Why extraterrestrial life may not seem alien
quantamagazine.org
quantamagazine.org
We do not know if our evolutionary pressures are universal. We do not know if the evolutionary solutions developed here are appropriate even on other Earth-like planets, much less everywhere. Sensitive dependence on initial conditions could lead to radically different planetary environments, necessitating radically different mechanical solutions to survival, some (many, most?) of which we will never have even imagined.
What creatures would form under an intense magnetic field? In methane? In close orbit around a dim star? In a hot cloud nebula? Could we even recognize them as alive, much less intelligent? Definitely not if we're looking for bats and monkeys and octopuses
No, I think the whole genre of "life is much the same everywhere" suffers from a profound lack of imagination
Every single life form on Earth today had exactly the same time to do its evolution in. Us, bats, dolphins, tapeworms, birch trees, amoeba, mushrooms, all of that had exactly the same chance(s) in the same time span.
And we don't even know if and how mushrooms and trees communicate, let alone if they "think", for our near-sighted definition of thoughts. We don't even know what to make of birds, e.g. crows, with respect to the size of their brains and what they can do.
Is our planet, taken as a whole, alive, in some form of the Gaia hypothesis? The correct answers as of this time are either "we don't know" or "it depends on the definition of alive."
That Star Trek trope of "everything in the Universe is just like us with different faces" really needs to be put to rest.
Even H.R. Giger was boring and unimaginative with regards to how he envisioned the Alien. That's clearly a creature influenced by Earth-ism - a quadruped, with a single head and mouth and a flexible spine and claws, it's basically a weird cat.
Budget constraints aside, Star Trek aliens were used as a prop to explore extremes of terrestrial human behaviour and culture from an outside perspective - take a human and remove emotions and have them governed purely by logic, you get a Vulcan. Take a human and exaggerate their tendencies towards violence and honour, you have a Klingon, and so on.
Even in the original series there were truly alien aliens - for example the Squire of Gothos was a being of pure energy who just assumed human form, Devil in the Dark had a silicon-based creature, and the Tholians were an intelligent crystalline species who could only exist in high temperatures.
The premise is wrong. The premise here is that intelligence is the only factor. Physics doesn't allow dolphins to enter the bronze age. Hell, even if dolphins grew arms and hands they couldn't enter the bronze age. They're probably smart enough to do so, but there are other factors limiting them.
We have looked at Earth. We can look to the stars at the same time. It isn't an "or" operation.
I don't think we should label dolphins as un-intelligent just because their physical environment doesn't allow them to smelt metal.
My point is - I'd like to avoid judging something as (not) alive or intelligent just because it is (or isn't) similar to our daily life.
I think this is fair, but I also think when people say "detect intelligent alien life" it is shorthand for "intelligent and technologically capable life that would also be able to develop things like radio and interstellar travel." The latter is pretty cumbersome. I don't think dolphins are unintelligent, I don't think an ant is either. But in this context that's not what we're talking about. Language has limits and we use shortcuts like this all the time. Let's just be clear what page we're on and let's try not to inject another page just because the same word is used to mean multiple things.
When the franchise came into being, you're probably right. But in all fairness, the back story and the biological concepts in the Alien universe has been refined since then. For example, the human-like qualities of the xenomorph creature is now explained by the biological merger of an alien substance with the host. When a human was infected, the substance developed into a parasite that took-on characteristics of the host.
Fundamentally, the black goo (i.e. the substance) we saw in Prometheus was pretty much the source of all the alien creatures. It was basically an instrument that deconstructed existing life forms and rebuilt weaponised variants of them.
This is patently false as these species have very different places within the phylogenetic tree. Emphasis on tree, since their adaptivity experiments did not have a linear timeline either; we didn’t evolve to have speech from scratch, we’ve adopted existing partial solutions, e.g. having a tongue, to develop it.
And we don’t need to delve into phenomenology of being a mushroom, adaptivity gives us an observable proxy to the “intelligence” of an organism; how general and efficient of a problem solver they are, the ultimate problem being surviving genes onward. Turns out humans do exceptionally well, for the problems they’ve encountered so far. We’ll see if/how we can solve anthropogenic coordination problems of our day.
> That Star Trek trope of "everything in the Universe is just like us with different faces" really needs to be put to rest.
You need to cook a "complex adaptive organism" solution with the same periodic table and a handful of forces. It's like coding a CRUD application with slightly different sub-requirements and the exact same programming language. How different can they be?
If you need more creativity you have to break apart from physical requirements and the right genre for that is fantasy.
By that logic the most intelligent animals is a cockroach
Viruses and prions reproduce, not only are they not intelligent, they are not even alive.
Firstly, please notice the quotes around intelligence; clearly we’re playing with a fast and loose definition.
Secondly, if humans had driven themselves into extinction with nuclear warfare, that would as well have been true.
Intelligence is not mere symbolic processing, nor symbolic processing is guaranteed to be adaptive, as evidenced with its failure modes in our perennial irrationalities.
> Viruses and prions reproduce, not only are they not intelligent, they are not even alive.
I know one particular virus twisting humanity’s arm these days, and in a way that is not fully intelligible to us yet. I wouldn’t readily diminish the internal logic that’s going on there.
> There are these two young fish swimming along, and they happen to meet an older fish swimming the other way, who nods at them and says, “Morning, boys. How’s the water?” And the two young fish swim on for a bit, and then eventually one of them looks over at the other and goes, “What the hell is water?”
On earth's carbon based life forms you mean. Its a huge blindspot, basically monkeys looking for other monkeys. If we believe our life is sufficiently compelex biochemically, it figures that other "life" may have the same complexity but with very different structures.
So the argument for ET life to have almost exact homologs of terrestial life is bordering on naievete at best, and dangerously intolerant at worst.
It is your kind of fantastical thinking that life somewhere else somehow isn’t subject to the same physics as life here that is naive. It’s not wanting to be bound by boring concepts like chemical reactions, gravity, perceiving your environment in some way, etc. We don’t take people seriously that say that stars in other galaxies are actually the heads of long bright snakes and us thinking they are just boring balls of gas is our “blindspot”.
We don't know factually if a beetle can think and remember.
We know about proteins.
We don't know how some aquatic life can survive in the mariana trench.
Biochemistry is indeed chemistry but it isn't as straight forward as we'd like to imagine. Till this day there are cell structures we are uncertain of and would be completely wandering in the dark were it not for cheap but powerful computation available 24/7.
Lets go smaller and things get blurry. The standard model looks...hmmm.
What does this mean? We don’t know the exact capacity of the mind of a beetle. We don’t know how its subjective experience compares to our own. But we know that the structure of neuronal tissue allows information to be stored, just like we know that the structure of DNA allows information to be stored. The relay on chemicals, temps, and pressures where weak chemical bonds and be reliably broken and made.
> We don't know how some aquatic life can survive in the mariana trench.
Again, what does this mean? This feels like the misunderstanding when we say “we don’t know how the pyramids were built” which means we don’t know everything about the exact methods used, but we understand the general technological levels of the time. While people take it as “the ancient Egyptians had a secret technology” or “they couldn’t have built them”. We haven’t been able to observe certain behaviors or exact mechanics or feeding habits for some animals, but we understand how they survive.
> Biochemistry is indeed chemistry but it isn't as straight forward as we'd like to imagine. Till this day there are cell structures we are uncertain of and would be completely wandering in the dark were it not for cheap but powerful computation available 24/7.
Understanding the exact mechanisms is not the same as understanding why cells would be round, or why a semi permeable membrane is important, or why they need energy to resist entropy, or how they need a reliable way to encode and store information,etc.
Understanding very specific and exact biological processes is not the same as understanding basic constraints placed on all matter. If its too cold for chemical reactions to regularly take place, that is a constraint. If a material does not have a structure that can be broken down and remade, that is a constraint. The inverse square law is true everywhere, which is why we can say we won’t see giant flying dragons on any planet.
What are those constraints? Can you enumerate some of them?
Also, physics and chemistry change under certain environments.
I'm personally expecting something like 80% humanoids and 20% exotic forms. Maybe I'm primed incorrectly by cheesy soap operas and sci-fi TV shows, but I think they're not far off (even if for unrelated reasons like SFX/VFX budget and character empathy).
Cyclops got by with one eye and throwing rocks.
A head is pretty universal because eyes are so important and a feeding hole near your sensory organs is a massive advantage.
Having hands seems almost a pre-requisite to become truly intelligent and tool-using.
Earlier, you mentioned that beaks can't make spaceships. Well, maybe neither can hands. What we call a spaceship might be laughable nonviable. In fact, we know it is.
We're struggling at limits that some other lifeform might not have. We're hill climbing for tools that will let us do things we really want to do. Quite likely a lot of our progress is orthogonal or even oppositional to what we need to do to get off the planet.
We have no idea if some of our progress might be backsliding or entirely halting our future progress. Due to our natures. Due to our beaks.
Except hands did create spaceships...
The "beaks can't make spaceships" is a comment about crows not having hands. Crows use their beaks to manipulate objects. This does not imbue cows with great motor control. The use of tools is very different than the ability to finely manipulate tools. Aliens could have beaks, but these would not be their way to build spaceships. Similarly they wouldn't have pincers. Such grasping mechanisms just are extremely inefficient and don't allow for certain tasks.This excludes a lot of classes of tools from crows. This isn't biology, this is physics.
And they would have tools as multipliers for their natures, just as we use tools to extend ours.
Our wonderful inventions might be another species child's play. Our herculean efforts to reach the stars might be a triviality to a species that can synthesize novel compounds in their bodies, and/or those of their stock animals. We're just at the early stages of doing that with algae, after a very long climb from first making fire.
Just as I could train and arrange to walk to Mexico, they might be able to self modify and reach the stars. No spaceship needed.
Our great ideas and dreams might be trite to bigger minds out in the galaxies. They could have easily skipped over what we struggle with.
"Humans can't even excrete flexible ceramics. They need air. They need heat. They can't stand up to ionizing radiation. This isn't biology, this is physics!"
Cephalopods have got onto land at least twice. Nothing says they can't do it again.
Sure? But isn't that my point? They sure looked different and had different physical attributes when they lived on land.
> They can't stand up to ionizing radiation. This isn't biology, this is physics!
I wouldn't compare this to the ability to use a screwdriver. Or in a more abstract way, be able to grasp, twist, and push.
They already have, it's called praying mantis.
May insect forms are very non-humanoid and are very viable.
I am not clear on calories - are insects inefficient?
So basically if you can get food and don't have to spend significant time thinking to do so, there isn't going to be a selective pressure to encourage brain growth. And if you have a selective pressure to devote energy to the brain you're also probably going to have a selective pressure to reduce energy from elsewhere.
Additionally, I'll add that humans both lost fur and stood up because it is better for thermal regulation (there are other pressures too, there's never _one_ reason). So this also helps with the surface area-volume issue.
Basically what I'm saying is that there's these locally optimal conditions that need to exist at the same time to produce intelligent, tool using, civilization making creatures. (I mentioned in another comment that environment matters too. Can't get a bronze age underwater. But I also didn't mention you can't get a bronze age if you don't have a social structure, something, for example, octopi lack). Basically what astrobiologists are looking for are the combination of these optima necessary to produce certain traits. What many commenters here are missing is the combination part, mostly thinking that only intelligence matters to create a space fairing civilization, but you can't get to space if you can't create advanced composites, explosives, and many other things. Or in other words, the astrobiologists aren't idiots and probably know what they are talking about despite what it looks like. It only looks like they are dumb because people are overly simplifying the problem.
Also, what if a non-protein based molecular machinery can be so energy efficient and powerful that species having that can skip some seemingly necessary part of development? But I’m by no means an expert on the topic, just asking. If the reasoning was about absolute limits, I would be much more accepting of them (eg. Energy required by the simplistic work done, like a given skeletal structure picking up a weight with muscles only consuming the minimal physical necessity)
There is no natural speed that life has to operate at. Any aliens we encounter are much more likely to be very, very slow, because it is they who can stand the vast chill void between stars. If they visit, and you dare to chop one down, you wouldn't find anything recognizable as brain inside.
> metal structural systems for animals
Something resembling this has actually been observed in a species of deep sea snails. Iron sulfide is incorporated into the hard bits (shell, foot armor). (https://en.wikipedia.org/wiki/Scaly-foot_gastropod)
And if you consider dinosaurs humanoid, then so is that meme cat that can walk on its two back legs.
If there was an apex predator in every tree of life, in the "humanoid" shape, and I'm talking "humanoid ants" here, then it would be reasonable to assume that there's something beneficial in the "humanoid" shape that helps long-term survival.
And that's not even taking the majority of lifeforms into account - those in the seas, and greatly discounts birds. We still can't agree on if dolphins and crows are intelligent.
So, no, chances that the "humanoid" shape is somehow special out there are basically 0, since it's not even special here on Earth. We're an accident. Insects, mushrooms, plants - all those life forms are better adapted for mere survival than us (judging by cumulative mass of live organisms).
And that dinosaur comment - I don't know what to do with that. Dinosaurs only walked on two legs in internet memes? That's so far wrong I can't comment.
The convergence between dolphins and ichthyosaurs is even more remarkable. Ichthyosaurs were marine reptiles; air breathing tetrapods that, like dolphins, had ancestors that walked on land but eventually returned to the sea to kick fish ass.
https://en.wikipedia.org/wiki/Ichthyosaur#/media/File:Ichthy...
Those fish are overwhelmingly more closely related to horses than to sharks.
What about the branches that happened early on? We essentially have only two lineages of macroscopic organisms that are actually fundamentally different: Plants and animals.
I would expect any kind of macroscopic extraterrestrial life to be at least as distinct from Terran plant and animal life as they are from each other.
That's not true, we also have fungi as a macroscopic lineage.
Or maybe you put them in the plant group? If so, that's a mistake, as they are more closely related to animals than they are to plants.
And then consider the selective pressures from plants vs fungi. A fungi gets its environment. Plants do some, but also need to perform photosynthesis. These have very different selective pressures for these lifeforms.
So the idea we'll see some vastly different concepts with different starting blocks is possibly unfounded.
Alien life might be very different at low level depending on their environment, but in terms of macroshapes, things like the formation of a head with eyes and mouth, upper and lower limbs, bilateral symmetry and so on will repeat over and over.
We'll see (in another life probably).
Considering that we have a whole class of lifeforms that have nothing like a head with eyes and mouth or limbs, the idea that this would evolve independently more likely than something completely different, is also possibly unfounded.
Plenty of animals that have 2 eyes and no 3d vision, they try to get as close to 360 coverage as possible.
That feels like a really bold claim given the evidence.
Unless we find a planet composed entirely of solid smooth rock we won't find wheeled animals.
Think about how some LCLLAS talked about how silicon life is probably a thing. First off, it it were, given Earth's crust is mostly silicon and its the most habitual place ever discovered, it would have evolved here. but it didnt. It turns out silicon is just too ridged, and to get life going you need all sorts of chemical properties that just aren't congruent to life.
We are carbon / oxygen organisms for a chemical reason. despite the availability of other resources, other forms of lifeforms didn't develop for a reason. maybe other forms of life does exist in some methane ocean on Saturn like planets, but its not going to be very complex, and definitely not intelligent life building space ships.
The thing is, life has almost infinite time to evolve out of these various elements. The fact that it didn't evolve here on Earth means absolutely nothing, seeing as Earth alone has billions of years left where such life could arise, and there are literally countless planets everywhere in the universe where the random dice of evolution roll every second.
Except the ratio of hydrogen to deuterium is a function of astronomy and more specifically fusion. No naturally formed planet is going to end up with that imbalance. Which means no natural deuterium based life forms. So while some alien civilization create deuterium life, it’s not going to be part of natural ecosystems.
And so it goes for most possible interesting edge cases. Dependency on rare elements like Neptunium means any competitors without that dependency have huge advantages.
On the other hand if proto life is extremely common then silicon proto life might always be out competed by more efficient alternatives. For example the fact Silicon dioxide is a solid where carbon dioxide is a gas is a major advantage or using carbon.
Hybrids are a different story, but I doubt that’s what anyone is talking about by silicon based life forms.
You don't get to constrain alien life to your preconceptions. Even some Earth life secretes SiO2. Using carbon for some things would not invalidate its Si-basedness any more than diatoms have given up carbon-basedness.
Silicon's near absence from our favored solvent, like iron's, is a product of toxic levels of biogenic atmospheric oxygen. Our early oceans were saturated with iron products, and are now starved of them. There is no reason to assume oxygen would be their favored oxidant.
That goes back to astronomy no other option is going to be nearly as plentiful.
> You don’t get to constrain alien life with your preconceptions.
It’s not a preconception it’s the solubility of silicon and silicon compounds. Yes, CO2 and SiO2 aren’t the only option for respiration, but CO2 was and is a near endless supply of carbon and oxygen. Without that growth simply slows down dramatically. Even with a photosynthetic equivalent you simply don’t get the great oxygen event from silicon lifeforms in even 10 billion years.
PS: To be clear I am not saying silicon life would be impossible just that it’s at a huge disadvantage head to head and would have a vastly slower progression to large scale multicellular life.
Carbon is a good choice for our temperature range, but there are plenty of temperature ranges as well or better represented. Life will not sneer at the others. Most life on Earth cannot make any use of the carbon in CO2, no matter how much of it there is; in fact, the more of it there is, the worse off most living creatures are, only green plants excepted. You would die in a room with the nitrogen replaced by CO2, despite that you use none of the nitrogen at all. (Only bacteria can "fix" nitrogen, and only some of them.)
Iron is very plentiful in the cosmos and in Earth's constitution, and most life depends on it, but it is practically nonexistent in the open ocean; yet life thrives there. Even where iron is plentiful, life uses hardly any. Silicon is extremely plentiful, too, yet used by our life even less -- until just lately!
So, your argument from plenitude utterly collapses. Life as we know it is a product of history and circumstance. Given different circumstances and different history, you should expect a different product. There will certainly be similarities dictated by physics: e.g., cells are very, very likely, and equally so use of liquids. Aperiodic fibers to encode genes, cognate to our DNA, and others to fold up and carry out processes, cognate to our peptide chains a.k.a. proteins, are quite likely. But there is no reason to imagine that any of the details of the encoding would match.
That’s a huge misconception about biology and evolution. Basic cellular biochemistry is extremely well conserved. There is almost no pressure to use more iron, but significant pressure to use less. Photosynthesis for example is Iron dependent and that acts as a major limiting factor on ocean ecosystems. Yet, we don’t have an iron free alternative adapted to utilize that giant ecological niche. Life is seemingly using as little as possible.
That should suggest why primarily silicon life is such a poor option.
> There are plenty of temperature ranges as well or better represented.
For complex life it’s not just about temperature but also pressure and access to sunlight. Anyway, the normal argument is that silicon based life could thrive in extremely high temperatures. That’s all well and good for silicon but not so much the other chemicals it’s interacting with. Life is dependent on being able to reliably create and break relatively weak chemical bonds. However, when you start to look at the actual chemical options at those temperatures you run into serious problems. The kind of large molecules you want for complex life are either unstable or too stable at those temperatures.
At room temperature. Silicon life, if it exists, would be basically using lava instead of water. Glassblowers work at 600 degrees, i imagine thats the sort of temperatures where we will see any silicpn chemistry take place at non glacial pace
Net result you might get the equivalent of very simple multicellular life, but intelligence becomes extremely unlikely.
Chlorophyll photosynthesis does not work well at high temperature, but that says less than nothing about whether photosynthesis of different products using a different molecule and a different process could evolve. What we can say is that if it could, it would, somewhere.
You have no basis beyond your own preconceptions for any statements about likelihood. Thus, your estimate is 100% confabulation.
In case you didn't know, Earth has about one billion years of water left.
https://www.sciencedaily.com/releases/2013/12/131216142310.h...
by definition, the most probable form of life in the universe is the 1 we are observing. you only need math and probability to figure that out. We also have observational evidence. As far as we can tell, there is no other life in our solar system. We have 8 other planets and many moons that have failed at creating life in any form - that's literally hundreds of billions of years of failed attempts at life.
you can't just pick an element and think its going to work. you need ALL the elements, ALL the states of matter, and the right ratios and amounts of elements to work. Even if you get that lined up, expecting complex life to form under enough pressure to create diamonds in thousands of degrees centigrade also puts the probability of complex life off the table.
I don't known who this is hard to understand. in the simplest example as the article states, if you want to fly, there are things that necessitate something that will fly, such as wings. no wings, no fly. sure its POSSIBLE you can fly without wings, but UNLIKELY. given that we have multiple lineages of evolution taking different paths that end up with the same solution is evidence of that.
The Earth is the edge case, is the point we're making. All of the conclusions and deductions about what life must be like elsewhere that use Earth as their implicit foundation are going to be overfit to the data, so to speak. Organisms on Earth converge to similar forms: dolphins and fish, bats and birds, for instance, so the form is useful on Earth is a valid observation. Therefore, we can expect to see these forms throughout the Universe is a quite a jump.
You do not know that. All available evidence points to the opposite: We have no knowledge, not even a hint, of any other physical process that could sustain life than that of Earth's carbon-based chemistry.
The idea that life could take a myriad of different forms is beautiful, but it is pure fantasy, based on no evidence at all.
Again, how can you be so certain of it? Life could have existed in some form on Mars or Venus or even Mercury millions if not billions of years ago, only to be extinguished by the changing conditions in the solar system and ground to absolute dust by time. Maybe not advanced space faring civilization, but life could have existed in those places and you simply don't know.
>> you only need math and probability to figure that out.
Yes, and maths and probability are telling me something very opposite to what you are saying. That if you are observing a solar system like ours(forget the entire universe for a second) for a ~100 years out of billions of its existance, then sorry, but you don't know anything about it, certainly not if it harboured life in the past or not, not to a degree that you seem to be certain of.
Buoyancy in water is different than in air. Lighter than air natural controlled flight, even in a relatively dense atmosphere like Earth or Titan, is highly unlikely. Fish maintain buoyancy with oil in their livers which is a relatively low energy process.
Hot air balloons and other LTA vehicles work by having a mean density lower than the containing medium e.g. the atmosphere. Even with Earth's relatively dense atmosphere there's not a lot of lifting gases that are effective without significant heating. Definitely not readily made by biological chemical processes. That leaves thermal balloons. The amount of energy to heat the air in a hot air balloon is pretty significant and requires energy dense fuels.
So a hot air balloon animal would need to produce and then burn energy dense hydrocarbons and have a strong yet lightweight natural gas envelope and body structure that could handle the burning of that fuel. Burning I would note at temperatures that would sterilize surfaces.
Not balloons perhaps, but spiders float on strands of silk using very similar principles.
Pollen and seeds frequently use some kind of floating device to spread as far as possible - again, you probably wouldn't call it flying as such, but they can move through the air for the purposes of reproduction without having wings.
2. Buoyancy in air has been achieved with an industrial level of success using hydrogen. Producing hydrogen is easily within the energetic range of biological processes. Air-buoyant animals could have existed for millions, even hundreds of millions of years before being outcompeted by pterosaurs and birds, and then left no trace.
Sharks are fish, so this clearly isn't categorically true. You probably mean either bony fish (for which I think it's kind of questionable that its true) or more specifically lobe-finned fish (for which the case is stronger.)
“Fish with air bladders do not, in fact, use oil in their livers for buoyancy. They have an ‘air bladder’, which you may read about. [...] Fish with air bladders are much more closely related to you than to sharks, so it is a big error.” is critically different than what you actually wrote upthread, and is obviously kind of silly. It also would have made no sense in response to the post it responded to, which also referenced “fish” in general and not “fish with air bladders”.
It could be that silicon based life is in fact constrained by temperature and can only arise in planets where the mean temperature is in the thousands. This could in fact mean that we do have a parallel silicon based biosphere underneath our feet. There is obviously no evidence for this whatsoever but then again, there is no reason to assume that the occasional leakage in the form of volcanic eruptions would leave any trace that we could use to deduce that these samples were once living entities.
I'm at best doubtful about life on Mars because I find it hard to imagine some form of life that occupies a small part of Mars i.e. it's only in the parts we haven't seen. I tend to think if there's any life on Mars it'll find a way to deal with the conditions on all of Mars. By the same token if there's any silicon based life then it'll pop up in places that we can find as well as those we can't. Maybe it does best in places we can't but surely there would be some oddball silicon based creature that would beat the odds.
The macro example would be the extinction of the South American marsupials when the North and South American land masses merged. All the placental animals in North America went south and all the marsupials in South America went extinct. Except for Opossums which for whatever weird reasons not only survived but went into North America.
We have no evidence of a void ecology in near earth orbit or of life persisting close to the Moho barrier - where the crust meets the mantle. There are hard limitations to the encroachment of life that only technology or radically different chemistry can circumvent.
The same hard barriers might also mean that life on Mars is largely constrained to those few underground liquid water lakes that we have recently found evidence for. Keep in mind that even the most barren deserts on Earth have several orders of magnitude more water present in the air than on Mars.
Other areas that are similar, sure. But if you're asserting that we can be confident there are no subterranean mantle-creatures because we don't see any wandering about out here, I don't think it's a good argument, for the same reason we can't go down there ourselves and look
Like, if it failed to do so, it would fail the definition of life? I don’t think anyone defines life that way, and I don’t think it would be a good definition (would I even count as alive under such a definition? It seems like no.)
For all that after several billion years it's just carbon based life forms in these parts. You'd think that there must be some area where silicon based life would provide an advantage. Unless it's a case that carbon based life is an overwhelmingly superior product but on some hypothetical world it's simply filled with silicon and there's virtually zero carbon.
Additionally we find organic molecules everywhere from comets to gas clouds in galaxies. We don't really find as much interesting silicon-based chemistry everywhere.
We have only a single very specific data point. That, and the human tendency to opine confidently about that which we cannot know.
Just give it a few more decades ...
The common ancestor of octopods, insects, and humans had eyes, and coded where to put them with the same gene in all lineages that have eyes. This was demonstrated by inserting a vertebrate "eye here" gene into a fruit fly embryo, causing an eye to grow there.
On the other hand, If life is that which can use an energy differential to create more order within it (an entropy pump) then sure there are likely forms of “life” out there that we’d have a harder time imagining (that perhaps operate at physical scales and timescales beyond us — thinking nebulae)
... in Earth-like conditions, and useful in Earth-like conditions. Vibration of denser or rarified gasses could require other solutions to exploit, if it's possible at all
> If life is that which can use an energy differential to create more order within it (an entropy pump)
Now that's the ticket! Under this definition, I suspect most life in the Universe is not carbon based, but far more exotic (to us)
Before the question of what you have the question of if.
Then you have the question of continuous constraints. Sensitive dependence on initial conditions still has to operate in a constraint space, and maybe constraints for complex adaptive living systems are much tighter to begin with. Tornados are also sensitive to initial conditions, they are even self organizing, but they are not living beings for example.
Imagination is fine when you’re not burdened by starting a working system from first principles. Conceivable sounds probable when you know less about the constraints.
Meh. I mean, sure, when all is said and done, everything is constrained by physics and chemistry and imagination has no bearing on this reality. On that we agree, to the point that stating it outright is almost a non-sequitur: a true statement that has no relevance to the discussion at hand.
Human culture, in the 400 years of since the first glimmering of the scientific method, has made gigantic leaps in understanding objective truths about our Universe and what lies within it.
At every step, highly educated people confidently assert that we know all that is worth knowing and everything henceforth will just be filling in the details. At every step, these assertions have been a failure of imagination.
I can confidently state with only historical evidence to go by that our current understanding of the Universe is deeply flawed and will be completely overturned someday. Or if not, it would be because we're just not intelligent enough as a species to do it, and not because we know it all*
It is this sense that I mean, when I say that asserting all life throughout the Universe will have forms like those found here, is a failure of the imagination.
* Everything that we ever will discover is constrained by the form of our bodies, our evolutionary history, our psychology, and to a lesser degree by our cultural outlook and worldview. There are truths about the universe that are literally forever beyond our discovering because we are incapable of discovering them.** Were we to encounter alien entities that made use of such hypothetically inaccessible principles, especially if their physical forms were based on them in some way, we would literally not understand what we're looking at.
** As an aside, that is my favorite explanation for the Fermi Paradox, that the interstellar cosmos is thrumming with the signs of life and civilization, but we only partly and minimally understand what we're looking at, and so miss these signs.
On the one hand, the conditions under which some lifeforms are thriving here on Earth are already pretty extreme.
On the other hand, indeed, we may not yet be in a position to be able to imagine, realistically, all that we would (eventually) agree to call a lifeform. (Life built from phonon "particles" in a planet-size crystal, anyone?) Sure, there may be constraints, such as life, in a meaningful sense, may only be realizable based on polymers, in which case the conditions must be such that they allow polymerization of simple substances to take place.
Not really. They are all within +/-5km of the planet surface, live under 1g of gravity, as a rule, are not exposed to X-rays, gamma rays, cosmic rays, strong magnetic fields or nuclear radiation, or extreme temperatures. There's nowhere on Earth that receives more than about average solar radiation or gets much above 100C where life survives.
Life generally has access to ample oxygen, though a few anaerobic organisms exist. They're all DNA-based, have access to ample amino acids, aren't bathed in thousands of completely toxic chemicals, have liquid water (and not, e.g. liquid methane). The list goes on and on.
Yeah, there are a few extremophiles, but they are by far the minority, and are clearly adapted incrementally from other organisms that evolved in non-extremophile environments. In essence, there's a large reservoir of easy-pickins living that generates biodiversity to cross over into extremophile environments.
Now imagine 5x the gravity, 100-1000x the solar irradiance, the lack of magnetic field (and thus direct exposure to solar winds), no atmosphere, or atmosphere entirely composed of a toxic gas, extreme exposure to X-rays, etc. The universe is full of many places where Earth life, even extremophiles, would have no chance of survival. And such places don't have reservoirs of biodiversity from which to adapt to these conditions. They're just dead.
This is not accidental. There is more genetic variation in humans in Africa than the whole rest of the world, and more variation in English dialects in England than the whole rest of the world. We -- everything we knew existed until recently -- evolved from extremophiles. They came first. The world changed around them. Some changed to match, eventually giving rise to us, while others found places more like what they were used to. The latter are still to be found in those places, and in many others they have also adapted to.
Common types like us are adapted to currently common conditions. When the environment changes radically, and all the life we knew of up until recently is extinct, the extremophiles will radiate a new ecosystem adapted to new conditions.
We have exactly one example of an environment that nurtures life. It does not logically follow hence that it is the only environment where life can thrive (unless we choose to define life as that which thrives in an Earth-like environment)
I do agree that probably most of the Universe is hostile, not only to Earth-like life, but to life of any definition. But we cannot be certain. We have never visited nor sent a probe to a 5g planet "100-1000x the solar irradiance, the lack of magnetic field (and thus direct exposure to solar winds), no atmosphere, or atmosphere entirely composed of a toxic gas, extreme exposure to X-rays".
I'm more of the "Boltzmann Brain" persuasion. Life might take the form of electromagnetic waves or metallic structures that are respirating, self-replicating, information-processing things. In my more paranoid days, I think the internet is alive, as it is kind of like a life-form growing our the substrate of our collective digital actions.
It seems unfathomable to me that life could be composed of bosonic particles, since Pauli exclusion seems to be one of the most important reasons why matter (never mind living organisms!) has the property of spontaneously structuring itself in a rich and complicated way.
> At some point we're either going to murder ourselves or create a Von Neumann machine capable of interstellar flight.
There are many, many possibilities for human futures that are between those two and not do extreme. It is absolutely possible we survive millions of years without interstellar travel or self destruction.
> Since that obviously hasn't happened with alien machines
I also think it is not so obvious that this hasn't happened or isn't happening with alien machines. It certainly could be and we would not know either way. A la 2001: A Space Odyssey, perhaps in fact we are a product of alien machines themselves.
Because if you don't, someone who does is going to invade for energy and resources. Therefore, refusing to expand is a slow form of suicide, unless you can be somehow certain there's no entity like that in the potentially accessible space.
At some point growth in any star system is going to be finished - energy extraction near maximum, no free matter left to convert into computronium. After that, only two solutions remain: stagnation (death) or expansion. Assuming no instant communication (not just FTL - instant), the bandwidth argument only means it makes more sense to haul energy and computronium from the rest of the accessible space into one point.
We may very well already see it somewhere far away, thinking it's "natural" rather than a construct. I think under current knowledge the most likely prediction is something resembling a sphere (minimizing distances between points) that utilizes black hole power plants, feeding them matter from stars and nebulae.
From the outside, it would look like a giant void with nothing in the center. Maybe there's something like that in the center of the Boötes void?
I've heard that described as "where are the supernova defense systems?" Of course, I'm not aware of any explanations for why it's physically impossible to have a relatively small system sufficiently "hardened" to survive a supernova, or perhaps a way to defend oneself (including hiding) that doesn't require stasis.
why do it?
Everyone doesn't have to do it. Just one person out of billions does. Think of the strange and perverse collection of behaviors we observe in a population of a few hundred million people online and speaking English. Expand that to billions of hyperintelligent minds and somebody is going to want to colonize the universe.
But anyway back to the discussion:
>The mass of one planet being able to simulate billions of planets is only possible if the simulation is rather poor
The mass of one solar system! And you don't need to simulate the system to a planck length. In fact the book specifically addresses that scenario - different simulations have different planck lengths and planck times, depending on the needs of the users of that simulation. For most users (certainly your average modern baseline human) that length might be on the orders of fractions of a mm, and some users might not require a physically meaningful interface at all!
>Everyone doesn't have to do it. Just one person out of billions does.
That's assuming that the culture doesn't have significant bans on von-neumann style self-replicating machines. If they allowed such devices of course you'd expect an expanding light cone of computronium around every significantly advanced culture but any sane long-lived culture would recognize that such machines are just about the only existential threat that a culture with those capabilities would face. That might significantly limit the 'explorer' class to those entities willing to do the equivalent of taking an ice pick to the frontal cortex in modern humans in order to undertake a multi-multi-millennia solitary journey into the void. Some fraction of those trips would fail, and the successes would take a non-trivial amount of time to launch another. Maybe those growth rates are smaller than we would suppose and the universe has only had stars capable of producing the elements of life for a little while on a universal scale, maybe those light cones just haven't reached this corner of space yet.
Definitely. In fact, I think they are almost certainly unique in our entire local galaxy cluster, and we will never find anything even close.
We could very well find something interesting, enlightening, sophisticated or using what we might be able to squint and call technology, but I suspect we will never find an alien civilization intentionally broadcasting for example the fibonacci sequence or prime numbers so that we can learn to exchange culture and communicate ideas.
I'm not so sure. We can't even be sure if cetaceans, in particular orcas, have thought patterns similar to ours. Of course, they lack the physicality and environment to develop written history and knowledge and also technology, but we currently have no way of knowing what their thoughts are.
Most would argue against a species being intelligent if we could not communicate with it. "These are just automatic processes, like sophisticated software"
If we focus on recognizable features, we may look for organisms with self-replication skills (a feature of living organisms) and prediction skills (a feature of intelligent organisms).
On the intelligence aspect, the skill to predict the future in general, and imminent threats in particular is useful for structured organisms less resistant than rocks to survive. On that matter I wonder, do unicellular organisms on earth have prediction skills?
What also helped those fragile structures to continue existing along rocks after a long time might be their ability to replicate themselves before being destroyed. Reproductive skills might actually be the first interesting feature to look for in extraterrestrial organized structures.
Sure, but I imagine this is easier said than done. We 21 c. humans would be most likely to recognize as intelligent life something obviously not a natural feature of the landscape, that operates on a time scale under a year and above a split second or so, that predicts that which we can predict, and most importantly has a form corresponding to Earth creatures. Without ticking all those boxes, especially in a truly strange chemical environment, we will have people asserting that they are a complicated chemical processes, but in no sense alive the way we are alive, if we can even recognize them at all.
That said even in any other fluid I doubt we’ll ever look at an organism and say “it swims like …<blank>“ because there wasn’t an earth organism that swims anything like it. Of course that means comparing to every method of swimming locomotion on earth which is a staggering diversity from the microscopic up to whales.
Unless other forces are involved (e.g electromagnetism isn’t used for locomotion on earth to my knowledge) and the fluid is incompressible like water, then I’m (armchair) guessing “to swim” doesn’t have that many evolvable solutions, regardless of pressure/temperature and the specific chemistry.
Hey, whatever sells a pop science book pounded out over a long weekend.
It's funny how sure everyone was about slowing expansion of the universe and the idea of close rocky planets/distant Jupiters, but only lucky guessers are remembered.
It could simply be that patterns for lifeforms on Earth were set so long ago that everything sort of rhymes. Veer that path at the beginning and you end up with a significantly different answer.
They had a common ancestor of a coral-like sea squirt (If I remember right). That looked nothing like a fish.
https://www.goodreads.com/quotes/78268-a-poet-once-said-the-...
Nit: Isn't the estimated age of the universe 14 billion and earth 4.5 billion? I wouldn't call that nothing.
https://en.wikipedia.org/wiki/Future_of_an_expanding_univers...
For example, if life--any life--forms on a planet, it is likely that some macro-organisms will evolve that consume other organisms.
On Earth we have plants that are eaten by animals that are eaten by other animals and so forth and these all act as a form of "battery" in that solar power is converted into energy and increasingly stored in larger "blobs". This is almost necessary for large life to exist. Well, for carnivores at least (eg many whales eat krill and there are a bunch of filter-feeders).
So the chemistry of life elsewhere may be similar or it may be totally different but something like a carnivorous trait is I think almost inevitable.
Once you have that then certain other traits became almost inevitable. Flight, for example. It may be that flight is impossible given local conditions (eg high gravity, atmosphere or the lack thereof). That doesn't mean we'll end up with feathers and birds per se but evolutionary pressure will likely mean available niches are filled. On Earth almost every environment has life, only really excluding the coldest, driest, highest and deepest of places.
Also, consider sensory organs. I expect the ability to detect parts of the EM spectrum, sound, taste/smell and tactile feedback will all likely evolve with sufficient time. And that itself has consequences for what life looks like.
Given the age of our universe, sun, earth and humans:
Universe 14 000 million
Sun 4 600 million
Earth 4 550 million
Earth Life 3 500 million
Humans .2 million (200,000 years)
Second, you're ignoring the fact that life as we think of it can really only evolve around at least 3rd-generation stars because you need enough heavy elements. That cuts the age of the "life-capable" universe by at least half, so the window of relatively modern life on earth with respect to the age of the life-capable Universe really isn't that small... let's say 350My out of 7Gy, so about 5%.
This means that the star’s solar system at that point has sufficient quantities of heavy elements which cannot be produced by stellar fusion, as these elements are produced by super novae and from solar radiation.
Basically all the neutrons that are produced when a star goes boom create the elements that are above iron in the periodic table.
I suspect that the claim that life as we know it can only evolve there is because life as we know it needs a wide variety of chemical elements. We need carbon and oxygen, of course, but also iron and calcium and magnesium and potassium and so on. You're not going to get that around a first generation star. You might not get enough of it around a second generation star.
And most importantly first gen stars can’t form planets other than gas giants and even gas giants are questionable because our current understanding that other than a few failed stars these also usually require a heavy element core as a seed.
2nd gen stars are a possibility in a region of space that had a lot of 1st gen stars to nova and there might be sufficient amount of heavy elements already there to form a solar system.
So unless life can form from hydrogen, helium, lithium and beryllium then no life in 1st gen stars.
2nd gen is highly dependent on the region of space although I would posture that any region active enough to create sufficient amount of heavy elements would probably remain too active during the 2nd generation for life or at least complex life to form.
Due to our physical laws elements with larger rooms for reaction via chemistry are familar.
The chances of a replicating agent just anthropologically emerging from the surface of a 2nd generation hydrogen dominant star with an accumulation disc composed of little higher orders elements is inconceivably less likely than the relative petri dish organic molecules provide.
Regardless, the species is naturally incapable of averting averting crises that are foreseeable but distant.
Evolution has no agenda or goals, other than to select for survival. Most species on this planet have a low intelligence yet are successful, and don't seem to evolve into the direction of intelligence.
The preferred chirality of organic molecules could absolutely have arisen by chance, but it's an interesting to see this in meteorites.
On the unrelated subject of handedness, I saw an interesting thread on Twitter today [1] speaking about how we're starting to synthesize reverse chirality polymers and enzymes, most notably DNA and replication enzymes.
There are a lot of interesting implications.
You can't get rid of L-DNA without reverse DNase, leading to an accumulation of information and transcription. So they need to remake all the enzyme steroisomers.
That alone is interesting, but you can take it further to the limit and produce reverse biology that synthesizes reverse sugars that can't be metabolized by much of extant life [2]. Suddenly a lab-escaped reverse autotroph can out-compete all of us right-handed lifeforms because nothing can eat them. Bacteria, plankton, the entire food web collapses. When we have nothing left to fish or farm, we die too.
Never thought nanotech's grey goo was plausible. Now I see something that rhymes with it, and I could see it happening within our lifetimes.
It'd make a crazy MAD bioweapon on par with or potentially worse than nukes.
Wild tangent, sorry.
[1] https://twitter.com/eigenrobot/status/1420952351968432130
> Such negative values occurring shortly after the GOE require a rapid reduction in primary productivity of >80%, although even larger reductions are plausible. Given that these data imply a collapse in primary productivity rather than export efficiency, the trigger for this shift in the Earth system must reflect a change in the availability of nutrients, such as phosphorus. Cumulatively, these data highlight that Earth’s GOE is a tale of feast and famine: A geologically unprecedented reduction in the size of the biosphere occurred across the end-GOE transition.
But I assume they're not immune-invulnerable.
To be clear, evolution of viruses is probably inevitable. But on what time scale does it take for them to arrive ex nihilo? Millennia? Longer?
https://en.wikipedia.org/wiki/Microbial_metabolism
Water, sunlight, carbon sources, phosphorous sources, nitrogen sources. And any additional think they have enzymes to break down and process. Advanced organisms could feed off complex organic molecules, but this isn't necessary.
The point is that with reverse chiral sugars, polymers, etc., they wouldn't be a meal for anything in the wild. (At least not one with nutritional value.) No predation and no competition leads to massive expansion, and they could exhaust resources that other necessary parts of the food web require.
This would make a fantastic "phase one" alien bioweapon to aid in wiping out a planet's existing lifeforms and replace ecosystems with one better matching their own. Assuming post-biology aliens care about biology.
The first type is incidental: we've already encountered meteorites from Mars and the Moon, for example, so it's not hard to imagine life bearing material arriving that way.
The second would be intentional: either ET seeds planets or merely visits them with contaminated boots or probes.
Either way, we would pick up some DNA from offworld.
https://www.onezoom.org/life.html/@=111445?img=best_any&anim...
(hopefully that links to the right place)
There’s some speculation that a large amount of their genetics were transferred from other animals.[1] I wonder how much this muddles the tracing through the evolutionary tree.
If I recall correctly, the tardigrades (and extremophiles like D. radiodurans) have evolved to handle damage brought on by desiccation. As a fortunate side-effect, this general robustness also protects against radiation.
I'd do a life myself, I'd make it post-metallic, post-silicon, post static: I'd make it use water and carbon, so that it can exist everywhere. I would make it so that it can become intelligent on a small time scale, say a few billion years, all on its own, from scratch, on any rock :D
Not saying we have an engineer, but you think of engineered life as you are now as a simple software programmer. But an engineer in 500k years trying to expand more, would probably think of chemical automata that can evolve and adapt in harsh conditions. Say for instance if humanity decided it would be enjoyable for life to exist on Jupiter. It'd have to make something that can try a lot of variations with a very simple first formula to consume whatever gas there is there and survive whatever pressure.
Is there any example that backs this up?
In fact, if we do discover something from another civilization, it is quite reasonable that it would be some sort of Von Neumann probe. It might be made of mechanical parts, "biological" parts, or something in between.
A Von Neumann probe would be highly engineered, and might have no trace of evolution to it.
Wikipedia article here: https://en.wikipedia.org/wiki/Evolution_(Baxter_novel)
Except that the very fact that it exists represents many evolved traits. If they are sending probes then their are either curious or expansionist, both evolved traits tied to competition for resources and/or survival. A species totally devoid of any history of evolutionary pressures wouldn't act that way, which is one of many possible great filters: once we have access to the infinite resources of space, perhaps we just stop caring and don't bother expanding. Such logic allows us to learn much simply from the existence of an otherwise silent Von Neumann probe.
But when dealing with infinity, we must appreciate the likelihood of the unlikely too.
Personally, I favor the prospect of the insanely lucky idiot race, that clumsily and completely by chance manage to launch a probe so seemingly sophisticated that every sentient race that discovers it readily submit to its perceived superiority.
Unless star trek is real. Faster than light travel opens up the door to infinities.
Or just a digital clone of a once-biological being that can live for infinity exploring the Universe. Why would you explore the Universe in a meat suit?
Without that, it sounds to me more like hell than heaven.
Maybe we are the Von Neumann probe.
To draw an analogy from fiction, what would happen if one sent Giger's Alien in all its glory, razor tail and all, to compete in an entry-level boxing match? The Alien has no rules, has acid for blood, tongue-crushes the skull of the referee, and so on.
Yeah, they got vented into space et cetera, but I'd say in the first 2 movies humans actually failed to kill the xenomorphs (eggs on LV-426 and aboard Sulaco). At the end of the third movie the newly born xenomorph queen clearly dies. However, in the fourth movie the xenomorphs are again brought back through cloning.
Also, in "Prometheus" and "Alien: Covenant" it becomes apparent that the original crashed ship on LV-426 in "Alien" was not one of a kind, there were tons of ships carrying the gooey secret sauce of xenomorphs.
Also, at the end of the second movie the queen xenomorph was simply vented into space, but whether it died or not was not very clear. I mean, the xenomorphs seemed to be quite resilient and not too picky about things like atmosphere and cold temperatures.
So, not really alien at all.
If we were somehow able to segment evolutionary pressures, and normalize their values such that they sum to one, I'd hypothesize that as the average evolutionary pressure goes to zero (meaning high number of evolutionary pressures that are generally uniformly distributed), then this author's hypothesis is true. But as the average evolutionary pressure grows (fewer pressures, or highly skewed distribution of pressures), I imagine it would lead to VERY different looking life. I'd also hypothesize that as the average value increases, it leads to system instability.
This is far from certain. They can be designed by someone who was designed by someone who evolved, for example. The evolved life forms may be extinct for millions of years.
Even simple life forms on other planets may be designed, e.g. for someones (analogous to) amusement.
For these reasons I think we can expect that aliens really will be quite alien to us.
Cooperations in humans has emerged only as a way of better milking of resources from otherwise dangerous environments for one individual-at-the-time endevour of surviving.
The evolution of complex thought on Earth had a lot to do with other species competing with humans for food, and simultaneously hunting humans as a food source.
I share your opinion about not automatic cross-species cooperation, but baselining to peace is not what's happening on our society of speaking predators, most of the order (in the whole planet), of the apparently peaceful society, is being continously kept by sheer force or menace of inmediate violence retribution (nation-states, others).
I.E. You could turn-off the lights of big city for a couple of days and few will have doubts about a tragic outcome.
As we are the only society of intelligent species (at least, we are speaking folks), we know, we should be carefully analyzing those facts when hypothesizing about alien intentions.
Turning the lights off in a big city will revert us back to our base/evolutionary goals - so perhaps we better hope these aliens aren't too desperate!
We literally built rockets and started spacial exploration out of a pissing contest. It has been clearly on mankind history that we don't need to cooperate as a unified peaceful race to advance technological progress.
Whether those morals extend to preserving other intelligent life forms (I.e. humans) seems unlikely since the prosperity of other life forms will inevitably lead to more competition for scarce resources.
The fact that human moral constructs apply to other intelligent species seems to be a bug that arises solely from the fact that we’re currently capable of out competing all other intelligent species.
I don't think any morally advanced culture would be willing to accept an indefinite policy of "live and let live" between the cultures as a whole; there are some injustices (slavery, murder, torture) that wouldn't be tolerable to exist in the known universe.
I agree that equally powerful societies face the hardest choice; whether to risk everything to save everyone or to knowingly allow atrocities to continue while preserving themselves.
Aliens will probably eat, breathe, see, smell, and hear, but might do it in ways that would fail to qualify under definitions we can write based on life we know.
And they will probably have processes and senses we don't, or even just don't yet know any earth creatures have.
We never would have even looked for a magnetic-line slope-angle sense without inventing compasses, and then also understanding the structure of the earth's magnetic field. Likewise, we only understood echolocation after we invented it; before, we had no clue any animal used it. Octopods have no sense of joint angle. Some bugs taste what they walk on.
Thinking the only interesting phenomena in the universe are ones we already know about, or know something useful to do with, is akin to the fundamental failing of TFA.
Now, it is known that creatures can lose limbs through evolution, but never gain them, so it is likely that multi-legged species would gradually lose extra limbs over time.
Wait, so where did the limbs come from anyway, if they could not be gained?
It seems that vertebrates have certain period when this layout was 'cast in stone' [1]
[1]: https://biology.stackexchange.com/posts/21793/revisions
Take two runners, give one a 15 kg weight in one hand, and give another 15 kg weights in both hands (30 kg total). I think the runner with weights in both hands would run faster than the one with one weight.
Thus, moving species evolve to be bilaterally symmetric.
If the organism has no need to move in certain direction, it doesn't really have bilateral symmetry, like trees or bushes (though big trees generally tend to have their center of mass close to their vertical axis).
Did spiders start with more?
No, humans are too useful to just eat! Even for menial tasks. You could think of slavery as a primitive form of human farming, but it's inefficient: being too harshly treated means poor health and mental performance, which means the tasks they can work in are limited. No, the farmers that would be worthy of farming humans would be more astute.
It's far more efficient to let a farmed kind live just comfortably enough to be healthy and develop themselves (free range), as long as they (1) are imposed with an element of scarcity that will force them to struggle to be useful in exchange for the scarce element and (2) the farmer is positioned in such a way that they extract value from these useful activities, with no downside.
As a bonus, because there's an element of competition for the scarcity, the farmed kind will police themselves (fairly or not), and band together, cooperating to generate an oversized portion of the scarce element at a certain level of increased risk for the leaders of the band - we can call them stakeholders. Winning stakeholders will be rewarded with increased amounts of the scarce element, and losers will be punished with a loss of scarce elements.
Extraordinarily successful stakeholders would be rewarded with benefits, and benefit not unlike the farmers - they are to be rewarded for their feats.
Those that are successful enough will be invited to travel to the farmers' homeland riding on a giant space phallus...
How about purely informational beings with no physical body. Could they be considered 'alive?'. We can already simulate the nervous system of a nematode (http://openworm.org/), what if you scale that up to a fruit fly? Or an octopus? If it's 'thinking' in exactly the same way as a flesh-and-blood creature, is it conscious? Sapient? Sentient?
We know they have to use tools. You might point to crows, dolphins, or others and note that they use tools. But they don't in the same way that apes do. We're much better equipped to manipulate objects by using hands than using a mouth. Tentacles might be a better comparison but actually fingers allow for a lot of fine manipulation. Though I'm sure octopi could make tools that better work for them there's some mechanical reasons to believe hands are better. I mean there's the fractal nature of an arm helps with fine manipulation.
We know there's things like milk that help impart high nutrient content diets to young and there are correlations between lactate and fat to brain mass. We know this is a more efficient delivery system than say what birds to: eat, per-digest, and regurgitate. We actually expend a lot of energy to create milk.
These are just two (very incomplete and naive) examples, but what I'm trying to say is that not all options are equally likely. Maybe it won't be a hand. Maybe it'll be a tentacle with fractaling appendages (personally I wouldn't expect this because such a system is more complex) but I wouldn't expect something with (non-vestigial) wings, especially like a bat wing. Membranes can be easily punctured when working with objects and makes it hard to reach into confined spaces because of the necessity for large surface area to be able to fly.
So while yes, we only have Earth as a reference point we also have a lot of physics, biology, evolutionary pressures, game theory, and an understanding of tools and mechanics to lean on as well. I do think this does provide some restrictions to what is likely. _Not everything is on the table or equally likely._ I don't think it's naive to think that we have some good ideas of some basic characteristics that alien life would look like (we can apply similar ideas to non-highly intelligent life). I think it's naive to believe that anything is possible. These are claims that "sound smart" but are very naive and actually demonstrate a lack of basic knowledge.
So can we stop pretending like astrobiologists are idiots and haven't thought about this stuff? I don't know about you but I trust them more than I trust myself. They've spent significantly more time thinking about these things and have a far better background than us (except the handful of biologists and astrobiologists that are here).
How would you even detect them? Communicate with them? You can't just send a message, because they would instantaneously "forget" it (since they process information backwards), and vice versa. I doubt we could consider them "alive" at all.
Also, their laws of physics would be so different. Imagine shards of glass, at rest on our world, suddenly start joining together into a glass bottle. That's what life looks like to them.
Yet everything else is the same. They live in the same, the same laws of physics. They could even exist on our planet. Except we exist in a state of increasing entropy, and they exist in a state of decreasing entropy.
Much more realistic, IMO, would be a civilization that was made entirely of dark matter. Perhaps they might be able to infer our existence if we built some insanely powerful particle accelerator (and vice versa). If not then we would presumable only be able to communicate through gravitational effects...
Sure, there will be Da Vincis, Einsteins, Pollocks along the way, but they are not the standard not very imaginative sapiens-sapiens by any measure.
At a certain point, there's no limits to survivability. You can redesign yourself in any way, and not die from it (or have back-ups if you do).