Understanding the Universe (part 5)

Part 5 of 6 part Series of Understanding the Universe :-

Equation 5 :- S = (C^3 k.A) / 4.h.G


Imagine you think that you have done a perfect crime leaving no clues at all. No one saw you do the crime, and you left no trace. The only way anyone could prove that you did this, is by finding the journal of your master plan. so you thinks that if i get rid of this journal & i will be free no one will ever know that i am the culprit.
so thinks thinks various ways to destroy the journal. So if you simply toss the journal in the trash someone might find it, you will get caught.
So maybe you should make pieces of journal and then toss it in the trash. That would be better, but someone could take the pieces and carefully put them back together, and your crime would be revealed.
Maybe you should burn the journal. aahha surely that would destroy it. That would probably be good enough, but if someone observed the ash and smoke very carefully, and made really precise measurements, they might be able to figure out where all of it came from and reconstruct the information in the book bcoz the information was still present in the form of ash & smoke.
That is very unlikely to happen, but this journal is the only thing standing between you and the perfect crime. You want to be absolutely, 100% certain that the information it contains is permanently destroyed. How do you get the job done?

This hypothetical story highlights a very real question in physics. Is it possible to permanently destroy information? Or is information, like mass-energy and charge, conserved?
The question is important because it strikes at the heart of what science is ?
With the help of science, we develop theories about how the universe works. These theories describe certain aspects of the universe. In other words they contain information about the universe.
Though our theories are not 100% perfect, but as we (scientist) learn more about the universe, they develop better theories, which contain more and more accurate information about the universe.

Basically the universe is driven by a set of ultimate physical laws, and if we can figure out what those laws are, then we could in state to know about the universe. If this is true, then anything that happens in the universe contains a particular amount of information. For example, the motion of the Earth around the Sun depends on their masses, the distance between them, their gravitational attraction, and so on. All of these information tells us what the Earth and Sun are doing.

Scientists generally assume information is conserved for two reasons. The first is a principle known as Determinism. If you throw a ball in a particular direction at a particular speed, you can figure out where it’s going to land. Just determine the initial speed and direction of the ball, then use the laws of physics to predict what its motion will be. The ball doesn’t seems to have any choice in the matter. It has to follow the laws of physics only. Once it leaves your hand it will land in a particular spot that you have already predicted by those laws. Its motion is determined by the physical laws of the universe.

Everything in the universe is driven by these physical laws, so if we have an accurate description of what is happening right now, we can always predict what will happen later. Thus the future can be determined by the present.

The second principle is known as reversibility. If the speed and direction of the ball as it hits the ground are already given or know, then we can use physics to trace its motion backwards to know where it came from. By observing the ball now, we can know from where the ball was thrown. The same applies for everything in the universe. By observing the universe today we can know what happened billions of years ago. The present is predicated by the past. These two principles are just a precise way of saying the universe is predictable, but it also means information must be conserved.
If the state of the present universe is determined by the past, then the past must have contained all the information of the present universe.
Likewise, if the future is determined by the present, then the present must contain all the information of the future universe. If the universe is predictable, then information must be conserved.

Now i am bringing your attention to new thing called Quantum mechanics though i am not fully aware of Quantum mechanics but i know something in it.
In quantum mechanics, individual outcomes might not be predictable, but the odds of those outcomes are predictable.

It’s kind of like a casino. They don’t know which particular players will win or lose, but they know very precisely that what percentage will lose, so the casino will always make money.

So it looks like you’re in trouble. Since information is conserved, there is no way for you to destroy that journal. You can make the information very difficult to find, but you can’t permanently erase it.
But being an evil genius, you have an idea. You’ll simply throw the journal into a black hole. After all, nothing can escape a black hole, so once you’ve tossed it in, no one can ever get it back. All that incriminating evidence destroyed forever thus the perfect crime !

well may be....

It seems like a good idea. According to Einstein’s theory of general relativity, a black hole has only three basic properties: mass, charge and rotation. If you know those three things then you know everything about a black hole. So if you toss your journal into a black hole, all those plans of the perfect crime are reduced to mass, rotation and charge. All of the information in the journal has been destroyed.

But Einstein didn’t account for quantum mechanics in his theory. Through quantum mechanics, things can escape a black hole.
One of the fundamental principles of quantum theory is known as the uncertainty principle. Basically, the uncertainty principle states that there is a limit to what you can know about an object.
I want to bring your attention to a famous thought experiment called schrodinger's cat(http://en.wikipedia.org/wiki/Schrödinger%27s_cat) by Erwin Schrödinger
to know about the uncertainty (Possibilities).

let us take one more e.g:- suppose you put a marble in a small box. Seal up the box and the marble can’t get out, right? According to the uncertainty principle, there’s a small chance that it could get out. If the marble is in the box, then you know exactly where it is, but you are not allowed to know exactly where it is, only probably where it is. So there’s a very small chance that you may return to find the marble has escaped. Seems to be Strange, it is a very real effect is known as quantum tunneling. For things like marbles the odds of it happening (i.e escaping marble from the box) are so low that they are essentially zero, but at atomic & subatomic level (atoms & electrons) it happens all the time. Your computer wouldn’t work and the Sun wouldn’t shine without it.

A black hole is basically a gravitational box where gravity is so strong that nothing can escape from its gravitational field not even light. Anything put into a black hole should be trapped, but because of the uncertainty principle things can escape.
but over time, the mass and energy of the black hole will escape, and it will radiate away through a process known as Hawking radiation (named after Stephen Hawking). Through the uncertainty principle black holes gradually radiate away.
But this means that the information of a black hole is more than just mass, charge and rotation. It must also contain the information of all the particles it will radiate away. So just how much information does a black hole contain?

The answer is given by the equation below, known as the Bekenstein-Hawking equation. Here S is the information of the black hole, C is the speed of light, h (with a line in the top) is known as Planck's constant, and relates to the uncertainty principle, K is known as Boltzmann's constant, G is Newton's gravitational constant, and A is the area of the black hole's event horizon(http://en.wikipedia.org/wiki/Event_horizon), which is just another way to measure its mass.


What the equation says is the information contained within a black hole is proportional to its size. If you toss something into a black hole, you increase the mass of the black hole, which increases the information contained in a black hole. So tossing your journal into a black hole doesn't make the information disappear.

The Bekenstein-Hawking equation states that the amount of information you toss into a black hole is the same as the amount of information a black hole contains. But according to our understanding of gravity, Hawking radiation is perfectly random. So the black hole will eventually release the right amount of information, but not the same information. This means that information tossed into a black hole really is destroyed. But according to quantum theory, the black hole must somehow retain the information of what is tossed into it. This means Hawking radiation is not random, and the information is not destroyed. This contradiction is known as the black hole information paradox, and scientist don't yet know how to solve it. Most scientists think quantum mechanics is probably right, but we can't prove it yet.

So tossing your journal into a black hole, leads to a perfect crime…!!!
or not !!!!

Understanding the Universe (part 4)

Part 4 of 6 part Series of Understanding the Universe :-

Equation 4: - F = (K. Q1.Q2)/R^2

In 1752, so the story goes, Benjamin Franklin flew a kite in a thunderstorm. The most likely outcome of such an experiment is that you would get yourself killed, so there is some debate as to whether it actually occurred. We do know that similar experiments with lightning rods did occur. What Franklin and others were trying to do is to show that lightning was a kind of electricity.
By the mid-1700s, we had a basic understanding of electricity. We knew that there were two types of charge (positive and negative) and that charge could be transferred between objects. Similar charge repels each other & opposite charges attracts each other.
Then in 1785 Charles Augustin de Coulomb published a work on charge that included the equation shown above. This equation is now known as Coulomb’s law. In this equation F is the force between two objects, the Qs are the charges of those objects, R is the distance between them, and K is a constant known as Coulomb’s constant.

If you remember Part 2 on Newton’s gravity (https://www.facebook.com/photo.php?fbid=290154581116435&set=a.173415186123709.39828.100003656865563&type=1), you might think this equation looks familiar, and you could be right. Like gravity, charged objects have a mutual force between them. This force is stronger when they are close together, and weaker when far apart. The force between charges is, in fact, exactly the same as the force of gravity except for one key difference. Gravity is always an attractive force but where as this force could be positive or -ve depending on charges.
This similarity between Coulomb’s equations and Newton’s led some scientists to think if there was a deeper connection between things like charge and mass. It also drove some scientists to search for a similar equation describing magnetism.
In many ways magnets are very similar to charges. Magnets have two poles(north and south).
Like charges, similar poles push away from each other, while opposite poles attract. You could also magnetize certain materials like iron by rubbing it against a magnet.
In particular, if you break a magnet in half, you don’t get a separate north pole and south pole, you instead get two smaller magnets, each with their own north and south pole.Charges could be separated into positives and negatives, but magnets always came in north-south pairs. that means we can have electric monopole (either positive charge or negative charge) but magnetic monopole does not exist.This was a big mystery. Magnets and charges seemed so similar, and yet they didn’t seem to be connected.

By the early 1800s, electricity could be controlled & Charges could be made to move through metal wires, creating a flow of electricity called a current. In 1819, Hans Christian Oersted accidentally move a compass near one of his wires having current flowing through it, and he noticed that an electric current deflected the compass.
it seems that flowing current produces magnetic field.
In 1831 Michael Faraday demonstrated that moving a wire near a magnet could create an electric current in the wire. or moving the magnet near the wire producess current in the wire. Electricity and magnetism were connected. Electric currents could create magnets, and magnets could create electric currents.

Then in the 1860s James Clerk Maxwell started to work and published a set of elegant and beautifully equations, of which the equation above is just the first. & all these equations are now called Maxwell’s equations.
it just describes the force between two charges. But how does one charge pushes or pulled by the other charge? How do they interact across the empty space between them. Maxwell’s idea was that each charge must reach out to each other with some kind of energy. That is, a charge is surrounded by a field of electricity, a field that other charges can detect. Charges possess electric fields, and charges interact with the electric fields of other charges. The same must be true of magnets. Magnets possess magnetic fields, and interact with magnetic fields. Maxwell found the connection between electricity and magnetism.

They were connected by their fields. A moving electric field creates a magnetic field, and a moving magnetic field creates an electric field. Maxwell had created a single, unified description of electricity and magnetism. He had united two different forces into a single unified force, which we now call electromagnetism.

Maxwell’s theory had another interesting consequence. Since a moving electric field could produce a magnetic field, and a moving magnetic field could produce an electric field, it was possible for an electric field to produce a magnetic field which in turn produce an electric field. Back and forth, over and over, creating a continuing wave of electric and magnetic fields. Maxwell calculated the speed of such a wave. It was exactly the speed of light. In combining electricity and magnetism, Maxwell proved that light is an electromagnetic wave.

Maxwell’s equations are still central to modern astronomy. We now observe a wide range electromagnetic waves from visible light, to radio waves to x-rays. These waves interact with magnets and charges, and those interactions tell us about the universe.
But the equation above is important for another reason as well. Coulomb’s equation was the first of what became Maxwell’s unified theory of charges, magnets and light.
Over the years we have discovered other unified theories.
The unified theories helps us to understand the earliest moments of the big bang, and the workings of black holes. but there are still many cosmic mysteries where we don’t yet know the connections. How does quantum mechanics connect to gravity? Is dark energy a separate field, or is it connected to the fields we know? So we continue to search for deeper and more connections, hoping to find a single description of all the forces and fields and particles in the universe.

Understanding the Universe (part 3)

Part 3 of 6 part Series of Understanding the Universe..

Equation 3:-     T' = T. sqrt root(1-V^2/C^2)


==>Time dilation:-

Imagine you are in a train & is at stand still position Then suppose if i ask you what is your speed at that moment you will laugh on me since it is zero because it is at rest.
Now let the train starts moving with some velocity & now i ask you what is your speed? then you will say aaha same as the speed of train.
Now suppose you started moving in the train in same direction of trains with some velocity. & then i ask you what is your speed now? you will give answer train speed + my speed. this is true as per your knowledge about speed.
now lets say a passenger is sitting on his seat & you started walking inside the train(at 10kmph) & trains is in motion(100kmph). A person watching you go from outside the train, thinks that your velocity is greater that train (which is 110kmph) but the passenger sitting inside the trains sees that you are only moving with 10KMPH).
Why is it so?
It is because that your speed is relative i.e it depends upon the aspect of what you are measuring it against(w.r.t whom). since Relative to another passenger your speed is slow, but relative to the ground person your speed is fast. This is relativity.

so guys when some one ask you what is your speed then ask him give me the reference for measurements.

let me ask you one question when you are sitting on chair then are at at Rest position (steady, Not moving at all). If you say Yes then think again you might be be sitting on chair which is not moving but earth (where you lives) is not at rest position it is moving at speed of 30 km/sec around the Sun & The whole solar planets are moving around the Black hole which is at center of our Galaxy & our Galaxy itself not steady so how could you be at rest position, think for it!!!!!!!

Before Galileo’s time it may have been known, because motion could always be measured relative to the fixed Earth. But as we learned the Earth moves around the Sun, & this raised an interesting philosophical puzzle. Is there any place or the point against which all speeds can be measured, or is it really the case that speed is always relative? Is there such a thing as absolute speed?

Now let me move you towards Light. In the mid-1800s, physicists came to understand that light was a wave. At the time it was thought that all waves travel through a medium. Sound waves travel through air, water waves travel through water, and so on. That means there must be a medium through which light travels.
Physicists couldn’t observe this medium, but they called it the "luminiferous (light-bearing) ether". There soon started to observe the ether, because the ether was a way to measure absolute speed.

for e.g : If you drop a pebble or stone in a calm water, you can see the ripples flow outward at a particular speed. The ripples flow with the same speed in every direction. But if you were moving in a boat and dropped a pebble into the water, the ripples would seem to move slower in the direction of the boat’s motion, and faster in the opposite direction. Because of the boat’s motion, the speed of the ripples would be different in different directions.
The same would be true with the ether. Since the Earth must be moving through the ether, the speed of light must be different in different directions.
So In 1887, Albert Michelson and Edward Morley performed an experiment to measure this difference in the speed of light. But what they found is really the amazing result which was the one the Best outcomes of an experiment. They found that Speed of light remains same in all the direction no matter what direction light traveled, no matter how they oriented their experiment, the speed of light never changed. hence the concept of ether was failed.
but it directly violating the principle of relativity since the speed is not changing that means for any observer speed is same(whether he is in train or standing outside of train).
Then in 1905 Albert Einstein published a solution to the problem, known as special relativity. He demonstrated that if the speed of light is absolute, then time must be relative, as given in the equation below. It relates the different times of two observers, say you and me.

[since Speed = Distance/Time, if distance is kept constant then if speed is changing time Must slow down
e.d let Dist is 3 lakh km & speed is 300km/s then time required will be 1000 sec
now if the speed is 3 lakh km/s then time required will be 1 sec (i.e Speed ^ time goes down)]

here in the expression, T is your time as you measure it, T’ is your time as I measure it, V is your speed relative to me, and C is the speed of light. What it says is that your time appears slower to me than it does to you. The faster you move relative to me, the slower your time appears to me. This sounds crazy. How can time be relative? It is, however, it is real.

We can see how this works if we imagine a clock made with light. Take two mirrors and place one above the other and facing each other & let us assume that they have inbuilt clock which tick when a pulse of light strikes onto it , then bounce a pulse of light between them. as you are the observer & you are with the setup & you are the reference. so you will see that light is bouncing between two mirrors at same speed (i.e at speed of light) the graph would be a straight line. now let us suppose you are moving with the setup in horizontal line & a person watching you from certain distance so what he will see is pulse move at the speed of light, but from my view the light can’t move straight up and down instead person sees the pulse move diagonally up then diagonally down, which is a slightly longer distance between each bounce. That means it would take the light longer to travel from bounce to bounce. So from my point of view the ticks of your clock are slower than ticks as you see them(i.e person standing outside & watching it)
Your clock appears to be running slow because of your motion relative to me.
The faster you move relative to me, the more your clock will slow down from my point of view.
I know its hard to digest that is why i am linking one video to it so that you get the idea of time relativeness..
(http://www.youtube.com/watch?v=KHjpBjgIMVk)

there are practicle example that has been found are as follows: -
1. In the CERN LHC (At Jeneva) a huge particle accelerator has been established to study the particles at atomic levels. there it has been observed that collision of a particles when traveling at nearly the speed of light produces its subatomic particles (Pi mesons http://en.wikipedia.org/wiki/Pion) whose life (which is 26 billionths of a second) has been increased by 30%.

2. A GPS determines your location by receiving signals from satellites orbiting the Earth. Those satellites broadcast their time and location, which your GPS uses to determine your position, so it is important that the satellites broadcast the proper time. But the satellites are moving at high speed relative to you, which means their clocks run slightly slow. To give you the accurate time the satellites have to account for that slowdown effect.
This is special relativity.

 

Understanding the Universe (part 2)

Part 2 of 6 part Series of Understanding the Universe..
Equation 2:- "F = (M1.M2. G)/R^2"

Earlier in the history a Greek philosopher "Aristotle" gave the idea that motion is divided into earthly lines & heavenly Circles & so the planets must moves in the perfectly circles. Astronomers soon learned this wasn’t true, but the ideas of Aristotle
was so deeply rooted in the minds of scholars that astronomers imposed circular motion upon the heavens for a thousand years.

Then in the early seventeenth century Johannes Kepler published simple rules that described the motion of the planets. They are now known as Kepler’s laws of planetary motion. Kepler did not use circles to move the planets. Kepler suggested that planets moves in elliptical orbit. Kepler’s theory was the first step toward modern astrophysics, giving us an accurate description of planetary motion. But Kepler’s laws were still merely a description of motion.

It was Sir Isaac Newton who gave us the mechanism. In the late seventeenth century Newton published his Principia, which described a world which is governed by a simple set of rules for forces and motion ( three laws of Motion which governed motion of body & a law of Gravitation)
Here F represents the force between two bodies, the M’s are the masses of the two bodies, R is the distance between them, and G is a number known as the gravitational constant.
What the equation says is that bodies are attracted towards each other through gravitational attraction. The strength of their attraction is greater if they are close together, and lesser if they are more distant. This force of attraction exists between any two bodies. Between Sun and planet, between Earth and moon, and between me and you.
Newton's laws are so accurate that he could use his rules to explain why the planets moved in ellipses.
There is, however, a mysterious consequence of Newton’s equation. The force of gravity is always attractive, and the closer two bodies are the stronger their attraction.
It would seem then that if large enough masses got close enough together the gravitational attraction would be so strong that the objects would be crushed under their own weight. Gravity would pull ever stronger, squeezing the objects more and more, making them smaller and smaller until they finally collapsed into a single, infinitely dense point. A gravitational singularity. which is also called A Black hole where gravitational attraction is so strong that nothing can escape its pull, not even light therefore it is Black hole.
In 1974, radio astronomers discovered an intense energy source at the center of our galaxy. Named Sagittarius A*, it appeared to be a large black hole.

Newton’s equation gave us the mechanism behind the motion of the planets. It tells how we are connected to everything in the universe through mutual attraction.

Understanding the Universe (part 1)

 Most of people like me have interest in Astronomy, Universe. They have so many questions in their mind about universe like how it works? What are those laws which governs its working. so for all those people here are some posts which can tell you everything about universe.


Part 1 of 6 part Series of Understanding the Universe..
Equation 1:- "E=MC^2"

Earlier in the History there was a serious problem for Astronomy that How the stars shines? & we are well aware of conservation of energy.(That is, energy must come from somewhere, and it must go to somewhere) & thermodynamics. When something is squeezed Heat is generated.This gave a mechanism which could cause the stars to shine
The basic idea of this mechanism is that for a large body like a planet or star, gravity tries to compress the star or planet smaller and smaller. due to this compression Core of the body is heated & which in turn radiated the energy in the form of light.
In this way a star could be heated by its own weight. This is a very real effect for gas planets and brown dwarfs (http://en.wikipedia.org/wiki/Brown_dwarf). Jupiter, for example, radiates more heat than it receives from the Sun because of this mechanism.
But for a star such as the Sun there is a problem. Gravity can only squeeze a body so far, so there’s a limit to how much heat can be generated by the mechanism. And by conservation of energy, once the Sun has radiated all its heat energy as light, it is done shining. It’s fairly easy to estimate the rate at which the Sun loses energy given its brightness and size.
Its also fairly straightforward to calculate just how much energy the Sun could gain by gravitational compression. If you apply conservation of energy, then you can determine how long the sun could shine before it runs out of energy, and you get a clear answer: about twenty million years. But it disagreed horribly with geology, where fossil evidence demonstrated that life existed on Earth for several hundred million years, likely much longer.

How is that possible that the Sun could only be tens of millions of years old & earth 100 of million years old?
So the Sun must have shone for billions of years, but astronomers and physicists had no explanation for how that was possible.Gravitational compression couldn’t provide enough energy, nor could chemical reactions, and what else was there?

Then came Albert Einstein, In 1905 he published his paper on special relativity where he suggested Energy and Mass are two sides of the same coin.They are connected.
Not only that, mass can become energy and energy can become mass. This connection is summarized in equation below. In the equation E stands for energy, m for mass, and c for the speed of light.
it simply states that a mass can be converted to its equivalent energy & vice versa.
Einstein gave us the key to understanding the stars.

e.g: if we could convert one paper clip entirely to energy, it would produce enough electrical energy to power the entire world for about 800 billion years.

Somehow the Sun was converting a bit of its mass into energy, and with it’s great mass the Sun could shine for billions upon billions of years.
Fission process only works for heavy elements.
The process which works on the Surface of SUN is the Fusion process where lighter elements like hydrogen fused together to become Helium. We then learned how helium could become carbon, nitrogen and oxygen, and on to heavier and heavier elements.(of course the energy which requires for this process could be in billions of billion amount)

It not only gave us fusion as the source of a star’s power, but explained from whence the diversity of elements came. Hydrogen and helium fusing into heavier elements.
When the star exploded it scatters all its matter across the cosmos which could contain these elements. then because of gravity they combines to form other stars or planets (one of which is home to us).

So from single equation we now knows we are dust of stars since we are also made up of these elements (carbon, nitrogen, oxygen, Hydrogen etc are found in our DNA & DNAs are the basic building blocks of a biological cell)

Newton's Gravity Continued...

http://vaibhavkhamgaonkar.blogspot.com/2011/05/newtons-gravity.html
                                            (link to previous post)

As in the previous post we have found out the Newtons most famous equation i.e. Law of Gravitation which is given by

F = G*(m1 * M2)/r^2
where G is the gravitational constant = 6.67 * 10 ^-11
m1 & M2 are the masses of an object experiencing gravitational force.
r is the distance between two object.


Now lets see what does it mean, it simply tells that if a objects having mass (m1 & M2) which are separated by certain distance (r) then according to Newton, they will experience some kind of attraction (they will experience force of attraction) which depends on products of there Masses & the Square of Distance between them. This is often called as Inverse square law.


Now with this we can find the force of attraction between two object. But wait if it is true that two object separated by certain distance they will experience a force then why we not experiencing that force since we are pretty close to various objects around us.
let me clarify you, in day today life we used to pass through various objects but we haven't experience that kind of attraction.
Why ?
Well if you look at the Equation carefully, there is a term called Gravitational constant "G" & whose value is very very small. now if u thing that u should experience the same kind of force then the only thing is to overcome that value is the mass but  you don't have enough mass to overcome thus we aren't experience this force. This phenomenon occurs only for the the objects whose mass is very very high (like Planets, Stars, Galaxies etc)

Now just tell me that if you are having two objects of different masses lets say 1 is of 1Kg & other is of 10 kg. they both are falling from 100 stories building. so which one will fall first on the ground if they are start falling at same time...?

If u say that they will going to fall at same time then u are corrects....
let me tell u how :-

what is the force:-
F = m * a ----------------------- (m= mass , a = Acceleration)


According to Galileo's model

F = - m * g ------------------------------ ( - because object is accelerating downward)

equating 1 & 2
 m * a = = - m * g

thus  a = -g --------------------------------i.e acceleration will be equal to gravitational force pulling the object down word with 10 m/s^2

Now lets consider an object of mass (m) who is falling towards earth having mass (M).
Now according to newtons gravitational law
the force of attraction between two objects (m &M ) are given by

F = (m * M) * G / r^2

& also we know that object of mass 'm' is moving & is being attracted towards 'M' by certain force & that can be given by

F= m * a

therefore on comparing these  2 equations we have
m * a = (m * M) * G / r^2
Which finally gives

a =  (M * G) / r^2 ---------------------------------------------( Note down here the mass of small object falling to earth is not appearing)

Acceleration of small object is independent of its mass. i.e if there are no. of objects falling towards earth then their acceleration will not depend on their individual masses but it depends on the the other object on which they are falling.
Thus we can say that every object falling on ground will take same time provided they are dropped at same time.

Newton's Gravity

Everybody knows who is the father of gravity. He is none other than Sir Isaac Newton. He accidentally invented the gravity. As you all know by just seeing apple falling on the ground. He called this force as Gravity. It is the force that attracts every object towards the center.(Gravitation is a natural phenomenon by which physical bodies attract with a force proportional to their mass).

 At the time of Newton, Everybody knows that planets orbits around the Sun but the question was how does the planets moves, what held them around the orbit ?

The most famous theory comes from the french Philosopher(Henri Decart), he thought a universe as a giant machine like a clock & even the orbit of planets can be explained by simple mechanical interaction of the part of the machine. But Newton had trouble accepting this concept.

With the falling Apple from the tree he realized that what held the planets in the orbit is not a physical mechanism as suggested by (Decart) but an invisible force he called "Gravity" & he was convinced that force pulling apple down the earth & the motion of the moon around the earth is one & the same thing.

The Italian Scientist (Galileo) has already proved that motion of an all object falling down word picks up the same speed regardless the Mass of an object & finding a average speed (of an object) is an straight forward process.
e.g:- If you want to find the average speed of falling apple, all you have to divide the distance traveled by apple & time taken by apple to fall down.
 i.e.
              Avg Speed = 60 ft / 2 sec
                                = 30 ft per sec

 
 But the Newton was not satisfied with this.
=> What would be the speed of an apple which is constantly accelerating at every point along the way?
=> What would be the apple velocity at half way point?
                                     
To find out this, you have to measure avg speed for smaller & smaller period of time. shorter the internal closer you get to knowing the apple speed at that moment. But to find the precise speed at a single instance you have to reduce time interval close to zero as you can [ Newton invented a way to make time interval infinitesimally small ]
 with this technique it was possible to calculate quantities that are constantly changing like speed of an apple at any particular moment or our planet position changes over time. With this technique Newton invented a new branch of Mathematics called Calculus ( It is the quantitative understanding of how the things changed ).

At those days scientist thought that Sunlight (white light) was pure & colors are produced by physically modifying the white light which they believe passing it through Prism did.
 But newton did something different he send a light beam through a prism & he produces spectrum of colors & then he moved one more step further he then send red ray of light  to 2nd prism he found instead of having new color it remains Red. Newton concluded that White light is not pure but it is the combination of all the colors of rainbow.
Galileo has spent years studying motion on earth & he determined that projectile always follows a curved path called a parabola. But he believed motion of celestial object like moon was very different.
 Newton disagreed to this & he thought same law must be govern on earth & on the Heaven.
 He then made his 3 laws of motion.

 1) An object in motion will remain in motion forever unless acted by an external force
 2) An object's rate of acceleration is proportional to force exerted on it
 3) Every action there is equal & opposite reaction

These laws makes scientist to make accurate prediction about how object moves & they are still used today to send Rockets into Space & to explore other  world. But explaining the orbital motion of planet requires other ingredient. 
To show how gravity works on earth & heaven newton decided a thought experiments.
 lets imagine cannon ball is going to fire from top of an mountain.
--> From the first law if the cannon ball is fired then it would travel in a straight line forever but gravity pulls the ball down word.
 --> If the speed is low then cannon ball hits the earth down the mountain
 -->Higher the speed, farther  away the ball lands
 -->But if the speed is high enough then the cannon ball would travel all the way around the earth & settle down in the orbit.
 Newton then thought the moons orbit around the earth & cannon ball motion on earth are govern by same law of gravity.
 now if the gravity govern the motion on moon on earth then why not Jupiter or other planet & their moon;Why not the Entire solar System?

 In other words this invisible force (Gravity) operated every where in the Universe.
Newton called this "Universal Law of Gravitation" & it is given by single mathematical expression

F = G*(m1 * M2)/r^2
where G is the gravitational constant = 6.67 * 10 ^ -11
m1 & M2 are the masses of an object experiencing gravitational force.
r is the distance between two object



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