If Loud Aliens Explain Human Earliness, Quiet Aliens Are Also Rare
Given these two constraints:
1. The speed of light is a hard speed limit. This means there's also no cheating with warp drives, other forms of FTL, crossing dimensions, parallel universes or time travel; and
2. The laws of thermodynamics as we understand them hold true.
then the outcome of spacefaring civilization I believe is generally inevitable. That is, the ultimately limiting factor is energy and mass.
The easiest way to get both is with Dyson Swarms. This requires no new physics and no exotic materials.
If so, then a galaxy-spanning civilization is going to be completely obvious from a million light years away from the spectrum. Why? Because a full Dyson Swarm would have a very unique spectrum, specifically very little visible light and a lot of IR. That's just basic physics. The only realistic way to get rid of heat in space is to radiate it away and the wavelength of that is a function of temperature.
This is discussed in the context of the Fermi Paradox, which has the advantage that you don't need to determine what every alien civilization does, you just need to know if there are any exceptions.
Example: if there were 1000 spacefaring civilizations in the Milky Way, what are the odds that all 1000 of them (assuming they were within out light cone) would remain quiet or hidden? Couple that with mass and energy ultimately being limited then there is a strong incentive and advantage in becoming as large as possible. So even if 99% of civilizations remain quiet, the 1% will still make themselves visible.
Additionally, on the notion of hidden civilizations in particular, it's essentially impossible to remain hidden to a K2 or K3 civilization so there's really no point.
This is what gives me confidence that the Milky Way isn't teeming with spacefaring life. In fact I consider it much more likely we're the only such civilization in the Milky Way (within our light cone).
"If we assume that our knowledge is the pinnacle of knowledge, we are the first to reach it" is a bit tautological, no?
You can apply a very similar reasoning to an isolated tribe stuck at, say, stone-age level on a remote island. With barely seaworthy canoes. They very likely have no idea we exist, and their assumption will be that if there were better canoes, and people had them, they would've made contact. So clearly, they must be among the first.
I am continually amused by the gyrations we go through to avoid saying "we don't know".
I mean, last I checked we couldn't even account for 85% of the matter in the universe that should exist according to the laws of physics as we know them. If we can't even find the vast majority of matter, why do we think we'd do better with civilizations?
Interesting points, though the abstract is quite hard to follow. I guess it makes sense:
1. aliens spread at a certain speed after developing spaceflight 2. they're not here 3. there are no spacefaring aliens in the galaxy currentlyIf you look at the realistic reach of the signals of human civilization, it's a few tens of lightyears at best.
And once you factor in how inhumane it'd be to send children out to colonize foreign solar systems ... are we really sure we'll do that? That's 10 generations that live their entire lives in small metal boxes ... without the vast majority of everything we have on earth. Not so much as a single field of grass (or field of anything, building a big room in space will be a great challenge, especially since weightlessness means you don't really need room).
10 generations that will have absolutely zero power to do anything about their situation. It will take 100+ generations before anything remotely resembling earth level comfort will happen (assuming the planets encountered can at any point support human life. If they need to be terraformed, we're easily talking 1000+ generations)
I never understood these kind of analyses that talk about aliens reaching "humanity’s level" like it's inevitable or somehow special.
We could blast radio waves with ABBA songs into space to find whether there are other Swedish-speaking civilizations, or whether we are alone in the Universe. We don't because it's silly to think of the Swedish language as a necessary step for "advanced life".
Why do we think that human-like intelligence is special?
Full paper: https://arxiv.org/pdf/2102.01522.pdf
One issue here is that there’s no economic reason for the home planet to mount the sort of resources it would take to fund an interstellar trip. Stars are farther away than you think. The only way I can see that it would happen is for religious reasons, if the belief system of the religion required them to do it. Because there’s no economic reason.
The other issue is that it’s not clear how long technological civilizations last. We might be close to exhausting our own planet just 150 years after the invention of radio. Maybe technological civilizations bloom in the dark like beautiful flowers, then burn out quickly before they can spread to other systems.
I find these kinds of analyses to be hopelessly oversimplified.
First of all, we are talking about predicting the actions of superintelligent aliens. We aren't talking about slime molds or a bacterial infection, but beings with more intelligence than us, like orders of magnitude more complicated reasoning processes. They are effectively unpredictable, because if they weren't, wouldn't we be just as smart as they are? That level of intelligence comes with new levels of reflectiveness that are frankly not accessible to our weak brains. Like, maybe after reaching the next level of enlightenment, they decide that expansion throughout the universe like a worm is not actually what they want or that is what is good for the universe? Maybe they decide to rather study the universe and not interfere, the way biologists study, say, apes, without wanting to disrupt their natural behavior with their presence? Or maybe superintelligent beings find a way out of our universe, and pass into another dimension (cyberspace? black holes? disappearing through quantum foam? heaven?). Or maybe something else insane happens, like being superintelligent inevitably makes you completely terrified of everything, because you realize how powerful other aliens are and your calculations unequivocally show it's safer to stay at home and fart around doing the super-intelligent analog of baking chocolate-chip cookies? Not being superintelligent, we are like ants trying to contemplate human civilization. We have no context or experience, and we simply don't have the mental capacity to even imagine what we don't know.
Second, these probabilistic models are so fundamentally stupid. It's impossible for us to reliably estimate the probability of any event that's happened only once (without reasoning about the process that gave rise to that event), as we cannot estimate posterior probabilities without lots of samples. And humans on Earth have a massive chain of single-occurrence events that all seem to be absurdly improbable. Besides that, and perhaps even because of that, it's not even a foregone conclusion that our universe even selects from the middle of the distribution (i.e. is not biased). We could perfectly estimate the shape of a probability curve and yet live in a universe that stubbornly selects from the end of the distribution, all the time. All of our math could be totally right, but crazy shit just keeps happening.
Third, the anthropic principle is a total bitch. It means that we will never be able to estimate probabilities of events that were required to create us, because no matter how improbable they were, if they didn't happen, we're not even here to argue about it. If there are infinite universes (a multiverse, see Tegmark), then forget this whole mathematical sophistry, because then there is no need to live in some "average" universe; we can easily live in some stupidly improbably snowflake universe that has the 90 trillion improbable things that make apes possible; infinity doesn't care.
> Which seems bad news for SETI.
SETI conceded many years ago that the evidence of a "Loud" alien species > a few Million years ago might be virtually undetectable today.
Observations or assumptions about the presence or prevalence of life which take as a premise that we could detect them are IMO meaningless.
In particular, work like this makes assumptions about what it means to be "loud" which contain what amounts IMO to a profoundly inane belief that advanced civilizations would employ communications that are similar enough to our own that we could detect them, or, would leak energy in a fashion we could detect.
Both of these premises are deeply anthropocentric, in specific, they extrapolate from our current and 20th c. level technologies and understanding of physics, material science, etc., not even touching on philosophical matters like the dark forest hypothesis,
which are so myopic as to be comical.
Idle comment, sometime in the last year or so there was a detailed write up of a zero-day no-touch exploit for the iPhone, which included a nice tour through the wireless stacks and hacks Apple uses to do things like proximal device detection and networking.
What struck me at the time and continues to inform my opinion on these SETI questions is,
without the frame for understanding the why- and how- going on in the iPhone,
the scale of effort it would take a naive investigator to build a basic model of what was going on and why, is already at the threshold of human comprehension.
While in this specific case what's at issue is EMF using crudely comparable encoding schemes,
the point is simply that even knowing about various obvious ways of encoding binary information for transmission in a noisy environment,
the active signal(s) are already close to the edge of discernible from noise, especially complex but true noise.
I.e., even in the EMF domain, we're already for fungible consumer goods dealing with multiple frequency-hopping handshakes and sniffs and stochastic back-off and retry and error correction.
But there is no good reason to assume some other civilization at some other level of advancement would have any use for EMF. There are even with known technologies all sorts of exotic, more efficient, more targeted, ways of doing long-distance communication. Helically polarized lasers come to mind...
Anyway. I think the authors of these things need to be a lot more humble about their presumptions, or at minimum, spell them out plainly...
For more background and related material, look at Hansons blog[0] or the dedicated website[1].
I remember seeing somewhere that witnessing the cosmic radiation of the big bang is something we have a fairly lucky time-slot to be able to do.
If that's the case, and we're early to the universe, it seems like the kind of data we should try to make sure survives beyond us.
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What if aliens nearly exhausted their home planet resources and scaled back industrial life?
Perhaps too many technical missteps, social unrest, meant they’ve linearly creeped along making no technological leaps, but still providing a decent life to each other, until so much time went by, they realized too late about the possibility of space travel?
This is always feels like humans looking for our doppelgängers to sell a sensational concept.
> We estimate that loud alien civilizations now control 40-50% of universe volume, each will later control ~10^5 - 3x10^7 galaxies, and we could meet them in ~200Myr - 2Gyr.
This is utter nonsense.