共查询到20条相似文献,搜索用时 31 毫秒
1.
S. D. Agashe 《Foundations of Physics》2006,36(7):955-1011
Einstein, in his “Zur Elektrodynamik bewegter K?rper”, gave a physical (operational) meaning to “time” of a remote event in describing “motion” by introducing the concept of “synchronous stationary clocks located at different places”. But with regard to “place” in describing motion, he assumed without analysis the concept of a system of co-ordinates.In the present paper, we propose a way of giving physical (operational) meaning to the concepts of “place” and “co-ordinate system”, and show how the observer can define both the place and time of a remote event. Following Einstein, we consider another system “in uniform motion of translation relatively to the former”. Without assuming “the properties of homogeneity which we attribute to space and time”, we show that the definitions of space and time in the two systems are linearly related. We deduce some novel consequences of our approach regarding faster-than-light observers and particles, “one-way” and “two-way” velocities of light, symmetry, the “group property” of inertial reference frames, length contraction and time dilatation, and the “twin paradox”. Finally, we point out a flaw in Einstein’s argument in the “Electrodynamical Part” of his paper and show that the Lorentz force formula and Einstein’s formula for transformation of field quantities are mutually consistent. We show that for faster-than-light bodies, a simple modification of Planck’s formula for mass suffices. (Except for the reference to Planck’s formula, we restrict ourselves to Physics of 1905.) 相似文献
2.
J. Reichardt D. R. White 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(2):217-224
We present a framework for automatically decomposing (“block-modeling”) the functional classes of agents within a complex
network. These classes are represented by the nodes of an image graph (“block model”) depicting the main patterns of connectivity
and thus functional roles in the network. Using a first principles approach, we derive a measure for the fit of a network
to any given image graph allowing objective hypothesis testing. From the properties of an optimal fit, we derive how to find
the best fitting image graph directly from the network and present a criterion to avoid overfitting. The method can handle
both two-mode and one-mode data, directed and undirected as well as weighted networks and allows for different types of links
to be dealt with simultaneously. It is non-parametric and computationally efficient. The concepts of structural equivalence
and modularity are found as special cases of our approach. We apply our method to the world trade network and analyze the
roles individual countries play in the global economy. 相似文献
3.
Themodel of degenerate weakly nonideal Bose gas is considered without the assumption on the C-number nature of creation and annihilation operators of particles in the zero-momentum state. It was shown that the “density-density”
Green’s function pole defines the Bogolyubov spectrum of phonon-roton-type collective excitations. The single-particle excitation
spectrum is characterized by the gap whose value is defined by the particle density in the “condensate”. 相似文献
4.
Alexander L. Kholmetskii 《Foundations of Physics》2006,36(5):715-744
In this paper we pay attention to the inconsistency in the derivation of the symmetric electromagnetic energy–momentum tensor for a system of charged particles from its canonical form, when the homogeneous Maxwell’s equations are applied to the symmetrizing gauge transformation, while the non-homogeneous Maxwell’s equations are used to obtain the motional equation. Applying the appropriate non-homogeneous Maxwell’s equations to both operations, we obtained an additional symmetric term in the tensor, named as “compensating term”. Analyzing the structure of this “compensating term”, we suggested a method of “gauge renormalization”, which allows transforming the divergent terms of classical electrodynamics (infinite self-force, self-energy and self-momentum) to converging integrals. The motional equation obtained for a non-radiating charged particle does not contain its self-force, and the mass parameter includes the sum of mechanical and electromagnetic masses. The motional equation for a radiating particle also contains the sum of mechanical and electromagnetic masses, and does not yield any “runaway solutions”. It has been shown that the energy flux in a free electromagnetic field is guided by the Poynting vector, whereas the energy flux in a bound EM field is described by the generalized Umov’s vector, defined in the paper. The problem of electromagnetic momentum is also examined. 相似文献
5.
Paul Ehrenfest (1880–1933) received his Ph.D. degree at the University of Vienna in 1904 and moved with his wife and young
daughter to St. Petersburg in 1907, where he remained until he succeeded Hendrik Antoon Lorentz (1853–1928) in the chair of
theoretical physics at the University of Leiden in 1912. Drawing upon Ehrenfest’s correspondence of the period, we first examine
Ehrenfest’s difficult and insecure years in St. Petersburg and then discuss his unsuccessful attempts to obtain a position
elsewhere before he was appointed as Lorentz’s successor in Leiden.
Pim Huijnen is writing a doctoral dissertation in history; the present paper is based upon his Master’s Thesis, “‘Die Grenze
des Pathologischen’: Het leven van fysicus Paul Ehrenfest, 1904–1912,” University of Groningen, 2003. A.J.Kox is Pieter Zeeman
Professor of History of Physics at the University of Amsterdam. 相似文献
6.
We analyze the forgotten communication of Ettore Majorana (1906–1938?) on the Thomas-Fermi statistical model of the atom,
which he presented on December 29, 1928, during the XXII General Meeting of the Italian Physical Society in Rome, and which
was published in Il Nuovo Cimento, the Society’s journal, in 1929. His communication was not mentioned subsequently in any of the numerous publications of
Enrico Fermi (1901–1954) and his group in Rome, nor in any of the later accounts of Majorana’s life and work. We place Majorana’s
contribution within the context of contemporary research on the subject, point out its influence on the final formulation
of the Thomas-Fermi statistical model by Fermi and Edoardo Amaldi (1908–1989) in 1934, and discuss Majorana’s other scientific
contributions before his mysterious disappearance in 1938.
Francesco Guerra is Professor of Theoretical Physics in the Department of Physics at the University of Rome “La Sapienza.”
His main fields of research are quantum-field theory, statistical mechanics of complex systems, and the history of nuclear
physics. Nadia Robotti is Professor of History of Physics in the Department of Physics at the University of Genoa. Her main
fields of research are the history of atomic physics, quantum mechanics, and nuclear physics. 相似文献
7.
Max Jammer 《Physics in Perspective (PIP)》2007,9(3):266-280
I summarize the historical development of concepts of time in physics from antiquity to the end of the twentieth century.
Editors’ Note: Max Jammer received the American Physical Society/American Institute of Physics Abraham Pais Prize for the
History of Physics for 2007, “For his groundbreaking historical studies of fundamental concepts in physics, including his
comprehensive account of the development of quantum mechanics.” We publish here his Pais Prize Lecture, which was presented
at the APS meeting in Jacksonville, Florida, on April 16, 2007. 相似文献
8.
R. E. Kastner 《Foundations of Physics》2009,39(10):1139-1144
A modified version of Young’s experiment by Shahriar Afshar indirectly reveals the presence of a fully articulated interference
pattern prior to the post-selection of a particle in a “which-slit” basis. While this experiment does not constitute a violation
of Bohr’s Complementarity Principle as claimed by Afshar, both he and many of his critics incorrectly assume that a commonly
used relationship between visibility parameter V and “which-way” parameter K has crucial relevance to his experiment. It is argued here that this relationship does not apply to this experimental situation
and that it is wrong to make any use of it in support of claims for or against the bearing of this experiment on Complementarity. 相似文献
9.
We analyze in some detail the course that Ettore Majorana gave on theoretical physics at the University of Naples between
January and March 1938, just prior to his mysterious disappearance. We discuss, in particular, the recently discovered Moreno
Lecture Notes, in which all of Majorana’s lectures are recorded, six of which are not present in those that are preserved
in the Domus Galilaeana in Pisa, Italy.
Antonino Drago is a retired professor of history of physics at the University of Naples “Federico II.” Salvatore Esposito
is a researcher on theoretical physics and history of physics at the University of Naples “Federico II.” 相似文献
10.
Ruth Lewin Sime 《Physics in Perspective (PIP)》2012,14(1):59-94
As the co-discoverer of nuclear fission and director of the Kaiser Wilhelm Institute for Chemistry, Otto Hahn (1879–1968)
took part in Germany‘s nuclear-fission project throughout the Second World War. I outline Hahn’s efforts to mobilize his institute
for military-related research; his inclusion in high-level scientific structures of the military and the state; and his institute’s
research programs in neutron physics, isotope separation, transuranium elements, and fission products, all of potential military
importance for a bomb or a reactor and almost all of it secret. These activities are contrasted with Hahn’s deliberate misrepresentations
after the war, when he claimed that his wartime work had been nothing but “purely scientific” fundamental research that was
openly published and of no military relevance. 相似文献
11.
12.
Howard E. Brandt 《Foundations of Physics Letters》2002,15(3):287-292
In honor of the centennial of Eugene Wigner’s birth, a possible interpretation is given of the density matrix appearing in
his classic paper, “Remarks on the mind-body question.” It is argued that nearinstantaneous vanishing of the quantum coherences
of the reduced density matrix of the measured object would occur either in the case of Wigner’s friend, or in the case of
any complex measuring automaton (conscious or not) making the measurement. 相似文献
13.
Steven Weinstein 《Foundations of Physics》2009,39(8):921-936
Bell’s theorem is purported to demonstrate the impossibility of a local “hidden variable” theory underpinning quantum mechanics.
It relies on the well-known assumption of ‘locality’, and also on a little-examined assumption called ‘statistical independence’
(SI). Violations of this assumption have variously been thought to suggest “backward causation”, a “conspiracy” on the part of
nature, or the denial of “free will”. It will be shown here that these are spurious worries, and that denial of SI simply implies nonlocal correlation between spacelike degrees of freedom. Lorentz-invariant theories in which SI does not hold are easily constructed: two are exhibited here. It is conjectured, on this basis, that quantum-mechanical phenomena
may be modeled by a local theory after all.
This paper is dedicated to the memory of John A. Wheeler. 相似文献
14.
Thomas Filk 《International Journal of Theoretical Physics》2006,45(6):1166-1180
The famous “spooky action at a distance” in the EPR-scenario is shown to be a local interaction, once entanglement is interpreted as a kind of “nearest neighbor” relation among quantum systems. Furthermore, the wave function itself is interpreted as encoding the “nearest neighbor” relations between a quantum system and spatial points. This interpretation becomes natural, if we view space and distance in terms of relations among spatial points. Therefore, “position” becomes a purely relational concept. This relational picture leads to a new perspective onto the quantum mechanical formalism, where many of the “weird” aspects, like the particle-wave duality, the non-locality of entanglement, or the “mystery” of the double-slit experiment, disappear. Furthermore, this picture circumvents the restrictions set by Bell’s inequalities, i.e., a possible (realistic) hidden variable theory based on these concepts can be local and at the same time reproduce the results of quantum mechanics.
PACS: 03.65.Ud, 04.60.Nc 相似文献
15.
John G. Jenkin 《Physics in Perspective (PIP)》2011,13(2):128-145
In the 1930s Ernest Rutherford (1871–1937) repeatedly suggested, sometimes angrily, that the possibility of harnessing atomic
energy was “moonshine.” Yet, as war approached he secretly advised the British government to “keep an eye on the matter.”
I suggest that Rutherford did not really believe his “moonshine” claim but did have profound reasons for making it. If I am
correct, then this casts additional light on his personality, stature, and career. 相似文献
16.
Paul J. Werbos 《International Journal of Theoretical Physics》2008,47(11):2862-2874
The classic “Bell’s Theorem” of Clauser, Holt, Shimony and Horne tells us that we must give up at least one of: (1) objective
reality (aka “hidden variables”); (2) locality; or (3) time-forwards macroscopic statistics (aka “causality”). The orthodox
Copenhagen version of physics gives up the first. The many-worlds theory of Everett and Wheeler gives up the second. The backwards-time
theory of physics (BTP) gives up the third. Contrary to conventional wisdom, empirical evidence strongly favors Everett-Wheeler
over orthodox Copenhagen. BTP allows two major variations—a many-worlds version and a neoclassical version based on Partial
Differential Equations (PDE), in the spirit of Einstein. Section 2 of this paper discusses the origins of quantum measurement
according to BTP, focusing on the issue of how we represent condensed matter objects like polarizers in a model “Bell’s Theorem”
experiment. The backwards time telegraph (BTT) is not ruled out in BTP, but is highly speculative for now, as will be discussed.
The views herein are not anyone’s official views, but this does constitute work produced on government time. 相似文献
17.
We analyze the influence of Enrico Fermi’s theory of beta decay, which he formulated in December 1933, on his experimental
discovery of neutron-induced artificial radioactivity four months later, in March 1934.We discuss Gian Carlo Wick’s application
of Fermi’s theory in interpreting Frédéric Joliot and Irène Curie’s discovery of alpha-particle-induced artificial radioactivity,
and how Fermi was then influenced by his theory in planning his neutron-bombardment experiments, in his decision to use a
radon-beryllium (Rn-Be) neutron source, and in his choice of the elements he bombarded with Rn-Be neutrons. Our analysis is
based crucially on Fermi’s first laboratory notebook, the Hirpine Notebook, which is preserved in the Oscar D’Agostino Archives
in the Technical Institute “Oscar D’Agostino” in Avellino, Italy, and on the materials that are preserved in the Fermi Archives
in the Domus Galilaeana in Pisa. These documents enable us to reconstruct Fermi’s discovery of neutron-induced artificial
radioactivity and to assign an exact date to it of March 20, 1934. 相似文献
18.
Sara Lippincott 《Physics in Perspective (PIP)》2006,8(4):408-450
Robert F. Christy, Institute Professor of Theoretical Physics Emeritus at Caltech, recalls his wartime work at Los Alamos
on the critical assembly for the plutonium bomb (“the Christy bomb”); the Alamogordo test, July 16, 1945; the postwar concerns
of ALAS (Association of Los Alamos Scientists); his brief return to the University of Chicago and move to Caltech; friendship
with and later alienation from Edward Teller; work with Charles and Tommy Lauritsen and William A. Fowler in Caltech’s Kellogg
Radiation Laboratory; Freeman Dyson’s Orion Project; work on the meson and RR Lyrae stars; fellowship at Cambridge University;
1950s Vista Project at Caltech; his opposition to the Strategic Defense Initiative; and his post-retirement work for the National
Research Council’s Committee on Dosimetry and on inertial-confinement fusion. 相似文献
19.
E. Estrada 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(4):563-574
We study the property of certain complex networks of being both sparse and
highly connected, which is known as “good expansion” (GE). A network has
GE properties if every subset S of nodes (up to 50% of the nodes) has a
neighborhood that is larger than some “expansion factor” φ
multiplied by the number of nodes in S. Using a graph spectral method we
introduce here a new parameter measuring the good expansion character of a
network. By means of this parameter we are able to classify 51 real-world
complex networks — technological, biological, informational, biological and
social — as GENs or non-GENs. Combining GE properties and node degree
distribution (DD) we classify these complex networks in four different
groups, which have different resilience to intentional attacks against their
nodes. The simultaneous existence of GE properties and uniform degree
distribution contribute significantly to the robustness in complex networks.
These features appear solely in 14% of the 51 real-world networks studied
here. At the other extreme we find that ∼40% of all networks are
very vulnerable to targeted attacks. They lack GE properties, display skewed
DD — exponential or power-law — and their topologies are changed more
dramatically by targeted attacks directed at bottlenecks than by the removal
of network hubs. 相似文献
20.
As quantum information science approaches the goal of constructing quantum computers, understanding loss of information through
decoherence becomes increasingly important. The information about a system that can be obtained from its environment can facilitate
quantum control and error correction. Moreover, observers gain most of their information indirectly, by monitoring (primarily
photon) environments of the “objects of interest.” Exactly how this information is inscribed in the environment is essential
for the emergence of “the classical” from the quantum substrate. In this paper, we examine how many-qubit (or many-spin) environments
can store information about a single system. The information lost to the environment can be stored redundantly, or it can
be encoded in entangled modes of the environment. We go on to show that randomly chosen states of the environment almost always
encode the information so that an observer must capture a majority of the environment to deduce the system’s state. Conversely,
in the states produced by a typical decoherence process, information about a particular observable of the system is stored
redundantly. This selective proliferation of “the fittest information” (known as Quantum Darwinism) plays a key role in choosing
the preferred, effectively classical observables of macroscopic systems. The developing appreciation that the environment
functions not just as a garbage dump, but as a communication channel, is extending our understanding of the environment’s
role in the quantum-classical transition beyond the traditional paradigm of decoherence. 相似文献