Archive for the ‘Somewhat Technical’ Category

The Seeds of Mathematics

November 23, 2015

Mathematics is an introspective science, as opposed to experimental sciences(Physics, Chemistry etc). Unlike experimental sciences, progress in mathematics doesn’t require getting data from deep sky, probing into an atom or colliding elementary particles at high speeds. Numbers and other concepts are in our head and all open problems are in our head. This suggests a possibility, that even if we locked ourselves in a cave, cutting off all communications with the nature, we may still be able to continue our progress in mathematics. The subject of this blog post is to examine if  this is really possible.

The converse of this question has a clear answer: Halting mathematical progress would halt progress in all experimental sciences. Mathematics develops ways of thinking, that are employed in understanding the nature. It appears that mathematics is on its own; it doesn’t depend on any of the other sciences. It can continue progressing without any other sciences. This view is expressed in this xkcd comic. But I am going to contradict this view (and I am going to contradict other aspects of that cartoon in my next blog post :D).

Although it is not apparent, progress in mathematics requires us to experimentally probe into nature. The ideas involved in mathematical research are seeded by our experimental probes. Exploration of nature is a key not only to develop physical sciences, but also to develop mathematics, although it is a purely logical subject. A problem is deemed solved, only after a logically consistent solution is found. However, the question “what is an interesting problem to solve?” doesn’t quite have a logical answer.  G. H. Hardy has described  this question to be akin to asking where do poets, writers and other artists get ideas for their work. Conceiving new problems is a work of imagination. And imagination is always seeded by reality.

The classic example for an interesting problem is the one that led to Fermat’s last theorem: ‘are there integers a, b and c such that an+b= cn for some integer n?’. Surely, the complete answer to this problem was profoundly useful, only because large number of people worked on it and it developed a great deal of understanding of numbers. However, the problem was presumably seeded by the Pythagoras theorem. We have integers, like (3,4,5) such that 32+42=52, so  a curious question like ‘what if we change the exponent to a number other than 2?’, would have been the origin of Fermat’s last theorem.

Another question in mathematical research that doesn’t have a logical answer is “what set of axioms should we choose?”. Axioms, like problems, are chosen by taking a cue from previous mathematical theories. The resulting structural similarity between different mathematical theories has been capitalized in a theory called category theory.

Where do these ‘previous mathematical theories’ get their axioms and problems from? There must be a starting point, a seed for every mathematical idea. These seeds come from outside- from our interaction with nature. Cutting off interaction with nature will cut off the supply of new seeds. But that doesn’t entirely stop mathematical progress; instead, ideas for new mathematical theories will be entirely dependent on the old mathematical theories. Over a timescale of several hundred years, this is a significant setback to mathematical progress. Seeding of mathematics by interaction with nature is a slow process. In fact, we are still benefiting from the seeds of Pythagoras theorem.

The seeds of Pythagoras theorem

‘Geometry’ stands for measurement of the earth. ‘Earth’ here doesn’t mean the planet earth or the globe; it means land; real estate. Geometrical ideas were developed as a result of extensive measurement of land, during early human settlements. The most influential of these was the Pythagoras theorem. Let me go through its development, in its three chronological stages: the content, the statement and the proof, to identify its seeds.

Given two sides of a right triangle, knowing how to calculate the third side is the essential content of Pythagoras theorem. This may be done using a formula, or using tabulated data or using similarity of triangles. All these methods carry the basic wisdom– “the third side of a right triangle is not an independent variable”. Any civilization that built large planned settlements knew the content of Pythagoras theorem.

Explicit statements probably came several thousand years after the content. Early statements of Pythagoras theorem were in terms of areas. There are records of statements in Babylonian scriptures(2000 BC), in the Vedas(Shulva Sutras, 800 BC) and Chinese scriptures. An explicit statement  could’t have brought any change in the applicability. Perhaps, the room/house in which the statements were written was constructed using the content of Pythagoras theorem :D. However, it brought big changes in theory. Geometrical shapes were understood by cutting them into triangles. Triangles were now understood by cutting them in to right triangles. Right triangles took precedence over other triangles, leading to a new branch- Trigonometry.

A partial proof was recorded in 800 BC(Shulva Sutras) and a complete proof in 500 BC(Pythagoras). Presumably, there were unrecorded proofs prior to this. There are some theories that Pythagoreans might have been communicating with Chinese schools of mathematics. The proof was seeded by two pieces of intuition, which were developed when planning settlements. One is that land can be measured in areas, which can be added and subtracted by joining and cutting pieces of land. The second is scaling; a big piece of land can be scaled down and represented on paper or a flat stone. All proofs of the Pythagoras theorem are based on areas of triangles or scaling of small triangles to big ones(A book, The Pythagorean Proposition lists 370 proofs). Scaling is in fact a logical implication of the properties of areas. But it is likely that it was developed independently.

The proof, of course, had no practical implications. Proofs generally store methods of thinking. Even today we feel its impact on our thinking. The proof raised the status of the mere formula, ‘a2 + b2=c2′ to a theorem, resulting in the discovery of irrational numbers. Furthermore, it redefined the whole of geometry in terms of a single quantity- the distance between two points. The more advanced forms of geometry- Riemannian geometry and even Differential geometry contain the germs of Pythagorean distance.

The Pythagoras theorem and all of its intellectual impact on Mathematics are seeded by man’s physical exploration in to measuring land. A writer, within his lifetime travels extensively to gain experiences of reality that can seed his imagination. Mathematics is also seeded by explorations of real world, but this seeding has a longer timescale, much longer than a mathematician’s lifetime.



Conceiving and convincing

May 30, 2012

Imagine, we are given a task to fill up as many pages as possible on word, in a given time, with the letter ‘A’. One way is to copy ‘A’ into the clip board and keep pressing Ctrl V. This is the AP(Arithmetic Progression) way. There is another way; we can copy ‘A’ and keep pressing ctrl C, Ctrl A, ctrl V in sequence. This is the GP way. Mathematics tells us that although Ctrl V appears once in three buttons, the GP method is faster. This is not obvious for a common man at the first sight. And most of the public, are insensitive to logical arguments. Nevertheless, one can convince anyone of this fact, simply by demonstrating it.

The above is an example of what I call as an operationally testable statement. However there are statements which are not operationally testable. The man on the platform, says “the train is moving”; while, the man in the train says “the platform is moving”. Usually, a common man assumes that the man on the train is wrong; he knows the ‘truth’- the train is moving. The profound realisation is that, neither of them are wrong. But there is no way to demonstrate it! This concept of relative motion is operationally un-testable. So much so, that this un-testability was responsible for the Galileo affair. (besides religious concerns)

In fact, most of the statements with profound reasoning are operationally un-testable. For instance, the counter intuitive results of cantor, like the number of points on a side of a cube, the number of points on a face and the number of points inside its volume, are all equal; it is impossible to trisect an angle using a straight edge and a compass. A common man certainly has problems with accepting it. And unfortunately, there is no operational way to convince him of this fact; i.e, a person who assumes the contrary will not be punished for being wrong. 😀 Hence it is apparent that there is no way to convince the public of these facts.

To digress a bit, I often say utilising an object is to do something with it, which cannot be done without using it :D. By that token, reasoning should be used to conceive (currently)un-testable facts. Because, operationally testable facts can be conceived even without reasoning. Hence, real utilisation of reasoning is to conceive operationally un-testable facts.

How do I convince a common man of such facts? In the first place, should one care to convince someone who is not sensitive to logic? To answer these questions, I shall consider examples from the history where the task of convincing the public has been accomplished.

The earth is not flat, but spherical, and further, it is not at rest, it is rotating and revolving. These two are among the most profound, but operationally un testable realisations. However, they are widely accepted by the public!. Let us examine how were the public convinced of these. Aristotle conceived that the earth is spherical. At that time this would have been counter intuitive and operationally un testable; So, he would have had a great trouble in convincing people about it. It is clear that he did care about convincing people about it; why else would he list down the common fallacies in logic committed by people 😀 (see ‘Aristotle’s 13 fallacies’). And the way he did it, was to impose it as a belief. This is clear from how people believed everything that Aristotle said.

Most of the public today, believe that the earth is in a complicated motion. They just believe– they don’t really know the reasoning which led to this fact!. In fact, to really go through the reasoning, one has to understand relative motion. This was the major trouble with accepting Galileo’s arguments; he was asked to prove that the earth is moving (for which he gave a wrong argument :P). And it is apparent that most of the public don’t really appreciate relative motion. So, it is clear that they have been convinced of the heliocentric theory, just by imposing it as a belief. This, is not very different from religion!. Isn’t it unjustified for an intellectual to impose a belief?

Majority of people are insensitive to logical reasoning; ie, if the result of a logical reasoning is against their intuition or religious or any other concerns, they cease to accept it. Therefore, it is impossible to propagate the picture of moving earth, through reasoning. If it was not propagated as a belief, the public would have accepted a different picture of the earth, still as a belief!. Hence it is not unjustified, to propagate a belief, if it is necessary to convince them of these facts.

It is clear that whether or not a statement gets propagated as a belief among the public doesn’t depend on whether the statement is based on a sound reasoning or not!. It depends on the ability to impose a belief among the public, of the person who conceived it. This means, almost anything can be propagated as a belief!. That is a little disturbing :D. There ought to be a fundamental difference between conceiving a statement out of rigorous logical reasoning, and claiming without a strong logical background. I guess this difference is brought out in the confidence: the confidence attained by conceiving a fact through thorough reasoning is stronger. I guess(hope :P) this difference can be utilised to beat the propagation of unsupported claims.

Finally, I come to the question I postponed to the end. Is it necessary to care about convincing others? Again let’s ask (old)people :D.Usually, mathematicians don’t care about the public; after conceiving a result, they wouldn’t worry about convincing. Kepler, who went a long way ahead of Galileo, at the same time, didn’t care to convince everyone; that is why he doesn’t have an affair attached to his name, unlike Galileo :D. Apparently, he was able to go that far simply because he didn’t care about convincing people. It is clear that Galileo and Aristotle cared about convincing people. If none of the physicists and mathematicians care about convincing others, their next generation to be physicists and mathematicians will find it hard to see the facts amidst misconceptions. Avoiding this is the only possible motivation for a physicist/mathematician to get in to the job of convincing, as far as I can see right now. This post is the longest one so far, and has crossed 1K words 😀 and so I stop here 😀 😀

The Car

March 23, 2012

Ever since one of our profs said ‘most of the beautiful things are useless’, I was disturbed by the fact that in mathematics and physics, most of the intellectually deeper works don’t have practical value. This means, there is no value associated with the ability to do such a deep work. Also many of my friends keep asking me what is the point of all the hard core theory in physics, and why do I study them? The best way to analyse it is to look at the history.

‘His’ story
When he(mentioning who ‘he’ is, is irrelevant 😛 ) was on his way back from his work, his car broke down. He went to a mechanic, got it repaired, and reached home. At home, relaxing on a chair, he was thinking about his car’s history. Half an hour ago, it was at the mechanic shop. The mechanic is an important person in the car’s and its owner’s immediate history. If he hadn’t done his job, the man wouldn’t be home by now. His work has had immediate effects on the car and it’s owner. However, the job wasn’t a high skill-demanding one; in fact, with a little experience, anyone could have done that job. Also, the guy is not remembered; the man paid him and forgot about him. That completes the first layer of the car’s history.

Where was the car before this? The next interesting part in it’s history is when it’s model was designed. At this stage, it is not just it’s history, it is the history of all cars of it’s model. This was about a decade ago. The car was on paper, on the desk of the man who designed it. This man, is another person who influenced the car’s future. His job, unlike the mechanic’s, didn’t have an immediate impact. If he hadn’t done his job, that would have probably gone un noticed after all! The effect of his effort would have taken a couple of years to come out. But this guy is actually skilled; any arbitrary person cannot be trained to do this work. One needs to be a little talented to be able to learn to do such a job. And, at least people in his company will remember him for designing that model. So That’s the second layer.

The third layer is over 250 years ago.(that’s exponential in time! 30 mins-10yrs-200yrs). This car and several other machines had their common point in history, on the notebooks of the guys who discovered the laws of thermodynamics. Now there is a trend!. This piece of work takes 100s of years to yield its value!. At the time they did it, no one could have imagined that someone will make an auto-mobile out of it, 200 years later!. Coming to the skill required, even a considerably talented person cannot be trained to do such a job. It requires a rare capability. And after 200 years, we still remember them for their work!

I have spoken about three quantities-the time scale in which the work will be utilised, the skill levels required and the reward in terms of people remembering the man who did it. And, the trend is clear :D. That summarises all I have to say about the value of hard core theory.

However everything that looks deep and, useless at the moment is not necessarily going to be useful some 100 years later :D. In fact, most of them are so, which is to be understood from G H Hardy’s A Mathematician’s apology, where he justifies the work of a mathematician saying they are harmless, rather than useful :D. To foresee what could be useful in the long run is unimaginably non trivial!. It is possible that a great mind can foresee it; but they usually work for the fun of it, rather than its impact on the society in the long run. It seems to me, that Newton might have foreseen the impact of his laws of motion-the industrial revolution, although this impact was none of the reasons why he did all this work. But I believe he did not foresee the giant impact(we are able to watch TV today!) of his law of gravitation.

Mystery is a guide to hope

January 14, 2012

Once, I was walking down along with my prof, discussing a result I had just managed to prove. He said “well, you have managed to prove it, but you should also understand your result”. We generally believe we certainly understand something that we developed ourselves. For the first time, I was talking to someone who had, in his mind, a genuine definition of understanding. I knew how I arrived at the result, but it was counter intuitive. That means, there is a flaw in our mental picture of the subject. So, reconstructing our intuition, based on this result is a more important part of understanding it. In fact, this is the value attached to the result.

The above instance speaks also about the value hidden behind a mystery. A mystery points at something that we don’t understand. A counter intuitive result is also a mystery. The moment we encounter a mystery, we can hope for something radical, coming out of resolving the mystery. In fact, look at almost any radical change in human thinking, there would have been a mystery out of which it emerged! Quantum mechanics was itself found hidden behind a mystery. Also, the theory of relativity was born out of a mystery!. Another classic example is quantum computation. This example is too technical to be written in a blog, but I prefer to mention it because, I myself solidified the thoughts behind this post using this example. It all started with Einstein pointing out an apparent contradiction in quantum mechanics, and Bell clarifying that this was no contradiction, but it was only a mystery. They called this mystery ‘entanglement’. It took a while for people to understand it; but a revolutionary looking idea did emerge out of it. That was quantum computing.

The examples I gave are of a huge magnitude :D, and very specific(to physics). One may not expect to encounter mysteries of this magnitude, but the idea works at all scales. A big mystery leads to a big revolution; a small one to a small one :D. So when we confront a mystery, we can expect something new coming out of resolving it. However, every mystery need not lead to something fruitful, but we can hope!.

‘Sneak’ into the Gaps

September 3, 2011

While walking on the roads of the campus, if someone casually asked me ‘where are you going?’ I would reply ‘Nowhere..I am just moving parallel to the road’ 😀 😀 I always believed that most of our path is decided by the road, we just move along the road!; It’s only at the turnings where we get to make our choice. Yet, we get complete freedom to choose our final destination!. I was always amused at it. Probably because, I used time/length as a measure of domination. When I say we always walk along the road, and make a choice only once in while, I mean, our walk is dominated by instances where the road decides the path. Invariably I am comparing the chosen part of the travel and the predetermined part of the travel in terms of the time spent or the distance travelled. This is clearly an incorrect measure to quantify and compare how much do we get to choose and how much is predetermined.

Recently I came across a formal study of similar properties in a language. A language has got some rules in the form grammar etc.. As in, once I start writing, I don’t have complete freedom to decide the next character. There are restrictions to it. There are choices left to us and, in between the restrictions, we make use of the choices to give the meaning at our will. This is beautifully captured in what is known as redundancy of a language. This is a number between 0 and 1. A completely random language has zero redundancy; any character can appear after any character. It is completely up to our choice. A language where the user gets no chance to choose is a completely redundant language; every character is uniquely decided by its previous character. Anything in between these two extremes is assigned a number between 0 and 1(there are more beautiful results; the redundancy of a language is related to existence of arbitrary infinite n-dimensional cross word puzzles!). I was so fascinated that, in fact I started using the word ‘redundancy’ almost whenever I feel like! 😀 😀

Rules might seem like they are restrictions on our freedom. However, even in a very general abstract system, rules are very much necessary. I started comparing the rules and the freedom in a system to those of a game. There is no game without rules; also, there is no game with the moves completely determined by the rules. It’s a proper combination of freedom and redundancy which makes the game interesting. There are rules to be followed while playing a game. However, the real playing happens in the free region; If I am spending all his energy to merely be religious in following the rules, and doing nothing with the freedom, I am not playing at all! To play is to find gaps in between the rules and sneak into them!

So to play a game is to sneak in to the gaps between rules to get our job done. We might expect it to be easier to do so with lesser rules. But it is just the opposite!. The reason is, rules just give us a platform to work on; we are actually working in the free region. So, larger the free region, difficult it is. This is quite the reason why simplifying assumptions are made to begin with a new theory. We just don’t know how to work with very few constraints!. The extra assumptions give us the guidelines to work. That seems to be the purpose of rules. This post is abstract..probably because, the thoughts are so 😀 😀


October 31, 2010

The idea of giving such a title to this post isn’t entirely mine. It is inspired by someone else’s idea of naming something else( 😀 :D). What it means is something the reader has to imagine after reading the post :P. This post is not related to the original PvsNP problem; but it is certainly inspired by that problem. It is about the question of questions.

A question, has a shape. It has two components.

1.) A solution space. (i.e., one should know how the answer ‘looks like‘)

2.) A verifiable condition.

The question is to look for some element in the ‘solution space’, which satisfies the condition. As an example, the question 2-3 = ? can given a shape.
1.) the solution space is the set of integers
2.) the condition is, 2+x=3.
That’s rather numerical. But the scope of this shape of a question is much wider than questions related to numbers. The space and the condition are much more abstract in many useful cases. An essay; everyone knows how to check for the condition. But what is the solution space? You could use “the set of all essays”, if the meaning of essay is known. Or, the “set of combinations of the 26 letters, the space( ) and the other symbols used” :D. That looks awkward. However, the point is that one should know what the answer looks like or what are we looking for. That is the job of the solution space. The two examples should be read and forgotten, the crux of the story is yet to come.

So, why not always take the so called universal set as the solution space, and reduce the structure of a question to just a condition? (which is what most of us think of a question as). Well, the universal set, if it exists (no, it doesn’t!) doesn’t tell us anything about how the answer looks like. A solution space can be any big. But it must tell us what we are looking for. By the way, for those who were surprised at my earlier remark, the universal set does not exist. One can not create something out of nothing. Assuming that there is something which contains everything results in a paradox, called the Russell’s paradox. All it means is, ‘you cannot put all thinkable objects in a single set’.

Constructing the solution space turns out to be the major issue in building a question. Most questions which seem to be unanswerable are so simply because they don’t have a solution space(I mean, we don’t really know what we are looking for!). Just an attempt to construct a solution space resolves many of such queries. So, whenever a perplexing query comes to mind, one has to stop and think what am I looking for

As it turns out, it is a very non-trivial job to build such a structure to the queries of the human mind. As a matter of fact, the problem of finding such structures is itself a structured question!. However, in this case, the verifiable condition is given by the satisfaction of the mind. That makes it somewhat different from ordinary questions. In fact, it makes it interesting(=less boring :D). Figuring out what our mind is looking for forms the core of thinking.

What does one do after structuring the query? nothing! :D. “The real job of a mathematician is to get equations, not to solve them!”. Solving them is the job of a computer. whatever needs to be done next is too ordered to interest the human mind. However, it seems ‘finding’ the answer turns out to be either too trivial or unimportant. So, before asking “how can a man pass through a wall?” one has to stop and think what exactly is our mind looking for, and in many cases, such an attempt alone can resolve the query.

Why is a mirror image upright?

June 6, 2010

I am blogging on this topic rather unwillingly. My thoughts upon this problem are nearly two years old. I was reluctant to blog this one for two reasons: one, this is an old and well known question; hence I expected a handful of articles addressing this one on the net, providing answers close to mine. Surprisingly, I found no answer close enough to mine. And two, this topic is technically way too specific to appear in my blog. However, I have tried my best to use the problem just to illustrate what I want to say.

Well, let’s begin with the question. “why is a mirror image laterally inverted and not vertically inverted ?” I have observed that quite a few people, after a second’s reflection, don’t even realise that there actually is some trouble with the image. The question as such is not clear and hence needs to be defined properly. Here, I have described the ‘trouble’ with the mirror image in a slightly different language.

The mirror has a plane. And it has an axis, perpendicular to the plane. The human body has three directions intrinsically defined along three axes. Feet to head defines the directionality of the vertical axis. Back to front defines the directionality of one of the horizontal axes. Left to right defines the directionality of the other horizontal axis. What the mirror does is, it reverses the directionality of the axis pointing towards the mirror, i.e, the axis perpendicular to the mirror. It does not change the directionality of the axes parallel to the surface of the mirror(at least this is what one would expect). Let’s look at what the mirror does to the human body. The front-back of the image is opposite to that of the object, as one would expect. The top-down of the image is same as that of the object, again as one would expect. However, the left-right of the image is not same as that of the object. This is the trouble that we are referring to in the problem. It’s a serious violation of symmetry between the two directions parallel to the mirror.

One must reflect for a while and convince themselves that above problem is same as the one we have in our mind when we say ‘why is a mirror image laterally inverted and not vertically inverted?’ for the case when the object is a human being (Let us take up the cases of the other objects later). Once formulated this way, it is immediately solved. The left-right is fundamentally different from the other two directions. The top-down and the front-back are defined through asymmetries in the appearance of the human body. While, it is impossible to define left-right just by appearance! They look perfectly alike. But still, we manage to unambiguously define left-right. How? We live in a 3 dimensional space-this is the answer. Any object with two directionalities defined, can be given a third directionality, arbitrarily, as a convention. Once this convention is set, it can be followed unambiguously, since we live in 3 dimensional space. This definition of the third directionality uses the two already defined directionalities. Mathematically bent people can, with a little reflection, convince themselves that this is indeed, ‘defining of the cross product‘. In fact, the ‘left-right = back-front X bottom-top, once the cross product is defined the way it is defined now. Now, why is the left-right reversed in the image? The image preserves the bottom top, but the back-front gets reversed, hence, the left-right, which is defined based on these two directionalities also gets reversed.

About the case of non-human objects, even if the object is perfectly assymmetrical, we attach our left-right to everything (we read and write from the ‘left’ etc) All those troubles are closely related to this. I don’t want to get in to those, since all of them involve just one thing: defining the problem properly.

Now the crux; as said earlier, the purpose of this blog was not to solve the mirror problem(:D). It was to illustrate that mathematics is simply thinking. Putting the problem in a clear language is what we call ‘formalism’.

Mathematics vs Physics

January 13, 2010

My ‘mathematician’ friends call me a ‘physicist’ and my ‘physicist’ friends call me a ‘mathematician’!. However, I don’t want to be a ‘mathematical physicist’ :D. This conflict between the so called ‘mathematical’ and the so called ‘physical’ approach had always existed in my mind. Now, I feel there is no room for such a conflict for, I have concluded that there is no real difference between them.

A person who propagates a new idea, or a new religion (or anything! ), has a two circles of followers around him. The 1st circle, is the immediate circle around him. It consists of people who follow his ideas, and understand them, to a certain extent. The second circle is often larger, consisting of people who merely follow him. They dont understand his ideas; they just appreciate them. They just get a feel of it. The real difference between the 1st and the 2nd circle is in the ability to defend the idea. The 1st circle is capable of defending the idea. The propagator is responsible for the idea and hence is able to defend it. The second circle, is often characterized by people shifting sides. One can easily jump from the 2nd circle of one idea to the 2nd circle of a different idea(most commanly the contrasting idea! :D). People in the 2nd circle are brought by just convincing them of the validity of the idea.

On the lines of the above story, a theory too has a propagator, a 1st circle and a 2nd circle. The so called physical approach, seldom lands anyone in the 1st circle. It is a good tool just to get convinced of the theory. Most of the so called physical reasonings are worthy observations, but fail in providing philosophical insights in to nature. There is nothing called the mathematical approach. Presence of large number of equations is not mathematics; There is just one approach, and we could call it the rational or, the logical approach!

The story of billiard balls

September 29, 2009

This blog is my first one, based on my thoughts, as mentioned at the end of the blog. I conceived this thought and the idea of blogging while travelling in a train, back from Kanpur to Bangalore.

A little kid, who does not know what ‘color’ is, comes across a bag of colorful billiard balls. what would be his reaction? His childish curiosity drives him towards the bag. He is attracted by the appearance of the balls…I mean, the colors, though he doesn’t know what it is….

Most children stop there. But, imagine, an extraordinary( hypothetical, if you feel so) child, who can proceed further. The next thing he would do is, look for similar balls (balls which look like each other) The child has a way to tell whether two balls look like each other or not, by visual inspection. (looking like each other in our language means same color).
Next, the child can divide the bag of balls in to groups of like balls. Every pair of balls within a group would look alike. Hence, each group can be represented by a single ball. If the child is given new balls, he can easily put them in to respective groups. Or, if it doesn’t look like any of the group representatives, it makes a new group.
Now, he is close to defining color. The representatives of each group are not balls, they are colors. He can name each group at his will. This is precisely what man did, over generations. The names he gave were red blue green et al.
Now, a formal look at the procedure adopted by the child. An important comment to be made at this point is about the way the child decides if two balls are alike. If balls 1 and 2 are alike , and balls 2 and 3 are alike, inevitably, balls 1 and 3 will fall in the same group. Hence, they should look alike. Formally speaking, his definition of alike should be trasitive. By using ‘two balls look alike’, and not ‘one looks like the other’, I have already meant that the like is symmetric. A little more thought will convince you that the like needs to be reflexive as well, for successful classification. Thus, it gives a reason to the mathematical definition of equivalence relation. Formally, those groups arising out of the equivalence relation are called classes. Once the classes are made, a mathematician may do various things with his classes….order them etc.
This is how most of the seemingly undefinable terms like color, size, mass, charge, cardinality, etc are defined(?).
The purpose of this blog is to express my thought flow, which at the moment says, mathematics is a way of thinking, formalized.

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