# Allen I. Janis's research while affiliated with University of Pittsburgh and other places

## Publications (28)

Article
It is argued that Grn's criticism of our treatment of the rotating disk in special relativity is incorrect: Our results pertain to an acceleration program different from his but physically no less legitimate.
Article
Dirac's classical electrodynamics countenances "preaccelerations" of charged particles at a time t as mathematical functions of external forces applied after the time t. These preaccelerations have been interpreted as evidence for physical retrocausation upon assuming that, in electrodynamics no less than in Newton's second law, external forces sus...
Article
In classical electrodynamics, the imposition of Dirac's asymptotic boundary condition on the differential equation of motion for a charged particle leads to the prediction of preacceleration; that is, the particle's acceleration at time t depends on external forces acting at times later than t. Since force is usually considered to be the cause of a...
Article
All nondiverging algebraically special _boxclose\tilde \tau vanishes.
Article
Rebuttal is given to the criticisms of Cavalleri and Spinelli. It is shown that their point of view could lead to the conclusion that a test particle in Minkowski space moves with a speed approaching that of light. It is reaffirmed that a test particle in the Schwarzschild field crosses the Schwarzschild radius with a speed less than that of light.
Article
In his (1924; 1969), Hans Reichenbach discussed the status of a twodimensional spatial geometry on a disk rotating with respect to an inertial frame in the Minkowski space time of the special theory of relativity (‘STR’). Since then, the literature on this topic has grown very considerably.1
Article
Explicit nonspreading (i.e., characteristically propagating) solutions to a certain class of two-dimensional, hyperbolic, differential equations are found. This class of equations is a generalization of equations that arose in a study of radiation in cosmological backgrounds.
Article
A representation of tensors and spinors at a point of space-time as spin and conformally weighted functions on the unit sphere is derived. Methods for performing algebraic operations on tensors and spinors in this representation are discussed.
Article
The purpose of this investigation is to find the conditions for characteristic propagation of multipole radiation in Friedmann backgrounds. The radiation fields studied are Klein–Gordon scalar fields, conformally invariant scalar fields, electromagnetic fields, and gravitational fields. The behavior of electromagnetic and conformally invariant scal...
Article
All diverging algebraically special solutions of the complex vacuum Einstein equations which are left (or right) conformally flat (H-spaces) are found explicitly. These metrics contain four arbitrary functions of two variables. (AIP)
Article
It is often said that the speed of a freely falling test particle in the Schwarzschild field approaches the speed of light at the Schwarzschild radius. It is shown that this is not the case.
Article
Conditions are found that are sufficient to insure the development of trapped surfaces in space-times whose metrics satisfy the Einstein field equations in vacuum or in the presence of a massless scalar field. These conditions involve a topological requirement that a certain two-surface be compact and inequalities that must be satisfied by certain...
Article
A comparison is made of two ways of introducing auxiliary variables into Maxwell's equations. The first is the usual introduction of potentials. The second introduces twice the usual number of potentials. Although both formalisms lead to the usual vacuum-field equations when expressed in terms of the original variables (the components of the electr...
Article
Using the Newman‐Penrose spin‐coefficient approach to gravitational radiation, we consider necessary conditions for stationary‐radiative‐stationary transitions to occur between states in a Riemannian space‐time which satisfies the empty‐space Einstein field equations everywhere outside of a spatially bounded timelike cylinder. It is found that for...
Article
Simple solutions of the Einstein scalar and Brans-Dicke field equations are exhibited, and the nature of the Killing horizons of some static solutions is discussed.
Article
Properties of event horizons are examined for static, axially symmetric, vacuum space-times. Israel has shown that under fairly general conditions such horizons are singular. One would expect that a positive-mass point particle would correspond to a pointlike singular horizon. It is shown, however, that the horizons cannot be pointlike. The geometr...
Article
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Article
A first‐order quadrupole sandwich wave of gravitational radiation exploding from a first‐order Schwarzschild mass is examined to second order. If the second‐order field preceding the sandwich wave vanishes, it is shown that the region of space‐time following the sandwich wave contains a second‐order, imploding quadrupole wave. The rest of the secon...
Article
A method is presented for studying asymptotically flat spaces possessing both incoming and outgoing gravitational radiation at infinity. The method uses multipole expansions and the invariance of general relativity under time reversal; calculations are facilitated by a small‐parameter perturbation approach. Some calculations are carried out to seco...
Article
The purpose of this paper is to propose a definition of multipole structure of gravitational sources in terms of the characteristic initial data for asymptotic solutions of the field equations. This definition is based upon a detailed study of the corresponding data for the linearized equations and upon the close analogy between the Maxwell and the...
Article
It is shown that by means of a complex coordinate transformation performed on the monopole or Schwarzschild metric one obtains a new metric (first discovered by Kerr). It has been suggested that this metric be interpreted as that arising from a spinning particle. We wish to suggest a more complicated interpretation, namely that the metric has certa...
Article
A new approach is presented for defining and obtaining rigid frames of reference. The results are shown to be equivalent to those of Rosen. The advantage of the present approach is that exact solutions can be obtained in certain simple cases, as well as approximate solutions in general.
Article
We have investigated the effect that coordinate conditions and similar conditions will have on the formal properties of covariant theories. Two distinct types of coordinate conditions were included, those involving first derivatives of the field variables (such as the gauge condition of Lorentz and the coordinate conditions of De Donder) and those...
Article
In this paper we clarify a number of questions connected with the Lagrangian formulation of canonical transformations and commutator brackets. We make a distinction between "regular" and "singular" theories, the latter having such a structure that the Euler equations cannot be solved uniquely with respect to the accelerations. For "regular" theorie...

## Citations

... Furthermore, Frisch also ignores A. Grü nbaum's penetrating analyses of problems II and III (published in this very journal; cf. Grü nbaum 1976;and Grü nbaum and Janis 1977). This is the reason why we judge his presentation of CED to be partisan if not grossly misleading. ...
... As we shall see, the emission of radiation is always accompanied by the appearance of vorticity of world lines of observers. Furthermore, the calculations suggest that once the radiation process has stopped, there is still a remaining vorticity associated to the tail of the wave, which allows in principle to prove (or disprove) the violation of the Huyghens principle in a Riemannian spacetime (see [43][44][45][46][47][48][49] and references therein for a discussion on this issue), by means of observations. ...
Citing article
... On the one hand, we want to explore the combined effect of rotation and electric charge parameters on the topological number of black holes, on the other hand, for the general consideration of the solution of four-dimensional black holes in the pure Einstein-Maxwell gravity theory, in this section, we turn to investigate the topological number of four-dimensional Kerr-Newman black hole [26,27], whose metric and Abelian gauge potential are ...
... Moreover, in the paper by Bronnikov [8], a regularization of the static spherically symmetric configuration in the presence of a scalar field was considered. The solution is the regularized version of the Fisher solution [9], and it can be seen as an exact solution of general relativity in the presence of a self-interacting scalar field and of a magnetic field (it is important to note that the Fisher solution was rediscovered many times and studied in different contexts [10][11][12][13][14][15][16][17]). An interesting transformation between the phantom scalar field and the standard scalar field was obtained. ...
... Kr π α = 1 e ·g βγ ·u γ ·h βα = 1 e ·u β ·h βα , Kr π i = 1 e ·g kl ·u l ·h ki = 1 e ·u k ·h ki , (11) Kr s = 1 e · h u (g)(Kr)(u) = Kr s α · e α = Kr s i · ∂ i , ...
Citing article
... A hint about how to proceed in the general case can be found in a paper by Hansen, Janis et al [19] where a representation of a Minkowski vector at a point P as a function on the light cone of P is discussed. Given a vector U a at P, the authors associate a scalar U = U a l a to every null-vector l a at P with t a l a = 1, where t a is a future-pointing time-like unit-vector, the first member of an orthonormal basis at P. This defines a function U on the unit-sphere of nullvectors l a at P which automatically satisfies the equation ð 2 U = 0. ...
... Indubitably, the most important legacy of the 1965 singularity theorem is the fundamental notion of closed trapped surface, a certainly prolific idea with many applications. It is not only very useful in the general analysis of gravitational collapse, in the formation of black holes [2,17,18,19,33,90,79], and in cosmic censorship, numerical relativity (section 6) and isoperimetric inequalities (subsection 7.3), it has also become an object of interest for mathematicians -see for instance the use of trapped surfaces to prove the decay rate of gravitational radiation flux [80]-and it has evolved into a richer fauna of interesting "trapped-like" submanifolds with many geometrical and physical implications. ...
... Physically, they are the only quantities that lend themselves to observations in (conceptual) experiments that are constructed within the conceptual framework of the theory. (Bergmann & Janis, 1958). ...
... Bergmann and his school had discussed these matters clearly before and would do so again (Bergmann, 1949(Bergmann, , 1962Goldberg, 1958). While it seems to me that this clear understanding of the origins of the transport term should have been a reductio ad absurdum of the idea of 6 The paper by Bergmann, I. Goldberg, Janis and Newman (Bergmann et al., 1956) talks a good deal about invariant transformations (those changing the Lagrangian density by at most a divergence and hence preserving the Euler-Lagrange equations). This paper is worth mentioning here, but seems less relevant than the others and would require detailed study to identify where specific ideas about observables are presupposed. ...
... and the master equation reduces to the system of two equations Assume first the existence of null and proper homothetic vector 13 . With χ 0 = 0 one can always gauge away what implies Ω = 0. Then a proper homothetic vector takes the form K = 2χ 0 (x∂ x + y∂ y ). ...