This book help us clarify with what has happened out there in space and how it happen. this book helps to answer these questions:
what do we really know about universe?
how do we know it?
where did universe come from?
where is it going?
did universe have beginning? if so, what happened before it begin? will it ever come to the end?
what is the nature of time? will it ever come to the end?
can we go backward in time?
The first chapter: thinking about universe
I know about people's perspective toward the meaning of space and universe, "how did they think about what out there?" but our human never give up on researching and discovering about what happen out there from earth, they have tried many methods and wrote a lot of theoretical explains about what they think there would be and what make their explanation correct.
From the past time, people always have different ideas about what happen out there in space and they also had their own evidence support what they think.
for the ancient time, they said earth is just a straight land straightening on the back of turtle. Their ideas was mainly shaped by what they had been listening to everyday like religion. The light shining on the sky was just tiny fires floating that they could not reach. They had no idea Mars, Mercury and universe
For ancient Chinese civilisation, they built wall to reach stars.
Chapter 2: Our Evolving Picture of The Universe
In this chapter, (1st part) I learned a lot of how people think toward the question "is the world is flat of square?"
from the time Christopher Columbus, there were many people thought that the world is flat and there were a lot of argument about this as well.
But there were many evidence proving that the earth is square not flat. From the ancient Greek, about 300 B.C. Aristole wrote a book call On the Heaven, this book was written to prove that the earth is square. Base on One argument stated that The earth is square based on the eclipses of the moon, Aristole wrote that the eclipses was actually the shadow of the earth by the sun and the earth shape is square, so it appeared that the earth actually square. Another Greek reason was the earth is square because when ship was sailing they could see the sea's surface is actually round. Also Greek at the time liked to study about star, after observation by Aristole, he claimed that thousands of stars are moving wander off the east-west path and then double back. Except for the 5 stars that never moved, and then they created the name for those star as "Planet" and those 5 stars were actually Mercury, Venus, Mars, Jupiter and Saturn.
After proving that the earth is round, there was arguments toward questions "how did the stars and planets rotate themselves? and how about the earth?"
Based on Ptolemy’s model, there are 8 rotating spheres surrounded the earth (the earth is in the middle), each sphere was successively larger than the one before it and the earth was the centre of the spheres. the stars remain in same position, so when the sphere rotate, the stars relatively rotate as a group. but the planet rotation was more complicated than the stars rotation Ptolemy admitted that. and Christianity adopted that model.
Another model was proposed in 1514 by a polish priest, Nicolaus Copernicus. but at that time he was anonymously kept it because of the fear of religious punishment. His idea was that the sun was stationary at the center of the solar system and that the earth and planets moved in circular obits around the sun. Nearly a century passed his idea was adopted seriously by 2 astronomers the german Jonhannes Kepler and Italian Galileo Galilei, they both started publicly support his theory.
Galileo proved that each planet was accompanied by several satellites of moons that orbited around it which proved that everything is not orbit the earth.
And Kepler proved that planets move was not in a circle but ellipses.which made the theory of Ptolemy went death. his idea was based on nature not on any observation.
in 1687, Sir Isaac Newton published his philosophise Naturalis Principia Mathematica. in this Prinipia Newton. He proved that describe how the effect of force cause an object to move or change the motion. and the reason why the planet move ellipses because there is the force to move them and that force is similar to what make object fall to the earth and he called it “Gravity”.
and he proved that this law applied everything in this universe from the a falling apple to stars and planet. and it was the beginning of modern physics and astronomy.
Chapter 3 The nature of a scientific theory
Before knowing the nature of the universe and discuss on question “whether it has a beginning or an end? we need to understand about what a scientific theory is first.
What make good theory? -> A good theory is the theory that satisfy 2 requirements.
1- it must accurately describe a large class of observations on the basis of a model that contain only a few random element.
2- it must make definite predictions about the results of future observations.
For example: Aristole believed Empedocles’s theory that everything was made out of 4 elements: earth, air, fire and water. this theory was simple enough but it did not make any definite predictions.
In contrast, Newton’s theory of gravity was based on the simpler model. when bodies attracted each other with a force that was proportional to a quantity called their mass and inversely proportional to the square of the distance between them. and it predicts the motion of the sun, the moon and other planets in a high level of accuracy.
But in physic theory u just cannot prove it 100% perfect. no matter how many times the results of the experiment agree with the theory but next time you cannot assure whether the result will agree again or not. in another word, u can disprove a theory by finding a single observation that disagree with it.
Chapter 3 cont.
from the 1st of chapter 3, it mainly focus on definition of theory and what makes good theory and why theory fail.
right now it show how theory develop itself:
in practice, the new theory often happened to be the extension of the old theory.
for example, Einstein’s theory actually the extension of Newton’s theory. It appeared that Einstein’s theory is more matched to what was seen than the Newton’s theory but still people gave more credit to the founder (Newton) because it’s simpler and fit to the general practical purposes.
every scientist worked on clearly one same purpose “is to provide a single theory that describes the whole universe.” but the scientists actually separated it into 2 parts:
1st- there are laws that tell us how the universe change with time. if we know what the universe look like at one time, the laws of physic will us how it look like at any time.
2nd- there is the question of the beginning state of the universe. this question happened to deal with religious people who always claim that universe was created by GOD.
scientists found it very difficult to focus in one particular theory to describe the university, so they break the problem down to small pieces then find a theory for each piece. make it just like piece of cake!
after knowing what is theory and what makes good theory and how it develop from time to time. Now let’s see what are the theories describe the universe.
today scientists describe the universe in terms of 2 basic theories - the general theory of relativity and quantum mechanics. one deals with very very BIG things and another one deals with very very SMALL things.
the general theory of relativity describes the force of gravity and the large-scale structure of the universe; that is, the structure on scale from only a few miles to as large as million million million miles, the size of the observable universe.
Quantum mechanics deals with phenomena on extremely small scales, such as a millionth of a millionth of an inch.
and these two theory are known to be inconsistent or in other words, they cannot be both correct. and what mainly describe in this book is the search of a new theory and will incorporate them both “a quantum theory of gravity”. (from atom to galaxy)
after knowing what are the 2 basic theories - the general theory of relativity and quantum mechanics, and now it show how these 2 theories developed and what are the concern toward the new finings?
the theory itself would determine the outcome of our search for it.
it would appear to have several questions asking why should it determine that we come to the right conclusions from the evidence? and might it not equally well determine that we draw the wrong conclusion? or no conclusion at all?
the only answer to all these questions is based on Darwin’s principle of natural selection.
the idea of this principle is that any individuals have different genetic material . And these differences will mean that some individuals are better able than others to draw the right conclusion about the world around them and to act accordingly. these individual will be more likely to survive and reproduce so their behaviour and thought will dominate others. it might be true that in the past there were several scientific discovery to take several survival advantages. But we are still not clear that scientist would take us to the wrong conclusion and we might just destroyed by those theories. We still need to find a unified theory so that it would not lead us to the wrong conclusion.
however, from the past until now we made several accurate predictions in all the problems that had been raised but the most extremely one is the search if ultimate theory of universe seem difficult to justify. With all the research and handwork, we have discovered nuclear energy and microelectronic evolution that break down the theory of relativity and quantum electric.
today we eager to know why we are here and where we came from. and we never give up from generation to generation and our goal is always be the same, it’s nothing less than a compete description of the universe we live in.
Chapter 4: Newton Universe
this chapter is mainly focusing on Newton’s theories and how it developed:
At Aristole time, people believe him that a heavier body should fall faster than a light one because it would have a greater pull toward the earth. it was not until Galileo break this theory on different weights did in fact fall at different speeds. according to his experiment of dropping weights from the Learning Tower of Pisa in Italy. He rolled the balls of different weights down a smooth slope. the situation is similar to that of heaving bodies falling vertically. his measurements indicated that each body increased its speed at the SAME RATE, not matter what it’s weight. of course the lead weight would fall faster than a feather but that is only because a feather is slowed down by air resistance. if you drop 2 bodies that dont have much air resistance, such as 2 different lead weight, they fall at the same rate.
Galileo’s measurements were used by Newton as the basis of his law of motion. In Galileo’s experiment, as a body rolled down the slope it was always acted on by the same force (its weight) and the effect was "speed up”.
it showed that the real effect of a force is always to change speed of a body.
it also meant that whenever a body is not acted on by any force, it will keep on moving in a straight line at the same speed. this idea was first stated in 1687, in Newton’s Principia Mathematica, and it is knows as Newton’s first law.
after knowing the 1st law of Newton, now here come the 2nd law of him.
Newton’s second law is describe what happen to a body when a force does act on. this theory stated that the body will accurate, or change its speed, at the rate this is proportional to the force. for example the more powerful the engine, the greater the acceleration but the heavies the car, the smaller the acceleration for the same engine.
in addition to his laws of motion, Newton’s theory of gravity describes how to determine the strength of once particular type of force “gravity”. if item A and B crashing each other, this additional force adding twice of its original force. (the total force between A and B would be twice the original force)
it applies to all bodies falling at the same rate, a body of twice the weight will have twice the force of gravity pulling it down.
but according to Newton’s law also tells that the farther apart the bodies, the lesser the force. this law predict the orbits of the earth, the moon, and the planets with great accuracy. if the law was wrong, the orbits of the planets would not be elliptical; they would either spiral into the sun or escape from the sun.
another test, there is a man bounce a ping pong ball straight up and down hitting the table twice on the same sport one second apart. to him the location of the first and second bounces is on the same spot. On the other hand, to someone standing beside the track, the two bounces would seem to take place about forty meters apart, because the train would have traveled that distance down the track between the bounces.
according to Newton, the two observers have an equal right to consider themselves at rest, so both views are equally acceptable.
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