Philosophical Interpretations and Misinterpretations of the Theory of Relativity
2. The Theory of Relativity Explains Phenomena, Not by Means of a Physical Hypothesis, but By Introducing a New Conception of Space and Time
The contraction of bodies in their motion through the ether was explained before Einstein in approximately the following way. All bodies are made up of electrically charged particles which attract and repel each other in accordance with Coulomb's law. In the state of rest relative to the ether, every body has a definite length resulting from the fact that the particles, at a certain relative distance, exert electrostatic forces upon one another which just balance. When the body is moved through the ether, then the moved charges have the effect of electrical currents, and in addition to the electrical forces, there arise magnetic forces analogous to those exerted by electrical currents upon one another. The equilibrium is disturbed. The particles which constitute the body have to assume new relative distances such that the electrical forces, augmented(increased) by the magnetic ones, just balance each other. Thus the motion brings about a new equilibrium-shape of the body, namely, a shape flattened in the direction of motion; there results what is called the Lorentz contraction, which changes every sphere into an ellipsoid of revolution flattened in the direction of motion. The contraction is thus explained by a physical theory, namely, by the additional magnetic forces arising on account of the motion. From these forces the new equilibrium may be calculated.
Einstein's theory of relativity, many authors tell us, no longer explains the contraction by a physical hypothesis, but uses instead a new conception of space and time. In those textbooks of physics which are thought through more carefully, one no longer finds the assertion that the theory of relativity has replaced a physical hypothesis by something totally different, but one will hardly find a textbook of this kind in which it is not maintained that the theory of relativity has introduced a new conception of space and time, or that it no longer recognizes the old conception of space and time. This mode of expression is, however, a very dangerous one. For the words "conception of space and time" always create the impression that through the theory of relativity, a novelty is introduced into psychology, since a "conception of space and time" obviously belongs in psychology. These words may, of course, be construed(해석되다) quite differently, and this the physicist always does instinctively, as long as he deals with physics. For the philosopher, however, who reads books on physics, expressions like these always occasion misinterpretations. It is therefore expedient(~하는 것이 상책이다), as we shall see, not to speak at all of a "change in the conception of space and time", but to choose a mode of expression which is not open to misinterpretation even in the boundary domains of physics.
In order to determine how far this juxtaposition(倂置) of "physical hypothesis" and "change in the conceptions of space and time" is justified, one need only try to express both views in such sentences as are verifiable by experiments, that is, in sentences which are reducible to verifiable sentences.
The explanation of the contraction on the basis of the ether hypothesis starts out from the classical Maxwell-Lorentzian theory of electromagnetic phenomena. When we formulate a suitable hypothesis as to the way in which bodies are built up of electrical charges, then we can deduce(연역추론하다) from the fundamental equations of the electromagnetic field that every body, when moved through the ether, must alter its shape and thus contract itself. Or, stated more exactly, the contraction is a logical consequence of several simultaneous hypotheses, namely, the validity of the electromagnetic field-equation and laws of force, and the hypothesis that all bodies are built up of electrical charges.
Now, Einstein's theory of relativity rests on two hypotheses of a much more general character. According to the first of these, there is a rigid system S having the property that, relatively to S. light is propagated through the vacuum in all directions with the same velocity, and moreover, independently of the velocity relative to S of the source of light (hypothesis of the constancy of the velocity of light). The second hypothesis states that if a rigid system S' moves relatively to S in a straight line and uniformly with the velocity v, then all processes can be calculated with respect to S' from their initial conditions with respect to S' according to certain laws which do not contain the relative velocity v of S' with respect to S' (hypothesis of relativity). Or, briefly expressed, all processes can be described with reference to S' by the same set of formulas as with reference to S, if the formulas contain merely the calculation of later states on the basis of the initial ones.
When we try to formulate these two hypotheses in such a way as to render them reducible to verifiable sentences, then it is easily seen that they are hypotheses concerning the behavior of so-called measuring rods and clocks, i.e. of rigid bodies in motion, in relation to the propagation of light. The hypotheses set up by ether theory for the sake of explaining the contraction are then of the same kind, provided that we express them also by experimentally verifiable sentences. They say something about the behavior of rigid bodies in relation to electromagnetic processes.
The difference consists only in thus: The hypotheses of the theory of relativity are very general assertion about the behavior of rigid bodies, about uniform revolution(回轉) and electromagnetic radiation. In this connection, terms like "rigid body", "uniform revolution", and so on, occurring in these assertions, are defined by indication of concrete examples, sys, of an iron road as "rigid body" of a pocket watch as a "uniformly revolving body", and so on.
Classical dynamics, on the other hand (and in particular those sentences which lead to an explanation of the Lorentz contraction), consists of more special assumptions concerning the connection btw electrical field strengths and electrical charges, e.g. Maxwell's field equations, and of assumptions concerning the construction of solid bodies out of electrical charges. If the theory of relativity is right, then no special sentence of electrodynamics can be contradictory(모순된) to the fundamental hypotheses of the theory of relativity. It happens to be one of the greatest advantages of the theory of relativity that from its fundamental assumptions (constancy of velocity of light and principle of relativity) a great deal can be deduced about the behavior of bodies in an electromagnetic field without ever using the Maxwell equations themselves. Similarly, a great deal can be deduced and predicted concerning the behavior of rigid bodies in the case of motion without using any particular assumption about the construction of bodies out of electrical charges. Thus, for example, the contraction of bodies through motion can be predicted without bringing in the alteration(변경) of the electrical forces due to the motion.
For anyone who is somewhat familiar with nineteenth-century physics, understanding of the logical structure of the theory of relativity will be facilitated(순조롭다) by way of an analogy. Precisely speaking, it is a question of the logical structure of the system consisting of the following sentences: the relativity hypothesis, the electromagnetic field equations, the description of the atomic structure of bodies, and those verifiable sentences which are deducible from these fundamental assumptions.
The Same role as is played by the relativity hypothesis today was played in the 19C theory of heat by the first and second laws of thermodynamics, if we direct our attention towards the logical structure of the theories. From these general hypotheses (which are essentially those of the impossibility of a perpetuum mobile of the first and second kind), it was possible to deduce sentences which are experimentally verifiable. These same sentences, however, were also capable of being deduced from a set of special hypotheses consisting of the following assumptions: the theorems of Newtonian mechanics in conjunction with some statistical hypotheses, and the hypotheses concerning the molecular structure of bodies.
Here, again, no contradiction can arise btw the consequences of the general thermodynamic hypotheses and the special mechanical theories. This is true because the main theorems of thermodynamics, those asserting the impossibility of a perpetuum mobile of the first or second kind, mean in more exact language this : "All special theories concerning the motion and the molecular structure of bodies ought to be qualified in such a way as to fit into the framework prescribed by the two principles of thermodynamics; that is to say, it must not be the case that from a correct molecular theory a sentence can be inferred that contradicts those general principles."
In just the same way Einstein's principle of relativity prescribed a framework into which all special theories concerning the electromagnetic field and the construction of bodies out of electrical charges have to fit. If the Einstein theory is correct, then any law about the construction of bodies out of charges that may ever be discovered must not lead to sentences which contradict the hypothesis of relativity. The value of this hypothesis consists in the fact that it permits the formulation of laws about the behavior of bodies out of electrons and about the laws of the field effects. But, in this connection, we must keep in mind that Einstein's hypotheses, if formulated in a language reducible to verifiable sentences, are also hypotheses concerning the behavior of rigid bodies in relation to the propagation of electromagnetic waves. Now, Einstein's theory of relativity is usually formulated in a language in which the terms "length of an iron rod", "temporal distance of two events", "simultaneity of two events", and such like, are combined in a manner different from that customary in the language of every-day life or (what here amounts to the same thing) in the language of classical mechanics.
If, as often happens, Einstein's theory is said to bring with it new conceptions of space and time, then one ought to consider the following fact. When the velocities of bodies are small as compared to the velocity of light, then the Einstein theory coincides with the Newtonian, and everything can be described within the language of classical physics, that is, with the space and time concepts of every-day life; or, more exactly, words like "length of a rod", and so on, are combined according to the rules ordinary syntax. if, now, one wants to grasp the terms "conception of space", "conception of time", and so on, in their real sense, i. e. as they occur in sentences about verifiable facts, one has to take them in the psychological sense.It should then be said that on the basis of Einstein's theory we are in a position to make statements about our psychological space and time conceptions different from those made on the grounds of classical physics. it would thus follow that the theory of relativity has also brought us progress in psychology.
We ought to be able therefore to indicate psychological experiments which, according to the theory of relativity, should turn out otherwise than would be expected on the basis of classical physics. If we exclude so-called introspection(자기반성) as a method of scientific psychology, because it results can never be expressed in an intersubjective(간주관적인) language which is generally and unambiguously comprehensible(명백하게 이해할 수 있는), then all psychological experiments depend on the observation of the behavior of test-persons, i. e. ultimately on physical observations. It can here only be a question of observing how a person reacts to changes in the spatial and temporal relations of the world. In the case of an experiment that we reckon(산출하다) as psychological, we never have to do with the motions of bodies whose velocity is great enough to approach the velocity of light. All psychological experiments are concerned with what are called "small velocities"in this sense. But in this range there is no difference at all btw the laws of classical and of relativity physics. Thus the theory of relativity cannot lead to nay new theorems of psychology, or the field of space and time "conceptions", if this world is taken in tis psychological sense.
The whole mode of expression which implies that the theory of relativity has introduced new conceptions of space and time is therefore quite misleading if applied outside the most narrow realm of physics. If it is desired to formulate what happens in the physical theory of relativity in a manner(어떤 의미로는) that is really logically correct, this can be done without giving rise to confusions in neighboring domains. As we have already indicated in the first section, we should say : "For the description of motions with large velocities, it is expedient to carry out the construction of sentences out of the terms "length of an iron rod", "simultaneity of two events", and so on, in accordance with syntactical rules other than those used in every-day life and in classical physics." These two sets of syntactical formation rules for sentences are certainly not compatible with one another. But it leads to gross misunderstandings if this state of affairs in the domain of logical syntax is expressed in an apparently psychological language as follows : "the conception of space and time of the theory of relativity is incompatible with that of classical physics". For this would mean that there are psychological experiments which according to Einstein should yield results different from what had been expected earlier. Of course, one might think up such experiments, but there is at present none which even approximately falls within the limits of so-called psychological experiments, i. e. experiments concerning the behavior of human beings.
If, however, we wish to express the difference btw the theory of relativity and classical physics not merely as a fact of logical syntax(according to which we may only state that we are confronted with two mutually contradictory sets of formation rules), then we may formulate the difference btw the two theories as two different hypotheses about the actual world of sense-experiences. That is, we may say: The syntactical rules (formation rules) according to which the words "length of an iron rod", and so on, were combined into sentences before Einstein, have always been employed to describe the processes of motion with which we have to do in every-day life. These rules have proved to be practical in this field, and even in the more general application which Newton gave them in his mechanics. But this syntax turned out to be unsuitable for the representation of experiences involving very rapid motions. As we have shown in the first section, these formation rules permit the importation of many meaningless sentences into physics. For this reason Einstein proposed new formation rules to represent these rapid motions.
The achievements of the theory of relativity which are new as contrasted(대조적으로) with the older physics may therefore be divided from the stand-point(관점) of the logic of science into two kinds: Firstly, new general hypotheses have been established concerning the behavior of rigid bodies and light waves. Only experimentation can show whether these lead to results which contradict experience. They can only be rejected if such contradictions show up, or if - as compared with the old hypothesis - they do not bring to light any new facts. Secondly, however, as previously mentioned, a new syntax concerning the usage of such terms as "length of an iron rod", "simultaneity of two events" has been proposed by Einstein. This is a proposal and not an assertion. It can therefore never be declared correct or false, but in the course of application it has to be determined whether of not the proposal is more expedient than the old one. There can be no refutation by referring to spatio-temporal(時空의) sense-experiences(감각경험), because nothing is therein asserted about psychological facts.
On the basis of all these considerations we see very clearly the point of importance for the physicist in the doctrines of logical syntax and of the logic of science. They do not help him to find something new in physics itself. One can go even further and say that only rarely will they help him to arrive at clearer formulations in physics itself. For that which appears obscure to the non-physicist is often perfectly comprehensible to the physicist, since he constantly sees - so to speak - how these concepts are being employed, since - to use logical terms - he has always before his eyes the "correlating definitions" of which the non-physicist is not aware at all while reading physical treaties, because they are written "between the lines". On the other hand, logical syntax is an invaluable instrument for the physicist when he wants to establish the connection between his sentences and those of neighboring sciences, e. g. psychology, and with sentences of the general theory of science. And if he does not establish this connection in a scientific manner, then it will inevitably be established by traditional philosophy and metaphysics, thus turning physics from an enlightening(계몽적인) science into a source of confusion and sometimes even of infection of the whole intellectual life.
PHILIPP FRANK
2. The Theory of Relativity Explains Phenomena, Not by Means of a Physical Hypothesis, but By Introducing a New Conception of Space and TimeThe contraction of bodies in their motion through the ether was explained before Einstein in approximately the following way. All bodies are made up of electrically charged particles which attract and repel each other in accordance with Coulomb's law. In the state of rest relative to the ether, every body has a definite length resulting from the fact that the particles, at a certain relative distance, exert electrostatic forces upon one another which just balance. When the body is moved through the ether, then the moved charges have the effect of electrical currents, and in addition to the electrical forces, there arise magnetic forces analogous to those exerted by electrical currents upon one another. The equilibrium is disturbed. The particles which constitute the body have to assume new relative distances such that the electrical forces, augmented(increased) by the magnetic ones, just balance each other. Thus the motion brings about a new equilibrium-shape of the body, namely, a shape flattened in the direction of motion; there results what is called the Lorentz contraction, which changes every sphere into an ellipsoid of revolution flattened in the direction of motion. The contraction is thus explained by a physical theory, namely, by the additional magnetic forces arising on account of the motion. From these forces the new equilibrium may be calculated.
Einstein's theory of relativity, many authors tell us, no longer explains the contraction by a physical hypothesis, but uses instead a new conception of space and time. In those textbooks of physics which are thought through more carefully, one no longer finds the assertion that the theory of relativity has replaced a physical hypothesis by something totally different, but one will hardly find a textbook of this kind in which it is not maintained that the theory of relativity has introduced a new conception of space and time, or that it no longer recognizes the old conception of space and time. This mode of expression is, however, a very dangerous one. For the words "conception of space and time" always create the impression that through the theory of relativity, a novelty is introduced into psychology, since a "conception of space and time" obviously belongs in psychology. These words may, of course, be construed(해석되다) quite differently, and this the physicist always does instinctively, as long as he deals with physics. For the philosopher, however, who reads books on physics, expressions like these always occasion misinterpretations. It is therefore expedient(~하는 것이 상책이다), as we shall see, not to speak at all of a "change in the conception of space and time", but to choose a mode of expression which is not open to misinterpretation even in the boundary domains of physics.
In order to determine how far this juxtaposition(倂置) of "physical hypothesis" and "change in the conceptions of space and time" is justified, one need only try to express both views in such sentences as are verifiable by experiments, that is, in sentences which are reducible to verifiable sentences.
The explanation of the contraction on the basis of the ether hypothesis starts out from the classical Maxwell-Lorentzian theory of electromagnetic phenomena. When we formulate a suitable hypothesis as to the way in which bodies are built up of electrical charges, then we can deduce(연역추론하다) from the fundamental equations of the electromagnetic field that every body, when moved through the ether, must alter its shape and thus contract itself. Or, stated more exactly, the contraction is a logical consequence of several simultaneous hypotheses, namely, the validity of the electromagnetic field-equation and laws of force, and the hypothesis that all bodies are built up of electrical charges.
Now, Einstein's theory of relativity rests on two hypotheses of a much more general character. According to the first of these, there is a rigid system S having the property that, relatively to S. light is propagated through the vacuum in all directions with the same velocity, and moreover, independently of the velocity relative to S of the source of light (hypothesis of the constancy of the velocity of light). The second hypothesis states that if a rigid system S' moves relatively to S in a straight line and uniformly with the velocity v, then all processes can be calculated with respect to S' from their initial conditions with respect to S' according to certain laws which do not contain the relative velocity v of S' with respect to S' (hypothesis of relativity). Or, briefly expressed, all processes can be described with reference to S' by the same set of formulas as with reference to S, if the formulas contain merely the calculation of later states on the basis of the initial ones.
When we try to formulate these two hypotheses in such a way as to render them reducible to verifiable sentences, then it is easily seen that they are hypotheses concerning the behavior of so-called measuring rods and clocks, i.e. of rigid bodies in motion, in relation to the propagation of light. The hypotheses set up by ether theory for the sake of explaining the contraction are then of the same kind, provided that we express them also by experimentally verifiable sentences. They say something about the behavior of rigid bodies in relation to electromagnetic processes.
The difference consists only in thus: The hypotheses of the theory of relativity are very general assertion about the behavior of rigid bodies, about uniform revolution(回轉) and electromagnetic radiation. In this connection, terms like "rigid body", "uniform revolution", and so on, occurring in these assertions, are defined by indication of concrete examples, sys, of an iron road as "rigid body" of a pocket watch as a "uniformly revolving body", and so on.
Classical dynamics, on the other hand (and in particular those sentences which lead to an explanation of the Lorentz contraction), consists of more special assumptions concerning the connection btw electrical field strengths and electrical charges, e.g. Maxwell's field equations, and of assumptions concerning the construction of solid bodies out of electrical charges. If the theory of relativity is right, then no special sentence of electrodynamics can be contradictory(모순된) to the fundamental hypotheses of the theory of relativity. It happens to be one of the greatest advantages of the theory of relativity that from its fundamental assumptions (constancy of velocity of light and principle of relativity) a great deal can be deduced about the behavior of bodies in an electromagnetic field without ever using the Maxwell equations themselves. Similarly, a great deal can be deduced and predicted concerning the behavior of rigid bodies in the case of motion without using any particular assumption about the construction of bodies out of electrical charges. Thus, for example, the contraction of bodies through motion can be predicted without bringing in the alteration(변경) of the electrical forces due to the motion.
For anyone who is somewhat familiar with nineteenth-century physics, understanding of the logical structure of the theory of relativity will be facilitated(순조롭다) by way of an analogy. Precisely speaking, it is a question of the logical structure of the system consisting of the following sentences: the relativity hypothesis, the electromagnetic field equations, the description of the atomic structure of bodies, and those verifiable sentences which are deducible from these fundamental assumptions.
The Same role as is played by the relativity hypothesis today was played in the 19C theory of heat by the first and second laws of thermodynamics, if we direct our attention towards the logical structure of the theories. From these general hypotheses (which are essentially those of the impossibility of a perpetuum mobile of the first and second kind), it was possible to deduce sentences which are experimentally verifiable. These same sentences, however, were also capable of being deduced from a set of special hypotheses consisting of the following assumptions: the theorems of Newtonian mechanics in conjunction with some statistical hypotheses, and the hypotheses concerning the molecular structure of bodies.
Here, again, no contradiction can arise btw the consequences of the general thermodynamic hypotheses and the special mechanical theories. This is true because the main theorems of thermodynamics, those asserting the impossibility of a perpetuum mobile of the first or second kind, mean in more exact language this : "All special theories concerning the motion and the molecular structure of bodies ought to be qualified in such a way as to fit into the framework prescribed by the two principles of thermodynamics; that is to say, it must not be the case that from a correct molecular theory a sentence can be inferred that contradicts those general principles."
In just the same way Einstein's principle of relativity prescribed a framework into which all special theories concerning the electromagnetic field and the construction of bodies out of electrical charges have to fit. If the Einstein theory is correct, then any law about the construction of bodies out of charges that may ever be discovered must not lead to sentences which contradict the hypothesis of relativity. The value of this hypothesis consists in the fact that it permits the formulation of laws about the behavior of bodies out of electrons and about the laws of the field effects. But, in this connection, we must keep in mind that Einstein's hypotheses, if formulated in a language reducible to verifiable sentences, are also hypotheses concerning the behavior of rigid bodies in relation to the propagation of electromagnetic waves. Now, Einstein's theory of relativity is usually formulated in a language in which the terms "length of an iron rod", "temporal distance of two events", "simultaneity of two events", and such like, are combined in a manner different from that customary in the language of every-day life or (what here amounts to the same thing) in the language of classical mechanics.
If, as often happens, Einstein's theory is said to bring with it new conceptions of space and time, then one ought to consider the following fact. When the velocities of bodies are small as compared to the velocity of light, then the Einstein theory coincides with the Newtonian, and everything can be described within the language of classical physics, that is, with the space and time concepts of every-day life; or, more exactly, words like "length of a rod", and so on, are combined according to the rules ordinary syntax. if, now, one wants to grasp the terms "conception of space", "conception of time", and so on, in their real sense, i. e. as they occur in sentences about verifiable facts, one has to take them in the psychological sense.It should then be said that on the basis of Einstein's theory we are in a position to make statements about our psychological space and time conceptions different from those made on the grounds of classical physics. it would thus follow that the theory of relativity has also brought us progress in psychology.
We ought to be able therefore to indicate psychological experiments which, according to the theory of relativity, should turn out otherwise than would be expected on the basis of classical physics. If we exclude so-called introspection(자기반성) as a method of scientific psychology, because it results can never be expressed in an intersubjective(간주관적인) language which is generally and unambiguously comprehensible(명백하게 이해할 수 있는), then all psychological experiments depend on the observation of the behavior of test-persons, i. e. ultimately on physical observations. It can here only be a question of observing how a person reacts to changes in the spatial and temporal relations of the world. In the case of an experiment that we reckon(산출하다) as psychological, we never have to do with the motions of bodies whose velocity is great enough to approach the velocity of light. All psychological experiments are concerned with what are called "small velocities"in this sense. But in this range there is no difference at all btw the laws of classical and of relativity physics. Thus the theory of relativity cannot lead to nay new theorems of psychology, or the field of space and time "conceptions", if this world is taken in tis psychological sense.
The whole mode of expression which implies that the theory of relativity has introduced new conceptions of space and time is therefore quite misleading if applied outside the most narrow realm of physics. If it is desired to formulate what happens in the physical theory of relativity in a manner(어떤 의미로는) that is really logically correct, this can be done without giving rise to confusions in neighboring domains. As we have already indicated in the first section, we should say : "For the description of motions with large velocities, it is expedient to carry out the construction of sentences out of the terms "length of an iron rod", "simultaneity of two events", and so on, in accordance with syntactical rules other than those used in every-day life and in classical physics." These two sets of syntactical formation rules for sentences are certainly not compatible with one another. But it leads to gross misunderstandings if this state of affairs in the domain of logical syntax is expressed in an apparently psychological language as follows : "the conception of space and time of the theory of relativity is incompatible with that of classical physics". For this would mean that there are psychological experiments which according to Einstein should yield results different from what had been expected earlier. Of course, one might think up such experiments, but there is at present none which even approximately falls within the limits of so-called psychological experiments, i. e. experiments concerning the behavior of human beings.
If, however, we wish to express the difference btw the theory of relativity and classical physics not merely as a fact of logical syntax(according to which we may only state that we are confronted with two mutually contradictory sets of formation rules), then we may formulate the difference btw the two theories as two different hypotheses about the actual world of sense-experiences. That is, we may say: The syntactical rules (formation rules) according to which the words "length of an iron rod", and so on, were combined into sentences before Einstein, have always been employed to describe the processes of motion with which we have to do in every-day life. These rules have proved to be practical in this field, and even in the more general application which Newton gave them in his mechanics. But this syntax turned out to be unsuitable for the representation of experiences involving very rapid motions. As we have shown in the first section, these formation rules permit the importation of many meaningless sentences into physics. For this reason Einstein proposed new formation rules to represent these rapid motions.
The achievements of the theory of relativity which are new as contrasted(대조적으로) with the older physics may therefore be divided from the stand-point(관점) of the logic of science into two kinds: Firstly, new general hypotheses have been established concerning the behavior of rigid bodies and light waves. Only experimentation can show whether these lead to results which contradict experience. They can only be rejected if such contradictions show up, or if - as compared with the old hypothesis - they do not bring to light any new facts. Secondly, however, as previously mentioned, a new syntax concerning the usage of such terms as "length of an iron rod", "simultaneity of two events" has been proposed by Einstein. This is a proposal and not an assertion. It can therefore never be declared correct or false, but in the course of application it has to be determined whether of not the proposal is more expedient than the old one. There can be no refutation by referring to spatio-temporal(時空의) sense-experiences(감각경험), because nothing is therein asserted about psychological facts.
On the basis of all these considerations we see very clearly the point of importance for the physicist in the doctrines of logical syntax and of the logic of science. They do not help him to find something new in physics itself. One can go even further and say that only rarely will they help him to arrive at clearer formulations in physics itself. For that which appears obscure to the non-physicist is often perfectly comprehensible to the physicist, since he constantly sees - so to speak - how these concepts are being employed, since - to use logical terms - he has always before his eyes the "correlating definitions" of which the non-physicist is not aware at all while reading physical treaties, because they are written "between the lines". On the other hand, logical syntax is an invaluable instrument for the physicist when he wants to establish the connection between his sentences and those of neighboring sciences, e. g. psychology, and with sentences of the general theory of science. And if he does not establish this connection in a scientific manner, then it will inevitably be established by traditional philosophy and metaphysics, thus turning physics from an enlightening(계몽적인) science into a source of confusion and sometimes even of infection of the whole intellectual life.
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