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Encounters with Einstein and Other Essays on People, Places and Particles
In nine essays and lectures composed in the last years of his life, Werner Heisenberg offers a bold appraisal of the scientific method in the twentieth century--and relates its philosophical impact on contemporary society and science to the particulars of molecular biology, astrophysics, and related disciplines. Are the problems we define and pursue freely chosen according to our conscious interests? Or does the historical process itself determine which phenomena merit examination at any one time? Heisenberg discusses these issues in the most far-ranging philosophical terms, while illustrating them with specific examples.
152 pages, Paperback
First published January 1, 1980
About the author
Werner Heisenberg
90 books348 followersWerner Heisenberg was a German theoretical physicist who made foundational contributions to quantum mechanics and is best known for asserting the uncertainty principle of quantum theory. In addition, he made important contributions to nuclear physics, quantum field theory, and particle physics.
He won the 1932 Nobel prize in physics "for the creation of quantum mechanics, the application of which has, inter alia, led to the discovery of the allotropic forms of hydrogen".
He won the 1932 Nobel prize in physics "for the creation of quantum mechanics, the application of which has, inter alia, led to the discovery of the allotropic forms of hydrogen".
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Displaying 1 - 9 of 9 reviews
November 6, 2018
Heisenberg makes the point that conceptually, we still use the concepts of Democritus. Reality is described as particles (atoms for Democritus; particles for modern physics), whereas in the quantum world this infinite regressive search for the basic stuff of reality (particles, sub-particles, elementary particles) no longer applies. On this point, Heisenberg says that “We have always asked the question: ‘of what does this object consist, and what is the geometrical or dynamical configuration of the smaller particles in the bigger object?” Actually, we have always gone back to this philosophy of Democritus; but I think we have now learned from Dirac that this was the wrong question.” Later, Heisenberg says that these “questions are wrongly put, since the words divide or consist of have largely lost their meaning. “Good physics,” he states, “is unconsciously being spoiled by bad philosophy.”
As to how to understand reality at the quantum level, Heisenberg says that we have to replace the concept of a fundamental particle “by the concept of a fundamental symmetry.” “Elementary particles” are created out of energy (of the kinetic energy of motion) per Einstein’s E=MC2, and a hard-to-understand reference to the symmetry of the “particle-anti-particle conjugation." Is this the fundamental symmetry Heisenberg is talking about? There are new combinations of existing particles that have something to do with symmetry (a balance of energy?), without a sub-dividing of them. On this point, Heisenberg writes “that, in very high energy collisions, any number of particles can be created, provided only that the initial symmetry is identical with the final symmetry,” adding that “The elementary particle was not elementary anymore. It is actually a compound system, rather a complicated man-body system….” Still, with that, the concept of symmetry is not clear. Heisenberg writes that the quest “is not to look for “fundamental particles, but fundamental symmetries.” That term, “fundamental symmetry,” “means that the natural law which determines the spectrum of particles and their interactions is invariant under certain groups of transformations.” Heisenberg has examples in mind, but I found them too technical to follow.
As to how to understand reality at the quantum level, Heisenberg says that we have to replace the concept of a fundamental particle “by the concept of a fundamental symmetry.” “Elementary particles” are created out of energy (of the kinetic energy of motion) per Einstein’s E=MC2, and a hard-to-understand reference to the symmetry of the “particle-anti-particle conjugation." Is this the fundamental symmetry Heisenberg is talking about? There are new combinations of existing particles that have something to do with symmetry (a balance of energy?), without a sub-dividing of them. On this point, Heisenberg writes “that, in very high energy collisions, any number of particles can be created, provided only that the initial symmetry is identical with the final symmetry,” adding that “The elementary particle was not elementary anymore. It is actually a compound system, rather a complicated man-body system….” Still, with that, the concept of symmetry is not clear. Heisenberg writes that the quest “is not to look for “fundamental particles, but fundamental symmetries.” That term, “fundamental symmetry,” “means that the natural law which determines the spectrum of particles and their interactions is invariant under certain groups of transformations.” Heisenberg has examples in mind, but I found them too technical to follow.
February 20, 2014
Reminiscing with Werner Heisenberg about the evolution of quantum mechanics
This book is a collection of nine essays/lectures delivered by Werner Heisenberg in the last few years of his illustrious career in the contribution to the understanding of physical reality. This group of essays deals, briefly, with the historical development of quantum mechanics, and how the concept of matter as a particle was replaced by energy and by fundamental symmetry. These essays not only touch of upon one of the most fundamental aspects of physical reality but also some of the most private moments in the lives of the founding fathers of modern physics. The title of the book "Encounters with Einstein" is somewhat misleading since only one essay (chapter 7) deals with this subject and this chapter has the same title as the book.
Heisenberg was a student of Sommerfeld at Munich who was a close friend of Einstein and a supporter of theory of relativity who use to share Einstein's letters with his students, and discuss the physics written in these letters. Heisenberg describes his interest in meeting Einstein as he started working in the developing field of quantum physics. This was during 1920s when quantum mechanics was beginning to take shape. It was also the time when the Third Reich was gaining momentum and anti-Semitism was soaring in Germany. Einstein was most respected in the academic world and obviously he was the target of nationalists. At the 1922 congress of German scientists held at the Leipzig, the students of one of the most respected association of German Experimental Physicists distributed red leaflets suggesting "that the theory of relativity is totally unproved Jewish speculation, and that it had been undeservedly played up through the puffery of Jewish newspapers on behalf of Einstein, a fellow member of the race." Heisenberg recalls this as the poisoning of science by political passions. It is ironic if we recall that Islamic countries and Islamists brand 9/11 terrorist attack to Jews and Israel: This is certainly very saddening.
According to one of the Einstein's work; the requirement that a physical theory should only contain quantities that can be directly observed will guarantee a connection between the mathematical formalism and the phenomena. In one of his discussion with Einstein, Heisenberg argued that the path of the electron within an atom must be abandoned from the theory because no such path is experimentally observed except for the light frequencies radiated by the atom, intensities and transition probabilities. Heisenberg stated that he was astonished to see that Einstein did not agree with him and in fact argued that the theory in fact also contains unobservable quantities. When Heisenberg pointed out that Einstein had made a similar assumption (existence of only observable quantities) in the special theory of relativity, he responded simply by stating; "Perhaps I did use such philosophy earlier, and also wrote it, but it is nonsense all the same." Einstein had revised his philosophical outlook. His vision was that the concept of observation was problematic because it presupposes that there is an unambiguous connection between the observed phenomenon and the sensation that enters consciousness. We can be sure of this connection if we know the natural laws by which it is determined. These laws do not include consciousness in equations. This interaction between the two great physicists illustrates the confusion that existed in making sense out of quantum reality, and Heisenberg recalls that this conversation had deep impact on his development of uncertainty principle. Another point of discussion Heisenberg recalls is that statistical nature of quantum reality arises because of our incomplete knowledge of a system. Einstein was steadfast in his conviction that it is not statistical even though in 1918 he introduced such statistical concepts. There is an interesting routine interaction with Einstein and Bohr during the well known 1927 Solvay conference, and how he use to come up with his little thought experiment and beaten by Bohr. The Einstein's watchword was "God does not play at dice" and the response by Bohr (less-known in literature) was; "But still, it cannot be for us to tell God, how he is to run the world." Heisenberg concludes that physics is a reflection on the divine ideas of creation, therefore physics is divine service.
This book is a collection of nine essays/lectures delivered by Werner Heisenberg in the last few years of his illustrious career in the contribution to the understanding of physical reality. This group of essays deals, briefly, with the historical development of quantum mechanics, and how the concept of matter as a particle was replaced by energy and by fundamental symmetry. These essays not only touch of upon one of the most fundamental aspects of physical reality but also some of the most private moments in the lives of the founding fathers of modern physics. The title of the book "Encounters with Einstein" is somewhat misleading since only one essay (chapter 7) deals with this subject and this chapter has the same title as the book.
Heisenberg was a student of Sommerfeld at Munich who was a close friend of Einstein and a supporter of theory of relativity who use to share Einstein's letters with his students, and discuss the physics written in these letters. Heisenberg describes his interest in meeting Einstein as he started working in the developing field of quantum physics. This was during 1920s when quantum mechanics was beginning to take shape. It was also the time when the Third Reich was gaining momentum and anti-Semitism was soaring in Germany. Einstein was most respected in the academic world and obviously he was the target of nationalists. At the 1922 congress of German scientists held at the Leipzig, the students of one of the most respected association of German Experimental Physicists distributed red leaflets suggesting "that the theory of relativity is totally unproved Jewish speculation, and that it had been undeservedly played up through the puffery of Jewish newspapers on behalf of Einstein, a fellow member of the race." Heisenberg recalls this as the poisoning of science by political passions. It is ironic if we recall that Islamic countries and Islamists brand 9/11 terrorist attack to Jews and Israel: This is certainly very saddening.
According to one of the Einstein's work; the requirement that a physical theory should only contain quantities that can be directly observed will guarantee a connection between the mathematical formalism and the phenomena. In one of his discussion with Einstein, Heisenberg argued that the path of the electron within an atom must be abandoned from the theory because no such path is experimentally observed except for the light frequencies radiated by the atom, intensities and transition probabilities. Heisenberg stated that he was astonished to see that Einstein did not agree with him and in fact argued that the theory in fact also contains unobservable quantities. When Heisenberg pointed out that Einstein had made a similar assumption (existence of only observable quantities) in the special theory of relativity, he responded simply by stating; "Perhaps I did use such philosophy earlier, and also wrote it, but it is nonsense all the same." Einstein had revised his philosophical outlook. His vision was that the concept of observation was problematic because it presupposes that there is an unambiguous connection between the observed phenomenon and the sensation that enters consciousness. We can be sure of this connection if we know the natural laws by which it is determined. These laws do not include consciousness in equations. This interaction between the two great physicists illustrates the confusion that existed in making sense out of quantum reality, and Heisenberg recalls that this conversation had deep impact on his development of uncertainty principle. Another point of discussion Heisenberg recalls is that statistical nature of quantum reality arises because of our incomplete knowledge of a system. Einstein was steadfast in his conviction that it is not statistical even though in 1918 he introduced such statistical concepts. There is an interesting routine interaction with Einstein and Bohr during the well known 1927 Solvay conference, and how he use to come up with his little thought experiment and beaten by Bohr. The Einstein's watchword was "God does not play at dice" and the response by Bohr (less-known in literature) was; "But still, it cannot be for us to tell God, how he is to run the world." Heisenberg concludes that physics is a reflection on the divine ideas of creation, therefore physics is divine service.
April 19, 2024
Conclusion: I love Heisenberg <3
July 6, 2021
Werner Heisenberg wrote this collection of essays, originally a set of lectures, toward the end of his life.
Below is a summary of each chapter for my own records, to be completed as I go because Goodread's crappy draft interface keeps losing unposted draft sections.
1. Tradition in science
The central thesis here is that tradition influences scientific activities in the following ways:
a. Problem selection
b. Application of the Scientific Method
c. Use of concepts as tools
On a. tradition exerts its influence by how we are bound in history, our personal relationships with other researchers and the practical problems of our times which require a solution and which serve as effective tests to check that new scientific ideas "really work". He says "history teaches us that it is not usually the consistency, the clarity of a theory which makes it acceptable but the hope that one can participate in its elaboration and its verification."
On b. he says we still essentially follow the methods of Galileo and Copernicus, where "experience" meant "experience illuminated by mathematical constructs" which suggest new experiments merely descriptive theories would not have suggested. Two essential features of their method was therefore the design of new and accurate experiments, and their comparison with these constructs, which they called natural laws. Originally, the basis for this approach was theological, but we still follow it because it has been so successful. Even quantum mechanics, with its epistemological difficulties, in the end shows that what can be observed is inseparable from the theory. Goethe made an attempt to return to Aristotelian descriptive methods, but it did not influence the course of science.
On c. he says that the history of science is not just that of discoveries and observations, but also of concepts. The early success of Newtonian concepts led to efforts to reduce new concepts to the older ones. They sometimes succeeded, as in the case of the reduction of thermodynamics to statistical mechanics, and sometimes did not, as in the case of classical electrodynamics. For relativity and quantum mechanics, traditional concepts could easily be construed as a prejudice hindering further progress, but one cannot begin to form new concepts without the old ones, as the words we use and the thinking we employ to describe them is necessarily grounded in traditional concepts. Thus, " In a state of science where fundamental concepts have to be changed, tradition is both the condition for progress and hindrance."
Heisenberg says that in paricle physics we should abandon the use of essentially the same fundamental concepts as Democritus and instead adopt the concept of fundamental symmetries, as the former is not going to lead to deeper progress. Alas, the fundamental symmetry concept is traditional, too, having been espoused by Plato.
2. Development of concepts in the history of quantum mechanics.
Heisenberg describes the development of 3 concepts that were important for his own work in quantum mechanics:
a. The concept of the stationary state:
b. The concept of state, not necessarily stationary or discrete
c. The concept of an elementary particle
On a. He says the concept was first introduced by Niels Bohr in 1913 in order to connect three seemingly disconnected phenomena: the stability of atoms, their spectral laws, and Rutherford's model of the atom. It worked well in some cases, e.g. the H spectrum, fine structure and the Stark effect, but not so well in others e.g. the frequency of the electronic orbit could never be observed and depended on the field directionality, even when the field was too weak to turn the atom around. The picture of an electronic orbit had to be abandoned and the concept of a stationary state came to be associated just with transition probabilities and dispersion.
On b. he says that various attempts to associate it with a picture, such as by Schrödinger with his interpretation of his wave mechanics, failed, so that it could only be described in terms of finding the electron at a given place or more abstractly, as a vector in Hilbert space. Some scientists resisted this, e.g. Einstein said:"...such a scheme cannot be a final description of nature".
On c. he says that the picture of an elementary particle as a pointlike charge with few properties had to be abandoned as first spin was discovered, then antimatter, then the fact that particle number was not conserved, and finally that an elementary particle can be expressed in terms of a combination of other particles so long as both obey the same kinds of fundamental symmetry. He claims"The elementary particle...is actually a compound system, rather a complicated many-body system..." and that "every particle consists of all other particles". What remains of the elementary particle concept is just its associated fundamental symmetry. He considers the Lorentz group, SU(2), the scaling law and PCT genuine fundamental symmetries, and SU(3) as approximate.
3. The Beginnings of Quantum Mechanics in Göttingen.
Planck's original quantum theory was first only researched in Copenhagen by Bohr and in Munich by Sommerfeld, until Born and Franck were appointed to the faculty in Göttingen. Each center corresponded to a tendency toward a particular approach: Copenhagen to a conceptual or philosophical one, Munich to a phenomenological one, and Göttingen to a mathematical one.
Quantum mechanics at Göttingen began in 1922 with the Bohr Festival (analogous to the Händel festival begun there shortly before), where Bohr gave a comprehensive set of lectures on his theory, followed the next semester by a seminar, given by Born, on the problems of Bohr's theory. They found that classical approaches always turned out to be "half-right", so that Bohr's correspondence principle provided a valuable guide to finding the correct quantum formations.
While working on these problems, Heisenberg had a Hay fever attack and went to Helgoland to recover. He was then able to put the framework together in short order. Born and Jordan translated his work in the more familiar language of matrix algebra, and Pauli showed that the application of the framework to various problems, such as the H atom, yielded correct results. Heisenberg was still unhappy with its conceptual foundation.
In 1926, Schrödinger presented an alternative formation which he believed would ground quantum mechanics again in classical concepts. He showed that his wave mechanics was mathematically equivalent to Heisenberg's matrix mechanics, but in the course of a series of discussions at a seminar in Munich, it became clear that it could not be interpreted in terms of classical concepts, as the wave turned out to be in configuration space, not real space, and the absolute square of the wave function over a region had to correspond to the probability of finding it there.
By 1927, Heisenberg, heavily influenced by Bohr, arrived at an interpretation according to which the theory determined which questions to ask, that by asking whether there are "in nature only such experimental situations as can be represented in the mathematical formalism of quantum theory" one is naturally led to the uncertainty relations, and that therefore familiar classical concepts like paths " may be used only with the degree of inexactness characterized by the fact that the product of the uncertainty of position and the uncertainty of the associated momentum cannot be smaller than planks quantum of action."
4. Cosmic radiation and fundamental problems in physics.
Cosmic rays contain information on the behavior of matter in the smallest and largest dimensions, therefore they have been particularly valuable in testing the concepts of daily life in relation to the meaning in physics.
a. In the late thirties Blau and Wambacher discovered in photographic plates exposed at high altitudes so-called stars, events in which from the same point in the plate a great number of tracks start. These showed that the concepts of "dividing" and "consisting of" have only a limited range of applicability with respect to elementary particles: In highly energetic collisions between 2 particles, new particles are created out of the kinetic energy, And cosmic rays are the most energetic radiation we can observe.
b. the muon was discovered as a result of cosmic-ray research. It revealed that the spectrum of particles is divided into 2 only weekly combining term systems: Leptons and hadrons. Heisenberg also mentions that muons help to settle a question regarding the acceptability of relativity, a theory denied by the Nazis, because it predicted that muons in motion decay more slowly due to time dilation, and in due course the experimental results confirmed this prediction.
c. The discovery of the Pion confirmed that various particles are stationary states of the system matter, different through their different behavior under the transformation of the fundamental group. The groups are more fundamental than the particles, he says.
d. Other particles were discovered through cosmic ray research which had unexpectedly long lifetimes, and eventually led to the discovery of a new quantum number, called strangeness, and the corresponding symmetry (or transformation property).
e. In astrophysics, cosmic radiation became a valuable new tool which promised information beyond that obtained from the visible or infrared light of the stars, in particular on the origin of the radiation. Heisenberg says that the consensus seems to be that such radiation originates from supernovae and supernovae and their relics, the pulsars.
f. Heisenberg says cosmic ray radiation may also help settle the question of whether the cross-section or other characteristics of particle showers after collisions change with energy in the range of extremely high energies. Theoretical predictions are that there should be an asymptotic region, but the total cross-sections in this region should not be constant, they should increase logarithmically.
g. Heisenberg says that Cosmic ray research may also settle the question of predictions of the SU(3) symmetry of new particles, such as quarks, W-mesons, partons, gluons, magnetic poles and charm particles. He expresses skepticism on the existence of all of these.
h. Heisenberg says that cosmic ray research may also contribute to our knowledge of the dynamics of matter. Stars with densities higher than even neutron stars, such as a star of large mass undergoing gravitational contraction, may contain a mixture of particles, in which case it is more reasonable to speak of continuous matter. Heisenberg considers the dynamical behavior of this continuous matter to be the central problem in particle physics.
i. According to Heisenberg, cosmic ray research may also advance our understanding of the dynamical behavior of continuous matter through the analysis of the collision spectrum of high energy cosmic particles, as the density of the initial disk in a collision involving such a particle can be a 1000 times greater than in a neutron star. The difference between the previous phenomenon and this one is that gravity plays a role in the former but not in the latter.
5. What is an elementary particle?
In formulating an answer to this question, Heisenberg distinguishes between answers based on experiment and those based on philosophy, grounded on his view that "perhaps...good physics has been inadvertently spoiled by bad philosophy."
On the experimental side he mentions the verification of Dirac's prediction of the electron's anti-particle, Fermi's discovery of "artificial radioactivity"[comment: Irène and Frédéric Joliot-Curie are normally credited with its discovery], and the observation of showers of secondary particles coming out of the collision between primary particles, which rendered the concept of a "division" of a particle obsolete. He comes to the conclusion that "it would be simplest of all to say that a proton just consists of continuous "matter".
The experiments suggest an analogy in which each elementary particle corresponds to a particular stationary state, and gives the spectrum of "matter". Its transformation properties are given by the appropriate symmetry principles, just as for stationary states, so that the elementary particle corresponding to the ground state is the most stable, yet is in no way more elementary than the unstable ones. Also, the weakly combining term systems of elementary particles , the leptons and the baryons, correspond to the spectra of ortho-and para-helium.
The near-completeness of these analogies answers the question of what an elementary particle is qualitatively, Heisenberg says. To answer the question quantitatively one must first answer a prior question: what is it, anyway, to understand a spectrum in quantitative terms? Two elements are necessary for quantitative understanding: the exactly formulated knowledge, in mathematical terms, and the boundary conditions, which can be regarded as "contingent", as determined, that is, by local circumstances. In particle physics, this becomes a question of first ascertaining by experiment the dynamical properties of the matter system, then formulating them in mathematical terms, and finally, as a contingent element, add boundary conditions which consist essentially of statements about so-called empty space.
Heisenberg speculates that the spectrum of elementary particles depends to such an extent on the boundary conditions that in a black hole it might be completely different than in our reality.
Philosophically guided answers to the question of what an elementary particle is have been influenced most strongly by that of Democritus, according to which matter can be divided into ever smaller parts until it no longer can, i.e. until one encounters atoms. In Aristotle's philosophy, he says, the concept of a minimal particle is not so sharply defined, but amounts to the idea that matter is infinitely disvisible. In Plato's philosophy, he says, continual division of matter ultimately leads to mathematical forms, idealizations of the objects of our everyday experience. These forms themselves are not matter, but shape it, and since they can be defined through their associated symmetries, Plato's philosophy comes closest to the experimental findings in particle physics, Heisenberg claims.
In his view, the Platonist view also resolves Kant's antinomy-that it is very hard to think of matter as infinitely divisible, but also difficult to imagine this division as eventually coming to an enforced stop-in an unexpected fashion: that's the concept of "division" itself eventually loses meaning.
With the advent of Newtonian mechanics, he says, the Democritean idea of an atom became an integral part of the physicist's view of the material world, and a such also became unavoidable in language that seeks to ask deeper questions on the elementary properties of matter e.g. " What does a proton consist of?", "Is the electron divisible or not?".
But these questions are falsely put, since words like "divisible" have lost their meaning, and so by way of a Democritean philosophy false ideas and questions creep into particle physics.
He compares the model of quarks as constituent particles of the proton to a purely phenomenological model by Voigt of the D-lines in the optical spectrum of sodium, which turned out to contribute nothing to the understanding of atomic structure, and claims that in each case, the respective hypothesis is not taken seriously by its exponents, and therefore critical questions concerning discrepancies of each model are left in obscurity. If the quark hypothesis were taken in earnest, he says, it would be necessary to make a precise mathematical approach to the dynamics of quarks, and the forces that hold them together, and to show that, qualitatively at least, this approach can reproduce correctly the many different features of particle physics, such that there should be no question in particle physics to which this approach could not be applied. He says attempts along these lines are not known to him.
Finally, he stresses that the particle spectrum can be understood only if we know the underlying dynamics of matter, "all else would be merely a sort of word painting based on the tabulated record."
6. The role of elementary particle physics in the present development of science.
Heisenberg observes a general agreement that elementary particle physics plays a very important role in contemporary science. He attributes it in part to interesting applications of particle physics in other areas, such as solid state physics, nuclear physics and astrophysics but more importantly, he says, particle physics' importance can be attributed to its directly addressing the question of whether the natural laws from which the particles are constructed can act as a general basis for all laws.
After giving a short quasi-historical account of the history of elementary particle experiments from modest labs to multinationally supported gigantic particle accelerators, he voices his discomfort with some of the effects of the latter on sociological aspects of physics, such as the inhibitory effect of long lead times on disseminating skills and knowledge acquired at the project back to the scientists' host countries, the fractionated perspective on the project compelled by high degree of specialization, and the inability of single physicist to carry out the project, But he sees these as unavoidable consequences of elementary particle physics having become a part of big science.
At the same time he sees in the International character of particle physics an opportunity for different countries to come together and cooperate.
Finally, he addresses the question of whether particle physics is such a fundamental field of science that great material sacrifices for its exploration can be justified. He says that although in the past each step to higher energy has opened up a new field, there may be reasons for suspecting that this will not continue. Skeptically passing over the argument that ever bigger particle accelerators should be built because they represent symbols of our age comparable to how the Egyptian pyramids or medieval cathedrals symbolized their representative ages, he considers a series of surprising discoveries which force a re-evaluation of what we consider fundamental: the change in the meaning of the concept of a state brought on by the replacement of Newtonian mechanics by quantum mechanics, and the mutability of every single particle predicted and confirmed by Dirac's theory of the electron and the discovery of the positron.
These discoveries render the
Below is a summary of each chapter for my own records, to be completed as I go because Goodread's crappy draft interface keeps losing unposted draft sections.
1. Tradition in science
The central thesis here is that tradition influences scientific activities in the following ways:
a. Problem selection
b. Application of the Scientific Method
c. Use of concepts as tools
On a. tradition exerts its influence by how we are bound in history, our personal relationships with other researchers and the practical problems of our times which require a solution and which serve as effective tests to check that new scientific ideas "really work". He says "history teaches us that it is not usually the consistency, the clarity of a theory which makes it acceptable but the hope that one can participate in its elaboration and its verification."
On b. he says we still essentially follow the methods of Galileo and Copernicus, where "experience" meant "experience illuminated by mathematical constructs" which suggest new experiments merely descriptive theories would not have suggested. Two essential features of their method was therefore the design of new and accurate experiments, and their comparison with these constructs, which they called natural laws. Originally, the basis for this approach was theological, but we still follow it because it has been so successful. Even quantum mechanics, with its epistemological difficulties, in the end shows that what can be observed is inseparable from the theory. Goethe made an attempt to return to Aristotelian descriptive methods, but it did not influence the course of science.
On c. he says that the history of science is not just that of discoveries and observations, but also of concepts. The early success of Newtonian concepts led to efforts to reduce new concepts to the older ones. They sometimes succeeded, as in the case of the reduction of thermodynamics to statistical mechanics, and sometimes did not, as in the case of classical electrodynamics. For relativity and quantum mechanics, traditional concepts could easily be construed as a prejudice hindering further progress, but one cannot begin to form new concepts without the old ones, as the words we use and the thinking we employ to describe them is necessarily grounded in traditional concepts. Thus, " In a state of science where fundamental concepts have to be changed, tradition is both the condition for progress and hindrance."
Heisenberg says that in paricle physics we should abandon the use of essentially the same fundamental concepts as Democritus and instead adopt the concept of fundamental symmetries, as the former is not going to lead to deeper progress. Alas, the fundamental symmetry concept is traditional, too, having been espoused by Plato.
2. Development of concepts in the history of quantum mechanics.
Heisenberg describes the development of 3 concepts that were important for his own work in quantum mechanics:
a. The concept of the stationary state:
b. The concept of state, not necessarily stationary or discrete
c. The concept of an elementary particle
On a. He says the concept was first introduced by Niels Bohr in 1913 in order to connect three seemingly disconnected phenomena: the stability of atoms, their spectral laws, and Rutherford's model of the atom. It worked well in some cases, e.g. the H spectrum, fine structure and the Stark effect, but not so well in others e.g. the frequency of the electronic orbit could never be observed and depended on the field directionality, even when the field was too weak to turn the atom around. The picture of an electronic orbit had to be abandoned and the concept of a stationary state came to be associated just with transition probabilities and dispersion.
On b. he says that various attempts to associate it with a picture, such as by Schrödinger with his interpretation of his wave mechanics, failed, so that it could only be described in terms of finding the electron at a given place or more abstractly, as a vector in Hilbert space. Some scientists resisted this, e.g. Einstein said:"...such a scheme cannot be a final description of nature".
On c. he says that the picture of an elementary particle as a pointlike charge with few properties had to be abandoned as first spin was discovered, then antimatter, then the fact that particle number was not conserved, and finally that an elementary particle can be expressed in terms of a combination of other particles so long as both obey the same kinds of fundamental symmetry. He claims"The elementary particle...is actually a compound system, rather a complicated many-body system..." and that "every particle consists of all other particles". What remains of the elementary particle concept is just its associated fundamental symmetry. He considers the Lorentz group, SU(2), the scaling law and PCT genuine fundamental symmetries, and SU(3) as approximate.
3. The Beginnings of Quantum Mechanics in Göttingen.
Planck's original quantum theory was first only researched in Copenhagen by Bohr and in Munich by Sommerfeld, until Born and Franck were appointed to the faculty in Göttingen. Each center corresponded to a tendency toward a particular approach: Copenhagen to a conceptual or philosophical one, Munich to a phenomenological one, and Göttingen to a mathematical one.
Quantum mechanics at Göttingen began in 1922 with the Bohr Festival (analogous to the Händel festival begun there shortly before), where Bohr gave a comprehensive set of lectures on his theory, followed the next semester by a seminar, given by Born, on the problems of Bohr's theory. They found that classical approaches always turned out to be "half-right", so that Bohr's correspondence principle provided a valuable guide to finding the correct quantum formations.
While working on these problems, Heisenberg had a Hay fever attack and went to Helgoland to recover. He was then able to put the framework together in short order. Born and Jordan translated his work in the more familiar language of matrix algebra, and Pauli showed that the application of the framework to various problems, such as the H atom, yielded correct results. Heisenberg was still unhappy with its conceptual foundation.
In 1926, Schrödinger presented an alternative formation which he believed would ground quantum mechanics again in classical concepts. He showed that his wave mechanics was mathematically equivalent to Heisenberg's matrix mechanics, but in the course of a series of discussions at a seminar in Munich, it became clear that it could not be interpreted in terms of classical concepts, as the wave turned out to be in configuration space, not real space, and the absolute square of the wave function over a region had to correspond to the probability of finding it there.
By 1927, Heisenberg, heavily influenced by Bohr, arrived at an interpretation according to which the theory determined which questions to ask, that by asking whether there are "in nature only such experimental situations as can be represented in the mathematical formalism of quantum theory" one is naturally led to the uncertainty relations, and that therefore familiar classical concepts like paths " may be used only with the degree of inexactness characterized by the fact that the product of the uncertainty of position and the uncertainty of the associated momentum cannot be smaller than planks quantum of action."
4. Cosmic radiation and fundamental problems in physics.
Cosmic rays contain information on the behavior of matter in the smallest and largest dimensions, therefore they have been particularly valuable in testing the concepts of daily life in relation to the meaning in physics.
a. In the late thirties Blau and Wambacher discovered in photographic plates exposed at high altitudes so-called stars, events in which from the same point in the plate a great number of tracks start. These showed that the concepts of "dividing" and "consisting of" have only a limited range of applicability with respect to elementary particles: In highly energetic collisions between 2 particles, new particles are created out of the kinetic energy, And cosmic rays are the most energetic radiation we can observe.
b. the muon was discovered as a result of cosmic-ray research. It revealed that the spectrum of particles is divided into 2 only weekly combining term systems: Leptons and hadrons. Heisenberg also mentions that muons help to settle a question regarding the acceptability of relativity, a theory denied by the Nazis, because it predicted that muons in motion decay more slowly due to time dilation, and in due course the experimental results confirmed this prediction.
c. The discovery of the Pion confirmed that various particles are stationary states of the system matter, different through their different behavior under the transformation of the fundamental group. The groups are more fundamental than the particles, he says.
d. Other particles were discovered through cosmic ray research which had unexpectedly long lifetimes, and eventually led to the discovery of a new quantum number, called strangeness, and the corresponding symmetry (or transformation property).
e. In astrophysics, cosmic radiation became a valuable new tool which promised information beyond that obtained from the visible or infrared light of the stars, in particular on the origin of the radiation. Heisenberg says that the consensus seems to be that such radiation originates from supernovae and supernovae and their relics, the pulsars.
f. Heisenberg says cosmic ray radiation may also help settle the question of whether the cross-section or other characteristics of particle showers after collisions change with energy in the range of extremely high energies. Theoretical predictions are that there should be an asymptotic region, but the total cross-sections in this region should not be constant, they should increase logarithmically.
g. Heisenberg says that Cosmic ray research may also settle the question of predictions of the SU(3) symmetry of new particles, such as quarks, W-mesons, partons, gluons, magnetic poles and charm particles. He expresses skepticism on the existence of all of these.
h. Heisenberg says that cosmic ray research may also contribute to our knowledge of the dynamics of matter. Stars with densities higher than even neutron stars, such as a star of large mass undergoing gravitational contraction, may contain a mixture of particles, in which case it is more reasonable to speak of continuous matter. Heisenberg considers the dynamical behavior of this continuous matter to be the central problem in particle physics.
i. According to Heisenberg, cosmic ray research may also advance our understanding of the dynamical behavior of continuous matter through the analysis of the collision spectrum of high energy cosmic particles, as the density of the initial disk in a collision involving such a particle can be a 1000 times greater than in a neutron star. The difference between the previous phenomenon and this one is that gravity plays a role in the former but not in the latter.
5. What is an elementary particle?
In formulating an answer to this question, Heisenberg distinguishes between answers based on experiment and those based on philosophy, grounded on his view that "perhaps...good physics has been inadvertently spoiled by bad philosophy."
On the experimental side he mentions the verification of Dirac's prediction of the electron's anti-particle, Fermi's discovery of "artificial radioactivity"[comment: Irène and Frédéric Joliot-Curie are normally credited with its discovery], and the observation of showers of secondary particles coming out of the collision between primary particles, which rendered the concept of a "division" of a particle obsolete. He comes to the conclusion that "it would be simplest of all to say that a proton just consists of continuous "matter".
The experiments suggest an analogy in which each elementary particle corresponds to a particular stationary state, and gives the spectrum of "matter". Its transformation properties are given by the appropriate symmetry principles, just as for stationary states, so that the elementary particle corresponding to the ground state is the most stable, yet is in no way more elementary than the unstable ones. Also, the weakly combining term systems of elementary particles , the leptons and the baryons, correspond to the spectra of ortho-and para-helium.
The near-completeness of these analogies answers the question of what an elementary particle is qualitatively, Heisenberg says. To answer the question quantitatively one must first answer a prior question: what is it, anyway, to understand a spectrum in quantitative terms? Two elements are necessary for quantitative understanding: the exactly formulated knowledge, in mathematical terms, and the boundary conditions, which can be regarded as "contingent", as determined, that is, by local circumstances. In particle physics, this becomes a question of first ascertaining by experiment the dynamical properties of the matter system, then formulating them in mathematical terms, and finally, as a contingent element, add boundary conditions which consist essentially of statements about so-called empty space.
Heisenberg speculates that the spectrum of elementary particles depends to such an extent on the boundary conditions that in a black hole it might be completely different than in our reality.
Philosophically guided answers to the question of what an elementary particle is have been influenced most strongly by that of Democritus, according to which matter can be divided into ever smaller parts until it no longer can, i.e. until one encounters atoms. In Aristotle's philosophy, he says, the concept of a minimal particle is not so sharply defined, but amounts to the idea that matter is infinitely disvisible. In Plato's philosophy, he says, continual division of matter ultimately leads to mathematical forms, idealizations of the objects of our everyday experience. These forms themselves are not matter, but shape it, and since they can be defined through their associated symmetries, Plato's philosophy comes closest to the experimental findings in particle physics, Heisenberg claims.
In his view, the Platonist view also resolves Kant's antinomy-that it is very hard to think of matter as infinitely divisible, but also difficult to imagine this division as eventually coming to an enforced stop-in an unexpected fashion: that's the concept of "division" itself eventually loses meaning.
With the advent of Newtonian mechanics, he says, the Democritean idea of an atom became an integral part of the physicist's view of the material world, and a such also became unavoidable in language that seeks to ask deeper questions on the elementary properties of matter e.g. " What does a proton consist of?", "Is the electron divisible or not?".
But these questions are falsely put, since words like "divisible" have lost their meaning, and so by way of a Democritean philosophy false ideas and questions creep into particle physics.
He compares the model of quarks as constituent particles of the proton to a purely phenomenological model by Voigt of the D-lines in the optical spectrum of sodium, which turned out to contribute nothing to the understanding of atomic structure, and claims that in each case, the respective hypothesis is not taken seriously by its exponents, and therefore critical questions concerning discrepancies of each model are left in obscurity. If the quark hypothesis were taken in earnest, he says, it would be necessary to make a precise mathematical approach to the dynamics of quarks, and the forces that hold them together, and to show that, qualitatively at least, this approach can reproduce correctly the many different features of particle physics, such that there should be no question in particle physics to which this approach could not be applied. He says attempts along these lines are not known to him.
Finally, he stresses that the particle spectrum can be understood only if we know the underlying dynamics of matter, "all else would be merely a sort of word painting based on the tabulated record."
6. The role of elementary particle physics in the present development of science.
Heisenberg observes a general agreement that elementary particle physics plays a very important role in contemporary science. He attributes it in part to interesting applications of particle physics in other areas, such as solid state physics, nuclear physics and astrophysics but more importantly, he says, particle physics' importance can be attributed to its directly addressing the question of whether the natural laws from which the particles are constructed can act as a general basis for all laws.
After giving a short quasi-historical account of the history of elementary particle experiments from modest labs to multinationally supported gigantic particle accelerators, he voices his discomfort with some of the effects of the latter on sociological aspects of physics, such as the inhibitory effect of long lead times on disseminating skills and knowledge acquired at the project back to the scientists' host countries, the fractionated perspective on the project compelled by high degree of specialization, and the inability of single physicist to carry out the project, But he sees these as unavoidable consequences of elementary particle physics having become a part of big science.
At the same time he sees in the International character of particle physics an opportunity for different countries to come together and cooperate.
Finally, he addresses the question of whether particle physics is such a fundamental field of science that great material sacrifices for its exploration can be justified. He says that although in the past each step to higher energy has opened up a new field, there may be reasons for suspecting that this will not continue. Skeptically passing over the argument that ever bigger particle accelerators should be built because they represent symbols of our age comparable to how the Egyptian pyramids or medieval cathedrals symbolized their representative ages, he considers a series of surprising discoveries which force a re-evaluation of what we consider fundamental: the change in the meaning of the concept of a state brought on by the replacement of Newtonian mechanics by quantum mechanics, and the mutability of every single particle predicted and confirmed by Dirac's theory of the electron and the discovery of the positron.
These discoveries render the
May 31, 2012
Not light reading. Be prepared with pen in hand to mark up your margins.
April 22, 2020
This was a great flea market find.
The “Encounters with Einstein“ of the title actually account for only a small part of the slim, dense volume. Heisenberg’s musings collected here lean much more toward the definition / meaning of “elementary particles” as he had come to understand the term in the early to mid 1970s. (I assume tossing Einstein’s name on the cover just made the collection more marketable.)
Now, I’m no physicist, yet (with some patience and google at hand), I was able to understand the lion’s share of what he was saying. He died in 1976, just as the big particle accelerators were beginning to find evidence of many hitherto ‘theoretical’ elementary particles, and I wonder how much his opinions / thoughts might have changed (if at all) had he lived to see these experimental results.
Still, these are interesting historical documents from which much can be learned (from a man who “was in the room where it happened”) about the history of quantum mechanics and the strange twists and turns it took over its first 50 years of development.
The “Encounters with Einstein“ of the title actually account for only a small part of the slim, dense volume. Heisenberg’s musings collected here lean much more toward the definition / meaning of “elementary particles” as he had come to understand the term in the early to mid 1970s. (I assume tossing Einstein’s name on the cover just made the collection more marketable.)
Now, I’m no physicist, yet (with some patience and google at hand), I was able to understand the lion’s share of what he was saying. He died in 1976, just as the big particle accelerators were beginning to find evidence of many hitherto ‘theoretical’ elementary particles, and I wonder how much his opinions / thoughts might have changed (if at all) had he lived to see these experimental results.
Still, these are interesting historical documents from which much can be learned (from a man who “was in the room where it happened”) about the history of quantum mechanics and the strange twists and turns it took over its first 50 years of development.
March 13, 2024
Heisenberg wrote down lots of personal experience of how "objective" hardcore scientific discovery was actually made. The hardcore science, due to its own nature, is often regarded to be separate from human's perspective, as being as objective as possible. But we should never forget that it is always human beings' endeavor and creation from their mind.
Feynman is the first person I know who is willing to add some color and juice into science. His lectures are popular and enjoyed by lots due to this unique feature. Heisenberg here gives me a second example. The pure and innocent soul behind the words of the book completely conquers me.
The book is really a masterpiece!
Feynman is the first person I know who is willing to add some color and juice into science. His lectures are popular and enjoyed by lots due to this unique feature. Heisenberg here gives me a second example. The pure and innocent soul behind the words of the book completely conquers me.
The book is really a masterpiece!
August 12, 2023
Li esse de encontro com big bang porque tinha muitas teorias que eu precisava entender melhor sobre física mecânica, é uma leitura bem técnica mas eu gostei bastante.
July 3, 2016
This book had been sitting on my shelf for decades. Finally got around to reading it. It is for a general audience but one already versed in particle physics. So it is a bit dense. It's interesting from a historical standpoint. One the one hand much hasn't changed since his day. On the other much has but built on the foundation that he and others in the early 20th century created.
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