But individual behavior is not about preventing climate change, it’s about doing what’s right. It’s wrong to pollute the environment, one way or another. A single person not stealing won’t reduce the crime rate in a country yet it is the right thing to do.
That's not a fair comparison. Everything we do affects the environment. The goal is to limit that effect where it matters. It's not ethical, it's practical.
This depends very much on what "practical purposes" are. For almost all conceivable technology, relativistic quantum mechanics for electrons and light, ie QED, is sufficient fundamental theory. This is unlike before quantum mechanics, when we basically didn't have fundamental laws for chemistry and solid-state physics.
The vast majority of useful things cannot be computed with QED from fundamental principles. You cannot compute even simple atomic energy spectra.
The fundamental laws of chemistry have not been changed much by quantum physics, they just became better understood and less mysterious. Quantum mechanics has explained various cases of unusual chemical bonds that appeared to contradict the simpler rules that were believed to be true before the development of quantum physics, but not much else has practical importance.
Solid-state physics is a much better example, because little of it existed before quantum physics.
Nevertheless, solid-state physics is also the most obvious example that the current quantum physics cannot be used to compute anything of practical value from first principles.
All solid-state physics is based on experimentally-measured parameters, which cannot be computed. All mathematical models that are used in solid-state physics are based on guesses about how the solutions could behave, e.g. by introducing various fictitious averaged potentials in equations, like the Schroedinger equation, and they are not based on computations that use primary laws, without guesses that do not have any other justification, except that when the model is completed with the experimentally-measured values for its parameters, it can make reasonably accurate predictions.
Using empirical mathematical models of semiconductor materials, e.g. for designing transistors, is perfectly fine and entire industries have been developed with such empirical models.
However, the fact that one must develop custom empirical models for every kind of application, instead of being able to derive them from what are believed to be the universal laws of quantum physics, demonstrates that these are not good enough.
We can live and progress very well with what we have, but if someone would discover a better theory or a mathematical strategy for obtaining solutions, that could be used to compute the parameters that we must now measure and which could be used to model everything that we need in a way for which there would be guarantees that the model is adequate, then that would be a great advance in physics.
You seem to be familiar with the field, yet this is a very strange view? I work on exactly this slice of solid state physics and semiconductor devices. I’m not sure what you mean here.
The way we construct Hamiltonians is indeed somewhat ad hoc sometimes, but that’s not because of lack of fundamental knowledge. In fact, the only things you need are the mass of the electron/proton and the quantum of charge. Everything else is fully derived and justified, as far as I can think of. There’s really nothing other than the extremely low energy limit of QED in solid state devices, then it’s about scaling it up to many body systems which are computationally intractable but fully justified.
We don’t even use relativistic QM 95% of the time. Spin-orbit terms require it, but once you’ve derived the right coefficients (only needed once) you can drop the Dirac equation and go back to Schrödinger. The need for empirical models has nothing to do with fundamental physics, and all to do with the exorbitant complexity of many-body systems. We don’t use QFT and the standard model just because, as far as I can tell, the computation would never scale. Not really a fault of the standard model.
> The fundamental laws of chemistry have not been changed much by quantum physics, they just became better understood and less mysterious. Quantum mechanics has explained various cases of unusual chemical bonds that appeared to contradict the simpler rules that were believed to be true before the development of quantum physics, but not much else has practical importance.
Um, false? The fundamentals of chemistry are about electron orbitals (especially the valence ones) and their interactions between atoms to form molecules. All of my college chemistry courses delved somewhat into quantum mechanics, with the biggest helping being in organic chemistry. And modern computational chemistry is basically modeling the QED as applied to atoms.
The hydrogenoid atoms and ions, with a single electron, are the exception that proves the rule, because anything more complex cannot be computed accurately.
The spectrum of hydrogen (ignoring the fine structure) could be computed with the empirical rules of Rydberg before the existence of quantum physics. Quantum physics has just explained it in terms of simpler assumptions.
Quantum physics explains a great number of features of the atomic spectra, but it is unable to compute anything for complex atoms with an accuracy comparable with the experimental measurements.
The QED calculations with "14 digits" of precision are for things that are far simpler than atomic spectra, e.g. for the gyromagnetic ratio of the electron, and even for such things the computations are extremely difficult and error-prone.
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The hydrogenoid atoms and ions, with a single electron, are the exception that proves the rule, because anything more complex cannot be computed accurately.
Rather: there is no known closed-form solution (and there likely won't be any).
If you let the computer run for long enough, it will compute any atomic spectrum to arbitrary accuracy. Only QFT has non-divergent series, so at least in theory we expect the calculations to converge.
There’s an intrinsic physical limit to which you can resolve a spectrum, so arbitrarily many digits of precision aren’t exactly a worthy pursuit anyway.
Europe was a bit customer for Russia energy, and Russia invaded an EU neighbor nonetheless. After which it stopped being the customer. So it seems like that incentive didn't really work.
I think that was raincole's point. I guess we can't account for Russia or the US making decisions that are completely counter to the benefit of their people.
Same here. And while I may be on HN for a long time, I would fall asleep within minutes of a (good) book. Which tells me something about these two modes of entertainment
I’m guessing what was meant is that the price of things that are to be invested in is growing wrt the price of things that are to be consumed. Which naively makes sense to me in an economy based on growth where the total consumption starts to stagnate—the surplus still has to go somewhere. Is it so or is reality more complicated than that?
I think it should have been “If you need oxygen and have a CNS, then you need sleep.” Other tissues can take oxidative break during wakefulness, but since CNS is _generating_ wakefulness, if it takes a break, by construction there is sleep.
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