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It Looks Like Einstein Was Right! Speed of Light and Gravity are Equal! - Windows to the Universe

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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, Einsteinís 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 planetís gravity made the quasar appear to move in the shape of an ellipse through the sky. The scientists used the shape of the quasarís 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 by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF