The speed of light on the Earth and in the gravity-free space

Author(s):  
Ting-Hang Pei
Keyword(s):  
Geophysics ◽  
2005 ◽  
Vol 70 (4) ◽  
pp. G95-G100 ◽  
Author(s):  
Changchun Yin ◽  
Greg Hodges

For the purpose of shallow-earth geophysical mapping, progressively higher frequencies have been developed for helicopter electromagnetic (HEM) systems. However, concern has been expressed about the vulnerability of high-frequency EM signals to the influence of the displacement current, especially the phase shift of the HEM signal resulting from the finite speed of light that describes the propagation of the EM wave in free space. In this paper we investigate the influence of the displacement current and the finite speed of light on HEM responses, based on a full solution of the EM field for a conductive, magnetically, and dielectrically polarizable earth half-space and an overlying half-space of air with free-space dielectric permittivity. We calculate the amplitude change and the phase shift of the HEM signal and the change in the apparent resistivity. We find that the displacement current, when both the air and the earth half-space assume the free-space dielectric permittivity, has a small influence on the HEM signal, while substantial influence may occur when the earth is dielectrically polarizable. The finite speed of the EM propagation in free space does not result in significant phase changes in the HEM signal.


Geophysics ◽  
1984 ◽  
Vol 49 (11) ◽  
pp. 2061-2063 ◽  
Author(s):  
James R. Wait

In a previous communication I proposed an analytical model to simulate the electromagnetic (EM) and induced polarization (IP) response of a metal well casing (Wait, 1983). To facilitate the analysis, the earth was idealized as a homogeneous conducting half‐space of electrical properties (σ, ε, μ). The well casing was represented as a filamental vertical conductor of semiinfinite length that was characterized by a series axial impedance to account for eddy currents and interfacial polarization. A further basic simplification was to neglect displacement currents in the air; this was justified when all significant distances were small compared with the free‐space wavelength. Initially, the source was taken to be a horizontal electric dipole or current element I ds on the air‐earth interface. By integration of the results, the mutual impedance between two grounded circuits could be ascertained. In the absence of the vertical conductor (i.e., the well casing) the results reduced to those given by Sunde (1968) and Ward (1967).


2012 ◽  
Vol 27 (07) ◽  
pp. 1250033 ◽  
Author(s):  
ICHIRO ODA

The OPERA Collaboration has announced to have observed superluminal neutrinos with a mean energy 17.5 GeV, but afterward the superluminal interpretation of the OPERA results has been refuted theoretically by Cherenkov-like radiation and pion decay. In a recent work, we have proposed a kinematical resolution to this problem. A key idea in our resolution is that the OPERA neutrinos are not superluminal but subluminal since they travel faster than the observed speed of light in vacuum on the earth while they do slower than the true speed of light in vacuum determining the causal structure of events. In this paper, we dwell upon our ideas and present some concrete models, which realize our ideas, based on spin 0, 1 and 2 bosonic fields. We also discuss that the principle of invariant speed of light in special relativity can be replaced with the principle of a universal limiting speed.


Lightspeed ◽  
2019 ◽  
pp. 49-57
Author(s):  
John C. H. Spence

The story of the astronomical observations of James Bradley in the eighteenth century, whose measurements of the small movements of a star throughout the year provided an independent estimate of the speed of the Earth around the Sun relative to the speed of light. His work provided the first experimental evidence in support of Copernicus’s theory that the earth is in motion, and against the idea that it is stationary at the center of the universe. His simple telescope at home, his brilliant idea and perseverance, and his life’s work and influence. The importance of his result for the development of Einstein’s theory of relativity and for theories of the Aether in the following centuries.


Lightspeed ◽  
2019 ◽  
pp. 18-26
Author(s):  
John C. H. Spence
Keyword(s):  
The Sun ◽  

The story of the first measurement of the speed of light by Ole Roemer in 1676. Galileo had discovered the moons of Jupiter with his new telescope, and proposed using observations of their eclipse every forty-two hours as a universal clock for our planet, since they could be seen from practically anywhere. This would keep track of the time at home, and so give a traveller his or her local longitude. (The King of Spain had offered a prize for longitude determination to avoid disasterous shipwrecks.) Roemer noticed that the eclipses were sometimes a little late, which he concluded was due to the time it took light to get from Saturn to Earth and the movement of the Earth between eclipses. His estimate of the time for light to travel from the Sun to Earth was quite accurate. Roemer’s remarkable life story and many other achievements are told.


1892 ◽  
Vol 51 (308-314) ◽  
pp. 98-101 ◽  
Keyword(s):  

The paper begins by recognising the distinction between ether in free space and ether as modified by transparent matter, and points ant that the modified ether, or at least the modification, necessarily travels with the matter. The well-known hypothesis of Fresnel is discussed and re-stated in modern form.


Geophysics ◽  
1963 ◽  
Vol 28 (3) ◽  
pp. 490-490
Author(s):  
D. Rankin

I am indebted to Weaver if he has indeed clarified certain points which I had previously considered to be obvious. Cagniard (1953) states explicitly the magnitude of the wavelengths in free space and it is further implicit in the work of Rankin (1962) that it is indeed this same electromagnetic field which is being considered. The plane wave aspect of the problem arises from the extent of and not the distance from the source so that truly it is the induction field and not the radiation field that is under discussion. I had believed, until this note by Weaver, that d’Erceville and Kunetz (1962) also considered a plane wave incident on the earth and in fact that I was merely following both Cagniard and d’Erceville and Kunetz in this matter. The consistency of the results would tend to confirm this belief.


1965 ◽  
Vol 21 ◽  
pp. 177-215
Author(s):  
Irwin Shapiro

A comprehensive review is given of the Earth-Venus measurements made with the Lincoln Laboratory Millstone radar in 1959 and 1961. The time-delay and Doppler shift data yield a value for the Astronomical Unit of 499.0052 ± 0.001 light-sec. Using 299 792.5 km/s for the speed of light leads to an AU of 149 598 000 ± 300 km. With the radius of Earth taken as 6 378.15 km, the solar parallax then becomes 8″.79416 ± 0″.00002. This value is consistent with measurements made at various other laboratories to about one part in 105.


2013 ◽  
Vol 22 (4) ◽  
pp. 345-349 ◽  
Author(s):  
Dan Lester

One of the primary goals of human spaceflight has been putting human cognition on other worlds. This is at the heart of the premise of what we call space exploration. But Earth-controlled telerobotic facilities can now bring human senses to other worlds and, in that respect, the historical premise of exploration, of boots on the ground, no longer clearly applies. We have ways of achieving remote presence that we never used to have. But the distances over which this must be achieved, by humans based on the Earth, is such that the speed of light seriously handicaps their awareness and cognition. The highest quality telepresence can be achieved not only by having people on site, but also by having people close, and it is that requirement that truly mandates human spaceflight. In terms of cost, safety, and survival, getting people close is easier than getting people all the way there. It is suggested here that to the extent that space exploration is best accomplished by achieving a sense of real human off-Earth presence, that presence can be best achieved by optimally combining human spaceflight to mitigate latency, with telerobotics, to keep those humans secure. This is culturally a new perspective on exploration.


2009 ◽  
Vol 87 (9) ◽  
pp. 999-1008 ◽  
Author(s):  
Victor de Haan

Two optical fiber Mach–Zehnder interferometers were constructed in an environment with a temperature stabilization of better than 1 mK per day. One interferometer consisted of a length of 12 m optical fiber in each arm, with the main direction of the arms perpendicular to each other while the other consisted of a length of 2 m optical fiber in each arm, where the main direction of the arms are parallel, and served as a control. In each arm, 1 m of fiber was wound around a ring made of piezo material, enabling the control of the length of the arms by means of an applied voltage. The influence of the temperature on the optical phase difference between the interferometer arms was measured. The temperature change induced a variation of the interaction region of the optical fiber couplers. Further, the influence of rotation of the interferometers at the Earth surface on the observed phase differences was determined. For one interferometer (with the long and perpendicular arms), it was found that the phase difference depends on the azimuth of the interferometer. For the other one (with the short and parallel arms), no relevant dependence on the azimuth has been measured.


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