The Governmental Film Archive of the German Democratic Republic presents Film Archive of Personalities Privy Councilor - Max Planck If you are like me in your 85th year of life, you will probably feel more strongly than ever the need to understand how life has gone, to take a look back at your life so far, and to give a comprehensive summary to yourself and others about what you have achieved and what you have strived for. And finally, to also take a last look into the future. I come from a family of Swabians. My great-grandfather moved from Nürtingen near Stuttgart to Göttingen. And from this point on, his children, grandchildren and great-grandchildren moved to North Germany and spread there. Most of them were theologians, philologists, and I am probably the only one who steped out of line and became a natural scientist. I put this on environmental influences. Because in my school, I was encouraged by my math teacher, Hermann Müller. A very humorous, strict man, who was enthusiastic about everything that had to do with mathematics and natural science. On the one hand, the strictness of the mathematical method, on the other hand, the greatness and beauty of the laws that rule in nature. Even then, the ideal of my entire scientific activity, which I still follow today, was to feel the harmony that prevails, on the one hand, between the strictness of mathematics and, on the other hand, between the fullness of the laws of nature that surround us. And this corresponds to the possibility of mastering nature with the sharpness of our logic, of human thought. To seek the harmony of these logical laws with the laws of nature. In this way, we also achieve domination over nature. This always seemed to me to be the most beautiful goal of all scientific pursuit. As I said, we grew up in North Germany, although we were originally Swabians. I was born in Kiel and later came to Munich, where my father was appointed professor at the university. My father was a strict Augustenburger, a Schleswig-Holsteiner, and was not at all satisfied with the fact that Schleswig-Holstein was annexed by Prussia. This essentially made him to move from Holstein to Munich and the University there. Later, peace was established between the Augustenburgers and the Prussians, which lead to our princess, the daughter of the Duke of Augustenburg, becoming a German Empress. I still have the memory of this time in Kiel and how she received me there one time as an Empress. It was very nice. There was a ceremony at the royal court and I had to pass by her in a large parade and bow to her. Then, I mentioned something about Kiel to her and she pulled me into a conversation, which took so long, such that the court ceremony master later came to me to ask very curiously what was going on and what the Emperess had spoken to me about. I had to laugh about this little episode. So we came to Munich and I studied there. There was my mathematics teacher who made me enthusiastic about mathematics and I started my studies there. I went to the University later and during my last year, I studied in Berlin and started my career as a private lecturer. In this way, my life went on in a very ordinary way. I was a private lecturer and later became a professor in Kiel and in Berlin. Since 1889, I have been here in Berlin at the University. First as an Extraordinary, then as an Ordinary and now I am an Emeritus professor. So I am actually an old Berliner. But actually there are no real old Berliners who were born here. It all goes back and forth in academic circles. You come from one university to another and if one considers that I am actually very sedentary. But once you have moved to Berlin, you can hardly get away from here, because here is the center of all the spiritual movements in all of Germany. It has become stronger and stronger with time. In a certain sense, it is regrettable that it has become more and more centralized. I used to be very fond of the noble aspirations of the different royal courts of Darmstadt, Dresden, Munich and Weimar and whatever they are all called. There are many others, Karlsruhe, Dresden, Leipzig. But all of this has now been faded in favor of Berlin. That is actually a pity. But that is probably due to the course of time. Now I would like to tell you something scientific about me. That is probably what most people are interested in. But maybe not everyone understands what I am going to say now. It will be quite physical. As I said, I started my university studies in Munich, where I went to school. There, the professors Ludwig Seidel and Gustav Bauer introduced me to mathematics and Philipp von Jolly to physics. I keep a grateful memory of all three. But I cannot by all means forget the words of the last man, Mr. von Jolly, when I said goodbye to him to study my last semester in Berlin which covered mainly theoretical physics. He told me that theoretical physics is a very nice subject, although there are currently no open professorships for it. And he added further that I will hardly be able to find out anything new in theoretical physics. Because with the discovery of the principle of the preservation of energy, the foundations of theoretical physics are set completly. He said that one can probably find a little bit of something here and there if one looks hard enough, but one will never be able to find anything new in principle. However, these words did not stop me from taking the exciting path towards theoretical physics. I didn't actually expect that I could do something new, but I rather had the desire to research the laws of nature a little more deeply. Coming to Berlin, I then turned to the main topic of my entire work, namely, to the study of the main laws of thermodynamics. As classical mechanics seemed to me to be completely exhausted, the main laws of thermodynamics which have to be valid for all natural processes, regardless of whether one thinks of matter atomistically or continuously, seemed more intriguing to me. At the time when I came to Berlin, Professor Hermann Helmholtz as an experimentalist and Gustav Kirchhoff as a theoretician shone in the sky Physics. I listened to both of their lectures, but I was not very interested in them as they did not cover anything about heat. It was much more the writings of Rudolf Clausius which, through their simplicity, clarity and their preciseness, made me so enthusiastic that I now dedicated myself entirely to the study of these laws of heat theory. In particular, I was interested in the concept of entropy introduced by Clausius. Entropy is a quantity that, in addition to energy, probably corresponds to one of the most important variables of nature. While energy remains constant, entropy always grows and can never be reduced. And this is the essence of the second main law of thermodynamics, meaning the fact that the entropy of a system of bodies can always only increase. In the limiting case, it remains the same. If it increases, then the process is irreversible. If it remains the same, then the process is reversible. Which means that you can also let it run backwards. This is the big difference between all laws of nature. And thermodynamic equilibrium is present when the entropy has reached its maximum value. If entropy can no longer grow, then no change can occur. It is from this statement that all properties of a thermodynamic equilibrium emerge. And it was this statement which I applied to physical-chemical as well as to radiation equilibria. Regarding physical-chemical equilibria, an American was faster than me. That was Josiah Willard Gibbs, professor in Baltimore. He thus took away a success for me. Regarding the radiation equilibrium, however, it turned out that it was me who build the foundations. And my main achievement lies in this. However, I did not find the entropy of heat radiation, i.e. the dependency of the entropy of the radiation intensity, by purely theoretical means in the beginnig. I only found it by reference to experimental measurements, conducted on the one hand by Otto Lummer and Ernst Pringsheim from the Physical-Technical Reichsanstalt, and on the other hand by Heinrich Rubens and Friedrich Kohlbaum from the Technical University. In order to interpret these laws, which were found experimentally, I was guided by the great thoughts of Ludwig Boltzmann. Since it was him who was able to interpret the entropy of a gas, from the standpoint of the atomic theory, as the logarithm of the probability of the state of the gas. The application of Boltzmann's procedure to black body radiation, could only succeed if one considered radiation as atomistic, if one considered radiation as a combination of individual, special quanta. And it was this requirement which led, unavoidably, to the assumption of such radiation atoms or radiation quanta of a very specific size, whose size were known exactly by the previous measurements. At first, I did not like this hypothesis, because it contradicted all the ideas of classical atomistics. But there was no other way. And later on, thanks to the work of numerous colleagues, it has been shown that it corresponds to reality. Of course, it took a number of years until the physics community took notice of my theory. Because initially it was misunderstood by many people and was completely ignored, as it is often the case with such new things. But I did not allow myself to be somehow sad or afraid by this lack of recognition, because I was too sure of my work to doubt its final success. So I could lay back, relax and observe the development without being worried. This development then took place much faster than I thought at first. Due to more precise measurements that were then made possible, it became very clear very soon that the values of the most important physical constant, namely the electric elementary quantum (today: Planck's constant), were getting closer to the value that I had predicted from the radiation measurements. And this showed that this radiation measurement and the subsequent calculation was the right way to get to these values. So far I have mainly spoken of thermodynamics. I would like to say one more word about mechanics. I had always considered mechanics, as most physicists, as the basis of all physical sciences. And in a sense it still is today. Because mechanics does not count with any other variables than with those of space and time. And they are indispensable in all areas of nature. Because of this, the theory of relativity arouse my special attention right from the beginning. And it filled me with a lively satisfaction when I found out that the theory of relativity, in which energy and momentum are set equal, actually represents the completion and culmination of the whole foundation of theoretical physics. I have also devoted some of my work to it, at the time were it had not been completled yet. I generally have always turned my interest to questions which possibly lead to a simplification of the whole system of theoretical physics. Currently, the latest development of physics is in the context of the introduction of quantum theory. Quantum theory is a new step on the path to knowledge about nature. And many excellent physicists are inclined to consider the current state of physics as a new final point, meaning as the final conclusion of our investigation into the laws of nature. I do not belong to them. I believe that quantum theory has not yet reached its full maturity, its full final point. I believe that we still have to make some generalizations, some abstractions in order to reach a similar understanding of the laws of nature as the classical theory had once permitted, which we had to give up now. I believe that research still has to go much further before we reach such a conclusion. This is somewhat unsatisfactory, but on the other hand it is also very appropriate and joyful. Because we will never reach the final conclusion about nature. Scientific pursuit will never stop. It would be terrible if it would stop. If there were no more problems, one would sit back and take things easy, turn of one's head off and would not work anymore. Such a calmness is stagnation and such calmness is death in a scientific sense. The happiness of the scientist lies not in possessing the truth, but in discovering the truth. And in this continuous, successful search for truth lies the satisfaction. The search itself is not satisfactory, of course. It has to be successful. But this successful work is what represents the source of every effort and the source of every spiritual pleasure. If this source is dried up, that is if the truth is found, then it is over. Then one can go to sleep mentally and physically. But it is ensured that we do not experience this and that is the foundation of our happiness. Now I would like to say one last word, which should clear my conscience. I have followed a friendly invitation here today on the 15th of December 1942, here in Berlin, on Jägerstraße 26. I have spoken a few words for the film archive, so that later generations, if they are interested, can take note of my personality. But I would like to emphasize that what you hear and see here is not a final image of my personality. What I said here was mostly improvised and said directly just as I thought of it. I could not prepare myself in the way I would have done otherwise, if I had known, prior to arriving, on how to appear here. So I ask you to view this as an attempt to express myself such that at least something will remain of me. For those who want to find out more about me, I ask you to stick to what I wrote and what I printed as I can stand up for that. The older you get, the more you feel the responsibility for what you say. And that is why I got used to, in the latest years, to carefully prepare myself and to think through everything I will be saying or presenting beforehand. That did not happen today. Therefore, I have to set a question mark behind everything I have said here today and I ask you kindly to consider this.
