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The Theory of Gravity and Its Applications
Transcript of The Theory of Gravity and Its Applications
Hilario Brief Description of How gravity and Motion were viewed historically before Newton and friends. Everyone thought that the Earth was the center of everything and that it was revolved upon galileo's view Determined that objects fall at the same rate, regardless of their weight Aristotle's View Aristotle established general principles of change that govern all natural bodies; both living and inanimate, celestial and terrestrial—including all motion, change in respect to place, change in respect to size or number, qualitative change of any kind, and coming to be and passing away. Kepler's view Kepler believed that the sun did not sit passively at the center of the solar system but that through some mysterious power or "virtue" actually compelled the planets to hold to their orbits.
The life and times of issac newton Isaac Newton was born in Woolsthorpe, Lincolnshire, England on Christmas Day. His father had died three months earlier, and baby Isaac, very premature, was also not expected to survive. It was said he could be fitted into a quart pot. When Isaac was three, his mother married a wealthy elderly clergyman from the next village, and went to live there, leaving Isaac behind with his grandmother. Two years later, Newton went away to the Grammar School in Grantham, where he lodged with the local apothecary, and was fascinated by the chemicals. He turned out to be a total failure as a farmer. Newton’s first major public scientific achievement was the invention, design and construction of a reflecting telescope. He ground the mirror, built the tube, and even made his own tools for the job. This was a real advance in telescope technology, and ensured his election to membership in the Royal Society. The mirror gave a sharper image than was possible with a large lens because a lens focusses different colors at slightly different distances, an effect called chromatic aberration. This problem is minimized nowadays by using compound lenses, two lenses of different kinds of glass stuck together, that err in opposite directions, and thus tend to cancel each other’s shortcomings, but mirrors are still used in large telescopes. Henry Cavendish he first experiment to measure the force of gravity between masses in the laboratory, and the first to yield accurate values for the gravitational constant. Role of equivelance and gravitational properties in the deveploment of general relativity That equivalence plays a crucial role. The central idea of General Relativity is that there are many different ways of assigning spacetime coordinates to events, all of which ways can be described by the same laws of physics. These ways include coordinate systems that are accelerating with respect to each other. In one coordinate system, all the objects at rest in the other seem to be accelerating, with nearby ones accelerating at the same rate. In that coordinate system you'd need a gravitational field to explain why, for no other reason, all the objects in some region were accelerating together.
Now lets look at the Newtonian version of this, which not only has inertial masses, mi, but also gravitational masses, mg. Since the gravitational force on an object is proportional to its mg, and the acceleration is given by F/mi, the acceleration would be proportional to mg/mi. Unless every object has the same mg/mi then gravity will cause nearby objects to accelerate differently. That's completely different from the effects of changing coordinate systems.
So General Relativity only makes sense if every object has the same mg/mi. It's most convenient then to just call both masses the same thing. gracity and the bending of the space time fabric The fabric of spacetime twists like a vortex. Einstein tells us that all gravitational forces correspond to a bending of spacetime; the "twist" is gravitomagnetism. schwarzschild radius
The Schwarzschild radius gives the radius at which the Schwarzschild metric becomes singular, and is therefore the "size" of a black hole. It can naively (although incorrectly) be derived by letting the escape velocity of a black hole equal to the speed of light.
where G is the gravitational constant, M is the mass of the black hole, and c is the speed of light.
What are black holes?
are they real? Before going further, we first must determine what a black hole is and is not. Black holes do have mass. In fact, it is because they have mass that they can become black holes. So black holes have gravity. But black holes are not cosmic vacuum cleaners. It is true that anything entering a black hole cannot re-emerge again; however, it is not true that black holes are sucking in matter from all over the universe, causing everything to fall into them. How does gravity bend light? Did you know that very strong gravity can actually bend light? Gravitational lenses are formed when light from a very distant source is bent around an object with a very large mass. Albert Einstein’s general theory of relativity predicted this phenomenon.
Albert Einstein published an article describing this effect in 1937, but it wasn’t until 1979 that the effect was confirmed by direct observation of the “Twin QSO” SBS 0957+561. The gravity from a massive object – like a galaxy cluster or a black hole warps space and time and bends everything, including light, around it. You can see this effect in the picture above. Notice the faint arcs of light. That is light from a very distant galaxy that has been bent around a closer galaxy cluster. Interestingly enough, gravitational lensing acts equally on all types of electromagnetic radiation, not just visible light. Gravitational lensing STRONG LENSING: Where there are easily visible distortions of light such as Einstein Rings, arcs and multiple images. The picture at the top of the post is an example of this.
WEAK LENSING: Where the distortions of background sources are much smaller and can only be detected by analyzing large numbers of sources to find coherent distortions of only a few percent.
MICROLENSING: Where no distortion in shape can be seen, but the amount of light recieved from a background object changes over time.