stern@bnl.UUCP (eric) (06/09/85)
> > An interesting, related bit of trivia is the fact that "left" and > "right" are concepts which can only be communicated among two > parties if both parties can "see" each other. In other words, if > we ever contact an alien civilization which is so far away that we > can communicate with them only by radio, and there is no astronomical > object which both we and they can view, then we would have no way to > tell them what we mean by "left" as opposed to "right"--or, for that > matter, how to tell the north pole of a magnet from the south pole. This is not strictly true, because parity and charge conjugation or not conserved quantities. T.D. Lee in his book "Particle Physics and Introduction to Field Theory", discusses the case of two advanced civilizations who can communicate using only unpolarized electromagnetic radiation. If further contact were to be possible, the two civilizations would have to decide on the sign of the proton, and the definition of left and right. The answer lies in the breaking of symmetry between matter and antimatter, and between left and right, in weak interactions. A physicist in a alien civilization could decide whether his/her/its world was made of matter or antimatter by looking at the decay of the long-lived neutron kaon. The neutral K has semileptonic three body decay modes K -> e+ pi- nu, and K -> e- pi+ nu, with the ratio between the decay rates of 1.00648 +- 0.00035. Thus, if the alien physicist observed a larger decay rate for the channel with the electron that has the same sign as the proton, he/she/it knows that the world is made of matter. Determining left from right is a simple matter, after the sign of the proton charge is pinned down. The spin of the neutrino is always pointing opposite to its direction of motion. The convention of the direction of spin determines clockwise and counterclockwise, from which it is easy to figure out what left and right should be. The nonconservation of Charge-conjugation and parity (CP) was discovered in 1964 by Cronin and Fitch, see Phys. Rev. Lett. 13, 138(1964). Nonconservation of parity was proposed theoretically be Lee and Yang in 1956 and confirmed experimentally by two groups under the leadership of C.S. Wu and L. Lederman. Eric G. Stern Dept of Physics, SUNY StonyBrook, NY 11794 stern@bnl.arpa stern@bnl.bitnet ...!philabs!sbcs!bnl!stern
roy@gitpyr.UUCP (Roy Mongiovi) (06/14/85)
> the two civilizations > would have to decide on the sign of the proton, and the definition of > left and right. The answer lies in the breaking of symmetry between > matter and antimatter, and between left and right, in weak interactions. Um, this is totally off the wall, but since QM is so observer oriented, what if the alien's TOTALLY different interpretation of the universe doesn't have particles? Is such a thing even wildly possible? -- Roy J. Mongiovi. Office of Computing Services. User Services. Georgia Institute of Technology. Atlanta GA 30332. (404) 894-6163 ...!{akgua, allegra, amd, hplabs, ihnp4, masscomp, ut-ngp}!gatech!gitpyr!roy The Map is Not the Territory
scent@sask.UUCP (Scent Project) (06/16/85)
> > > > An interesting, related bit of trivia is the fact that "left" and > > "right" are concepts which can only be communicated among two > > parties if both parties can "see" each other. > ... > A physicist in a alien civilization could decide whether his/her/its > world was made of matter or antimatter by looking at the decay of > the long-lived neutron kaon. The neutral K has semileptonic three > body decay modes K -> e+ pi- nu, and K -> e- pi+ nu, with the ratio > between the decay rates of 1.00648 +- 0.00035. Thus, if the alien physicist > observed a larger decay rate for the channel with the electron that > has the same sign as the proton, he/she/it knows that the world is > made of matter. Determining left from right is a simple matter, after ^^^^^^ > the sign of the proton charge is pinned down. The spin of the neutrino > is always pointing opposite to its direction of motion. The convention > of the direction of spin determines clockwise and counterclockwise, > from which it is easy to figure out what left and right should be. > Don' sound simple to me! [:-)] Ken McDonald