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I read with interest the “This Month in Physics History” column in the January APS News on Wolfgang Pauli and the exclusion principle. Although the article is essentially correct, fair and accurate, I have a few little objections to it. In particular:
1) In January, 1925, as stated, Pauli formulated the exclusion principle, BUT it was of course in the frame of the Old Quantum Theory.
Hence, the first statement is NOT forbidding fermions to be in the same quantum STATE. What Pauli said is this: There cannot be two electrons with the same four quantum numbers.
2) I am not aware of Pauli being disconcerted with the Old Quantum Theory of Sommerfeld. On the contrary, he for example encouraged Heisenberg to work on it. Later he wrote a masterly exposition of the Old Quantum Theory for the first edition of the Handbuch der Physik (1925).
3) The first clear attribution to the spin, as an internal angular momentum responsible of the electron’s fourth quantum number is by the US physicist Ralph Kronig, who in January, 1925 was in Tübingen, Germany when Pauli was visiting. Actually, Pauli, in his usual sarcastic way, rejected Kronig’s idea right away, saying it was a “good joke” (the full story, narrated by Kronig, is in “Sources of Quantum Mechanics” edited by van der Warden). In fact, Kronig was a bit angry with the later Uhlenbeck-Goudsmit hypothesis, as he had advanced it before.
4) It is not true that “... In the two years after Pauli’s ...exclusion principle, the new quantum mechanics took off...”
Here’s the record: Heisenberg’s decisive Quantum (Matrix) Mechanics was ready in June, 1925, and appeared during that summer. Dirac’s important contribution (conmutators from Poisson brackets) is of November, 1925, and even Erwin Schrödinger’s wave mechanics is of January, 1926. Not two years later.
5) Among the many things due to Pauli you omit, the most important one is that, with Heisenberg, he was responsible for the formulation of Quantum Theory of Fields, in two papers in 1929 and 1930.
6) It is true that he devoted a lot of time and energy to philosophical and other issues, but that was throughout his whole life, not only at the end, and until the very end, he was concerned with fundamental physical problems: in 1955 he produced a fundamental paper on the CPT theorem, and even replied by letter, in early 1957, to the news of parity violation.
Luis J. Boya
Regarding the picture with the headline “Getting high on physics”, published in the March 2007 APS News, I would like to inform you that the number of students in the physics class at Tribhuvan University in Nepal has increased. This happened because of the demonstration by students on December 12, 2006 in front of Nepal’s Ministry of Education and Sport, as shown in the picture, in which they demanded greater access to physics classes.
Tirtha Raj Joshi
Editor’s note: The author, a master’s student in physics at the University of Akron, is from Nepal.
“The Back Page” article in the March APS News last month entitled “The Embargo Should Go” urged that scientific journals not put embargoes on publicity relating to their articles. There has not been any embargo of news stories published in Physical Review and Physical Review Letters for over 22 years. See the Editorial by an earlier Editor-in-Chief [D. Lazarus, Phys. Rev. Lett. 52, 2101 (1984)]. So APS members can be assured that our journals anticipated, and followed, the advice in the “Back Page” quite a while ago.
Mehrdad Adibzadeh (Letters, March APS News) writes, “What is disturbing... is the claim that an almost-effortless experiment would have a certain outcome to support a certain point of view, when it apparently has never been carried out.” While I agree that this is disturbing, allow me to point out that this statement applies not only to claims of humble versus arrogant scientists, but also to so many of the thought experiments of the early 20th century on the foundations and interpretation of quantum mechanics, thought experiments that can be found in many classic textbooks on quantum mechanics.
The letter by Mike Jacobs [APS News, March 2007], which touts wind energy as a viable contribution to solving our energy problems, contains several mistakes and omissions that are not apparent in a non-technical discussion. To judge what wind energy can actually contribute, one has to work with realistic numbers.
I illustrate this with the example of the 150-MW wind park planned in the Gulf of Mexico opposite Galveston, Texas (at a cost of $300 million). This park will deliver, at best, at the rate of 30 MW. Comparing with the actual energy use of Texas, this will provide electrical power for less than one extra minute per day for Texas. Moreover, if one wants to keep up with a 1.5% annual increase in electrical usage in Texas by installing only wind power facilities, one would have to build about 25 of these wind parks every year!
The reasons that in an actual comparison with conventional power generation, wind energy performs so dismally are the following: 1. Air is a very dilute medium that moves at low speeds. 2. The energy that can be extracted from the wind varies as the 3rd power of the wind speed; so, for example, if the wind speed drops by one half, the energy drops by a factor of eight. As a result, wind turbines don’t produce any energy for low wind speeds, i.e. below Beaufort 4 (a ‘moderate breeze’,12-18 mph, the prevailing wind in most cases). 3. Over a period of days the wind can be extremely variable so that energy is not produced in a steady stream but in a succession of spikes between zero and full power, which can create a serious challenge for the grid operators. The combined result of these facts is that the wind turbines deliver only a modest fraction (20-25%) of the installed power capacity.
Germany is half the size of Texas but has more than twice the installed wind power capacity of the entire US, namely 20,424 MW (in 2006). Nevertheless, the large investment in wind energy (16,394 MW in 2004), produced only 4.9% of Germany’s electricity usage. The problems created by large investments in wind power are discussed honestly (a rarity) in the Wind Report 2005 of E.ON Netz (Ref. 1), Germany’s second largest electrical utility. One conclusion of the report is that the possibility of wind replacing conventional energy sources is quite limited. Germany’s wind-energy system in 2004 could only contribute 8% of its output capacity (1312 MW) to secure production of the system. So an extra conventional generating capacity of about 90% of the installed wind capacity had to be available as backup. This requires an enormous additional investment.
The report also stated that the feed-in of wind energy can change often and quite dramatically. On Christmas Eve 2004, wind production in Germany fell 4000 MW in 10 hours, representing the capacity of eight 500 MW coal fired power plants! This created an enormous challenge for the operators of the grid and it could easily have led to a vast blackout in central Europe. About 7000 wind turbines spread out over Germany (from the North Sea to the Swiss border) were feeding into the grid, but Fig. 3 of Ref. 1, which displays the wind energy feed-in for the entire year, clearly shows frequent variations between 0.2% and 38% of the daily peak grid load. This contradicts what Jacobs asserts about a leveling effect of geographically dispersed wind turbines.
Production and usage of electrical energy must be completely matched at all times; any mismatch can lead to blackouts. In the case of the German system this can lead to blackouts covering large parts of Europe; it has come so close a couple of times that the Dutch and Polish grids were also threatened.
Jacobs’ statement that Denmark manages to generate 20% of its electricity from wind “without storage and back-up capacity” is completely wrong; Norway and Sweden perform these functions for Denmark. Excess Danish wind energy is shipped to these countries where it relieves the load on the hydroelectric reservoirs; in turn electricity shortages in Denmark get replenished by these countries. Without these arrangements Denmark would be subject to many crippling black-outs. Finally, Jacobs’ assertion that not a single MW of back-up capacity for wind energy has been required in the US is probably due to the fact that the US wind energy system consists of so many widely dispersed (relatively) small systems, so that the local base-load generators can still take care of any fluctuations. This will change in the future when a substantial fraction of the base load (e.g. 20%) is supposed to come from wind energy.
The E.ON Report should be required reading for all those people who think and say, “The more wind energy the better.”
1. E.ON Netz Wind Report 2005 (in English) available at www.eon-netz.com/EONNETZ_eng.jsp
Frits de Wette
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