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> there may be quantum effects involved Quantum Mechanics is why atoms and molecules exist and form bonds. QM is the physics of chemistry. Without QM, chemistr

> there may be quantum effects involved Quantum Mechanics is why atoms and molecules exist and form bonds. QM is the physics of chemistry. Without QM, chemistry does not happen. The universe would just be a big churning mess of particles and you would never get little lego pieces that snap together according to repeatable rules that, when repeated, form macroscopic substances of innumerable description up to and including life itself. So QM is no doubt involved, but on this scale it is either a trivial fact or an indication that someone tried to lean on a classical approximation, it broke, and they had to revise it (which arguably says more about the approximation than it says about the underlying behavior). Apologies for the nitpick. It's a pet peeve of mine that discussions of QM tend to focus so hard on the strange behavior that they forget to mention where QM fits into the bigger picture and leave people with the impression that it only matters under special circumstances when in fact it matters so much that you can hardly have "matter" without it. ------------ Re: anesthetic, a large fraction of simple halocarbon compounds have intense neural effects, so anyone doing halocarbon chemistry would quickly be put on the "scent" even if they weren't tasting everything in the Sigma Aldrich catalog.

bordercases 3y ago
Do you know for sure they meant only those quantum effects which operate near or at the classical limit?
PakG1 3y ago
As a non-physicist and non-chemist who keeps running into quantum mechanics only through headlines, extra thanks for pointing this out. It's quite obvious in retrospect to acknowledge that quantum mechanics is the physics of chemistry, and I don't know why I didn't see that before. It certainly helps to view a lot of things in a new light.
deleted 3y ago
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akoboldfrying 3y ago
I would say everyone understands that "quantum effects" refers to situations in which classical approximations break down. Likewise when we say "numerical issues", it's understood that we're talking about situations in which the usual approximation of real numbers by floating point representations breaks down. "Disk corruption" doesn't necessarily mean anything is physically wrong with the disk, only that its contents have become inconsistent with the filesystem abstraction it normally supports, etc.
- fuzztester 3y ago
  >Likewise when we say "numerical issues", it's understood that we're talking about situations in which the usual approximation of real numbers by floating point representations breaks down. Guys, try this in your desktop or mobile app calculator: do square root of 2. then subtract from it the result that you see on screen. for me: √2−1.41421356237 i get: 3.095048801E−12 i.e. not 0. I discovered this on a physical Casio electronic calculator long back, and also verified it just now on a stock Android mobile calculator app. what is your result, and interpretation of it?
  - anamexis 3y ago
    It's just the difference between internal and displayed precision. sqrt(2) ≈ 1.414213562373095048801 So if you type in sqrt(2) - 1.41421356237, you're just getting the next 10 digits after that. 1.414213562373095048801 - 1.41421356237 _________________________ 0.000000000003095048801 = 3.095048801e12
    - fuzztester 3y ago
      yes, exactly :) that's what i figured out when i first came across this, in school.
  - TacticalCoder 3y ago
    > what is your result, and interpretation of it? that the square root of 2 is not 1.41421356237.
    - fuzztester 3y ago
      true, because the √2 is an irrational number. but I was looking for an answer more along the lines that anamexis gave.
- jdewerd 3y ago
  The numerical version of this sin is typedef float real; which promotes a similar confusion of concepts, even if the true meaning is understood by experts. That said, I think the QM/not QM lingo from the molecular dynamics community is considerably worse because it stokes a common misunderstanding: that the universe runs on classical mechanics except in lasers, particle accelerators, and other "exotic circumstances." By contrast, nobody thinks that the universe runs on float32s except in lasers and spaceships where it runs on float64s. Where confusion does not exist, we do not need to fight it, but where it does, we should probably try.
ddellacosta 3y ago
(In support of your point about QM:) To contrast with an example of where quantum mechanics is relevant at the level of biology--this is one I'm familiar with: https://www.sciencenews.org/article/quantum-fragility-may-help-birds-navigate https://www.sciencenews.org/article/quantum-fragility-may-he... Unfortunately I'm not finding anything related to anesthesia except for hand-wavy pieces about "quantum consciousness" (anyone, please do correct me with a link or two if I'm wrong). I blame Sir Roger Penrose, if only because him talking speculatively about it (even in a sophisticated, informed way) seems to give so many others leeway to speak far more casually about the same topic, with far less coherence. This is why we can't have our cake and eat it too I guess
- johngossman 3y ago
  More discussion in "Life on the Edge: The Coming of Age of Quantum Biology." I can't recommend the book unreservedly, but it's worth checking out reviews.
  - ddellacosta 3y ago
    Will take a look--thanks. Also, re: anesthesia, appreciate that you linked to the "Electron spin changes..." paper in the other comment, will check it out!
johngossman 3y ago
I understand your frustration, sorry for the poor wording. "Electron spin changes during general anesthesia in Drosophila" https://pubmed.ncbi.nlm.nih.gov/25114249/ https://pubmed.ncbi.nlm.nih.gov/25114249/ I learned about this from Nick Lane's book "Transformer: The Deep Chemistry of Life and Death"

bordercases 3y ago

Do you know for sure they meant only those quantum effects which operate near or at the classical limit?

PakG1 3y ago

As a non-physicist and non-chemist who keeps running into quantum mechanics only through headlines, extra thanks for pointing this out. It's quite obvious in retrospect to acknowledge that quantum mechanics is the physics of chemistry, and I don't know why I didn't see that before. It certainly helps to view a lot of things in a new light.

deleted 3y ago

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akoboldfrying 3y ago

I would say everyone understands that "quantum effects" refers to situations in which classical approximations break down. Likewise when we say "numerical issues", it's understood that we're talking about situations in which the usual approximation of real numbers by floating point representations breaks down. "Disk corruption" doesn't necessarily mean anything is physically wrong with the disk, only that its contents have become inconsistent with the filesystem abstraction it normally supports, etc.

fuzztester 3y ago
>Likewise when we say "numerical issues", it's understood that we're talking about situations in which the usual approximation of real numbers by floating point representations breaks down. Guys, try this in your desktop or mobile app calculator: do square root of 2. then subtract from it the result that you see on screen. for me: √2−1.41421356237 i get: 3.095048801E−12 i.e. not 0. I discovered this on a physical Casio electronic calculator long back, and also verified it just now on a stock Android mobile calculator app. what is your result, and interpretation of it?
- anamexis 3y ago
  It's just the difference between internal and displayed precision. sqrt(2) ≈ 1.414213562373095048801 So if you type in sqrt(2) - 1.41421356237, you're just getting the next 10 digits after that. 1.414213562373095048801 - 1.41421356237 _________________________ 0.000000000003095048801 = 3.095048801e12
  - fuzztester 3y ago
    yes, exactly :) that's what i figured out when i first came across this, in school.
- TacticalCoder 3y ago
  > what is your result, and interpretation of it? that the square root of 2 is not 1.41421356237.
  - fuzztester 3y ago
    true, because the √2 is an irrational number. but I was looking for an answer more along the lines that anamexis gave.
jdewerd 3y ago
The numerical version of this sin is typedef float real; which promotes a similar confusion of concepts, even if the true meaning is understood by experts. That said, I think the QM/not QM lingo from the molecular dynamics community is considerably worse because it stokes a common misunderstanding: that the universe runs on classical mechanics except in lasers, particle accelerators, and other "exotic circumstances." By contrast, nobody thinks that the universe runs on float32s except in lasers and spaceships where it runs on float64s. Where confusion does not exist, we do not need to fight it, but where it does, we should probably try.

ddellacosta 3y ago

(In support of your point about QM:) To contrast with an example of where quantum mechanics is relevant at the level of biology--this is one I'm familiar with: https://www.sciencenews.org/article/quantum-fragility-may-help-birds-navigate https://www.sciencenews.org/article/quantum-fragility-may-he... Unfortunately I'm not finding anything related to anesthesia except for hand-wavy pieces about "quantum consciousness" (anyone, please do correct me with a link or two if I'm wrong). I blame Sir Roger Penrose, if only because him talking speculatively about it (even in a sophisticated, informed way) seems to give so many others leeway to speak far more casually about the same topic, with far less coherence. This is why we can't have our cake and eat it too I guess

johngossman 3y ago
More discussion in "Life on the Edge: The Coming of Age of Quantum Biology." I can't recommend the book unreservedly, but it's worth checking out reviews.
- ddellacosta 3y ago
  Will take a look--thanks. Also, re: anesthesia, appreciate that you linked to the "Electron spin changes..." paper in the other comment, will check it out!

johngossman 3y ago

I understand your frustration, sorry for the poor wording. "Electron spin changes during general anesthesia in Drosophila" https://pubmed.ncbi.nlm.nih.gov/25114249/ https://pubmed.ncbi.nlm.nih.gov/25114249/ I learned about this from Nick Lane's book "Transformer: The Deep Chemistry of Life and Death"