Lab tech’s undergrad experiment published in leading physics journal – “knowledge doesn’t do anything if you don’t share it”

It took Albert Einstein 24 years to publish his calculation for gravitational lensing.

Instructor and lab technician Daniel FitzGreen spent eight years turning Einstein’s calculation into a first-of-its-kind undergraduate physics experiment. FitzGreen then summarized his experiment in a single-author paper that was featured in the October edition of the American Journal of Physics.

The journal editor noted FitzGreen’s experiment can be added across the physics curriculum as a standard three-hour lab in an introductory course, a longer experiment in more advanced lab courses and as independent student project.

“It’s great to have this work out there and to know that others find it as neat, clever and interesting as I do,” says FitzGreen. “I knew this was something no one had done yet in any other undergrad lab. I think it’s important for everyone to publish the new things they’re doing – knowledge doesn’t do anything if you don’t share it.”

What FitzGreen is sharing is a pretty remarkable achievement, says colleague and associate professor Pat Clancy in the Department of Physics & Astronomy. “The American Journal of Physics is one of the top journals for physics education and innovative teaching techniques. It’s very rare for instructional assistants to publish in the journal. It’s also far from easy to bring astrophysics and general relativity to a benchtop experiment but that’s exactly what Dan has done. He’s creating a really unique learning experience for our students.”

Gravitational lensing is a headline-making cosmic phenomenon that happens when light from a distant background object passes a massive foreground object, like a black hole or galaxy cluster. When the background and foreground objects are in perfect alignment with Earth, the light bends into a glowing halo called an Einstein Ring. “It’s an extremely rare and awesome cosmic illusion,” says FitzGreen.

Einstein predicted gravitational lensing back in 1912, three years before publishing his general theory of relativity. He didn’t share the calculations he wrote in his notebook, believing gravitational lensing was unobservable and astrophysically unimportant. Rudi Mandl, an electrical engineer and amateur scientist disagreed, visited Einstein in 1936 and persuaded him to publish his calculation. Einstein relented and submitted a brief paper to the journal Science, telling the editor his paper was of little value and was only being submitted as a favour to Mandl.

“Some time ago, R. W. Mandl paid me a visit and asked me to publish the results of a little calculation, which I had made at his request. This note complies with his wish,” wrote Einstein.

It turns out Einstein got it wrong when he dismissed the importance of gravitational lensing. It acts as a natural magnifying glass, making it possible for astronomers to see objects in the early universe that would otherwise be invisible. Astronomers can also use lensing to map dark matter and find exoplanets beyond our solar system.

FitzGreen wanted an experiment where students could see gravitational lensing and apply the calculations Einstein created more than a century ago.

The experiment uses low-cost acrylic lenses to simulate the gravitational deflection of light. The fabricated lenses generate images that are analogous to modern observations of strong, weak, and microgravitational lensing. Students apply image analysis techniques from modern astronomy to the data they collect in the lab to determine the effective mass of the object used in the design of the lenses.

FitzGreen has designed and constructed more than a dozen physics experiments designed to give undergrads a preview of graduate studies and advanced research. He spent the better part of eight years perfecting his gravitational lensing benchtop experiment. “It was always there in the back of my mind – I’m not a fan of loose ends.” Before publishing his paper, the American Journal of Physics sent back a week’s worth of edits that further refined his experiment. Making the changes was time well spent, says FitzGreen.

Along with summarizing his experiment, FitzGreen provided instructional videos, notes, CAD files for lenses, ImageJ macros for image analysis, and Python code for designing lenses and collecting and analyzing data.

FitzGreen says the gravitational lensing experiment is the easiest he’s built at McMaster. “Once you have the acrylic lenses, all you need is a camera and a black dot on a white sheet of paper. That’s a big part of what makes this experiment so satisfying – nearly anyone anywhere can do it. The hardest part of the experiment is analyzing the data and making the calculations.”

The hardest part for students is what FitzGreen finds so rewarding as an instructor. “Nothing compares to seeing students initially struggle and then finally understand the connections between what they do with their hands in the lab and the equations and concepts they’re learning in class.”

FitzGreen has no immediate plans to turn another experiment into a paper. “Having said that, we have so much interesting work going on in the Physics Department that it would be easy to find a project to dig into. Soft matter physics, condensed matter physics and nuclear research are all very active fields right now for our department.”