There are so many other explanations for Fermi Silence - from the reality of extremely limited sampling to the creeping suspicion that we're too mediocre and underdeveloped to recognise truly intelligent life - that grand assumptions about our specialness seem more than a little premature.

None of this requires aliens who will teach us anything, one way or the other. It requires aliens who ignore us because we're about as interesting as a termite mound.

And once you've seen a few billion of those, you've more or less seen them all.

The ~50% probabilities from the paper are not fundamentally more founded in reality than "Did another planet in our galaxy develop intelligent life yet that attempted to communicate? I don't know, so let's assume 50% either way. Therefore, we are alone with 50% probability." Should that number be 50%? Or 10%? Or 99%? You're choosing some prior there. So does this paper, and the priors chosen gravely affect the result. Of course, the paper has more intricate math and more solid reasons for their priors, but fundamentally it is still just assigning almost arbitrary probability distributions to parameters that we have no grasp on. Specifically (see my other comment), the numbers that they get primarily depend on the choice of prior distribution for the abiogenesis rate, which overshadows all other parameters. It has such massive error bars (>200 orders of magnitude by their own account) that arriving at a concrete probability (in the way that you understood it when reading the paper) is somewhere between misleading and a lie, because it's more or less just a projection of that prior into a single number.

In other words, I'm convinced they could have easily arrived at probabilities like 0.1% or 99.9% by reasonably varying their prior distribution for that parameter alone.

I think you are misinterpreting the conclusion of the paper. The conclusion is that there is "a substantial probability that we are alone in our galaxy". This extra probability is because of the extra uncertainty within our estimates of the parameters in the Drake equation. But "substantial probability" is something entirely different than being sure.

The keyword is "observable" universe what about probability of life in unobservable universe. When we discovered microscope and telescope only then you could say that we started "observing" something. Modern science is only 100 years old and we can not even imagine what would be invented and discovered for 50 or 100 years.

http://cista.net/tomes/Carl%20Jung%20Princeton%20imprint/10%...

fc - "the fraction of civilizations that develop a technology that releases detectable signs of their existence into space"

This term for many people, is near 1. They assume that "detectable" means that WE can detect them with our current level of technology, and/or that "releases" means that it would be something familiar like radio or laser beam transmission.

...but the scope of this assumption is based upon a scant hundred years of human history. The rate of technological and AI advancement (on galactic timescales) is so brief, it is imperceptible. ...and recall that if life exists, the average age of such civilizations would be hundreds of millions to billions of years older than ours.

When we look at popular sci-fi media, one thing that is blatantly obvious is our inability to even imagine what our "civilization" will look like beyond a few hundred years - and often those shows are even superficially wrong.

If AI surpasses us (or integrates us, or exterminates us), our technological existence to "release detectable signals" will be a relative flash in the pan. Remember that AIs aren't limited by our meat lifespans. To them, taking 100 million years to populate the entire galaxy, is a reasonable amount of time. To them, WE may not be the life they are looking for - the emergence of an AI might be of some significance (or perhaps even not), and we are just the slime on the surface of the rock. ...the precursor to what THEY consider THEIR abiogenesis.

...and if AIs encountering one another in space are constructive rather than combative, then the rate of abiogenesis may not be all that relevant. It might simply be like adding another drop of water to an already full glass.

Because mainstream media is saying that the military is admitting to tracking aliens for years now.

And that's just one of the many ways coming where any average person can decide to ruin the world. It's already possible today for a single rich person, if they wanted to, to destroy the world. I don't remember exactly how. Something like buy 1k airplanes and have them seed the atmosphere IIRC. Those kind o things get cheaper and cheaper until their in reach of your average joe

Most civilisations will have just enough of a life support to keep the machines running. They might be spurred into action each time a sun burns out, but other than that why bother with the outside world?

I'm not so sure why this supposed to make intuitive sense. Life is a gradient, so any metabolic process that happens on a energy gradient can be considered 'alife'. I really don't see how an early Great Filter would work - are you going to stop energy gradients from happening? I've read -- will try to dig up the source -- that -- at least simple life -- is pretty much a given since -- even though it creates pockets of lower entropy -- allows for the most paths to thermodynamic equilibrium.

In my opinion a late filter makes more sense. That is; any species that evolves in the confinements of competition for resources and natural selection is -- due to the requirements that competition for resources creates -- necessarily unable to properly transition to a steady-state mode with no competition for resources and no (or limited) natural selection.

The reason for that is that the transition phase from competition for resources to the steady-state phase is simply too short. I'm convinced that this is what we are currently seeing with Humanity on a global scale; even though there's no need for competition for resources, we're still biologically and socially 'programmed' to compete with each other for resources, mates and habitats.

(Biologically, all humans are more closely related to each other than -- for example -- any two chimpanzee tribes. We are not very diverse, genetically.)

That inability to quickly change a species 'modus operandi' to a steady-state model together with the immense power multiplication of technology and cooperation that make it possible for civilization to literally dominate their ecosphere, I don't see how any species is ever going to survive that threshold.

The result of that inability to switch to a steady-state model and the powers achieved - tools and cooperation are the ultimate exploits! -- is simply extinction by habitat destruction.

I think that the current observations quite neatly match this.

Given the galaxy, and given billions of years, the Great Filters that seem most likely are the ones that occur on the edges of the timeline: before multi-cellular life begins, or after a hyper-dominant intelligent species arises.

Having said that, I think you’re absolutely right about mammals and societies. If the Great Filter does occur in between life and intelligence, it seems like it would happen where the first signs of intelligence begin. And for earth, that means mammals and the arms race of mind-modeling that their social lives initiated. No other type of animal on earth has parental-care so fully built into its biology: milk glands and placentas force mammals to be social from the start.

A great book that doesn’t deal with intelligence and mammals directly, but provides a key connection, is “Consciousness and the Social Brain.” The book makes a strong argument that consciousness sprung from evolutionary pressures that were essentially social — that being able to model (and predict) the mind of another is essential for communication and cooperation. But one can only model the mind of another if you first model your own mind, and thus, consciousness (which I would argue is just another name for general intelligence).

Well, we do see this behaviour in other animals, and not just humans, or mammals even.

I realise that's not broadening the net much - we share a common ancestor with everything that could be considered "living" on this planet, so ultimately it's all "human-centric" to an extent.

But if there are forms of life that are wildly different, to the point we can't communicate with them or even understand that they're "alive" in any meaningful sense, then that's kinda out of scope ;) The definition of "alien intelligence" only includes things that we would be able to recognise as an alien intelligence. Otherwise we're just talking to the trees, and they're dull conversationalists.

You just need to see what faint a signal we receive form the Voyagers, which are deliberately pointing their antennas at us and are thousands of times closer to us than any star to appreciate how improbable it would be for us to ever detect extraterrestrial communication.

I agree, but for different reasons. My favourite way to dissolve the Fermi Paradox is to simple state that the main assumption, i.e. "the lack of evidence of extraterrestrial civilizations", is just wrong :)

The entire Earth's history is hundreds of millions of data points.

Each year that a habitable Earth existed prior to life evolving can be seen as a data point. ... and with life emerging very very near its habitability transition, this reduces the drake error bars considerably.

The real limitation of the Drake equation is the duration at which life sends out radio signals - which given technological advancement and AI is probably only a couple hundred years.

Lacking any credentials on the subject whatsoever, and based on what (little) I know about abiogenesis, intuition tells me it happens with a probability of 1, if (and here's the key) the conditions are right, and given enough time. (A fun corollary of this is that intelligent life also happens with a probability of 1, under proper conditions [1]).

So, we just need to find how many planets have had the right conditions for a long enough period of time.

[1] p(abiogenesis)=1 + "evolution is a universal law" => p(intelligent_life)=1

Everything about UFOs is so implausible that the alternative explanation of "we don't know what we saw, but almost certainly not a UFO" seems to be much better.