= 27d567bc2d48d9f40e9ccc20ea370b15)
NancyLebovitz comments on Open thread for December 9 - 16, 2013 - Less Wrong Discussion
You are viewing a comment permalink. View the original post to see all comments and the full post content.
= 783df68a0f980790206b9ea87794c5b6)
Loading…= b715d02e85f7b3b4ae65ca3d3e450868)
Subscribe to RSS Feed
Powered by Reddit
= f037147d6e6c911a85753b9abdedda8d)
You are viewing a comment permalink. View the original post to see all comments and the full post content.
Comments (371)
Life is a concept we invented
Discussion of why it plausibly does not make sense to look for a firm dividing line between life and non-life.
Just because a boundary is fuzzy doesn't mean it's meaningless.
It just doesn't matter very much - certainly not enough to keep wrangling over the exact definition of the boundary. As long as we understand what we mean by crystal, bacterium, RNA, etc., why should we care about the fuzzy dividing line? Are ribozymes going to become more or less precious to us according only to whether we count them as living or not, given that nothing changes about their actual manifested qualities? Should they?
-- Karl Popper, from The Poverty of Historicism
The definition of life matters because we want to be able to talk about extraterrestrial life as well.
The precise definition of life will not be the thing that will determine our opinion about possible extraterrestrial life when we come across it. It will matter whether that hypothetical life is capable of growth, change, producing offspring, heredity, communication, intelligence, etc. etc. - all of these things will matter a lot. Having a very specific subset of these enshrined as "the definition of life" will not matter. This is what Popper's quote is all about.
It's possible that extraterrestrial life will be nothing but a soup of RNA molecules. If we visit a planet while its life is still in the embryonic stages, we need to include that in our discourse of life in general. We need to have a word to represent what we are talking about when we talk about it. That's the only purpose any definition ever serves. If you want to go down the route of 'the definition of life is useless', you might as well just say 'all definitions are useless'.
Why did you post this quote? It seems like a good example of diseased thinking, but I'm not sure if that was your point.
Are you saying you think the quote exhibits diseased thinking or just that it was about diseased thinking?
To me, the quote seemed to clearly make the same point that Anatoly's first paragraph did, so it seems straightforward why he would include it.
The quote says that biologists don't deal with questions such as "what is life?" because that's essentialism and that's Bad. Similarly, physicists certainly don't study ideal systems like atoms or light. The disease is in the false dichotomy.
Oh, hmm, I thought what he was saying about atoms and light is not that physicists don't study those things, but that they don't study some abstract platonic version of light or atom derived from our intuitions, but instead use those words to describe phenomena in the real world and then go on to continue investigating those phenomena on their own terms.
So, for example, "Do radio waves really count as light?" is not a very interesting question from a physics perspective once you grant that both radio waves and visible light are on the same electromagnetic wave spectrum. Or with atoms we could ask, "Are atoms really atoms if they can be broken down into constituent parts?" These would just be questions about human definitions and intuitions rather than about the phenomena themselves. And so it is with the question, "What is life?"
That's what it seemed like Popper was saying to me. Did you have a different interpretation? Also, I'm not sure I've understood your comment -- which dichotomy are you saying is a false dichotomy?
Asking whether radio waves really count as light is just arguing a definition. That's not interesting to anyone who understands the underlying physics.
Notice that the questions he gives for essentialists are actually interesting questions, they're just imprecisely phrased, e.g. "what is matter?" These questions were asked before we'd decided matter was atoms. They were valid questions and serious scientists treated them. Now these questions are silly because we've already solved them and moved on to deeper questions, like "where do these masses come from?" and "how will the universe end?"
When a theorist comes up with a new theory they are usually trying to answer one of these essentialist questions. "What is it about antimatter that makes it so rare?" The theorist comes up with a guess, computes some results, spends a year processing LHC data, and realizes that their theory is wrong. At some point in here they switched from essentialist (considering an ideal model) to nominalist (experimental data), but the whole distinction is unnecessary.
Yes, they most certainly do. QED is an extremely abstract idea, derived from intuition about how the light we interact with on a classical level behaves. This is called the correspondence principle.
String theorists come up with a theory based entirely on mathematical beauty, much like Plato.
I think you're reading Popper uncharitably, and his view of what physicists do is about the same as yours. He really is arguing against arguing definitions. "What is matter?" is an ambiguous question: it can be understood as asking about a definition, "what do we understand by the word 'matter', exactly?", and it can be understood as asking about the structure, "what are these things that we call matter really made of, how do they behave, what are their properties, etc.?". The former, to Popper, is an essentialist question; the latter is not.
Your understanding of "essentialist questions" is not that of Popper; he wouldn't agree with you, I'm sure, that "What is it about antimatter that makes it so rare?" is an essentialist question. "Essentialist" doesn't mean, in his treatment, "having nothing to do with experimental data" (even though he was very concerned with the value of experimental data and would have disagreed with some of modern theoretical physics in that respect). A claim which turns out to be unfalsifiable is anathema to Popper, but it is not necessarily an "essentialist" claim.
Oh, hmm. I see now that we were interpreting Popper differently, and I may have been wrong.
If Popper did mean to exclude that kind of inquiry, then I agree with you that he was misguided.
In that case, it sounds like you would agree with the rest of Anatoly's comment, just not the Popper quote. Is that right?
That's right, more or less.
Gotcha, thanks!
Which disease are you referring to?
"Diseased thinking" here is probably jargon; see Yvain's 2010 post "Diseased thinking: dissolving questions about disease".
My favorite example is challenging people to show that stars (in space) are any less alive than stars (in Hollywood).
What's the Darwinian evolution involved in stars? (Are you thinking of the hypothesis that universes evolve to create black holes?)
What I meant is that stars are born, they procreate (by spewing out new seeds for further star formation), then grow old. Stars "evolved" to be mostly smaller and longer lived due to higher metallicity. They compete for food and they occasionally consume each other. They sometimes live in packs facilitating further star formation, for a time. Some ancient stars have whole galaxies spinning around them, occasionally feeding on their entourage and growing ever larger.
Don't traits have to be heritable for evolution to count? I'm not an expert or anything, but I thought I'd know if stars' descendants had similar properties to their parent stars.
Descendant stars might have proportions of elements related to what previous stars generated as novas. I don't know whether there's enough difference in the proportions to matter.
Can you give an example of a property a star might have because having that property made its ancestor stars better at producing descendant stars with that property?
Sorry, I'm not an expert in stellar physics. Possibly metallicity, or maybe something else relevant. My original point was to agree that there is no good definition of "life" which does not include some phenomena we normally don't think of as living.
See here.
Do stars exhibit teleological behavior?
Why do you ask?
Isn't teleology fundamental to some conceptions of life?
Feel free to elaborate.
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.