The Laws of Physics, Officer, Outrank the Laws of California

By Veronique Greenwood | April 18, 2012 9:38 am

I think this picture says it all, officer. Clear as day!

To all those police officers out there on traffic duty: Be real careful about ticketing physicists. You might be proven wrong in elaborate mathematical detail.

Dmitri Krioukov, a physicist at UC San Diego, was pulled over for running a stop sign. However, he had not in fact run it, and his sense of injustice was apparently so inflamed that he undertook a rigorous mathematical explanation of what had happened, eventually posting a paper on the ArXiv showing that the police officer had fallen prey to a perceptual illusion (although the paper was posted on April 1, if it’s a joke, Krioukov is sticking to his guns; he’s spoken to PhysicsCentral about the work). At the stop sign, he had seen Krioukov’s car, a Toyota Yaris, disappear on the far side of a station wagon in the lane closest to the officer and subsequently accelerate away, but he mistakenly concluded that Krioukov had not stopped during that moment, because—this is the clincher—he had been visually measuring not the linear but the angular speed of the car! To put it in Krioukov’s own words:

“Police officer O made a mistake, confusing the real spacetime trajectory of car C1—which moved at approximately constant linear deceleration, came to a complete stop at the stop sign, and then started moving again with the same acceleration, the blue solid line in Fig. 5—for a trajectory of a hypothetical object moving at approximately constant linear speed without stopping at the stop sign.”

“However, this mistake is fully justified, and it was made possible by a combination of the following three factors:
1. O was not measuring the linear speed of C1 by any special devices; instead, he was estimating the visual angular speed of C1;
2. the linear deceleration and acceleration of C1 were relatively high; and
3. the O’s view of C1 was briefly obstructed by another car C2 around time t = 0.

Basically, he both stopped and started his car so quickly that, to someone observing from the far side of a large vehicle, he essentially looked like he never stopped moving. To err is human, though, and Krioukov munificently allows that through no fault of his own, “the O’s perception of reality did not properly reflect reality.”

Krioukov did not have to pay the fine of $400. He does not say, however, whether that’s because the judge found his argument sound, or because the judge took one look at the paper, blanched, and let him off the hook.

He also mentioned to PhysicsCentral that he wanted readers to test the strength of his argument. If you see something amiss in the paper, post in the comments.

Image courtesy of Krioukov

CATEGORIZED UNDER: Crime & Punishment
  • Fly_ry_guy

    Aren’t you supposed to stop for a full three seconds? Seems he couldn’t have done that. Not sure the laws in Cali, but where I live it’s a complete stop for 3 full seconds.

    • Scáthach

       Nope. No 3 seconds. You just need to make a full and complete stop.

  • Teddy

    A stop is usually defined as a cessation of forward motion not a time limit. However this guy should have been ticketed for reckless driving. In order to conform to his paper he would have to decelerate at about 1 g and then accelerate at 1 g.  This is about the limits of what you can do in a normal car. He either came to a panic stop and then floored it or more likely, he concocted the paper to escape a $400 dollar fine.

    • Crookedlake

      Try taking a physics class and understand what he is talking about 

      • Scáthach

         I am starting to wonder if you are Krioukov checking up on what people are saying about the story and paper. Frankly it was a waste of time. The officer did not actually see Krioukov’s vehicle stop or not stop. The station wagon blocked his view. No see em’, no ticket. Best excuse for beating a ticket in court.

  • fgoodwin

    Is he claiming car 2 also “rolled” through the intersection?  Because if it didn’t, then I don’t buy his bogus April Fool’s Day argument.  

    He snowed the judge with a crapified, techy-looking argument on the assumption that neither the judge nor the officer would have a clue what he’s talking about, and he did indeed get lucky.

    • Crookedlake

      Take a physics course before you comment

  • anon

    fgoodwin; car2 was on a different, parallel street altogether–one without a stop sign. Mad skills to this guy for getting away with this. I’m not an expert on math or physics, but it would make sense if he didn’t stop for the full required amount of time, and just happened to get lucky with his physics-babble. 

    • Jennifer McGaffey

       That’s not what the diagram shows – it says c2 was in Lane #2. No idea how accurate the physics are (and CrookedLake, if there’s something we’re missing, try explaining rather than dismissing) – the diagram lacks considerable info, like the angles (the distance from the officer to the street with the stop sign) and speeds involved.

  • Scáthach

    As a former law enforcement officer I can say or a fact that the cop was wrong and no physics paper is required to prove it. A traffic ticket is an infraction and for an officer (California law) to cite an individual, the officer has to witness the infraction.

    In this case, “Krioukov’s vehicle …disappeared on the far side of a station
    wagon in the lane closest to the officer.” This means that that the officer did not actually see Krioukov’s vehicle violating the law because his view was blocked by the station
    wagon. The officer made an assumption and broke the rules by issuing a ticket. I have a feeling that this is the real reason the judge tossed the case but I am sure this paper gave everyone, except the officer, a good laugh.


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