2 ms·

Why couldn't we just tell the aliens to observe the direction of the field lines of electromagnetism? We could define for them "lower potential energy direction

Why couldn't we just tell the aliens to observe the direction of the field lines of electromagnetism? We could define for them "lower potential energy direction" by describing gravity, then use that phrase for describing the motion of the electrons in a conducting wire around a magnetic coil.

griffzhowl 2y ago
How would that allow you to distinguish the coil from its mirror image?
- dotancohen 2y ago
  No coil, see my other comment here: https://news.ycombinator.com/item?id=41195886 https://news.ycombinator.com/item?id=41195886
jxy 2y ago
We chose a random direction as a convention, just as we chose a random charge as positive.
- dotancohen 2y ago
  No, the electrons actually move in the same direction always, just as a free falling object always moves towards the locally dominant mass. We could call the direction of electron movement "right".
  - snarkconjecture 2y ago
    It's the magnetic field that has the arbitrary sign convention. You can't determine the direction of a magnetic field from observations without using the right hand rule.
    - dotancohen 2y ago
      You don't have to know the sign, you could tell which way the electrons are going. We tell the aliens: you take all sorts of organics with liquid inside (on earth we typically use a lemon, but other organics will do), and put a stake of element 29 in one side and a stake of element 30 in the other. You then connect them with a length of element 29. Keep trying different organics until you find one that works. They might not have lemons, but there is a good chance that something will eventually work. You'd need to predefine what the atomic numbers mean and some other things, but we're already assuming some level of communication already being established so this aspect is not far-fetched.
      - pgalvin 2y ago
        Okay, I’ve got elements 29 and 30. Which side do I put each on? See the problem? :)
        dotancohen 2y ago
        No, it really doesn't matter. Have you never made a lemon or potato battery before?
        immibis 2y ago
        The electrons are flowing towards the element 29 side. Is that left or right?
        dotancohen 2y ago
        Now arrange the apparatus such that the element 29 side is near you, and the element 30 side is far from you. Additionally, ensure that the wire is up (further from the locally dominant gravitational mass). Now place an election between the "lemon" and the wire. See which way the election moved? That was right (or left, I don't remember).
        2y ago

griffzhowl 2y ago

How would that allow you to distinguish the coil from its mirror image?

dotancohen 2y ago
No coil, see my other comment here: https://news.ycombinator.com/item?id=41195886 https://news.ycombinator.com/item?id=41195886

jxy 2y ago

We chose a random direction as a convention, just as we chose a random charge as positive.

dotancohen 2y ago
No, the electrons actually move in the same direction always, just as a free falling object always moves towards the locally dominant mass. We could call the direction of electron movement "right".
- snarkconjecture 2y ago
  It's the magnetic field that has the arbitrary sign convention. You can't determine the direction of a magnetic field from observations without using the right hand rule.
  - dotancohen 2y ago
    You don't have to know the sign, you could tell which way the electrons are going. We tell the aliens: you take all sorts of organics with liquid inside (on earth we typically use a lemon, but other organics will do), and put a stake of element 29 in one side and a stake of element 30 in the other. You then connect them with a length of element 29. Keep trying different organics until you find one that works. They might not have lemons, but there is a good chance that something will eventually work. You'd need to predefine what the atomic numbers mean and some other things, but we're already assuming some level of communication already being established so this aspect is not far-fetched.
    - pgalvin 2y ago
      Okay, I’ve got elements 29 and 30. Which side do I put each on? See the problem? :)
      - dotancohen 2y ago
        No, it really doesn't matter. Have you never made a lemon or potato battery before?
        immibis 2y ago
        The electrons are flowing towards the element 29 side. Is that left or right?
        dotancohen 2y ago
        Now arrange the apparatus such that the element 29 side is near you, and the element 30 side is far from you. Additionally, ensure that the wire is up (further from the locally dominant gravitational mass). Now place an election between the "lemon" and the wire. See which way the election moved? That was right (or left, I don't remember).
        2y ago