28 November 2015

25 November 2015

The influence of intellectuals: hubris and humility

Intellectuals (and I take the term in its widest acceptance) have often believed that their ideas could change the world. Some of them, from Plato to Heidegger, tried to influence directly those in power; others hoped for a posthumous effect (or at least for cultural immortality). Criticism of this belief is as old as the belief itself and has two aspects: a pragmatic one (attempts to influence the course of history through ideas usually fail miserably) and a moral one (knowledge engenders obligations and must be used responsibly).

Elias Canetti, in his short essay The Poet’s Profession1, looks at this attitude from a very different angle: the responsibility of a writer not to humanity, but to words themselves, as tools of his trade. The true poet both understands the tremendous power of words and accepts his inability to change the world using this power.

1. In Das Gewissen der Worte [The Conscience of Words], Hanser (1975).

22 November 2015

Do nano-objects have color?

I've been reading Jim Pivarski's blog Coffeeshop Physics for some time, and I always find the topics interesting and the perspective refreshing. However, I think that his latest post "Viruses have no color" contains a number of fundamental errors, beyond the imprecisions inherent in a simplified account.

Pivarski's stated point is that objects smaller than the wavelength of light have no color, and he explains this by the uncertainty principle. Instead, he illustrates that small objects scatter less light than large ones, using a "geometrical" point of view that ignores the composition of the objects and sees them simply as opaque to the incoming light. Of course, in this approximation even large objects are colorless, since their scattering properties will not change much over the visible spectrum1.

The relevant parameter when discussing the color of an object is not the wavelength but the frequency of the incoming light. For instance, gold nanoparticles a few tens of nanometers in diameter both absorb and scatter green light more effectively than at other visible frequencies because in this range the electromagnetic field couples very effectively with the oscillation modes (plasmons) of the conduction electrons in the particle. Dispersions of such particles are therefore green when seen in reflection and red in transmission, as illustrated by the Lycurgus cup. Even atoms can be said to "have color" if we think of their characteristic transition lines (for instance, sodium lamps glow yellow).

The uncertainty principle1 only tells us that the image of the nanoparticles cannot be sharper than the wavelength used to look at them, not that this image is colorless (see such colored images here and here).

1. I neglect here the λ4 dependence in Thompson scattering, leading to the "blue-sky effect".
2. I preserve here the author's terminology, although "the uncertainty principle" is generally associated with quantum mechanics. Here the reasoning is completely classical, so we might as well call the result "the Abbe resolution limit".

20 November 2015

Why the aspect ratio? Shape equivalence for the extinction spectra of gold nanoparticles

My paper just got published in The European Physical Journal E !

In it, I argue that when describing elongated gold nanoparticles as ellipsoids (to the purpose of modelling their light extinction spectra) the natural comparison criterion is the equivalence of the various moments of mass distribution, rather than the length-to-diameter (aspect) ratio generally used in the literature. I also show that it leads to better spectral correspondence between the various shapes.

18 November 2015

CNRS positions - the 2016 campaign

The detail of the 2016 campaign for permanent research positions at the CNRS (Centre national de la recherche scientifique) has been published in the Journal Officiel, but the submission site is not yet open. The submission deadline is January 6th 2016. There are 215 open positions at the CR2 level (3 more than in 2015), 77 CR1 (no change), 253 DR2 (no change) and no DR1 (-2).

See last year's post for more details.

3 November 2015

The myth of innovation

What is it about the Wall Street Journal and science? It looks like any argument against state action (concerning e.g. climate change) is good, no logic required. Last week, it was the turn of state support for basic science. Matt Ridley's essay goes like this:
  1. Technology progresses inexorably.
  2. Basic science contributes nothing to new inventions.
  3. Discoveries and inventions are made independently by many people.
  4. Technology is a living organism that may soon "build and maintain itself". Innovation occurs inevitably, and people are only "pawns in the process".
  5. Prohibiting technological development does not work, and what cannot be stopped cannot be directed.
  6. Patents and prizes are inherently unfair.
  7. Technology causes advances in science, and not viceversa.
  8. As per the OECD and other sources, "publicly funded research had no economic impact whatsoever."
  9. Although publicly funded science does lead to some discoveries, we do not know what would have happened if the state would have refrained from collecting this money via taxes. Private initiative may have led to an even better outcome.
  10. Conclusion: instead of doing stuff, the government should just get out of the way!
This is a linear synopsis of the article, but the various points are interrelated (e.g. 3 and 6, 2 and 8 etc.) and fall under a few general arguments:

Technology evolves all by itself (points 1, 4 and partly 7)

This is akin to saying that our cities clean themselves: a position that contradicts some fundamental principle, but does seem to explain reality quite well (until the next garbage strike, at least).

Credit for discovery (points 3 and 6)

Discoveries are often made simultaneously by several parties (point 3), and this may be relevant to the patent system and the incentives it creates, but what does it have with the usefulness of basic science?

The causality relation between basic science and technology (points 2 and 7)

Almost by definition, basic research does not immediately yield practical results. One must follow the causal chain a couple of steps further. Speaking of causality, Ridley confuses the efficient and the final causes (in Aristotle's terms): it may well be that innovation is the (final) cause for advances in basic science by providing the motivation and financial incentive, but basic science can still be the (efficient) cause of innovation.

Return on investment (points 8-10)

If basic science contributes nothing to economic growth (a big if, considering that electricity was once studied with no hope for applications), maybe the state should refrain from financing it and let private actors do their work. It so happens that the French state goes even further, by subsidizing private research, with almost no strings attached, to the tune of several billion euros per year (much more than any other OECD country.) However, this does not lead to faster technical advances in France, and the mechanism is largely seen as ineffective.

2 November 2015

Mom and Dad

An interesting point on the universality of language (in particular, that of the words for mother and father). I have written about this topic before (1,2,3).

25 October 2015

The average of five people

It has been said that “You are the average of the five people you spend the most time with.” By a relative of the mean value theorem (used e.g. in electrostatics) it then follows that there are no local extrema in society.

Varying the counter ion changes the kinetics, but not the final structure of colloidal gels

Our paper just got published in the Journal of Colloid and Interface Science !

Free download until December 25th!