> How, when given the evidence of practically infinite planets out there [...] can we even consider the possibility that this is the only planet with life?
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.
I agree with you in that we will probably never have contact with another sentient species of extra terrestrial origin. The distances are to vast, the lifetimes of civilisations and even species too short and so on.
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.
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.
But it's fairly likely to be carbon-based, as carbon is the simplest existing element with the maximum amount of valence electrons. And generally, simpler (= lower ordinal number) means more stable, as well as more likely to arise (as less energy is required, e.g. in stars).
There are other theoretical biochemistry possibilities[1]. Silicon, for example, works well in low-pressure environments. It's an immense stretch of the imagination to think about life-forms that use semiconductors to do useful work, but is certainly a fun thought experiment.
Hmm, true. But then, interaction with elemental matter life forms (like us) would become terribly difficult; it might be hard to even notice there's a life form existing in anti-matter.
That's the general assumption, even though there might be another stable "island" of fairly stable isotopes for higher-order elements than observed so far. But as I said, they'd need to be created first through nuclear fusion of lower elements, so their existence is obviously less likely, let alone life forms evolving on top of them.
> I see the chances of any contact to ever occur as zero.
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 don't know all the factors under which life can exist. Even the lifeforms that we do know of, occupy a very broad spectrum in all metrics, existing at all sorts of extremes.
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.
There's a huge difference between what evolved organisms can adapt to, and the conditions necessary to start life.
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.
Out of which some 3 billion years had to pass before unicellular forms of life evolved into multicellulars.
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.
> Out of which some 3 billion years had to pass before unicellular forms of life evolved into multicellulars.
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
That is the odd thing about the history of life on Earth isn't it? Prokaryote popped up almost as soon as was conceivably possible. And then. Nothing. For billions of years. The plausible explanation is that you need Oxygen for Eukaryotes and that's how long it to change the chemistry of a planet. It just seems weird to me.
"Let me make my position clear. The miracle, and I do not mean it in the religion sense, I mean it in the evolutionary sense, the miracle of the evolution, is the cell. While there are theories involving an RNA world and selforganising, it remains a mystery. Once you had the eukaryotic cell from the point of view of evolution and development it was downhill all the way, very very easy. "
But not in nearly as many emvironments as we can today. We can assume, over time, life learns to live under absurd conditions; but its hardly safe to think it can start in those same conditions.
I think humans are a bad example - we use our own relatively highly developed intelligence to solve problems, and that means we had to feel safe enough from the environment long enough to develop that. But if we look at older organisms, like the tardigrade, there are some incredibly robust creatures out there.
However, all the life we know of is part of the same Earth system. Just because some extremophile exists in a freezing desert or boiling pool does not necessarily mean that the same environments on other planets would have those organisms.
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.
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.
Why not both. We could also be descendants of an invasive alien species that killed off all of Earth's native lifeforms.
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.
Great reality check. I'll remember this point every time I read an article spouting the "there MUST be life out there because there are SO many planets" line.
> Personally I'm not sure either way, and I think being sure (either way) is just naive.
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.
I believe the post above was working out math that would make it so the probability would be 1 / #(of planets in the universe), which, following the law of large numbers, would mean that given an infinite number of universes, those universes would tend to have exactly one planet (Earth in our universe's case) that would have life.
In other words, the odds of there being life elsewhere in the universe is:
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?
In most variations of such a calculation the expected number of planets would be 0. The fact that the actual answer is >= 1 might suggest that the calculation is not an accurate representation of reality.
I'm not sure I'm understanding. It is a well-defined probability question to ask about the "expected number" of planets with life if there are 10^24 of them each with probability 10^-24, and the answer is 1.
I wonder how long much longer it will take for the astronomers to get the technology that would allow them to hunt for life in other stellar systems so that we can check all this out.
Depends on the size of the dish, really. You need to resolve the 'signs of life' at stellar distances.
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.
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.