Today is the birthday (1901) of Werner Karl Heisenberg, a German theoretical physicist and one of the key pioneers of quantum mechanics. He published his seminal work on quantum mechanics in 1925 in a breakthrough paper. In a subsequent series of papers with Max Born and Pascual Jordan, in the same year, this matrix formulation of quantum mechanics was substantially elaborated. In 1927 he published his uncertainty principle, upon which he built his philosophy and for which he is best known publicly, even though it is not necessarily his most important contribution to physics. Heisenberg was awarded the Nobel Prize in Physics for 1932 “for the creation of quantum mechanics.”
He also made important contributions to the theories of the hydrodynamics of turbulent flows, the atomic nucleus, ferromagnetism, cosmic rays, and subatomic particles, and he was instrumental in planning the first West German nuclear reactor at Karlsruhe, together with a research reactor in Munich, in 1957. He was a principal scientist in the Nazi German nuclear weapon project during World War II. He traveled to occupied Copenhagen where he met and discussed the German project with Niels Bohr.
Following World War II, he was appointed director of the Kaiser Wilhelm Institute for Physics, which soon thereafter was renamed the Max Planck Institute for Physics. He was director of the institute until it was moved to Munich in 1958, when it was expanded and renamed the Max Planck Institute for Physics and Astrophysics.
Heisenberg was also president of the German Research Council, chairman of the Commission for Atomic Physics, chairman of the Nuclear Physics Working Group, and president of the Alexander von Humboldt Foundation.
Once we get into Heisenberg’s work, particularly on the uncertainty principle, we immediately get embroiled in mathematics, much of which I don’t understand myself (except to know that formulations of the principle in words lack the rigor of mathematical descriptions). Historically, people have confused the uncertainty principle with a different effect in physics, called the observer effect, which notes that measurements of certain systems cannot be made without affecting the systems, that is, without changing something in the system. Originally Heisenberg offered such an observer effect at the quantum level as a physical explanation of quantum uncertainty. It has since become clear, however, that the uncertainty principle is inherent in the properties of all wave-like systems, and that it arises in quantum mechanics simply due to the matter-wave nature of all quantum objects. Thus, the uncertainty principle actually states a fundamental property of quantum systems, and is not a statement about the observational success of current technology. It must be emphasized that measurement does not mean only a process in which a physicist-observer takes part, but rather any interaction between classical and quantum objects regardless of any observer. Here we collide with Schrödinger and his cat, but I’ll leave that subject alone.
Throughout the main body of his original 1927 paper, written in German, Heisenberg used the word, “Ungenauigkeit” (“indeterminacy”), to describe the basic theoretical principle. Only in the endnote did he switch to the word, “Unsicherheit” (“uncertainty”). When the English-language version of Heisenberg’s textbook, The Physical Principles of the Quantum Theory, was published in 1930, however, the translation “uncertainty” was used, and it became the more commonly used term in the English language thereafter.
Today is National Sacher-Torte Day in Austria, so I think that it’s a good day to make Sacher-Torte even though it is Austrian and not German. I do know the difference. However, I’d like to believe that Heisenberg enjoyed this chocolate delight once in a while. It is best savored in a coffee house in Vienna, but you can make a decent copy if you have some baking skills.
4 ½ oz high-quality bittersweet chocolate, finely chopped
9 tbsp (1 stick plus 1 tbsp) unsalted butter, at cool room temperature
1 cup confectioners’ sugar
6 large eggs, separated, at room temperature
1 tsp vanilla extract
½ cup granulated sugar
1 cup all-purpose flour
1 cup Apricot Glaze (see below)
1 small batch Chocolate Glaze (see below)
sweetened whipped cream, for serving
To make the torte, position a rack in the center of the oven and heat to 400°F. Lightly butter a 9-inch springform pan and line the bottom with a round of parchment or wax paper. Dust the sides of the pan with flour and tap out the excess.
In the top part of a double boiler over very hot, but not simmering, water, or in a microwave at medium power, melt the chocolate. Remove from the heat or the oven, and let stand, stirring often, until cool.
Beat the butter in the bowl of a heavy-duty standing mixer fitted with the paddle blade on medium-high speed until smooth, about 1 minute. On low speed, beat in the confectioners’ sugar. Return the speed to medium-high and beat until light in color and texture, about 2 minutes. Beat in the egg yolks, one at a time, scraping down the sides of the bowl. Beat in the chocolate and vanilla.
Beat the egg whites and granulated sugar in a large bowl with a handheld electric mixer on high speed just until they form soft, shiny peaks. Do not overbeat. Stir about one quarter of the beaten whites into the chocolate mixture to lighten it, then fold in the remaining whites, leaving a few visible wisps of whites. Sift half of the flour over the chocolate mixture, and fold in with a large balloon whisk or rubber spatula. Repeat with the remaining flour.
Spread evenly in the pan. Bake until a toothpick inserted in the center comes out clean, about 45 minutes. (The cake will dome in the center.) Cool on a wire rack for 10 minutes. Remove the sides of the pan, and invert the cake onto the rack. Remove the paper and re-invert on another rack to turn right side up. Cool completely.
To assemble, using a long serrated knife, trim the top of the cake to make it level. Cut the cake horizontally into two equal layers. Place one cake layer on an 8-inch cardboard round. Brush the top of the cake layer with the apricot glaze. Place the second cake layer on top and brush again. Brush the top and sides of the cake with the remaining glaze. Transfer the cake to a wire rack placed over a jelly-roll pan lined with waxed paper. Let cool until the glaze is set.
Make the chocolate glaze (it must be freshly made and warm). Pour all of the warm chocolate glaze on top of the cake. Using a metal offset spatula, gently smooth the glaze over the cake, allowing it to run down the sides, being sure that the glaze completely coats the cake (patch any bare spots with the spatula and the icing that has dripped). Cool until the glaze is barely set, then transfer the cake to a serving plate. Refrigerate until the glaze is completely set, at least 1 hour. Remove the cake from the refrigerator about 1 hour before serving.
To serve, slice with a sharp knife dipped into hot water. Serve with a large dollop of whipped cream on the side.
Small Batch Chocolate Glaze
1 cup sugar
½ cup water
4 oz high quality bittersweet chocolate
In a heavy-bottomed medium saucepan (no larger than 1 quarts or the mixture will reduce too rapidly and burn before it reaches the correct temperature) over high heat, bring the sugar, water, and chocolate to a boil over medium-high heat, stirring occasionally. Attach a candy thermometer to the pan. Reduce the heat to medium and cook, uncovered, stirring, until the mixture reaches 234°F., about 5 minutes.
Remove from the heat and stir to cool and thicken slightly, about 1 minute. Use immediately. When pouring, do not scrape the pan.
1 ¼ cups apricot preserves
2 tablespoons golden rum (or water)
Bring the preserves and rum to a boil in a small saucepan over medium heat, stirring often. Cook, stirring often, until the last drops that cling to the spoon are very sticky, 2 to 3 minutes. Strain through a wire sieve into a small bowl, pressing hard on the solids. Use warm.