## Muhammed Zafar Iqbal book list

Muhammed Zafar Iqbal is a Bangladeshi Physicist. He and Hasibul Ahsan are collaborating to find the unified field theory of physics. They are known to each other for long time.## Pascal’s triangle

A binomial expression is one which contains two terms connected by a plus or minus sign. Thus (p+q), (a+x)2, (2x+y)3 are examples of binomial expressions. Expanding (a + x)n for integer values of n from 0 to 6 gives the results as shown at the bottom of the page. From these results the following patterns emerge: (i) ‘a’decreases in powermoving from left to right. (ii) ‘x’increases in power moving from left to right. (iii) The coefficients of each term of the expansions are symmetrical about the middle coefficient when n is even and symmetrical about the two middle coefficients when n is odd. (iv) The coefficients are shown separately in Table 7.1 and this arrangement is known as Pascal’s triangle. A coefficient of a term may be obtained by adding the two adjacent coefficients immediately above in the previous row. This is shown by the triangles in Table 7.1, where, for example, 1 + 3 = 4, 10 + 5 = 15

## Books

Muhammed Zafar Iqbal has written many books on quantum mechnics and thoery of special relativity. He has not written any on general relativity. I asked him why he had not written anything on GR. He actually excelled at experimental physics and he is not much expert at theoretical physics. I have read many other books of him. He must be regraded as a man of science , who works for his own motherland in spite of possessing a great prospect abroad. He realizes that our nation need more scientists rather than engineers and doctors. He also acknowledges us in his book several times. But my opinion is that he should be writing more theory related books than science fictions.

Kolpo, a 13-year-old reader, requested for new science fiction at a stall in the Amar Ekhushey Book Fair. He told Dhaka Tribune that he was waiting for his copy of the new science fiction book by Prof Muhammed Zafar Iqbal. “I like his stories,” said Kolpo. “I forget that what I am reading is in fact not realistic.” Sanjida Hossain is a lecturer at Brac University. She, too, came to buy her copy of Zafar Iqbal’s new science fiction at the book fair. Titled “Tratina”, the book has seen bestseller in the book fair until now. According to its publisher, Somoy Prokashon, it has already sold 30,000 copies. “Within the first 10 days, more than 5,000 copies of ‘Tratina’ were sold,” said Mahmud Piyash, a salesman at Somoy Prokashon. However, Piyash added that they have had to approach visitors to let them know about publications from other, new science fiction authors. Somoy Prokashon published two more science fiction thrillers this year at the book fair- “Turash” by Biswajit Das and “Beyond the Man-Made Universe” by Tasruzzaman Babu. Another publication house, Anannya, has published five sci-fi thrillers this year. One of them is Tanvir Rana Mustafiz’s sci-fi collection “Science Fiction Shomogro”, featuring stories about galaxies, aliens and exotic animals. A salesman of Anannya said that keeping pace with visitors’ demands, they have also published translations of different works of science fictions. Oitijjhyo, another leading publication house, has published a sci-fi translation of “Norby: The Mixed-Up Robot”, the first in the series of 11 books by Janet and Isaac Asimov and translated by Khandaker Istiaque Mahmud. Samiul Alam, a sci-fi lover from Narayanganj, opined that most of the local science fiction books are teen thrillers rather than actual science fiction. “The sci-fi novels that I have been going through in the Ekushey book fair are mostly teen thrillers,” said Samiul. “That is why I am inclined to go for translations. But Seba Prokashoni is the best place for me. I am going to hit its stall right after I am done visiting others.”

## Bigyani Sofdor Alir Moha Moha Abisker

A man was very lonely and he used to spend most of his time alone. This is a story of remote place in bangladesh where he lives. He suddenly started questioning everything. All the big questions like where had he come from? , how did the universe begin ?, can time run backwards? can we go to our past? and many other philosophical and scientific questions came into his mind. He started buying books on consmology, relativity, quantum mehcanics and mathematical and philosophical books. He stays alone in his room and looks outside to find something special. He has a computer which he keeps switched on for long time. He searches the web day and night to find something new. Suddenly a thought came in his mind . Why do we think that everything exists? What is its connection to our memory? He had learned about theory of relativity and quantum theory in the meantime after reading a lot of books. Now he tries to combine these two theories to find the ultimate theory of the universe. No scientist had been able to find the grand unified theory. Maxwell had told that scientists can not find the ulitmate secret of the nature because what we are trying to find is very part of uurselves. It is apparent that he was mentioning our mind.{not consistent}

He now thinks about what might have gone wrong. Why are scientists not finding the ultimate theory of nature? May be physics will not help us. So we need some philoshophical theory. This kind of thinking keeps him always busy to find something new. If physics were the answer then it would been found long ago. String theory has not been verified yet. He thinks what if memory creates reality. There is no past and future , which Einstein taught us. Nothing happened in our past. We think that something happened because our mind gives us false impression of the past. It just made us recollect certain memory in our mind. Memory is not necessarily the past events. It is like the informations stored in the hard disk of computer. Physical world is just an illusion. He is now very thrilled. This also seems to correspond to the simulation theory. Simulation theory is the theory that says we are nothing but simulation inside a computer. But it is not the same as simulation. Nobody is provinding these memories into our mind. He thinks that our conventional theory of nervous system is wrong. We see and taste not because our senses send electrical impulse to our brain to process. We feel and hear not because of this electrical signal. There is something wrong with this theory that medical science promotes. Electricity and electons are too mysterious to be seen or percieved with bare senses. Why would nature build such a system to process its own electricity? There must be other explanation.

## Theory of relativity

He now thinks about general theory of relativity and its connection with our body and mind. It says events are prime or fundamental entities in the universe. What we call mind is the group of events connected with certain relation. He thinks this could be a clue to the mystery. An event is a collection of four numbers or coordinates (x1, x2, x3, t). So mind is composed of all the events that are of particular type ( space-like). What we see , hear, taste or feel are events happening inside our minds. The physical world is continuous with the events in our mind. For every event happening to a piece of matter there is a corresponding event in our mind. These events are simultanuous. We see not because light comes to our eye but there are simultaneous events. This also corresponds to the fact that there is no existence of light between emission and absorption. The case with other senses is the same as the case of seeing. Thus we can dispense with the electricity based theory of our reality and everything ???## Special relativity

Special theory of relativity is concerned with time dilation and relativistic mass increase. A set of equations completely determines the laws of special relativity. Muhammed Zafar iqbal seems to have explained the mathematics concerning coordinate transformations and energy- mass equivalence. But he has forgotten some useful informations which laid the foundation of relativity. I now briefly explain this :All velocities are relative. If we can compare or make relation between two reference frames we can account for all the facts about relativistic effects. So Einstein used two reference frames whose relative velocity we know. Many other facts like why we need four coordinates instead of three and constancy of velocity of light are very vaguely explained in his books. You can vist this page and understand the theory easily.

The most basic thing about relativity is that we must add a more dimension of time t to usual three dimensions of space x, y, z to describe perfectly something happening.

## Zafar Iqbal's mathematics

Muhammed zafar Iqbal has written many books on mathematics. He has written about geometry and algebra and also calculus. He has developed Bangladeshi
group of international mathematics olimpiad. But I do not like his style at all. He has retained the old tradition of teaching and instructing. Our
country is not getting something new. Where are the fundamentals of mathematics gone? Should we not be teaching our children what is mathematics and what
is its purposes. We can not make our children interested in learning unless we
make the subject pleasant. I do not think the education system is totally wrong but it is
fundamentally weak and old-fashioned. Mathematics should start with few basic principles. For example theory of natural numbers can form the foundation of
the whole branch of algebra and analysis. Geometry can be reduced to few axioms and propositions.
For example Euclid's geometry is concerned with twenty propositions from which other theorems and corollaries can be developed.
Muhammed Zafar Iqbal does not stress on the fundamentals that are needed to study the true nature of mathematics. This seems to
be the same case with our academic institutes. Let me say a few things about difference between logic and mathematics.

The distinction of mathematics from logic is very arbitrary, but if a distinction is desired , it may be made as follows.
Logic consists of the presmisses of mathematics, together with all other propositions which are concerned exclusively
with logical constants of the premisses which asserts formal implications containing variables, together with such
of the premisses themselves as have these marks. Thus some of the presmisses of mathematics , e.g the principle of the syllogism,
"if p inplisq and q implied r, then p implies r," will belong to mathematics , while others, such as "implication is a relation"
will belong to logic but not to mathematics. But for the desire to adhere to usage , we might identify mathematics and logic, and
define either as the class of propositions containing only variables and logical constants; but respect for tradition leads me
rather to adhere to the above distinction, while recognizing that certain propositions belong to both sciences.

## Arithmetic

Some useful arithmetic operations are :## Least Square fitting

This method was invented by Carl Friedrich Gauss. Least square method enable us to define a relationship between various data. Given a set of data we can approximate a curve that will best predict the relationship. Mathematically it will be as follows:The correct mathematical analysis involves differentiation. The problem is to find the curve or straight line that approximate the best fitting. First we start with a straight line having slope m1 and constant m2. The next step is to differentiate the difference R(n) with respect to m1 and m2. We now have two equations with two unknown \ variables to solve. This is always possible. :

This method is also known as linear regression analysis. After finding the parameters we come up with a curve like this one.

The linear regression model will be , mathematically ,

## Gaussian distribution

Gaussian distribution is the curve that has special properties. It is also called the "bell curve". This special curve has many applications in statistics and mathematical physics. The general form of such gaussian curve is as follows:## Geometry equation

Geometry and algebra help us calculate many useful properties of solids and two dimensional figures. We can use the theorems of algebra and geometry to calculate area of a trapezium, parallelogram and others. Some general useful formulas are :If we are given three sides of a triangle we can calculate the are of a triangle. If we know the height and a side we can calculate the area of a parallelogram as given in the figure.

Some elementary geometry formulas are given in a single package :

## Great Circle

Great circle is the shortest route on the surface of a sphere. It the curve spanning a plane that goes through the center of the sphere. If you hold a rubber string tout on the surface of a sphere it will lie along great circle. The distance between any two points on it will be shortest. The equation of great circle is :Where σ and &lamda; are coordinates representing longitudes and latitudes in angles. r is the radius of the sphere.

## First and second Fundamental form

If you want to understand general theory of relativity you will encounter first and second fundamental form which Gauss discovered long ago. It is related to curved surfaces. The distance in curved surface is defined through Gauss's first fundamental form. It has the following form :## Set theory

Set theory was developed by Goerge Cantor. He first gave the definition of set. A set is a collection of well defined objects. Some useful properties of set are given:This formula mentioned can be generalized to more than two or three sets as follows:

## Newton-Rapshon method

Newton-Rapshon method is a process to find root of some equation by iteration method.## Hyperfuncion

Hyperfunctions are generalizations of functions as a jump from one holomorphic function to another at a boundary. A hyperfunction on the real line can be concieved of "as the difference between one holomorphic function on the upper- half plane and one holomorphic function on the lower half-plane. That is , a hyperfunction is specified by a pair (f, g) where f is the holomorphic function on the upper half plane and g is the holomorphic function on the lower half plane.Informally , a hyper function on the real line can be given as the difference f-g so that adding a same holomorphic function to both f and g would not change the result f-g.

As an example Heaviside step function can be represented as this pair of functions.

## Integration formula

Integration is the most useful method in mathematical physics. It is a branch of calculus. Its appication can be seen in theory of relativity , quantum field theory and string theory. It is quite ubiquitous now. There are some basic rules of integrating hyperbolic functions. Here are they:Hyperbolic functions are defined in this way:

Some useful properties of definite integral :

Integration by parts is an useful method in evaluating complicated integral. Here is the formula along with other methods:

Many integrations are done by method of substitution. Here are some such methods:

## Cauchy's Integration formula

Cauchy was a great mathematician and he first gave a rigorous definition of limit. His theorem of complex integration is very well known to us. He also developed the theorem of repeated integration.## Calculus of variation

Calculus of variation is perhaps the most useful topic in differential geometry. It is used to find the maximum and minumum value of a function and even an inflection point where a curve changes its concavity. A summary of calculus of variation can be put in a figure like this :## Differential geometry

Geometry in theory of general relativity is not constant. Hence it is called differential geometry. Differential geometry is the study of surfaces and curved spaces. It is entirely different geometry and it involves a concepts like tensors. Without tensors we can not study such geometry. In three dimensions we can construct a model of such geometry as follows:Normal curvature is defined in this way:

Here E , F , G, L, M and N are the functions of coordinates u and v . Differential geometry is so vast a subject that it can not explained here briefly. But these are the basic ideas.

## Theory of Relativity

General relativity says that spacetime curvature creates gravity. Russell's exposition on general relativity is perhaps most exciting than others. He was able to explain it to the mass people in layman terms at the time when few people understood it. I now recite one of his explanations , which is related to relativistic momentum:

It was found that when an object moves, momentum in a given direction is equal to the invariant mass multiplied by the component of velocity in the given direction.
Invariant mass is the mass measured in the rest frame of the object. There is another mass which is measured in a reference frame other than the object's frame.
This mass increases as the speed of the object increases. When we substitute distance travelled in unit time by distance travelled in per unit interval of spacetime,
the momentum in any given direction remains the same. For ordinary velocity this is a slight change as the distance traveled is very less (the interval is almost equal to
the time lapse between the events). And instead of relative mass we take the proper or rest mass .
These two changes decreases the mass but increases but the velocity. As a result the momentum remains the same.
But invariant mass is replaced by the mass of the object. It seems that the object possesses another kind of momentum.
This is the momentum which equals the mass of the object multipled by the time traversed when traveling an unit interval.

Mathematics of general theory of relativity is hard. It is full of tensor equations and ccalculus. Here is an example of the complexity of equations:

## Russell's account

**The Nature of the problem**

Apart from pure mathematics , the most advanced of the science is physics. Certain parts of theoretical physics have reached the point which makes it possible to exhibit a logical chain from certain assumed premisses to consequences apparently very remote, by means of purely mathematical deductions. This is true especially of everything that belongs to the general theory of relativity. It cannot be said that physics as a whole has yet reached this stage, since quantum phenomena, and the existence of electrons and protons, remains, for the moment, brute facts. But perhaps this state of affairs will not last long ; it is not chimerical to hope that a unified treatment of the whole of physics may be possible before many years have passed.

In spite, however, of the extraordinary successes of physics considered as a science , the philosophical outcome is much less clear that it seemed to be when less was known. The purpose here is to discuss what is meant by the "philosophical outcome" of physics, and what methods exist for determining its nature.

There are three kinds of questions which we may ask concerning physics or, indeed, concerning any science. The first is: What is its logical structure, considered as a deductive system? What ways exist of defining the entities of physics and deducing the propositions from an initial apparatus of entities and propositions? This is a problem in pure mathematics , for which, in its fundamental portions, mathematical logic is the proper instrument. It is not quite correct to speak, as we did just now, of "initial entities and propositions". What we really have to begin with , in this treatment, is hyppotheses containing variables. In geometry, this procedure has become familiar. Instead of "axioms" supposed to be "true" we have the hypothesis that a set of enities (otherwise undefined) has certain enumerated properties. We proceed to prove that such a set of entities has the properties which constitute the propositions of Euclidean geometry, or of whatever other geometry may be occupying our attention. Generally it will be possible to choose many different sets of initial hypotheses which will all yield the same body of propositions; the choice between these sets is logically irrelevant, and can be guided only by aesthetic considerations. There is , however, considerable utility in the discovery of a few simple hypotheses which will yield the whole of some deductive system, since it enables us to know what tests are necessary and sufficient in deciding whether some given set of entities satisfies the deductive system. Morever, the word "entities" which we have been using, is too narrow if used with metaphysical implication. The "entities" concerned may , in a given application of a deductive system, be complicated logical structures. Of this we have examples in pure mathematics in the definitions of cardinal numbers, ratios, real numbers, etc. We must be prepared for the possibility of a similar result in physics, in the definition of a "point" of spacetime and even in the definition of an electron or a proton.

The logical analysis of a deductive system is not such a definite and limited undertaking as it appears at first sight. This is due to the circumstances just mentioned-namely , that what we took at first as primitive entities may be replaced by complicated logical structures. As this circumstance has an important bearing upon the philosophy of physics, it will be worth while to illustrate its effect by examples from other fields.

One of the best examples is the theory of finite integers. Weistrass and others had shown that the whole of analysis was reducible to propositions about finite integers, when Peano showed that these proposistions involving three undefined ideas. The five initial propositions might be regarded as assigning certain properties to the group of three undefined ideas, the properties in question, every propostition of arithmethic and analysis is true of this triad, provided the interpretation appropriate to this triad is adopted. But it appeared further that there is one such triad corresponding to each infinite series x1, x2, x3, x4,... xn,.. , in which there is just one term corresponding to each finite integer. Such series can be defined without mentioning integers. Any such series could be taken, instead of the series of finite integers, as the basis for our arithmetic and analysis. Every proposition of arithmetic and analysis will remain true for any such series, but for each series it will be a different proposition from what it is for any other series.

## "It is your life and it is ending one minute at a time.."

Take, in illustration, some simple proposition of arithematic, say: "The sum of the first n odd numbers is n(squared). Suppose we wish to interpret this proposition as applying to the progression x(0), x(1), x(2),... x(n),.. In this progression , let R be the relation of each term to its successor. Then "odd numbers" will mean "terms having to x1 a relation which is a power of R(squared)" where R(squared) is the relation of an x to the next x but one. We can now define R(xn) as meaning that power of R which relates x0 to xn , and we can further define xm + xn as meaning that x to which xm has the relation R(xn). This decides the interpretation of "the sum of the first n odd numbers". To define n(squared), it will be best to define multiplication. We have defined R(xn) ; consider the relation formed by the relative product of the converse of R together with R(xn); its cube relates x3 to x(3n) etc. Any power of this relation can be shown to be equivalent to a certain power of the converse of R multplied relatively by a certain power of R(xn). These is thus one power of this relation which is equivalent to moving backward from xm to x0 , and then forward; the term to which the forward movement takes us is defined as xmXxn. Thus we can now interpret xn(squared). It will be found that the proposition from which we started is true with this interpretation.It follows from the above that , if we start from Peano's undefined ideas and initial propositions, arithmetic and analysis are not concerned with definite logical objects called numbers, but with the terms of any progression. We may call the terms of any progression 0,1,2,3.., in which case, with a suitable interpretation of + and X , all the propositions of arithmetic will be true of this terms. Thus 0,1,2,3,4,... become "variables". To make them constants , we must choose some one definite progression; the natural one to choose is the progression of finite cardinal numbers as defined by Frege. What were, in Peano's methods, primitive terms are thus replaced by logical structures, concerning which it is necessary to prove that they satisfy Peano's five primitive propositions. This process is essential in connecting arithmetic with pure logic. We shall find that a process similar in some respects, though very different in others, is required for connecting physics with perception.

The general process of which the above is an instance will be called the process of interpretation. It frequently happens that we have a deductive mathematical system, starting from hypotheses concerning undefined objects, and that we have reason to believe that there are objects fulfilling these hypotheses, although, initially , we are unable to point out any such objects with certainty. Usually , in such cases, although many different sets of objects are abstractly available as fulfilling the hypotheses, there is one such set which is much more important than the others. In the above instance, this set was the cardinal numbers. The substitution of such a set for the undefined objects is "interpretation" . This process is essential in discovering the philosophical import of physics.

## "the best teacher is your previous mistake."

The difference between an importantand an unimportant interpretation may be made clear by the case of geometry. Any geometry , Euclidean or non-Euclidean, in which every point has co-ordinates which are real numbers, can be interpreted as applying to a system of sets of real numbers-i.e a point can be taken to be the series of its co-ordinates. This interpretation is legitimate, and is convenient when we are studying geometry as a branch of pure mathematics. But it is not the important interpretation. Geometry is important, unlike arithmetic and analysis, because it can be interpreted so as to be part of applied mathematics- in fact, so as to be part of physics. It is this interpretation which is really interesting one, and we cannot therefore rest content with the interpretation which makes geometry part of the study of real numbers, and so , ultimately , part of the study of finite integers. Geomtery, as we shall consider it in the present work, will be always treated as part of physics, and will be regarded as dealing with objects which are not either mere varibles or definable in purely logical terms. We shall not regard a geometry as satisfactorily interpreted until its initial objects have been defined in terms of entities forming part of the empirical world, as opposed to the world of logical necessity. It is , of course, possible, and even likely, that various different geometries , which would be incompatible if applied to the same set of objects, may all be applicable to the empirical world by means of different interpretations.

So far , we have been considering the logical analysis of physics. But in relation to the interpretation of geometry we have already been brought into contact with a very different problem- namely , that of the application of physics to the empirical world. This is , of course, the vital problem; althought physics can be pursued as pure mathematics, it is not as pure mathematics that physics is important. What is to be said about logical analysis of physics is therefore only a necessary preliminary to our main theme. The laws of physics are believed to be at least approximately true, although thery are not logical necessary; the evidence for them is empirical. All empirical evidence consists, in the last analysis, of perceptions; thus the world of physics must be , in some sense, continuous with the world of our perceptions, since it it the latter which supplies the evidence for the laws of physics. In the time of Galileo, this fact did not seem to raise any very difficult problems, since the world of physics had not yet become so abstract and remote as subsequent research has made it. But already in the philosophy of Descartes the modern problem is implicit and with Berkeley it became implicit. The problem arises because the world of physics is , prima facie, so different from the world of perception that it is difficult to see how the one can afford evidence for the other; moreover , physics and physiology themselves seem to give very accurate grounds for supposing that perception cannot give very accurate information as to the external world, and this weaken the props upon which the y are built.

## "We are all the singing and dancing crap of the world.."

This difficulty has led , especially in the works of Dr Whitehead, to a new interpretation of physics , which is to make the world of matter less remote from the world of our experience. The principle s which inspire Dr Whitehead's work appear to me essential to a right solution of the problem , although in the detail I should sometimes incline to a somewhat more conservative attitude. We may state the problem abstractly as follows:

The evidence for the truth of physics is that perceptions occur as the laws of physics would lead us to expect-e.g we see an eclipse when the astronomers say there will be an eclipse. But physics itself never says anything about perceptions; it does not say that we shall see an eclipse , but says something about the sun and the moon. The passage from what physics asserts to the expected perception is left vague and causal; it has none of the mathematical precision belonging to physics itself. We must therefore find an interpretation of physics which gives a due place to perceptions; if not, we have no right to appeal to the empirical evidence.

This problem has two parts: to assimilate the physical world to the world of perceptions and to assimilate the world of perceptions to the physical world. Physics must be interpreted in a way which tends towards idealism and perception in a way which tends towards meterialism. I believe that matter is less material and mind less mental, than is commonly supposed , and that , when this is realised, the difficulties raised by Berkley disappear. Some of the difficulties raised by Hume, it is true have not yet been disposed of; but they concern scientific method in general, more particularly induction. On these matters I do not propose to say anything in the present volume, which will throughout assume the general validity of scientific method properly conducted.

The problems whihc arise in attempting to bridge the gulf between physics( as commonly interpreted) and perception are of two kinds. There is first epistomological problem: what facts and entities do we know of that are relevant to physics, and may serve as its empirical foundation? This demands a discussion of what, exactly, is to be learnt from a perception , and also of the generally assumed physical causation of perceptions-e.g by light-waves or sound-waves. In connection with this latter question, it is necessary to consider how far, and in what way, a perception can be supposed to resemble its external cause, or, at least, to allow inferences as to characterstics of that cause. This, in turn, demands a careful consideration of causal laws, which , however, is in any case a necessary part of the philosophical analysis of physics. Throughout this inquiry , we are asking ourselves what grounds exists for supposing that physics is "true". But the meaning of this question requires some elucidation in connection with what has already been said about interpretation.

Apart altogether from the general philosophical problem of the meaning of "truth" there is a certain degree of vagueness about the question whether physics is "true" . In the narrowest sense, we may say that physics is "true" if we have the perceptions which it leads us to expect. In this sense, a solipsist might say that physics is true; for although he would suppose that the sun and moon , for instance , are merely certain series of perceptions of his own, yet these perceptions could be forseen by assuming generally recieved laws of astronomy. So, for example, Liebniz says:

"Although the whole of this life were said to be nothing but a dream , and the visible world nothing but a phatasm , I should call this dream or phanthasm real enough , if, using reason well , we were never deceived by it".

A man who, without being a solipshist , believes that whatever is real is mental, need have no difficulty in declaring that physics is "true" in the above sense, and may even go further, and allow the truth of physics in a much wider sense. This wider sense , which I regard as the more important, is as follows: Given physics as a deductive system, derived from certain hypotheses as to undefined terms, do there exist particulars or logical structures composed of particulars, which satisfy these hypotheses? If the answer is in the affirmative , then physics is completely "true". We shall find , if I am not mistaken , that no conclusive reason can be given for a fully affirmative answer , but that such an answer emerges naturally if we adopt the view that all our perceptions are causally related to antecedents which may not be perceptions. This is the view of common sense and has always been, at least in practice, the view of physicists. We start, in physics, with a vague mass of common-sense beliefs , which we can subject to progressive refinements without destroying the truth of physics ( in our present sense of truth); but if we attempt , like Descartes, to doubt all common-sense beliefs, we shall be unable to demonstrate that any absurdity results from the rejaction of the above hypothesis as to the causes of perceptions, and we shall therefore be left uncertain as to whether physics is "true" or not. In these circumstances, it would seem to be a matter of individual taste whether we attempt or reject that may be called the realist hypothesis.

The epistomological problem, which we have just been stating in outline, will occupy us latter. There is still something to talk about ontology-i.e with the question: what are the ultimate existents in terms of which physics is true ( assuming that there are such) ? And what is their general nature.

## Physics major subjects

Physics is a very vast subject. Classical physics includes all the concepts and ideas prior to Issac Newton and Einstein. Modern physics includes quantum mechanics and relativity.The rest of the advanced physics topics are basically combination of quantum mechanics and relativity. Quantum mechanics have deep philosophical consequences. In classical physics electromagnetism plays a vital role. In electromagnetism magentic field created by a moving charge obeys a rule named Flemming right hand rule.

Viscosity is the measure of fluid's resistance to flow. If you know the viscosity of milk you can calculate how long it will take for milk to pass through the pores of cookies. This is the equation :

## Cosmology

Cosmology is the universe as a whole. It describes the motion of planets and other massive ojects. It also deals with the evolution and formation of stars , galaxies. After the discovery of Einstein's general relativity cosmology gained momentum. Einstein's formulation of gravity helped scientists study the shape and size of the universe as a whole. However , general relativity breaks down when describing certain phenomena like black hole singularity and big bang. But it gives an impeccable and precise structures of our solar system and the rest of the universe.The first equation is the field equation of Einstein. It describes the basic interplay between space, time , matter and energy. Friedman developed the metric from this equation which is the quantity ds^2. Friedman analysed the time-time component of field equation and showed that the universe may be expanding. The scale factor a(t) is some parameter which is a function of time. Hubble parameter H is just a function of this scale factor and its derivative.

The second equation of Friedman comes from the other component field equations.

The theory of general relativity can be summarised in the following way:

Spacetime curvature creates gravity.

## Pendulum physics

A pendulum is a peridic motion. Tick tok tick tock is the proper designation of a pendulum. Pendulum has a equation which can be expressed with differential equation.The angular momentum is the moment of inertia multiplied angular velocity. Angular accelaration is the average change of angular velocity :

We can use double derivative to compute volume of some solid object as follows :

## Dirichlet's box principle

This principle states that if there are n+1 things and n boxes then at least one box will contain more than one things when distributing those things among the boxes. A proof can also be given. This can be prooved using proof by contradiction as follow:Suppose we distribute exactly one things to one box. Then there will be a total of n things in n boxes. So n+1-n = 1 thing will be left over. This is a contradiction as we have to distribute n+1 things. One box must contain more than one things. This is as simple as that.

## Heat transfer

Heat is a form of energy. It is the measure of how much energy a hot body contains. Although it is believed that it is entirely different form of energy, it is neverthless an energy that arises due to the random motion of atoms and molecules in matter. It is studied in the subject that is called the kinetic theory of heat. However heat is transferred from one body to another in three different ways:1. conduction: It is a heat transfer process in which heat is transferred by direct contact of one body with another. The atoms in one body vibrates and when one body is put into contact with another body the atoms impart their kinetic energy to other atoms.

2. Convection: It is a heat transfer process in which heat is transferred by the mass motion of the atoms from one part of a body to another part.

3. Radiation: It is the process in which heat is transferred in the form of radiation. The heat from the sun comes to the earth in the form of radiation.

General equation of heat transfer in any matter can be expressed with a second order differential equation.

## "with a few symbols on a page you can describe a wealth of physical phenomena.."

## A clock

A clock's reading can be represented with mathematics like :## Statistics

Statistics is concerned with quantities like average, standard deviation , mean. Statistics deal with a lot of data at once. Here are the equations of statistics in a single package:Statistics tells us how many people will die or how many children will be born in a year in a specific country. Besides it has a lot of applications in finance, marketing and accounting. Business persons rely on statistical facts every time to run their business. In physics, expecially in quantum mechanics , statistics plays a vital role too. It is a scheme to interpret common properties of a collection of data.

Mean is the average of a given number of data. Mode is the value that appears most often in a given number of data. Here is the

## Mapping

Mapping and function have the same meaning in mathematics. Mapping assigns each and every element of a set to one or several elements in another set. An example of mapping is given below :Various types of mapping can be represented with a signle diagram :

A function should have this property :

A function is actually defined through one-to-one mapping which maps each element of a set to exactly one element in another set.

With this notion of mapping a useful theorem can be constructed :

Given a set of X number of elements and another set of Y number of elements , there are X^Y( X to the power Y) number of possible functions. For more analysis about functions in detail you can follow this page.

There are many theorems and definitions concerning mapping.

A fixed point is the point which is mapped to itself. That is to say, if x is a point then f(x) = x .

## Zermelo - Fraenkel set theory

Zermelo - Fraenkel set theory is an axiomatic system that was proposed to remove paradoxes like "Russell's Paradox" . The axioms are as follows:The last one of these is the axiom of choice. Axiom of choice formally states that given a collection of non-empty sets there is at least one set which contains exactly one representative from each one of them even if the collection is infinite.

## Algebra

Ratio is a relation between two numbers. There are some basic rules for manipulating ratios as follows::Algebra cheat sheet.

## Rule of law

Skoll the wolf who shall scare the Moon

Till he flies to the Wood-of-Woe:

Hati the wolf, Hridvitnir’s kin,

Who shall pursue the sun.

—“GRIMNISMAL,” The Elder Edda

N VIKING MYTHOLOGY, Skoll and Hati chase the sun and the moon. When the wolves catch
either one, there is an eclipse. When this happens, the people on earth rush to rescue the sun or
moon by making as much noise as they can in hopes of scaring off the wolves. There are similar
myths in other cultures. But after a time people must have noticed that the sun and moon soon
emerged from the eclipse regardless of whether they ran around screaming and banging on things.
After a time they must also have noticed that the eclipses didn’t just happen at random: They
occurred in regular patterns that repeated themselves. These patterns were most obvious for
eclipses of the moon and enabled the ancient Babylonians to predict lunar eclipses fairly accurately
even though they didn’t realize that they were caused by the earth blocking the light of the sun.
Eclipses of the sun were more difficult to predict because they are visible only in a corridor on the
earth about 30 miles wide. Still, once grasped, the patterns made it clear the eclipses were not
dependent on the arbitrary whims of supernatural beings, but rather governed by laws.

Despite some early success predicting the motion of celestial bodies, most events in nature
appeared to our ancestors to be impossible to predict. Volcanoes, earthquakes, storms, pestilences,
and ingrown toenails all seemed to occur without obvious cause or pattern. In ancient times it was
natural to ascribe the violent acts of nature to a pantheon of mischievous or malevolent deities.
Calamities were often taken as a sign that we had somehow offended the gods. For example, in
about 5600 BC the Mount Mazama volcano in Oregon erupted, raining rock and burning ash for
years, and leading to the many years of rainfall that eventually filled the volcanic crater today
called Crater Lake. The Klamath Indians of Oregon have a legend that faithfully matches every
geologic detail of the event but adds a bit of drama by portraying a human as the cause of the
catastrophe. The human capacity for guilt is such that people can always find ways to blame
themselves. As the legend goes, Llao, the chief of the Below World, falls in love with the beautiful
human daughter of a Klamath chief. She spurns him, and in revenge Llao tries to destroy the
Klamath with fire. Luckily, according to the legend, Skell, the chief of the Above World, pities the
humans and does battle with his underworld counterpart. Eventually Llao, injured, falls back

inside Mount Mazama, leaving a huge hole, the crater that eventually filled with water.
Ignorance of nature’s ways led people in ancient times to invent gods to lord it over every aspect
of human life. There were gods of love and war; of the sun, earth, and sky; of the oceans and
rivers; of rain and thunderstorms; even of earthquakes and volcanoes. When the gods were
pleased, mankind was treated to good weather, peace, and freedom from natural disaster and
disease. When they were displeased, there came drought, war, pestilence, and epidemics. Since the
connection of cause and effect in nature was invisible to their eyes, these gods appeared
inscrutable, and people at their mercy. But with Thales of Miletus (ca. 624 BC– ca. 546 BC) about
2,600 years ago, that began to change. The idea arose that nature follows consistent principles that
could be deciphered. And so began the long process of replacing the notion of the reign of gods
with the concept of a universe that is governed by laws of nature, and created according to a
blueprint we could someday learn to read.
Viewed on the timeline of human history, scientific inquiry is a very new endeavor. Our species,
Homo sapiens, originated in sub-Saharan Africa around 200,000 BC. Written language dates back
only to about 7000 BC, the product of societies centered around the cultivation of grain. (Some of
the oldest written inscriptions concern the daily ration of beer allowed to each citizen.) The earliest
written records from the legendary civilization of ancient Greece date back to the ninth century BC, but
the height of that civilization, the “classical period,” came several hundred years later, beginning a
little before 500 BC. According to Aristotle (384 BC–322 BC), it was around that time that Thales
first developed the idea that the world can be understood, that the complex happenings around us
could be reduced to simpler principles and elucidated without resorting to mythical or theological
explanations.
Thales is credited with the first prediction of a solar eclipse in 585 BC, though the great precision
of his prediction was probably a lucky guess. He was a shadowy figure who left behind no
writings of his own. His home was one of the intellectual centers in a region called Ionia, which
was colonized by the Greeks and exerted an influence that eventually reached from Turkey as far
west as Italy. Ionian science was an endeavor marked by a strong interest in uncovering
fundamental laws to explain natural phenomena, a tremendous milestone in the history of human
ideas. Their approach was rational and in many cases led to conclusions surprisingly similar to

what our more sophisticated methods have led us to believe today. It represented a grand
beginning. But over the centuries much of Ionian science would be forgotten—only to be
rediscovered or reinvented, sometimes more than once.
According to legend, the first mathematical formulation of what we might today call a law of
nature dates back to an Ionian named Pythagoras (ca. 580 BC–ca. 490 BC), famous for the theorem
named after him: that the square of the hypotenuse (longest side) of a right triangle equals the sum
of the squares of the other two sides. Pythagoras is said to have discovered the numerical
relationship between the length of the strings used in musical instruments and the harmonic
combinations of the sounds. In today’s language we would describe that relationship by saying that
the frequency—the number of vibrations per second—of a string vibrating under fixed tension is
inversely proportional to the length of the string. From the practical point of view, this explains
why bass guitars must have longer strings than ordinary guitars. Pythagoras probably did not really
discover this—he also did not discover the theorem that bears his name—but there is evidence that
some relation between string length and pitch was known in his day. If so, one could call that
simple mathematical formula the first instance of what we now know as theoretical physics.

## What is reality

FEW YEARS AGO the city council of Monza, Italy, barred pet owners from keeping goldfish
in curved goldfish bowls. The measure’s sponsor explained the measure in part by saying that it is
cruel to keep a fish in a bowl with curved sides because, gazing out, the fish would have a
distorted view of reality. But how do we know we have the true, undistorted picture of reality?
Might not we ourselves also be inside some big goldfish bowl and have our vision distorted by an
enormous lens? The goldfish’s picture of reality is different from ours, but can we be sure it is less
real?
The goldfish view is not the same as our own, but goldfish could still formulate scientific laws
governing the motion of the objects they observe outside their bowl. For example, due to the
distortion, a freely moving object that we would observe to move in a straight line would be
observed by the goldfish to move along a curved path. Nevertheless, the goldfish could formulate
scientific laws from their distorted frame of reference that would always hold true and that would
enable them to make predictions about the future motion of objects outside the bowl. Their laws
would be more complicated than the laws in our frame, but simplicity is a matter of taste. If a
goldfish formulated such a theory, we would have to admit the goldfish’s view as a valid picture of
reality.
A famous example of different pictures of reality is the model introduced around AD 150 by
Ptolemy (ca. 85—ca. 165) to describe the motion of the celestial bodies. Ptolemy published his
work in a thirteen-book treatise usually known under its Arabic title, Almagest. The Almagest
begins by explaining reasons for thinking that the earth is spherical, motionless, positioned at the
center of the universe, and negligibly small in comparison to the distance of the heavens. Despite
Aristarchus’s heliocentric model, these beliefs had been held by most educated Greeks at least
since the time of Aristotle, who believed for mystical reasons that the earth should be at the center
of the universe. In Ptolemy’s model the earth stood still at the center and the planets and the stars
moved around it in complicated orbits involving epicycles, like wheels on wheels.

This model seemed natural because we don’t feel the earth under our feet moving (except in
earthquakes or moments of passion). Later European learning was based on the Greek sources that
had been passed down, so that the ideas of Aristotle and Ptolemy became the basis for much of
Western thought. Ptolemy’s model of the cosmos was adopted by the Catholic Church and held as
official doctrine for fourteen hundred years. It was not until 1543 that an alternative model was put
forward by Copernicus in his book De revolutionibus orbium coelestium (On the Revolutions of
the Celestial Spheres), published only in the year of his death (though he had worked on his theory
for several decades).
Copernicus, like Aristarchus some seventeen centuries earlier, described a world in which the sun
was at rest and the planets revolved around it in circular orbits. Though the idea wasn’t new, its
revival was met with passionate resistance. The Copernican model was held to contradict the
Bible, which was interpreted as saying that the planets moved around the earth, even though the

Bible never clearly stated that. In fact, at the time the Bible was written people believed the earth
was flat. The Copernican model led to a furious debate as to whether the earth was at rest,
culminating in Galileo’s trial for heresy in 1633 for advocating the Copernican model, and for
thinking “that one may hold and defend as probable an opinion after it has been declared and
defined contrary to the Holy Scripture.” He was found guilty, confined to house arrest for the rest
of his life, and forced to recant. He is said to have muttered under his breath “Eppur si muove,”
“But still it moves.” In 1992 the Roman Catholic Church finally acknowledged that it had been
wrong to condemn Galileo.
So which is real, the Ptolemaic or Copernican system? Although it is not uncommon for people to
say that Copernicus proved Ptolemy wrong, that is not true. As in the case of our normal view
versus that of the goldfish, one can use either picture as a model of the universe, for our
observations of the heavens can be explained by assuming either the earth or the sun to be at rest.
Despite its role in philosophical debates over the nature of our universe, the real advantage of the
Copernican system is simply that the equations of motion are much simpler in the frame of
reference in which the sun is at rest.
A different kind of alternative reality occurs in the science fiction film The Matrix, in which the
human race is unknowingly living in a simulated virtual reality created by intelligent computers to
keep them pacified and content while the computers suck their bioelectrical energy (whatever that
is). Maybe this is not so far-fetched, because many people prefer to spend their time in the
simulated reality of websites such as Second Life. How do we know we are not just characters in a
computer-generated soap opera? If we lived in a synthetic imaginary world, events would not
necessarily have any logic or consistency or obey any laws. The aliens in control might find it
more interesting or amusing to see our reactions, for example, if the full moon split in half, or
everyone in the world on a diet developed an uncontrollable craving for banana cream pie. But if
the aliens did enforce consistent laws, there is no way we could tell there was another reality
behind the simulated one. It would be easy to call the world the aliens live in the “real” one and the
synthetic world a “false” one. But if—like us—the beings in the simulated world could not gaze
into their universe from the outside, there would be no reason for them to doubt their own pictures
of reality. This is a modern version of the idea that we are all figments of someone else’s dream.

These examples bring us to a conclusion that will be important in this book: There is no picture- or
theory-independent concept of reality. Instead we will adopt a view that we will call modeldependent
realism: the idea that a physical theory or world picture is a model (generally of a
mathematical nature) and a set of rules that connect the elements of the model to observations.
This provides a framework with which to interpret modern science.
Philosophers from Plato onward have argued over the years about the nature of reality. Classical
science is based on the belief that there exists a real external world whose properties are definite
and independent of the observer who perceives them. According to classical science, certain
objects exist and have physical properties, such as speed and mass, that have well-defined values.
In this view our theories are attempts to describe those objects and their properties, and our
measurements and perceptions correspond to them. Both observer and observed are parts of a
world that has an objective existence, and any distinction between them has no meaningful
significance. In other words, if you see a herd of zebras fighting for a spot in the parking garage, it
is because there really is a herd of zebras fighting for a spot in the parking garage. All other
observers who look will measure the same properties, and the herd will have those properties
whether anyone observes them or not. In philosophy that belief is called realism.
Though realism may be a tempting viewpoint, as we’ll see later, what we know about modern

physics makes it a difficult one to defend. For example, according to the principles of quantum
physics, which is an accurate description of nature, a particle has neither a definite position nor a
definite velocity unless and until those quantities are measured by an observer. It is therefore not
correct to say that a measurement gives a certain result because the quantity being measured had
that value at the time of the measurement. In fact, in some cases individual objects don’t even have
an independent existence but rather exist only as part of an ensemble of many. And if a theory
called the holographic principle proves correct, we and our four-dimensional world may be
shadows on the boundary of a larger, five-dimensional space-time. In that case, our status in the
universe is analogous to that of the goldfish.
Strict realists often argue that the proof that scientific theories represent reality lies in their
success. But different theories can successfully describe the same phenomenon through disparate
conceptual frameworks. In fact, many scientific theories that had proven successful were later
replaced by other, equally successful theories based on wholly new concepts of reality.
Traditionally those who didn’t accept realism have been called anti-realists. Anti-realists suppose a
distinction between empirical knowledge and theoretical knowledge. They typically argue that
observation and experiment are meaningful but that theories are no more than useful instruments
that do not embody any deeper truths underlying the observed phenomena. Some anti-realists have
even wanted to restrict science to things that can be observed. For that reason, many in the
nineteenth century rejected the idea of atoms on the grounds that we would never see one. George
Berkeley (1685–1753) even went as far as to say that nothing exists except the mind and its ideas.
When a friend remarked to English author and lexicographer Dr. Samuel Johnson (1709–1784)
that Berkeley’s claim could not possibly be refuted, Johnson is said to have responded by walking
over to a large stone, kicking it, and proclaiming, “I refute it thus.” Of course the pain Dr. Johnson
experienced in his foot was also an idea in his mind, so he wasn’t really refuting Berkeley’s ideas.
But his act did illustrate the view of philosopher David Hume (1711–1776), who wrote that
although we have no rational grounds for believing in an objective reality, we also have no choice
but to act as if it is true.
Model-dependent realism short-circuits all this argument and discussion between the realist and
anti-realist schools of thought

According to model-dependent realism, it is pointless to ask whether a model is real, only whether
it agrees with observation. If there are two models that both agree with observation, like the
goldfish’s picture and ours, then one cannot say that one is more real than another. One can use
whichever model is more convenient in the situation under consideration. For example, if one were
inside the bowl, the goldfish’s picture would be useful, but for those outside, it would be very
awkward to describe events from a distant galaxy in the frame of a bowl on earth, especially
because the bowl would be moving as the earth orbits the sun and spins on its axis.
We make models in science, but we also make them in everyday life. Model-dependent realism
applies not only to scientific models but also to the conscious and subconscious mental models we
all create in order to interpret and understand the everyday world. There is no way to remove the
observer—us—from our perception of the world, which is created through our sensory processing
and through the way we think and reason. Our perception—and hence the observations upon
which our theories are based—is not direct, but rather is shaped by a kind of lens, the interpretive
structure of our human brains.
Model-dependent realism corresponds to the way we perceive objects. In vision, one’s brain
receives a series of signals down the optic nerve. Those signals do not constitute the sort of image

you would accept on your television. There is a blind spot where the optic nerve attaches to the
retina, and the only part of your field of vision with good resolution is a narrow area of about 1
degree of visual angle around the retina’s center, an area the width of your thumb when held at
arm’s length. And so the raw data sent to the brain are like a badly pixilated picture with a hole in
it. Fortunately, the human brain processes that data, combining the input from both eyes, filling in
gaps on the assumption that the visual properties of neighboring locations are similar and
interpolating. Moreover, it reads a two-dimensional array of data from the retina and creates from
it the impression of three-dimensional space. The brain, in other words, builds a mental picture or
model.
The brain is so good at model building that if people are fitted with glasses that turn the images in
their eyes upside down, their brains, after a time, change the model so that they again see things
the right way up. If the glasses are then removed, they see the world upside down for a while, then
again adapt. This shows that what one means when one says “I see a chair” is merely that one has
used the light scattered by the chair to build a mental image or model of the chair. If the model is
upside down, with luck one’s brain will correct it before one tries to sit on the chair.
Another problem that model-dependent realism solves, or at least avoids, is the meaning of
existence. How do I know that a table still exists if I go out of the room and can’t see it? What
does it mean to say that things we can’t see, such as electrons or quarks—the particles that are said
to make up the proton and neutron—exist? One could have a model in which the table disappears
when I leave the room and reappears in the same position when I come back, but that would be
awkward, and what if something happened when I was out, like the ceiling falling in? How, under
the table-disappears-when-I-leave-the-room model, could I account for the fact that the next time I
enter, the table reappears broken, under the debris of the ceiling? The model in which the table
stays put is much simpler and agrees with observation. That is all one can ask.
In the case of subatomic particles that we can’t see, electrons are a useful model that explains
observations like tracks in a cloud chamber and the spots of light on a television tube, as well as
many other phenomena. It is said that the electron was discovered in 1897 by British physicist J. J.
Thomson at the Cavendish Laboratory at Cambridge University. He was experimenting with
currents of electricity inside empty glass tubes, a phenomenon known as cathode rays. His experiments led him to the bold conclusion that the mysterious rays were composed of minuscule
“corpuscles” that were material constituents of atoms, which were then thought to be the
indivisible fundamental unit of matter. Thomson did not “see” an electron, nor was his speculation
directly or unambiguously demonstrated by his experiments. But the model has proved crucial in
applications from fundamental science to engineering, and today all physicists believe in electrons,
even though you cannot see them.
Quarks, which we also cannot see, are a model to explain the properties of the protons and
neutrons in the nucleus of an atom. Though protons and neutrons are said to be made of quarks, we
will never observe a quark because the binding force between quarks increases with separation,
and hence isolated, free quarks cannot exist in nature. Instead, they always occur in groups of three
(protons and neutrons), or in pairings of a quark and an anti-quark (pi mesons), and behave as if
they were joined by rubber bands.
The question of whether it makes sense to say quarks really exist if you can never isolate one was
a controversial issue in the years after the quark model was first proposed. The idea that certain

particles were made of different combinations of a few sub-subnuclear particles provided an
organizing principle that yielded a simple and attractive explanation for their properties. But
although physicists were accustomed to accepting particles that were only inferred to exist from
statistical blips in data pertaining to the scattering of other particles, the idea of assigning reality to
a particle that might be, in principle, unobservable was too much for many physicists. Over the
years, however, as the quark model led to more and more correct predictions, that opposition
faded. It is certainly possible that some alien beings with seventeen arms, infrared eyes, and a habit
of blowing clotted cream out their ears would make the same experimental observations that we
do, but describe them without quarks. Nevertheless, according to model-dependent realism, quarks
exist in a model that agrees with our observations of how subnuclear particles behave.
Model-dependent realism can provide a framework to discuss questions such as: If the world was
created a finite time ago, what happened before that? An early Christian philosopher, St.
Augustine (354–430), said that the answer was not that God was preparing hell for people who ask
such questions, but that time was a property of the world that God created and that time did not
exist before the creation, which he believed had occurred not that long ago. That is one possible
model, which is favored by those who maintain that the account given in Genesis is literally true
even though the world contains fossil and other evidence that makes it look much older. (Were
they put there to fool us?) One can also have a different model, in which time continues back 13.7
billion years to the big bang. The model that explains the most about our present observations,
including the historical and geological evidence, is the best representation we have of the past. The
second model can explain the fossil and radioactive records and the fact that we receive light from
galaxies millions of light-years from us, and so this model—the big bang theory—is more useful
than the first. Still, neither model can be said to be more real than the other.

Some people support a model in which time goes back even further than the big bang. It is not yet
clear whether a model in which time continued back beyond the big bang would be better at
explaining present observations because it seems the laws of the evolution of the universe may
break down at the big bang. If they do, it would make no sense to create a model that encompasses
time before the big bang, because what existed then would have no observable consequences for
the present, and so we might as well stick with the idea that the big bang was the creation of the
world.
A model is a good model if it:

1. Is elegant

2. Contains few arbitrary or adjustable elements

3. Agrees with and explains all existing observations

4. Makes detailed predictions about future observations that can disprove or falsify the model

if they are not borne out.

For example, Aristotle’s theory that the world was made of four elements, earth, air, fire, and
water, and that objects acted to fulfill their purpose was elegant and didn’t contain adjustable
elements. But in many cases it didn’t make definite predictions, and when it did, the predictions
weren’t always in agreement with observation. One of these predictions was that heavier objects
should fall faster because their purpose is to fall. Nobody seemed to have thought that it was
important to test this until Galileo. There is a story that he tested it by dropping weights from the
Leaning Tower of Pisa. This is probably apocryphal, but we do know he rolled different weights
down an inclined plane and observed that they all gathered speed at the same rate, contrary to
Aristotle’s prediction.
The above criteria are obviously subjective. Elegance, for example, is not something easily
measured, but it is highly prized among scientists because laws of nature are meant to
economically compress a number of particular cases into one simple formula. Elegance refers to
the form of a theory, but it is closely related to a lack of adjustable elements, since a theory
jammed with fudge factors is not very elegant. To paraphrase Einstein, a theory should be as
simple as possible, but not simpler. Ptolemy added epicycles to the circular orbits of the heavenly
bodies in order that his model might accurately describe their motion. The model could have been
made more accurate by adding epicycles to the epicycles, or even epicycles to those. Though
added complexity could make the model more accurate, scientists view a model that is contorted to
match a specific set of observations as unsatisfying, more of a catalog of data than a theory likely
to embody any useful principle.
We’ll see in Chapter 5 that many people view the “standard model,” which describes the
interactions of the elementary particles of nature, as inelegant. That model is far more successful
than Ptolemy’s epicycles. It predicted the existence of several new particles before they were
observed, and described the outcome of numerous experiments over several decades to great
precision. But it contains dozens of adjustable parameters whose values must be fixed to match
observations, rather than being determined by the theory itself.
As for the fourth point, scientists are always impressed when new and stunning predictions prove
correct. On the other hand, when a model is found lacking, a common reaction is to say the

experiment was wrong. If that doesn’t prove to be the case, people still often don’t abandon the
model but instead attempt to save it through modifications. Although physicists are indeed
tenacious in their attempts to rescue theories they admire, the tendency to modify a theory fades to
the degree that the alterations become artificial or cumbersome, and therefore “inelegant.”
If the modifications needed to accommodate new observations become too baroque, it signals the
need for a new model. One example of an old model that gave way under the weight of new
observations was the idea of a static universe. In the 1920s, most physicists believed that the
universe was static, or unchanging in size. Then, in 1929, Edwin Hubble published his
observations showing that the universe is expanding. But Hubble did not directly observe the
universe expanding. He observed the light emitted by galaxies. That light carries a characteristic
signature, or spectrum, based on each galaxy’s composition, which changes by a known amount if
the galaxy is moving relative to us. Therefore, by analyzing the spectra of distant galaxies, Hubble
was able to determine their velocities. He had expected to find as many galaxies moving away
from us as moving toward us. Instead he found that nearly all galaxies were moving away from us,
and the farther away they were, the faster they were moving. Hubble concluded that the universe is
expanding, but others, trying to hold on to the earlier model, attempted to explain his observations
within the context of the static universe. For example, Caltech physicist Fritz Zwicky suggested
that for some yet unknown reason light might slowly lose energy as it travels great distances. This
decrease in energy would correspond to a change in the light’s spectrum, which Zwicky suggested
could mimic Hubble’s observations. For decades after Hubble, many scientists continued to hold
on to the steady-state theory. But the most natural model was Hubble’s, that of an expanding
universe, and it has come to be the accepted one.
In our quest to find the laws that govern the universe we have formulated a number of theories or
models, such as the four-element theory, the Ptolemaic model, the phlogiston theory, the big bang
theory, and so on. With each theory or model, our concepts of reality and of the fundamental
constituents of the universe have changed. For example, consider the theory of light. Newton
thought that light was made up of little particles or corpuscles. This would explain why light
travels in straight lines, and Newton also used it to explain why light is bent or refracted when it
passes from one medium to another, such as from air to glass or air to water.

The corpuscle theory could not, however, be used to explain a phenomenon that Newton himself
observed, which is known as Newton’s rings. Place a lens on a flat reflecting plate and illuminate
it with light of a single color, such as a sodium light. Looking down from above, one will see a
series of light and dark rings centered on where the lens touches the surface. This would be
difficult to explain with the particle theory of light, but it can be accounted for in the wave theory.
According to the wave theory of light, the light and dark rings are caused by a phenomenon called
interference. A wave, such as a water wave, consists of a series of crests and troughs. When waves
collide, if those crests and troughs happen to correspond, they reinforce each other, yielding a
larger wave. That is called constructive interference. In that case the waves are said to be “in
phase.” At the other extreme, when the waves meet, the crests of one wave might coincide with the
troughs of the other. In that case the waves cancel each other and are said to be “out of phase.”
That situation is called destructive interference.

In Newton’s rings the bright rings are located at distances from the center where the separation
between the lens and the reflecting plate is such that the wave reflected from the lens differs from
the wave reflected from the plate by an integral (1, 2, 3,…) number of wavelengths, creating
constructive interference. (A wavelength is the distance between one crest or trough of a wave and
the next.) The dark rings, on the other hand, are located at distances from the center where the
separation between the two reflected waves is a half-integral (½, 1½, 2½,…) number of
wavelengths, causing destructive interference—the wave reflected from the lens cancels the wave
reflected from the plate.

In the nineteenth century, this was taken as confirming the wave theory of light and showing that
the particle theory was wrong. However, early in the twentieth century Einstein showed that the
photoelectric effect (now used in television and digital cameras) could be explained by a particle
or quantum of light striking an atom and knocking out an electron. Thus light behaves as both
particle and wave.
The concept of waves probably entered human thought because people watched the ocean, or a
puddle after a pebble fell into it. In fact, if you have ever dropped two pebbles into a puddle, you
have probably seen interference at work, as in the picture above. Other liquids were observed to
behave in a similar fashion, except perhaps wine if you’ve had too much. The idea of particles was
familiar from rocks, pebbles, and sand. But this wave/particle duality—the idea that an object
could be described as either a particle or a wave—is as foreign to everyday experience as is the
idea that you can drink a chunk of sandstone.

Dualities like this—situations in which two very different theories accurately describe the same
phenomenon—are consistent with model-dependent realism. Each theory can describe and explain
certain properties, and neither theory can be said to be better or more real than the other.
Regarding the laws that govern the universe, what we can say is this: There seems to be no single
mathematical model or theory that can describe every aspect of the universe. Instead, as mentioned
in the opening chapter, there seems to be the network of theories called M-theory. Each theory in
the M-theory network is good at describing phenomena within a certain range. Wherever their
ranges overlap, the various theories in the network agree, so they can all be said to be parts of the
same theory. But no single theory within the network can describe every aspect of the universe—
all the forces of nature, the particles that feel those forces, and the framework of space and time in
which it all plays out. Though this situation does not fulfill the traditional physicists’ dream of a
single unified theory, it is acceptable within the framework of model-dependent realism.
We will discuss duality and M-theory further in Chapter 5, but before that we turn to a
fundamental principle upon which our modern view of nature is based: quantum theory, and in

particular, the approach to quantum theory called alternative histories. In that view, the universe
does not have just a single existence or history, but rather every possible version of the universe
exists simultaneously in what is called a quantum superposition. That may sound as outrageous as
the theory in which the table disappears whenever we leave the room, but in this case the theory
has passed every experimental test to which it has ever been subjected.

### Reference materials:

Law of thermodynamics

A briefer history of time by S. Hawking

A brief history of time by S. Hawking

Quantum mechanics

Grand Design by Stephen Hawking

perihelion of mercury by Feynman