Philosophical Interpretations and Misinterpretations of the Theory of Relativity
INTRODUCTION
THROUGHOUT THE PERIOD of the unquestioned rule of mechanistic physics, philosophical interpretations played a comparatively modest role. Discussions of this kind existed only on the borderlands(소속이 불확실한 경계점, 어중간한 상태) of science, between physics and biology, between natural science and religion, and so on. Within actual physical discourse(자연에 대한 담론) so-called philosophical matters were considered only on solemn occasions, such as the seventieth birthday of a famous physicist or the centennial of a scientific society. This state of affairs(사태, 형세) has changed considerably since the theory of relativity came into being and received increasing recognition. Not only did the theory of relativity give rise to a series of strange speculations(추측, 억측) within the fields of psychology, metaphysics, politics, ethics, and last but not least, race theory, but philosophical interpretations even found their way into the scientific journals on physics.
It is hardly possible to open a textbook on the theory of relativity - even if written by an otherwise competent physicist - without coming upon(신세를 지다) sentences of an entirely metaphysical character. Such sentences, wholly meaningless in physics, stand side by side with obviously physical sentences. It it therefore not amazing that great confusion occurred among young physicists and also in wider circles of educated people, and that the opinion arose that the theory of relativity is of an entirely different character from all previous physical theories: that it is constructed less logically and contains many contradictions(모순). One cannot blame the philosophers who sought enlightenment(깨달음) in the writings of physicists for believing that all statements in these papers were the outcome of physical research. But in spite of their sincere desire for scientific enlightenment, they assimilated(동화되다f, 소화하다) from those papers on physics a host of purely metaphysical sentences. As previously mentioned, such sentences may be found in the publications of very important and competent physicists. In the first two sections of this paper we will deal with philosophical sentences and interpretations of the kind which sometimes appear in the writings of physicists on the subject of the theory of relativity. But there are also physicists who are so much under the influence of traditional philosophy that they actually develop a coherent(시종일관) philosophical interpretation of the theory of relativity. Such systematic philosophical interpretations are then employed to support all sorts of metaphysical systems, now the Hegelian philosophy, now fatalism(운명론), and so on. With interpretations of this kind we shall deal in the last section.
1. In the Theory of Relativity the Observing Subject Plays a Greater Part than in Classical Physics
An attempt is often made to characterize the difference between the relativity mechanics of Einstein and the classical mechanics of Newton in the following fashion : While in Newton's mechanics there occur only sentences treating of objective facts, the sentences of Einstein's relativity mechanics also contain statements about the observing subject. Thus, in Newtonian physics, sentences such as the following occur: "This iron rod has a length of three feet." There is no mention of an observer. "Length" is considered an objective(客觀적인) property of the rod. In relativity mechanics, the place of such sentences is taken by sentences of this kind : "This rod has a length of three feet for an observer who is at rest with respect to the rigid system S." In this case the sentences of physics mention the observer quite explicitly.
This mode of expression, however, is not very adequate(충분한). For it leads to great confusion in the opinions concerning the logical structure of the theory of relativity. it promotes the view that there is an essential difference between the sentences of classical Newtonian physics and those of the theory of relativity as to the manner in which references to physical object and observer occur.
The illusion of such a difference arises because the observer is explicitly mentioned in the sentences of the theory of relativity, but not in those of classical physics. This illusion vanishes at once, however, when one tries to cast the sentences of both theories into a form in which they are verifiable by direct experiments. For then we obtain in each of the two theories a sentence of the following syntactical form (논리적 구문 형태) : "If, with respect to the iron rod, a certain quite concretely described measuring procedure is carried out, then any arbitrary observer reads its length as three feet on the measuring stick used." The measuring procedure applied in the case of the theory of relativity is, however, a more special one than that applied in classical physics. Roughly speaking, a more special one than that laying a rigid measuring stick along the iron rod to be measured. In classical physics it is irrelevant(관계없는, 무의미한) in this connection whether the iron rod and the measuring stick are in relative rest or motion. The magnitude of the length read off the scale of the measuring stick is entirely independent of this relative velocity. In relativity physics on the other hand, the statement of this velocity is part of the description of the measuring procedure. To different velocities there correspond different measuring procedure and therefore possibly different reading on the scale. But the role of the observer is exactly the same as in classical physics. He has nothing to do but to read the scale, or more precisely, to find out which marks on the scale coincide(부합하다) at a certain moment with the ends of the iron rod to be measured. How the observer moves is entirely irrelevant. Nothing is said of this in the description of the measuring procedure.
The difference btw the two theories consists in the fact that in the classical description of how to measure lengths the term "velocity" does not occur at all, while in relativity mechanics the statement of the velocity of the measuring stick relative to the body to be measured constitutes an essential part of the description. The designation of the result of the measurement must therefore also contain a reference to this velocity. In order to indicate this, the magnitude defined by the measuring procedure is designated as the "length of the iron rod in a certain frame of reference S", namely, in the frame of reference in which the measured rod has the velocity v.
There are, so far, only differences in definitions, or, more precisely, in the correlations by means of which the measuring procedures are brought into correspondence(一致) with physical quantities that bear certain names. The difference btw the physical theories themselves we cannot determine until we know whether the magnitude of length obtained with various velocities v of the measuring rod are really different, or whether they only bear different names. Only experiment can show which is the case. And the theory of relativity sets up hypotheses from which it follows that, with respect to different frames of reference, or, to put it differently, in the case of different velocities, the lengths of an iron rod turn out to be different on experimental examination; while according to the hypotheses of classical physics, all these quantities turn out to be equal.
Thus relativity physics differs from classical physics in precisely the same way as distinct(별개의) physical theories differ from one another in general, namely, in making different assertions(주장) about the results of experiments carried out under quite concretely described circumstances. In the case in question they assert something different about the results of measurements of lengths that are carried out with differently moved measuring sticks.
In order to formulate different physical theories it is often convenience to avail oneself of different modes of expression. Using a terminology introduced by Wittgenstein(비트겐슈타인) and employed very frequently and fruitfully by Carnap(카르납), any physical theory may be stated most simply if formulated in a grammar - or, more exactly, a syntax - especially suited to it and to the sentential forms occurring in it. In other words, in every theory there are different rules (formation rules) in accordance with which it is to be decided whether or not a certain combination of words constitutes a meaningful sentence. On the basis of this view it may be said that classical and relativity physics differ in the fact that, with respect to them, different syntactical - and, in particular, formation - rules are valid for sentences containing expressions such as "length of an iron rod" or "duration of the vibration of a pendulum."
But in order not to precipitate(~상태에 빠지다) logical confusion, it is necessary to differentiate clearly btw the physical content of a theory, i. e. the statements it makes about experimentally verifiable facts, and the syntactical form in which the sentences of the theory are formulated. It is quite possible by means of sentences of the same syntactical form to express different physical facts, and vice versa.
According to the syntactical formation rules of classical physics, the sentence "this iron rod has a length of three feet" has a definite sense, but according to the syntax of the theory of relativity that is not the case. The words "this iron rod is three feet long" do not form a significant(의미있는) sentence, but a meaningless combination of words. The word-combination "this iron rod has a length of three feet with respect to the system S", on the other hand, is a significant sentence in the syntax of the theory of relativity, while it is a meaningless combination of words in the syntax of classical physics.
In themselves the formative rules of the two syntaxes are, of course, entirely arbitrary. It is, for instance, quite possible to express the physical content of relativity mechanics in sentences which are formed according to the formation rules of the syntax of classical physics. Thus we may start out from the fact that the contraction of bodies through motion belongs to the physical facts asserted by the theory of relativity. This may be expressed in the linguistic form of classical physics as follows : "an iron rod having a length of three feet in the state of rest, has a length of only two feet if moved sufficiently fast". Here, by "state of rest" we may understand "rest with respect to the ether(에테르)".
But if one consider the physical content of theory of relativity to be correct, then there is no correlation by means of which the expression "an iron rod three feet in length" can be brought into correspondence with observable facts. For "velocity of a certain rod with respect to the ether" does not occur in any sentence which asserts a fact verifiable by observation, or - still more logically expressed - in any verifiable sentence. But the expression "length of an iron rod" always occurs in sentences which can only be verified by using at the same time the velocity of the rod with respect to the ether. Therefore all the sentences in which something is stated about the "length of a rod" are completely isolated from the former constitute a system of sentences which is coherent and isolated from the verifiable sentences. One usually calls these isolated sentences "meta-physical" sentences which state something about a real world. Being non-verifiable sentences they are meaningless as far as science is concerned. if therefore one wants to express the physical content of the theory of relativity with the help of sentences which comply with the syntactical rules of classical physics, it is possible to express all physical true sentences, but one also introduces whole system of meaningless sentences.
If, on the other hand, one wants to formulate classical electrodynamics, say the theory of the motionless ether according to which bodies are contracted by motion through the ether, then it is perfectly legitimate to retain(유지하는 것이 합당하다) the syntax of classical physics. For it is possible to determine by experiments the velocity of a rod relative to the ether. Consequently, sentences speaking of the length of an iron rod are verifiable sentences, and hence meaningful.
But the relativity hypothesis creates a state of "splendid isolation" for sentences about the length of a rod, and make it impossible to reduce them to verifiable sentences. Philosophers often expand these isolated sentences into a large system of sentences all logically connected with one another, but from which there is no bridge leading to the scientifically verifiable sentences. The danger of such large isolated systems of sentences consists in the fact that their existence and logical consistency readily leads to the belief that they are systems of statements about a realm of things. This belief constitutes the foundation of the philosophical misinterpretations of physical theories, and make it possible to look upon modern physics as a confirmation to the traditional philosophy.
PHILIPP FRANK
INTRODUCTIONTHROUGHOUT THE PERIOD of the unquestioned rule of mechanistic physics, philosophical interpretations played a comparatively modest role. Discussions of this kind existed only on the borderlands(소속이 불확실한 경계점, 어중간한 상태) of science, between physics and biology, between natural science and religion, and so on. Within actual physical discourse(자연에 대한 담론) so-called philosophical matters were considered only on solemn occasions, such as the seventieth birthday of a famous physicist or the centennial of a scientific society. This state of affairs(사태, 형세) has changed considerably since the theory of relativity came into being and received increasing recognition. Not only did the theory of relativity give rise to a series of strange speculations(추측, 억측) within the fields of psychology, metaphysics, politics, ethics, and last but not least, race theory, but philosophical interpretations even found their way into the scientific journals on physics.
It is hardly possible to open a textbook on the theory of relativity - even if written by an otherwise competent physicist - without coming upon(신세를 지다) sentences of an entirely metaphysical character. Such sentences, wholly meaningless in physics, stand side by side with obviously physical sentences. It it therefore not amazing that great confusion occurred among young physicists and also in wider circles of educated people, and that the opinion arose that the theory of relativity is of an entirely different character from all previous physical theories: that it is constructed less logically and contains many contradictions(모순). One cannot blame the philosophers who sought enlightenment(깨달음) in the writings of physicists for believing that all statements in these papers were the outcome of physical research. But in spite of their sincere desire for scientific enlightenment, they assimilated(동화되다f, 소화하다) from those papers on physics a host of purely metaphysical sentences. As previously mentioned, such sentences may be found in the publications of very important and competent physicists. In the first two sections of this paper we will deal with philosophical sentences and interpretations of the kind which sometimes appear in the writings of physicists on the subject of the theory of relativity. But there are also physicists who are so much under the influence of traditional philosophy that they actually develop a coherent(시종일관) philosophical interpretation of the theory of relativity. Such systematic philosophical interpretations are then employed to support all sorts of metaphysical systems, now the Hegelian philosophy, now fatalism(운명론), and so on. With interpretations of this kind we shall deal in the last section.
1. In the Theory of Relativity the Observing Subject Plays a Greater Part than in Classical Physics
An attempt is often made to characterize the difference between the relativity mechanics of Einstein and the classical mechanics of Newton in the following fashion : While in Newton's mechanics there occur only sentences treating of objective facts, the sentences of Einstein's relativity mechanics also contain statements about the observing subject. Thus, in Newtonian physics, sentences such as the following occur: "This iron rod has a length of three feet." There is no mention of an observer. "Length" is considered an objective(客觀적인) property of the rod. In relativity mechanics, the place of such sentences is taken by sentences of this kind : "This rod has a length of three feet for an observer who is at rest with respect to the rigid system S." In this case the sentences of physics mention the observer quite explicitly.
This mode of expression, however, is not very adequate(충분한). For it leads to great confusion in the opinions concerning the logical structure of the theory of relativity. it promotes the view that there is an essential difference between the sentences of classical Newtonian physics and those of the theory of relativity as to the manner in which references to physical object and observer occur.
The illusion of such a difference arises because the observer is explicitly mentioned in the sentences of the theory of relativity, but not in those of classical physics. This illusion vanishes at once, however, when one tries to cast the sentences of both theories into a form in which they are verifiable by direct experiments. For then we obtain in each of the two theories a sentence of the following syntactical form (논리적 구문 형태) : "If, with respect to the iron rod, a certain quite concretely described measuring procedure is carried out, then any arbitrary observer reads its length as three feet on the measuring stick used." The measuring procedure applied in the case of the theory of relativity is, however, a more special one than that applied in classical physics. Roughly speaking, a more special one than that laying a rigid measuring stick along the iron rod to be measured. In classical physics it is irrelevant(관계없는, 무의미한) in this connection whether the iron rod and the measuring stick are in relative rest or motion. The magnitude of the length read off the scale of the measuring stick is entirely independent of this relative velocity. In relativity physics on the other hand, the statement of this velocity is part of the description of the measuring procedure. To different velocities there correspond different measuring procedure and therefore possibly different reading on the scale. But the role of the observer is exactly the same as in classical physics. He has nothing to do but to read the scale, or more precisely, to find out which marks on the scale coincide(부합하다) at a certain moment with the ends of the iron rod to be measured. How the observer moves is entirely irrelevant. Nothing is said of this in the description of the measuring procedure.
The difference btw the two theories consists in the fact that in the classical description of how to measure lengths the term "velocity" does not occur at all, while in relativity mechanics the statement of the velocity of the measuring stick relative to the body to be measured constitutes an essential part of the description. The designation of the result of the measurement must therefore also contain a reference to this velocity. In order to indicate this, the magnitude defined by the measuring procedure is designated as the "length of the iron rod in a certain frame of reference S", namely, in the frame of reference in which the measured rod has the velocity v.
There are, so far, only differences in definitions, or, more precisely, in the correlations by means of which the measuring procedures are brought into correspondence(一致) with physical quantities that bear certain names. The difference btw the physical theories themselves we cannot determine until we know whether the magnitude of length obtained with various velocities v of the measuring rod are really different, or whether they only bear different names. Only experiment can show which is the case. And the theory of relativity sets up hypotheses from which it follows that, with respect to different frames of reference, or, to put it differently, in the case of different velocities, the lengths of an iron rod turn out to be different on experimental examination; while according to the hypotheses of classical physics, all these quantities turn out to be equal.
Thus relativity physics differs from classical physics in precisely the same way as distinct(별개의) physical theories differ from one another in general, namely, in making different assertions(주장) about the results of experiments carried out under quite concretely described circumstances. In the case in question they assert something different about the results of measurements of lengths that are carried out with differently moved measuring sticks.
In order to formulate different physical theories it is often convenience to avail oneself of different modes of expression. Using a terminology introduced by Wittgenstein(비트겐슈타인) and employed very frequently and fruitfully by Carnap(카르납), any physical theory may be stated most simply if formulated in a grammar - or, more exactly, a syntax - especially suited to it and to the sentential forms occurring in it. In other words, in every theory there are different rules (formation rules) in accordance with which it is to be decided whether or not a certain combination of words constitutes a meaningful sentence. On the basis of this view it may be said that classical and relativity physics differ in the fact that, with respect to them, different syntactical - and, in particular, formation - rules are valid for sentences containing expressions such as "length of an iron rod" or "duration of the vibration of a pendulum."
But in order not to precipitate(~상태에 빠지다) logical confusion, it is necessary to differentiate clearly btw the physical content of a theory, i. e. the statements it makes about experimentally verifiable facts, and the syntactical form in which the sentences of the theory are formulated. It is quite possible by means of sentences of the same syntactical form to express different physical facts, and vice versa.
According to the syntactical formation rules of classical physics, the sentence "this iron rod has a length of three feet" has a definite sense, but according to the syntax of the theory of relativity that is not the case. The words "this iron rod is three feet long" do not form a significant(의미있는) sentence, but a meaningless combination of words. The word-combination "this iron rod has a length of three feet with respect to the system S", on the other hand, is a significant sentence in the syntax of the theory of relativity, while it is a meaningless combination of words in the syntax of classical physics.
In themselves the formative rules of the two syntaxes are, of course, entirely arbitrary. It is, for instance, quite possible to express the physical content of relativity mechanics in sentences which are formed according to the formation rules of the syntax of classical physics. Thus we may start out from the fact that the contraction of bodies through motion belongs to the physical facts asserted by the theory of relativity. This may be expressed in the linguistic form of classical physics as follows : "an iron rod having a length of three feet in the state of rest, has a length of only two feet if moved sufficiently fast". Here, by "state of rest" we may understand "rest with respect to the ether(에테르)".
But if one consider the physical content of theory of relativity to be correct, then there is no correlation by means of which the expression "an iron rod three feet in length" can be brought into correspondence with observable facts. For "velocity of a certain rod with respect to the ether" does not occur in any sentence which asserts a fact verifiable by observation, or - still more logically expressed - in any verifiable sentence. But the expression "length of an iron rod" always occurs in sentences which can only be verified by using at the same time the velocity of the rod with respect to the ether. Therefore all the sentences in which something is stated about the "length of a rod" are completely isolated from the former constitute a system of sentences which is coherent and isolated from the verifiable sentences. One usually calls these isolated sentences "meta-physical" sentences which state something about a real world. Being non-verifiable sentences they are meaningless as far as science is concerned. if therefore one wants to express the physical content of the theory of relativity with the help of sentences which comply with the syntactical rules of classical physics, it is possible to express all physical true sentences, but one also introduces whole system of meaningless sentences.
If, on the other hand, one wants to formulate classical electrodynamics, say the theory of the motionless ether according to which bodies are contracted by motion through the ether, then it is perfectly legitimate to retain(유지하는 것이 합당하다) the syntax of classical physics. For it is possible to determine by experiments the velocity of a rod relative to the ether. Consequently, sentences speaking of the length of an iron rod are verifiable sentences, and hence meaningful.
But the relativity hypothesis creates a state of "splendid isolation" for sentences about the length of a rod, and make it impossible to reduce them to verifiable sentences. Philosophers often expand these isolated sentences into a large system of sentences all logically connected with one another, but from which there is no bridge leading to the scientifically verifiable sentences. The danger of such large isolated systems of sentences consists in the fact that their existence and logical consistency readily leads to the belief that they are systems of statements about a realm of things. This belief constitutes the foundation of the philosophical misinterpretations of physical theories, and make it possible to look upon modern physics as a confirmation to the traditional philosophy.
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