In fact I think the most likely explanation for the Fermi paradox is that we are kept isolated from other civilizations within range.
What we think we know, says that self replicating systems are possible because we are ourselves an example, and that PV and lasers are possible, and that light imparts momentum.
All of this suggests that it is possible for a civilisation that only doubles in numbers every 30 years to be able to make a Dyson swarm in 30 * log2(mass of mercury/mass of a minimal human colony and support equipment) years, which even in the most pathologically extreme case for lightweight starting colonies isn't going to be more than 2174.5 years.
It appears that with a Dyson swarm, much of the future light cone of the universe can be colonised directly without needing to focus on nearby stars first. But we don't know until we try.
I do like your idea that we're in a quarantine though.
And for UFOs-as-ETs, these intelligences would have had to spawn pretty near our solar system, and their existence overlap in time with mankind's tiny fraction of existence (truly a blip in the lifespan of the universe), and detect our existence (or at least our system as a worthwhile destination), and develop tech to take them here, and be interested in this undertaking, and have the resources for it, and not wipe themselves out in an accident, ecological disaster or global war, and after all of this choose to just do mysterious flybys and abductions and no formal contact with Earth.
Too many "and"s for me...
Why do you believe that our current understanding of physics is the final one?
Let me propose a thought experiment. Let’s just say for the sake of argument that humanity has survived 100,000 years into the future. Now, let’s put you in a time machine and fast forward you to that distant future.
Would you be surprised to learn that relativity, and the limits it imposes, are viewed by those future humans as anachronistic and silly? Barely remembered artifacts of humanity’s Stupid Ages? That new discoveries were made over those thousand centuries, discoveries that we 21st century humans can only vaguely begin to comprehend?
Because you raised my biggest problem with modern cosmology: it’s arrogant assumption that Einstein is the end. But more importantly, that evidence indicating that relativity is not in fact the end — such as UAPs — is completely disregarded.
And the reason it is disregarded? Because relativity is the end! It’s circular reasoning at its absolute worst.
It doesn't have to be final, it just has to be reasonably descriptive of reality.
Even if we review our understanding, the universe is still a massive place and humanity's existence a mere blip. It becomes more about statistics and probability than physics, but yeah, our understanding of physics also makes ETs visiting Earth very unlikely.
If you mean to say "a major revision of physics would make it more feasible", I don't know. Maybe? Or maybe even less feasible! We have to approach this rationally, and so far reason and evidence both lean to "extremely unlikely".
> Let me propose a thought experiment [...] Would you be surprised to learn that relativity, and the limits it imposes, are viewed by those future humans as anachronistic and silly?
As a thought experiment it's a decent piece of science fiction, but as any sort of serious thought it seems like begging the question to me.
Which it only is if you limit cosmology to spectroscopy and ignore UAP. If you start to examine UAP as a real thing, and ask questions about “how”, then it all falls apart.
Which is exciting.
The "U" just means "unidentified", not "contradicting our understanding of physics" or "extraterrestrial intelligence".
There are many life forms on Earth that remain unidentified by many estimations, and we keep discovering new organisms. "Unidentified" doesn't have to violate our understanding of the universe.
One of the common reported characteristics of some UAP is that they are able to accelerate hypersonic speeds without a sonic boom.
If that is true then there are things to be learned here. You appear to be saying that this obviously cannot be true because it violates what we currently know.
I think that is tragically unscientific.
That's a big "if". If magic exists, then maybe Gandalf is real.
That there are new things to discover there is no doubt. I don't know how it relates to your need to believe in ETs visiting Earth, but rest assured we have plenty of things to discover about the universe. Most things we will never know.
> One of the common reported characteristics of some UAP is that they are able to accelerate hypersonic speeds without a sonic boom.
> I think that is tragically unscientific.
What's tragically unscientific is cherry picking reports (sometimes by people who are not even claiming the final implication you'd like), disregarding the obvious implications (hoax, liars, top secret military tech, etc) and jumping to conclusions.
What's tragically unscientific is not understanding the scientific method and that extraordinary claims require extraordinary evidence.
Seems very unlikely to me.
Fascinating stuff really.
They're not there, or they're far away in time and space, with a remaining tiny chance that something incredibly unlikely happened.
I have this idea that sedentary agrarian urban civilization was something created by nomadic peoples to farm slaves. Hunter gatherers and pastoral peoples would be very hard to control. But if they took children, and raised them to be sedentary and dependent on agriculture they could have a stable of slaves.
Maybe the norm is that intelligent life lasts a long time and we just happen to be born in the first tiny fraction of humanity.
But the observational evidence is that even given multicellular life, intelligence is extremely rare, and there is no evidence at all that it is likely to last very long.
It might depend on the origin of the universe. One theory involves an exponentially expanding spacetime driven by a quantum field. Fluctuations in that field can case a region of that expanding spacetime to greatly slow down its expansion and that region becomes a universe.
If that's how it happened our universe would just be one in a very very large collection of universes. In particular the rate of universe creation would grow exponentially and so the fraction of old universes would be exponentially smaller than the fraction of young universes.
If it takes a few billion years for the first human level intelligence to develop in a given universe and then hundreds of millions more years for the second intelligence to develop then of all the universes with at least one intelligence only a very very very small fraction of them would have more than one intelligence.
> In fact I think the most likely explanation for the Fermi paradox is that we are kept isolated from other civilizations within range.
Another interesting possibility is that civilizations isolate themselves. It seems very unlikely that neighboring civilizations would be at the same level of technological development--there is just too much luck involved in becoming a civilization and in developing technology.
That suggests that first meetings between civilizations are very likely to involve civilizations with vastly different technology levels. They also are likely to have vastly different cultures and vastly different ethics and vastly different philosophies.
Maybe the more advanced will see it as their duty to help the other progress. Or maybe they they will view them like Europeans viewed the occupants of the Americas in the 16th century. Or maybe they will see them as animals and give them about as much consideration as we give the animals on a patch of wilderness that we want to use for something.
You can model how civilizations should behave when they learn of other civilizations using game theory. When a civilization learns of another than hasn't yet learned of them their choices are: (1) try to keep themselves secret from the other, (2) try to contact the other, and (3) try to destroy the other.
(We would not be able to choose #3 because we aren't technologically advanced enough, but we know ways to do #3 that we'll probably be capable of in a few hundred to a couple thousand years from now).
Assuming that a civilization puts much much much more value on its own survival than on the survival of other civilizations #3 is the option with the highest expected value. If you aren't to the point where #3 is possible than #1 gives the highest expected value.
In short, we could be in a galaxy full of civilizations but they are all avoiding doing anything that would let others detect them because they don't want to be the target of someone else's option #3.
A few months ago there was a PBS Space Time episode on this so called "Dark Forest" scenario, which you might enjoy: https://www.youtube.com/watch?v=aXYf47euE3U
You can also consider the possibility that the intelligent civilizations of the universe don't even consider us a life form. I think about that a lot. "Maybe god and its creatures are not even aware we're here."
Moist pebble apes might be a short lived fluke. Our civilization has existed for an insignificant amount of time and even primates could be just a flare in the pan.