Relative Velocity | Presentation Slide

Each ray of light moves in the coordinate system 'at rest' with the definite, constant velocity V independent of whether this ray of light is emitted by a body at rest or a body in motion.

~ Albert Einstein

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Scientist Capture the first image of a black hole:

Renowned physicist Stephen Hawking was days from death, but that didn't stop him working.

Credit: Event Horizon Telescope Collaboration

 The Event Horizon Telescope Collaboration, called EHT, is a global network of telescopes that captured the first-ever photograph of a black hole. More than 200 researchers were involved in the project. They have worked for more than a decade to capture this. The project is named for the event horizon, the proposed boundary around a black hole that represents the point of no return where no light or radiation can escape.

"We have taken the first picture of a black hole," said EHT project director Sheperd S. Doeleman of the Center for Astrophysics | Harvard & Smithsonian. "This is an extraordinary scientific feat accomplished by a team of more than 200 researchers." 

The massive galaxy, called Messier 87 or M87, is near the Virgo galaxy cluster 55 million light-years from Earth. The super-massive black hole has a mass that is 6.5 billion times that of our sun. The image shows a bright ring formed as light bends in the intense gravity around a black hole. This long-sought image provides the strongest evidence to date for the existence of super-massive black holes and opens a new window onto the study of black holes, their event horizons, and gravity.

Details of the observation were published in a series of six research papers published in The Astrophysical Journal Letters.

Theory of Gravity - General Relativity

“Einstein, my upset stomach hates your theory [of General Relativity] - it almost hates you yourself! How am I to' provide for my students? What am I to answer to the philosophers?” 

~ Paul Ehrenfest

Let’s talk about the birth of our most successful theory of gravity - general relativity.

Prior to Einstein, it was Newton’s Law of Universal Gravitation that was the accepted theory of gravity. All of the gravitational phenomena in the Universe, from the acceleration of masses on Earth to the orbits of the moons around the planets to the planets themselves revolving around the Sun, his theory described it all. 

Objects exerted equal-and-opposite gravitational forces on one another, they accelerated in inverse proportion to their mass, and the force obeyed an inverse square law. By the time the 1900s rolled around, it had been incredibly well-tested, and there were no exceptions. Well, with thousands upon thousands of successes to its credit, there were almost no exceptions, at any rate.

In the Newtonian picture of gravity, space and time are absolute, fixed quantities, while in the Einsteinian picture, spacetime is a single, unified structure where the three dimensions of space and the one dimension of time are inextricably linked.

The first major development was that space and time, previously treated as a separate three-dimensional space and a linear quantity of time, were united in a mathematical framework that created a four dimensional “spacetime.” This was accomplished in 1907 by Hermann Minkowski:

The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. […] Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality.

This worked only for flat, Euclidean space, but the idea was incredibly powerful mathematically, as it led to all the laws of special relativity as an inevitable consequence. When this idea of spacetime was applied to the problem of Mercury’s orbit, the Newtonian prediction under this new framework came a little closer to the observed value, but still fell short.

Minkowski’s spacetime corresponded to an empty Universe, or a Universe with no energy or matter of any type.

Countless scientific tests of Einstein’s general theory of relativity have been performed, subjecting the idea to some of the most stringent constraints ever obtained by humanity. Einstein’s first solution was for the weak-field limit around a single mass, like the Sun; he applied these results to our Solar System with dramatic success. (LIGO scientific collaboration / T. Pyle / Caltech / MIT)

Einstein was able to find a solution where you had a Universe with one single, solitary point mass source in it, and with the stipulation that you were outside of that point. This reduced to the Newtonian prediction at great distances, but gave stronger results at closer distances. 

These results not only agreed with the observations of Mercury’s orbit that Newtonian gravity failed to predict, but it made new predictions about the deflection of starlight that would be visible during a total solar eclipse, predictions that were later confirmed during the solar eclipse of 1919.

This article is adapted from the  medium.com. Click here for more details.

What is Gravity?:

The Natural force that tends to cause physical things to move towards each other. 

First, [Newton's Law of Universal Gravitation] is a mathematical in its expression.... Second, it is not exact. Einstein had to modify it.... There is always an edge of mystery, always a place where we have some fiddling around to do yet.... But the most impressive fact is that gravity is simple.... It is simple, and therefore it is beautiful.... Finally, comes the universality of the gravitational law and the fact that it extends over such enormous distances....

~ Richard P. Feynman.

Sir Issac Newton:                                          Albert Einstein:

                            

$F = G\frac{m_1 m_2}{r^2}$	$G\mu \nu = 8\pi GT\mu \nu$
» It is a force.	» It is a  distortion of space and time.
» It depends on mass and distance.	» It depends on Energy.

» Newton's stated that the force of gravity is always attractive. It affects everything with mass, work instantaneously at a distance and has an infinite range. "Every mass attracts every other mass in the universe (across the empty space)", Newton had imagined. [1]

» But in Einstein's model, gravity is not a force. It is a warping of space-time. Space is really curved, and as a result objects are deflected from a straight path in a way that looks like a force. According to Einstein: "Mass tells space how to bend, and space tells mass how to move".

DREAM Big - spl BiNal

"Start by doing what’s necessary, then what’s Possible, and suddenly you are doing the Impossible."

- Francis of Assisi

The secret of learning anything (Albert Einstein’s advice to his Son):

“That is the way to learn the most, that when you are doing something with such enjoyment that you don’t notice that the time passes.” - Albert Einstein.

In 1915, Albert Einstein was living in Wortorn Berlin, while his estranged wife (Mileva) & their two sons (Hans Albert & Eduard Tete) lived in comparatively safe Vienna. On November 4 of that year, Albert Einstein just completed the masterpiece page – Theory of General Relativity. At that time Einstein sent the following letter (The secret of learning anything) to his 11-year old Son – Hans Albert.

“My dear Albert, 

Yesterday I received your dear letter and was very happy with it. I was already afraid you wouldn’t write to me at all anymore. You told me when I was in Zurich, that it is awkward for you when I come to Zurich. Therefore I think it is better if we get together in a different place, where nobody will interfere with our comfort. I will in any case urge that each year we spend a whole month together, so that you see that you have a father who is fond of you and who loves you. You can also learn many good and beautiful things from me, something another cannot as easily offer you. What I have achieved through such a lot of strenuous work shall not only be there for strangers but especially for my own boys. These days I have completed one of the most beautiful works of my life, when you are bigger, I will tell you about it.

I am very pleased that you find joy with the piano. This and carpentry are in my opinion for your age the best pursuits, better even than school. Because those are things which fit a young person such as you very well. Mainly play the things on the piano which please you, even if the teacher does not assign those. That is the way to learn the most, that when you are doing something with such enjoyment that you don’t notice that the time passes. I am sometimes so wrapped up in my work that I forget about the noon meal. . . .

Be with Tete kissed by your

Papa.

Regards to Mama.”

If you want to know more about Albert Einstein, Click in this link.