摘要:

It has been known for some time that the value &Lgr; of the vacuum energy density affects the propagation equation for gravitons — the analogue of photons for the gravitational field. (For historical reasons, &Lgr; is also called “cosmological constant”.) More precisely, if &Lgr; is not zero, then a mass term appears in the propagation equation, such thatm2=−&Lgr;. As a consequence, the polarization states of gravitons also change, because a massless particle has only two polarization states while a massive particle has more. This effect of the &Lgr;‐term has been confirmed by recent calculations in a curved background, which is actually the only proper setting, since solutions of the classical Einstein equations in the presence of a &Lgr;‐term represent a space with constant curvature. A real value for the mass (when &Lgr;<0) will show up as a slight exponential damping in the gravitational potential, which is however strongly constrained by astronomical data. The consequences of an imaginary mass (for &Lgr;>0) are still unclear; on general grounds, one can expect the onset of instabilities in this case. This is also confirmed by numerical simulations of quantum gravity which became recently available. These properties gain a special interest in consideration of the following. (1) The most recent cosmological data indicate that &Lgr; is positive and of the order of 0.1 J/m3. Is this value compatible with a stable propagation of gravitons? (2) The answer to the previous question lies perhaps in the scale dependence of the effective value of &Lgr;. It could then happen that &Lgr; is actually negative at the small distance/large energy scale at which the quantum behavior of gravitational fields and waves becomes relevant. Applications for an advanced propulsion scheme is that local contributions to the vacuum energy density (remarkably in superconductors in certain states, and in very strong static electromagnetic fields) can change locally the sign of &Lgr;, and so affect locally the propagation and the properties of gravitons. The graviton wavefunction, for different values of the parameters, may be characterized by superluminal phase velocity or by unitarity only in imaginary valued time. This may indicate a connection between gravitons and Faster‐Than‐Light travel. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649691

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We study the interplay of Einstein’s Gravitation (GR) and Maxwell’s Electromagnetism, where the distribution of energy‐momentum is not presently known (The Feynman Lectures, Vol 2, Chapter 27, section 4). As Feynman himself stated, one might in principle use Einstein’s equations of GR to find such a distribution. GR (born in 1915) presently uses the Levi‐Civita connection, LCC (the LCC was born two years after GR as a new concept, and not just as the pre‐existing Christoffel symbols that represent it). Around 1927, Einstein proposed for physics an alternative to the LCC that constitutes a far more sensible and powerful affine enrichment of metric Riemannian geometry. It is called teleparallelism (TP). Its Finslerian version (i.e. in the space‐time‐velocity arena) permits an unequivocal identification of the EM field as a geometric quantity. This in turn permits one to identify a completely geometric set of Einstein equations from curvature equations. From their right hand side, one may obtain the actual distribution of EM energy‐momentum. It is consistent with Maxwell’s equations, since these also are implied by the equations of structure of TP. We find that the so‐far‐unknown terms in this distribution amount to a total differential and do not, therefore, alter the value of thetotalEM energy‐momentum. And yet these extra terms are at macroscopic distances enormously larger than the standard quadratic terms. This allows for the generation of measurable gravitational fields by EM fields. We thus answer affirmatively the question of the title. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649692

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Unification of gravitation with other forms of interactions, particularly with electromagnetism, will have tremendous impacts on technology and our understanding of nature. The economic impact of such an achievement will also be unprecedented and far more extensive than the impact experienced in the past century due to the unification of electricity with magnetism and optics. Theoretical unification of gravitation with electromagnetism using classical differential geometry has been pursued since the late nineteen twenties, when Einstein and Cartan used teleparallelism for the task. Recently, Vargas and Torr have followed the same line of research with more powerful mathematics in a more general geometric framework, which allows for the presence of other interactions. Their approach also uses Ka¨hler generalization of Cartan’s exterior calculus, which constitutes a language appropriate for both classical and quantum physics. Given the compelling nature of teleparallelism (path‐independent equality of vectors at a distance) and the problems still existing with energy‐momentum in general relativity, it is important to seek experimental evidence for such expectations. Such experimental programs are likely to provide quantitative guidance to the further development of current and future theories. We too, have undertaken an experimental search for potential electrically induced gravitational (EIG) effects. This presentation describes some of the practical concerns that relates to our investigation of electrical influences on laboratory size test masses. Preliminary results, appear to indicate a correlation between the application of a spatially inhomogeneous electric field and the appearance of an additional force on the test mass. If confirmed, the presence of such a force will be consistent with the predictions of Vargas‐Torr. More importantly, proven results will shed new light and clearer understanding of the interactions between gravitational and electromagnetic effects. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649693

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Flyer acceleration by ablation plasma pressure produced by irradiation of intense pulsed ion beam has been studied. Acceleration process including expansion of ablation plasma was simulated based on fluid model. And interaction between incident pulsed ion beam and a flyer target was considered as accounting stopping power of it. In experiments, we used ETIGO‐II intense pulsed ion beam generator with two kinds of diodes; 1) Magnetically Insulated Diode (MID, power densities of <100 J/cm2) and 2) Spherical‐focused Plasma Focus Diode (SPFD, power densities of up to 4.3 kJ/cm2). Numerical results of accelerated flyer velocity agreed well with measured one over wide range of incident ion beam energy density. Flyer velocity of 5.6 km/s and ablation plasma pressure of 15 GPa was demonstrated by the present experiments. Acceleration of double‐layer target consists of gold/aluminum was studied. For adequate layer thickness, such a flyer target could be much more accelerated than a single layer. Effect of waveform of ion beam was also examined. Parabolic waveform could accelerate more efficiently than rectangular waveform. Applicability of ablation propulsion was discussed. Specific impulse of 7000∼8000 seconds and time averaged thrust of up to 5000∼6000N can be expected. Their values can be controllable by changing power density of incident ion beam and pulse duration. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649694

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The essence of any propulsion concept is to overcome gravity. Anti‐gravity is a natural means to achieve this. Thus, the technology to pursue anti‐gravity, by using superheavy elements, may provide a new propulsion paradigm. The theory of superluminal relativity provides a hypothesis for existence of elements with atomic number up to Z = 145, some of which may possess anti‐gravity properties. Analysis results show that curved space‐time exists demonstrating both gravitic and anti‐gravitic properties not only around nuclei but inside the nuclei as well. Two groups of elements (Z < 64 and 63 < Z <145) exist that demonstrate these capabilities. The nuclei of the first group of elements have the masses with only the property of gravity. The nuclei of the elements of the second group have the masses with both properties: gravity and anti‐gravity in two different ranges of curved space‐time around the nuclei.. The hypothetical element with Z = 145 is the unique among all elements whose nucleus has only anti‐gravity property. It is proposed that this element be namedHawking, in honour of Stephen W. Hawking. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649695

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The Power Chips technology employs a gap of 4–10 nanometers in a gap diode to allow for efficient thermal conversion with very low thermal leakage. The design &Dgr;T is on the order of 400 degrees single stage, with operation possible from 1 K to 1600 K, depending on configuration and meeting engineering challenges. Efficiency is projected to be in the range of 70&percent; of Carnot‐defined maximum. R&D work on this approach has been in progress since 1997. The main technical challenge of fabricating and maintaining the required gap has been overcome; thin film and packaging issues remain. The technology is anticipated to be ideal in terms of size, weight, efficiency, and reliability. Power Chips can be packaged identically as conventional thermoelectrics making them a drop‐in replacement in many cases including RTGs. Applications for Power Chips include RTGs as well as thermal conversion from a waste heat stream or solar‐thermal conversion. This paper was originally published without all of the proper acknowledgments. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649696

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

A review of various technologies discussed by Dr. Robert Forward is presented as a tribute to Dr. Forward, and is based on selections from his writings and those of subsequent investigators. Some emphasis is placed on the new frontiers of space propulsion, power and communication. Many of these concepts and technologies are presented within the STAIF 2004 “1st Symposium on New Frontiers and Future Concepts.” These range from highly speculative notions to hardware that has now been demonstrated in space flight. Among these concepts and technologies to be discussed are future communications, antimatter propulsion, space elevators and tethers, beamed energy propulsion, and emerging gravity theories and concepts. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1649697

出版商:AIP    

年代:1904

数据来源: AIP