I know there was a thread on this topic, but I don’t remember any keywords that search would recognize. So if you can point to the old thread, great.
The issue was/is: if all we had to communicate with some alien civilization was radio, how could we indicate to them the concepts of left and right?
The picture that was attached to one of the early planetary probes (I’m not sure which one – Voyager maybe) was designed to give some basic data about our solar system, planet, chemistry, etc., along with sound recordings of significant sounds in our culture. I was always amazed at how much was assumed about the intelligence and imagination of an alien species which might have next to nothing in common with us except the ability to send/receive radio transmissions.
That said, does anybody have a foolproof way of distinguishing left from right for some being that may not have a body anything like ours, a sun anything like ours, etc.?
There are certain chemical compounds that are left- or right-handed. You could easily say “orient the molecule of x so that the y atom is pointing directly at the ground. The z atom is on the left hand side.”
This sort of reply was among those on that old thread, IIRC. Do we have any reason to expect that sort of chemistry in an alien ecology? Also, do we have to assume the alien civilization has such additional technologies as microscopics?
Just FWIW, I was hoping to keep this discourse in the macro world to see if there’s something we overlooked in the old thread. (I don’t remember reading a convincing technique that didn’t require quantum mechanics or things at the very very small level.)
Even without chirality of molecules (and I can’t imagine a civilization capable of contact via radio that hadn’t developed microscopes or something like it (if they’re non-visual)), there are other effects, like the “right hand rule” in electromagnetism that would allow you to distinguish. Even the chirality of molecules manifests itself in macroscopic phenomena like polarization rotation (which you can build detectors for, even if you can’t see visible light).
There are plenty of chemical compounds that show this aspect. One or two should be known to any civilization that has radio (and by the time the messages get there, they’ll have further time to develop it.
You could also have them recreate the Parity experiment of Lee and Yang; we were able to do it in the 50s, so it shouldn’t be too hard, and by the time we asked the question, they’d be able to do it.
The problem with this is that while amongst biological systems on Earth there’s a consistent asymmetry in the molecules involved, it’s hardly obvious that even on a planet with a similarly consistent asymmetry that it goes the same way as on Earth. Chemistry on Earth would be exactly (with a minor caveat to be noted below) the same as it is now were all right-handed molecules to be swapped with left-handed ones and vice versa. What’s usually suggested (again with the caveat) is therefore that which of the two versions of the asymmetry is present on any particular planet is merely the result of an historical accident on that planet. In the standard thought experiment that Zelder is (vaguely) remembering, we can’t therefore be sure that the alien planet simply hasn’t all its chiral molecules reversed compared to the ones we’re used to. Even if they were reversed, all the laws of chemistry on that planet would be exactly the same as on Earth. We couldn’t thus use chemistry to establish whether their particular molecule was the same way round as ours.
The immediate problem with using something like the right-hand-rule is how do you agree what a positive magnetic field is.
You can use the beam you’re transmitting with to convey an agreement about right and left. Wiggle the beam in an agreed fashion for a start. Or, to pick up from CalMeacham’s example, use circular polarisation of the beam to define clockwise and anticlockwise. Once you agree on that, left and right are easy. However, the standard formulation of the philosophical problem here invariably rules out solutions that require both parties being able to observe the same object. That’s too trivial. And that includes schemes that rely on using the properties of the particular radio beam. Hence no wiggling or measuring polarisation.
Parity violation, as predicted by Lee and Yang, does get to the heart of the matter in that this does answer the problem as traditionally stated. You can explain to an alien civilisation what you’re defining as left and right, but it uses this rather subtle nuclear effect.
The classic discussion of the entire problem, including explanations of why it’s harder than it looks, how parity violation solves it, why this was bloody surprising back in 1956 and much else is still Martin Gardner’s oft-reprinted (and, at some point, revised) 1964 book The Ambidextrous Universe. Very, very highly recommended.
The caveat mentioned above? Some scientists (including, most notably, Abdus Salam) have occasionally suggested that parity violation in weak interactions has biased which way the symmetry in chemistry has spontaneously broken. If they are right, planets with biological molecules would tend to agree on matters of chirality. Personally, I’ve never been convinced: it’s a small effect that will have been washed out.