What’s wrong with ‘A self-sustaining (through an external energy source) chemical process characterized by the existence of far-from-equilibrium chemical species and reactions.’?
Suspect you would have a difficult time defining “external energy source” in a way that excludes fire but includes mitochondria.
True; what is meant is a simple external energy source such as radiation or a simple chemical source of energy. It’s true that this is a somewhat fuzzy line though.
Which equilibrium? Stars are far from the eventual equilibrium of the heat death, and also not at equilibrium with the surrounding vacuum.
I specifically said far-from-equilibrium chemical species and reactions. The chemistry that goes on inside a star is very much in equilibrium conditions.
Not clear whether viruses, prions, and crystals are included or excluded.
Viruses are not self-sustaining systems, so they are obviously excluded. You have to consider the system of virus+host (plus any other supporting processes). Same with prions. Crystals are excluded since they do not have any non-equilibrium chemistry.
what is meant is a simple external energy source such as radiation or a simple chemical source of energy.
I do not see how this answers the objection. All you did was add the qualification ‘simple’ to the existing ‘external’. Is this meant to exclude fire, or include it? If the former, how does it do so? Presumably plant matter is a sufficiently “simple” source of energy, since otherwise you would exclude human digestion; plant matter also burns.
The chemistry that goes on inside a star is very much in equilibrium conditions.
Again, which equilibrium? The star is nowhere near equilibrium with its surroundings.
Viruses are not self-sustaining systems,
Neither are humans… in a vacuum; but viruses are quite self-sustaining in the presence of a host. You are sneaking in environmental information that wasn’t there in the original “simple” definition.
Look at my reply to kalium. To reiterate, the problem is that people confuse objects with processes. The definition I gave explicitly refers to processes. This answers your final point.
All you did was add the qualification ‘simple’ to the existing ‘external’. Presumably plant matter is a sufficiently “simple” source of energy, since otherwise you would exclude human digestion; plant matter also burns.
I already conceded that it’s a fuzzy definition. As I said, you are correct that ‘simple’ is a subjective property. However, if you look at the incredibly complex reactions that occur inside human cells (gene expression, ribosomes, ATP production, etc), then yes, amino acids and sugars are indeed extremely simple in comparison. If you pour some sugars and phosphates and amino acids into a blender you will not get much DNA; not nearly in the quantities that it is found in cells. This is what is meant by ‘far from equilibrium’. There is much more DNA in cells than you would find if you took the sugars and fatty acids and vitamins and just mixed them together randomly.
Again, which equilibrium? The star is nowhere near equilibrium with its surroundings.
Ok, chemical equilibrium. This does not seem to me like a natural boundary; why single out this particular equilibrium and energy scale?
As I said, you are correct that ‘simple’ is a subjective property.
I think you’re missing my point, which is that I don’t see how your definition excludes fire as a living thing.
The definition I gave explicitly refers to processes. This answers your final point.
I don’t think it does. A human in vacuum is alive, for a short time. How do you distinguish between “virus in host cell” and “human in supporting environment”?
why single out this particular equilibrium and energy scale?
Because the domain of chemistry is broad enough to contain life as we know it, and also hypothesized forms of life on other planets, without being excessively inclusive.
I think you’re missing my point, which is that I don’t see how your definition excludes fire as a living thing.
I tried to answer it. The chemical species that are produced in fire are the result of equilibrium reactions http://en.wikipedia.org/wiki/Combustion . They are simple chemical species (with more complex species only being produced in small quantities; consistent with equilibrium). Especially, they are not nearly as complex as compared to the feedstock as living chemistry is.
I don’t think it does. A human in vacuum is alive, for a short time. How do you distinguish between “virus in host cell” and “human in supporting environment”?
They are both part of living processes. The timescale for ‘self-sustaining’ does not need to be forever. It only needs to be for some finite time that is larger than what would be expected of matter rolling down the energy hill towards equilibrium.
As I said, you have to consider the system of parasite+host (plus any other supporting processes).
I think a lot of the confusion arises from people confusing objects with processes that unfold over time. You can’t ask if an object is alive by itself; you have to specify the time-dynamics of the system. Statements like ‘a bacterium is alive’ are problematic because a frozen bacterium in a block of ice is definitely not alive. Similarly, a virus that is dormant is most definitely not alive. But that same virus inside a living host cell is participating in a living process i.e. it’s part of a self-sustaining chain of non-equilibrium chemical reactions. This is why I specifically used the words ‘chemical process’.
So this is a definition for “life” only, not “living organism,” and you would say that a parasite, virus, or prion is part of something alive, and that as soon as you remove the parasite from the host it is not alive. How many of its own life functions must a parasite be able to perform once removed from the host in order for it to be considered alive after removal from the host?
How many of its own life functions must a parasite be able to perform once removed from the host in order for it to be considered alive after removal from the host?
As the definition says. It must demonstrate non-equilibrium chemistry and must be self-sustaining. Again, ‘simple forms of energy’ is relative, so I agree that there’s some fuzziness here. However, if you look at the extreme complexity of the chemical processes of life (dna, ribosomes, proteins, etc.) and compare that to what most life consumes (sugars, minerals, etc.) there is no ambiguity. It’s quite clear that there’s a difference.
Are you sure that all life is chemical? There’s a common belief here that a sufficiently good computer simulation of a human being counts as being that person (and presumably, a sufficiently good computer simulation of an animal counts as being an animal, though I don’t think I’ve seen that discussed), and that’s more electrical than chemical, I think.
I have a notion that there could be life based on magnetic fields in stars, though I’m not sure how sound that is.
I guess it depends on your philosophical position on ‘simulations’. If you believe simulations “aren’t the real thing”, then a simulation of chemistry “isn’t actual chemistry”, and thus a simulation of life “isn’t actual life.” Anyways, the definition I gave doesn’t explicitly make any distinction here.
About exotic forms of life, it could be possible. A while ago I had some thoughts about life based on quark-gluon interactions inside a neutron star. Since neutron star matter is incredibly compact and quarks interact on timescales much faster than typical chemistry, you could have beings of human-level complexity existing in a space of less than a cubic micrometer and living out a human-lifespan-equivalent existence in a fraction of a second.
But these types of life are really really speculative at this point. We have no idea that they could exist, and pretty strong reasons for thinking they couldn’t. It doesn’t seem worth it to stretch a definition of life to contain types of life we can’t even fathom yet.
What’s wrong with ‘A self-sustaining (through an external energy source) chemical process characterized by the existence of far-from-equilibrium chemical species and reactions.’?
Suspect you would have a difficult time defining “external energy source” in a way that excludes fire but includes mitochondria.
Which equilibrium? Stars are far from the eventual equilibrium of the heat death, and also not at equilibrium with the surrounding vacuum.
Not clear whether viruses, prions, and crystals are included or excluded.
True; what is meant is a simple external energy source such as radiation or a simple chemical source of energy. It’s true that this is a somewhat fuzzy line though.
I specifically said far-from-equilibrium chemical species and reactions. The chemistry that goes on inside a star is very much in equilibrium conditions.
Viruses are not self-sustaining systems, so they are obviously excluded. You have to consider the system of virus+host (plus any other supporting processes). Same with prions. Crystals are excluded since they do not have any non-equilibrium chemistry.
I do not see how this answers the objection. All you did was add the qualification ‘simple’ to the existing ‘external’. Is this meant to exclude fire, or include it? If the former, how does it do so? Presumably plant matter is a sufficiently “simple” source of energy, since otherwise you would exclude human digestion; plant matter also burns.
Again, which equilibrium? The star is nowhere near equilibrium with its surroundings.
Neither are humans… in a vacuum; but viruses are quite self-sustaining in the presence of a host. You are sneaking in environmental information that wasn’t there in the original “simple” definition.
Look at my reply to kalium. To reiterate, the problem is that people confuse objects with processes. The definition I gave explicitly refers to processes. This answers your final point.
I already conceded that it’s a fuzzy definition. As I said, you are correct that ‘simple’ is a subjective property. However, if you look at the incredibly complex reactions that occur inside human cells (gene expression, ribosomes, ATP production, etc), then yes, amino acids and sugars are indeed extremely simple in comparison. If you pour some sugars and phosphates and amino acids into a blender you will not get much DNA; not nearly in the quantities that it is found in cells. This is what is meant by ‘far from equilibrium’. There is much more DNA in cells than you would find if you took the sugars and fatty acids and vitamins and just mixed them together randomly.
I feel like we’re talking past each other here. I explicitly (and not once, but twice in the definition) referred to chemical processes: http://en.wikipedia.org/wiki/Chemical_equilibrium
Ok, chemical equilibrium. This does not seem to me like a natural boundary; why single out this particular equilibrium and energy scale?
I think you’re missing my point, which is that I don’t see how your definition excludes fire as a living thing.
I don’t think it does. A human in vacuum is alive, for a short time. How do you distinguish between “virus in host cell” and “human in supporting environment”?
Because the domain of chemistry is broad enough to contain life as we know it, and also hypothesized forms of life on other planets, without being excessively inclusive.
I tried to answer it. The chemical species that are produced in fire are the result of equilibrium reactions http://en.wikipedia.org/wiki/Combustion . They are simple chemical species (with more complex species only being produced in small quantities; consistent with equilibrium). Especially, they are not nearly as complex as compared to the feedstock as living chemistry is.
They are both part of living processes. The timescale for ‘self-sustaining’ does not need to be forever. It only needs to be for some finite time that is larger than what would be expected of matter rolling down the energy hill towards equilibrium.
In what sense are parasitic bacteria that depend on the host for many important functions self-sustaining while viruses are not?
As I said, you have to consider the system of parasite+host (plus any other supporting processes).
I think a lot of the confusion arises from people confusing objects with processes that unfold over time. You can’t ask if an object is alive by itself; you have to specify the time-dynamics of the system. Statements like ‘a bacterium is alive’ are problematic because a frozen bacterium in a block of ice is definitely not alive. Similarly, a virus that is dormant is most definitely not alive. But that same virus inside a living host cell is participating in a living process i.e. it’s part of a self-sustaining chain of non-equilibrium chemical reactions. This is why I specifically used the words ‘chemical process’.
So this is a definition for “life” only, not “living organism,” and you would say that a parasite, virus, or prion is part of something alive, and that as soon as you remove the parasite from the host it is not alive. How many of its own life functions must a parasite be able to perform once removed from the host in order for it to be considered alive after removal from the host?
Precisely.
As the definition says. It must demonstrate non-equilibrium chemistry and must be self-sustaining. Again, ‘simple forms of energy’ is relative, so I agree that there’s some fuzziness here. However, if you look at the extreme complexity of the chemical processes of life (dna, ribosomes, proteins, etc.) and compare that to what most life consumes (sugars, minerals, etc.) there is no ambiguity. It’s quite clear that there’s a difference.
Are you sure that all life is chemical? There’s a common belief here that a sufficiently good computer simulation of a human being counts as being that person (and presumably, a sufficiently good computer simulation of an animal counts as being an animal, though I don’t think I’ve seen that discussed), and that’s more electrical than chemical, I think.
I have a notion that there could be life based on magnetic fields in stars, though I’m not sure how sound that is.
I guess it depends on your philosophical position on ‘simulations’. If you believe simulations “aren’t the real thing”, then a simulation of chemistry “isn’t actual chemistry”, and thus a simulation of life “isn’t actual life.” Anyways, the definition I gave doesn’t explicitly make any distinction here.
About exotic forms of life, it could be possible. A while ago I had some thoughts about life based on quark-gluon interactions inside a neutron star. Since neutron star matter is incredibly compact and quarks interact on timescales much faster than typical chemistry, you could have beings of human-level complexity existing in a space of less than a cubic micrometer and living out a human-lifespan-equivalent existence in a fraction of a second.
But these types of life are really really speculative at this point. We have no idea that they could exist, and pretty strong reasons for thinking they couldn’t. It doesn’t seem worth it to stretch a definition of life to contain types of life we can’t even fathom yet.