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Gravity Probe B

Testing Einstein's Universe

Special & General Relativity Questions and Answers

Is the amount by which light is bent important in cosmology?

Yes it is important, however the cosmological model itself already takes this into consideration. Big Bang cosmology is based on Einstein's theory of general relativity which incorporates the bending of light automatically as the trajectory of null geodesics. Gravitational lensing as it is called is an important effect which has been detected in a variety of circumstances. It was first seen for stars near the Sun's limb in the 1919 solar eclipse. It has also been detected in the distorted images of quasars 'lensed' by foreground galaxies along the line-of-sight to us. The number of these extragalactic lensed quasars is an important measure of the total mass density of the universe. If there were 'a lot' of galaxies, we should see many of these lensed objects at fainter and fainter levels. A careful statistical analysis on the number of these gravitational lens systems suggests a density of matter well below what is needed to close the universe.

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All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the NASA Astronomy Cafe, part of the NASA Education and Public Outreach program.