As has become evident from historical studies, science does not proceed in the coherent and predictable way that basic science texts would have us believe. I will argue that an excellent counter-example is an episode from the historical development of quantum mechanics in which the incompatibility of the particle and the wave representations of the electron and light were destined to be encompassed by two mathematically equivalent, but conceptually quite different theories. I shall argue that the appearance of two such different, yet equivalent, quantum theories was not surprising at all and I claim even predictable. As Einstein himself wrote in 1909: ‘It is my opinion that the next phase in the development of theoretical physics will bring us a theory of light that can be interpreted as a kind of fusion of the wave and the [particle] theory.’ Certainly, the interpretative content of Werner Heisenberg's and Erwin Schrödinger's theories could not have been more different. By mid-1926, the theoretical foundations had been laid for a scientific and emotional battleground between the particle and the wave. I suggest that an important element in the debate was not the incompatibility itself but actually coming to terms with ambiguity in science. For, in the end, ambiguous and vague interpretations of the same phenomena became part of science, where science was supposed to give a clear and unambiguous description of nature.
As has become evident from historical studies, science does not proceed in the coherent and predictable way that basic science texts would have us believe. I will argue that an excellent counter-example is an episode from the historical development of quantum mechanics in which the incompatibility of the particle and the wave representations of the electron and light were destined to be encompassed by two mathematically equivalent, but conceptually quite different theories. I shall argue that the appearance of two such different, yet equivalent, quantum theories was not surprising at all and I claim even predictable. As Einstein himself wrote in 1909: ‘It is my opinion that the next phase in the development of theoretical physics will bring us a theory of light that can be interpreted as a kind of fusion of the wave and the [particle] theory.’ Certainly, the interpretative content of Werner Heisenberg's and Erwin Schrödinger's theories could not have been more different. By mid-1926, the theoretical foundations had been laid for a scientific and emotional battleground between the particle and the wave. I suggest that an important element in the debate was not the incompatibility itself but actually coming to terms with ambiguity in science. For, in the end, ambiguous and vague interpretations of the same phenomena became part of science, where science was supposed to give a clear and unambiguous description of nature.
Wave-particle duality has been one of the guiding concepts in the development of modern physics.Even though duality has been extensively studied, the concept possessing multiple definitions has not received due attention.The article, to begin with, establishes the plurality associated with duality by highlighting the presence of multiple interpretations in the history of quantum mechanics and also demonstrates how prominent scientific pedagogic texts, drawing from these different threads of development, differ in the depiction of duality.This plurality has not been recognized for several reasons.Among these, the article criticizes the simplistic historical depiction of duality by showing how the narration of this concept undergoing linear development glosses over crucial historical details.Following that, the nature of the concerned plurality is analysed by comparing it with other kinds of plurality found in science.The article concludes by emphasising the relevance of this discussion for the current scientific research and for the pedagogy of quantum mechanics.
In an interesting series of articles published few years ago Afshar and coworkers [1,2] reported an optical experiment in which they claimed to refute the well known N. Bohr principle of complementarity [3, 4]. Obviously this result, if justified, would constitute a serious attack against the orthodox interpretation of quantum mechanics (known as the Copenhagen interpretation). This work stirred much debate in different journals (see for examples references [5–12]). We think however that there are still some important misunderstandings concerning the interpretation of this experiment. In a preprint written originally in 2004 [5] (and following some early discussions with Afshar) we claimed already that the interpretation by Afshar et al. can be easily stated if we stay as close as possible from the texts written by Bohr. The aim of the present article (which was initially written in 2005 to precise a bit the thought developed in [5]) is to comment the interpretation discussed in [1]. We will in the following analyze the meaning of Bohr principle and show that far from disproving its content the experiment [1] is actually a complete confirmation of its general validity. The difficulties associated with the understanding of this principle are not new and actually complementarity created troubles even in Einstein mind [3] so that we are here in good company. To summarize a bit emphatically Bohr’s complementarity we here remind that this principle states that if one of a pair of non commuting observables of a quantum object is known for sure, then information about the second (complementary) is lost [3, 4, 15, 16]. This can be equivalently expressed as a kind of duality between different descriptions of the quantum system associated with different experimental arrangements which mutually exclude each other (read in particular [3,4]). Later in the discussion we will try to precise this definition but for the moment it is enough to illustrate the concepts by examples Consider for instance the well known Young double-pinholes interference experiment made with photons. The discrete nature of light precludes the simultaneous observation of a same photon in the aperture plane and in the interference pattern: the photon cannot be absorbed twice. This is already a trivial manifestation of the principle of Bohr. Here it implies that the two statistical patterns associated with the wave in the aperture plane and its Fourier (i. e., momentum) transform require necessarily different photons for their recording. It is in that sense that each experiment excludes and completes reciprocally the other. In the case considered before the photon is absorbed during the first detection (this clearly precludes any other detection). However even a non-destructive solution for detection implying entanglement with other quantum systems has a radical effect of the same nature: the complementarity principle is still valid. For example, during their debate Bohr and Einstein [3] discussed an ideal which-way experiment in which the recoil of the slits is correlated to the motion of the photon. Momentum conservation added to arguments based on the uncertainty relations are sufficient to explain how such entanglement photon-slits can erase fringes [15–19]. It is also important for the present discussion to remind that the principle of complementarity has a perfidious consequence on the experimental meaning of trajectory and path followed by a particle. Indeed the unavoidable interactions existing between photons and detectors imply that a trajectory existing independently of any measurement process cannot be unambiguously defined. This sounds even like a tragedy when we consider once again the two-holes experiment. Indeed for Bohr this kind of experiments shows definitely the essential element of ambiguity which is involved in ascribing conventional physical attributes to quantum systems. Intuitively (i. e., from the point of view of classical particle dynamic) one would expect that a photon detected in the focal plane of the lens must have crossed only one of the hole 1 or 2 before to reach its final destination. However, if this is true, one can not intuitively understand how the presence of the second hole (through which the photon evidently did not go) forces the photon to participate to an interference pattern (which obviously needs an influence coming from both holes). Explanations to solve this paradox have been proposed by de Broglie, Bohm, and others using concepts such as empty waves or quantum potentials [20, 21]. However all these explanations are in agreement with Bohr principle (since they fully reproduce quantum predictions) and can not be experimentally distinguished. Bohr and Heisenberg proposed for all needed purposes a much more pragmatic and simpler answer: don’t bother, the complementarity principle precludes the simultaneous observation of a photon trajectory and of an interference pattern. For Bohr [3]: This point is of great logical consequence, since it is only the circumstance that we are presented with a choice of either tracing the path
Heisenberg argued that wave and particle are too exclusively different in properties, making the intrinsic wave-quantum unity of light impossible to visualize and describe by the language. He invented mathematical Quantum Theory to circumvent visualization and inadequacy of language. But mathematics too is a language to supplement description. He used it to superimpose hidden concepts leading to the Uncertainty Principle. In Unified Theory the wave & particle aspects of electromagnetic radiation and moving material particle coexist blended together as wave-quantum UNITY. This is also supported by experiments. The wave-or-quantum DUALITIES of Quantum Theory appear due to experimental limitations to observe only one and not both of the two aspects simultaneously. Conservation of mass & momentum are inviolable. Matter‘s creation from, or dissolution into, ‘nothing’ is unrealistic. So the Heisenberg’s Uncertainty Principle is rejected as unrealistic and new Principle of Null Action with universal applications is introduced. The Copenhagen interpretation of Quantum Theory is reappraised critically. This paper will bring out and rectify the unreality of Heisenberg-Bohr [1] approach and also explain from sharmon medium of the Unified Theory [2], the Wave-Quantum 'unity' appearing as Wave-or-Quantum 'duality', which the Quantum Theory was all about but could not explain satisfactorily. The Uncertainty Principle will be rejected as unrealistic and a new Principle of Null Action with universal applications introduced. The Copenhagen interpretation of Quantum Theory will be critically reappraised. 1. The objective reality exists irrespective of the observer We observe an object through the signals, emanating or reflected from it, received by our senses and interpreted by the brain/mind. The human senses and intellect have their own limitations and the mediating signals themselves introduce some distortion or uncertainty of observation. It turns precise objective reality into imprecise subjective appearance. Heisenberg [1] made the subjective imprecision as the very nature of things and based his Quantum Theory on the observer's imprecise view of the intrinsically precise physical reality. But the physical objects, phenomena and events, which their theories purport to describe, do not actually need any observer for their existence and are, in fact, governed by NOT the observed but actual magnitudes of their physical parameters like energy, momentum, time, length etc. For instance, the moon or distant galaxies or invisible submicroscopic particles exist not only during the attention of the viewer but also without an observer. In order to formulate physical laws in terms of the observed or measured magnitudes, the Quantum Theory is erroneously based on “what can be known”, instead of on “what actually there is”, in the objective reality. That is on the observed, and not on the actual magnitudes, putting the observer's imprecise view super-most in derogation of the inherent precision in the observed objective reality. 2. Wave-or-Quantum duality of matter & radiation in Quantum Theory Heisenberg [1] noted with scientific curiosity and concern that the -rays emitted from radioactive elements showed definite tracks in Wilson photographs like fast moving particles.
This thesis is a study about the insights and challenges provided by the concept of wave-
particle duality for the understanding of physical entities. I specifically analyse the duality
claim of photons and the related interference phenomena. To begin, I explore several
notions of duality found in mathematics and various branches of science and present the
similarities and differences amidst them. After this, with regard to wave-particle duality of
radiation, I highlight the plurality associated with this concept based on a few important
interpretations of duality. I then focus on the wave-particle duality claim about photons
articulated in the context of two experiments: the anti-correlation experiment and photons’
behaviour in the Mach-Zehnder interferometer experiment. I argue that this claim can
neither be substantiated through the complementarity principle nor by claiming that
photons behave analogously to classical waves and particles. This detailed examination
of the experiments brings to the forefront yet another confusion about photons that
I subsequently evaluate. I discuss the controversy concerning the interpretation of the
interference phenomenon of photons and identify the sources of this confusion. Through
these arguments and conclusions drawn in this thesis, I demonstrate how philosophical
analysis is crucial for the understanding of scientific entities.
A textbook interpretation of quantum physics is that quantum objects can be described in a particle or a wave picture, depending on the operations and measurements performed. Beyond this widely held believe, we demonstrate in this contribution that neither the wave nor the particle description is sufficient to predict the outcomes of quantum-optical experiments. To show this, we derive correlation-based criteria that have to be satisfied when either particles or waves are fed into our interferometer. Using squeezed light, it is then confirmed that measured correlations are incompatible with either picture. Thus, within one single experiment, it is proven that neither a wave nor a particle model explains the observed phenomena. Moreover, we formulate a relation of wave and particle representations to two incompatible notions of quantum coherence, a recently discovered resource for quantum information processing.For such an information-theoretic interpretation of our method, we certify the nonclassicality of coherent states - the quantum counterpart to classical waves - in the particle picture, complementing the known fact that photon states are nonclassical in the typically applied wave picture.
Neither particle nor wave The information about the particle behaviour and the wave behaviour of light, presented in the preceding chapter, forms an extremely peculiar combination when taken together. And yet both are true: the experiments have been done as described, with the outcome as stated. There are experiments that tell us clearly that light consists of waves; there are others that tell us, equally clearly, that light consists of particles. Somehow we must find a description of light that incorporates both kinds of behaviour. This is a formidable undertaking, but there is one cheerful fact: in absolutely none of the experiments that have ever been done did the particle and the wave behaviours occur simultaneously . Because this is a fact that covers the entire history of physics, we feel justified in assuming that this is a general feature of Nature, and that there cannot ever be an experiment in which the wave and particle behaviours both occur at the same time. This is a generalization, for we can never expect to do all possible experiments. This generalizing hypothesis was first announced by Bohr, who had the wonderful combination of daring and insight to postulate that the observation of certain quantities excludes the simultaneous observation of certain others.