The paradox take into account the vast distance between stars. The idea is that in the billion of year of the universe, even when going very slow, even if it take 1000+ year to get to the next star with a generational ship, and then another 1000 year to build a society on that planet before launching the next ship, the univers is so old, that if there was an intelligent alien, it must already have colonized ALL the milky way. ALL of it, every star, and there are a lot. As big is the space, the age of the universe is far far bigger. Another counter argument, beside the usual (earth is a zoo monitored by hidden alien; life is super rare; intelligence is super rare and we are the first; there is a great filter that kill any intelligent life during their time, alien dont care to expand as in the article..) ; so another one is from kurzgesagt : It state that life appears so fast on earth, and grew so fast, that it must have been already a long way into its evolution. The first microbe was already super complex. So, may be it took the billions of years of the universe to get to that first microbe. So we are amongst the first intelligent life that can exist, because life took so long to get the first microbe. And only now can start the colonization for every intelligent species
Wouldn’t life have to spring up pretty quickly to make this feasible? To get from primordial cells to us took 5 billion years. Then it’s 2K years per system, which might mean 2.5 million stars 10 billion years after life begins on the planet in question. There are 100 billion in just the Milky Way (and I think anyone outside of that could safely be neglected as we cannot possibly detect them. So less than 1% of all stars in a galaxy within several billion years? I just don’t understand why anyone was asking the question.
Because in popular culture HG Wells postulated Martians to explain the (non-existent) canals, "little green men" started populating science fiction and the CIA used an "alien crash" at Roswell to provide a cover story for Project Mogul, thereby launching an outsized pop culture trend. Meanwhile, theoretical physics was still so young that Fermi, Teller, York and Konopinski could all be hanging out at UChicago but old enough that the age of the sun could be known at around 5 billion years, the age of the planet at around 3 billion years and the age of the universe at around 14. So on the one hand, popular culture insisted that everything weird was little green men but on the other hand, those with a grounding in physics or astronomy knew that the little green men had a substantial head start. Considering the rapid technological progress the human race was currently experiencing (cotton gin to nuclear weapons in 150 years), Fermi was having a hard time squaring eleven billion years of technological progress with how thin aliens were on the ground. I just don’t understand why anyone was asking the question.
You might be right. I never looked at the calculation, just report what I read. I suppose it is about the exponential of the growth, every planet you reach launch a new ship: 1 planet -> 2 planet -> 4 planet- 8,16,32... ... by the 36th time (72k years in my example) you did that you're at 34 billions planets. And that not even counting the fact, that the first planets can continue to launch new ships in the meantime. So the paradox is : since none of that happened, what prevented it. You can tweak the time to reach planet , rate of new planet conquest, and stuff and it still should have happened, so there must one fondamental reason it didnt, hence the article about living in equilibrium with your planet
The universe is 14 billion years old. I’m not sure how long it would take for the first truly habitable planets to form. You need to cycle through enough stars to form heavy elements and AFAIK you need the building blocks of carbon based matter so it might take 5 billion years just to get to the point of life being possible, let alone complex life, we’re talking just barely enough to support E. coli. Life on earth took 5 billion years to go from E. Coli to Elon Musk and being able to go to the moon and hopefully Mars. Being optimistic, I think you might have a window of opportunity from 10 billion years ago to a couple billion years in the future. It might be that you need more than just a marginally habitable planet. We might be lucky because we have outer planets to stop asteroids from hitting the earth, we have a moon to create seasons, we aren’t tidally locked, and we have lots of liquid water. If you get all life on the planet destroyed by asteroids and comets, or the seasons are too short, or only the twilight zones between the super hot tidally locked zone and the frozen night zone— all of this might make it hard to start life and might make colonization difficult.