However I do think that you vastly underestimate the probability of life. Take a look at https://en.wikipedia.org/wiki/Earliest_known_life_forms . See how quickly life appeared once the earth had cooled down? It's almost immediately!
I'm pretty convinced that almost all star systems have some complex energy conversion cycles that could be classified as life. Let's not make the mistake of assuming all life has to be carbon based.
https://en.wikipedia.org/wiki/Panspermia
I find this a compelling possibility.
DNA's 'half-life' is about 500 years. Meaning that each nucleotide-bond has a 50% chance of breaking every 500 years.[0] At the time scales of interstellar travel, DNA based life is very unlikely to survive.
EDIT: This then means that DNA based life was likely a local phenomenon. This also means that other planets may have done the same and that a 'interstellar seed' is not required.
[0] https://www.the-scientist.com/?articles.view/articleNo/32799...
[1]: https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemi...
What if life can only appear as a planet is finishing to cool down?
Yes, especially if you take into account the speed that entire galaxies travel in space. It's mind boggling high. So the effort for any civilization to build technology that allows them to travel through intergalactic space until they get "hooked" by Milkyway's black hole magnetic field is infinitely complex. That's where the whole idea around worm holes makes sense.
We even have evidence of life we have never seen, will never encounter, and may never even have conceived as being possible to exist without that evidence: the enormous dinosaurs.
Look, humans already adapted to being in space for prolonged periods of time. We adapted to every climate. But drop a naked human in a random spot on our planet, and he will die with high degree of probability. And that's after billions of years of evolution.
Who knows if this jump alone should be taken for granted - plus, not many planets could provide 3 billion years of "good weather" (or staying habitable) to start with.
We might be a slow developer and poor representative sample in that respect, but without more data it's hard to tell.
> plus, not many planets could provide 3 billion years of "good weather" (or staying habitable) to start with.
I suspect the opposite will be true, red dwarfs are the most common type of star and are stable for trillions of years. Even if the average time it took multi cellular life was 30 or 300 billions years then it might not matter for life evolving there. They do come with some other caveats though: https://en.wikipedia.org/wiki/Red_dwarf#Habitability
Lewis Wolpert : https://link.springer.com/chapter/10.1007/978-3-0348-8026-8_...
Life on Earth evolved and spread under specific conditions - our gravity, sun brightness, geology, magnetic field, large moon, etc etc. It then spread to all possible environments on the planet and evolved to live there.
Unfortunately, it could be that the 'growth conditions' for life are quite specific even if - once it gets going - life can evolve to more general environments.
But all lifeforms we know evolved from one common ancestor, it's one tree of life. As far as we know life evolved here only once.
So we know that once life happens it can become completely ubiquitous, but it doesn't say anything about that crucial first step.
That's not nessisarily true. Single celled organisms have a rather fluid exchange of genetic information even our 'single cells' are really several different organisms. It's possible life evolved many times on earth and current single celled organisms and thus all life has a mismatch of ancestors.
Further, life may regularly evolve even today, but simply get eaten due to the stiff competition.
PS: We know life evolved at least once, but the high end could be multiple times a second on earth.
It's also possible it evolved elsewhere and rode here on a meteor - or was brought here by some other lifeform several orders of magnitude more advanced than us, using earth as their own cosmic terrarium.
It's good practice to assume the simplest possible solution. However, the full range of the full range of what might have happened is ridiculously large.
I think it's worth pointing out that there's lot of space between "absolutely sure there is" and "absolutely sure there isn't", and I doubt any fairly intelligent person actually holds either of those absolute positions. Which is to say that really, the arguments are over the degrees to which we think it's likely there is life, or intelligent life, elsewhere.
Meaning if there are 24 factors crucial for life to
evolve, and each has a 10% chance of occurring - it's
actually quite likely only one planet would win on
this lottery.
a very large number of planets * a very small chance of life forming = ???
We don't really know how small the chances of life are. It may be that the chances of life forming are so small it dwarfs the number of planets in magnitude. It may be an incredible miracle that we live.
It seems that whenever an article says "there are more planets than we expected", someone concludes "this makes it more likely that there is life somewhere out there", but it's also fair to conclude that "this means the odds of life forming are lower than we previously thought" since we haven't actually found any other life. As Fermi asked, where is everybody?
Street-Math time!:
Lets assume that means you need to resolve a meter sized elephant on another planet. Lets choose Vega, as that is ~25ly away, really the furthest star we can go to (and return from) and still have someone alive here to have a beer with afterwards (50 year round trip). 25ly is about 2.3E19 meters away.
A 1 meter sized elephant at 2.3E19 meters is about 4.3E-20 radians.
Lets use wavelengths in the visible spectrum. Hydrogen's Balmer peak at 656nm is a nice red color to look at (though stellar issues abound here).
The resolution of a telescope is approximately : R = L/D. R is resolution, L is the wavelength, D is the diameter. Rearranging we get the diameter to be : D = L/R. Plugging in a L of 656nm (~6.6E-7m) and a R of 4.3E-20radians and you get D.
D is about 1.5E13 meters.
For reference the earth is about 1.2E7 meters, about 6 orders of magnitude smaller. 1.5E13 meters is about 14 light-hours, much larger than the Earth-Sun distance.
Soooooo, I think it's going to be a while ...
;)
Human minds aren't good with very large numbers. What seems "practically infinite" to us - isn't, really.
The number of all planets in the universe is said to be in the ballpark of 10^24.
Meaning (obviously) if you keep on dividing it by 10, in just 24 steps you get down to 1.
Meaning if there are 24 factors crucial for life to evolve, and each has a 10% chance of occurring - it's actually quite likely only one planet would win on this lottery. (At a given point in time, that is - that's another aspect of course).
Or 12 factors, but each with a 1% chance. And suddenly it doesn't seem like a number big enough to warrant certainty claims...
Basically it is the "wheat and chessboard" problem in reverse.
You start with a huge pile of planets, but once you start splitting the pile, it shrinks very very fast.
Personally I'm not sure either way, and I think being sure (either way) is just naive.
I believe there is microbial life out there, and I accept a slim chance we may actually discover it - say, over the course of the next few centuries - but I'm sceptical about the existence of intelligent life, and even if it did exist, I see the chances of any contact to ever occur as zero.