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Testing Gravity

4. Testing the Universality of Free Fall

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In this mini-lecture, we explore experiments that test the universality of free fall, which can be used to test for Equivalence Principle violation. We introduce two ways to test the universality of free fall: dropping objects and using a torsion balance. We focus on the latter method as done at the University of Washington in Seattle, WA, focusing in particular on: (i) the rotating torsion balance setup, including images of the experiment; and (ii) the experiment’s results, which found no violation of the Equivalence Principle.


In this course, Professor Jens Gundlach (University of Washington) explores gravity, in particular, gravity experiments. In the first mini-lecture, we give an overview of how our understanding of gravity and the Universe has evolved from ancient to modern times, emphasising various experiments, observations and theories that developed along the way. In the second mini-lecture, we introduce the modern theory of gravity, General Relativity. The third mini-lecture explores the big picture of physics, discussing the incompatibility between General Relativity and the Standard Model, and how physicists are searching for a unifying ‘Theory of Everything.’ In the fourth and fifth mini-lectures we turn towards gravity experiments, including those done at the University of Washington. In particular, we discuss experiments that test for Equivalence Principle violation and precisely measure the gravitational constant G.


Jens Gundlach is a Professor in the Department of Physics at the University of Washington in Seattle, Washington. He was a recipient of the 2021 Breakthrough Prize in Fundamental Physics for precision fundamental measurements that test our understanding of gravity, probe the nature of dark energy, and establish limits on couplings to dark matter. Naturally, his research interests include experimental fundamental physics, however Professor Gundlach also conducts research in biophysics. In particular, he is interested in nanopore sequencing of DNA.

Cite this Lecture

APA style

Gundlach, J. (2022, January 12). Testing Gravity - Testing the Universality of Free Fall [Video]. MASSOLIT.

MLA style

Gundlach, Jens. "Testing Gravity – Testing the Universality of Free Fall." MASSOLIT, uploaded by MASSOLIT, 12 Jan 2022,

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