As we can see by this announcement they wouldn't have detected the first primal soup that formed life (we don't have any probes), but given enough time they would have sent a probe to our planet and detected single celled life, and they would have seen evidence of life.
At 5 light years (the closest start is just less than that) they wouldn't have had a chance before about 1900, and they might needed until 1960 (I give a range because there is room for debate on exactly what would be proof, they might have not been sure) to detect out radio transmissions. We would probably have made contact with them in the 1970s.
At up to 100 light years the above applies with more of a timeshift. After 200 we don't have the ability to detect ourselves (the technology of 1820 didn't give any emissions to go on.) I'm not sure if they would know there is a planet with water where we are (There has been great progress in detecting small planets but I don't know what their abilities are).
The farther out you go the harder it gets. Eventually they are still seeing the big bang form our galaxy and so have no idea life will eventually happen here (or where we will be as the universe is moving all along in directions that they cannot predict)
Back when we started broadcasting radio, we needed very powerful transmitters since the receivers were pretty primitive - you could make receivers with no power source at all (Galena radios).
Then we started using them for other purposes. Powerful radars appeared. TV was invented. Later on we added digital signals and most traffic shifted to binary for computer to computer communication.
Now we have things like WIFI and 5g. The problem is that the technology has advanced so much that cellular antennas can talk to puny transmitters from miles away, while the transmitters are only outputting milliwatts. We can also electronically 'steer' transmissions so they will 'point' at the other party (beamforming).
Long range communication is shifting to satellites and fiber optic cables. Those are pretty directional and not very strong signals, by comparison (and fiber optic of course has none). We have been slowly shutting down TV stations in favor of internet streams.
Civilian radars still exist but they are relatively weak. They are also slowly being phased out in favor of technologies like ADS-B, which broadcast a fraction of the power. GPS signals are very weak.
Military radars are also more sensitive than before - and increasingly look like background noise. Given the high emphasis on stealth, they are also more directional and lower power than before. And may not even be on all the time.
Given this, it is possible that, if you are taking a SETI approach, there's only a very small window before a civilization switches to more efficient and less noisy RF comms.
> At up to 100 light year
At 100 light years you'll have very faint, possibly undetectable signals, as the strength decreases with distance squared. Unless they are pointing at us.
Great Filter is neat because it bundles many different solutions together into one class. Any solution saying that civilizations in the Milky Way are incredibly rare is basically a variation on Great Filter.
>why should we assume anything about our ability to determine life beyond our Solar System?
It isn't farfetched to assume that sufficiently expansionist/numerous Kardashev type 2+ civilizations should be easier to detect from Earth than bacteria on Venus.
I think you are in fact laundering the very large assumption you're making.
However, it does seem that the Milky Way is not collonised (not even the other galaxies as far as we can tell), and if that's truly the case, then it would suggest that there is some kind of filter barring all civilizations from ever doing it.
I consider interstellar travel not ever being viable a legitimate filter.
Of course there is a plethora of other solutions as well.
A galactic civilization is expected to leave traces. The most advanced civilizations are expected to use a huge amount of energy (information is energy too). Even if we don't find spaceships, we could see otherwise unexplained high/low entropy regions. In fact, there is a theory that says that life is the most powerful entropy generator, and that Earth has a distinct IR glow because of it.
Currently, it doesn't seem there is anything preventing us from colonizing interstellar space in the far future. Lots of unanswered questions but the laws of physics don't exclude it.
The Great Filter theory is that because we don't see any sign of a galactic civilization, there is something in the way. It can be behind us (ex: the appearance of life) or ahead of us (ex: civilizations tend to get wiped off before they can colonize other star systems).
And even if the great filter is simply that even the most advanced civilizations can stay undetected (so no real filter), finding evidence that the great filter is less likely to be behind us make it more likely to be ahead of us (or inexistant).
I also wanted to point out that life on Venus would not even necessarily move the great filter. It is possible, though not experimentally proven, that lifeforms could survive a cataclysmic ejection from one planet after an asteroid impact and float to another planet in the same system. In other words, the life on Venus may have come from Earth or vice-versa.
"ANY AND EVERY" is not remotely a part of any plausible premise of either the Great Filter or the Fermi paradox. Please be charitable in stating assumptions of theories you disagree with.
Space is difficult, interstellar space exponentially more so. It isn't necessary to make any claims about any or all civilizations if the nature of physics alone makes it extremely unlikely for any species, however curious, to ever make it out of their local gravity well, much less sustain the technological infrastructure, knowledge base, energy consumption, unified political will (despite vast cultural and biological evolution) and control over every other variable across millions of years as a species to be able to stumble across our planet even once among the billions upon billions of galaxies' worth of stars in the observable universe.
One might say "it only has to happen once." I submit that it could have happened a thousand times and we could still never know.
So it seems reasonable that if any interstellar civilization were out there, one would have found us by now, or their presence would be obvious to us. After all, Rome knew of China, even if they never directly interacted, and Spain eventually stumbled across the New World. Von Neumann probes make sense because it doesn't occur to us that the chances of any arbitrary path along the universe intersecting with a star would be effectively zero. We look up at the night sky and we can see so many of them, and they seem so close together, obviously you'd run into one no matter which way you went, sooner or later. Right?
It's more comforting to make up rationales as to why we might be alone than deal with the ramifications of being surrounded by life we may never see in a universe in which the entirety of physical reality amounts to a rounding error in a zero.
[0]https://en.wikipedia.org/wiki/Hubble_Deep_Field
[1]https://www.theatlantic.com/technology/archive/2014/12/the-c...
There's a point where it's all just "big". A million and a billion seem equally big. Even though, as it has been said before, that the difference between 1 billion and 1 million is about 1 billion.
There are so many fundamentally difficult problems with deep space exploration, that it may never be logistically possible to over come them. And that's of the ones we know about.
Given modern technology, we would be able to observe both without being noticed. It would be pretty trivial from space. It wouldn't be quite so trivial close up, but it would be possible.
A time difference of ten thousand years? The invisibility would be rather more effortless, and might even include direct memory manipulation in the victims.
A million years? Can anyone even imagine what a million year difference would look like? Never mind the technology - we can't even imagine what its motivations would be.
So assuming an advanced civ is going to do what we'd do - build ships, colonise, hoard and transform resources - is more than a little naive and unimaginative.
It's not unlike a protohominid assuming that life is about hunting, and any other two legged creature they meet is going to want to talk about flint knapping and these new arrowhead shapes.
The assumption is weaker than you suggest. It's not that your typical advanced civ will do what we'd do, just that some proportion (perhaps extremely small) of civilizations will be expansionary.
Any process that involves replication will eventually need more resources.
If a single civilization in our galaxy made a machine capable of replicating itself and going to other star systems less than a billion years ago, we should have seen that.
> it doesn't occur to us that the chances of any arbitrary path along the universe intersecting with a star would be effectively zero
I fail to see how this is a strong critique of Von Neumann probes, maybe you can clarify.
Allow me to attempt to clarify.
Let's say a civilization creates Von Neumann probes. Ignore whether such devices are even technically feasible. It sends these Von Neumann probes out into the universe in all directions.
The chances of any one of them ever encountering anything larger than a grain of dust before the heat death of the universe is practically zero. In almost all possible universes, all of the probes are swallowed up by the void. In almost all of the rest, one probe finds enough material to be able to replicate, and all of those are swallowed up into the void.
The scenario whereby a stable chain of exponential reproduction and growth via interstellar transfer occurs lasting long enough for a significant amount of stellar matter to be consumed and for an obvious trace to be left which just happens to be visible to us, is not the most likely scenario in a universe where such devices exist, it is still so unlikely that its feasibility borders on requiring sorcery. Because the universe is just that empty.
It's the sort of idea that only works on graph paper assuming a "perfectly spherical cow in a frictionless vacuum" kind of universe. The lack of a universe awash in Von Neumann probes is not a strong argument against the existence of life or advanced civilization in the universe, it is, itself, a strong argument against the feasibility of Von Neumann probes.
This is why no civilization would randomly fire off Von Neumman probes in random directions. They would understand that this is a problem.
If you want to efficiently use them, you fire them at nearby stars. They will either find materials and restart the process, or they won't (and potentially report this, but it's not required). A non-zero number of them may encounter sufficient material (given how plentiful planets seem to be, that's a fair assumption). Those star systems would now fire off a bunch of probes, at near stars. Rinse and repeat. It's a slow process, initially, but given the exponential nature, it should be surprisingly quick.
"Aiming" at star is not something that's too complex even for us. It might require mid-course corrections to account for errors, but we could build a probe that would conceivably reach a star. Ensuring it would be alive and operational by then is more challenging, but it is an engineering one. Actually entering the star's orbit might be even trickier depending on relative speed. But that's peanuts for a civilization that could build such things.
> The lack of a universe awash in Von Neumann probes is not a strong argument against the existence of life or advanced civilization in the universe, it is, itself, a strong argument against the feasibility of Von Neumann probes.
It is. But that's assuming we can even recognize one.
Haha okay. I think most would view this as a pretty uncharitable assumption (appears contingent on these civilizations not having telescopes or AI), but if that's your view I can understand why we disagree.
If the goal is to mine the resources of one specific location, then a targeted probe makes sense. But if the goal is to proliferate and explore (or consume) as much of the universe as possible as efficiently as possible, then targeted probes seem less likely to succeed over the scale of time necessary.
I'd argue that your argument is either
a. not intrinsically true of complex probes or
b. just a modified version of the great filter argument
You could imagine an advanced civilization that creates an artificially intelligent probe that is pretty effective at problem solving and resilient to these sorts of failures. Even if targeted probes have to remain active, there is no reason they couldn't consume energy harvested from their origin world to course correct.
If your claim is that every form of intelligence will inevitably fall to mechanical or software failure, etc. then that claim seems to just be identical to the great filter claim.
> targeted probes seem less likely to succeed over the scale of time necessary.
Your own GP seems to provide a very compelling reason why this is not true.
>But if the goal is to proliferate and explore (or consume) as much of the universe as possible as efficiently as possible, then targeted probes seem less likely to succeed over the scale of time necessary.
Less likely than non targeted ones that you say wouldn't get past the first generation?
The idea is that "probability mass they'll cross paths with another and each can mutually grok the other exists" is a monotonically increasing function of the number of other civilizations, which bridges the problem you've identified.
> 1. it extremely unlikely for any species, however curious, to ever make it out of their local gravity well
ie. it is more likely that they would go extinct before making it out of their local gravity well, which means the discovery of other life local to us would make it substantially more likely that filter preventing us from attaining interstellar travel is ahead of us.