• TheMadFool
    This forum may not be the right place to ask this question but I don't mind getting a philosophical perspective on it.

    My question isn't complicated and high-school biology is probably sufficient for a reasonable opinion on the matter.

    What do I want to say?

    It's like this...If you search wikipedia you'll notice that all lifeforms described in biology so far are solid-liquid hybrids. You all know that matter has 3 states: solid, liquid and gas. There's a fourth state, plasma, which can be considered too if you like.

    The solid-liquid hybrid ensures that most lifeforms are in the semi-solid spectrum. However there have been no discoveries of life in the other states of matter like liquid-gas or solid-gas.

    Why is this the case?

    Is it that life isn't possible in solid-gas or liquid- gas combinations? Are there chemical or physical barriers to such lifeforms?

    Of course if you really give it some thought all life consists of all three states because all lifeforms breathe some form of gas.

    That however isn't my point. I'm searching for answers why physical gas-liquid or solid-gas combinations of lifeforms don't exist. Or do they?
  • Metaphysician Undercover
    Lots of gas in me! Actually gas is dissolved in liquids, and can be locked up in solids, so there is a lot of gas in a living being. You already named it with breathing gas, the oxygen gets absorbed into the blood, and moved around to the various body parts. The human being really is solid-liquid-gas. And I wouldn't be surprised if they discovered some form of plasma within us as well.
  • Pattern-chaser
    My (very limited!) knowledge of biology says that gases are too amorphous to maintain the physical structures of life, without them just breaking up as the gas moves naturally around. Too simple? :chin:
  • StreetlightX
    Gas can't form a membrane. No membrane, no life.
  • Shamshir
    There's plenty of gaseous lifeforms, provided you look up.
  • Fine Doubter
    RNA in meterorites probably resembles a solid more than the other configurations. As for the "stuff" in "space" or "vacuums", scientists know little as yet.

    Philosophically, I think, like Streetlightx, membranes are the core concept because membranes are about boundaries which are about integrity.
  • Coben
    Hey, maybe. It would have to have some way to be matter that shows certain attributes that include 'responsiveness, growth, metabolism, energy transformation, and reproduction.' I don't know how that would all work in a gas, but it's hard to rule out. It would be, well duh, very different from us.
  • petrichor
    Life involves a highly integrated sort of complexity. It is highly structured, but has many degrees of freedom. It requires a balance of freedom and necessity. Notice that we find life mostly on the surface of the planet, at the interface between a solid interior and open space.

    Think of open, empty space as pure freedom, and solidity as pure necessity. A joint in your skeleton is a place of freedom, and it is a space. In order for a wheel to turn on a shaft, you need a space. For movement, you need space. But pure freedom is no good. To have any structure at all, you need constraints. Think of the advantages of having solid pieces of bone, of having strong, limiting, connective tissues. How would you ever develop a sense organ that can focus light like an eye without some constraints and stability?

    Imagine a game with no pieces and no rules, no constraints at all. It isn't anything, is it? Now imagine a game with no freedom in it, one where nothing changes. Not a game either! Neither of these extremes is interesting.

    Living things, useful machines, and so on, all involve a nice balance of freedom and constraint.

    Gas involves too much freedom. It is too loose. Too much space. You can't form stable structures in it. It is too dominated by entropy. There is no mechanism for replication, no heritability of form, so natural selection has little to work with. There is little opportunity for causal patterns to develop.

    In order to have evolution, you need a balance of strict inheritance and mutation or some other source of variation. If you have perfect cloning, with no possibility of variation, there is no evolution, and you never get beyond the most basic replicator. If you have no inheritance whatsoever, if the next generation is randomized completely, you'll just have mush, and there's no possibility of any adaptation, any maintenance of strategies that work, in other words, no "learning from experience". You could think of a perfect solid as something that transmits its form into the future with no change at all. This is perfect inheritance. Pure space, on the other hand, has no form and transmits no information to the future.

    You won't find intelligent or even interestingly structured gas. Neither will you find intelligent pure solids. And by pure solids, I mean some object in which no change can take place.

    Our bodies are not solids. Neither are they liquids or gases. They are combinations of all of these. There are lots of intricately structured systems of constraint as well as lots of spaces for movement.

    Why is water so important for life? Lots of complex chemistry can happen in it. Things are close, so lots of interactions can happen. But things are able to move a lot, so there's room for lots of change. This isn't really the case in gases or solids. In gases, contact is much more rare. In solids, it is too consistent. Also, water mediates a lot of chemistry, donating protons, and all sorts of other useful stuff.
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