Gravitational red shift

Mossbauer resonance of Zn to study the influence of the gravitational field on electromagnetic radiation. A Ga ZnO source (4.2 K) was used at a distance of 1 m from an enriched ZnO absorber (4.2 K). A red shift of the photons by about 5% of the width of the resonance line was observed. The corresponding shift with Fe as Mossbauer isotope would be only 0.01%. The result is in accordance with Einstein s equivalence principle. Further gravitational red shift experiments using the 93.3 keV Mossbauer resonance of Zn were performed later employing a superconducting quantum interference device-based displacement sensor to detect the tiny Doppler motion of the source [66, 67]. 

Figure 3. Mass-radius relation for a pure HS described within the GM1 model and that of the HyS or SS configurations for several values of the Bag constant and ms = 150 MeV and as = 0. The configuration marked with an asterisk represents in all cases the HS for which the central pressure is equal to I The conversion process of the HS, with a gravitational mass equal to Mcr, into a final HyS or SS is denoted by the full circles connected by an arrow. In all the panels a is taken equal to 30 MeV/fm2. The dashed lines show the gravitational red shift deduced for the X-ray compact sources EXO 0748-676 (z = 0.35) and IE 1207.4-5209 (z = 0.12-0.23).

The 93-26-keV excited state of Zn has a lifetime of 9400 ns. This gives an unusually narrow Mossbauer linewidth of = 3T2 x 10 mm s. The potentially high precision which this offers promised spectacular results in measurements of, for example, the gravitational red-shift. However, the normal level of acoustic vibrations in the laboratory is greater than the natural linewidth, and consequently the first attempts to observe the resonance were unsuccessful [13]. 

Pound worked with his associate, Glen A. Rebka, Jr., carrying out an experiment using the Mossbaucr effect to measure the gravitational effects of electromagnetic radiation and to test (lie predictions of Einstein s theory of general relativity. Pound s experiments continued and results predicted the Red Shift discovery. 

The sensitivity of electronic configurations to gravitational fields offers an immediate explanation of the enormously different red shifts of light emitted by a quasar and by less massive objects, physically associated with the quasar. The furore [106] over the anomalous Fraunhofer lines of common metals in a quasar corona could also be defused by the conclusion that the electron configurations of elements within the quasar, and hence their spectroscopic properties, differ from their laboratory equivalents. The observed shifts are therefore not due to a fine-structure constant changing with time, but to the response of electronic energy levels to high pressure. 

The gravitational field that exists in the nebula causes a characteristic shift for each metal, which cannot be explained by assuming a constant red-shift for all metals. No other satisfactory explanation of the observed effect has been reported. Where others look at a time-dependent fine-structure constant or variable c or h to account for the modified spectra, we ascribe the observation to a simple response to space-time curvature. 

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