Stephen Hawking, a theoretical physicist, cosmologist, and author, has always tried to explain complex astrophysical phenomena in simple language that everyone can understand. The subtitle of this book is "a further explanation of a science classic made more accessible". To his surprise, his book A Brief History of Time was a bestseller and was on the top ten list for 237 weeks and sold one copy for every 750 people on Earth. The book was a remarkable success for a modern physics book. Many people were asking for a sequel to the book. A Brief History of Time explained how Newtonian Astrophysics described the laws that control planets and stars' movement. This book takes into consideration the most recent theoretical and observational results.
How light speed is finite and constant at 299,792,458 m/s. Since the speed of light is constant, to explain the different observations for different observers, time must be relative. Producing the twin paradox, i.e., time slows down for you relatively as you approach the speed of light than for an observer - time dilation. The twin not travelling at the speed of light will age more slowly relative to the twin on Earth. Although it is all relative and the time for both twins will be the same. Gravity slows down time, and this has been proven by using very sensitive clocks and is what we put in the calculations using GPS; if not, you will be off by a few kilometres or so. Light behaves as both a particle and a wave (Wave–particle duality). When a star with a very high mass dies, it collapses into a singularity called a black hole. Here, the laws of physics cannot change; light cannot escape a black hole because of its extensive gravity. Hawking radiation, a type of black-body radiation, is the type of radiation that escapes a black hole. That, The universe is expanding and not static, and the speed of expansion is getting faster and faster.
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| Professor Stephen Hawking |
Recently, scientists claim to have found and solved the issue of dark matter. Since I am reading the astrophysics book simultaneously as these discoveries are made, it has been very interesting for me. Scientists have thought that the mass of the universe has always been deficient, in that it seems a lot is missing from their calculations and simulations of the universe. It's estimated to make up about 85% of the universe's mass. Also, there seems to be a lot of stuff holding the universe together, as its expansion rate is slower than expected, and it acts sometimes as if carrying extra mass. Also, light, which is affected by gravity, bends around some yet to be detected large masses. Also, there seems to be conditions that can only be explained by there being "stuff" or matter there, but until recently detection of this matter has proved very elusive. However, recent measurements of the diffuse ionised hydrogen surrounding galaxies account for some of the missing mass, although this has to be confirmed by further observations and may take some time before it becomes widely accepted. But this is what is currently at the cutting edge of astrophysics.
The book stated that the ancient people tried to understand the universe, but lacked our science and mathematics and did not have technological tools like increasingly powerful computers and telescopes to comprehend it. The nearest star is so far away that it does not sense in measuring the distance in feet, metres, miles, kilometres or even thousands of kilometres or miles. Instead, they measure the distance in light years, that is, the distance light travels in one year. Ole Roemer, a Danish astronomer, in 1676, noticed that light has a finite speed. In one second, light travels 186,000 miles, which was thought to be instant, but after he noticed variations in the eclipses of the moons of Jupiter. Jupiter is between 33 and 54 light minutes away from Earth. Christopher Columbus knew that the Earth was a globe-like structure, but he thought it was smaller than the Greeks had calculated or assumed that China and India were nearer. People who knew better told him so, but he thought till his death that he had discovered a new way to India. That's why the American Indians are called Indians and the Caribbean islands are known as the West Indies. But from then till now, some people believed that the world is flat. Aristotle believed that the world was the centre of the solar system, as well as Ptolemy (geocentrism). This model was picked up by the Catholic Church, although Nicolaus Copernicus, a Polish Catholic priest, believed in a Sun-centred solar system (heliocentrism).
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| Geocentric Model of the Solar System |
Today, scientists describe the universe in 2 basic theories, one is the general theory of relativity, which describes the force of gravity on a large scale. Then there is quantum mechanics, which deals with extremely small scales, about a millionth of a millionth of an inch. The two theories are inconsistent with one another, i.e. they are correct for their realms but wrong for the other. But they cannot be both correct and wrong at the same time. One of the major endeavours of physics today and the theme of the book is the search for the complete unified theory of everything. That combines and explains both theories into one.
Both Aristotle and Newton believed in an absolute time. But due to light having a finite speed. This gave rise to the field of relativity, that the speed of light is constant for every observer. James Clerk Maxwell succeeded in unifying the partial theories of electricity and magnetism into electromagnetic force. Maxwell demonstrated mathematically the presence of waves and not particles. Maxwell's equations predicted that there could be wavelike disturbances in the electromagnetic field and that these waves would travel at a fixed speed at exactly the speed of light. Waves with wavelengths shorter than the visible length are now known as ultraviolet light, X-rays, and gamma rays. Waves with longer wavelengths are radio waves (about a metre), microwaves (about a centimetre), infrared radiation, about a thousandth of a millimetre - a micron (µm).
In general relatively space-time is not flat but curved or warped, and planets move along the dips in it. Also, from the law of relativity, it means nothing can go faster than the speed of light. The faster it goes, the heavier it becomes, and the more energy is required to move it. Hence, for to travel to some far parts of the universe would require folding space on itself (i.e. wrapping - considering 4-dimensional space) and creating a tunnel between one region to another, i.e. wormholes and tunnels. These are still theoretical, and until very recently, thought to be impossible, but it is possible at a microscopic level. This is a kind of cheating as it enables one to travel faster than light. In every episode of StarTerk they go at warp speed and engage the warp drive, which is a fictional engine that allows them to go at warp speed by the warp engines. Although this does cause further paradoxes, as according to relativity, if you could go faster than light, it is possible to go back in time, i.e. you may arrive back before you start the journey.
There was a young lady of Wright
Who travelled much faster than light
She departed one day.
In a relative way,
And arrived on the previous night
The planets move in this curve, hence an elliptical orbit, but it is actually the shortest distance on a wrapped space-time. Relativity redefined our understanding of gravity not as a force but objects taking the easy route in the space-time fabric, and knowing that space can wrap objects, move along the shortest distance between them. But also stars with massive gravity wrap light and deflect light. But also due to the laws of relativity, actual time slows down the higher the gravity, a phenomenon known as gravitational time dilation. Hence, your feet will be younger than your head. Or someone living in the mountains will be older than people living on the ground. But on Earth, these figures are so small because the masses are relatively smaller. There are changes in the orbit of Mercury due to the effect of our Sun, which are so small and confirmed by measurement by increasingly sensitive instruments. The closer you get to the speed of light, the slower time becomes. Hence, the journey to the stars may take a relatively short time for you. But by the time you have arrived back, everyone you knew may have died hundreds of years ago.
The universe is expanding, and this is not only due to background radiation, light from the Big Bang, but also to being shifted to the microwave spectrum (Cosmic Microwave Background Radiation - CMBR). Hence, it is heard everywhere in the universe. Then, when looking at the other star spectra, Dr Edwin Hubble noticed that almost every star has a redshifted. The redshift is that the wavelength has moved to the longer end of the spectrum as sound waves become higher-pitched, also known as the Doppler effect. It is as if everyone is trying to get away from us, but on further analysis, it is that every star is going away from each other, and the further away it is, the faster they are moving. Einstein believed in a static universe and had to put in a variable while doing his equation in relativity to counteract gravity, a sort of antigravity constant to keep the universe in equilibrium, which he called the Cosmological Constant (Λ), but this was unnecessary. As Professor Alexandrovich Friedmann, a Russian, was able to prove that if you took into consideration that the universe was expanding at a specific rate, you need not put in the Cosmological Constant. Later, Einstein called the incorporation of the Cosmological Constant his "biggest blunder". But on further examination, there is some stuff that we cannot see or explain holding the Universe together, dark matter. Before the glossary, Prof Hawking gives more information on three of the greatest minds of Astronomy. Isaac Newton was not a pleasant man. Isaac was petty, mischievous and arrogant. He had a clash with Astronomer John Flamsteed and used his position a President of the Royal Society and part of the governing body of the Royal Observatory to remove all references to Flamsteed and his work. Although both he and the German philosopher Gottfried Leibniz independently developed a branch of mathematics called calculus around the same time. It is Newton who discovered calculus years before Leibniz published his work. But Newton destroyed Leibniz by destroying his integrity, and drained his soul. On learning of Leibniz's death, Newton was reported of said he gained great satisfaction in "breaking Leibniz's heart". Later, he used his talents of "deviousness and vitriol" to track down those counterfeiting and send several men to their deaths. Galileo Galilei was mild in comparison, but was more tricky. He argued that the Bible was not intended to tell us about scientific theories or to be used as a textbook. If there was a conflict with common sense, it was being allegorical. When refused publication of his work, he stated that he would present an argument for both sides, Aristotelian and Copernican sides, but in Italian, not in Latin. He was subsequently arrested and placed under house arrest, where he was able to smuggle a manuscript for another book in support of Copernican theory, which was published in Holland.
Einstein rejected the ideal of a Bibilical God, but as a secular Jew after the rise of the Nazi's he became a Zionist. Initially, he was anti-war, and in 1933, when Hitler came to power, he was in the US. He declared that he would not travel back to Germany. Later, he renounced pacifism and wrote a letter to the US president urging that the US develop the atomic bomb first.
I have always been fascinated by Space. The book mixes Science, history, and a little bit of philosophy. Prof. Stephen Hawking breaks down complex phenomena and makes them easy to digest and understand. I would recommend this book to anyone interested in astronomy.
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