The Book of General Relativity and Gravity of The Bible According to Einstein

The Gravitational Theory of Einstein

The sixth book of Physics

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208                        The Bible According to Einstein

The sixth book of Physics, called

General Relativity and Gravity

And spacetime shall be curved.

Chapter I: The Equivalence Principle

And because Newtonian gravity and relativity are not compatible, Newtonian gravity is slightly wrong and it contains a lie. But the lie is hard to see. And when shall not the lie be visible? It shall not be visible when the gravitation force is weak. But when the gravitation force is strong, the lie will be exposed and the gravity of Newton will be wrong.
     And in the past, it came to pass that Newton’s gravity, a product of seventeenth century observation, was superseded by Einstein’s gravity, a product of twentieth century thought. Thus a new and better theory of gravity was so created. And it was provided with a name. And The Theory of General Relativity and Gravity was its name.
     And if thou be in outer space in a rocket far from the Earth, far from the Sun and far from other heavenly bodies, then thou art weightless. And thou floatest in thy cabin and objects also float about thee. And this is so because around thee there is no gravity.
     And if thou be in an elevator on a high floor in a tall building and the cable suddenly should break, then thou, the others with thee, and the elevator cabin all fall. But since thou fallest at the same rate as the cabin, thy feet, with the slightest push, leave the floor, and thou floatest. And since the others with thee fall at the same rate as the cabin, they float too. Thus while thou art falling freely thou seemest to feel no gravity. And it is like being in a rocket in empty outer space. And it is as if some great being had suddenly turned off gravity.
     Next supposest thou be floating in a windowless cabin in outer space. And suppose one end of a cable be attached to the cabin’s roof and the other end be tied to a rocket. And suppose the rocket blasts its engines and begins to move. Then the cable will become taut and pull the cabin. And as the rocket accelerates, the cabin will accelerate with it. Then thou wilt seem to stop floating, and thy feet will touch the floor. And why shall this be so? It shall be so because of the First Law of motion: When the rocket moves and begins to pull the cable, thou remainest motionless because thou, who art a body at rest, shalt remain at rest. But the cabin, being pulled upward by the rocket, will rise until it hits thy feet. And from thy point of view, it will seem as if some great being had suddenly turned on gravity and made thou fallest to the floor. So now thou art standing and thy feet are on the floor. What dost thou feel? Thou feelest the floor pushing against thy feet with a force. And why is this so? It is so because of the Second Law of motion: As the rocket blasts its engines, it pulls the cabin so that the cabin does accelerate. And since thou standest on the floor, thou acceleratest with the cabin. Thus thou art compelled to change thy speed. Thus by Newton’s Second Law a force acts on thee. And it is the push of the floor against thy feet that is this force. And thou, in thy ignorance and lack of perspective, dost not know of the rocket. And thou thinkest gravity be pulling thee down against the floor.


 
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The New Testament                                       209

     And in 1916, this new insight enlightened Einstein and mankind about the force of gravity – the insight into gravity was suddenly turned on, like someone turning on a light.
     And the elevator cabin and rocket shall embody the strong equivalence principle, which says that it shall be impossible to distinguish gravity from an accelerating system.

Chapter II: Curved Spacetime

Now how shall the strong equivalence principle be incorporated into general relativity? The answer shall be by making spacetime curved. Gravity shall be the result of the curvature of space and time. The First Law of Newton shall be generalized. A body, whether or not it be under the influence of gravity, shall follow a path of minimum length in the geometry of spacetime. And such a path shall be a geodesic. Now on a flat surface a geodesic shall be a line. Thus the shortest path between two points on a tabletop shall be a line. And when there is no gravitational field, spacetime shall be flat. And the straight lines in flat spacetime shall correspond to constant motions. Thus in the absence of a gravitational field, a body at rest shall remain at rest, or a body moving at a constant speed in a line shall continue to move at a constant speed in that same line. Thus in the absence of gravity, Newton’s First Law of motion shall follow from general relativity. But when a gravitational field is present, spacetime shall be curved, and geodesics shall not be straight. Spacetime shall be distorted as is like a sphere – the shortest path between two points on the surface of a sphere is a great-circle arc.194 And when a body moves along a geodesic in curved spacetime, it shall accelerate because it shall follow a curved path. And because it accelerates, a force shall be said to act upon it. And this force shall be Einsteinian gravity.
     Thus in the absence of other forces but in the presence of gravity, bodies shall follow geodesics. And this motion shall be as natural as it could be.
     And what shall cause spacetime to curve? It shall be mass. And concentrated mass shall make spacetime curve a lot. And lots of curvature shall make geodesics highly curved. And a highly curved geodesic shall correspond to high acceleration and hence strong force. And near a heavy object shall the curvature be great. But far from such an object shall the curvature be weak. Thus the force of gravity shall diminish with the distance. And for weak gravitation, Einsteinian and Newtonian gravity shall almost coincide.

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194 Great-circle arcs are the arcs of the largest circles that can be draw on a sphere. For example, a segment of a line of longitude of Earth is a great-circle arc.

 
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210                        The Bible According to Einstein

     Now how shall Earth be attracted to the Sun? The Sun shall be like unto an iron cannon ball, the Earth shall be like unto a marble, and the surface of a bed shall be like unto spacetime. And if an iron cannon ball is placed upon a bed, shall not the surface of the bed depress? And if a marble is tossed, lands on the bed and rolls, shall it not roll toward the iron cannon ball? And why does the marble so behave? It does so due to the surface of the bed – the surface is not flat.

Chapter III: Consequences of Einsteinian Gravity

And as for planetary motion, Einstein’s theory of gravity shall produce small differences from Newton’s theory of gravity. And for example, the orbit of Mercury, which is an ellipse, shall through Einsteinian effects rotate forty-three seconds of arc per century.
     And let it be known to thee and all around thee that gravitational waves exist. A gravity wave shall be like an electromagnetic wave, but gravitational fields will oscillate instead of electric and magnetic fields. But alas, gravity waves will be too weak to be detected by feeble twentieth-century scientific instruments. But the binary pulsar 1913+16 will radiate such unseen waves. And the energy lost through gravitational radiations will cause minute changes in the pulsar’s beats. And with a radio telescope, scientists will measure the minute effects and indirectly "sense" the waves. So scientists will see by listening.
     And since, in the presence of a massive body, space is curved, light like matter shall be affected. Thus light shall bend around a heavy body such as the Sun, a galaxy, or a dark dwarf-star-sized body – light shall be deflected by the force of gravity. So starlight from a star behind the Sun shall be bent as the starlight passeth by the Sun. And distant light from a quasar when it passeth by a massive galaxy shall refract, thereby creating a double image of the quasar. And this shall be like the thick glasses on a person which produce a "double-eye" in the eye-glass lens. And when light passeth by a dwarf-star-sized dark body, it shall be focused. Thus such a body behaveth like a convex lens. And so when such a non-luminous body passeth in front of a star, the star shall brighten. And contrary to one’s intuition, the starlight shall not be blocked by the body but shall be focused – the effect shall be like unto a magnifying glass which createth a bright spot of sunlight on a piece of paper.
     And all these astrophysics objects shall be gravitational lenses. And gravitational lensing shall this effect be called.


 
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The New Testament                                       211

     Now gravity shall affect light in other ways. Light shall take longer to traverse a region of space where there is gravity. And it will seem as if the speed of light be less than in a vacuum. And for example, when light neareth the Sun, the light shall enter a region of curved space. And while passing by the Sun, the light shall travel a longer distance than if the Sun were not there. And it is like unto a marble which rolls down a bowl and out – such a path is longer than if the marble moved from brim to brim. Now a second Einsteinian gravity effect is this: Photons shall lose energy as they climb out a gravity. And so if one stands on Earth and "throws photons upward," then the photons, like rockets, balls or birds, shall lose kinetic energy. Now when photons lose energy, their wavelengths shall increase. And this shall render blue light a little yellow, and yellow light a little red, and red light even redder. Thus the spectrum shall shift a bit toward the red. This shall be called the gravitational energy red-shift. Thus light, originating on the surface of the Earth, shall be slightly red-shifted high above the Earth. And the same shall be true of light emitted from the surface of any massive body.
     And let it be known to thee and all around thee that, as a consequence of general relativity, the Universe must either be expanding or contracting. And indeed, the Universe has been and is expanding. And the expansion of the Universe shall be because spacetime can bend and be dynamic – it shall stretch, twist and/or contract.
     Now if a great quantity of mass be concentrated in a tiny space, spacetime shall curve so much as to close upon itself. And it shall be impossible for anything, including light, to then get out. Such an object shall be a black hole. And so in general relativity shall there be black holes. And indeed, black holes will be "seen by man," not with his eyes but by other means.
 
 
 
 
 
 
 
 
 
 
 
 


 
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