Does anyone recall the name of a SF first contact story where humans encounter an alien ship, and use the weak force to define left and right. At the very end, as the human and alien space walk out to meet each other, the alien extends its left hand to shake ....

I first read this story in the late 1970's I believe. I recall the style as possibly being similar to Niven's, but cannot swear to that.

  • 3
    I ... think I understand why the revelation of the aliens being made of antimatter was made at the very end of the story...
    – akaioi
    Sep 22, 2017 at 1:14
  • @akaioi Hey, what does it matter why, as long as everyone lived happily ever after! PS I have a good feeling about this.
    – Misha R
    Apr 3, 2019 at 3:50
  • I have read your question and the two existing answers, and I can't figure out what they would both walk out on. Unless they are floating free in space, the ending comes before the handshake. Apr 3, 2019 at 17:27
  • @JamesJenkins Unless that, yes :)
    – Misha R
    Apr 6, 2019 at 4:26

2 Answers 2


Could this be a story within Beyond Einstein: The Cosmic Quest for the Theory of the Universe? - it was published in 1987 so too late for your given time frame and is non-fiction.

There is a chapter where they are explaining anti-matter and they are talking to aliens that do not understand clockwise, left and right nor up and down.

The humans on the radio explain north through the electrons of Cobolt-60 attracting to the north pole within a magnetic field. From this they understand the concept of clockwise.

Then they say what if we went to meet the aliens?

When the day comes, we meet and stick out our right hands. Suddenly, we notice that the aliens have stuck out their left tentacles. In a flash we realise that there's been a mistake. The aliens are actually made of anti-matter, who conducted an experiment on ticobolt-60 and measered the spin of anitelectrons that went south.

This story itself is based on a story told by the physicist Richard Feynman at Caltech in the 60s to illustrate a point about anti-matter and charge parity

Imagine you were in two-way contact with some alien species, but only by “telegraph” (i.e., light flashes or radio signals). The well known procedures of SETI (Search for Extraterrestrial Intelligence), starting with prime numbers and progressing to pictures, physics, and chemistry information could be used to develop a common language and arrive at a good level of communication.

You could tell the alien how tall you are by expressing your height in mutually understood wavelengths of light. You could tell the alien how old you are as some large number of ticks of a light-frequency clock. Now you want to explain how humans shake hands when they meet, and you describe extending your right hand. “Wait a moment!” says the alien. “What do you mean by ‘right’?”

Feynman also had a punch line to this story.

Suppose, after lots of communication you finally can go into space and meet your alien counterpart. If, as you approach one another, the alien extends its left hand to shake, watch out! He’s made of antimatter!

Here are the full Caltech Lecture Notes from Richard Feynman. Good read if you want to feel really unintelligent.

I cannot find a fiction story based on this story but hope it might point someone to the actual answer for you.

  • Yes, I won a copy of those Feynman Lectures while in High School - I still pick them up once or twice a year for fun reading. This phenomenon has been widely known in the Physics community since the 1960's, and is called the Ozma problem (physics.stackexchange.com/questions/61134/…), but I am still sure I first encountered it in the fiction story I am inquiring about: Feb 2, 2016 at 13:22
  • As I recall, when the ships first approach in orbit there is puzzlement on why the alien ship seems to be glowing slightly. Then only as it extends it's left hand does the reason for the glow occur to everyone on board. Feb 2, 2016 at 13:26
  • I have read the story in question and as I recall each ship sends someone out in a shuttlecraft. A man from the one ship and a woman from the other. They meet. To put it mildly, it does not go well. I am at the moment drawing a complete blank as to the title or author, but will return if it percolates to the surface. Oct 25, 2017 at 1:27

I was looking for a similar (the same?) story, and another user (Mike Stone) helped me identify it. The story I was looking for was "Chance Encounter" by Bertram Chandler. It was first published in New Worlds of Science Fiction #81 (March 1959). I must have come across it in Starships (1983), a short story collection edited by Asimov, et al. In the story, two ships--one made of matter, the other of anti-matter--meet up at the edge of the galaxy, and there's a huge explosion when a shuttle craft from the one ship meets up with a woman in a space suit from the other. But there's nothing in the story about using the weak force to define "left" and "right," so it might not be the one you're looking for. In "Chance Encounter," the two ships communicate by telepathy.

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