Define "left".

[Colophon]

To be honest, once you start getting to the basic “assume no knowledge of anything” level, it’s impossible to define just about anything.

– A table? Well, it’s a piece of furniture, usually with four l…

– What’s “furniture”?

– Well, it’s… that’s not important right now. A table is a thing with a flat surface on top…

– What’s “top”?

– The side furthest from the ground. Now listen. It usually has four legs…

– Wha…

– Shut up! That is a leg. [thwock]

– Ow!

– Got it? Right, it has four of them and a flat bit on top, and it’s usually made out of wood, which… shut up, wait – which is what trees are made out of.

– Okay, so what’s a tree?

– Come here. Close your eyes. No… eyes! These things! [jab]

– Ow!

– Now, keep them closed… now put your head down. Like this [yank]. Okay… keep walking…

donk

– That is a tree. Okay?

[Squink]

Start with a definition of chiral.
Arbitrarily assign the label ‘left’ to one member of a chiral pair.
Extend that convention to other objects.

[Colophon]

Tell them to go to a posh dinner party and observe which way the port is passed.

[BrainGlutton]

You might want to check out this book, Revenant.

[matt_mcl]

Similarly:

Einstein was asked by his hostess at a social gathering to explain his theory of relativity. Said the great mathematician,
“Madam, I was once walking in the country on a hot day with a blind friend, and said that I would like a drink of milk.”
“Milk?” said my friend, “Drink I know; but what is milk?”
“A white liquid,” I replied.
“Liquid I know; but what is white?”
“The colour of a swan’s feathers.”
“Feathers I know; what is a swan?”
“A bird with a crooked neck.”
“Neck I know; but what is this crooked?”
"Thereupon I lost patience. I seized his arm and straightened it. “That’s straight,” I said; and then I bent it at the elbow. “That’s crooked.”
“Ah!” said the blind man, “Now I know what you mean by milk!”

[Hampshire]

Mathematically or geometrically left would be -90 degrees and right would be 90 degrees to the 0 degree direction you are facing.

[nivlac]

@Colophon

So what, now everybody uses the Latin alphabet?

Fine. Then what about:
Hold out your hands with your palms facing down, fingers spread. “Left” is the side in which the thumb and forefinger on the hand make a shape that looks like this: L

Of course, this presupposes that the person knows what’s a hand, palm, down, thumb, forefinger, shape, and of course, can see! OK, I give up.

[Alan_Smithee]

I seem to remember a few years ago reading that physicists had discovered some slight inequality that would permit a universal definition of “left” and “right” requiring no knowledge other than particle physics (which is presumably the same for any aliens as for us.) Perhaps that is what Chronos was describing.

[matt_mcl]

Incidentally, what was wrong with “Left is the side your heart is on”?

Admittedly it doesn’t account for the occasional extremely rare case of situs inversus, but still. Anyway, several dictionaries define it this way, including Le Petit Robert, the Diccionario de la Real Academia Española, and the Plena Ilustrita Vortaro de Esperanto.

[Szlater]

The ratio of right to left handed individuals is something like 15%.

Tell the person to bend over and pick up a small object with one hand.

Tell them that the hand they used is their right hand, and you’ll be correct roughly 85% of the time.

Obviously this won’t work at all for non-human species.

[Kevbo]

Hold your hands fingers upward, with the thumbs pointed at each other. The hand where the thumb and forefinger form a capital L is the left.

[RadicalPi]

I would just do it this way:

XXXXX XXXXX

The red XXXXXs are to the left of the blue XXXXXs. Now they’re set unless their computer screen is upside down.
ETA: I didn’t realize this was a zombie. My apologies.

[panache45]

All words (knowledge) are contextual (not the same as subjective). It’s impossible to define a word while ignoring the context in which it exists, i.e. how it relates to other words. If you are looking for the definition of a word, it’s assumed that you have some knowledge of other words to which it’s related.

[septimus]

@Chronos

Define “positive charge” to be the charge of the lepton preferrentially produced by the decay of the long-lived neutral kaon (this preference is very slight; something like 501 times out of 1000). Now consider a positive muon, which decays in such a manner that the electron neutrino produced is travelling upwards relative to the center-of-mass frame. Now consider a macroscopic object rotating such that its angular momentum is parallel to the angular momentum of this neutrino. We can define “left” as the side of that macroscopic object which is moving forward.

I came here to post a link this, but see Chronos beat me to it. … By more than 4 years. :smack:

However, OP’s concern is that the definition be usable by aliens who don’t have a heart on the left side of their body. Can’t we extrapolate this concern to worry about aliens from an antimatter galaxy, who get the opposite result from Chronos’ experiment?

[Johanna]

@Colophon

So what, now everybody uses the Latin alphabet?

Hold your fingers upward, with the thumbs pointed at each other. The hand where thumb and forefinger form an Arabic letter lām ل is the right.

[Johanna]

In Arabic, the name for Yemen, اليمن al-Yaman, literally means ‘the right side’. Because if you’re in Mecca and face east, Yemen, the south, is on your right. Likewise, the old Arabic name for Syria is الشام al-Shām, from a root whose meaning was originally connected with ‘left side’* because if you’re in Mecca facing east, Syria, the north, is on your left.

*al-Shām is from the same root as شؤم shu’m ‘evil omen, misfortune’, while al-Yaman is from the opposite-meaning root of يمن *yumn *‘good omen, good fortune’ and also يمين yamīn ‘right hand’. This does not mean that Arabic speakers think of Yemen as lucky and Syria as unlucky. The directional words are clearly distinguished from the superstition words. However, because of the inauspicious connotation, the word for left has been euphemized twice in the history of Arabic. First, the word شمال shimāl ‘north’ was substituted for the original root of ‘left’ (and alliterates with it). Then shimāl itself was euphemized with the word يسار yasār literally meaning ‘ease’, and alliterating with yamīn ‘right’.

[Peter_Morris]

Some other stabs at answers to this question showed up in Radio-only communications with Aliens: left and right?

Assuming that aliens have a similar biology to us, and a similar level of technology and science:

Shine white light through a prism. The white light will be split into bands of colour. Stand facing the prism. Blue is the left side of the spectrum, red is the right side.

If aliens don’t understand what ‘blue’ and ‘red’ are, explain in terms of the Doppler shift.

[biqu]

@septimus

I came here to post a link this, but see Chronos beat me to it. … By more than 4 years. :smack:

However, OP’s concern is that the definition be usable by aliens who don’t have a heart on the left side of their body. Can’t we extrapolate this concern to worry about aliens from an antimatter galaxy, who get the opposite result from Chronos’ experiment?

What about aliens who choose the opposite convention to define macroscopic angular momentum? Ours is just another right-hand rule definition, which begs the question of how we know right from left to begin with. Aliens could conceivably choose the opposite sign convention and explain the same physics that we do with an appropriately modified theory of rotational dynamics.

[robert_columbia]

What about defining it in some way related to the Left Hand Rule?

Or, perhaps defining it in terms of vector crossing in threespace?

[orcenio]

@matt_mcl

Incidentally, what was wrong with “Left is the side your heart is on”?

Admittedly it doesn’t account for the occasional extremely rare case of situs inversus, but still. Anyway, several dictionaries define it this way, including Le Petit Robert

Have you seen that thing? If they can’t appropriately describe their own book, why should I trust their definition of “gauche?”