Realistic theories

We can safely say that chemical explanation from the late eighteenth century onward has been consistently characterized, like physics, by one or more of three kinds of theoretical approaches that are well known to analysts of scientific method (1) "realist," (2) "positive," and (3) "conventional." In this schema, realist theories can be characterized as hypotheticodeductive, with varying degrees of truth probability for their "picture" or "system" of the... 

The progress undergone in recent years toward a solution of the problem raised by Einstein 1927 has become possible because of two developments (1) A few experimental techniques, in particular, the methods for measuring very short times with good accuracy, have permitted in recent years the execution of several experiments which in their essence are practical versions of the thought experiment proposed and discussed in 1935 by Einstein, Podolski, and Rosen.39 (2) A procedure of analysis of their results has been made possible by the work of Bell40 who has derived in the frame of local realism a relation (the Bell inequality) obeyed by local realistic theories but violated by quantum mechanics. 

In spite of the widespread recognition of the theoretical inadequacies of classical nucleation theories, attempts to formulate more realistic theories have met with limited success, in part because nucleation rate measurements are notoriously difficult to make. Consequently, the available data base with which to evaluate various theories is inadequate. Molecular level approaches would seem to hold promise of providing more rigorously acceptable theories without resorting to the use of uncertain bulk properties in treating clusters that are intrinsically molecular. Furthermore, new experimental techniques, such as molecular beams and cluster spectroscopy, make the properties of small clusters amenable to investigation at the molecular level. 

The idea of action at a distance was resisted both by Newton, and by Einstein [42] who called it "spooky", but it has now been demonstrated experimentally [43, 44] that local realistic theory cannot account for correlations between measurements performed at well separated sites. The conclusion is that quantum theory permits hidden variables and is non-local. This conclusion is at variance with relativity, but, as pointed out by Bohm [34], the nonlocality of quantum theory only applies to complex wave functions and does not imply that the quantum potential can be used to transmit signals faster than light. 

The first experiments to analyze EPR correlations used polarized light beams rather than electronic spin systems. The results obtained by Aspect [44] are especially relevant since the systems for study were prepared to be separated space-like. Aspect analyzed the polarization of pairs of photons emitted by a single source toward separate detectors. Measured independently, the polarization of each set of photons fluctuated in a seemingly random way. However, when two sets of measurements were compared, they displayed an agreement stronger than could be accounted for by any local realistic theory. 

Examining the various disciplines of science, physics and chemistry seem to be thus far the disciplines least affected by the emergence of fuzzy logic. This may be explained by the fact that the use of classical mathematics has been quite successful in these disciplines and, consequently, there is no need to revise the various theories based on classical mathematics. Thus far, contributions describing the use of fuzzy logic in chemistry have been rare. This is likely to change within the next decade or so. The expressive richness of fuzzy mathematics will undoubtedly lead to more realistic theories even in these hardest of scientific disciplines. In this... 

A second method of adapting Eq. (11) to a physically more realistic theory is due to Kausch and Becht who consittered tire eff t of chain length d ribution on the accumulation of fractured diains. This theory is considered further in Section 3.7. and is able to explain both tire tinre and strain pendence of motecular fracture events observed by ESR in stressed fibres. In particular it explains why, at comtant specimen load, the rate of fr radical production falls to zero after a rrertain tinre, in apparent contradiction to Eq. (1) which would imply a constant rate of molmilar fracture under constant stress. 

The Bell states have a unique feature that all the information on polarization properties is completely contained in the (polarization-) correlations between the separate photons, while the individual particle does not have any polarization prior to measurement. In other words, all the information is distributed among two particles, and none of the individual systems carries any information. This is the essence of entanglement. At the same time, these (polarization-) correlations are stronger than allowed classically, since they violate bounds imposed by local realistic theories via the Bell-inequality [Bell 1964] or they lead to a maximal contradiction between such theories and quantum mechanics as signified by the Greenberger-Horne-Zeilinger theorem... 

The original theory of double-layer interaction dealt with the problem of the repulsion between two isolated, charged colloidal particles and could, strictly, be applied only to very dilute dispersions. More realistic theories must handle concentrated systems where the interaction between many particles has to be considered. This more complex situation has been, and will continue to be, the subject of important theoretical studies. 

S. Marcelja, Toward a realistic theory of the interaction of membrane inclusions, Biophys. J., 1999, 76, 593-594. 

A realistic theory of nematics should, of course, incorporate the attractive potential between the molecules as well as their hard rod features. There have been several attempts to develop such hybrid models. Equations of state have been derived based on the Percus-Yevick and BBGKY approximations for spherical molecules subject to an attractive Maier-Saupe potential.However, a drawback with these models is that they lead to y = 1 (see (2.3.18)). 

These studies emphasize the fact that any realistic theory of the statistical mechanics of discotic phases cannot treat the molecules as rigid discs, but has to take into account the conformational degrees of freedom of the hydrocarbon chains. 

The two courses represented in Holzmann s notebook covered most of the new ideas that Kekule introduced in his two theoretical publications of 1857-58 and the first installment of his textbook published in 1859, including carbon tetravalence and self-linking. Consistent with Kussmaul s testimony, the names of Gerhardt and Williamson appear often, and Holzmann s notes show that Kekule gave clear preference to Williamson s realist theory of atomic linkages rather than to Gerhardt s... 

This terminates the routine analysis of the PVT data, where one obtains the V= V(T, P) and the two derivatives, with the possibility of detecting the secondary transitions, pertinent for polymer processing and performance of the finished products. To extract additional information from these data (i.e., free volume and the interaction parameters), an adequate and realistic theory is required. For this purpose the equations of state need to be employed. 

The motives for transparency views such as the foregoing are multifarious. Sometimes the motive is to make room for direct realist theories of perception — theories according to which we are aware of external things and not merely goings-on in our own minds. Sometimes the motive is to make the world safe for materialism — if we are not aware of intrinsic features of our experiences, then we cannot claim that experiences have features that no brain state could have. And sometimes the motive is to pave the way for a representationalist or intentionalist view of experience — a view according to which the character of experience is exhausted by its representational or propositional content. Intentionalism itself may be desired either for its own sake or as a means to the ends of direct realism or materialism. I shall not be concerned with these larger issues here, but shall concentrate on transparency in its own right. 

One of the issues is to provide a realistic theory for the summing of London forces over the geometry of a probe tip. This has been carried out by various groups, and found to differ from the standard Hamaker expressions for sphere approaching flat, especially when the probe was very fine, e.g. less than lOnm diameter at the tip. The results obtained for the force on the tip as a function of separation could then be explained, and the Hamaker constant determined. Alternatively, a small sphere could be glued to the cantilever, in which case the... 

Most of what is discussed in this paper is applicable to saturated (or dry) soils but in many eases soils in practice are unsaturated. There is eurrently no simple and realistic theory for strength and stiffness of unsaturated soil similar to the effeetive stress theory for saturated soil. Clearly ground professionals should know that soils may be unsaturated but, in the absence of a simple theory, detailed analyses for unsaturated soils may be beyond the eore skills of most geotechnieal engineers and engineering geologists. 

This nonlocality and lack of realism inherent in quantum mechanics has inspired many attempts through the years to explain the results in terms of a theory that is both local and realistic. Without a specific local realistic theory it is, of course, not possible to predict a value for (a, b) to compare with the quantum mechanical value qm(<>> b) in Eq. (14). However, in 1964 J. S. Bell showed for the first time that such theories place constraints on (o, b), or rather combinations of (a, b), for different values of a and b. 

However, the low efficiency of the photomultipliers used in all these experiments leaves open the possibility that the results could be explained in terms of local realistic theories if the no-enhancement hypothesis is not made. Consequently, no experiment to date can be considered to have provided grounds for a completely unequivocal rejection of such theories, and, indeed, if such an assumption is not made, it has been shown by several authors that it is possible to explain all existing experimental results in local realistic terms. Thus it seems likely that, in future, experimental work will be carried out either in situations where it is not necessary to make the no-enhancement hypothesis, for example in experiments of the type suggested by Lo and Shimony or Selleri, or in situations where the no-enhancement hypothesis can be subjected to direct experimental test, for example in experiments of the type suggested by Garuccio and Selleri. ... 

As mentioned in the introduction to Parts A and B, new experimental methods have enriched and advanced the field of atomic spectroscopy to such a degree that it serves not only as a source of atomic structure data but also as a test ground for fundamental atomic theories based upon the framework of quantum mechanics and quantum electrodynamics. However, modem laser and photon correlation techniques have also been applied successfully to probe beyond the traditional quantum mechanical and quantum electrodynamical theories into nuclear stracture theories, electro-weak theories, and the growing field of local realistic theories versus quantum theories. 

While two-photon absorption spectroscopy has been widely applied for precision measurements of atomic structure, the polarization correlation of the simultaneous two-photon emission from the metastable Is state of atomic hydrogen has only been measured very recently. The emission of the coincident two photons can be described by a single state vector which determines the circular and linear two-photon polarization. Compared to the two-photon cascade experiments the polarization correlation of the simultaneous two-photon decay of metastable hydrogen is conceptually closer to the original proposals by Bell and Bohm for tests of the foundation of quantum mechanics. More than SO years have elapsed since the famous Einstein-Bohr debate on microphysical reality and quantum formalism. The present and future outcome of the hydrogen two-photon correlation experiment is considered to be a most crucial test with regard to the rivalry between quantum mechanics and local realistic theories. 

In the experiments reported in Figure 17, the particle diameter, d, is smaller than 5 pm [82] while 6 was larger than 50 pm [l35j. With the experimentally observed E - 3.5, the data suggest a 0.35. However, with no more data available, eqn (55) remains speculative. For intermediate values of dp in the order of 0.5-10 Dj /kL (= 5 in film theory) equation (54) is too simplistic. Derivation of a realistic theory in this area might prove to be rather... 

The results of several molecular theories that describe the smectic ordering in a system of hard spherocylinders enable us to conclude that the contribution from hardcore repulsion can be described by the smoothed-density approximation. On the other hand, a realistic theory of thermotropic smectics can only be developed if the intermolecular attraction is taken into account, The interplay between hard-core repulsion and attraction in smectic A liquid crystals has been considered by Kloczkow-ski and Stecki [17] using a very simple model of hard spherocylinders with an ad-ditonal attractive r potential. Using the Onsager approximation, the authors have obtained equations for the order parameters that are very similar to the ones found in the McMillan theory but with explicit expressions for the model parameters. The more general analysis has been performed by Me-deros and Sullivan [76] who have treated the anisotropic attraction interaction by the mean-field approximation while the hardcore repulsion has been taken into account using the nonlocal density functional approach proposed by Somoza and Tarazona. 

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