Cosmological Astrophysics

Today is April 13. Let me introduce you to an American man whose myriad scientific contributions figured in many of the research advances of the 20th century. He was one of 's last collaborators and, in later years, became the father of modern general relativity. He learned best by teaching. According to him, Universities have students, to teach the professors. That great American man is our "scientist of the day" today.

It's death anniversary of , one of the foremost physicists of the 20th century - - -

(Scientist of the Day - 13 April)

Wheeler worked with in explaining the basic principles behind nuclear fission. Together with Gregory Breit, he developed the concept of the Breit-Wheeler process but he is best known for using the term "Black-Hole" for objects with gravitational collapse already predicted during the early 20th century.

Wheeler introduced the concept of wormholes. He devised a concept of quantum foam; a theory of “virtual particles” popping in and out of existence in space (similarly, he conceptualized foam as the foundation of the fabric of the universe). Further he coined the terms "neutron moderator", Superspace and "it from bit". He hypothesized the "one-electron universe". referred to him as the "hero of the black hole story".

He was a driving force in the development of both the atomic and hydrogen bombs. He also helped launch the careers of many prominent modern theoretical physicists, among them the late Nobel laureate .

He was the co-author of the standard textbook on Einstein's general theory of relativity. He won numerous prizes, awards & received honorary degrees from 18 different institutions. In 2001, Princeton used a $3 million gift to establish the John Archibald Wheeler/Battelle Professorship in Physics.

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This Day in Science History - -

(April 12)

in 1898, observed a meeting of the French Academy of Sciences, where one of her teachers, Prof. announced her discovery of substances much more radioactive than uranium.

A full article:-

In follow-up to Becquerel, who had observed that uranium compounds cause air to conduct electricity, Curie measured the conductivity of air around other compounds and gradually became convinced that radiation was an atomic property. To test whether it occurred elsewhere, she examined every other known element, in compounds as well as the pure state, and discovered that compounds of thorium also emitted rays like those in uranium. This led to the more remarkable discovery that a mineral ore called pitchblende emitted more Becquerel radiation than the compounds of either uranium or thorium, and Curie began to suspect that the powerful radioactive substance might be an element hitherto unknown. On April 12, 1898, in a preliminary note to the Academy of Sciences, she made her scientifically stunning announcement about the possibility of a powerful new radioactive element, present in ordinary pitchblende. The Atomic Age was born.

At this point, entered into a formal collaboration with his wife. The couple speculated that radioactivity in pitchblende was probably caused by the presence of two new elements, one of which they called radium, and the other of which Marie named polonium after her homeland. (They announced these elements in later months - 1898). Although the discovery drew considerable scientific attention, the couple knew that the existence of the two materials would not be proved until they obtained samples in pure form. (Polonium and radium were present in very small amounts in pitchblende, along with larger quantities of uranium. Isolating the very small amounts of the new elements took years of work).

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There are three fundamental mechanisms of heat transfer :- conduction, convection & thermal radiation (Radiant Heat). The primary method by which the Sun transfers heat to the Earth is thermal radiation. This energy is partially absorbed and scattered in the atmosphere, the latter process being the reason why the sky is visibly blue. Let me introduce you today to an Italian man who first demonstrated that this radiation could be reflected, refracted and polarised in the same way as light. He is our "scientist of the day" today.

It's the birthday of , the man who demonstrated that radiant heat has similar physical properties to those of visible light - -

(Scientist of the Day - 11 April)

Melloni studied the magnetism of rocks, electrostatic induction and photography but as a physicist, he is best known for his discovery in radiant heat, that he made with the aid of the thermomultiplier, a combination of thermopile and galvanometer.

Sir William Frederick Herschel discovered infrared radiation in 1800, but research stalled until the invention of a thermopile. That instrument was a series of strips of two different metals that produced electric current when one end was heated.

In 1831, soon after the discovery of thermoelectricity by Thomas Johann Seebeck, he improved the thermopile and used it to detect infrared radiation. With Leopoldo Nobili, he employed the instrument in experiments especially concerned with characteristics of black-body radiation transmitted by various materials. He used an optical bench fitted with thermopiles, shields and light and heat sources, such as Locatelli's lamp and Leslie's cube, in order to show that radiant heat could be reflected, refracted and polarised in the same way as light. In 1846, from an observation point high on Mount Vesuvius, he measured the slight heating effect of moonlight. He showed also that Rock Salt, being transparent to infrared, made suitable lenses and prisms to demonstrate the reflection, refraction, polarization and interference of infrared in the same manner as visible light.

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That First Black Hole Image Validates The Einstein's Physics - - -

(7th anniversary of the 1st Image)

's general theory of relativity has passed a number of serious tests from the universe's most extreme conditions in the last few years. One of them was about spanning from horizons to the stars.

General relativity describes gravity as a consequence of the warping of space-time. Massive objects create a sort of dent or well in the cosmic fabric, which passing bodies fall into because they're following curved contours.

The theory makes specific predictions about how this warping works. For example, the theory posits that black holes exist, and that each of these gravitational monsters has an — a point of no return, beyond which nothing, not even light, can escape. Further, the event horizon should be roughly circular and of a predictable size, which depends on the black hole's mass.

And that's just what we saw in the unveiled EHT images, which show show the silhouette of the supermassive black hole at the heart of , a giant elliptical galaxy that lies 55 million light-years from Earth.

"The shadow exists, is nearly circular and the inferred mass matches estimates due to the dynamics of stars 100,000 times farther away," EHT team member , of the University of Waterloo and the Perimeter Institute for Theoretical Physics in Canada, said during a news conference (on 10 April 2019) at the National Press Club in Washington, D.C.

That mass, by the way, is 6.5 billion times that of Earth's sun. That's huge even by supermassive-black-hole standards; for comparison, the behemoth at the heart of our MilkyWay galaxy weighs in at a mere 4.3 million solar masses.

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This Day in Science History - - -

(April 10)

, seven years ago, had finally been dragged out of the shadows. The first ever direct image of a black hole and its vicinity was released by the collaboration (a network of eight linked radio telescopes around the world).

Look at the image, it shows the supermassive black hole at the center of the galaxy 87 (M87* — a massive galaxy in the nearby Virgo galaxy cluster) — the shadow of the black hole, surrounded by a bright ring of hot gas and plasma.

This was the first time a black hole had been imaged, and it provided strong evidence for the existence of black holes and their role in galaxy formation.

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In 1754, an Italian young man wrote a letter to famed mathematician , in which he solved the isoperimetrical problem which for more than half a century had been a subject of discussion among mathematicians. The problem, stated simply in two dimensional form, was to find the form of a closed curve such as a loop of string which is able to encompass the maximum area for a fixed perimeter. To affect the solution, the young man employed what would later be named by Euler the "calculus of variations". He recognized that the young Italian might have time to complete his work. That young Italian man is our "scientist of the day" today.

It's death anniversary of , the man who transformed Newtonian mechanics into a new branch of analysis, Lagrangian mechanics - -

(Scientist of the Day - 10 April)

Lagrange made significant contributions to the fields of analysis, number theory, and both classical and celestial mechanics. He was one of the creators of the calculus of variations and invented the method of solving differential equations known as variation of parameters, applied differential calculus to the theory of probabilities and worked on solutions for algebraic equations. He proved that every natural number is a sum of four squares. He studied the three-body problem for the Earth, Sun and Moon in 1764 and the movement of Jupiter's satellites in 1766 and in 1772 found the special-case solutions to this problem that yield what are now known as "Lagrangian points". Lagrange is best known for transforming Newtonian mechanics into a branch of analysis, Lagrangian mechanics, and presented the mechanical "principles" as simple results of the variational .

Lagrange is one of the 72 prominent French scientists who were commemorated on plaques at the first stage of the Eiffel Tower when it first opened. The lunar crater Lagrange and the asteroid 1006 Lagrangea also bear his name.

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Theory of Relativity is one of the foundational pillars of our Modern Physics. The theory usually encompasses two interrelated physics theories by the genius - special theory of relativity and general theory of relativity, proposed and published in 1905 and 1915, respectively.

See the image to understand the mathematics — Special relativity applies to all physical phenomena in the absence of gravity. General relativity explains the law of gravitation and its relation to the forces of nature.

The theory transformed theoretical physics and astronomy during the 20th century, superseding a 200-year-old theory of mechanics created primarily by . It introduced concepts including 4-dimensional spacetime as a unified entity of space and time, relativity of simultaneity, kinematic and gravitational time dilation, and length contraction. With relativity, cosmology and astrophysics predicted extraordinary astronomical phenomena such as neutron stars, black holes, and gravitational waves.

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In 1822, a German man noticed that a loop created by connecting two semicircular pieces of bismuth and copper can deflect a nearby compass when there is a temperature gradient along the loop. This was the first thermoelectric effect discovered. That German man is our "scientist of the day" today.

It's the birthday of , the man who discovered a relationship between heat & magnetism - - -

(Scientist of the Day - 09 April)

In numerous experiments on the magnetizability of various metals, Seebeck observed the anomalous reaction of magnetized red-hot iron, which eventually resulted in the phenomenon now known as hysteresis. Continued experiments with different metal pairs and a variety of conductors revealed that it was possible to place the many conducting materials in a thermoelectric series.

His most important contribution, however, was the "Seebeck effect". In 1822, Seebeck found that a circuit made from two dissimilar metals with junctions at different temperatures would deflect a compass magnet. Seebeck believed this was due to magnetism induced by the temperature difference. Based on this result, Seebeck elaborated a table relating different metal junctions and the deflexion of the compass. His main conclusion at the end of these experiments was about the influence of the metals and volcanoes on Terrestrial magnetism.

After the discovery of the electron and its fundamental charge, it was quickly realized that Seebeck's effect was an electric current that is induced, which by 's law deflects the magnet. More specifically, the temperature difference produces an electric potential (voltage) which can drive an electric current in a closed circuit.

Today, the Seebeck effect is used to measure temperature with great sensitivity & accuracy (like, thermocouple) and to generate electric power for special applications.

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In 1965, Dr. won the Nobel Prize in physics and the same year a British man made his breakthrough. It was an era when the tools of the trade were pencil and paper. He outlined what came to be known as the Higgs mechanism, an explanation for how elementary particles, which make up all that is around us, gained their masses in the earliest moments after the big bang. That British man is our "scientist of the day" today.

It's death anniversary of Prof. , one of the greats of particle physics - - -

(Scientist of the Day - 08 April)

In the 1960s, he proposed that broken symmetry in electroweak theory could explain the origin of mass of elementary particles in general and (particularly of the W and Z bosons). This so-called Higgs mechanism, which was proposed by several physicists besides Higgs at about the same time, predicts the existence of a new particle, the , the detection of which became one of the great goals of physics. His theory about what binds the Universe together, sparked a 50-year search for the Holy Grail of physics.

On July 04, 2012, announced that they had experimentally established the existence of a Higgs-like boson, but further work would be needed to analyse its properties and see whether it had the properties expected from the Standard Model Higgs boson. On 14 March 2013, the newly discovered particle was tentatively confirmed to be + parity and zero spin, two fundamental criteria of a Higgs boson, making it the first known fundamental scalar particle to be discovered in nature. The same year, he shared the in Physics with François Englert.

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You all must have heard the name of Galvanometer. It has been essential for the development of science and technology in many fields. Galvanometers came from the observation, first noted by in 1820, that a magnetic compass's needle deflects when near a wire, having electric current. But it was not Ørsted, it was a German man who invented this device and he is our "scientist of the day" today.

It's the birthday of , the man who invented the Galvanometer - - -

(Scientist of the Day - 08 April)

In 1820, Danish physicist & chemist Hans Christian Ørsted discovered that electric currents create magnetic fields, which was the first connection found between electricity and magnetism. Using his observation, the same year, Johann Schweigger built the first sensitive galvanometer. He developed the galvanometer as a tool for measuring the strength and direction of electric current by wrapping a coil of wire around a graduated compass (look the shown image).

The instrument was initially called a multiplier. , who gave mathematical expression to Ørsted's discovery, named the instrument Galvanometer, after the Italian physicist , who in 1791 discovered the principle of the frog galvanoscope - that electric current would make the legs of a dead frog jerk.

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It's April 06. On this day in 1949, Horst Ludwig Störmer was born in Germany. Today he turns 77.

Wishing a very happy birthday to you - -

(Scientist of the Day - 06 April)

After receiving his PhD from the University of Stuttgart in 1977 for his thesis on investigations of electron hole droplets subject to high magnetic fields, Störmer moved to the US to work at Bell Labs, where he carried out the research that led to his Nobel prize.

His most important work for which he won the Nobel prize is his invention of "modulation doping", a method for making extremely high mobility two dimensional electron systems in semiconductors. This enabled the later observation of the "fractional quantum Hall effect", which was discovered by Störmer and Tsui in October 1981 in an experiment carried out in the Francis Bitter High Magnetic Field Lab at the Massachusetts Institute of Technology. Within a year of the experimental discovery, was able to explain its results. Störmer, Tsui and Laughlin were jointly awarded the 1998 Nobel Prize in Physics for their work.

In picture (right side), you are looking the computer graphics visualizing the Laughlin wave function for the nu=1/3 FQHE (fractional quantum hall effect) state. The green balls represent electrons that are pinned momentarily in the two-dimensional plane. The blue mountain represents the charge distribution of one "free" prototype electron moving in the presence of the magnetic field and the potential of the other (green) electrons. The black arrows are magnetic flux quanta bound to electrons.

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Today is April 06. It's death anniversary of , the man who developed several branches of modern mathematics - -

After a slow start in school, he began to show mathematical genius by the age of 15. At 16, he gave a rigorous proof of the binomial theorem valid for all numbers, extending Euler's result which had held only for rationals. Abel wrote a fundamental work on the theory of elliptic integrals, containing the foundations of the theory of elliptic functions.

In 1823 Abel wrote a paper titled "a general representation of the possibility to integrate all differential formulas". He applied for funds at the university to publish it. However the work was lost, while being reviewed, never to be found thereafter.

His most famous single result is the first complete proof demonstrating the impossibility of solving the general quintic equation in radicals. This question was one of the outstanding open problems of his day, and had been unresolved for over 250 years. Abel showed that there is no general algebraic solution for the roots of a quintic equation, or any general polynomial equation of degree greater than four. To do this, he independently invented a branch of mathematics known as "Group Theory", which is invaluable not only in many areas of mathematics, but for much of physics as well.

He died in poverty at age 26, just two days before his talent was recognized and he was to be offered a professorship in Berlin. Most of his work was done in six or seven years of his working life. French mathematician Charles Hermite said: "Abel has left mathematicians enough to keep them busy for five hundred years." Another French mathematician, Adrien Marie Legendre, said: "What a head the young Norwegian has!"

The in mathematics, originally proposed in 1899 to complement the Nobel Prizes (but first awarded in 2003), is named in his honour.

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