# Physicist Uses Math To Avoid Traffic Penalty

After presenting a paper called “The Proof of Innocence,” California physicist gets let off the hook

We've never been falsely accused of a traffic violation, having earned every last second of our time before a judge, but when it does happen to us, we'll certainly want to brush up on our physics.

A California physicist fought the law when he was issued a traffic citation for running a stop sign. And with the help of a mathematical paper, the physicist argued his way out of the fine and has even won a prize for his efforts.

Dmitri Krioukov is a physicist based at the University of California in San Diego. When faced with a court hearing over allegedly driving through a stop sign, he put together a paper called The Proof of Innocence. The abstract for the paper reads: "A way to fight your traffic tickets."

The paper was awarded a special prize of \$400 that the author did not have to pay to the state of California.

Krioukov's argument is based upon the premise that three coincidences happened at the same time to make the police officer believe that he had seen the physicist run a red light, when, in fact, he hadn't. He writes:

"[In this paper], we show that if a car stops at a stop sign, an observer, e.g., a police officer, located at a certain distance perpendicular to the car trajectory, must have an illusion that the car does not stop, if the following three conditions are satisfied:

(1) The observer measures not the linear but angular speed of the car; (2) The car decelerates and subsequently accelerates relatively fast; and (3) There is a short-time obstruction of the observer's view of the car by an external object, e.g., another car, at the moment when both cars are near the stop sign."

As Physics Central explains, because the police officer was around 30m from the intersection where the stop sign was situated, "a car approaching the intersection with constant linear velocity will rapidly increase in angular velocity from the police officer's perspective."

The physicist even created graphs showing what would have happened to his angular velocity if he had either been driving at a constant linear velocity or had made a quick stop and then accelerated back to speed, which is what he claims happens (actually, he sneezed, causing him to brake harder than usual). It was during this sneeze stop that another vehicle obscured the police officer's view of Krioukov's car, argues the paper.

The conclusion of the paper? It isn't the police officer's fault but he/she was wrong as their "perception of reality did not properly reflect reality."

Bet that's a statement the other officers loved to remind them of.

You can read The Proof of Innocence here.

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