Category Science & Technology

The General Theory of Relativity predicted that the space-time around Earth would be warped and twisted due to Earth’s rotation. The theory gave a new framework for all of physics and proposed new concepts of space and time.

In 1907, Einstein had certain realizations about his theory. He understood that special relativity could not be applied to gravity or to an object undergoing acceleration. Consider a person sitting inside a closed room on Earth. That person experiences Earth’s gravity. Now imagine if the same room was placed in space, away from the gravitational influence of any object.

If it is given an acceleration of 9.8 m/s2 (same as Earth’s gravitational acceleration), the person inside the room won’t be able to tell whether he is feeling gravity or uniform acceleration. This idea laid the foundation of the General Theory of Relativity.

Einstein’s next question was how light would behave in the accelerating room. When we shine a torch across the room, the light looks like it is bending forward. This is because the floor of the room would be coming up to the light beam at an ever-faster speed, so the floor could catch up with the light. As gravity and acceleration are equivalent, light would bend in a gravitational field.

It took Einstein several years to find the correct mathematical expression of these ideas. In 1912, his friend, mathematician Marcel Grossman, introduced him to the tensor analysis of some mathematicians. This helped him. After three more years of work, the foundations of this theory were laid in the four papers he published in 1915.

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Einstein was not the first scientist to observe and study the photoelectric effect. However, he was the first to properly understand the nature of light and draw the correct assumptions from it. Physicists James Clerk Maxwell in Scotland and Hendrik Lorentz in the Netherlands had already proved the wave nature of light in the late 1800s. This was proven by seeing how light waves demonstrate interference, diffraction and scattering- which are common to all waves including water.

Einstein’s 1905 argument that light behaves as sets of particles (initially called quanta and later ‘photon’) was contradictory to the classical description of light as a wave. A completely new model of light was needed to explain the phenomenon. Einstein developed a model for this purpose and according to this, light sometimes behaved as particles of electromagnetic energy or photons. Though others had presented this theory before Einstein, he was the first to explain why it occurred and consider its potential.

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Photoelectric effect is the emission of electrons from a substance when electromagnetic radiations fall on it. For instance, when light falls on a metal plate, electrons are ejected.

Light with energy above a particular point frees electrons from the surface of the solid metal. Each photon (particle of light) collides with an electron and uses some of its energy to remove the electron. Photon’s remaining energy transfers to the free negative charge which is called a photoelectron. This was a discovery that revolutionized modern physics as it clarified many doubts regarding the nature of light.

The photoelectric effect proposed by Einstein in 1905 remains valuable in various areas of research such as material science and astrophysics. It is also the basis of many useful devices. The ‘electric eye’ door openers, light metres used in photography, solar panels and Photostat copying are all applications of the photoelectric effect.

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The equation E=mc2 is perhaps one of the most famous scientific equations of all time. As mentioned previously, this equation came up in the fourth paper Einstein published in 1905. It states that energy is equal to the product of mass and the square of the speed of light. Which means that, matter can transform into energy if it moves fast enough.

One of the factors making this equation so remarkable is that it establishes a connection between hitherto seemingly unrelated entities. Before Einstein’s fourth paper was published, time and Space, and mass and energy were separate entities.

Through establishing the concepts of space-time and E=mc2, he formulated his theory of relativity. Though special relativity is one of the last intuitive theories ever made in the history of science, it turned out to be a crucial one for physics.

Scientists proved all the theories Einstein proposed in 1905. The uses of these theories did not always turn out to be for the benefit of mankind. Changing matter into energy is the principle behind the generation of nuclear energy which provides electricity to millions of people.

However, the same principle was used to split atoms and release the destructive energy of atom bombs. Thus, the equation which is a blessing in electricity production and medical diagnostic tools also became the foundation of the nuclear bomb.

The Special Theory of Relativity was published in 1905. It presented the astonishing idea that space and time are not absolute but relative. Or simply put, changes in the measurements of distance and passing of time depends on the observer who is measuring them. Einstein added a fourth dimension (time) to the three existing dimensions (length, width and height).

Einstein revealed that time is experienced differently by observers in relative motion. Two events might appear as if they are happening at the same time for one observer, but they might happen at different times from the perspective of another. And the observers would be right in both cases.

Einstein later demonstrated this point with an experiment. Imagine a man standing on a railway platform as a train goes by. Each end of the train is struck by a bolt of lightning just as the midpoint of the train passes him. Because the lightning strikes are the same distance from the observer, their light reaches his eye at the same instant. Therefore, he would correctly say that they happened at the same time.

Meanwhile, there is an observer sitting in the exact midpoint of the train. From her perspective, the light from the two strikes also has to travel equal distances. She will therefore measure the speed of light to be the same in either direction.

However, as the train is moving, light from the lighting that struck the rear must travel more to catch up and will be slower to reach than the light from the front. This causes the observer inside the train to conclude that lightning struck the front of the train first rather than simultaneously. Einstein says that simultaneity is relative.

These new ideas were published in a paper titled On the Electrodynamics of Moving Bodies.

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Einstein too had an annus mirabilis like Newton. In 1905, Einstein published four scientific papers in the German journal Annalen der Physik. These four papers laid the foundation of modern physics by revolutionizing how the scientific community perceived fundamental concepts of space, time, mass, and energy. As all four papers were published in 1905, this year is considered Einstein’s annus mirabilis or miracle year.

The first paper introduced the revolutionary idea that light is composed of both energy and particles. The foundation for quantum physics that physical systems can behave both as waves (energy) and as particles (matter) began here.

The second paper, though without any revolutionary concepts, was important in its own right. Einstein discovered the empirical evidence behind Brownian Motion which refers to the random movement displayed by small particles that are suspended in fluids. Though many scientists had accepted this already, empirical evidence had been lacking.

The third paper which contained the special theory of relativity possibly had the most ground-breaking content among all four papers.

The last of these papers published on 21 November 1905 had the mathematical confirmation of the Special Theory of Relativity, the most famous equation: E=mc2.

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