Chapters Eleven and Twelve - The Unification of Physics & Conclusion

Einstein was a firm believer in not believing the reality of quantum mechanics, despite the important role he had in developing it. At the beginning of this century, it was thought that everything could be explained in terms of the properties of continuous matter (elasticity, heat conduction, etc.) However, the discovery of the atomic structure and the uncertainty principle put an end to that!

The partial theory of gravity, general relativity, and the partial theories that govern the weak, the strong, and the electromagnetic forces. These forces can be categorized into grand unified theories, or GUTs. However, these do not include gravity and because they contain a number of quantities that can't be precisely predicted from the theory, but instead have to be chosen to fit observations.

In an attempt to combine the uncertainty principle and general relativity, there are only two quantities that can be adjusted, those being: gravitational strength and the value of the cosmological constant. However, by adjusting these, it is still not enough to remove all of the infinities. In 1972, the idea of combining the uncertainty principle into general relativity became nearly impossible due to detailed calculations. Four years later, however, a possible solution called supergravity was suggested. Supergravity is the idea that by combining the spin-2 particle called the graviton with certain other particles of spin 3/2, 1, 1/2, and 0 could then be regarded as different aspects of the same "super particle". This would unify the matter particles with spin 1/2 and 3/2 with the particles of spin 0,1, and 2.

The final chapter of the book brings together all of the information provided thoughout our journey. In order to make sense of what is around us, we have created thousands of "world pictures" ranging from an infinite tower of tortoises to the theory of superstrings. The earliest theories of the universe began with the idea that it carries human emotions and thus acts in various unpredictable ways. After years of research pertaining to why this information might be incorrect, researchers have come only a little bit of the way to understanding how our universe really works, how we exist so cohesively, and what will happen when the world finally falls like the cup on the table did. As time moves forward, so do we, so does knowledge, and so does chaos.

Chapter Ten - Wormholes and Time Travel

Wormholes and time travel are very interesting to the majority of students in our class. Who wouldn't want to travel back in time and do something differently? Hawking, in order to explain the idea of time travel, uses a railroad. The train is time. It moves forward on a straight path into the future. However, what if there were twists or branches that the train could take to return to a previous train station, being that of a point in time. Is that possible?

The first indication that time travel might be possible came in 1949 with research by Kurt  Gödel. He discovered a new space-time allowed by general relativity. Gödel was a mathematician who earned
his fame by proving that it is impossible to prove all true statements. He called this the incompleteness theorem.
His space-time had the interesting idea that the whole universe was rotating with respect to directions that those 
little spinning tops and gyroscopes point in. 

Spinning Gyroscope

This idea allowed for the possibility that someone could take off in a rocket ship and return to earth before he ever set out. Although his theory seems plausible at first, scientists can prove that the universe does not rotate. Along with this information, the universe was originally formed without an existing curvature. Therefore, the only way time travel could be possible is if the universe had somehow formed curvatures throughout its existence.

Another problematic area is that in order to time travel, a body of mass must move faster than the speed of light. According to relativity, nothing can travel faster than the speed of light. There is one exception, however. Because all observers run on a different measure of time, the theory of relativity states that if an object were to perform a task at point B and arrive to point A, the observers at point B would say that the event took place at point A.

If one day, we are able to break the speed-of-light barrier, which we have come close to, time travel would become very much possible. However, in order to break the speed-of-light barrier, we would need to find a way to provide enough power to the object. Maybe one day, we'll be able to relive that awesome trip to the amusement park or retake that test we failed!

 

Chapters Eight and Nine - The Origin of the Fate of the Universe & The Arrow of Time

The universe was first described be the "Big Bang model". This stated that as the universe expands, the radiation and temperature drop by half. By using this theory, scientists can say that at the beginning of time, the universe was thought to have zero size, and thus infinite heat. But as the universe expanded, the temperature of the radiation decreased. Within only a few hours of the big bang, helium production would have ceased, along with other elements. And after that, for the next ~ million years, the universe would have continued expanding without much of anything happening. Eventually, all that is left in the universe would condense and collapse.

Chapter nine describes the idea of time. Hawking explains that at one point, all believed that time was a concrete idea that flowed evenly for everyone. This theory remained popular until quantum theory proved it wrong. Research about the speed of light led to the belief that time flows differently for every body. The second law of thermodynamics proves that as time moves forward, chaos increases. The example Hawking uses is a cup sitting on a table. The cup, in perfect condition, is at a high level of order. If the cup were to fall to the ground and shatter, the cup would be a very low level of order. The cup can not be completely repaired to the order level it was prior to the fall and return to the same position on the table because time can not flow backwards. 

Chapter Seven - Black Holes Ain't So Black

Chapter Seven took all of what I had learned in chapter six and turned it around. Hawking describes a black hole by stating that "the boundary of the black hole, the 'event horizon', is formed by the light rays that just fail to escape from the black hole, hovering just on the edge." The light must run parallel, or away from each other, though. If they were to run toward each other, the light would collide and fall into the black hole, leaving no event horizon.

Hawking reflects on the second law of thermodynamics. It states that the entropy of an isolated system always increases. When to systems are joined together, the entropy of the combined system is greater than the sum of the entropies of the individual systems. Everything checks out when using the second law of thermodynamics, except for one thing. In order to have entropy, a body must have temperature. And to have temperature, the body must emit radiation. Therefore, black holes are supposed to emit radiation. There very definition, however, states that they are objects that do not emit anything. The event horizon of a black hole, apparently, could not be used to measure its entropy.

It turns out, however, that a rotating black hole can emit radiation/particles. But how? By using quantum theory, the particles do not come from within the black hole, but from the empty space outside the black hole's event horizon.

Chapter Six - Black Holes

Chapter Six explores the knowledge we have and the mystery behind black holes. The term "black hole" is actually quite recent. It was first coined in 1969 by John Wheeler, an American scientist as a means to describe an idea that took place about 200 years ago. During this period, Jon Michell wrote a paper (1783) in the Philosophical Transactions of the Royal Society of London and stated that "a star that was sufficiently massive and compact could not escape." He also stated that the light produced by these stars would not be visible to us, however the gravitational pull could still be felt. Although his theory made sense, extensive research proved that a black hole was much more than that. They are, essentially, spots in the universe that are void of color and life. A black hole exists solely on two forces: mass and spin. The video below goes into this information in more depth.

Chapters Four and Five - The Uncertainty Principle & Elementary Particles and the Forces of Nature

Chapter Four goes in depth about energy, and more specifically, light energy. The main idea of the chapter, however, is the uncertainty principle. The uncertainty principle was created by a German scientist in 1926 by the name of Werner Heisenberg. His principle stated that: In order to predict the future position and velocity of a particle, one must first be able to measure its present position and velocity correctly. Hawking states that the easiest way to do this is to shine light on the particle. By doing so, some of the waves of light will be scattered by the particle, showing where the particle is. However, the position of the particle will not be accurately determined with a long wavelength, therefore a beam of light with a short wavelength must be used. Because of Planck's quantum hypothesis, a small amount of light can not be used anyways. A full quantum of one of more must be used. The quantum will change the particle's velocity because of the energy packed into it, though. This means that it can't be accurately determined. Thus, the uncertainty principle is formed. 

Chapter Five discusses the forces of nature and the effects they have on elementary particles. The forces of nature consist of air, water, fire, and earth. Elementary particles were originally thought to be protons and neutrons, but this theory has been disproved. The true definition of an elementary particle varies depending on the element. Their size determines the smallest particle within the atom, deciphering what the elementary particle is. The forces of nature (being air, water, fire, and earth) have varying impacts on the elementary particles, depending on what they are. This chapter was slightly confusing for me because everything was so "up in the air". There weren't very many concrete and definite theories.

Chapter Three - The Expanding Universe

The star with the closest proximity to us is affectionately named Proxima Centauri and is comfortably situated a mere twenty-three million million miles away from us. It is one of the trillions of stars located in our galaxy, which we now understand due to Sir William Heschel. He tortuously cataloged the positions and distances of thousands of stars so we could accurately say our galaxy was a spiral.

Chapter three provides insight into the history of our galaxy, the Milky Way, and the ways to detect the spectra of stars located inside of our galactic home. Hawking describes the Doppler effect, also. He states that it is a relationship between wavelengths and speed, resulting in changes in spectrum depending on where a mass is traveling. For instance, if a star moves closer to the observer, the star's spectra will be blue-shifted. If the star is traveling away from the observer, it will have a red-shifted spectra. Hawking also explains the works of Hubble and many others. Their experiments and studies led to or understanding of the universe as a whole, and our small galaxy in comparison.