Relativity Lite

48 | Relativity Lite slice of time, which also contains a slice of the Earth and Sun cylinders at one time. This is the convention in figures 3 and 5. Note that a ray of light traveling through this warped spacetime must follow this warped contour. It will be bent by the warped spacetime it has to travel through. Figure 3 shows this bending in the solid yellow line. The dashed line shows the apparent position of the star as seen from Earth. Einstein’s 1915 paper “Explanation of the Perihelion Motion of Mercury from the General Theory of Relativity” predicted that light passing close to the Sun should be bent by 1.7 seconds of arc. * On May 29, 1919, the theory was confirmed by the team of F. W. Dyson, A. S. Eddington, and C. Davidson, who measured the deflection of 12 stars during a solar eclipse and obtained values of 1.98 ± 0.16 and 1.61 ± 0.40 seconds of arc. † It was this dramatic result that brought general relativity to the attention of the general public and made Einstein a media star. Modern telescopes reveal truly dramatic confirmations of the warping of spacetime by mass. The light from distant galaxies will be gravitationally lensed by an intervening galaxy or galactic cluster along the line of sight. This produces the arc-shaped images of the galaxy in the photograph that is figure 4. Figure 4. This massive cluster of galaxies, called Abell 2218, shows several arc-shaped patterns, which are duplicate images of galaxies that lie 5 to 10 times farther than Abell 2218. This is caused by the huge mass of the cluster warping the spacetime that the light must pass over, under, and around to reach the Earth. Credit: NASA, ESA, A. Fruchter, and the ERO Team (STScI, ST-ECF). ‡ * A. Einstein, Königlich Preußische Akademie der Wissenschaften (Berlin). Sitzungsberichte , 831–39 (November 18, 1915), https://​einsteinpapers​.press​.princeton​.edu/​vol6​-trans/​126. There are 3,600 seconds of arc (") in a degree. † F. W. Dyson, A. S. Eddington, and C. Davidson, Phil. Trans. Roy. Soc. 220A , 291 (1920); Mem. Roy. Astron. Soc. 62 , 291 (1920). ‡ NASA, ESA, A. Fruchter, and the ERO Team (STScI, ST-ECF), The Galaxy Cluster Abell 2218 , Hubble Space Telescope, https://​www​.spacetelescope​.org/​images/​heic0113c/ (accessed May 7, 2020).