CCNY senior Refath Bari publishes first paper in peer-reviewed journal The Physics Teacher

City College of New York physics senior Refath Bari has published his first academic paper, "Simulating the Action Principle in Optics," in the peer-reviewed journal, The Physics Teacher. An undergraduate publishing a paper in a prestigious peer-reviewed journal is a rarity.

"We see light reflecting off mirrored surfaces, and it always appears to move in a straight line," said Bari. "But put a pencil in a glass of water, and the pencil appears to be bent," said Bari.

Light appears to obey one law at one moment and a different law at another. The Principle of Least Action, (PLA) is the single unifying principle in how light behaves. Light gets where it's going via the fastest route possible, which is not always a straight line.

Bari began delving into the PLA in 2021. Two years later, he published his first academic paper.

With this paper, said Bari, he wanted to describe the PLA and create a mathematical tool to simulate the PLA that solves numerically the famous brachistochrone problem, posed by Johann Bernoulli in 1696: What is the path of quickest descent between two points in an arbitrary gravitational field?

Bernoulli’s insight demonstrated that the mechanical problem of determining the quickest path was equivalent to the optical problem of determining the path light pursues in any non-homogenous medium, such as the Earth's outer atmosphere.

"As physicist Richard Feynman said, it's almost as if light 'smells all paths' and selects the path that takes the least action," said Bari.

The economy of light is like commuting on a busy freeway. Sometimes the fastest route is not the freeway in the midst of a traffic jam. The circuitous surface road may get you there in half the time.

Bari created a computational tool to give students an intuitive feel for the PLA. He wrote a program which students could use to simulate the consequences of PLA in geometric optics. "It demonstrates what we think we know about light is not the whole story," said Bari.

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