Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Formal statement of the right-hand rule?

  1. Jan 28, 2010 #1
    Is there a way to express the right-hand rule mathematically, without making references to... well, hands?
     
  2. jcsd
  3. Jan 28, 2010 #2

    Landau

    User Avatar
    Science Advisor

    Which right-hand rule exactly are you referring to? That rule concerning cross products?
     
  4. Jan 28, 2010 #3
    Yes, that's the one.
     
  5. Jan 28, 2010 #4

    Landau

    User Avatar
    Science Advisor

  6. Jan 28, 2010 #5
    I think that the right-hand rule is a consequence of the definition of the coordinate system. The three-dimensional euclidian vector space that is usually used in physics is by definition a "right-handed coordinate system". In other words, the versor products of the base 'i x j = k' , 'j x k = i' and 'k x i = j' are defined in this manner. In similar, the versor products in a left-handed coordinate system are defined: 'i x j = -k' , 'j x k = -i' and 'k x i = -j'.
     
  7. Jan 28, 2010 #6
    Apparently, every definition makes use of hands. I wonder if it's possible to define it without referring to that.
     
  8. Jan 28, 2010 #7
    Yes, but how is the "right-handed coordinate system" defined without reference to hands?
     
  9. Jan 28, 2010 #8
    You do not need to use hands.

    Use the duality between forms and vectors in Euclidean 3 space induced by the standard Euclidean metric.

    here are the steps:

    1) to each vector v associate its dual linear function, <v,>.

    2)Take the wedge product of these two dual forms. The wedge product is the oriented area element of the paralleogram spanned by the two vectors.

    3)Take the dual vector of the wedge product. This is the cross product.
     
  10. Jan 28, 2010 #9
    How? In the manner that I have defined in my prior post. In there I had established the cross products of the base of the space, it has not reference with hands or with the "common representation" of these base.
     
  11. Jan 28, 2010 #10

    LCKurtz

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Suppose you are in radio contact with an alien who "looks like us" in that he has an arm with a hand on each side of his body. You are trying to explain to him which side is his right side. I don't think it is possible unless there is some sort of asymmetric experiment you can ask him to perform, which I doubt. Even if he understood 3D and three mutually perpendicular axes, you couldn't explain which orientation is "right handed" either.

    I'm willing to be wrong about this though :uhh:
     
  12. Jan 28, 2010 #11
    You posted this in a mathematics folder, rather than a physics folder. If you had posted in physics we would refer handedness to measurable things like handedness in relation to the fingers on our hands, or the statistics of the weak particle decay.

    But in pure mathematics there are no physically measurable things. There is no reference to right-handed vs left-handed. They are simply duals of one another. We can call the labels anything we want. Left and Right are just labels to distinguish one from the other.
     
  13. Jan 29, 2010 #12

    Landau

    User Avatar
    Science Advisor

    As I said, not using the concept of oerientation. See wofsy's post.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook