The Ultimate Riddle

Posted on February 2, 2010 by Gil Kalai

 Click on the picture!

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16 Responses to The Ultimate Riddle

  1. Ori Gurel-Gurevich says:
    February 3, 2010 at 1:15 am

    Gil, whom did you hear this from?

    I assume it was recently, and just wondered whether it’s got anything to do with me showing this trick to several mathematicians in a conference last May.

    Reply

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  3. daveagp says:
    February 3, 2010 at 10:47 am

    There is a related trick I learned of in grad school: tie both of your shoe laces together, then you have to turn your pants inside out. I am grad that one is not available on YouTube!

    Reply
  4. Gil Kalai says:
    February 3, 2010 at 4:32 pm

    Ori, well, I remember a dinner 7-10 years ago at New Haven with John Conway demonstrating it and Hillel Furstenberg trying to repeat it, but I think I already knew this even before the dinner. I dont remember for sure.

    Reply
  5. Gil says:
    February 5, 2010 at 1:11 am

    Is there a simple explanation why when you do it one way it works and when you do it the other way it does not work?

    Reply
  6. Ori says:
    February 5, 2010 at 11:05 am

    Gil: just wondering whether it was a coincidence.

    Reply
  7. Gil says:
    February 5, 2010 at 11:09 am

    Dear Ori, Coincidences is a tricky subject to study and even to define. (But extremely interesting and rather important.) Whom did you hear this trick from?

    Reply
  8. Ori says:
    February 5, 2010 at 11:13 am

    Gil: I’ve known it since childhood, perhaps from my father, I should ask him.

    Reply
  9. Gil says:
    February 5, 2010 at 11:29 am

    Ori, Do you think this trick has a mathematical flavour?

    Reply
  10. Ori says:
    February 5, 2010 at 9:11 pm

    I don’t know about flavor, but it certainly has mathematical aspects.

    GK: What aspects?

    Reply
  11. Tom says:
    February 21, 2010 at 11:34 pm

    The simplest way I can explain it is: when you are touching your nose, your arms are crossed and one of them is on top (say the left one). In order for the trick to succeed, the left index finger must be on top of the right index finger. Thus, when you start the trick, you mix your fingers in such a way that the left index finger is below the right one, and it will come up on top when you twist.

    Reply
  12. Tom says:
    February 21, 2010 at 11:53 pm

    Equivalently, if the left (resp. right) arm is lower when you start the trick, then the left index finger (resp. right) must also be lower.

    Reply
  13. Ori says:
    March 25, 2010 at 8:16 pm

    A related trick (and afterward the coolest card trick ever).

    Reply
  14. jonas says:
    April 17, 2010 at 10:34 pm

    To daveagp: can’t you just take off your shoes with the laces still tied?

    Reply

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