Category Great Scientists

Are laser devices inspired by Einstein’s Theory of Stimulated Emission?

You might have come across laser pointers while attending a seminar or conference, or perhaps used it to play with your cat or dog. In the sixty years since physicists demonstrated the first laboratory prototype of a laser in 1960, it has been put to use in numerous ways from barcode readers to systems for hair removal.

The technology behind laser devices is based on Einstein’s Theory of Stimulated Emission. This theory came a year after the discovery of general relativity. Einstein imagined a bunch of atoms bathed in light. He had earlier discovered that atoms sitting in their lowest energy state can absorb photons and jump to a higher energy state. Similarly, higher energy atoms can emit photons and fall back to lower energies.

After sufficient time passes, the system attains equilibrium. Based on this assumption, he developed an equation that can be used to calculate what the radiation from such a system would look like. Unfortunately, Einstein’s calculations differed from the laboratory results. It was obvious that a key piece of the whole puzzle was missing.

Einstein resolved this by guessing that photons like to march in step. This would mean that the presence of a bunch of photons going in the same direction will increase the probability of a high-energy atom emitting another photon in that direction. Einstein labelled this process stimulated emission. He was able to rectify the disparity between his calculations and the observations by including this in his equations.

A laser is a device to harness this phenomenon. It excites a bunch of atoms with light or electrical energy. The photons released as a result are channelled precisely in one direction. Lasers are used in delicate surgery or industrial processes that require precision.

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Why is it said that Albert Einstein had even contributed to the daily functioning of Wall Street?

Wall Street in New York is the home of the New York Stock Exchange. An army of mathematicians are employed there to analyze and predict the stock price variations. Their employers can potentially earn millions of dollars based on their predictions about which way the prices will jump.

Mathematicians however say that stock markets follow a random walk. This means that unless some spectacular event occurs, the prices have the same chances of decreasing and increasing at the end of any day. If patterns do exist, they will be elusive and difficult to find, which is why financial mathematicians are paid huge sums.

Some of the intricate mathematics used for stock market analyses can be traced back to Einstein. He developed the fluctuation-dissipation   theorem to explain the random movement of particles found in liquids or gases.

This movement called ‘Brownian motion’ was first observed by the Scottish biologist Robert Brown. Brownian motion is highly similar to the price fluctuations seen in stock markets. The similarity was observed in 1970 and since then it has been used on Wall Street. Einstein’s paper on Brownian motion is still used as the basis for certain stock market predictions.

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Does GPS primarily use the General Theory of Relativity?

Einstein’s General Theory of Relativity has predominantly found applications in astronomy through gravity waves, big bangs and black holes. One of its rather unexpected applications was in the multi-billion-dollar industry centred around the Global Positioning System (GPS).

All GPS navigators including Google Maps work by measuring the distance from one point on Earth to one of the satellites orbiting our planet. Though GPS was originally developed with military use in mind, it has since become an inherent part of everyday life.

GPS is based on a collection of 24 satellites, each carrying a precise atomic clock. A hand-held GPS receiver which detects radio emissions from any satellite overhead can find the latitude, longitude and altitude with accuracy up to 15 metres and local time to 50 billionths of a second. The clocks on satellites are ahead of those on Earth by 38,000 nanoseconds. The reason for this is explained by the General Theory of Relativity. Though it may appear as an inconsequential amount of time, if these nanoseconds are not taken into account, GPS systems would be highly inaccurate.

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In which universities did Einstein serve as a professor till the 1930s?

Despite publishing four ground-breaking scientific papers in 1905 and earning his doctorate, Einstein still had difficulty finding a teaching job. He finally became a lecturer at the University of Berne in 1908. He received more opportunities in academia as his reputation as a theoretical physicist grew.

A year after joining the University of Berne he became an associate professor of physics at the University of Zurich. In 1911, he became a full professor at the University of Prague but returned after a year as a full professor to Zurich. The highlight of his academic career was when he became a professor at the University of Berlin and a member of the Prussian Academy of Sciences.

He had also been the Director of the Kaiser Wilhelm Institute for Physics. Einstein earned the salary of a professor without any teaching duties at the University of Berlin. As a result, he could pursue his research full time. He remained in the University of Berlin until the early 1930s.

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What was the role Satyendra Nath Bose played in Einstein’s scientific life?



Einstein received a paper from Indian scientist Satyendra Nath Bose in 1924. The paper was on a new perspective: to think of light as a gas filled with indistinguishable particles. Einstein recognized the relevance of the paper. He translated it to German and submitted it on behalf of Bose to the famous journal Zeitschrift fur Physik. Bose went to Europe and worked with Einstein at the X-ray and crystallography laboratories there.

Einstein worked with Bose to extend his idea to atoms and they predicted a new state of matter which came to be called the Bose-Einstein Condensate. A Bose-Einstein Condensate is a dense collection of particles with integer spin known as Bosons.

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Were Einstein’s researches after the General Theory of Relativity mostly based on universal field theories?

Einstein was primarily in pursuit of a universal field theory after the General Theory of Relativity. He engaged in a series of unsuccessful attempts to further generalize the theory of gravitation in order to unify and simplify the fundamental laws of physics, in particular, gravitation and electromagnetism.

This ‘theory of everything’ was supposed to refute the quantum theory. Though he published a paper in 1929 which supposedly had such a theory, Einstein himself had to acknowledge the errors in his argument.

Einstein remained in the cocoon of his research, largely ignoring other developments in physics and quantum theory. He however, did a few collaborations with the Indian scientist Satyendra Nath Bose, the Austrian Erwin Schrodinger and his Hungarian former student Leo Szilard.

In the 1930s he worked together with Russian physicist Boris Podolsky and the Israeli physicist Nathan Rosen. Nevertheless, his search for the ‘theory of everything’ and his distrust of the quantum theory consumed him in his later years.

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Why was Einstein not a great supporter of the quantum theory?

Einstein had also made contributions to the development of the quantum theory. The concept of light quanta (photons) was used by him in 1905 to explain the Photoelectric Effect and to develop the quantum theory of specific heat.

Despite playing a main role in its development, Einstein regarded the quantum theory only as a temporarily useful structure.

His efforts were primarily in formulating the unified field theory which he believed would turn out to be the reason behind quantization of energy and charge. He felt that the quantum theory lacked the simplicity and beauty befitting a rational interpretation of the universe.

He engaged in a series of private debates with physicist Niels Bohr about the validity of the quantum theory later on. The 1920s witnessed his prolonged public debates with Niels Bohr and Werner Heisenberg over quantum mechanics. Einstein was rather lukewarm about the quantum theory even from a philosophical standpoint, saying in 1926 that he was convinced God does not throw dice. However, Bohr showed the ambiguities in Einstein’s reasoning.

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Which was the year Einstein received the Nobel Prize?

The Nobel Prize in Physics 1921 was awarded to Albert Einstein “for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect.”

Albert Einstein received his Nobel Prize one year later, in 1922. During the selection process in 1921, the Nobel Committee for Physics decided that none of the year’s nominations met the criteria as outlined in the will of Alfred Nobel. According to the Nobel Foundation’s statutes, the Nobel Prize can in such a case be reserved until the following year, and this statute was then applied. Albert Einstein therefore received his Nobel Prize for 1921 one year later, in 1922.

However, Einstein did not attend his prize giving. Though he was informed that he was to receive the prize, he continued with a lecture tour of Japan.

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How did the General Theory of Relativity prove to be correct in 1919?

Einstein has published four papers on the general theory of relativity. In the third paper, he used general relativity to explain why Mercury’s closest point to the Sun (its perihelion) is erratic.

Gravitational influence of the Sun and other planets was not sufficient explanation for this movement. Some even went as far as to suggest in the 19th century that a new planet, Vulcan, orbiting close to the Sun was the reason! But this was disproved as Einstein succeeded in calculating the shift in Mercury’s perihelion using the general theory of relativity.

The theory not only explained previously unexplained phenomena, it could even predict events that have not occurred yet. In 1919, the theory was validated again when Sir Arthur Eddington, secretary of the Royal Astronomical Society of London travelled to the island of Principe off the coast of West Africa. There, he had the perfect view of the Sun during a total eclipse.

The light emitted from a certain strand was measured and it was found that the light was deflected, or bent, by just the amount that Einstein had predicted. Einstein’s fame skyrocketed after this.

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What is the General Theory of Relativity?

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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