September 4, 2011 | 14
In a recent post, I proposed a riddle on handedness and how one could communicate one’s notions of left and right to faraway aliens. It should perhaps surprise no one that the way I formulated the riddle was just a more cumbersome and less elegant version of one that Richard Feynman presented to Cornell students in 1964, as I found out thanks to our Blog Network Czar, Bora Zivcovic.
“Suppose that we were in a telephone conversation with a Martian, or an Arcturian or something,” Feynman said in his lecture. “We don’t know where he is and we would like to describe things to him.” One way to establish a communication, Feynman points out, is to start from the basics, and there’s nothng more basic than integer numbers (the same idea that Carl Sagan later exploited in Contact).
At some point, though, we presumably have learned how to communicate, and the Martian is curious to learn about us. “Suppose that he says, ‘You fellas’–after we get familiar with him–’You’re very nice; now I’d like to know what you look like.’”
Describing features such as body size would be easy, Feynman points out, because we could appeal to facts about the world that are the same everywhere–for example the size of a hydrogen atom.
But the Martian wants to know more. “And he says, ‘That’s very interesting; what do you look on the inside?’ So we describe the heart and so on, and we say, ‘Now, put the heart on the left side.’ Now the question is, how can we tell him which side is the left side?”
One point of reference we might be tempted to use is that of biochemistry. “‘Aw, you take beet sugar, see, and you put it in water, and it turns.’ Only trouble is, he has no beets up there.” Here, Feynman was referring to the fact that when polarized light goes through a solution of water and sucrose its polarization twists.
That effect is due to the fact that sucrose comes in two varieties whose molecular structures are mirror images of each other, and which have opposite effects on the polarization of light. (An even mix of the two has no effect on light.) All sucrose of biological origin is of the same variety, called right-handed, but we have no way of knowing if the aliens’ sugars–assuming they have any–have the same handedness as ours do.
The same is true of proteins and DNA. “We have no way of knowing … whether the accidents of evolution would have started with maybe the wrong-headed threads: there’s no way to tell.” (Incidentally, that is one reason why it would be a bad idea to eat alien pizza before doing some chemical analysis.)
Feynman’s lecture, entitled “Symmetry in Physical Law,” was part of a cycle of lectures he gave at Cornell in 1964 called “The Character of Physical Law,” which can be watched in full on a Microsoft educational web site. You can jump to section 11 of the lecture to see the part about handedness. But I recommend watching the whole thing. The presence and wits and charisma of the man were just extraordinary.
Spoiler alert: after talking about sugar Feynman proceeds to give away the solution to the riddle, which was based on physics that at the time was very new, having been discovered in 1957. (More details on that in a follow-up post.) Had he given the same lecture ten years before, one can only wondered what he would have said–perhaps, simply that there was yet no known way of telling left from right using the laws of physics.
To be continued!
The New Ambidextrous Universe: Symmetry and Asymmetry from Mirror Reflections to Superstrings: Third Revised Edition. By Martin Gardner. 2005.
The Handedness of the Universe. Roger A. Hegstrom and Dilip K. Kondepudi in Scientific American, Vol. 262, pages 108-115; January 1990.
Alien Pizza, Anyone? Davide Castelvecchi in Science News, Vol. 172, No. 7, pages 107-; August 18, 2007
Secrets of the Universe: Past, Present, FutureX