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Physics of Time Travel

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Hayden McCormick

on 10 May 2013

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Transcript of Physics of Time Travel

“...I give you the mausoleum of all hope and desire...I give it to you not that you may remember time, but that you might forget it now and then for a moment and not spend all of your breath trying to conquer it.”
William Faulkner, The Sound and the Fury Physics of Time Travel The World of Time The History of Time The Mechanics of Time The Problems with Time The Paradoxes of Time The End of Time During the late seventeenth century, Isaac Newton, one of the fathers of modern science, submitted the idea that time was absolute. Here, humanity undertook the great task of understanding the universe through scientific method. For centuries time preformed, at least to humans, as Newton had said. This version of time was solid and did not allow for travel between times. Time travel was pushed into the works of science fiction never capable of successful or even a theoretical possibility. However, the last hundred years have been kind to science, spurring more technological and scientific progress than all the years before it. In this new era, time-travel reemerges from the shadows to be judged again. Backed by modern physicians and given life by Einstein, the question repeats, is Time Travel possible? To understand the concepts and realities of time travel in modern physics, it is necessary to begin with our elementary understandings of time and move forward to our modern notions. Starting in 1700 A.D. our minds crafted time as a scientific element and a history that evolved it from there. "People assume that time is a strict progression of cause to effect, but actually — from a non-linear, non-subjective viewpoint — it's more like a big ball of wibbly-wobbly... timey-wimey... stuff." -The Tenth Doctor, Doctor Who "Blink" Suppose that all the problems with time-travel are solved; negative energy is discovered in plenty,we could use cold fusion to supply our own energy to smash together strings, and physics unlock the holy grail of science with the theory of everything. Ta-da! Time-travel is now commonplace and the average family goes to take a picture with a pharaoh rather than head to Disney World. What happens to history? If someone steps on a bug during the age of dinosaurs, would humanity disappear in some obscure butterfly effect? These questions about the nature of time are titled paradoxes and remain hot topics for philosophers and scientists alike however the focus here will be the most popular, the Grandfather Paradox. Time-travel has been a far off dream of mankind for as long as man has reasoned our what came before and what is to come. Science has been humanities sword in progressing through our natural state through technologies and new understandings. Physics now serves at the forefront of modern achievement daring to take on what was once thought of as impossible. Physics has succeeded in proving it can be done. Time travel, the mastery of time and history as we know it, is now commonplace as an achievable goal given enough development and, ironically enough, time. While our personal time machines still lay somewhere in the distant future, time itself might one day be in our grasp. 1916 Issac Newton: Albert Einstein: 1700 Kurt Gödel: 1949 Stephen Hawking 1991 2 years of effort to age a fraction of a second slower is not quite considered time travel, but that's why other theories have been produced. While time travel has become a theoretical possibility the notion of bouncing around time in a blue police box is not quite practical, no matter how great that may sound. So researchers and scientists crafted their own versions of time machines that might be a bit more productive at getting us from one time to another. The Methods of Time Sir Newton, discoverer of our beloved gravity, submits in his Principia Mathematica that time and space are absolute entities and are omnipresent and unchanging. This concept suited well with his ideas on Newtonian physics but was later found incomplete. The German-born universal revolutionary usurped the common understanding of the universe when his published completed Theory of Relativity came to be. A theory that explained time as a river flowing unevenly and at different speeds moving in the same direction.The theory came to change the era of science and became a part of a scientific golden age and opened doors to a complete notion of time. Newton's Absolute Time and Space: Newton established the first widely accepted scientific foundation for time with his introduction of absolute time and space. The concept was fairly simple, when Newton was building laws on the motion of objects he needed to define the universe they work in and established the theorem. The theory defined time as uniform and perfect, one second here was one second there. This concept served Newton well who worked with rudimentary laws of motion and pioneered the foundation of modern science however the law was later succeeded by Einstein's as it was found lacking in later years. The Austrian-born friend of Einstein, Kurt Godel, was a brilliant mathematician and upon thinking on Einstein's relativity discovered that if the universe was spinning and a person could travel around it at the speed of light, he would arrive before he left. This theory was shot down by finding no evidence of the universe spinning however it was the first practical idea of time travel in Einstein's new universe. Wormhole Theory Cosmic String Theory Kerr Black Hole Theory Imagine civilization has managed to create two devices that make wormholes or holes in space at allow an atom or, at large enough scales, people to travel between these two holes instantaneously with no travel time by pressing together the space between into almost nothing. Shoot one of these devices deep off into space soaring at the speed of light or close to it. After a year, a person enters the wormhole device he kept. He arrives through the wormhole to the other side to find he is a light-year away but since it was moving near the speed of light, only a month had passed. Congratulations, he has just traveled back in time 11 months because these wormholes allow for instantaneous travel through space and time In 1991, Richard Gott of Princeton proposed a posssible method for time travel which involved massive galaxy-long and incredibly thin strings left over from the big bang to collide with each other. The resulting crash would contain so much energy and mass during a collision that gravity would warp condensing around the crash. This warped gravity, Gott discovered produced an odd effect that if a person in a space ship spun around this crash, the gravity would move space so that every rotation would be complete without going 360 degrees. Rotating quickly enough around would mean the person would keep arriving before he left, traveling more and more to the past with each spin. Roy Kerr is a New Zealand physicist who studies Einstein's relativity of time and pointed out metaphorical "whirlpools" in this "river of time". Kerr continued with this examination until he discovered the later named, Kerr Black Holes. These black holes are shaped like ice cones spinning on its bottom tip where all the stuff gets sucked up by gravity through the wide top part. Kerr proposed that like Cosmic String theory, an atom could utilize the gravity of black hole to spin to the past or use the gravity to slow relative and move to the future. If we could move an atom through the wide top of a Kerr Black Hole and avoid the singularity or the crushing point of gravity, the gravity provided would make time travel relatively simple. Wormhole Theory Cosmic String Theory Kerr Black Hole Theory This wormhole theory is fundamentally sound; however what prevents us from shooting these invented devices to universes unknown for easy transport and time travel is the lack of negative energy. Negative energy is the driving principle of wormholes since the intense condensation of space between the holes would cause incredible amounts of gravitational force, we need a way to stabilize the wormholes and keep them from collapsing on themselves. Negative energy does this by countering the effect of gravity, repelling objects to gravity's attraction. This negative energy is theoretically allowed and to some, they'd say it does currently exist, however no one has discovered such a material as of late. Cosmic string theory is an incredible one of ultra-massive strings bulldozing each other like two trains producing so much energy and mass that space starts wrinkling up as you ride the waves to the past. Aside from the obvious observation that these cosmic strings, despite evidence that they should exist can not be found, this theory however as one fundamental flaw. Gott originally proposed in the same article he published the idea stating that the nature of energy consumption this method has requires energy of half the universe. Makise Kurisu jokingly paraphrases, "Even if you do find the strings, you need the energy to make them move at near-light speed. Just how much energy do you think you'd need to accelerate something as long as the milky way to near-light speed? I'm pretty sure it's a little bit more than 1.21 jigowatts" The major problem with Kerr Black Hole time travel isn't an impossible amount of energy or unknown element but rather a simple lack of knowledge. At event horizon, the place where space ends and the wide part of the black hole begins, the laws of relativity mix with quantum mechanics, essentially where the rest of sciencific laws come from. This is an issue because the two theories are contradicting so accurately predicting the exact nature of how the black hole will react and consequences of Kerr black holes becomes impossible until physicists unravel the theory of everything. The theory of everything is one unifying Einstein's gravity in relativity to the rest of the major forces. Until this theory is found, our knowledge of predicting time travel through jumping through black holes remains difficult. Grandfather Paradox Singular History Inevitable History Parallel Worlds What would happen if you traveled back in time, saw your grandfather, and killed him? If he's your grandfather he would never have your parent and thus never had you, preventing you from being born but at the same time preventing the grandfathers death since no one murdered him. This paradox has baffled many as to the nature of time regarding these matters but several prominent ones appear. This theory on time states that history is fixed and eternal before present and is the sum of all actions that have already taken place. If a time-traveler were to affect the events of the past then the events would already be factored into the present. This is a very clean and simple solution to paradoxes but is disputed because it does not allow for free-will. A time traveler going back to the past must follow the actions that the past has already determined you would do without deviation because that is how the present was made. You can not kill your grandfather if you travel back in time because you are born, therefore you will fail. The time traveler has no free will to change the past and thus affects the present by questioning our humanity if we indeed have no free will to change the past, how do you have any to begin with. This theory is very similar to Singular History however allows for free-will. The initial concept was proposed by a Russian named Igor Novikov, who said that present is still the fixed sum of past events however is a time travel went back in time he would be outside of that history. An example to the theory is applied to the Grandfather Paradox as you may try to kill your grandfather but unknown laws will prevent your success whether it be the gun jamming or bird flying the way, anything the universe can conspire against you. This theory is preferred over singular history since it allows humans to act on their own accord but still does not allow for fluid change of the present. Congratulations, you have just traveled back in time and murdered your own grandfather. Why are you not disappearing? What changed? This theory of time is one of physicists favorite, the idea of alternate dimensions. The man you have just killed is not the man who fathered your father who fathered you. The man dead is a man who looked exactly like that man in this timeline or parallel universe. In this universe you will not be born because your grandfather is dead however the you, the time traveler still has a grandfather where you came from. This notion of splitting timelines based on inconsistencies solve a majority of paradoxes since it can create another universe and allow another to start the action preventing infinite loops found in most paradoxes. Even with the literally hundreds of methods of time travel invented over the past century, there have been challenges and issues that arise preventing us from fulfilling our ambitions and showing our current limits as a species. Hawking, perhaps the greatest modern physicist alive, challenged students and colleagues back in the 90's to find a scientific law that disproves time travel. After decades of work none was found and recently in 2007, he admitted to time travel being possible albeit impracticable. A message to the acceptance of time travel by the scientific community. Einstein's Relative Time and Space Einstein was the first to conceive that time and space moved relativity to object. He went against the current standard of Newton, and through his thought experiments and backed observations determined time was more of a fluid than a solid. First, like a river, time flowed at differently depending on the speed of an object and discovered the faster an object is moving, the slower time flows around it. Objects moving at the speed of light would observe time normally but a second for it may be a day on Earth. Secondly, general relativity states that gravity warps how space is distributed and can crunch it down since gravity is just acceleration and, like speed, can be used to slow down time. The former is the part of relativity most used for time-travel since it easy warps time considering you can approach the speed of light. The further from it and the less time warps. The record of a human slowing time was held by a Russian astronaut named Sergei Avdeyev who after 747 days of 27,360 km/h speeds, aged .02 seconds less than an earthbound person.
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