Romantic reductionism

Which is more fundamental, neuroscience or string theory? A debate of this profound question even featured on prime time TV.

Another signature of hydrogen bonding

Previously I posted about how significant redshifts in the frequency of the O-H bond stretch can be a signature of hydrogen bonding. Furthermore, there is a fairly universal relationship between the frequency shift and the bond length and energy.

The graph above shows there is also a fairly universal relationship between the bond energy (horizontal scale) and the change in intensity of the O-H infrared absorption intensity, covering a factor of 200 fold variation in the energy. The details are summarised in this paper. The vertical scale is the bond energy calculated from the empirical relation −ΔH=12.2 ΔA^1/2 where ΔH is the enthalpy in kJ/mol and  ΔA is the change in intensity of the absorption line in units of 10⁻⁴ cm mmol⁻¹.

The scientist who cried "Breakthrough!"

The Boy who cried wolf is one of Aesop's fables. It illustrates the problem of losing credibility due to developing a reputation of make false claims in order to get attention. Yet, the tragedy occurs when a true statement is made; it is ignored because of the lack of credibility of the speaker.
Does it apply in science? I think so. After you have been in science for a while I think there are certain people you just ignore because of previous experience of seeing their claims not bearing the test of time.

The name is Bond, Hydrogen Bond

There is a fascinating (and useful) essay A Bond by Any Other Name by Gautam R. Desiraju in Angewandte Chemie International. It discusses the background behind the recent new definition of a hydrogen bond by IUPAC [International Union of Pure and Applied Chemistry]. [A detailed report is here]. Here is the new definition:

The hydrogen bond is an attractive interaction between a hydrogen atom from a molecule or a molecular fragment XH in which X is more electronegative than H, and an atom or a group of atoms in the same or a different molecule, in which there is evidence of bond formation.

A typical hydrogen bond may be depicted as XH⋅⋅⋅YZ, where the three dots denote the bond. XH represents the hydrogen-bond donor. The acceptor may be an atom or an anion Y, or a fragment or a molecule YZ, where Y is bonded to Z. In specific cases X and Y can be the same with both XH and YH bonds being equal. In any event, the acceptor is an electron-rich region such as, but not limited to, a lone pair in Y or a π-bonded pair in YZ.

Amusingly, one section of the paper is entitled, "The Name is Bond".
More seriously, the paper has a useful section 5.1 List of Criterial useful as evidence (for hydrogen bonding).

The quantum of the gaps

I remember a prominent quantum physicist excitedly describing to me with great passion some unusual experimental observations concerning molecular motors. He said that there was no clear explanation for how they worked and so thought quantum effects must play a role!

I think there is a similar approach (fallacy) with other proposals for "quantum biology", whether it is understanding consciousness (Roger Penrose), evolution (McFadden), smell (Luca Turin), or photosynthesis (a cast of many). 

This reminds me of a phrase, "The God of the gaps" which was coined by one of my heroes, Charles Coulson. Although, best known as one of the founders of quantum chemistry, Coulson also wrote several books about Science and Christianity. Coulson pointed out the fallacy of invoking God to explain what was not currently understood in science.

Entanglement in the 2 impurity Kondo model

At the cake meeting this week we discussed a  nice (short) review of the Kondo effect  by Barbara Jones. [It appeared in the Handbook of Magnetism and Magnetic Materials]. Much of the emphasis is on the two-impurity Kondo model which exhibits competition between the RKKY interaction I of the two impurity spins and the Kondo interaction J of each spin with the conduction electrons.
Of particular interest is the non-Fermi liquid fixed point (quantum critical point) which occurs for I=-2.2TK.

In 2006 Sam Young Cho and I published a paper in Phys. Rev. A which quantified the entanglement between the two impurity spins. A striking thing is that this entanglement vanishes at the quantum critical point. The quantum state of this model also provides a solid state realisation of Werner states [mixed states which have the intriguing property of being entangled but not violating Bell inequalities].

A simple challenge to theorists

[I am] concerned with the spirit that seems to pervade much of theoretical physics nowadays, and with the interests and preferences shown by some of its practitioners. Of course, theoreticians depend on their experimenter colleagues for the bread and butter of their work,  ..... And yet when I try to read some of the current literature or listen to some of my colleagues, I can't help asking: Are they in touch with reality? Are they seriously interested in physics? As an example let me cite antiferromagnetism, which is again a popular topic since the discovery of the superconducting copper oxides. Very sophisticated models of antiferromagnetism have been proposed and worked out in great detail by people who have neither heard of, nor do they care to learn about, hematite, or what everybody else knows as a rusty nail....

... Even among theoreticians the natural order of things should be electron-spin resonance in hemoglobin first, anti-unitary operators and quaternions second....

As a referee for scientific journals I have led a losing battle with authors who don't want to (or can't) explain their general ideas in terms of simple experimental systems, or even in terms of high school geometry as the best in our trade did, from Einstein to Feynman.

Martin Gutzwiller, Two questions physics can no longer avoid, Letter to Physics Today, August 1994.