Philosophy Of Science

"Some of the Greek philosophers who lived four or five hundred years before Christ formed a theory of the transformations of matter, which is essentially the theory held by naturalists to-day. ...Those investigators attempted to connect all the differences which are observed between the qualities of things with differences of size, shape, position, and movement of atoms... unchangeable, indestructible, and impenetrable particles ...not one of them can be destroyed, nor can one be created; when a substance ceases to exist and another is formed, the process is not a destruction of matter, it is a re-arrangement of atoms."

"The first principle in nature is asserted by Lucretius [Concerning the Nature of Things] to be that " Nothing is ever gotten out of nothing.""

"More than two thousand years passed before investigators began to make accurate measurements of the quantities of the substances which take part in those changes wherein certain things seem to be destroyed and other totally different things to be produced; until accurate knowledge had been obtained of the quantities of the definite substances which interact in the transformations of matter, the atomic theory could not do more than draw the outlines of a picture of material changes. A scientific theory has been described as "the likening of our imaginings to what we actually observe." So long as we observe only in the rough, only in a broad and general way, our imaginings must also be rough, broad, and general."

"The atomic theory was used by the great physicists of the later Renaissance, by Galileo, Gassendi, Newton and others. ... John Dalton, while trying ...to form a mental presentation of the atmosphere in terms of the theory of atoms, rediscovered the possibility of differences between the sizes of atoms, applied this idea to the facts concerning the quantitative compositions of compounds which had been established by others, developed a method for determining the relative weights of atoms of different kinds, and started chemistry on the course which it has followed so successfully."

"The pessimistic meta-induction seems to have some force in regard to fundamental physics: there, the change is much more rapid, and very little remains of past theories. … Non-fundamental concepts—such as cell or season—can survive significant shifts in fundamental theories, but obviously fundamental concepts like force or particle find it much more difficult to do so. … I think there is a view in the vicinity that is worth taking seriously: that we should be realists about non-fundamental science and at least somewhat skeptical of fundamental science."

"Some hold that fundamental ideas have changed so often within science—especially within physics—that we should always expect our current views to turn out to be wrong. Sometimes this argument is called the “pessimistic meta-induction.” The prefix “meta” is misleading here, because the argument is not an induction about inductions; it’s more like an induction about explanatory inferences. So let’s call it “the pessimistic induction from the history of science.” The pessimists give long lists of previously posited theoretical entities like phlogiston and caloric that we now think do not exist (Laudan 1981). Optimists reply with long lists of theoretical entities that once were questionable but which we now think definitely do exist—like atoms, germs, and genes."

"An anarchist is like an undercover agent who plays the game of Reason in order to undercut the authority of Reason (Truth, Honesty, Justice, and so on)."

"The debate between scientific realists and anti-realists is one of the classics of philosophy of science, comparable to a soccer match between Brazil and Argentina."

"There is a strange and wonderful reality out there, but until we devise an experiment that teaches us more than we presently know, it's better to embrace reality as we can measure it than to impose an additional structure driven by our own biases. Until we do that, we're superficially philosophizing about a matter where scientific intervention is required. Until we devise that key experiment, we'll all remain in the dark."

"Hawking gives a good description of how scientists come to the conclusion that something is real: we construct intellectual models that, within some range of phenomena, and to some degree of approximation, agree with observation. But he calls this “model-dependent reality,” and suggests that this is all there is to reality. Questions about the nature of reality have puzzled scientists and philosophers for millennia. Like most people, I think that there is something real out there, entirely independent of us and our models, as the Earth is independent of our maps. But this is because I can’t help believing in an objective reality, not because I have good arguments for it. I am in no position to argue that Hawking’s antirealism is wrong. But I do insist that neither quantum mechanics nor anything else in physics settles the question."

"Origin of knowledge. - Through immense periods of time, the intellect produced nothing but errors; some of them turned out to be useful and species-preserving; those who hit upon or inherited them fought their fight for themselves and their progeny with greater luck. Such erroneous articles of faith, which were passed on by inheritance further and further, and finally almost became part of the basic endowment of the species, are for example: that there are enduring things; that there are identical things; that there are things, kinds of material, bodies; that a thing is what it appears to be; that our will is free; that what is good for me is also good in and for itself. Only very late did the deniers and doubters of such propositions emerge; only very late did truth emerge as the weakest form of knowledge. It seemed that one was unable to live with it; that our organism was geared for its opposite: all its higher functions, the perceptions of sense and generally every kind of sensation, worked with those basic errors that had been incorporated since time immemorial. Further, even in the realm of knowledge those propositions became the norms according to which one determined 'true' and 'untrue' - down to the most remote areas of pure logic. Thus the strength of knowledge lies not in its degree of truth, but in its age, its embeddedness, its character as a condition of life."

"A scientific theory is usually felt to be better than its predecessors not only in the sense that it is a better instrument for discovering and solving puzzles but also because it is somehow a better representation of what nature is really like. One often hears that successive theories grow ever closer to, or approximate more and more closely to, the truth. Apparently generalizations like that refer not to the puzzle-solutions and the concrete predictions derived from a theory but rather to its ontology, to the match, that is, between the entities with which the theory populates nature and what is “really there.” Perhaps there is some other way of salvaging the notion of ‘truth’ for application to whole theories, but this one will not do. There is, I think, no theory-independent way to reconstruct phrases like ‘really there’; the notion of a match between the ontology of a theory and its “real” counterpart in nature now seems to me illusive in principle. Besides, as a historian, I am impressed with the implausability of the view. I do not doubt, for example, that Newton’s mechanics improves on Aristotle’s and that Einstein’s improves on Newton’s as instruments for puzzle-solving. But I can see in their succession no coherent direction of ontological development. On the contrary, in some important respects, though by no means in all, Einstein’s general theory of relativity is closer to Aristotle’s than either of them is to Newton’s."

"From among the various conceptual schemes best suited to these various pursuits, one—the phenomenalistic—claims epistemological priority. Viewed from within the phenomenalistic conceptual scheme, the ontologies of physical objects and mathematical objects are myths. The quality of myth, however, is relative; relative, in this case, to the epistemological point of view. This point of view is one among various, corresponding to one among our various interests and purposes."

"It will be difficult. But the difficulty really is psychological and exists in the perpetual torment that results from your saying to yourself, 'But how can it be like that?' which is a reflection of uncontrolled but utterly vain desire to see it in terms of something familiar. I will not describe it in terms of an analogy with something familiar; I will simply describe it. There was a time when the newspapers said that only twelve men understood the theory of relativity. I do not believe there ever was such a time. There might have been a time when only one man did, because he was the only guy who caught on, before he wrote his paper. But after people read the paper a lot of people understood the theory of relativity in some way or other, certainly more than twelve. On the other hand, I think I can safely say that nobody understands quantum mechanics. So do not take the lecture too seriously, feeling that you really have to understand in terms of some model what I am going to describe, but just relax and enjoy it. I am going to tell you what nature behaves like. If you will simply admit that maybe she does behave like this, you will find her a delightful, entrancing thing. Do not keep saying to yourself, if you can possibly avoid it, 'But how can it be like that?' because you will get 'down the drain', into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that."

"I claim that the success of current scientific theories is no miracle. It is not even surprising to the scientific (Darwinist) mind. For any scientific theory is born into a life of fierce competition, a jungle red in tooth and claw. Only the successful theories survive—the ones which in fact latched onto the actual regularities in nature."

""The physical world is real." That is supposed to be the fundamental hypothesis. What does "hypothesis" mean here? For me, a hypothesis is a statement, whose truth must be assumed for the moment, but whose meaning must be raised above all ambiguity. The above statement appears to me, however, to be, in itself, meaningless, as if one said: "The physical world is cock-a-doodle-do." It appears to me that the "real" is an intrinsically empty, meaningless category (pigeon hole), whose monstrous importance lies only in the fact that I can do certain things in it and not certain others."

"The most common misunderstanding about science is that scientists seek and find truth. They don't — they make and test models."

"There is something there. But just because your theory is good does not mean that the entities in your theory are "really there", whatever that might mean..."

"These lectures have shown very clearly the difference between Roger and me. He's a Platonist and I'm a positivist. He's worried that Schrödinger's cat is in a quantum state, where it is half alive and half dead. He feels that can't correspond to reality. But that doesn't bother me. I don't demand that a theory correspond to reality because I don't know what it is. Reality is not a quality you can test with litmus paper. All I'm concerned with is that the theory should predict the results of measurements. Quantum theory does this very successfully. It predicts that the result of an observation is either that the cat is alive or that it is dead. It is like you can't be slightly pregnant: you either are or you aren't."

"Physical concepts are free creations of the human mind, and are not, however it may seem, uniquely determined by the external world. In our endeavor to understand reality we are somewhat like a man trying to understand the mechanism of a closed watch. He sees the face and the moving hands, even hears its ticking, but he has no way of opening the case. If he is ingenious he may form some picture of a mechanism which could be responsible for all the things he observes, but he may never be quite sure his picture is the only one which could explain his observations. He will never be able to compare his picture with the real mechanism and he cannot even imagine the possibility or the meaning of such a comparison. But he certainly believes that, as his knowledge increases, his picture of reality will become simpler and simpler and will explain a wider and wider range of his sensuous impressions. He may also believe in the existence of the ideal limit of knowledge and that it is approached by the human mind. He may call this ideal limit the objective truth."

"I believe that the first step in the setting of a “real external world” is the formation of the concept of bodily objects and of bodily objects of various kinds. Out of the multitude of our sense experiences we take, mentally and arbitrarily, certain repeatedly occurring complexes of sense impression (partly in conjunction with sense impressions which are interpreted as signs for sense experiences of others), and we attribute to them a meaning—the meaning of the bodily object. Considered logically this concept is not identical with the totality of sense impressions referred to; but it is an arbitrary creation of the human (or animal) mind. On the other hand, the concept owes its meaning and its justification exclusively to the totality of the sense impressions which we associate with it."

"Einstein’s great friend and intellectual sparring partner Niels Bohr had a nuanced view of truth. Whereas according to Bohr, the opposite of a simple truth is a falsehood, the opposite of a deep truth is another deep truth. In that spirit, let us introduce the concept of a deep falsehood, whose opposite is likewise a deep falsehood. It seems fitting to conclude this essay with an epigram that, paired with the one we started with, gives a nice example:“Naïveté is doing the same thing over and over, and always expecting the same result.”"

"The other mistake that is widely attributed to Einstein is that he was on the wrong side in his famous debate with Niels Bohr over quantum mechanics, starting at the Solvay Congress of 1927 and continuing into the 1930s. In brief, Bohr had presided over the formulation of a “Copenhagen interpretation” of quantum mechanics, in which it is only possible to calculate the probabilities of the various possible outcomes of experiments. Einstein rejected the notion that the laws of physics could deal with probabilities, famously decreeing that God does not play dice with the cosmos. But history gave its verdict against Einstein—quantum mechanics went on from success to success, leaving Einstein on the sidelines. All this familiar story is true, but it leaves out an irony. Bohr’s version of quantum mechanics was deeply flawed, but not for the reason Einstein thought. The Copenhagen interpretation describes what happens when an observer makes a measurement, but the observer and the act of measurement are themselves treated classically. This is surely wrong: Physicists and their apparatus must be governed by the same quantum mechanical rules that govern everything else in the universe."

"The famous debate between Einstein and Bohr began at the Solvay Council in 1927. The debate was about the interpretation of quantum mechanics, but also addressed the fundamental question of what the purpose and aim of a physical theory should be. Their conflicting positions were based on two diametrically opposed philosophical approaches to the fundamental problems of physics. The many books popularising quantum mechanics quite rightly place the emphasis on the problem of interpretation: they discuss the opposing positions of Einstein’s “realism” and the “Copenhagen interpretation” of which Bohr is seen as the leading protagonist."

"The refutation of Einstein’s criticism does not add any new element to the conception of complementarity, but it is of great importance in laying bare a very deep-lying opposition between Bohr’s general philosophical attitude and the still widespread habits of thought belonging to a glorious but irrevocably bygone age in the evolution of science."

"In the famous Einstein–Bohr debates, Bohr defended quantum mechanics against Einstein's yearning for a more classical theory; but some of us are coming to feel in defending his hard-won ground he compromised too much. Quantum mechanics should be pushed as hard as possible, to the point where it can describe within itself a recognizable caricature of the world as it is experienced, and thus begin to provide its own self-consisted interpretation — or else there should be some definite change in its equations. As yet this task has not been accomplished."

"Einstein was not prepared to let us do what, to him, amounted to pulling the ground from under his feet. Later in life, also, when quantum theory had long since become an integral part of modern physics, Einstein was unable to change his attitude—at best, he was prepared to accept the existence of quantum theory as a temporary expedient. "God does not throw dice" was his unshakable principle, one that he would not allow anybody to challenge. To which Bohr could only counter with: "Nor is it our business to prescribe to God how He should run the world.""

"Bohr was inconsistent, unclear, willfully obscure and right. Einstein was consistent, clear, down-to-earth and wrong."

"The discomfort that I feel is associated with the fact that the observed perfect quantum correlations seem to demand something like the ‘genetic’ hypothesis [identical twins, carrying with them identical genes]. For me, it is so reasonable to assume that the photons in those experiments carry with them programs, which have been correlated in advance, telling them how to behave. This is so rational that I think that when Einstein saw that, and the others refused to see it, he was the rational man. The other people, although history has justified them, were burying their heads in the sand. I feel that Einstein’s intellectual superiority over Bohr, in this instance, was enormous; a vast gulf between the man who saw clearly what was needed, and the obscurantist. So for me, it is a pity that Einstein’s idea doesn’t work. The reasonable thing just doesn’t work."

"The EPR paper came out in 1935 and for at least two decades no one paid much attention to it. However, in 1964, the late John Bell published a paper that changed everything. He showed that Einstein’s idea that the results of quantum mechanics could be reproduced by a theory in which Einstein’s notions of realism were included could be tested in the laboratory. Having spent a good deal of time talking to Bell I can tell you that his heart was with Einstein. He often referred to Bohr as an “obscurantist.” But the experiments were carried out by Alain Aspect and others and showed that Einstein was wrong and Bohr was right. I cannot believe that anyone familiar with this would still agree with Einstein."

"Their dispute went to the fundamental heart of the design of the cosmos. Was there an objective reality that existed whether or not we could ever observe it? Were there laws that restored strict causality to phenomena that seemed inherently random? Was everything in the universe predetermined?"

"Einstein's thinking is always on the ontological level traditional in physics; trying to describe the realities of Nature. Bohr's thinking is always on the epistemological level, describing not reality but only our information about reality."

"His thought experiment with photon and film had not challenged Heisenberg's principle, but now Einstein did turn his attention there. He began looking for an experiment that would allow a more complete collection of data than the Heisenberg team thought possible. If he could find a technique that allowed the simultaneous discovery of position and momentum or time and energy, he would prove the quantum mechanics had indeed not yet brought us to the the secret of the Old One. This effort led the most famous set-pieces of the Einstein "debate" with Bohr over quantum mechanics. Einstein, Bohr, and Ehrenfest would meet in the hotel dining room for breakfast. Einstein would propose a thought experiment. Bohr would think about it. ... During the day's program at Solvay, Heisenberg and Pauli would analyze the experiment that Einstein had proposed. They would find some point where the uncertainty principle fought back, and over dinner, Bohr wold refute the experimental effort while Ehrenfest looked on."

"The mid-twentieth century “Bohr-Einstein debate” about quantum theory is often misinterpreted as a personal clash between wizards. So counter-intuitive are quantum theory’s predictions that, under the leadership of one of its pioneers, Neils Bohr, a myth grew that there is no underlying reality that explains them. Particles get from A to B without passing through the intervening space, where they have insufficient energy to exist; they briefly “borrow” the energy, because we are “uncertain” about what their energy is. Information gets from A to B without anything passing in between – what Einstein called “spooky action at a distance.” And so on....So, while most accounts say that Bohr won the debate, my view is that Einstein, as usual, was seeking an explanation of reality, while his rivals were advocating nonsense. Everett’s interpretation doesn’t make Einstein a demigod. But it does make him right."

"To recap, I had four numbers to add together. If the total came to under 2, then Einstein’s version of quantum reality was correct and the world is deterministic, rather than probabilistic, with quantum entities existing prior to being observed. But if the total came to over 2, then Niels Bohr was right and there is no objective reality out there in the absence of measurement and the subatomic world is ruled by chance and probability. [...] So, sorry Einstein, victory goes to Bohr instead."

"We, of course, were sure that on that particular debate Bohr was right and Einstein was wrong."

"Albert Einstein, who was in many ways the father of quantum mechanics, had a notorious love-hate relation with the subject. His debates with Niels Bohr—Bohr completely accepting of quantum mechanics and Einstein deeply skeptical— are famous in the history of science. It was generally accepted by most physicists that Bohr won and Einstein lost. My own feeling, I think shared by a growing number of physicists, is that this attitude does not do justice to Einstein’s views. Both Bohr and Einstein were subtle men. Einstein tried very hard to show that quantum mechanics was inconsistent; Bohr, however, was always able to counter his arguments. But in his final attack Einstein pointed to something so deep, so counterintuitive, so troubling, and yet so exciting, that at the beginning of the twenty-first century it has returned to fascinate theoretical physicists. Bohr’s only answer to Einstein’s last great discovery—the discovery of entanglement—was to ignore it."

"To this day, many researchers agree with Bohr's pragmatic attitude. The history books say that Bohr has proved Einstein wrong. But others, including myself, suspect that, in the long run, the Einsteinian view might return: that there is something missing in the Copenhagen interpretation. Einstein's original objections could be overturned, but problems still arise if one tries to formulate the quantum mechanics of the entire universe (where measurements can never be repeated), and if one tries to reconcile the laws of quantum mechanics with those of gravitation. But I am running far ahead in my story (I will return to this point in chapter 28). For a correct description of atoms and molecules, quantum mechanics is a perfect theory."

":...Vienna is the origin of so many schools of its own which were dominant in the 1920s. And one of the most fundamental and influential, in which we all were partially caught, was logical positivism. In fact, Mises’ brother, Richard von Mises, became one of the leading figures. Now he and I all grew up in this Ernst Mach philosophy that ultimately everything must be rationally justified…"

"Hayek thought there are two orders through which individuals consider the world: the sensory order and the physical order. The sensory order is what we sense. The physical world is the real world of existence beyond our senses that every sane person who is not a solipsist accepts on faith. According to Hayek, advances in science have rendered any correspondence between the real, physical world and the sensory world almost nonexistent. Instead, the natural, real world expresses itself in mathematical relationships. Hayek’s views tended philosophically to solipsism. While he believed in the existence of a physical world external to mind, he ascribed almost no (if any) properties to it. He was not as opposed to positivism as to logical positivism, and it is important to be clear about these terms. Positivism is simply the idea that there should be some correspondence with the material world extrinsic to one’s physical self that one perceives in order for statements about nature to be valid, to be true. Using this broad definition of positivism, Hayek was a positivist. Logical positivism tries to go a step beyond this position. The logical positivists sought to reduce all experience to sensory experience and to reduce every sensory experience to a conclusive or exact statement. This has proven an unattainable goal."

"Logical positivism is a very attractive view for people who do not want to worry about what they cannot observe. It is ultimately a theory about meaning, about the content of a theory. According to the positivists, a theory says no more than its observable consequences. Logical positivism has been killed many times over by philosophers. But no matter how many stakes are driven through its heart, it arises unbidden in the minds of scientists. For if the content of a theory goes beyond what you can observe, then you can never, in principle, be sure that any theory is right. And that means there can be interminable arguments about which theory is right that cannot be settled by observation."

"Unlike the physicist, the psychologist ... investigates processes that belong to the same order—perception, learning, thinking—as those by which he conducts his investigation."

"To conclude, logical positivism was progressive compared with the classical positivism of Ptolemy, Hume, d'Alembert, Compte, John Stuart Mill, and Ernst Mach. It was even more so by comparison with its contemporary rivals—neo-Thomisism, neo-Kantianism, intuitionism, dialectical materialism, phenomenology, and existentialism. However, neo-positivism failed dismally to give a faithful account of science, whether natural or social. It failed because it remained anchored to sense-data and to a phenomenalist metaphysics, overrated the power of induction and underrated that of hypothesis, and denounced realism and materialism as metaphysical nonsense. Although it has never been practiced consistently in the advanced natural sciences and has been criticized by many philosophers, notably Popper (1959 [1935], 1963), logical positivism remains the tacit philosophy of many scientists. Regrettably, the anti-positivism fashionable in the metatheory of social science is often nothing but an excuse for sloppiness and wild speculation."

"The difference between Hayek’s view and that of the logical positivists was that he moved in an idealist direction and they emphasized verification."

"Historically, the investigations of oscillatory motions was motivated by the desire to improve methods of telling time. ...In the seventeenth century the need to measure small periods of time accurately for the purpose of telling longitude at sea caused scientists to search for increasingly accurate clocks. The search resulted in some major successes that were at least as valuable for the advancement of mathematics and the study of other phenomena of nature, such as light and sound, as they were for the specific problem of measuring time. Scientists naturally concentrated on any physical phenomena that seemed to be periodic or repetitive and might therefore be related to the periodic motion of the planets. Two phenomena recommended themselves for closer investigation, the motion of an object or bob... on a spring, and the motion of a pendulum. The first of those attracted the attention of Robert Hooke... Suppose d is the increase or decrease in the length of the spring resulting from extension or contraction. Hooke found that the restoring force the spring exerts is proportional to d; that is, the force is a constant k, say, times d. This is the meaning of [Ut tensio, sic vis ("as the extension, so the force")]..."

"It is not an unusual phenomenon in the history of science that views which were once considered antiquated and out of date suddenly come into favor again, though in a more or less modified form. An extremely interesting case of this kind is presented by the revolution in our ideas of electric phenomena which has taken place within the last 10 years... The modern theory of electrical and allied optical phenomena... [i.e.,] the "electron theory," means practically a return to views as laid down in the sixties and seventies by Wilhelm Weber and Zöllner, but modified by the results of Maxwell's and Hertz's researches. W. Weber imagined electric phenomena as the actions of elementary electrical particles—so called "electric atoms"—whose mutual influence depended not only upon their positions but also upon their relative velocities and accelerations. ...most of the laws of electrodynamics when expressed from the standpoint of pure phenomenology in the shape of differential equations, are much more simple and convenient than Weber's formulæ. ...Faraday and Maxwell brought about a general feeling that... a finite rate of propagation would have to take the place of action at a distance. ...Maxwell's formulæ [were] wholly void ...of atomistic conceptions ...According to Maxwell... the vibrations of light were not mechanical, but electrical vibrations of the ether, and the two constants by which Maxwell defined the electric and magnetic behaviour of every body (the dielectric constant and the magnetic permeability) had also to be the determining elements in its refractive power. Although the condition... was well fulfilled in a number of bodies, ...many bodies, notably water...sufficed to prove the inadequacy of the theory... To this was added the dependence of the refractive index upon the colour [frequency], for which the original theory gave no explanation whatever. H. A. Lorentz showed that the foundations of an electromagnetic theory of dispersion could be laid in a manner quite analogous to the mechanical theory, by regarding every molecule as the origin of electric vibrations of a definite period. He says:—"Let there be in every material particle several material points charged with electricity, of which, however, only one be movable, and have the charge e and the mass μ." Lorentz derives the equations of dispersion from this fundamental assumption of vibrating charged particles. ... In his Faraday Memorial Address of 1881 Helmholtz points out that Faraday's law necessarily implies the existence of electric atoms. ...when a neutral molecule—say NaCl—splits up in +Na and -CI when dissolved in water, it is most probable that both the sodium and the chlorine atom had their charges beforehand... equal and opposite. But if we consider a ray of light traversing a crystal of salt, the charges and the atoms they accompany must be thrown into vibrations, and must influence the propagation of the light. ... In the years 1890-93 a number of works appeared by F. Richarz, H. Ebert and G. Johnstone Stoney, mostly dealing with the mechanism of the emission of luminous vapours, and in which attempts are made, on the basis of the kinetic theory of gases, to determine the magnitude of the elementary electrical quantity, called by Stoney... the now universally accepted name of electron. ...that one electron contains about 10-10 electrostatic units. ...a whole series of other methods... tend to very similar values. ... In 1896 a pupil of Lorentz, P. Zeeman, discovered a phenomenon whose existence Faraday had vainly sought for in 1862. If a luminous vapour, say a sodium flame, is brought into a strong magnetic field, the spectrum lines of the vapour show peculiar changes, consisting of a doubling or trebling, according to the line of vision. These changes are predicted by Lorentz's theory. The Zeeman phenomenon further permitted a determination of the inert mass connected with the vibrating charges, and then a striking result was obtained: the vibrating electron is always negatively charged, while the positive charge is stationary. ...The original and almost tacit assumption that the whole ion—i.e., the chemical atom plus its valency charge—was in oscillation must, therefore, be abandoned. We must suppose that the charge, just as is the case in electrolysis, has also an independent mobility in the light-emitting molecule, and that the mass concerned in the Zeeman phenomenon is that of the electron itself. We thus arrive at a view which nearly coincides with the old conception of Weber, but with the important difference that instead of a direct action at a distance we have an action transmitted by the ether, and further, that we have now a perfectly distinct numerical estimate of the magnitude of the electric atoms."

"A law explains a set of observations; a theory explains a set of laws. The quintessential illustration of this jump in level is the way in which Newton’s theory of mechanics explained Kepler’s law of planetary motion. Basically, a law applies to observed phenomena in one domain (e.g., planetary bodies and their movements), while a theory is intended to unify phenomena in many domains. Thus, Newton’s theory of mechanics explained not only Kepler’s laws, but also Galileo’s findings about the motion of balls rolling down an inclined plane, as well as the pattern of oceanic tides. Unlike laws, theories often postulate unobservable objects as part of their explanatory mechanism. So, for instance, Freud’s theory of mind relies upon the unobservable ego, superego, and id, and in modern physics we have theories of elementary particles that postulate various types of quarks, all of which have yet to be observed."

"When Galilei let balls of a particular weight, which he had determined himself, roll down an inclined plain, or Torricelli made the air carry a weight, which he had previously determined to be equal to that of a definite volume of water; or when, in later times, Stahl changed metal into lime, and lime again into metals, by withdrawing and restoring something, a new light flashed on all students of nature. They comprehended that reason has insight into that only, which she herself produces on her own plan, and that she must move forward with the principles of her judgments, according to fixed law, and compel nature to answer her questions, but not let herself be led by nature, as it were in leading strings, because otherwise accidental observations made on no previously fixed plan, will never converge towards a necessary law, which is the only thing that reason seeks and requires. Reason, holding in one hand its principles, according to which concordant phenomena alone can be admitted as laws of nature, and in the other hand the experiment, which it has devised according to those principles, must approach nature, in order to be taught by it: but not in the character of a pupil, who agrees to everything the master likes, but as an appointed judge, who compels the witnesses to answer the questions which he himself proposes. Therefore even the science of physics entirely owes the beneficial revolution in its character to the happy thought, that we ought to seek in nature (and not import into it by means of fiction) whatever reason must learn from nature, and could not know by itself, and that we must do this in accordance with what reason itself has originally placed into nature. Thus only has the study of nature entered on the secure method of a science, after having for many centuries done nothing but grope in the dark."

"The Copernican revolution... revealed that the earth is not the center of the universe... The second, the Darwinian revolution... revealed that we are not created divinely or uniquely but instead evolved from simpler animals by a process of natural selection. The third great revolution, the Freudian revolution of Vienna 1900, revealed that we do not consciously control our own actions but are instead driven by unconscious motives. This... later led to the idea that human creativity... stems from conscious access to underlying, unconscious forces."

"In spite of all the allegations of self-love, the facts at first associated with the name of a particular man end by being anonymous, lost forever in the ocean of Universal Science. Thus the monograph imbued with individual human quality becomes incorporated, stripped of sentamentalisms, in the abstract doctrine of the general treatise. To the hot sun of actuality will succeed—if they do succeed—the cold beams of the history of learning."