The evidence for strong emergence in chemistry

Reductionism became particularly popular during the highly fruitful development of physics in the 20th century. In this context, quantum mechanics and statistical mechanics became paradigmatic examples of the success of reduction as they illustrated that it is possible to describe, explain and predict the behaviour of macroscopic matter in terms of the interactions of its constitutive physical particles.

Secondly, through the formulation of quantum chemistry it has established a well-defined and explicit scientific connection to quantum mechanics, thus providing philosophers robust material that they can use in order to spell out its connection to fundamental physics. Thirdly, unlike biology, chemistry is not burdened with difficult questions around life or the nature of consciousness, thus allowing philosophers to focus on the ways in which chemical entities relate to interactions between fundamental physical particles.

Nevertheless, the matter of emergence in chemistry is far from settled. As philosophers of chemistry have shown, there are specific examples of chemical properties whose connection to fundamental physics cannot be straightforwardly understood in terms of either reduction or emergence. The most debated case is that of molecular structure. When one describes a molecule’s structure through quantum mechanics- i.e., by solving the relevant molecular Schrödinger equation- one cannot do so unless she presupposes certain facts about the examined structure.

Nevertheless, strong emergence maintains that molecular structure is not fully determined by the interactions of the molecule’s physical parts. This is because structure itself partly determines how the system’s quantum mechanical entities will behave. Put differently, the way a molecule is structured is part of the cause of how its subatomic particles interact. This idea is called downward causation as it posits a causal relation between a molecule’s structure and the interactions of its subatomic particles.

Seifert, V.A. Open questions on emergence in chemistry. Commun Chem 5, 49 (2022). https://doi.org/10.1038/s42004-022-00667-7

https://www.nature.com/articles/s42004-022-00667-7

Note to administrators: I checked the conditions for sharing content from the article before posting citations here.

I find that article to be peculiarly vague, but obviously you found it enlightening, so let me ask you:

What exactly does emergence in chemistry actually mean?

Why exactly is the Born Oppenheimer approximation singled out from a whole range of other approximations that go into any ab-initio quantum calculation of molecular structure.

Every particle in such a calculation (electrons and nuclei) is electrostatically attracted/repelled by every other one - that in an N-body problem. Every electron and many nuclei have spin, which would also complicated a complete calculation.

Much more seriously, any solution in terms of a wave function will be a function of 3N coordinates (3(N-1) coordinates if you use a centre of mass frame) - so the exact calculation would produce an impossibly difficult entity to manipulate.

It is a long time since I did any quantum chemistry, but in those far off days, a typical computer calculation proceeded as follows:

A distribution of charge from all electrons but one was guessed, and the motion of the one remaining electron was calculated (to a certain level of approximation) as it moved against a background of the charge distribution from all the others.

That of course generated a new charge distribution that replaced the original guessed distribution, and the process was iterated as computer time permitted.

There are approximations galore in there - even before you consider that the moving electrons should better be calculated using SR (itself, supposedly an approximation to GR)

Things have probably moved on since then, and I know there is something called Functional Density Theory, does that help with any of the above?

Above all, I don't understand what it would mean to say the structures of molecules are or are not "emergent".

David

Reductionism became particularly popular during the highly fruitful development of physics in the 20th century. In this context, quantum mechanics and statistical mechanics became paradigmatic examples of the success of reduction as they illustrated that it is possible to describe, explain and predict the behaviour of macroscopic matter in terms of the interactions of its constitutive physical particles.

How far can one reduce before one finds literally nothing?

How far can one reduce before one finds literally nothing?

Quantum Field Theory (QFT) is lowest known level of reduction.

I find that article to be peculiarly vague, but obviously you found it enlightening, so let me ask you:

What exactly does emergence in chemistry actually mean?

Well from the citations I provide emergence quite explicitly relate to the 3D structure of a molecule.

Why exactly is the Born Oppenheimer approximation singled out from a whole range of other approximations that go into any ab-initio quantum calculation of molecular structure.

That's a good question. I don't understand how the author finds QM approximations relevant in the broader context of his article and I haven't checked the reference he provides.

Every particle in such a calculation (electrons and nuclei) is electrostatically attracted/repelled by every other one - that in an N-body problem. Every electron and many nuclei have spin, which would also complicated a complete calculation.

Much more seriously, any solution in terms of a wave function will be a function of 3N coordinates (3(N-1) coordinates if you use a centre of mass frame) - so the exact calculation would produce an impossibly difficult entity to manipulate.

I understand these calculations are not solvable by current computing but I hope they will be with the emergence of quantum computing within a few years.

The interesting thing in the psiencequest context is that this will bring objective inquiry into the question about the existence of strong emergence at least in the context of chemistry.

Remember that the belief in reductionism itself is a philosophical stance.

I found another reference explaining that it’s the approximations to Schrodingers equation the pre-supposes the molecular structure, that’s why the Born-Oppenheimer approximation is relevant in this context.

Reduction didn’t seem to work out the way philosophers initially thought it would for chemistry. Instead, philosophers of chemistry argued that there is something about chemistry that makes it separate and autonomous from quantum physics.

More precisely, quantum mechanics describes molecules and their properties by solving the Schrödinger equation. Solutions to the equation provide a way to identify the molecule’s chemical properties, including its structure. However, quantum mechanics only identifies structure if certain assumptions are applied to the Schrödinger equation. Without making these assumptions, the Schrödinger equation is unable to differentiate between molecules that differ only in terms of their structure

https://www.jargonium.com/post/strong-em...-chemistry

This seems more like a point against Reductionism than for Emergence?

If Chemistry is not reducible to Physics, then even less reason to think Consciousness is...

This seems more like a point against Reductionism than for Emergence?

If Chemistry is not reducible to Physics, then even less reason to think Consciousness is...

Strong emergence is not solely about consciousness. Standing in stark contrast to reductionism—an unproven perspective borne from the triumphs of physics in the last century. It should be emphasized that strong emergence remains unproven dispite the links I provided here, and many physicists vigorously challenge the notion that any branch of science cannot be distilled down to physics, frequently hailed as the 'queen of sciences'.

I don’t think consciousness is reducible to physics at all. David Chalmers doesn’t think so too either. Reductionism can’t be true.

Strong emergence is not solely about consciousness. Standing in stark contrast to reductionism—an unproven perspective borne from the triumphs of physics in the last century. It should be emphasized that strong emergence remains unproven dispite the links I provided here, and many physicists vigorously challenge the notion that any branch of science cannot be distilled down to physics, frequently hailed as the 'queen of sciences'.

I don’t think consciousness is reducible to physics at all. David Chalmers doesn’t think so too either. Reductionism can’t be true.

But if there are structures of molecules that cannot be grasped just by physics alone, how much worse for [physical reduction of] Consciousness which is fundamentally different from the "physical" based on the definition of the "physical" provided by Physicalists.

Even with the irreducible structure of molecules...what exactly is providing the structure that "emerges" though...this all seems to [be] quite muddled because if the structure of molecules is not predicted by physics what exactly determines the structure? Physics + Special Laws...but "laws of nature" is in itself a problematic notion.

If a non-physical Natural Law can interact with the Physical, and only at a certain level above the lowest accepted levels of reduction, then it seems there is no Interaction Problem. Then given the difference in kind between Consciousness and the - according to Phyiscalists - non-mental character of the "Physical", there seems to be little reason to think Dualism suffers from any real issue...

I think it is important to realise that it should in principle be possible to determine this structure by some sort of iterative procedure- varying the positions of the atoms and repeating the calculation.

What we are really seeing here is the fact that QM systems (i.e. everything!) become hugely more complicated as the number of particles increases. I mean, if you ignore various weak effects, the hydrogen atom is completely soluble as a classroom exercise. The same applies to positive ions such as HE+ where you have the same super-simple system - one positively charged nucleus with one electron orbiting. However, now think about an uncharged helium atom:

The wave function of this system is a function of 6 coordinates - the physical positions of the two electrons. That represents a huge increase in complexity, but at least the system is spherically symmetric. However if we consider a still more complicated case, the hydrogen molecule (H2) the complexity rises again because of the loss of symmetry, and of course the molecule will also vibrate - QM forbids the atoms to be stationary..

Most of the molecules relevant to life are much larger and have no symmetry at all.

I was fascinated when I first learned about all this, and for a while I fantasised about finding a way to cut through all the complexity!! Needless to say, my fantasy never became reality!

What I really want to point out is that this is not philosophically different from solving the hydrogen atom - we don't require talk of 'emergence', we just are entering a realm in which the sheer complexity of the maths is overwhelming.

Even if SBU's quantum computers become reality, it won't change the philosophical position, so I don't see any meaning to emergence applied to chemistry, unless perhaps at some level interactions with a psychic reality start to become clear - but is that really what gets called 'emergence'?

David