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Comment by DiscourseFan | Hacker News Reader

But oftentimes theoretical chemistry is not as important as what we get out of experiments because unlike physics, which attempts to derive general laws of nature, chemistry has to deal with the nitty gritty of the diversity of actual miscroscopic interactions of things. Any theory that is not entirely rigorous or even has slight room for an exception will be ignored by necessity, and physics is chock full of such examples. Biology is in a certain sense better (since it deals with larger things) and in a certain sense worse (as it relies on dogma and mysticism, at its essence, to explain the systems of life), and still nobody has gone beyond Aristotle and Kant in giving anything close to a rigorous definition of life as such.

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I think that as you ascend the scale of complexity, and just system size, then necessarily empiricalism and rote learning/memorization has to take over from more reductionalist explanations.

Physics, whether at atomic level, or on a much larger scale, is simple enough that reductionism usually works and you can calculate behavior from first principles using a few memorized "laws"

Biology is well past the point of complexity where you can do this most of the time, unless perhaps you are at the level of aspects of cellular behavior that can be analyzed in terms of chemistry.

Chemistry is in-between physics and biology in terms of complexity. In simple cases chemistry can be explained in terms of physics, but as AlphaFold has shown when you get to a certain level of complexity (in this case protein folding) empiricism takes over and you need to perform experiments and memorize results.

I think modern science and philosophy has a reasonable understanding of what life is, even if you disagree. This is certainly more a matter of philosophy than science, but it seems the best definition of life is based on the ability of a system to actively maintain a boundary between itself and the external world, thereby combating the 2nd "law" (statistical tendency) of thermodynamics. Maybe an interesting/useful definition (which is somewhat arbitrary) also needs to involve something like consuming energy/resources from the environment.

> unless perhaps you are at the level of aspects of cellular behavior that can be analyzed in terms of chemistry.

Only in the most hand-wavey sense. Actual simulation of the cell interior with even comically coarse grained models is prohibitively expensive. It comes up a lot in neuroscience where it sure would be nice to be able to credibly simulate even a single neuron at the molecular level. (I'm several years out of date on the state of that field so it's possible someone managed to pull it off in the meantime but even if so the broader point still stands.)

> and still nobody has gone beyond Aristotle and Kant in giving anything close to a rigorous definition of life as such

You stopped reading after the 1800's? Schrödinger told us life is what feeds on negative entropy and that is pretty good.

I guess that is true, but it isn't much. But my basic point was that before you can have "life" you have to have a theory of life which ultimately requires metaphysics, and there hasn't been much of an update to our understanding of what would ground a definition of life beyond Aristotle and Kant, and even their work is not determinative by any means.

Just because you picked 2 guys it doesn't mean nobody else had any different ideas. What a weird position to have, unless you literally read everything. There's so many theories. You didn't even include religions

Look into Aristotle and Kant on ‘the organized /and self-organizing/ being’; apply a couple thermodynamic abstractions known to adolescents ; be named Erwin Schrödinger ; hackernews will respond accordingly.

Freezing water is life?

how does biology depend on "dogma and mysticism"? I am really curious - a Google search yielded nothing much relevant.

I think he's being a little facetious - what he probably means is that if you attempt to get any true scientific rigor of that is going on in biological or chemical systems you end up facing the limits of physics in being able to explain what is going on. So rather and try to have scientific rigor, you just accept things the way they are and memorize the outputs and if anyone asks "why is it like that", your answers are either:

* Because God said so

* Find out yourself and get a nobel prize

Either way, even if you don't know what the answers are, you can still do serious work at a higher level of abstraction.

I would think just because everything is so cumulatively complicated and interconnected that if you tried to trace a line through a complex biological processes and explain it all you will end up with 1,000 PhD thesis topics to figure out and thousands more you just hadn't noticed yet. And at the end of the day none of that might be all that useful for describing the larger process at work. So at some point when someone ask "Why does X do Y" you gotta just settle on "because that's the way it is" and move on.

biology is full of exceptions to exceptions to exceptions. like immunology

so there is no way to extrapolate/interpolate, anything which was not directly measured is basically unknown since it could be yet another exception

or in programming language, the worse spaghetti code you could imagine, full of feature flags randomly enabled inconsistently

Where is physics chock full pf exceptions?

Maybe we’d say “physics” is really just the delineation between things we have an accurate model for and everything else (the exceptions?). Theoretical physics would be the search for the “why” of everything, inside and out of that line in that case.

I’m not a physicist, so I’ll let them pipe up on how much is in and out of the descriptive line, and how much is in and out of the theoretical explanation line. But I don’t know many physicists who think we’re close to “done” with either endeavor.

I'm not a physicist but I've always seen physics as a bit hand-wavy myself.

Dark matter is a great example.

Our understanding of gravitation didn't cleanly apply at ultra-large scales so we had to add a massive fudge factor.

You can't "go faster" than the speed of light, but space in between things can expand faster than the speed of light.

It seems like things that are "settled" regularly get an "ope, but except for this special case..." treatment.

There is no handwaving involved. The layman explanations of these phenomena are not that good. The quantitative derivations that leads to those results are totally fine, but hard to follow without deep knowledge of the subject.

Physics education sometimes aligns with historical evolution of the theories, mostly because that builds intuition and because the mathematical founsations of the improved theories need to be taught first. That leads to the "but in this case..." moments, but you need to realize that what you get taught as a "fix" is practically always a careful evolution that also reproduces all predictions from the less complete earlier theory.

I think they meant the opposite; physics throws things out as soon as there's a need for exceptions, and there are examples of that.

Well, once they have a better explanation.

We know that mass of matter does not explain even half of the mass observed in the Universe; we haven't thrown out the explanations of mass and inertial gravity, but have a placeholder called "dark matter" to refer to the missing explanation.

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