4 ms·

I would use the phenomenon of the "right hand rule" from electrical engineering as the frame of reference. This is a universal chirality inherent in the use of

by ryandvm 15y ago

I would use the phenomenon of the "right hand rule" from electrical engineering as the frame of reference. This is a universal chirality inherent in the use of electronics. And if we're communicating with them via radio waves, we can safely assume they're comfortable with the domain. Of course, that is assuming that they don't exist in some sort of weird bubble of the universe that operates with antimatter instead of regular matter (and is therefore using some mysterious positron-based "electricity"). I suppose if that were the case, our rendezvous would be disastrous anyway, so destruction of the gate would probably be the best possible outcome...

ColinWright 15y ago
Doesn't that require that you agree on what "North" and "South" mean with regards magnetic fields?
Symmetry 15y ago
But the direction of a magnetic field is an arbitrary convention. If we used the left hand rule consistently we would make all the same predictions for the forces exerted on particles thanks to two reversals cancelling out. Now, if the aliens were sending us transmissions through circularly polarized waveforms that would be different, that's a matter of observation rather than communication. Now, there is a phenomenon where if some particles decay in a magnetic field the products tend to have their products go in different directions depending on the magnetic field. This was a bit of a shock since physicists had assumed left-right symmetry until then. http://en.wikipedia.org/wiki/Asymmetry http://en.wikipedia.org/wiki/Asymmetry
- jerf 15y ago
  Circular polarization is the solution I immediately thought of as well, but I'm actually replying to put up this link: http://en.wikipedia.org/wiki/Circular_polarization http://en.wikipedia.org/wiki/Circular_polarization It has a nice animation of what it is. Using some form of symmetry breaking works too but is a much worse solution from an engineering perspective since the circular polarization is so much simpler and more direct. But it would work.
jessriedel 15y ago
Physics grad student here. Commenter Symmetry is right; there is no inherent chirality in electromagnetism. If we're really not allowing anything that could be construed as a common observation, I think the only thing is to exploit parity violation in the weak force. http://en.wikipedia.org/wiki/Parity_violation#Parity_violation http://en.wikipedia.org/wiki/Parity_violation#Parity_violati... Now, the weak force is pretty weak, so you usually have to do sensitive experiments to isolate it. But it's conceivable that there is macroscopic evidence of parity violation sitting around the cosmos which don't require common observation, e.g. maybe black holes have a slight statistical preference for clockwise vs. counter-clockwise jets. (Ultimately, such evidence would have to be traceable back to the weak force.) I'm not sure.
Jun8 15y ago
The right hand rule is simplistic (as the direction is arbitrary); however, using physical laws (assumed to be universal) is the way to, I think. Even if the aliens wouldn't understand our concept of left and right, if they are sufficiently advanced, their physical theories should contain the concept of symmetry (the mathematical concept, not the colloquial one), see this PSE questions and answers: http://physics.stackexchange.com/questions/2690/what-is-the-symmetry-which-is-responsible-for-conservation-of-mass http://physics.stackexchange.com/questions/2690/what-is-the-.... Once that commonality is established we can start to explain to them the everyday concept of symmetry and how we give different names to different directions of symmetry.

by ryandvm 15y ago

ColinWright 15y ago

Doesn't that require that you agree on what "North" and "South" mean with regards magnetic fields?

Symmetry 15y ago

But the direction of a magnetic field is an arbitrary convention. If we used the left hand rule consistently we would make all the same predictions for the forces exerted on particles thanks to two reversals cancelling out. Now, if the aliens were sending us transmissions through circularly polarized waveforms that would be different, that's a matter of observation rather than communication. Now, there is a phenomenon where if some particles decay in a magnetic field the products tend to have their products go in different directions depending on the magnetic field. This was a bit of a shock since physicists had assumed left-right symmetry until then. http://en.wikipedia.org/wiki/Asymmetry http://en.wikipedia.org/wiki/Asymmetry

jerf 15y ago
Circular polarization is the solution I immediately thought of as well, but I'm actually replying to put up this link: http://en.wikipedia.org/wiki/Circular_polarization http://en.wikipedia.org/wiki/Circular_polarization It has a nice animation of what it is. Using some form of symmetry breaking works too but is a much worse solution from an engineering perspective since the circular polarization is so much simpler and more direct. But it would work.

jessriedel 15y ago

Physics grad student here. Commenter Symmetry is right; there is no inherent chirality in electromagnetism. If we're really not allowing anything that could be construed as a common observation, I think the only thing is to exploit parity violation in the weak force. http://en.wikipedia.org/wiki/Parity_violation#Parity_violation http://en.wikipedia.org/wiki/Parity_violation#Parity_violati... Now, the weak force is pretty weak, so you usually have to do sensitive experiments to isolate it. But it's conceivable that there is macroscopic evidence of parity violation sitting around the cosmos which don't require common observation, e.g. maybe black holes have a slight statistical preference for clockwise vs. counter-clockwise jets. (Ultimately, such evidence would have to be traceable back to the weak force.) I'm not sure.

Jun8 15y ago

The right hand rule is simplistic (as the direction is arbitrary); however, using physical laws (assumed to be universal) is the way to, I think. Even if the aliens wouldn't understand our concept of left and right, if they are sufficiently advanced, their physical theories should contain the concept of symmetry (the mathematical concept, not the colloquial one), see this PSE questions and answers: http://physics.stackexchange.com/questions/2690/what-is-the-symmetry-which-is-responsible-for-conservation-of-mass http://physics.stackexchange.com/questions/2690/what-is-the-.... Once that commonality is established we can start to explain to them the everyday concept of symmetry and how we give different names to different directions of symmetry.