“God doesn’t play dice with the universe”-- Einstein 

 Einstein believed that God doesn’t play dice with the universe. Although, he was not a believer, what he meant by the sentence is everything around us can be described or understood by physical law. There is no uncertainty. But it turned out he was wrong. God is the biggest gambler of us all. 

 It turned out that the world works on probability. Well, perhaps we can predict everyday’s phenomenon but the particles, atoms, molecules which turned out to be the building block of everything has their totally unpredictable motion. They are so small and so fast that we can never know for sure what is their position exactly in a particular moment? But that doesn’t mean that we can’t predict it to a certain extent. The word Prediction is deeply related to the word probability. Now the question is, what do I mean by probability? 

Well, when I was a child I was a fan of thriller movies. In one Indian movie there was a character of serial a killer. He used to give his victims choices before he kill them. If the outcome of the coin he is going to toss is head, the victim will live.  If it is tail victim has to die. So there is 50% percent probability of each outcome. It is called playing on luck or chance or in a gambler’s word it is a gamble. The same situation happens when we throw a dice. Here for each outcome the probability is one over six (1/6) as there can be any of those six outcome. If you say, it will come 3 the chance is 1/6. If you are lucky enough, you will win otherwise you will lose.

                                                  Dice | source

  A sacrifice for a new theory to come 

  I think, there is no physics and chemistry student who doesn’t know about Maxwell-Boltzmann probability distribution on motion of particle’s velocity. It is a theory used for speed of particles in ideal gas as the particles can move freely without interacting with each other. Anyway that is not the topics today. It is Boltzmann who believed in probability for constructing his atomic theory.  He was ahead of his time. So he had to go through a lot of criticism. In the end he gave up and hanged himself at the age of 62.   

                            

                                       Ludwig Boltzmann | source

  The greatest debate of physics

 Aristotle, Socrates and so many of the Greek philosophers believed that debating about a problem is the best way to reach to the best solution for that problem. The debate can be bitter but the focus is always to find the best solution for a problem. In political words we call it democracy.  But any way so many scientists had debated about the nature of light. Some said it is particle some said wave.

 The famous Sir Isaac Newton proposed that light is made of small particle called corpuscles. His theory could easily explain reflection and refraction of light but it couldn’t predict diffraction, polarization and interference of light. But this theory survived for about hundred years probably because of Newton’s fame.  

  “Nature and Nature's laws lay hid in night:
God said, Let Newton be! and all was light.”   -- Alexander Pope  

                                    Sir Issac Newton | source

 During his time Christian Huygens had another opinion about the nature of light. He said light is wave. His theory is called the wave front theory. Huygens proposed that- 

  “Every point on a wave-front can be thought of a source of secondary wavelet and they spreads out at the speed of light and the new wave-front is tangential to all the secondary wavelets.”   

                                              

                                                  Huygens wave-front theory | source

  This theory predicted diffraction and interference perfectly. But as Newton’s fame was so undeniable, this theory never came to limelight until a young physicist named Thomas Young showed by double slit experiment that wave theory can explain interference.  He believed wave theory explains the true nature of light.     

  Let us think of a football player shooting footballs toward the net but we put a wall in between the footballer and the net with two gaps.  Most of the balls would bounce back hitting the wall, but some of them would pass. Now if we close one of the gaps, we will observe there is a certain place where the footballs are gathering. Now if we close the first gap and open the other one, we will find another place where the football will gather. And now if we open both of them, the result is the sum of the previous result when one of the gaps was opened. This is like our everyday’s experience. But wait, here comes the twist. 

                          How Double slit experiment should look like | source

  But when we throw photons or other particles, the story is totally different. There is places where there is bright  band and the places in between each two bright band is a dark band. You may say “you are kidding, right?”  No, my friends I am not. 

           

                           Double slit experiment | source

  It happens because of light behaves like a wave here as it passes through those slits. The slits allow the waves to interfere. The place where the top of two waves meet, there we find the bright band and where top of one wave meets the bottom of other one, they cancel each other and we get the dark band. This how it shows the wave nature of light.  

  During 1860, a Scottish physicist named James Clerk Maxwell discovered that changing magnetic field can produce electricity which was based on experiment. He put forward four equations. When he tried to solve them he find wave like solution. As a result of solving those equations he found a number which is 310,740,000 meters per second and he immediately got that is the speed of light. He proposed light is an electromagnetic wave. But there was no proof until Hertz discovered radio waves and showed by experiment that light is of course an electromagnetic wave. So, people thought this the end of the debate.  

                                          Maxwell equations | source

  Photon  

  Beginning of 19th century was the beginning of new era. It was sure that light is an electromagnetic wave until a new invention came up called photoelectric effect. Now the question is what is photoelectric effect?   

  When light shines on a material, it emits electrons. What happens here is when light shines on a material it makes the atoms in the material to be excited and the atoms emit electrons. But the problem was that not every light emit electron, light with a particular frequency does that. If light is wave, this phenomenon should happen for all waves not depending on their frequency.   

 Albert Einstein was fascinated by this phenomenon and tried to explain it. He proposed light is neither wave  nor particle it is combination of both and he called it wave packet in other words photon which says light travels in discrete bundle of electromagnetic energy. In 1921, this theory won him the long awaited Noble Prize he deserved but it opened the gate for a new field called quantum mechanics which says we can’t predict everything precisely but to a certain extent we can. That means actually saying that everything works on probability. 

                                        

                                         Photo electric effect | source

 Wave particle duality of light  

  Light is wave at the same time particle. So what is a particle? Particle is something which has a fixed position. On the other side wave is something which doesn’t have a fixed position rather it has wavelength. So how can something be a wave and at the same time a particle?  

  Let me give you an example. Think that you have a girlfriend who studies with you and you are most of the time with her. So, now if a friend of yours asks another friend where you are now. The answer will be you are with your girl friend. So your position is fixed, you are a particle. But wait, now if he asks where you both are? Then the other friend said somewhere in the campus. Now your position is spread over the campus, there is certainty that in someplace where both of you usually go but it is not for sure. Here again comes the concept of probability. Now my friend, you are wave. Hope you have understood the concept of wave particle duality.   

  The proof came from De Broglie equation that says wavelength is equal to Plank’s constant over momentum. Here wavelength is a property of wave but momentum is a property of particle. This proved wave particle duality.  

 De Broglie equation |source 

  Uncertainty principle     

  “We can’t measure  position and momentum of a particle precisely at the same time. In another way the more precisely we measure the position, less precisely we know the momentum and vice-versa Multiplying the errors is always more than Plank’s constant over 2 pi.”  

 Uncertainty principle | source

  So it means that if we want to find a particle we can’t find exactly where it is. We can find a probability of the particle to be somewhere in a place. The sum of total probability is one. Einstein couldn’t
agree so he said that God doesn’t play dice with universe.  

  Conclusion 

  It is an infinite universe. Every single point is its center. But everything in this universe is made of tiny particles. Motions of these particles are unpredictable. Probability plays its role here. So our very existence depends on chance and still we are here, existing. So, God does play dice and he plays it better than anyone.