I've done some sleeping already because I went to bed early last night. I didn't have the patience to stay up late and watch television. I wanted to get comfortable under the duvet and drift off into sleep and dreamland. I don't remember if I dreamed or not. If I did, it wasn't very impressive because nothing stayed with me. They must have just been very ordinary things that weren't worth remembering.
I hope that when I go back to bed, the rest of my night will be like that also. There's not much to talk about when you're down to earth where you belong. I'm frantically searching in my mind for subjects to discuss and all I can think of are the things I already talked about on my other blog. I don't want to fall into repetition so I won't be discussing them.
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I suppose that I'm not as alert as I thought I was because normally I have no problem coming up with things to talk about. That warrants another cup of coffee and I'm drinking it now. Hopefully it will loosen me up a bit. It's a terrible thing when your mind lets you down. It's the one thing you have to be able to rely on. That's why you have to run a little interference every now and then and give it a little stimulance. Joanne rated it really liked it May 06, Sep 15, L. Thrussell rated it it was amazing. Very well written, it drew me in right from the start. Loved the story and the lessons.
Jennifer rated it really liked it Feb 23, Martin Baggen rated it it was amazing Apr 14, Lisa rated it it was amazing Jun 26, Em added it Feb 09, Beckie marked it as to-read Feb 11, Hannah marked it as to-read May 22, Lele marked it as to-read Jul 08, Darla Hiskett marked it as to-read Oct 23, Corey marked it as to-read Dec 15, Dark Luna Rose marked it as to-read Jan 22, Skye Atman marked it as to-read Jan 27, Marcelina marked it as to-read Mar 10, Denise marked it as to-read Mar 15, Angela marked it as to-read Mar 16, Iroulito91 marked it as to-read Apr 22, Mandyn marked it as to-read Jun 07, Christine Campbell marked it as to-read Jul 06, Jodine Turner marked it as to-read Jul 18, Many of his contemporaries, including German philosopher Heinrich Olbers , disagreed.
The origin of the universe represented another great topic of study and debate over the centuries. Early philosophers like Aristotle thought that the universe has existed forever, while theologians such as St. Augustine believed it was created at a specific time. Augustine also believed that time was a concept that was born with the creation of the universe. More than years later, German philosopher Immanuel Kant thought that time goes back forever. In , astronomer Edwin Hubble discovered that galaxies are moving away from each other.
Consequently, there was a time, between ten and twenty billion years ago, when they were all together in one singular extremely dense place. This discovery brought the concept of the beginning of the universe within the province of science. Today, scientists use two partial theories, Einstein's general theory of relativity and quantum mechanics , to describe the workings of the universe.
Scientists are still looking for a complete unified theory that would describe everything in the universe. Hawking believes that the discovery of a complete unified theory may not aid the survival of our species, and may not even affect our life-style, but that humanity's deepest desire for knowledge is justification enough for our continuing quest.
Stephen Hawking talks about how the Aristotle theory of absolute space came to an end by the Newton's theory that 'rest' and 'motion' can be the same state if an observer sees the event at rest or if he moves with the same speed as that of the event. So 'rest' can't be the standard position. Moreover, Galileo Galilei also disproves Aristotle theory that heavier body falls more quickly than the lighter one just because of its mass. He experimentally proves it by sliding objects of different weights, and even concludes that both these object would fall at same rate and would reach the bottom at the same time, unless external force acts on them.
Aristotle and Newton believed in absolute time. They believed that if an event is measured using two different clocks at different state of motion, they'll have to agree on the same time, if clocks used are synchronized, which by now we know it isn't. He observed that Io appeared sometimes quicker and sometimes later when it revolves around Jupiter, because the distance between Earth and Jupiter changes every time because of their orbital motion around the sun.
The actual propagation of light was published by James Clerk Maxwell who told that light travels with a fixed speed. Later, many argued that light must travel through a hypothetical fluid called Ether , which was disproved by Michelson—Morley experiment that there is nothing called Ether through which light travels. The Special Theory of Relativity is based on this, that light travels with a finite speed no matter what the speed of the observer is.
Moreover, the speed of light is assumed to be the ultimate speed. A new way of defining a metre using speed of light is also developed. The new 4-dimensions is also described, how different the path is seen when one changes reference from 3D to 4D or 3D to 2D. General Theory of Relativity explains about how path of light ray is affected by ' gravity ' which according to Einstein is a mere illusion in contrast to Newton's views.
It is space-time curvature where light moves in a straight path in 4D which is seen as a curve in 3D. These straight line paths are Geodesics.
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Twin paradox , a part theory of Relativity which explains that two twins can age differently if they move at relatively different speeds or even at different places where spacetime curvature is different. Special relativity is based upon arenas of space and time where events take place whereas General Relativity is dynamic where force could change spacetime curvature, which gives rise to the expanding universe. Hawking and Roger Penrose worked upon this and later proved using general Relativity that if the Universe had a beginning then it also must have an end.
In this chapter, Hawking first describes how physicists and astronomers calculated the relative distance of stars from the Earth. In the 18th century, Sir William Herschel confirmed the positions and distances of many stars in the night sky. In , Edwin Hubble discovered a method to measure the distance using brightness of the stars.
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The luminosity , brightness and distance are related by a simple mathematical formula. Using all these, he fairly calculated distances of nine different galaxies. We live in a spiral galaxy just like other galaxies containing vast amount of stars.
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The stars are very far away from us, so we only observe their one characteristic feature, their light. When this light is passed through a prism, it gives rise to a spectrum. Every star has its own spectrum and since each element has its own unique spectra, we can know a star's composition. We use thermal spectra of the stars to know their temperature. But in , when scientists were examining spectra of different stars, they found that some of the characteristic lines of the star spectrum was shifted towards the red end of the spectrum. The implications of this phenomenon was given by the Doppler effect , and it was clear that some stars were moving away from us.
So, it was assumed that since some stars are red shifted, some stars would also be blue shifted. But when found, none of them were blue shifted. In fact, Hubble found that the amount of redshift is directly proportional to relative distance. So, it was clear that Universe is expanding. Despite this the concept of a static universe persisted until the 20th century; Einstein was so sure of a static universe that he developed ' Cosmological Constant ' and introduced 'anti gravity' forces to persist to the earlier claim.
Moreover, many astronomers also tried to avoid the face value of General Relativity and stuck with their static universe except one Russian physicist Alexander Friedmann. He made two very simple assumptions: Homogenity and that this would be true wherever we look from i. His results showed that the Universe is non-static. His assumptions were later proved when 2 physicists at Bell's laboratory, Arno Penzias and Robert Wilson found extra microwave radiation noise not only from the one particular part of the sky but from everywhere and by nearly the same amount.
Then, Friedmann's first assumption was proved as true. At the same time nearly, Robert H. Dicke and Jim Peebles were also working on the microwave radiation. They argued that they should be able to see the glow of the early universe as microwave radiations. But, Wilson and Penzias already did this, so they were awarded with Noble Prize in In addition, our place in the Universe is no exceptional, so we should see the universe as the same from any part of space, which proved Friedmann's second assumption.
His work, though remained largely unknown until similar models were made by Howard Robertson and Arthur Walker. Friedmann's model gave rise to 3 different types of model of universe. First, the universe would expand for a given amount of time and if the expansion rate is less than the density of the universe leads to gravitational attraction , it would ultimately lead to the collapse of the universe at the later stage.
Secondly, the universe would expand and at sometime if the expansion rate and the density of the universe become equal, it would expand slowly and stop at infinite time and would lead to somewhat static universe. Thirdly, the universe would continue to expand forever if the density of the universe is less than the critical amount required to balance the expansion rate of universe. The first model depicts the space of universe to be curved inwards, somewhat earth like structure.
A Brief Moment in Time
In the second model, the space would lead to a flat structure, and in the third model resulted in negative curvature, or saddle shaped. Even if we calculate, the current expansion rate is more than the critical density of the universe including the dark matter and all the stellar masses. The first model included the beginning of the universe in a big-bang from a space of infinite density and zero volume known as ' singularity ', a point where General theory of Relativity Friedmann's solutions are based in it also breaks down.
This concept of the beginning of time was against many religious beliefs, so a new theory was introduced 'Steady state theory' by Hermann Bondi , Thomas Gold and Fred Hoyle to tackle the Big bang theory. Its predictions also matched with the current Universe structure. But the fact that radiowave sources near us are far less than the distant universe and there were numerous more radio sources than at present, resulted in failure of this theory and everybody finally stuck and supported the big bang theory.
Evgeny Lifshitz and Isaak Markovich Khalatnikov also tried to avoid the big bang theory but also failed. Finally, Roger Penrose used light cones and general Relativity and proved that a collapsing star could result in a region of zero size and infinite density and curvature called a Black Hole , so Hawking and Penrose proved together that the universe should have arisen from a singularity which Hawking himself disproved once Quantum effects are taken into accounts.
The uncertainty principle says that the speed and the position of a particle cannot be found at the same time. To find where a particle is, scientists shine light at the particle.
If a high frequency light is used, the light can find the position more accurately but the particle's speed will be unknown because the light will change the speed of the particle. If a lower frequency light is used, the light can find the speed more accurately but the particle's position will be unknown. The uncertainty principle disproved the idea of a theory that was deterministic, or something that would predict everything in the future.
How light behaves is also talked more about in this chapter.
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Some theories say that light acts like particles even though it really is made of waves; one theory that says this is Planck's quantum hypothesis. A different theory also says that light waves also act like particles; a theory that says this is Heisenberg's uncertainty principle. Light waves have crests and troughs. The highest point of a wave is the crest, and the lowest part of the wave is a trough.
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Sometimes more than one of these waves can interfere with each other - the crests and the troughs line up. This is called light interference. When light waves interfere with each other, this can make many colors. An example of this is the colors in soap bubbles. Quarks and other elementary particles are the topic of this chapter.
Quarks are very small things that make up everything we see matter. There are six different "flavors" of quarks: Quarks also have three "colors": There are also anti-quarks, which are the opposite of the regular quarks. In total, there are 18 different types of regular quarks, and 18 different types of anti quarks. Quarks are known as the "building blocks of matter" because they are the smallest thing that make up all the matter in the universe. All particles for example, the quarks have something called spin.