Video: Light Changes Color When It Falls

Is gravity secretly changing the color of light all around you? For 50 years, following Einstein’s publication of General Relativity, astronomers looked to the stars, hoping to confirm the prediction that the frequency of light changes when it travels up or down in a gravitational field. Einstein expressed the importance of this effect, “should [gravitational redshift] be absent, the whole theory should be abandoned.” The ingenious experiment that finally proved the effect was real didn’t involve looking to the sky, but instead looking just six stories upward through holes smashed through the floors of Harvard’s Jefferson Laboratory. This video brings us inside the building and the minds of the experimenters.

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Greg Kestin

    Greg Kestin holds a faculty position at Harvard University, where he conducts theoretical physics research, teaches, and produces educational online content. He earned his physics Ph.D. from Harvard, as a member of The Center for the Fundamental Laws of Nature, focusing on theoretical particle physics and quantum field theory. Over his career, he has also conducted research in nuclear physics, fusion energy, and gravitational wave physics. For over a decade he has been involved with innovative educational outreach endeavors, bringing science to both students and members of the public through his writings, videos, lectures, and multimedia.