"basically" is doing only what I suggested: a geometric series.
Here's exactly what work it's doing:
Pretend there's 10s of trillions of planets. That's 10-13 zeros depending on whose estimate you trust most.
1/10 factor cancels one zero.
at most 13 factors accumulated means you have 1 habitable planet out of all those planets.
We have just hypothesized a 1/10 factor in this thread - that leaves 12 more - and I've lised 6 more off the top of my head.
It's just a fermi question - ballpark estimates like that are a way of thinking of the relative scale. A 1/10 chance seems like it leaves a lot of planets left (as you say - 100s of billions), but there are already many 1/10 factors floating around.
The Milky Way alone has about 2.5 × 10^11 stars. The Andromeda Galaxy has around 10^12. Let's take 0.5 × 10^12 stars on average per galaxy.
There are about 2.5 × 10^11 galaxies in the observable universe.
This gives us around 10^23 stars in the universe to fiddle with. Assume every star has an average of 2 planets; some have more, some have none.
This is a pretty large number to trim down.
I'd argue the Drake equation is excessively conservative. Note that when microbial life first emerged on Earth 4.1 billion years ago, the Earth's atmosphere was rather reducing, and the Sun was around 30% less luminous than it is today. There was free water, but no free oxygen, and an extremely high-pressure CO2 atmosphere.
The universe is arguably extremely young; the longest-lasting stars will only burn out around 10^13 years from now, and the universe is barely 10^10 years old. It's fair to say that many sun-like stars haven't even formed yet.
Right but the unstated assumption that there is no other positive path isn’t any more well-supported than the converse. For example, observe the variety of life we have locally. I’m thinking particularly of the various life (or life-like but I digress) that exists in extremes like thermal vents or under-explored places like deep soil. So maybe it does eliminate 1/10 but maybe we forgot to add the other 1/10 for life that wants to
live at 100C (or whatever) — I’m pushing back on your assuredness, not the math.
Here's exactly what work it's doing:
Pretend there's 10s of trillions of planets. That's 10-13 zeros depending on whose estimate you trust most.
1/10 factor cancels one zero.
at most 13 factors accumulated means you have 1 habitable planet out of all those planets.
We have just hypothesized a 1/10 factor in this thread - that leaves 12 more - and I've lised 6 more off the top of my head.
It's just a fermi question - ballpark estimates like that are a way of thinking of the relative scale. A 1/10 chance seems like it leaves a lot of planets left (as you say - 100s of billions), but there are already many 1/10 factors floating around.