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Albert Einstein
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Courtesy of Tracey Keifer. Emilio Segre Visual Archives. American Institute of Physics.

It Looks Like Einstein Was Right! Speed of Light and Gravity are Equal!
News story originally written on January 9, 2003

To make his most well-know theory, physicist Albert Einstein had to guess that the speed of gravity was equal to the speed of light. Now, scientists have found that he was likely right!

In 1915, Einstein developed his General Theory of Relativity to explain how gravity and motion can affect time and space. Today, Einstein’s theory is very important for many scientists trying to understand the Universe.

His theory assumes that the force of gravity acts at the same speed as the speed of light. The speed of light can be measured, but scientists found that it is very difficult to accurately measure the speed of gravity. While Einstein's assumption appeared to be true, it had never been tested in detail before now.

Scientists had the opportunity to test it when, on September 8, 2002, Jupiter passed in front of a distant quasar. The planet’s gravity made the quasar appear to move in the shape of an ellipse through the sky. The scientists used the shape of the quasar’s motion to calculate that the speed of gravity is nearly the same as the speed of light!


Last modified January 9, 2003 by Lisa Gardiner.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA