We know vanishingly little about the day to day movements of the largest solar system objects. Anything smaller than a medium city is incredibly difficult to find and track.
Sorry, but we routinely track asteroids that are less than 100 metres in size [0]. We track objects in orbit down to a few cm in size [1].
[0] https://en.wikipedia.org/wiki/Asteroid_Terrestrial-impact_La...
[1] https://www.nasa.gov/mission_pages/station/news/orbital_debr...
This Wikipedia article [0] presents data measuring the (in)effectiveness of the current tracking systems ("the vast majority are still missed"), and describes flaws in the current approach, such as "blind spots" that exist for various reasons depending on tracking methodology, e.g.:
> all ground-based telescopes have a large blind spot for any asteroids coming from the direction of the Sun.... [but even] space-based telescopes which can observe a much larger region of the sky around Earth.... still cannot point directly towards the Sun.
From this perspective, not only do we fail to track every asteroid, but there are specific and predictable "blind spots" where we cannot track any objects. So if the argument is that aliens could park their ship where we can't see it, then it's not a sufficient counterargument to claim that we track a lot of asteroids, because (a) we still miss the vast majority of them, and (b) many of those we miss for predictable reasons that could be exploited by an adversary who wants to hide an object from our tracking systems.
[0] https://en.wikipedia.org/wiki/Asteroid_impact_prediction#Eff...
"""As of DE421, perturbations from 343 asteroids, representing about 90% of the mass of the main asteroid belt, have been included in the dynamical model"""
Using polynomial interpolation you can get more or less 100meter level accuracy for any major object at any time. If there are remaining large masses that we haven't identified, they must be fairly small, far, and very dark.
(this is one of the most important achievements in human history and represents one of the longest scientific/religious activities; people have been predicting orbital paths for thousands of years.)
How would you or anyone else know this?
> rest of the billions of miles of our solar system
Which we have to send satellites out to see, which image minuscule windows of space. Here are some of the very best pictures from ground based telescopes: https://phys.org/news/2017-07-ground-based-images-planets-pi... Entire continents of Earth would be missed with that sort of resolution. And, with the need to average over time, whatever massive structure would have to stay relatively still.
Most detection of distance objects is through occlusion of stars, not direct sensing. Good luck trying to find something something smaller moving at high/relativistic speeds, which would be a fairly reasonable requirement for not having to plan ahead for a multi thousands of years space trip.
I don't really believe that space ships are flying around in our solar system, but I don't think us not seeing them, with our limited sensing, acts as any sort of counter evidence.
One, rich humans sometimes like to go see exotic wildlife, why wouldn't aliens?
Two, how would we know if there were aliens looking around other places?
> and never clearly interacting with our physical world in any way
"Take nothing but pictures, leave nothing but footprints."
Thing is, accepting the idea of the extraordinary and inexplicable is rather difficult for humans. Doug Adams explained it pretty succinctly with his idea of the “somebody else’s problem” field, whereby you could paint a mountain bright pink, and it would become invisible to a majority of observers through its sheer jarring improbability and discontinuity with core beliefs about the nature of things.
My background is physics. I’m well versed in “weird but explicable stuff”, I don’t take anything on faith, and I have seen, with multiple witnesses, a truly inexplicable thing, without resorting to what a big part of me still regards as mummery. We all saw the same thing. We all talked about it, puzzled over it, frantically checked the news for an explanation.
The thing is, the people who I was with at the time, they all remember the incident, the sonic booms… and seeing a helicopter in distress, which was the story in the press later that day. The shift to “it was a helicopter” was amazingly quick.
It wasn’t a helicopter. I know what I saw - or rather, I know that I saw something that was absolutely not a helicopter, that fighter jets approached to then have disappear in a sudden cloud - and yet, a big, big part of me yearns to believe that I saw a helicopter, as the alternative is… well, posting stuff that you’ll read and will go “this guy is clearly nuts”, and me being inclined to agree, as again, it isn’t comforting in the slightest to hold in your mind the knowledge that things are not quite as they appear.
There’s even footage of the thing, freely available on YouTube, and there’s evidently no point in anyone removing it or so-forth, as anyone who thinks it’s real is clearly crazy.
I haven’t been quite the same since.
There is, however, a still from it in this article with the heading “Unexplained:”
https://www.dailymail.co.uk/news/article-2129133/amp/Sonic-b...
It hung in the sky exactly like a brick wouldn’t, and had a weird, knobbly shape - and as the jets approached, it became clear it was pretty sizeable. It was also quite definitely what the typhoons were there to investigate, as they immediately flew towards it, and I would be prepared to write it off as a weather balloon were it not for the ensuing cock-and-bull story, and the cloud that materialised around it as they neared.
Consider how many planets are capable of supporting intelligent (as we know it).
Now suppose we detect evidence of industrial behavior (certain pollutants, nuclear detonation, etc).
Would we not laser focus on that one planet and observe it with everything we have - including sending reconnaissance drones?
Furthermore, would we not want to avoid detection where possible, in case life does exist on said planet and it turns out to be an existential threat to humanity?
Also, it would be trivial to avoid detection in our own solar system. Duck behind a moon or planet, or just quietly float in the blackness of space, and no earthling will ever see you.
Still human-centric to assume they would know what we can detect.
Feels like we're approaching a God of the gaps scenario here, but with aliens.
Actually, now that you mention it . . .
yet we have thousands of reports of UFO sightings (the vast majority seem to be in the US for some reason). So the aliens who can travel here in...assuming they come from a nearby solar system 4 light years away, and they are arriving as a result of observing "pollutants and nuclear detontations", meaning if they started traveling in 1950 (upon receiving the light from the first nuclear detontation in 1945) and UFO sightings picked up by the 1960s they traveled 4 light years in about 10-15 years, and can be "undetectable" except.... for thousands of non-confirmable sightings per year.
I think the aliens aren't going to visit us until Zefram Cochrane achieves his first warp flight.