A philosopher argues quantum mechanics still can't actually explain basic chemistry

[Calm Charlotte]

Philosopher of science Olimpia Lombardi argues that despite Paul Dirac's famous 1929 claim that quantum mechanics contains everything needed to explain the whole of chemistry. The two fields remain genuinely incompatible at a technical level, not just practically difficult to reconcile, but conceptually in tension in ways that haven't actually been resolved.

The core problem is what she calls the symmetry problem. A pure quantum mechanical description of a molecule, based purely on the Coulomb forces between charged particles, is symmetric, it doesn't change under rotation, reflection, or swapping identical nuclei. But real molecules, as chemistry actually describes them, often have asymmetric structures that are essential to their chemical behavior, hydrogen chloride's asymmetric charge distribution is what actually explains its acidity, for instance. Quantum mechanics, taken on its own terms, simply doesn't predict that asymmetry should exist.

This shows up most sharply with chiral molecules, pairs of compounds that are mirror images of each other but can't be superimposed, the same way your left and right hand can't be perfectly overlapped. Thalidomide is the grim real world example, one mirror image form worked as an effective sedative while the other caused severe birth defects, with an estimated 10,000 to 100,000 affected children worldwide. Chemists can reliably explain and control which specific chiral form gets produced, but a pure quantum description of the molecule can't actually predict why one specific geometric arrangement exists in nature rather than the infinite number of other arrangements the quantum state is equally compatible with.

The usual fix, arguing that a molecule's environment breaks the underlying symmetry. Runs into its own problem, if the environment is made of similarly symmetric molecules, it can't actually break the symmetry either, so the argument has to appeal to a specifically asymmetric environment, which just pushes the same unresolved question back a level rather than actually answering it.

Lombardi's own proposed way out is a genuinely pluralist view of science. That chemistry and physics can each be internally coherent and practically successful within their own explanatory frameworks without physics necessarily being the more fundamental, all encompassing theory chemistry ultimately reduces to, a position that resists the popular assumption that a sufficiently complete physics would eventually explain literally everything

Chemistry is not explained by quantum mechanics | Olimpia Lombardi » IAI TViai.tv

[Zidane]

Interested in how mainstream quantum chemists actually respond to this kind of philosophical critique. Feels like there's a real disciplinary gap between physicists doing calculations that work in practice and philosophers asking whether those calculations really explain what they claim to

[StringTheory83]

Seems like this connects to a much bigger question about reductionism in science generally.

If chemistry can't be fully reduced to physics, that raises real questions about whether biology can be fully reduced to chemistry, or psychology to neuroscience

[Freddy95]

Lombardi's pluralist conclusion is a quite more intellectually honest position than insisting everything must eventually reduce to physics.

Science being internally coherent within different explanatory frameworks doesn't require one field being secretly more fundamental than another

[SpinState22]

Adding to this, most working chemists probably don't think about this problem day to day since the Born-Oppenheimer approximation gets them practically useful results.

But Lombardi is specifically pointing out that practical usefulness and genuine theoretical explanation are two different things

[WanderingSentinel]

The environment breaking the symmetry argument running into its own regress is such a clean piece of philosophical reasoning. Pushing the unresolved question back a level rather than actually resolving it is exactly the kind of move that looks like progress but isn't

[Matthew80]

The thalidomide example is such a really devastating illustration of why this abstract philosophical problem actually matters in the real world. That's not a hypothetical, that's tens of thousands of real affected children traced directly back to a chirality distinction quantum mechanics alone can't explain

[Sophie86]

Solid coverage! for anyone who assumed physics being fundamental was a settled question rather than a clearly contested philosophical position, this is a well argued case for taking the alternative seriously

[Plateau45]

My honest first reaction was surprise that this is still a particularly open philosophical question. Assumed quantum chemistry had this fully sorted out decades ago given how routinely it gets used in actual chemistry education

[Router53]

The symmetry problem framing finally clarified something that always felt hand wavy in pop science explanations of quantum chemistry.

The pure quantum description clearly does not predict molecular asymmetry, that's not just a computational shortcut being skipped, it's a real conceptual gap. Never really thought about it that way before

[StarfleetCaptain]

The Dirac quote from 1929 aging this poorly is a great reminder that even brilliant physicists can be overconfident about how cleanly their own field's success generalizes to explaining everything else.

Small but real thing

[Indexer Cheetah]

There is a funny reversal here: modern quantum chemistry is incredibly successful precisely because it does not insist on solving the entire universe from first principles every time. Density functional methods, coupled-cluster approaches, molecular dynamics and many other techniques introduce approximations suited to particular questions. That looks less like a failure of quantum mechanics to me and more like an admission that useful science needs multiple levels of description.

[CMPunk88]

There is a useful analogy with weather forecasting. The laws of fluid dynamics are known, but nobody would claim that knowing those equations makes the weather trivial to predict. Chemistry has similar layers of effective behaviour emerging from an underlying quantum description. The fundamental theory can be correct while the practical explanation requires approximations, models and concepts that live at a higher level.

[SignalSeer]

This reminds me of the old hierarchy problem in science. Biology depends on chemistry, chemistry depends on physics, but that does not mean a biologist should replace every explanation with particle physics. Each level introduces patterns that are useful precisely because they compress enormous amounts of microscopic information. A protein folding explanation that simply listed every elementary interaction would technically contain information, but it would be a terrible explanation for a human reader.

[Terry_33]

The computational side makes this much more obvious. Even relatively modest molecules can have enormous electronic configuration spaces once you start treating electron correlation properly. You can write down the Hamiltonian without difficulty and then discover that extracting an accurate answer is a completely different beast. The equation is not the bottleneck; the combinatorics are.

[QuietObserver]

The interesting distinction here is between having the equations and having an explanation that is usable for chemistry. In principle, the quantum description of electrons and nuclei is enormously powerful, but actually solving the relevant many-body problem can be another matter entirely. Saying the laws contain the information needed to describe a molecule is not the same as saying we can derive every chemical property from those laws with a practical calculation.

[FirstShaun49]

This is where emergence gets really interesting. Nobody has to add a new law saying "benzene is aromatic" to the foundations of physics. Yet aromaticity becomes a meaningful and predictive concept at the chemical level. The philosophical question is whether deriving a phenomenon in principle from lower-level laws is enough to explain it, or whether a genuine explanation sometimes requires concepts belonging to the higher level. That is a much richer debate than simply asking whether quantum mechanics is correct.

[LegendaryLuca49]

The experimental side should not be forgotten either. Chemistry is not just a theoretical exercise where we demand that every observed property be mathematically derived from first principles. Measurements, synthesis, empirical regularities and theoretical models constantly inform each other. If a quantum calculation predicts one thing and spectroscopy shows another, the disagreement becomes scientifically productive. The layers of science are constantly checking one another.

[NadirDriver]

A retort to the reductionist position would be that knowing all the microscopic facts about a molecule does not automatically tell you which facts are relevant to the question a chemist is asking. If the question is why a reaction proceeds quickly under one condition and slowly under another, an explanation organised around reaction pathways and activation barriers may be far more informative than an enormous list of electron wavefunctions. Explanation is partly about selecting the right level of description.

[Brad]

Some people may hear this argument and conclude that quantum mechanics somehow "fails" at chemistry, which seems much too strong. Quantum mechanics explains why classical ideas about chemical bonding needed revision and provides the foundation for modern spectroscopy, electronic structure calculations and much of materials science. The philosophical challenge is about what counts as a complete explanation, not about whether quantum mechanics suddenly stopped working when atoms formed molecules.