
Super-Saturated Chemistry - Hooke
http://inference-review.com/article/super-saturated-chemistry
======
Xcelerate
This article is extremely misleading. The author is a professor at the
University of Strasbourg, so he knows what he's talking about; however, he
words things in a weird way in an attempt to confirm some kind of overarching
point that experimental chemistry is still necessary (which seems kind of
obvious IMO).

Quantum mechanics can and does predict every element on the periodic table.
Whether we can _calculate_ what it predicts at the present time is a different
matter entirely. In the words of Peter Gill, "The field of quantum chemistry
has become an applied mathematics problem". Yes, it's well-known that naïve
quantum chemistry fails to predict experimental results for a variety of
reasons, but all of these reasons come back to the fact that we had to use
approximations to solve difficult equations that otherwise could not be
solved. If our predictions failed in some way _fundamental_ to QM/QFT, every
theoretical physicist alive would be shocked — it would be the biggest news in
the field in over a century.

As better and better numerical approximation schemes are developed, the
current issues with quantum chemistry will begin to disappear. Some people
argue there are fundamental limits on what a classical computer can discover
about quantum chemical systems, but then others argue that quantum computing
will surmount these barriers (and others argue that it won't).

~~~
jpmattia
> _so he knows what he 's talking about;_

I'm not so sure. For example:

> _The commutator of the Hamiltonian with the angular momentum of an electron
> does not vanish.8 Its eigenvalue is, therefore, not a constant of motion._

In fact, the Hamiltonian is invariant under rotations (the electron does not
care about which way the protons in the nucleus are rotated), which is why the
angular momentum even exists. (From the fact that the Lagrangian is invariant
under rotation: Noether's theorem tells you that there is a conserved quantity
associated with that invariance. It turns out that rotational invariance gives
rise to angular momentum.)

I haven't checked his reference 8, but "Boston Studies Series in the
Philosophy of Science" is not the first place I'd go to understand constants
of the motion and how they relate to things that commute with the Hamiltonian.

~~~
thisrod
The key word is _an_ electron. The total angular momentum is conserved, but
the way the electrons share it between them is not.

As I recall, actual atomic Hamiltonians have terms like σ₁·σ₂. The reason
involves some tricky correspondence between exchange and spin that I haven't
thought about in a long time, and would have to look up.

I agree with the broader point that this essay is odd and confusing.

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giardini
looks like a serious case of "physics envy", something usually found in the
social sciences!8-))

[https://www.google.com/search?hl=en&source=hp&biw=&bih=&q=ph...](https://www.google.com/search?hl=en&source=hp&biw=&bih=&q=physics+envy)

But seriously the guy sounds just like Ernst Mach (1838-1916) who cautioned
against attributing reality to "molecules" (at that time not directly
observed). I appreciate Professor Henry's viewpoint (chemistry is distinct
from physics, in fact chemistry is better and chemistry is cool) but almost
every part of his discussion uses the tools of _physics_ to support both
sides.

Perhaps he's irritated by the unspoken idea that chemistry is merely the yet-
to-be-straightened-out basement of physics, to be organized only after physics
has found the missing strings. (And perhaps string theory is physicists' way
of putting off the chemistry basement cleanup?8-))

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fuzzfactor
Well, here's a reaction that I believe could not have been predicted by
ordinary bench chemists:

[http://science.sciencemag.org/content/354/6319/1570](http://science.sciencemag.org/content/354/6319/1570)

but looks like it's occurring on their bench at will.

Anybody good enough at the quantum stuff to estimate how long it would take to
predict this with just the math?

OK, that's a tall order, how about just mathematically describing this now-
known reaction?

If not, then estimate how long it will take until things like this can be well
modeled?

I get the impression that these are extraordinary bench chemists, and advanced
quantum concepts might shed additional light.

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Etheryte
The article is too heavily weighed down by personal bias and some weird hatred
towards physics as to be reasonably readable. (I'm not a physicist nor a
chemist.)

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selimthegrim
The Born-Oppenheimer approximation isn't a non-quantum assumption, but the
simplest form of parallel transport on a curved space. The geometric phase is
a fundamental part of quantum mechanics. This is a succinct restatement of
what is learned by the second year of a good physics graduate education (and
maybe undergraduate one), and I'm not sure where the Goldstone bosons are
relevant or what his point is.

~~~
effie
The Born-Oppenheimer approximation is first and foremost a simplification of
the equations following from the time independent Schroedinger equation. The
author probably wanted to stress the fact that this simplification does not
follow from any other general principle of quantum theory but is necessary to
use it in order to make use of the Schr. equation in chemistry (most theory of
molecules is based on this approximation). If we do not make the
approximation, the equations are complex and we cannot derive the usual
results of quantum chemistry.

