Einstein and a Century of Physics
In the year 1905, Albert Einstein published three research papers. One created Special Theory of Relativity. The second, proposed that light is made of particles
(photons) and the third, dealt with Brownian Motion which paved the way for the experimental proof of the existence of the atoms.
Thus, Einstein made three fundamental discoveries in one year. This was unprecedented in the history of Science. So that year was named the Year of Miracles and hundred years later the year 2005 was celebrated as World Physics Year.
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In 2005, I lectured on these three discoveries and their influence on the next hundred years of the development of Physics, at various fora and also wrote articles. This essay is based on these.
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Classical Physics
To understand Einsteins's revolutionary discoveries, we must start with the Classical Physics of the period upto 1900.
Newton's Law of motion is: "the product of the mass of a body and its acceleration is equal to the force acting on that body". His law of gravitation is: Any two bodies attract each other. The force of attraction is proportional to the product of the two masses divided by the square of the distance between the bodies".
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Using these two laws, Newton could calculate the motion of any body, whether they are on the Earth or in the heavens.
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Maxwell created his Laws of the Electromagnetic Field on the basis of the experimental discoveries of many scientists. Faraday, who made many experimental studies of the electromagnetic phenomena had already created profound concepts about the electromagnetic field. Maxwell gave a precise form to these concepts through his mathematical equations.
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Important consequences followed from Maxwell's equations. From his equations Maxwell proved that electromagnetic waves exist and he calculated their speed to be 300,000 kilometer per second. It was already known that light has the same speed. So Maxwell concluded that light is an electromagnetic wave. This was a great discovery. For until then what light was had remained as a puzzle.
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In Classical Physics, there is a third system of Dynamics, which is Thermodynamics. But this is not an independant or autonomous system. Boltzman discovered that Thermodynamics is nothing but the average description of the dynamics of a large number of atoms or molecules, about . So Thermodynamics is the Statistical Mechanics of this large number of particles. But, for a long time, many physicists did not believe in the existence of atoms and Boltzmann waged a heroic battle against them.
Let us look at Einstein's 1905 discoveries one by one.
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Brownian Motion
The Botanist Robert Brown discovered in the year 1828 that if pollen are allowed to float in a liquid, they exhibit random movements. First it was thought to be due to some life-force. But this was proved to be wrong. For, particles of inanimate matter also showed the same movements. It became clear that these movements are caused by the molecules of the liquid impinging on the particle. Since the molecules collide on the particle from all directions, the motion is random.
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Einstein gave a precise mathematical description of Brownian motion. His formula showed the connection between Brownian motion and the number of molecules in the liquid. Later Jean Perrin, a French scientist, verified Einstein's formula experimentally and through that determined the number of molecules in the liquid. This number agreed with the number already estimated by physicists and chemists. Thus the existence of atoms and molecules was proved. This is the importance of Einstein's formula for Brownian motion. After that, everybody including those who had opposed Boltzmann's ideas realized the truth that
Theory of Relativity
At the end of nineteenth century, a big confrontation between Newton's Dynamics of Matter and Maxwell's Dynamics of Fields took place. This confrontation was about relative motion. Einstein argued that Maxwell's Laws are correct and changed Newton's Laws to be in conformity with Maxwell's Laws. This is the story of Einstein's Relativity Theory.
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Galileo and Newton had removed absolute motion and absolute rest from the dynamics of matter. Newton's law of motion contains only acceleration and not velocity. Acceleration compares velocities at two times and hence does not depend on absolute velocity. It depends only on relative velocity. Therefore, on a train that moves with constant speed and on the platform which is at rest, the same Newton's Laws are valid.
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But what is the situation as regards Maxwell's Laws? Before we answer this question, consider a light wave that travels with the speed of 300,000 kilometre per second. Let us look at that light wave from a space vehicle travelling in the same direction. We will expect that as observed from the space vehicle, the speed of the light wave will be less. This was the expectation before Einstein appeared.
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However, since the speed of light was calculated from Maxwell's equations and now the speed of the light wave depends on our speed, we will be pushed to the conclusion that Maxwell's Laws depend on our speed. So, although absolute motion and absolute velocity do not occur in Newton's Laws, they occur in Maxwell's Laws.
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What did the experiments say? In a famous series of experiments, Michelson and Morley showed that the speed of light did not depend on the speed of our vehicle. They used the Earth itself as the vehicle.
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Therefore, both experiments and Maxwell's Laws showed that the speed of light does not depend on the speed of our vehicle. In whatever direction and with whatever speed our vehicle or the Earth may be moving, the speed of light is always 300,000 km per sec.
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Einstein took this constancy of the speed of light as the basic principle. As a consequence, he had to change our ideas about space and time completely. This was the revolution unleashed by the Theory of Relativity.
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Newton's Laws of Motion were not consistent with with these new ideas. So Einstein changed Newton's laws of Motion. The famous equation
terrible aftermath were consequences of this.
The ideas on space and time that Einstein created are revolutionary. His teacher Herman Minkowsky said: "Henceforth separare space and time will disappear as illusions. Only the combined space-time will be reality." It is this combination space-time that became the arena for all the subsequent developments
in Physics in the last century. This is the revolution unleashed by Einstein's Relativity Theory, called Special Theory of Relativity.
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Einstein could not remain contented with Special Theory of Relativity. Remember there was another part in Newton's Dynamics, his Law of Gravitation. This also had to be brought into consistency with his new space-time. Einstein had to work for 10 years to do this. Finally in 1915 he succeeded. In that year his General Theory of Relativity was born. In this theory which is regarded as the greatest creation of the human mind, Newton's gravitational force was replaced by the curvature of space-time.
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In the last hundred years, General Theory of Relativity was confronted with many experimental and observational tests and the theory passed all the tests. Finally, in 2016, gravitational waves which are a consequence of General Relativity were caught in LIGO in USA.
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Quantum Theory
Of the two parts of Classical Physics Matter and Field, matter was known to be made of atoms, while field was considered to be continuous. Quantum Theory changed field as made of particles.
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In 1900, Max Planck discovered that heat energy was not continuous, but made of packets of energy, or quanta. This was the beginning of the quantum revolution.
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In 1905, Einstein went one step further. He proposed that light which was so far considered as a wave is also made of quanta. These are the photons. If light falls on a metal, electrons are emitted. This is called photoelectric effect. Einstein, through his quantum or photon idea, succeeded in explaining all the laws of photoelectric effect that had been inferred from experiments. If light was a wave, these laws would have remained as puzzles.
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However, it took almost the whole of the first half of the twentieth century for Quantum Theory to develop into full Quantum Mechanics. Many new concepts were created. Some of them are: Niels Bohr's model of the atom, Satyendra Nath's new statistics for photons and Louis de Broglie's completely unexpected and strange idea of matter waves.
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Ultimately, in 1924, Werner Heisenberg and Erwin Schrodinger created the definitive Quantum Mechanics. In 1928, Paul Adrien Maurice converted their nonrelativistic quantum mechanics into relativistic quantum mechanics.
de Broglie's matter waves established the unity between matter and field. Planck and Einstein had converted the continuous field to discrete quanta. de broglie converted matter made of discrete particles into continuous wave or field. Thus both matter and electromagnetic field were endowed with dual nature. Both appeared as particles and waves.
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Quantum Mechanics created by Heisenberg and de Broglie was about matter. It took some more years for the complete creation of the quantum mechanics of fields. In 1927 Dirac created the quantum mechanics of the electromagnetic field. But its full structure was developed only in 1949-50 by the work Richard Feynman, Julian Schwinger, Shin Ichiro Tomonaga and freeman Dyson. This is the final Quantum Field Theory.
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As far as quantum theory is concerned, Einstein's contributions did not stop with his 1905 discovery. He was the first to use quantum theory successfully in solid state physics. As a result, he solved a puzzle in the specific heat of solids. He extended the photon statistics of Bose and it is called Bose-Einstein statistics. He discovered the stimulated emission of photons. This is the basic principle behind LASER (Light Amplification by Stimulated Emission of Radiation).
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The later connection of Einstein with quantum mechanics concerns the shortcomings of quantum mechanics that he pointed out. The early debates that he had with Bohr have not yet reached any conclusion. The famous Einstein-Podolsky-Rosen paradox has not been solved fully. Einstein's main point was that quantum mechanics is an incomplete theory. Since quantum mechanics contains many counter-intuitive concepts, the debate started by Einstein still continues.
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The present state
Quantum Field Theory which was born by combining Quantum Mechanics and Special Relativity is at present the language of fundamental physics. Quantum Field Theory which was created to explain Quantum Electrodynamics, now serves as the vehicle for the strong and weak forces that act within the atomic nucleus. All the three forces, electromagnetic, weak and strong are now incorporated into quantum field theory and this theory is called the Standard Model. This Standard Model is a generalization of Maxwell's laws for electromagnetism. This was the glowing achievement of the closing years of the twentieth century.
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However, General Relativity and Quantum Mechanics could not be combined. Gravitation that was converted into the curvature of space-time in General Relativity stands separated from Quantum Mechanics. Therefore Quantum Gravity remains as the most important unsolved problem of Fundamental Physics and a challenge. String Theory is the only theory that can solve this. But this is not proved. So the journey continues.
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Nuclear bomb and Beyond
When the history of physics in the twentieth century is described, we cannot but talk about nuclear energy. The Inward Bound Journey that took us deeper and deeper into matter to know the secrets buried inside, showed us the enormous amount of energy locked inside the atomic nucleus. It is Einstein's equation that helped us to understand this energy.
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But this energy was first used to kill people. In 1945, two Japanese cities Hiroshima and Nagasaki were destroyed by nuclear bombs. This is something that should make all scientists, especially physicists, to bow their heads down in shame.
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This demon of nuclear weapons is still with us and is a constant threat. Until it is put into a bottle, there will be no relief for humanity.
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Einstein knew the danger that is threatening the world. After nuclear bombs were dropped over Japan, he said: "The only way by which humanity and human civilisation can survive is by having a World Government that acts according to laws."
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Until his end in 1955, he worked very hard to convince the world leaders to abolish the foolishness of nuclear stockpiling, eschew violence and use moral force. He expressed himself as follows.
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"For the human race to survive, a supranational system that acts according to laws must be created."
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"Only if Gandhi's methods are followed by the world at large, world peace can be protected."
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"What can we do to oppose evil? I cannot see any other way than Gandhi's noncooperation."
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His very powerful words about Mahatma Gandhi:
He lived with a deep faith. That faith was that there are Laws of Nature that we can discover. He devoted his life in discovering them. His wisdom and faith are reflected in his famous words:
( Many things in this essay need further explanation. They can be found in my other essays.)
All of Classical Physics is contained in the two sets of Dynamical Laws: one was the creation of Newton, about the dynamics of matter, and the other was the dynamics of field, created by Maxwell.
All Matter is made of Atoms.
Ages to come, people will wonder, whether such a man in flesh and blood really walked on this Earth.
Subtle is the Lord, but malicious He is not.