Journal Entry 1
Chapter 1 (Pg 1-14) Today, I began my book A Brief History of Time by Stephan Hawking. He talked about the earth’s shape and why it’s round and not flat by using information from a book written by Aristotle. I got to read about the theories on where the solar system was centered around, Isaac Newton’s theory on Gravity and how it affects the universe, and whether not the universe had a beginning or if the universe had just already existed. It included work from famous people like Galileo Galilee, Isaac Newton, Johann Kepler, & Aristotle. I read about the history of theories, arguments, & theses about whether the universe had a beginning or if it was already there. Then Stephan Hawking was talking about what makes a good theory by using Newton’s theory of gravity and Einstein’s theory of relativity as examples. I also read about a time in 1929 when Edward Hubble comes up with the theory of the Big Bang. I also read about relativity & quantum mechanics and how there is yet to be a combination of the two theories (the quantum theory of gravity). And that “our goal, of desiring knowledge, is nothing less than the description of the universe that we live in.
Journal Entry 2
Chapter 2 (Pg 15-35) Today, I started a new chapter about Space & Time. He talked about the theories of Galileo, Aristotle, & Newton. He said that each of them either disproved the other’s
theories or added on to it (Galileo on Aristotle, Newton on Galileo & Aristotle). He stated that “The big difference between the ideas of Aristotle and those of Galileo & Newton is that Aristotle believed in a preferred state of rest, in which any body would take up if it were not driven by some force or impulse.” It also talked about the lack of absolute space and Newton on lack of absolute space and Newton & Aristotle on absolute time. And he talks about the speed of light, ether, and how Einstein disagreed with the idea of ether and that it is unnecessary. I read about Einstein’s theory of relativity, how the speed of light is measured, and four coordinates of an event that specify its position in the four dimensional space. I read about how the speed of light should be the same as the speed of the source. I also read about how Einstein’s general theory of relativity came to be and what it is. I also learned what a geodesic is. I learned about the twins paradox on how if one twin leaves on top of a mountain and the other lives at sea level, one twin will age faster than the other. Also, I read about light rays & light deflection. I also learned that with this knowledge on space and time we can have a better understanding of the universe. And I read that Einstein’s general theory of relativity implies that our universe has a beginning and, unfortunately, an end.
Journal Entry 3
Chapter 3 (Pg 37-54) Today I read about the revolutionary discovery about how the universe isn't static and that it’s actually expanding and getting bigger. Two important people in this discovery were Edwin Hubble & Alexander Friedmann. I also read about stars, wavelengths, the idea of other galaxies in the universe, and I learned about the Doppler Effect. The Doppler Effect is the change of the frequency of a wave for someone who is moving relative to the source. I read about whether our universe is finite or infinite based off a model found by Friedmann and two other models. There was a short story about two American physicists discovering a sound coming from outside the atmosphere and they would get a Nobel Prize out of it despite two other physicists who also discovered the sound. I learned that our universe is expanding 5 to 10% ever thousand million years. of the wave. Then we revisited the argument on if the universe had a big bang or not and Stephen Hawking started to talk about how he was trying to get his PH.D despite having ALS. Stephen Hawking talked about how he was trying to prove that there must be a singularity only if the universe was expanding fast enough to avoid collapsing again. He then wrote a paper with Roger Penrose that finally proved that there must have been a big bang to start the beginning of the universe.
Journal Entry 4
Chapter 4 (Pg 55-63) In this chapter, Hawking starts to talk about the uncertainty principle created Werner Heisenberg. The uncertainty principle, as also stated in Wikipedia, is any variety of mathematical inequalities asserting a fundamental limit to the precision with which certain pairs of physical properties of a particle known as complementary varibales, such as position x and momemtum p, can be known simultaneously. I also read about Max Planck's Quantum Hypothesis. It's the theory that explains how light behaves as if it was composed of particles that can be emitted or absorbed in only packets or quanta, and interference between particles. I read about quantum mechanics (not in full detail though), the sum over histories, and a nice way of seeing the wave/particle duality.
Journal Entry 5
Chapter 5 (Pg 65-81) In this chapter, Stephan Hawking talks about Aristotle and his beliefs on how the world is made of Fire, Water, Earth, Air and that matter is continuous, but some Greeks like Democritus disagreed. This argument continued for centuries until Einstein wrote a paper on the Brownian motion, the effect of atoms of liquids colliding with dust particles. I read about the discoveries of the election, proton, neutron and the entire structure of the atom. I learned about quarks (the particles that make up a proton, neutron, & electron), a positron, an anti-electron, and that every particle has an antiparticle. I also read about how in quantum mechanics the forces or interactions of matter particles are carried by particles of an integer spin 0, 1, or 2, the three of four categories of force carrying particles (gravity, weak nuclear force, & electromagnetic force), the Weinberg-Salem Theory (a theory that's about weak nucler force), and the fourth force carrying particle strong nuclear force, I learned that confinement prevents you from seeing an isolated quark or gluon. I read about whether a proton or neutron can decay (but they can't since they live or function for more than 1 with thirty zeros after it years. I also read about how people believed that the law of physics obeyed the symmetries C, that the laws are the same for particles & antiparticles, T, that if you reverse the direction of motion in particles & antiparticles the system should go back to what it was at earlier times, & P, that the laws are the same for any situation and its mirror image. At the end he starts talking about Black Holes, which is the center of focus for the next chapter.
Journal Entry 6
Chapter 6 (Pg 83-101) Today, I read about two theories on light: one that states that light is composed of particles and the other states that light is composed of waves. I also read about the life cycle of stars, which is needed to understand in order to how black holes are formed. I read about how a black hole is formed. A black hole is formed due to the gravitational collapse of star in which it shrinks to critical radius where the gravitational field becomes so strong that nothing escapes. Today, I read about how Stephan Hawking & Roger Penrose’s they did in 1965 & 1970 inspired Penrose to create the cosmic censorship hypothesis, a theory that suggests singularities made by a gravitational collapse occur only in places like a black hole. I learned that the event horizon is a path in space-time where nothing can escape; it’s also like a gate to the black hole. Hawking then talks about how in 1967 a Canadian scientist Werner Israel revolutionized the study of black holes by showing that according to general relativity non rotating black holes must be very simple in that they were perfectly spherical, their size depended on their mass, and any two black holes with the same mass were identical. And I learned that to find the number of “primordial” black holes depends on the conditions in the early universe and that if we find that number and how much the number has decreased since then, we can learn about how the universe was in its early stages.
Journal Entry 7
Chapter 7 (Pg 103-117) Today, I started a new chapter that starts with Stephan Hawking talking about how he first got into studying and researching black holes. Then he talks about how light rays can never escape the event horizon and that lies right on the edge of it. Then he talks about entropy, the behavior of a physical quantity, and second law of thermodynamics. He mentions how Jacob Bekenstein suggested that the area of the event horizon was a measure of entropy of the black hole. He talks about how Jacob’s suggestion doesn't violate the second law of thermodynamics, but he noticed a fatal flaw in which that if a black hole has entropy, it must have a temperature. Today, I read about if and how rotating black holes can create and emit particles. Then he talks about how one part of a particle/antiparticle pair will have positive energy while the other will have negative energy. Today I learned that once a black hole’s mass gets incredulously small it disappears in a final burst of emission, the production and discharge of something, especially gas or radiation. It’s said that the gamma rays of a black hole is very useful to the earth since it can power more than 5 power stations. Then he says that once the black hole gets small due to a decreasing mass, it becomes white hot, proving that black holes aren't really black!
Journal Entry 8
Chapter 8 (Pg 119-145) Today I started a new chapter that starts with Stephan Hawking talking about how after he did research on black holes he started doing research on the origin and fate of the universe. So far he talks about the origin of the universe where once the big bang happened the temperature of the universe decreased up to where it stopped producing helium and other elements and started expanding (the temperature still kept decreasing). I read about how the earth was when it was initially created and that it was very hot with no atmosphere. And once there was an atmosphere it was very poisonous due to being made up of toxic gases like hydrogen sulfide. Thankfully the first primitive forms of life released oxygen into the air and changed the atmosphere to the one we have today. This allowed the creation of much higher forms of life like fish, mammals, reptiles, and humans. I read about the strong & the weak anthropic principle which is “how you see the universe the way it is because of how you exist”. It also talks about whether there is other life out there in the universe, if there was an initial configuration for the universe on how it started, and whether the universe is spatially infinite.
Journal Entry 9
Chapter 9 (Pg 147-157) The main focus of this chapter of the book is about the Three Arrows of Time: the thermodynamic arrow of time, the psychological arrow of time, and the cosmological arrow of time. The thermodynamic arrow of time is the direction in which the state of chaos in the universe increases. The psychological arrow of time is the direction in which we feel time pass. And the cosmological arrow of time is the direction in which the universe is getting bigger not smaller. The first arrow of the time, thermodynamic arrow, is based off the second law of thermodynamics in which there are disordered states then ordered ones. Like for example in a jigsaw puzzle there is only one correct arrangement while there are infinite amounts of incorrect arrangements. It explains that if all arrows are pointing in the same it would make sense that there would be someone to say why disorder increase as time goes by in which the universe is expanding?
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