thegoodfellas/blogset-br huggingface dataset:
no rational evidence that their matrix mechanics would prove correct under more realistic conditions. Indeed, they say "if the mechanics as here proposed should already be correct in its essential traits." As a matter of fact, the first application of their mechanics to a realistic problem, that of the hydrogen atom, was given several months later, by Pauli. This application gave results in agreement with experience. This was satisfactory but still understandable because Heisenberg's rules of calculation were abstracted from problems which included the old theory of the hydrogen atom. The miracle occurred only when matrix mechanics, or a mathematically equivalent theory, was applied to problems for which Heisenberg's calculating rules were meaningless. Heisenberg's rules presupposed that the classical equations of motion had solutions with certain periodicity properties; and the equations of motion of the two electrons of the helium atom, or of the even greater number of electrons of heavier atoms, simply do not have these properties, so that Heisenberg's rules cannot be applied to these cases. Nevertheless, the calculation of the lowest energy level of helium, as carried out a few months ago by Kinoshita at Cornell and by Bazley at the Bureau of Standards, agrees with the experimental data within the accuracy of the observations, which is one part in ten million. Surely in this case we "got something out" of the equations that we did not put in. The same is true of the qualitative characteristics of the "complex spectra," that is, the spectra of heavier atoms. I wish to recall a conversation with Jordan, who told me, when the qualitative features of the spectra were derived, that a disagreement of the rules derived from quantum mechanical theory and the rules established by empirical research would have provided the last opportunity to make a change in the framework of matrix mechanics. In other words, Jordan felt that we would have been, at least temporarily, helpless had an unexpected disagreement occurred in the theory of the helium atom. This was, at that time, developed by Kellner and by Hilleraas. The mathematical formalism was too dear and unchangeable so that, had the miracle of helium which was mentioned before not occurred, a true crisis would have arisen. Surely, physics would have overcome that crisis in one way or another. It is true, on the other hand, that physics as we know it today would not be possible without a constant recurrence of miracles similar to the one of the helium atom, which is perhaps the most striking miracle that has occurred in the course of the development of elementary quantum mechanics, but by far not the only one. In fact, the number of analogous miracles is limited, in our view, only by our willingness to go after more similar ones. Quantum mechanics had, nevertheless, many almost equally striking successes which gave us the firm conviction that it is, what we call, correct. The last example is that of quantum electrodynamics, or the theory of the Lamb shift. Whereas Newton's theory of gravitation still had obvious connections with experience, experience entered
the formulation of matrix mechanics only in the refined or sublimated form of Heisenberg's prescriptions. The quantum theory of the Lamb shift, as conceived by Bethe and established by Schwinger, is a purely mathematical theory and the only direct contribution of experiment was to show the existence of a measurable effect. The agreement with calculation is better than one part in a thousand. The preceding three examples, which could be multiplied almost indefinitely, should illustrate the appropriateness and accuracy of the mathematical formulation of the laws of nature in terms of concepts chosen for their manipulability, the "laws of nature" being of almost fantastic accuracy but of strictly limited scope. I propose to refer to the observation which these examples illustrate as the empirical law of epistemology. Together with the laws of invariance of physical theories, it is an indispensable foundation of these theories. Without the laws of invariance the physical theories could have been given no foundation of fact; if the empirical law of epistemology were not correct, we would lack the encouragement and reassurance which are emotional necessities, without which the "laws of nature" could not have been successfully explored. Dr. R. G. Sachs, with whom I discussed the empirical law of epistemology, called it an article of faith of the theoretical physicist, and it is surely that. However, what he called our article of faith can be well supported by actual examplesamany examples in addition to the three which have been mentioned. THE UNIQUENESS OF THE THEORIES OF PHYSICS The empirical nature of the preceding observation seems to me to be self-evident. It surely is not a "necessity of thought" and it should not be necessary, in order to prove this, to point to the fact that it applies only to a very small part of our knowledge of the inanimate world. It is absurd to believe that the existence of mathematically simple expressions for the second derivative of the position is self-evident, when no similar expressions for the position itself or for the velocity exist. It is therefore surprising how readily the wonderful gift contained in the empirical law of epistemology was taken for granted. The ability of the human mind to form a string of 1000 conclusions and still remain "right," which was mentioned before, is a similar gift. Every empirical law has the disquieting quality that one does not know its limitations. We have seen that there are regularities in the events in the world around us which can be formulated in terms of mathematical concepts with an uncanny accuracy. There are, on the other hand, aspects of the world concerning which we do not believe in the existence of any accurate regularities. We call these initial conditions. The question which presents itself is whether the different regularities, that is, the various laws of nature which will be discovered, will fuse into a single consistent unit, or at least asymptotically approach such a fusion. Alternatively, it is possible that there always will be some laws of nature which have nothing in common with each other. At
present, this is true, for instance, of the laws of heredity and of physics. It is even possible that some of the laws of nature will be in conflict with each other in their implications, but each convincing enough in its own domain so that we may not be willing to abandon any of them. We may resign ourselves to such a state of affairs or our interest in clearing up the conflict between the various theories may fade out. We may lose interest in the "ultimate truth," that is, in a picture which is a consistent fusion into a single unit of the little pictures, formed on the various aspects of nature. It may be useful to illustrate the alternatives by an example. We now have, in physics, two theories of great power and interest: the theory of quantum phenomena and the theory of relativity. These two theories have their roots in mutually exclusive groups of phenomena. Relativity theory applies to macroscopic bodies, such as stars. The event of coincidence, that is, in ultimate analysis of collision, is the primitive event in the theory of relativity and defines a point in space-time, or at least would define a point if the colliding panicles were infinitely small. Quantum theory has its roots in the microscopic world and, from its point of view, the event of coincidence, or of collision, even if it takes place between particles of no spatial extent, is not primitive and not at all sharply isolated in space-time. The two theories operate with different mathematical conceptsathe four dimensional Riemann space and the infinite dimensional Hilbert space, respectively. So far, the two theories could not be united, that is, no mathematical formulation exists to which both of these theories are approximations. All physicists believe that a union of the two theories is inherently possible and that we shall find it. Nevertheless, it is possible also to imagine that no union of the two theories can be found. This example illustrates the two possibilities, of union and of conflict, mentioned before, both of which are conceivable. In order to obtain an indication as to which alternative to expect ultimately, we can pretend to be a little more ignorant than we are and place ourselves at a lower level of knowledge than we actually possess. If we can find a fusion of our theories on this lower level of intelligence, we can confidently expect that we will find a fusion of our theories also at our real level of intelligence. On the other hand, if we would arrive at mutually contradictory theories at a somewhat lower level of knowledge, the possibility of the permanence of conflicting theories cannot be excluded for ourselves either. The level of knowledge and ingenuity is a continuous variable and it is unlikely that a relatively small variation of this continuous variable changes the attainable picture of the world from inconsistent to consistent. [10 This passage was written after a great deal of hesitation. The writer is convinced that it is useful, in epistemological discussions, to abandon the
idealization that the level of human intelligence has a singular position on an absolute scale. In some cases it may even be useful to consider the attainment which is possible at the level of the intelligence of some other species. However, the writer also realizes that his thinking along the lines indicated in the text was too brief and not subject to sufficient critical appraisal to be reliable.] Considered from this point of view, the fact that some of the theories which we know to be false give such amazingly accurate results is an adverse factor. Had we somewhat less knowledge, the group of phenomena which these "false" theories explain would appear to us to be large enough to "prove" these theories. However, these theories are considered to be "false" by us just for the reason that they are, in ultimate analysis, incompatible with more encompassing pictures and, if sufficiently many such false theories are discovered, they are bound to prove also to be in conflict with each other. Similarly, it is possible that the theories, which we consider to be "proved" by a number of numerical agreements which appears to be large enough for us, are false because they are in conflict with a possible more encompassing theory which is beyond our means of discovery. If this were true, we would have to expect conflicts between our theories as soon as their number grows beyond a certain point and as soon as they cover a sufficiently large number of groups of phenomena. In contrast to the article of faith of the theoretical physicist mentioned before, this is the nightmare of the theorist. Let us consider a few examples of "false" theories which give, in view of their falseness, alarmingly accurate descriptions of groups of phenomena. With some goodwill, one can dismiss some of the evidence which these examples provide. The success of Bohr's early and pioneering ideas on the atom was always a rather narrow one and the same applies to Ptolemy's epicycles. Our present vantage point gives an accurate description of all phenomena which these more primitive theories can describe. The same is not true any longer of the so-called free-electron theory, which gives a marvelously accurate picture of many, if not most, properties of metals, semiconductors, and insulators. In particular, it explains the fact, never properly understood on the basis of the "real theory," that insulators show a specific resistance to electricity which may be 1026 times greater than that of metals. In fact, there is no experimental evidence to show that the resistance is not infinite under the conditions under which the free-electron theory would lead us to expect an infinite resistance. Nevertheless, we are convinced that the free-electron theory is a crude approximation which should be replaced, in the description of all phenomena concerning solids, by a more accurate picture. If viewed from our real vantage point, the situation presented by the free-electron theory is irritating but is not likely to forebode any inconsistencies which are unsurmountable for us. The free-electron theory raises doubts as to how
much we should trust numerical agreement between theory and experiment as evidence for the correctness of the theory. We are used to such doubts. A much more difficult and confusing situation would arise if we could, some day, establish a theory of the phenomena of consciousness, or of biology, which would be as coherent and convincing as our present theories of the inanimate world. Mendel's laws of inheritance and the subsequent work on genes may well form the beginning of such a theory as far as biology is concerned. Furthermore,, it is quite possible that an abstract argument can be found which shows that there is a conflict between such a theory and the accepted principles of physics. The argument could be of such abstract nature that it might not be possible to resolve the conflict, in favor of one or of the other theory, by an experiment. Such a situation would put a heavy strain on our faith in our theories and on our belief in the reality of the concepts which we form. It would give us a deep sense of frustration in our search for what I called "the ultimate truth." The reason that such a situation is conceivable is that, fundamentally, we do not know why our theories work so well. Hence, their accuracy may not prove their truth and consistency. Indeed, it is this writer's belief that something rather akin to the situation which was described above exists if the present laws of heredity and of physics are confronted. Let me end on a more cheerful note. The miracle of the appropriateness of the language of mathematics for the formulation of the laws of physics is a wonderful gift which we neither understand nor deserve. We should be grateful for it and hope that it will remain valid in future research and that it will extend, for better or for worse, to our pleasure, even though perhaps also to our bafflement, to wide branches of learning.
(positivist)meaning of statements:(1.a) is a true sentence if and only if and only if physical object 1 is observed to have velocity x with respect to physical object 2.(4.a) is a true sentence if and only if n seconds are observed to have passedNotice that the concept of physicalobject does not exist in the above sentences, but only observation of physicalobjects. It may be that we dont need to define exactly what we mean by aphysical object, but what we mean bythe observation of physical objects in such and such state. Thissuddenly starts to resemble quantum mechanics. Could there be any link? I have struggled, yet withoutsuccess, to describe those ideas in a mathematical, rigorous way. One of myideas was to use model theory. Model theory is about interpreting a language,where by language I mean a set of symbols and string of symbols and deductivesystem built upon them. There may be statements from the set of all statementsbuilt upon those symbols whose truth or falsehood cannot be determined by thedeductive system itself, but only through an interpretation of the meaning ofsome of the symbols. It is usually used to study the fundamentals ofmathematics. For example, suppose A, B and C are mathematical statements ofsome sort about the real numbers. Then from (A->B) is true(B->C) is trueIt follows that (A->C) is true.But there are statements such as 3>2That are true or false only upon aninterpretation of the symbol >. The study of the interpretations of alanguage is model theory. Could that be of any help for theconstruction of the physics described above? Whereall this could take us? Maybe the idea may simply reveal not to be fruitful.But at least it seems certain that there may be different ways of conceivingmotion than those of the absolute or relational tradition, and that asystematic study of these possibilities is relevant for physics. Also it seemsthat new ways of conceiving motion are fundamentally a work of find the waysone can meaningfully describe the universe.By Daniel Wagner Fonteles Alves
revolucoes ocorreram simultaneamente no comeco do seculo passado, a mecanica quantica e a relatividade. As duas teorias tem excelente validacao experimental, mas costumam ser usadas em situacoes onde somente uma delas e importante. A mecanica quantica da uma descricao precisa do mundo num nivel sub-microscopico, enquanto os efeitos da relatividade so sao realmente importantes a altas velocidades e proximo a fortes campos gravitacionais. No seculo XX, a fisica avancou muito no sentido de mostrar como tudo se encaixava perfeitamente no paradigma quantico... particulas foram promovidas particula-onda e posteriormente a campos. E muito dificil explicar o mundo sub-microscopico sem usar o framework da mecanica quantica. O grande problema e que a relatividade e mecanica quantica usam conceitos muito diferentes de espaco e tempo, fazendo as duas teorias aparentemente inconciliaveis. E pra piorar a situacao, as energias em que os fenomenos de relatividade-quantica podem ser observdas e muito mais alta do que a que dispomos para a relizacao de nossos modestos experimentos terraqueos.Escrevi um pouco, no post passado, sobre como a relatividade geral explica o fenomeno da gravitacao usando a ideia de curvatura do espaco-tempo. A mecanica quantica admite em sua formulacao um espaco-tempo plano, e nao incorpora o fato de que a materia determina a geometria do mesmo. A teoria da gravitacao quantica e um grande objetivo e fonte de muitas controversias. Efeitos de gravitacao quantica sao cruciais para entender o que acontece perto de um buraco negro e momentos depois do big bang (ou quem sabe antes!) por exemplo. Porem tem sido muito dificil construir uma teoria que explique tudo isso e que contenha a relatividade geral e a mecanica quantica como casos especiais (e que seja testavel), justamente devido a dificuldades com o tratamento distinto dado ao espaco e ao tempo nas duas teorias. A pergunta ''o que sao o tempo e o espaco?'' pode ser reveladora na busca por respostas para o impasse atual da fisica. Na verdade, ate o fato de que e muito dificil responde-las me parece revelador. Percebemos o mundo a nossa volta, seus diversos fenomenos e os comunicamos a outras pessoas atraves da linguagem. Todo o objetivo da fisica e chegar a expressoes do tipo ''objetos X se comportam no tempo e espaco de forma Y''. As equacoes nada mais sao que frases cheias de numeros. Mas o fato e que ha um tempo e espaco linguisticos e um tempo e espaco fisicos cuja relacao nao e muito clara. Essa afirmacao e muito profunda e complexa. Nossa percepcao do mundo da origem a linguagem, cujo grande marca e a logica. Essa por sua vez e uma ferramenta que nos permite classificar como verdadeira ou falsa setencas obvias. E ha perguntas em particular que me pergunto bastante qual sua relacao exata com a linguagem...Por exemplo, o movimento e em sua essencia, absoluto ou relativo? A essa pergunta, ja muito dificil, adiciono outra: essa pergunta e epistemologica ou linguistica? Sempre que proferimos uma sentenca do tipo : ''X esta na posicao 3m'' so ha de fato um sentido quando especificamos em relacao a que esta sendo feita a
medida. Tambem, ''X tem velocidade de 4 m/s'' e uma setenca que precisa de um referencial... mas por motivos epistemologicos ou linguisticos? E se o motivo e linguistico, sera que estamos descobrindo a fisica do mundo a partir da nossa linguagem? Sera que o proprio conceito de velocidade precisa de um referencial por motivos obvios que estao contidos em sua definicao? Dada uma linguagem, seria possivel extrair principios fisicos dela? Existe outra linguagem? Vivemos num mundo relativamente estavel, que nos da a ilusao de que podemos atribuir a tudo um estado de movimento. Se um objeto esta parado, nao costumamos dizer que ele esta parado em relacao ao chao, porque o movimento da Terra foi por milhares de anos, imperceptivel. Isso mostra de um modo fraco que descobertas fisicas podem influir em nossa estrutura linguistica. Mas o que proponho e mais profundo.Nossa linguagem se desenvolveu a partir da triade ''COISA-TEMPO-ESPACO''. Mas sera que isso e realmente necessario? A fisica moderna mostra como esses conceitos sao frageis, e e exatamente isso que da a sensacao de esquisitice aos estudantes. O que exatamente o tempo e espaco da linguagem precisam ter em comum com o tempo e espaco fisicos? A relacao da logica com isso nao esta muito clara para mim, mas parece haver alguma coisa. A logica estuda setencas do tipo ''Se todos os X sao Y e todos os Y sao Z, todos os X sao Z''. O verbo ser/existir, tao fundamentalmente enraizado na logica, pressupoe uma certa intuicao extra-linguistica. Perguntas do tipo o ''movimento e absoluto ou relativo'' sao oriundas de duas filosofias (relacionista, absolutista) derivam da nossa linguagem COISA-TEMPO-ESPACO. E elas dao origem a duas fisicas diferentes. Temos, finalmente, o processo percepcao->linguagem->filosofia->fisica . O processo retro-ativo fisica->filosofia->fisica e muito comum. Mas sera que poderiamos criar um processo iterativo linguagem->filosofia-> fisica -> linguagem ?Sera que nossa dificuldade em definir tempo e espaco nao vem justamente da estrutura linguistica, que usa tempo e espaco para dar sentido a todo o resto? Sera que uma linguagem diferente poderia nos levar a uma fisica diferente? Seria possivel construir outra linguagem (e depois quem sabe ''traduzi-la'' para a linguagem ordinaria)?
casa, uma familia instala diversas cameras ao redor da casa. O problema e que eles descobrem que os eventos que ocorrem sao muito mais apavorantes do que eles imaginavam.INFORMACOESAudio: PortuguesTamanho: 800 MBFormato: AVIQualidade: DVDRipQualidade de Audio: 10Qualidade de Video: 10Ano de Lancamento: 2010Genero: Terror Duracao: 84 minDownloadMegaupload
precisa equilibrar o desafio de pacificar uma cidade ocupada pelo crime com as constantes preocupacoes com o filho adolescente. Quando o universo pessoal e o profissional de Nascimento se encontram, o resultado e explosivo.INFORMACOES Audio: PortuguesTamanho: 700 MBFormato: AVIQualidade: DVDRipQualidade de Audio: 10Qualidade de Video: 10Ano de Lancamento: 2010Genero: AcaoDuracao: 115 min DownloadMegaupload