Spring 2018 – 497-219: Galilean Test of the Einstein Principle of Equivalence

Meeting Days/Time
Tuesdays and Thursdays from 3:15 to 4:30 pm
Jeff Terry (PHYS) (terryj@iit.edu) and Thomas Roberts (PHYS)
Appropriate Majors
Aerospace Engineering, Applied Mathematics, Computer Engineering, Computer Science, Electrical Engineering, Materials Science & Engineering, Mechanical Engineering, Physics, Information Technology & Management
Technological Innovation

Was Einstein right? We have an opportunity to find out by testing his theory of gravity. Our goal is to repeat Galileo’s famous experiment of dropping two different masses simultaneously from the leaning tower of Pisa –– but, in our case, with _picometer_ precision! (And we won’t bother going to Italy –– we’ll do the experiment right here at IIT.)

By using two test masses made of different materials, we’ll carry out a unique test of Einstein’s Principle of Equivalence, which underlies the generally accepted theory of gravity, General Relativity. The Principle of Equivalence is exactly obeyed in General Relativity, but any potential quantum theory of gravity seems likely to exhibit deviations, for which we hope to search.

The apparatus was designed and built by a team at Harvard and donated to us with the experiment uncompleted. Our challenge is to improve its measurement precision, which will require a bit of engineering.

A small vacuum chamber floats up and down on a polished granite pillar, riding on air bearings. A feedback loop controls a linear-drive electric motor to overcome friction and keep the test masses in free fall, while laser beams bounce back and forth to measure the distance between them. If the cart rides smoothly with no perturbations, picometer (or better) precision should be achievable. We will need to observe and measure the perturbations, identify their cause, and figure out how to eliminate or damp them down.

This IPRO project started in the spring 2016 semester and has continued since then, with significant progress being made. We will continue the installation and development of the experiment, which will involve inventing methods to support the cables and vacuum plumbing attaching to the vacuum cart in such a way that the cart can move up and down unimpeded. We will also continue experimental studies of our infrared-laser picometer-alignment system.

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