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I completely disagree. I think the 'life can look like anything' (lets call them LCLLAs) train of thought suffers from a lack of understanding of constraint sat

I completely disagree. I think the 'life can look like anything' (lets call them LCLLAs) train of thought suffers from a lack of understanding of constraint satisfaction. 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.

gambiting 5y ago
I'm just always surprised how can we be so certain? Even here on Earth, for millions of years, life was literally nothing more than single cell organisms - also definitely "not intelligent life building space ships". And it would be very hard to see how could it possibly evolve into such, seeing as the atmosphere was full of incredibly toxic oxygen. 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.
- Retric 5y ago
  It’s a question of physics not just chemistry. Deuterium for example is similar to hydrogen chemically so while those differences are slightly toxic to us it’s easy to assume a planet similar to earth with an abundance of deuterium and a lack of hydrogen would evolve life forms with the opposite preferences. 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.
  - gambiting 5y ago
    Of course. But there are planets with abundance of silicon(including ours). There are planets with abundance of methane and even here we have lifeforms which can consume it. I'm just pointing out that as long as silicon based life is possible, then given the near infinite amount of time the universe can spend evolving such life, it will surely exist.
    - Retric 5y ago
      Sort of, it depends on how common various forms of proto life are. If their very rare and the first one to happen wins then you might expect silicon life of some form to be out there. 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.
      - ncmncm 5y ago
        The silicides would meanwhile say that the gaseous nature of CO2 makes carbon useless as a basis for life, and even go so far as to offer a plausible reason.
        rendall 5y ago
        It's an interesting point.
        Retric 5y ago
        Sorry, no. CO2 being gaseous is a major availability and energy advantage. For example you can’t get plankton equivalents as dissolved silicon is parts per trillion at the oceans surface. Hybrids are a different story, but I doubt that’s what anyone is talking about by silicon based life forms.
        ncmncm 5y ago
        CO2 (or SiO2) is only one of the possible outputs, or inputs, of metabolism. Even on Earth its primacy came very, very late. 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.
- autokad 5y ago
  I would say, get your head out of your edge cases. Before I go on, I hope you understand no one is saying its not physically possible, and that it absolutely does not exist anywhere in the multiverse, just that if we come across other life, it will most likely be similar to our own. 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.
  - d0mine 5y ago
    You won't see any wings on a hot air balloon. If you think it is not common, look at the fish in the ocean.
    - autokad 5y ago
      now you have de-evolved the conversation by trying to change the definition of fly to swim. if you are going to do that, there is no point in continuing the discussion. Furthermore, you are confusing buoyancy with flight.
      - d0mine 5y ago
        Both air & water are fluids (same equations can be applied to many problems). Equating them in the discussion about aliens is not a step too far which it doesn't require much imagination (compare it for example with an idea of a living nebula that might require some knowledge what is entropy, what is life in terms information, etc)
- depressedpanda 5y ago
  > seeing as Earth alone has billions of years left where such life could arise, In case you didn't know, Earth has about one billion years of water left. https://www.sciencedaily.com/releases/2013/12/131216142310.htm https://www.sciencedaily.com/releases/2013/12/131216142310.h...
  - gambiting 5y ago
    I do know that, but it's few billion before the earth is consumed by the expanding sun. Without surface water the planet is still there.
vimacs2 5y ago
I disagree with this assessment of silicon based life. While it is true that Earth's crust is mostly silicon, it's also at a temperature that would make metabolic processes using silicon very difficult until you get down to the mantle. 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.
- hackeraccount 5y ago
  Doesn't it intuitively seem like the life by definition would evolve out of any particular niche - say 1,000 Kilometers under the surface - to other areas? 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.
  - rendall 5y ago
    > Doesn't it intuitively seem like the life by definition would evolve out of any particular niche - say 1,000 Kilometers under the surface - to other areas? 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
rendall 5y ago
"Other forms of life didn't develop for a reason" isn't that convincing of an argument. We are somewhat knowledgeable about what chemical and physical processes can occur between, -100c to 1500C under 1atm or so, +-100 nanoteslas, in a timescale of under a human attention span. Beyond that, we become increasingly clueless. We have only a single very specific data point. That, and the human tendency to opine confidently about that which we cannot know.
hackeraccount 5y ago
What's the path-dependency-ness of life? Like, once you have carbon based life to what degree does it preclude silicon based life from evolving? How often does a feature evolve sui generis when the nich that the feature exploits is already filled? Clearly it happens sometimes so if you've got a good enough angle you can step into something that's seemingly already covered. 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.
- giantrobot 5y ago
  Carbon is a way better chemical for life than silicon. It can form vastly longer chains and produces IIROCC (if I recall organic chemistry correctly) much more robust bonds. 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.
torginus 5y ago
If we assume for a second that silicon life is a thing, would it be reasonable to think that it would be utterly alien? Probably it's chemical composition would be entirely different, but would it be unreasonable, that it could evolve eye, muscle, bone etc. analogs just like us, and the end result would be not entirely unfamiliar to our earthly eyes? The article talked about wings being one of the few viable modes of flight, and Richard Dawkins has made a lecture about eyes having evolved independently multiple time here on earth (like in, as the article states, mammals or octopi).
- ncmncm 5y ago
  Octopus eyes did not, in fact, evolve independently. This claim is repeated ad nauseam and is wholly false. 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.
amelius 5y ago
> 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. Just give it a few more decades ...
yawaworht1978 5y ago
Well, stage one to silicone life could be computer chips. Then for a transition period, the shell could be metallic followed by integration of the human mind to that almost indestructible body shell. Something like the bad guy terminator 2. But step one could be computer chips. Human designed and made rather than by strict definition of natural selection.

gambiting 5y ago

I'm just always surprised how can we be so certain? Even here on Earth, for millions of years, life was literally nothing more than single cell organisms - also definitely "not intelligent life building space ships". And it would be very hard to see how could it possibly evolve into such, seeing as the atmosphere was full of incredibly toxic oxygen. 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.

Retric 5y ago
It’s a question of physics not just chemistry. Deuterium for example is similar to hydrogen chemically so while those differences are slightly toxic to us it’s easy to assume a planet similar to earth with an abundance of deuterium and a lack of hydrogen would evolve life forms with the opposite preferences. 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.
- gambiting 5y ago
  Of course. But there are planets with abundance of silicon(including ours). There are planets with abundance of methane and even here we have lifeforms which can consume it. I'm just pointing out that as long as silicon based life is possible, then given the near infinite amount of time the universe can spend evolving such life, it will surely exist.
  - Retric 5y ago
    Sort of, it depends on how common various forms of proto life are. If their very rare and the first one to happen wins then you might expect silicon life of some form to be out there. 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.
    - ncmncm 5y ago
      The silicides would meanwhile say that the gaseous nature of CO2 makes carbon useless as a basis for life, and even go so far as to offer a plausible reason.
      - rendall 5y ago
        It's an interesting point.
      - Retric 5y ago
        Sorry, no. CO2 being gaseous is a major availability and energy advantage. For example you can’t get plankton equivalents as dissolved silicon is parts per trillion at the oceans surface. Hybrids are a different story, but I doubt that’s what anyone is talking about by silicon based life forms.
        ncmncm 5y ago
        CO2 (or SiO2) is only one of the possible outputs, or inputs, of metabolism. Even on Earth its primacy came very, very late. 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.
autokad 5y ago
I would say, get your head out of your edge cases. Before I go on, I hope you understand no one is saying its not physically possible, and that it absolutely does not exist anywhere in the multiverse, just that if we come across other life, it will most likely be similar to our own. 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.
- d0mine 5y ago
  You won't see any wings on a hot air balloon. If you think it is not common, look at the fish in the ocean.
  - autokad 5y ago
    now you have de-evolved the conversation by trying to change the definition of fly to swim. if you are going to do that, there is no point in continuing the discussion. Furthermore, you are confusing buoyancy with flight.
    - d0mine 5y ago
      Both air & water are fluids (same equations can be applied to many problems). Equating them in the discussion about aliens is not a step too far which it doesn't require much imagination (compare it for example with an idea of a living nebula that might require some knowledge what is entropy, what is life in terms information, etc)
depressedpanda 5y ago
> seeing as Earth alone has billions of years left where such life could arise, In case you didn't know, Earth has about one billion years of water left. https://www.sciencedaily.com/releases/2013/12/131216142310.htm https://www.sciencedaily.com/releases/2013/12/131216142310.h...
- gambiting 5y ago
  I do know that, but it's few billion before the earth is consumed by the expanding sun. Without surface water the planet is still there.

vimacs2 5y ago

I disagree with this assessment of silicon based life. While it is true that Earth's crust is mostly silicon, it's also at a temperature that would make metabolic processes using silicon very difficult until you get down to the mantle. 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.

hackeraccount 5y ago
Doesn't it intuitively seem like the life by definition would evolve out of any particular niche - say 1,000 Kilometers under the surface - to other areas? 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.
- rendall 5y ago
  > Doesn't it intuitively seem like the life by definition would evolve out of any particular niche - say 1,000 Kilometers under the surface - to other areas? 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

rendall 5y ago

"Other forms of life didn't develop for a reason" isn't that convincing of an argument. We are somewhat knowledgeable about what chemical and physical processes can occur between, -100c to 1500C under 1atm or so, +-100 nanoteslas, in a timescale of under a human attention span. Beyond that, we become increasingly clueless. We have only a single very specific data point. That, and the human tendency to opine confidently about that which we cannot know.

hackeraccount 5y ago

What's the path-dependency-ness of life? Like, once you have carbon based life to what degree does it preclude silicon based life from evolving? How often does a feature evolve sui generis when the nich that the feature exploits is already filled? Clearly it happens sometimes so if you've got a good enough angle you can step into something that's seemingly already covered. 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.

giantrobot 5y ago
Carbon is a way better chemical for life than silicon. It can form vastly longer chains and produces IIROCC (if I recall organic chemistry correctly) much more robust bonds. 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.

torginus 5y ago

If we assume for a second that silicon life is a thing, would it be reasonable to think that it would be utterly alien? Probably it's chemical composition would be entirely different, but would it be unreasonable, that it could evolve eye, muscle, bone etc. analogs just like us, and the end result would be not entirely unfamiliar to our earthly eyes? The article talked about wings being one of the few viable modes of flight, and Richard Dawkins has made a lecture about eyes having evolved independently multiple time here on earth (like in, as the article states, mammals or octopi).

ncmncm 5y ago
Octopus eyes did not, in fact, evolve independently. This claim is repeated ad nauseam and is wholly false. 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.

amelius 5y ago

> 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. Just give it a few more decades ...

yawaworht1978 5y ago

Well, stage one to silicone life could be computer chips. Then for a transition period, the shell could be metallic followed by integration of the human mind to that almost indestructible body shell. Something like the bad guy terminator 2. But step one could be computer chips. Human designed and made rather than by strict definition of natural selection.