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The "Ozma problem" was coined by Martin Gardner in his book "The Ambidextrous Universe", based on Project Ozma. Gardner claims that the problem of explaining the humans left-right convention would arise if we enter into communication (by radio waves, no images allowed) with life on another planet. We can ask the aliens to perform any experiment they want. It is claimed that the classical experiments with magnets, electrical currents, light polarization, gyroscopes etc. can't solve the problem. The only simple experiment that solves the problem is the beta decay in which the parity is not conserved and this can be used to distinguish humans left-right spatial relations. But all this are quite old, the parity violation in weak interactions was experimentally proved in 50s by Chien-Shiung Wu. I was wondering if something has changed since then and if there are some other experiments (maybe some thought experiments) and theories that can solve the Ozma Problem.

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I tend to just look at the back of my hands with my fingers and thumbs straightened, the left hand makes a nice 'L' shape. Not sure this is going to work for those aliens though ;-) – qftme Jul 16 '11 at 16:48
It is still the case that the violations of charge-parity symmetry derives from the weak interactions only and so is most easily visible in nuclear decays and the like. Why only the weak interaction violates CP and not the strong force as well is still an open problem. – BebopButUnsteady Jul 17 '11 at 2:31
Violation of CP as well as simple P allows you to establish both an absolute handedness convention and whether you and you distant corespondent are the same or anti-matter with respect to one another. – dmckee Jul 18 '11 at 16:17
Re "no images allowed" -- I don't think this is quite the right way to put the restriction. The aliens can look at our TV signals and figure out how to put them into images (as in the movie "Contact"). But they have no way of knowing whether to flip the images, so it doesn't do them any good. I think what is more relevant is that we want to rule out any mutually observable outside point of reference (Andromeda Galaxy,...) or the physical transmission of handed stuff (radio waves are right-hand polarized,...) – Ben Crowell Jul 21 '11 at 3:30
Ben Crowell hit the nail on the head. If you want the aliens to figure out right/left via a fundamental physics experiment (i.e. a measurement of something we didn't prepare), then beta decay is probably the easiest way. But since your problem posits that we're communicating by radio waves, we can just send them circularly polarized radio waves, and tell them to measure how the electric field rotates in time with respect to the axis of propagation. – Anonymous Coward Jul 22 '11 at 17:38
up vote 4 down vote accepted

I haven't read that book, but I did read Feynman's discussion of (sounds like) exactly the same thing. Easy: Tell the aliens how to build a telescope, then describe the configuration of some galaxies near them. OK OK, but suppose we rule that out: We can't see any objects in common. Easy: Send them circularly-polarized radio waves (thanks @Anonymous Coward). OK OK, let's say our radio waves must be linearly polarized. Easy: Tell them to look at almost any phenomenon related to the weak force, for example the beta-decay of cobalt-60 in a magnetic field. But then there's one more catch--what if the aliens are made of antimatter and they actually were watching the beta-decay of antimatter-cobalt-60? In Feynman's discussion (if I recall correctly), that's where it ends: There's no way to be really sure that the aliens understand right and left correctly, because they may be made of antimatter.

But since 1964, when CP-violation was observed, we can even eliminate that possibility: We tell the aliens how to watch kaons decay (for example) and then the aliens can figure out whether they're made of (what we call) matter or antimatter, and therefore they can figure out which way is left and right without any more ambiguity. So I guess that aspect is a slight update from pre-1964 descriptions.

Watching atoms decay in a magnetic field is a pretty simple thing to do by the standards of particle-physics experiments. I don't know of any parity-violating experiments that are much simpler than that. It just has to involve the weak force.

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Can you explain how exactly they would figure out whether they are made of matter or antimatter from kaons decay? – Andyk Jul 30 '11 at 6:40
"OK OK, let's say our radio waves must be linearly polarized" Nah. We're going to switch Rigel on and off in Morse code... – dmckee Aug 1 '11 at 23:50
@ANKU -- Nope. I have a strong impression that it should be possible, but I don't enough to spell out the procedure. I suppose I could be wrong. Maybe someone more knowledgeable will help... :-) – Steve B Aug 3 '11 at 3:58

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