ISSN:0094-243X    

DOI:10.1063/1.2948445

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Causality has a central role in physical thought; but there is wide variation, historically, in what is ascribed to particular causal properties such as degree of determinism, past‐future asymmetry, and requirement of physical plausibility. Doctrines of causality in Aristotle, Newtonian mechanics, David Hume, Bertrand Russell, and current quantum theory are examined. Although philosophical analysis is a determinant of views of causality, it is apparent that there is also a strong interdependence between what has been established in science and what is accepted as the principle of causality.

ISSN:0094-243X    

DOI:10.1063/1.2948447

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

It is pointed out that one must distinguish between causality as a general property of some physical theories expressing that the time development ofclosedsystems is determined if the initial state is suitably specified, and specific cause‐effect relations arising from the action of an outside agent on anopensystem. The connection between the space‐time structure of the special theory of relativity and its causality requirements is discussed briefly, and some common misunderstandings are clarified. The consequences of these requirements for classical relativistic theories of systems of interacting mass points are discussed; it is argued that they do not impose any restrictions on the description of closed systems, but only of open ones, since it is only the latter for which the concept of causal anomaly is physically meaningful. Thus no restrictions are imposed on the possible existence of particles moving faster than light (tachyons) within closed systems, but the possibility of purposeful production of and experimentation with tachyons must be excluded. Similarly, for closed systems, particles are not restricted to interactions describable by fields; indeed, at least to order c−2, any field‐theoretical interaction acting over intervals in or on the future light cone of the source (commonly mislabeled “causal”) is equivalent to an interaction (similarly mislabeled “noncausal”) acting over a space‐like interval.

ISSN:0094-243X    

DOI:10.1063/1.2948446

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Signal velocities greater than that of light are well known to be ruled out by a combination of the theory of relativity and causality, because their existence would lead to the possibility of causal cycles. We exhibit the reason for this prohibition and analyze the relevant aspects of the notion of causality. We argue that the logical basis of the distinction between cause and effect is not their temporal order, but that it rests on the issue of control. We then examine the notion of control in this context.

ISSN:0094-243X    

DOI:10.1063/1.2948448

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The basic question raised in this paper is the relationship between group theoretical and physical notions. In particular the physical significance of the mathematical entities occurring in group‐representations is examined in detail. For this reason a brief outline is presented of the mathematical definitions and status of non‐linear realizations of groups. Special non‐linear realizations of the Lorentz and Poincare´ groups are exhibited. The possible physical meaning of these realizations is discussed. It is shown that there is a fundamental interpretation question involved, which indicates that the identical formalism can describe a wide variety of physical phenomena. The classical (Wigner) theory of the representations of the Poincare´ group, allows the description of many‐particle systems in terms of elements and operators in tensor products of Hilbert space. An appropriate adaptation of this procedure suggests that the utilization of the non‐linear realization of the Poincare´ group, describes a relativistic many‐particle system in interaction. General requirements such as causality are shown to be compatible with the formalism of the non‐linear realizations.

ISSN:0094-243X    

DOI:10.1063/1.2948449

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The physical meaning of the macrocausality property of scattering transition probabilities is described, and the role of this property in S‐matrix theory and other physical theories is discussed. The macroscopic causality properties of theories with shadow particles, are examined and are shown to contradict the general interpretational principles of quantum theory. Shadow particles have been introduced to remedy the unitarity difficulties of indefinite‐metric field theories.

ISSN:0094-243X    

DOI:10.1063/1.2948450

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Starting with an analysis of the natural (but not inevitable!) assumptions of conventional quantum theory the desirability of a generalization is highlighted. I give an exposition of a new scattering theory in which a new class of states enter; these states are relevant for the dynamical description but do not contribute to probability. The transition amplitude in this theory is calculated; it obeys the unitarity relation. Its relation to the standard scattering amplitude enables us to calculate it by simple methods and to study its piecewise analyticity. Certain causality questions are discussed and certain paradoxes resolved. A number of deserving candidates for the role of shadow particles are listed. It is suggested that perhaps “general interpretational principles of quantum theory” are not as general as they should be or could be.

ISSN:0094-243X    

DOI:10.1063/1.2948441

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

If cosmological structure is the result of two metrical tensor fields, causal structure is surprisingly modified with signals traveling faster than light and effects preceding causes when viewed by certain inertial observers. Metrical structure is seen to be a property of matter rather than an attribute of the “space‐time” four‐dimensional event continuum.

ISSN:0094-243X    

DOI:10.1063/1.2948442

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

We extend a previously developed one dimensional causal theory of tachyons to three dimensions. The result is a three dimensional theory of interacting tachyons in which coordinates in reference frames with sub‐luminal relative velocity are related by the Lorentz transformations, and in which no paradoxes involving causal loops can arise. The resulting theory involves a preferred spatial direction and preferred velocity perpendicular to that direction, so that physical laws governing tachyons are not invariant under rotations or proper Lorentz transformations. This lack of invariance should manifest itself even in processes involving only bradyons, to the extent that coupling to virtual tachyons is important. We discuss the limits which experimental evidence on the validity of rotational invariance places on tachyon couplings in the theory and possible additional experiments for searching for lack of such invariance.

ISSN:0094-243X    

DOI:10.1063/1.2948443

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Life in general, and man's memory in particular, determine a preferred direction in time (“time arrow”). It is made plausible that the time direction in which the entropy increases is this same time arrow.In quantum theory, wave functions describe not real (single) physical systems, but ensembles of systems. Reduction of wave packets corresponds to treating a system as a member of a new ensemble. Similarly, splitting an electromagnetic field into IN‐field plus retarded field, or into OUT‐field plus advanced field, corresponds to different ensembles describing a scattering on which only partial information is available. Our desire to ascribe a source to any light observed is the reason for usually preferring retarded fields over advanced fields. Independent of the fact that retardation of light waves is shown experimentally by Fizeau's measurement of the velocity of light,Afterthought Oneshows that an eye‐object interaction by advanced fields would violate the second law of thermodynamics. This would relate the time arrow of electromagnetism to the one of life. A puzzle remains when this is applied to light traveling between stars and interstellar dust.The time arrow of cosmology (time direction of expansion of the universe) is sometimes related to the time arrow of life by an extension of Olbers' paradox. An example worked out inAfterthought Twoshows that this generalization of Olbers' paradox is not justified.Afterthought Threecontains some speculations about possible correlations between the time arrows of cosmology and of life.The time arrow of quantum theory is determined by the fact that quantum theory in general predicts future probabilities, and that it can retrodict (postdict) probabilities of the past only under specific conditions that often are not satisfied. This asymmetry becomes more understandable when quantum theory is applied to sequences of nonideal (irreproducible) measurements separated by the use of gadgetry that prepareschoseninitial conditions for the next measurement. The entering here ofchoiceindicates a relation between the mind with its built‐in time arrow, and the choice of the ensembles to which quantum theory then is applied objectively.We shall now return to the style of yesterday's meeting, talking about generalities. The only difference is that I will be thinking in terms of quantum theory instead of classical theory. Therefore the wordIndeterminismin the title of this talk.

ISSN:0094-243X    

DOI:10.1063/1.2948444

出版商:AIP    

年代:1974

数据来源: AIP