zondag 29 april 2012

On quarks, viruses and melting ice.

The introduction of ‘quarks’ as fundamental constituents of matter marked a revolutionary step forward in our understanding of the physical world. As revolutionary as the introduction of atoms, about five decades earlier.

Quarks and electrons and the forces between them: that is all that is needed to build up the material world.

As an example let us look at the proton, the simplest of all atomic nuclei, the nucleus of the hydrogen atom. It consists of three quarks ‘swimming’ in the force field that binds them together. As in taxonomy we label the quarks with (trivial) names for ease of description. Two of the three quarks in the proton are ‘u’ quarks and one is a ‘d’ quark. So a proton can be labeled ‘uud’. Quarks have a property that initially was impeding their acceptance as real, physical objects: their electrical charge is not equal to an integer multiple of the electron charge, the fundamental charge e. The u quark has positive charge 2/3 |e| and the d quark negative charge -1/3 |e|. A neutron is then ‘udd’. A third quark was required to ‘build’ the particles that were known at the time of the construction of the quark model: the s quark, with the same charge as the d quark. Using all three quark species for making combinations of three quarks it is possible to make ten combinations that form the so called baryon decuplet – baryon is the generic name for ‘proton like particles’, consisting of three quarks.

A spectacular confirmation of this quark picture was the discovery of the Ω- (Omega-minus) particle (in 1964): the ‘sss’ state that completes the baryon decuplet.

‘Baryon spectroscopy’ has revealed the existence of many hundreds of three quark states, including ‘excitations’ of the ground states. Although the underlying quark picture is very simple, the reality built on it, is very complex. What purpose this complexity serves is unknown. Perhaps this is what Steven Weinberg meant when he wrote: The more the universe seems comprehensible, the more it seems pointless.

The story does not end here. Three more quark species were discovered, the ‘c’, ‘b’ and ‘t’ quarks: charm, beauty and truth, or, somewhat more down to earth: charm, bottom and top. There are six quarks species, or, as the more commonly used nomenclature says: six quark flavors. (Why six? Nobody knows, but a lot can be said about it. I will not do that here.) So we can now build baryons by combinations of three quarks where each quark has one of six flavors. The ‘decuplet’ referred to above, thereby turns into a ’56-plet’.  (Please verify!).

The CMS collaboration at the Large Hadron Collider published this week the first ever detection of an excited state of the three quark combination ‘usb’. This particle is called ‘xi-star sub b’. It belongs to the ’56-plet’ I suspect. It is the good old ‘decuplet’ xi-star (‘uss’) with one ‘s’ quark replaced by a ‘b’ quark. For CMS this result is a by-product: the real aim is to find the Higgs boson and other ‘new physics’. But the measurement of this new baryon is an achievement that would have been deemed impossible a few years ago – it is possible thanks to superbly functioning state of the art technology of both the CMS setup and the LHC accelerator. Frontiers of technology were pushed back to achieve this result and new knowledge was added in a wonderful contribution to scientific culture. The article is freely available on arXiv.org prior to publication in an ‘official’ journal. Enjoy!

There was more news this week. The Dutch scientist Fouchier and his group have created a mutation of the virus (H5N1) causing bird flu that can be transferred to humans. This finding has been publicized by the scientists months ago, but they were not allowed to publish, because of the possible abuse of their results by terrorists. Good sense has finally prevailed and the arguments in favor of publication put forward by the authors have won (increased knowledge of the influenza virus, the subsequent development of vaccines, etc.) The publication is yet to appear and will, I understand, be published in Science. The main author, Fouchier, is relieved that finally the work can be published, and rightly so. He is quoted to have said: ‘together with the editors of Science we will now write the text in such a way that it is understandable for a broad audience, also in view of all the commotion that has surrounded our work’. Bravo! But... Science is not accessible to the general public. It is not Open Access, but published behind a pay-wall. I urge Fouchier and his co-workers to publish the article in a place that is freely accessible for everybody interested, as soon as it is written. I am almost sure that Science will not allow this...

Yet more news this week. Nature published an article co-authored by a leading Dutch scientist, Van den Broeke, entitled: ‘Antarctic ice sheet loss driven by basal melting of ice shelves’. A dramatic thinning is observed of the floating Antarctic ice sheet by warming up ‘from below’ by streams of warmed up seawater. If I understood correctly. The result was highlighted on Dutch national television and possible dramatic consequences for sea level rise were explicitly mentioned. This article has to appear in the public domain. The work has been publicly funded and it is not reasonable that the public should pay 32 dollars to Nature to be allowed to familiarize itself with these important findings!

All rich scientific results referred to above should be freely available for all of us – general public, politicians and scientists alike!

Jos Engelen
April 29, 2012

zondag 8 april 2012


An idea can be captured in a formula.

This has been successfully demonstrated in science. The idea comes first, it marks the most important moment in scientific research: the moment of creativity.

A famous example of such an idea is the one that led Einstein to the theory of relativity.

The idea is that it is impossible to measure ‘absolute motion’.

Close your eyes and imagine yourself drifting through empty space. There is nothing but you. According to Einstein’s idea it is impossible for you to know whether you are in motion or at rest. You were clever enough to bring a flashlight. You send flash of light into the direction ahead of you. The light will travel with a speed that equals the speed of light with respect to the flashlight plus the speed of the flashlight itself - your speed. So by measuring the speed of the light your flashlight emitted you can then determine whether you are in motion or not. No, Einstein says. He holds on to his idea and asserts: the speed of light is constant and independent of the state of motion of the source that emits it and independent of the state of motion of the observer that detects it. He extended this idea with a further assertion, somewhat more subtle. If ‘absolute motion’ is a meaningless concept, the state of motion of a particular observer, say a physicist conducting experiments, is irrelevant for the laws of nature this observer discovers. In other words: the laws of nature are invariant under transformations of one frame of reference to another. These two ideas have far reaching consequences. The most dramatic is that ‘time’ is not absolute, but relative. Relative to the state of motion of the observer with respect to the clock that is used for clocking the time. ‘Moving clocks run slower’ is the brief summary of this result of Einstein’s theory of relativity.

In a formula: t’=t/sqrt(1-v*v/c*c)

Imagine an elementary particle, like a muon (abundantly present in cosmic rays), that is unstable and has a characteristic natural lifetime. (Two millionth of a second in this particular case). If we observe this particle flashing by with a speed v then we see it decay after t’ seconds according to this formula. c is the speed of light, 300 000 km/sec. For speeds v approaching the speed of light, to 90 or even 99 percent or more, t’ can become much bigger than t and the particle can travel much further than one would expect according to its natural lifetime t. This is exactly what is observed in experiments. There is something else the formula tells us: v can never become bigger than c, no object can travel faster than the speed of light. In that case we would have to take the square root of a negative number and the formula becomes meaningless.

Physics stops at the speed of light.

When the OPERA experiment, employing a neutrino beam generated at CERN and a detector located at the Gran Sasso laboratory in Italy, announced the observation of neutrino’s travelling faster than light the theory of relativity was challenged. Before publicizing such an earthshaking result you better be very sure that your measurement is right. The measurement was wrong. Who should take responsibility for publicizing this erroneous measurement prematurely? The ‘spokesperson’ of the Opera team, Antonio Ereditato, has resigned over it. So be it. He took his responsibility even if he is no more guilty than many of his senior colleagues; that is the way it goes.

The publicity on superluminal neutrinos and the subsequent withdrawal of this claim has done considerable harm to CERN’s reputation as a center of excellence. Those responsible for its governance and management should speak up. They should explain themselves.

Jos Engelen