I don’t think there is a singular great filter. Instead I suspect there is a relatively constant probability of a black swan event across the entire existence o

I don’t think there is a singular great filter. Instead I suspect there is a relatively constant probability of a black swan event across the entire existence of a biosphere. It took over four billion years to get from simple replicators to what exists here now. It is quite possible that most biospheres simply don’t make it that long without such an event. We don’t know the probabilities, but over billions of years the continuous probability of biosphere extinction need not be very high to filter out almost all biospheres before they develop something capable of interstellar signaling or flight. Keep in mind that another prior we don’t know is the probability of a diverse biosphere developing this type of intelligence. We have no idea if that is likely or not even given sufficient time and energy inputs. Intergalactic flight is many orders of magnitude harder than interstellar flight, which in turn is many orders of magnitude harder than interplanetary flight. If the probability limits such intelligences to no more than an average of 1-2 per galaxy then there is your answer. We would be extremely unlikely to see intelligent aliens any time soon, even if we do find a lot of microbes. Given where Earth is now I would be surprised if it does not hatch an interstellar scale intelligence at some point in the remainder of its habitable life. Will that be us? Hopefully so. Given that we are already almost there (on evolutionary time scales) it is reasonably likely it will be us or an AI we create.