Mirror Reversal Problem

In the following video, deceased (1988) American physicist Richard Feynman amuses himself with an old puzzle – why do mirrors seem to switch left and right, but not top and bottom?

7 Responses to Mirror Reversal Problem

  1. Yes, all serriousness aside, he was quite a man, no joke.

    HOWEVER, on this one issue of the mirror, I have dared to think he was wrong… or at least incomplete.

    There is a more complete answer to the mirror riddle.

    Anyone interested?


  2. .

    Hint: the HUMAN PERCEPTION of a reversal is far more complicated than the reversal of a photon's trajectory.

    The riddle can be slightly altered tp show this reversal perception is not being full addressed by stating it thusly:

    Why does a mirror SEEM to reverse left and right but it never seems to reverse up and down.



  3. .

    Well, I thought I'd wait to see if anyone would twist my arm to post the FULL answer, but I guess I'll have to do it myself. Ouch, ouch, OUCH! Ok, ok, I'll post it if you insist……


    A New Approach to an Old Problem Part 1 of 2

    The mirror reversal puzzle is not so much a matter of the science of light rays,? ?optics,? ?and the Physics behind mirror reflection,? ?but is far more a PEOPLE thing.?

    I’d say it can best be solved by a science of human activities,? ?a science that deals with how people interact with complicated or subtle things.? ?The structure of? “?reversedness?” ?in a human being’s mental imagery is far more subtle than the reversal of a photon’s trajectory.

    When people want to compare any two nearly identical objects for some subtle difference there are two common strategies they can use.? ?These two strategies are often useful,? ?but they are also oddly contradictory.


    In one strategy,? ?the two objects are lined up to face in the same direction before they are compared.? ?For instance,? ?if two nearly identical pens are to be compared,? ?no one I know of would ever hold one pen horizontally,? ?the other vertically,? ?and then proceed to compare them.? ?People commonly want hold them facing in the same direction for such a task.?

    When a person uses this strategy in the mirror situation they like to imagine themselves rotating about a vertical axis for a comparison with their image.? ?This rotation brings them to face the same direction as their earlier image was pointing.? ?This also requires them to mentally freeze their image as it was when they faced the mirror.? ?When ALL this is done,? ?the Left/Right reversal is obvious.?

    It can get a little complicated,? ?but many people seem to have the mental circuitry to perform all this in a near subconscious flash of imagery.? ?Verbalizing it is far more difficult and hardly anyone can hold on to the images long enough to do that.


    The second common human strategy for dealing with complicated situations,? ?is to freeze EVERYTHING,? ?avoid disturbing the scene,? ?and look at the situation? “?as is?” ?in order to perform an analysis of the subtle differences between two objects.? ?This is the classic Sherlock Holmes approach to a crime scene.

    In the mirror setup,? ?performing this? “?as is?” ?strategy means NOT rotating anything at all before doing the comparison between image and object,? ?and the Left/Right reversal fails to show up.? ?Instead,? ?a Front/Back reversal is apparent in this? “?as is?” ?comparison.

    to be continued


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