. About both, we don't have hardly a clue. We are unsure about the Higgs field. We haven't unified gravity. We haven't detected gravitational waves. We're unsure about why galaxies have black holes at their centers. There remain questiona about the 'size' of our universe, especially given the evidence about the flatness of the geometry. We're really mixed up about EPR.
But not all is lost! Some of the new telescopes on the way into orbit are amazing, maybe count the hairs on the back of ETs head! Maybe!
So, why haven't we heard from ET? My guess, stated as just a guess, is that ET communicates by means we don't understand yet. Is this answer solid science? Nope! Might it be correct? Yup! Is there some historical, circumstantial evidence for it? Yup. Are we still in the dark? Yup.
I just want you to be clear on the fact that you are deliberately choosing to leave science behind and have entered the realm of science fiction. It used to be a lot more sensible to speculate that way, but the thing is, if there is some 'mysterious' way to communicate we can say with great confidence that it probably isn't useful from an engineering standpoint.
"Dark matter and dark energy."
We aren't as ignorant about them as you might think. For them to be useful for communication would require them to also not have the properties that they appear to have.
This fashionable claiming of extreme ignorance isn't quite as silly as the fashionable affectation of self-species-loathing in this debate, but it's only slightly more sensible...
... of course, part of it is that few people have learned enough math or the relevant science to actually understand just how thoroughly, for instance, FTL really isn't going to happen, or understand enough information theory to understand why communication channels must actually have certain properties to be useful, regardless of their form.
> I just want you to be clear on the fact that you are deliberately choosing to leave science behind and have entered the realm of science fiction.
Not really: I'm guessing. Or in more erudite terms, I'm conjecturing.
You seem to be saying that science is what is all wrapped up and solid and that anything else is "science fiction". That's a bit rigid! Also that view would keep us from ever discussing the unknown before it becomes known, and science is a long march through millions of small and dozens of huge cases of the unknown becoming known.
Indeed, if read Einstein's special relativity paper, it reads like conjecture or guessing. That is, when he wrote the paper it was not at all clear that the Lorentz transformation had any physical reality. That paper became accepted as the real physics only later.
There's no solid proof that we can't go faster than light (FTL), and I have much more than enough math and plenty of science to have seen the arguments.
Sure, for any particle with ordinary mass as we know it, as it goes faster through space and approaches light speed, its mass increases and at the speed of light would be infinitely large. Right. So, for that case, FTL would be impossible.
But we don't really know the deeper mechanism for this mass increase. Thus we are like someone in the 18th century saying that travel faster than 60 MPH would be impossible because no horse could move its legs fast enough. That is, once we understand the deeper mechanism that establishes the speed of light speed limit, maybe we could find a way around the mechanism and the limit. The mechanism seems likely connected with the Higgs field, and we don't understand that very well yet.
E.g., we know so little about dark matter we can't be very sure it can't go faster than the speed of light.
For dark energy, we are assuming conservation of energy much as we understand it, estimating the energy of dark energy, assuming that E = mc^2 also applies there, assuming that how matter and energy curve space in general relativity continues to apply, and then concluding the huge mass of dark energy. That's a lot of assumptions from extrapolations. We're assuming that what we see for ordinary matter in accelerators applies to dark energy; that's a GUESS.
So, in science we need to be able to talk about possibilities not yet established. Such "talk" is not the best science, but it's also not "science fiction".
I wish this had been a root level comment (so it would be more visible). I think this is by far the most plausible explanation especially if you think about human history and technology differences.
Imagine our current spy agencies with bleeding edge technology spying on the Romans. Its only a two thousand year difference, but there's absolutely no way they could detect our signals and/or equipment (unless we made a serious mistake).
It seems entirely reasonable that another civilization may be tens of thousands of years ahead of us in technological advancement. If you consider the increasing growth rate of technological advancement, its easy to see your explanation.
The issue is not radio waves--it's Dyson spheres (look it up). It does not take very long at all for a space-faring civilization to advance to such a point that it's artifacts would be (spectrographically) visible from our telescopes today.
It doesn't have to be Dyson spheres either. A large object moving near the speed of light through the interstellar medium would give off one of a few very specific and very strong spectral lines. Now there hasn't been a concerted effort to look for interstellar travelers, but nevertheless in all our years of searching such oddities haven't shown up.
Our nearest other star is 4 light years away. 1000 light years away may still not cover many planets good for ET to colonize. But for us now to see evidence of a colony on a planet 1000 light years away or more would be TOUGH.
Note: The planet hunters mostly don't actually see the planets but just shadows or evidence in star wobbles, etc.
But we are putting up some new telescopes with some astounding resolution, etc.
But if they're so advanced, they probably still have radio receivers somewhere though. They should be able to receive our signals and reply with some sort of super advanced method that appears as radio waves so that we can receive them, but that travel much faster so it doesn't take a thousand years to reach us.
I like the idea that these advanced civilizations are actually all around us and just don't interact with us at all because we are too stupid/too boring/not ready/etc.
They're all down there thinking "why aren't there any alien bacteria sending us some chemical messages already? It's clearly the best way to communicate"
Then we presume that all these advanced civilizations are somehow living peacefully together AND that they all agree not to mess with earth. That's extraordinarily unlikely. Evolution isn't good at producing life forms that peacefully co-exist.
Let's see: We've been okay with radio for less than 200 years so far. The earth was formed ballpark 4.5 billion years ago. The big bang was about 13.7 billion years ago.
Assume that to get a civilization need a planet and, thus, elements heavier than hydrogen and helium. Those heavier elements are created in big stars that supernova, that is, have their cores collapse under gravity and blow off their outer layers where during the explosion all the heavier elements in the periodic table are created by fusing together lighter elements. So to get a planet, have to have a star form, burn out, and supernova. So, assume that are getting candidate planets 3.7 billion years after the big bang. Then have been forming candidate planets for 10 billion years.
Now take the planets that have achieved mastry of radio (i.e., working with photons from 60 Hz up to gamma rays). Take the date when they first made this progress with radio. Take the distribution of those dates over the planets. That distribution is 'concentrated' on the last 10 billion years. Now in that distribution spread out over 10 billion years, what is the probability mass of the last million years? It's TINY. Maybe it's 0.01%. Then 99.99% of the civilizations that mastered radio did it over one million years ago and, thus, are a million years or more ahead of us. Done.
