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Left and Right - Definitely defineable

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sephalon
758086.  Sat Nov 06, 2010 2:30 am Reply with quote

If you want to tell an alien what "left" and "right" are, it's quite simple, presuming the alien has some very basic technology.

First, presume he has the concepts of "up" and "down" defined. (If not, you can still do it, I'll explain below). Tell him to make a straight conductive pole that stands vertically (with "up" and "down" you can define "vertical").

Then have him run a current through the pole, such that the electrons are moving downward. Because of a quirk in the way our science views electronics, that actually means the current is going up.

Then have your alien shoot a beam of electrons directly (perpendicular) at the pole. (Perpendicular does not need "left" or "right" to define it. It's simply such that the attack angles are identical when viewed from both sides).

The beam of electrons will deflect to the right.

So long as your alien lives under the same physical laws as you do, you can tell him to do that, and then he'll know left from right.

NO GRAVITY: If the aliens have no gravity, and have no concept of "up" and "down", have them pick an arbitrary direction for "up", then define "down" as the opposite. Then perform the above experiment while aligning himself with the pole.

 
Posital
758087.  Sat Nov 06, 2010 2:36 am Reply with quote

This may not work for any anti-matter aliens...

 
sephalon
758092.  Sat Nov 06, 2010 3:05 am Reply with quote

Actually, it would work for anti-matter aliens as well, because positrons would also deflect to the right. Because it would be flowing positrons that made the magnetic field.

 
Posital
758094.  Sat Nov 06, 2010 3:21 am Reply with quote

So we could send them direction to navigate to Regent's Park, but woe betide us when we shake hands...

 
teramut
758107.  Sat Nov 06, 2010 4:57 am Reply with quote

You are correct that they are defineable, but your scheme does not quite work: you need to specify two directions to the alien: up-down and front-back. Depending on the choices the alien makes, he'll either choose them in order up-front-down-back or up-back-down-front, and these give different answers.

To be more technical, one can show that Maxwell's equations are invariant under parity (x-> -x) and therefore you cannot use them to define left and right if you have absolutely no reference to other directions.

Instead what you have to do is use weak interactions. For more (slightly technical) details, you can check out for example http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/parity.html#c2

 
suze
758159.  Sat Nov 06, 2010 7:53 am Reply with quote

sephalon wrote:
NO GRAVITY: If the aliens have no gravity, and have no concept of "up" and "down".


As Mr Montgomery Scott told us all back in the day, ye cannae change the laws of physics. So can we take it as a given that the aliens will have gravity, and that we can thus use gravity to define up/down?

I then got to wondering about antimatter aliens, and whether gravity would work backwards in an antimatter world. Apparently the theories of relativity imply that the answer to this is "no", and that gravity would still work in the way with which we are familiar.

 
aTao
758164.  Sat Nov 06, 2010 8:12 am Reply with quote

Front is defined, or can be defined as the direction of movement of the electrons in the beam fired at the pole.

Apart from that, I remember that the question stated that radio communication was involved..

Imagine 3 torches tied together one red, one green and one sky-blue-pink. The torches are arranged so that they shine 3 beams fanned in a plane with red to the left, green to the right and sky blue pink in the middle.
Front is the way the torches point, left and right are defined, spin the whole lot 90 degrees and up and down are easy.



Ohh, hi.

 
Flash
758169.  Sat Nov 06, 2010 8:22 am Reply with quote

There are a couple of other threads about this, so I'll just re-post here what I have said elsewhere:
Quote:

It's a funny thing about this issue: however clearly you say that you're making a point about the limitations of language, people always come back and suggest some practical, non-linguistic solution to the problem which involves sharing a common physical reference such as the one you propose. This is what Stephen said:

Quote:
Thatís the point. You canít, semantically there is no explanation for left or right without reference to a physical world that someone can identify. You canít, you canít explain it just by language. That is really the point of the question.

 
davidbod
758189.  Sat Nov 06, 2010 10:24 am Reply with quote

Unfortunately, where that argument falls down is that there is a common reference point that's readily available throughout the known universe - atoms.

I distinctly remember a puzzle book (probably by Clifford A. Pickover, who specialises in these things) describing a definite answer to this problem that uses sub-atomic particles and their spin as a reference point.

Whether he was right or not is too advanced for me.

 
Flash
758190.  Sat Nov 06, 2010 10:29 am Reply with quote

That's just the point, davidbod - the argument doesn't fall down at all. In your own words, you need
Quote:
a common reference point

The point being made in the show was precisely that you can't convey the left/right distinction without a common reference point. It's a statement about language - whether or not a common reference point exists and can provide a practical solution to the problem is entirely beside the point.

 
sephalon
758245.  Sat Nov 06, 2010 4:10 pm Reply with quote

So what they're saying, in essence, is: "If you have no common frame of reference, things that are defined by common frame of reference are meaningless."

I suppose that's accurate. But it's more of a tautology than an observation.

 
davidbod
758248.  Sat Nov 06, 2010 4:31 pm Reply with quote

Quote:
The point being made in the show was precisely that you can't convey the left/right distinction without a common reference point. It's a statement about language - whether or not a common reference point exists and can provide a practical solution to the problem is entirely beside the point.


This is making my head spin. The second sentence doesn't quite marry with the first, does it? If there is a common reference point, and I think there may be one, then according to the first sentence you could possibly tell left from right.

sephalon wrote:
So what they're saying, in essence, is: "If you have no common frame of reference, things that are defined by common frame of reference are meaningless."


Moreover, I think it's missing the point of what makes this a famous puzzle.

I think we're assuming that the question is saying: "If you have an alien that you can somehow communicate with, how do you give them the same notion of left/right that we have?"

There's no reason why we couldn't say to the alien "Pick a point in space somewhere in front of you, and draw a line from your body's midpoint to that point in space."

The interesting version of the question is now: "How do we tell the area that what's on the left of the line is called 'left' and vice versa for 'right'?" without assuming any reference points or physical phenomena like magnetism (and possibly gravity?)

Annoying, the puzzle book that I thought covered this wasn't the right one. I'll keep looking.

 
suze
758255.  Sat Nov 06, 2010 5:26 pm Reply with quote

davidbod wrote:
There's no reason why we couldn't say to the alien "Pick a point in space somewhere in front of you, and draw a line from your body's midpoint to that point in space."


Yes there is - we need to be able to define "in front of you".

If our aliens are spherical beings with eyes and anuses arranged regularly all over their spherical bodies, "in front of you" doesn't really mean much.

 
Flash
758262.  Sat Nov 06, 2010 6:20 pm Reply with quote

sephalon wrote:
So what they're saying, in essence, is: "If you have no common frame of reference, things that are defined by common frame of reference are meaningless."

I suppose that's accurate. But it's more of a tautology than an observation.


Your logic may be impeccable, but your premise is flawed: that isn't what we're saying. That would be not so much tautological as fatuous.

What we're saying is: "The concepts "left" and "right" have the curious property of being unconveyable by any means other than demonstration. It's quite hard to think of any other concept (certainly any other concept which is so pervasive in ordinary language and daily life) which has this property. We think that is Quite Interesting."

And, as it has kicked off no fewer than four threads on this forum, I reckon we must have been right.

 
teramut
758353.  Sun Nov 07, 2010 5:53 am Reply with quote

Flash wrote:

What we're saying is: "The concepts "left" and "right" have the curious property of being unconveyable by any means other than demonstration. It's quite hard to think of any other concept (certainly any other concept which is so pervasive in ordinary language and daily life) which has this property. We think that is Quite Interesting."


To me it seems even More Interesting that this is actually not quite true! You can tell the aliens to put some cobalt-60 in a magnetic field. Most of the electrons emitted by cobalt 60 as it beta decays will travel to the north pole of the magnetic field. Then after you've told them what you mean by "north", you can also tell them what "clockwise" means and then explain left and right.

Even wikipedia knows this: http://en.wikipedia.org/wiki/Relative_direction

 

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