Tag Archives: human-body

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The difference between left and right

The concept of right and left is innate

It is impossible to teach anyone the concept of right and left. Yet all of us manage to learn it as kids.

Why do I say it is impossible to teach the concept of right and left? Well, how would you teach it? You’d perhaps take a few 2D pictures, draw a line through the middle and tell the kid “this side is left” and “that side is right” while pointing to the relevant sides of the pictures. After a few such demonstrations, the kid is able to identify “left” and “right” for pictures that he has not seen before. At the end of the experiment, you conclude that the child has learnt the difference between left and right because of the demonstrations.

I think this conclusion is wrong.. As a result of this demonstration, he merely learnt the words for a concept he already knew. If this was not the case, the kid would have never figured out why seemingly different parts of different pictures are being described by the same word “left”. You have to know the similarity already in some form in order to identify it.

This logic can be used for almost any example that you can use to teach a kid ‘right’ and ‘left’. All such examples merely provide the kid with the required words.

If you can come up with an example where this logic fails , then please post the example in the comment section below.

How distinguishable is left and right from birth?

If we accept the argument in the last Section,  then ‘left’ and ‘right’ are concepts that we are born with.  But the question remains: how well can we distinguish these two concepts when we are toddlers? There are two possibilities.

  1. We can distinguish them perfectly from birth. Left and right are like two cups that look completely different from the get go. One is round and another one is cylindrical, for example.
  2. We can distinguish them from birth, but the difference is very subtle. Left  and right are then, in analogy,  two cups that are made from the same cast, both being round perhaps. Initially they are indistinguishable except for the fact that they occupy different spatial regions. Later we add different decorations to the outer surface of the cup and then they become more distinguishable. Decorations here refer to our experiences in the real world which is inherently left right asymmetric (your right hand is perhaps stronger than your left or vice versa). This asymmetry helps us in distinguishing strongly two concepts which were almost indistinguishable to begin with.

Judging from my childhood experience, I think the second possibility is in fact the case. What do you think?

This is experimentally verifiable too. If a kid can learn the difference between “left” and “right” from a set of left-right symmetric picture (in the example mentioned in the last section) quickly, then 1 is true. If not, and if we need asymmetric pictures to help a child learn the difference quickly, then 2 is true. This can be verified by performing the relevant experiments with toddlers.

Left right asymmetry of the human body and the physical world

Assuming that the distinction between left and right is weak at birth, we need asymmetries in ourselves and the world around us to make the distinction stronger.

Fortunately, the world is riddled with such asymmetries.

The human body is left right asymmetric. This is one the major asymmetries that helps us in consistently distinguishing right from left.

  1. The human heart is typically offset towards the left.
  2. The right hand and the left hand usually differ in strength. In my case, my right hand is stronger.
  3. The right lung is bigger that the left lung.
  4. The left side of the brain tends to control many aspects of language and logic, while the right side tends to handle spatial information and visual comprehension.

The physical world is full of such asymmetries too. The houses on the right side of the street don’t look like that on the left side.

This ever present asymmetry in our daily existence and experience color our concepts of right and left and make them more distinguishable.

What would happen if the human body was symmetric?

If the human body was symmetric, perhaps we would not be born with the ability to distinguish left from right. However we cannot predict this with any certainty.

What would happen if the human body was asymmetric but the external world was symmetric?

The houses on a street are accidental asymmetries. They could have been symmetric for all we know. If they were indeed symmetric, could we distinguish between left and right consistently?

The answer seems to be “weakly” from the discussion in the first two sections. However Physics has a completely different answer to give.

The physical world is not “accidentally” symmetric, it is asymmetric by design

Here is where things get interesting. According to a landmark experiment performed in 1956 by a team headed by Madame Wu, nature was shown to differentiate between right and left strongly.

We aren’t talking about man made houses or asymmetries on the earth surface here. We are talking of the laws that govern elementary particles at the highest energy scales (smallest length scales) known to man. Nature was shown to distinguish between left and right at this fundamental level. This is commonly called Parity Violation in high energy Physics. You might have heard about it.

I wanted to dedicate an entire blog post to this revolutionary experiment. The link will appear here shortly. Meanwhile, you can look here for details on the experiment.

Conclusion

Right and left is distinguishable. The difference between left and right is not accidental. It is present in Nature by design.

  • Human kids can perhaps weakly distinguish between left and right as soon as they are born.
  • This distinction is made stronger by linking the concepts with accidental asymmetries in the physical world.
  • Not all asymmetries in the physical world are accidental. Nature distinguishes between left and right at the smallest length scales. In other words, it is possible to distinguish right from left by simply performing  certain Physics experiments on otherwise symmetric systems.
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