3 ms·

Make use of the right-hand rule, which will suffice so long as they're not made of antimatter.

• ISL 7y ago
  How will they know we're not made of antimatter?
  • benj111 7y ago
    Aren't matter and antimatter a matter of perspective? If so haven't we just reintroduced the left/right problem.
    • ISL 7y ago
      Precisely.
  • raldi 7y ago
    If we're not sure both sides of the conversation are made of the same particles, the situation is hopeless.
  • FreeFull 7y ago
    As far as astronomers can tell, there is very little antimatter in the observable universe (If there was more, we'd see it anihilating with matter more).
  • naturlich 7y ago
    They didn't explode when we shook hands (/tentacles/general-graspy-bits)
• infogulch 7y ago
  GP is right. If aliens don't know about CP violation, there is no way to communicate rotational direction that preserves the absolute direction without some shared reference. Because CP-violation is actually the only detectable way to discern between right handedness and left handedness. That is, without CPv, we would have no way to know that we aren't in a hypothetical mirror universe with all rotations reversed. Every other physical interaction behaves identically left or right. So we have a few options to deal with our rotationally-challenged alien friends: 1. Hope they can parse far down enough into the dictionary to understand what CP is and either know it or can test it. 2. Communicate using a shared reference, like pointing out two quasars that rotate relative to each other. (Quasars are pretty good galactic reference points.) 3. As long as it doesn't affect giving directions, just don't worry about it, the physics works out the same. If we ever meet and they try to shake our left hand, well, they get their very own "oops I guess electrons are negative then" situation. "And that, kids, is why you always negate earth-radians before using them in a formula."
  • raldi 7y ago
    I don't follow. If we're communicating with aliens that we somehow know are made of matter, we tell them that right is the direction a horizontal wire carrying positive current away from us gets pushed by a vertical magnetic field.
    • yorwba 7y ago
      That just shifts the problem to specifying the direction of the magnetic field, and you can't use the concept of left vs. right in that definition without creating a circular dependency.
      • pbhjpbhj 7y ago
        Vertically up it's just too a higher local gravitational potential, no? Sure, we flip right-left when we look at things upside down, but that's a nuanced usage.
        • yorwba 7y ago
          How do you determine whether your magnetic field is pointing up and not down?
          • goldenkey 7y ago
            Closer and farther can be used to explain up and down.
            • yorwba 7y ago
              How do you use closer and farther to determine whether a magnetic field is pointing up or down? It's not like there are little arrows on magnetic field lines you can just look at.
  • sp332 7y ago
    Feynman suggested shining polarized light through a solution of glucose and water. This will rotate the plane of the polarization clockwise. https://en.wikipedia.org/wiki/Glucose#History https://en.wikipedia.org/wiki/Glucose#History