Aug 122015

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Today is the birthday (1887) of Erwin Rudolf Josef Alexander Schrödinger (1887 ), a Nobel Prize-winning Austrian physicist who developed a number of fundamental ideas in the field of quantum theory, which formed the basis of wave mechanics. He formulated the basic wave equation (stationary and time-dependent Schrödinger equation) and, more popularly, proposed an original interpretation of the physical meaning of the wave function which led to his famous thought experiment “Schrödinger’s Cat” which supposedly illustrates the absurdity of the Copenhagen interpretation of quantum mechanics.


For those who know (and care) about the implications of this thought experiment I have to say that I’ve never seen the point of it. The Copenhagen interpretation states that the wave function of certain subatomic particles exists in two (or more) simultaneously contradictory states until they are observed, at which point the function “collapses” or resolves to one or the other. Erwin Schrödinger’s thought experiment involved a closed box within which was a chamber containing a very small amount of radioactive material a particle of which within a fixed span of time might decay or not decay. The state of the particle would be measured by a Geiger counter and if it had decayed would trigger the release of cyanide gas. Also in the box was a cat. Schrödinger’s point was that it was absurd to imagine that until the box was opened by an “observer” the decay state of the particle was unknown and therefore that the cat was simultaneously alive and dead. Here’s the original:

One can even set up quite ridiculous cases. A cat is penned up in a steel chamber, along with the following device (which must be secured against direct interference by the cat): in a Geiger counter, there is a tiny bit of radioactive substance, so small, that perhaps in the course of the hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer that shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts.

It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation. That prevents us from so naively accepting as valid a “blurred model” for representing reality. In itself, it would not embody anything unclear or contradictory. There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks.

—Erwin Schrödinger, Die gegenwärtige Situation in der Quantenmechanik (The present situation in quantum mechanics), Naturwissenschaften

(translated by John D. Trimmer in Proceedings of the American Philosophical Society)


Einstein had always been troubled by the idea that matter could simultaneously exist in two contradictory states and was so delighted by the thought experiment that he wrote:

You are the only contemporary physicist, besides Laue, who sees that one cannot get around the assumption of reality, if only one is honest. Most of them simply do not see what sort of risky game they are playing with reality—reality as something independent of what is experimentally established. Their interpretation is, however, refuted most elegantly by your system of radioactive atom + amplifier + charge of gunpowder + cat in a box, in which the psi-function of the system contains both the cat alive and blown to bits. Nobody really doubts that the presence or absence of the cat is something independent of the act of observation.

I don’t know where he got the gunpowder from, but that’s not the only mistake that he made. I’ve wondered for years why they thought that the wave function had to be observed by a human for it to collapse. Why isn’t the cat an observer? Why not the Geiger counter? Anything in the macro world that interacts with the wave function is an observer. Oh dear, Erwin, you should have taken an anthropology class with me.  I gather from recent reading that I am not the only person to have spotted the fallacy. Niels Bohr apparently made the same observation a long time ago. Oh well, it’s not surprising; he’s much smarter than I am.

The experiment as described is a purely theoretical one, and the machine proposed is not known to have been constructed. However, successful experiments involving similar principles, e.g. superpositions (that is matter in 2 states at the same time) of relatively large (by the standards of quantum physics) objects have been performed. These experiments do not show that a cat-sized object can be superposed (both alive and dead), but the known upper limit on “cat states” has been pushed upwards by them. In many cases the state is short-lived, even when cooled to near absolute zero.

1. A “cat state” has been achieved with photons.

2  A beryllium ion has been trapped in a superposed state.

3. An experiment involving a superconducting quantum interference device (“SQUID”) has been linked to the theme of the thought experiment: “The superposition state does not correspond to a billion electrons flowing one way and a billion others flowing the other way. Superconducting electrons move en masse. All the superconducting electrons in the SQUID flow both ways around the loop at once when they are in the Schrödinger’s cat state.”

4. A piezoelectric “tuning fork” has been constructed, which is both vibrating and still at the same time.


All this thinking makes me hungry but I don’t think I can do much with cyanide and a dead cat. So I am left with Schrödinger’s home of Vienna, which has already given me enough headaches. But . . . Vienna is well known for dishes made with a cheese called quark, which by silly coincidence is the name of an elementary sub-atomic particle. By an even sillier coincidence there are different types of quark particles which are referred to as “flavors.”

Quark the dairy product is made by warming soured milk until the desired degree of coagulation (denaturation, curdling) of milk proteins is met, and then strained. It can be classified as fresh acid-set cheese, though in some countries it is traditionally considered a distinct fermented milk product. Traditional quark is made without rennet, but in some modern dairies rennet is added. It is soft, white and unaged, and usually has no salt added.

Last time I gave a Viennese recipe I included a link for this video on how to make apple strudel:

Well , you can adapt it to make Viennese Topfenstrudel, using sweetened quark in place of apples. Problem solved.