Time travel is too dangerous for us to use. To prove this one must first understand time and whether time travel is possible. One must also look at the possible outcomes of traveling in time and take a look and space-time.
Time is relative; a day is a day because that is how long it takes earth to rotate on its axis. If we were to go another planet a day would be different, it could be longer or shorter. Also bodies moving at high velocities experience a time that ticks slower than the time measured at zero velocity. For example if someone were to take off from earth in a spaceship and travel at high speeds and then come back much more time would have passed on earth. On earth many years could have past while only a couple years passed for the traveler. This is called time dilation. Einstein's general and special theories of relativity allow for time travel into the future and past.
The future is defined by all events leading up to it. If a person travels to the future, meets his older self, and then commits suicide on the spot the existence of the older self is a paradox. He cannot exist if he committed suicide.
Time travel into the past is much more difficult. It would probably require speeds close to the speed of light and a source of energy as powerful as an exploding star. Wormholes and closed time like curves (CTC) can also be used for traveling into the past and future.
One other thing we have to look at before traveling in time is the Bucket Factor. In the Bucket Factor the universe can only hold so much matter. If someone were to go back into the past the past universe would have to much matter in it and so it would explode while the universe the time traveler came from would not have enough matter and would become a black hole. I like to call this making the universe suck and blow.
Space-time is four-dimensional. In space-time your life forms a four-dimensional "worm" with the head representation your birth and the tail end representing your death. An object is a three-dimensional cross section of this worm. The line upon which the object lies is its world line and relativity requires that this world line to be time like. Now the angle that someone's or something's world line makes with the time axis is a measure of that thing's speed. If massive objects were to distort space-time enough some worldliness would bend until they connected into closed loops. This world line would be time-like all around.
A world line that is time-like all around would have all the properties of time and space but would be a corridor to the past or a closed time-like curve (CTC). If we were to follow the CTC we could meet our past selves or if the loop was large enough visit our ancestors. Along the CTC you would come across everybody who has or will travel that CTC. But there are limits to a CTC. CTC's only reach back as far as they ere created you would only be able to back so far. Another thing is that CTC's can only hold a finite number of worldliness. It would get used up if traveled too much.
Wormholes are another way of traveling through time. Wormholes are holes on four-dimensional space-time; they are connected, and originate at different points in space and time. Wormholes provide a quick path between two points in space and time. A simple step into a wormhole and you would be transported to a different place and time. Wormholes would be the four dimensional equivalent of pinching two pieces of a folded sheet of paper together o make contact across the gap. Distortions in space cause the points separated be the gap to bulge out and connect. A machine could be made to create a wormhole but you'd only be able to go back as far as the machine was created.
There are many different theories as to the possible outcomes of time travel. The following are the most common theories.
Alternate universe- you travel back in time to save a person's life, return to your own time to discover you've only change an alternate reality.
Fate- you travel back in time to save a life only to find out it can't be avoided, or worse, you were the cause of their death.
Success- travel back in time and kill your great-grandfather, then you would never have been born so you couldn't have hone back to kill your great-grandfather.
Observer effect-you travel back and succeed in altering history, you would be the only person who would be capable of differentiating between the old reality and the new reality. With you existing out of time you may not be affected by the changes you inflicted on the timeline thus you become a stranger in the new present.
The blocked universe theory states that there is one timeline and travelers going into the past fulfill their destined roles. One flaw to this theory is that it assumes that the traveler is ignorant of the past and just stumble into it. But if the time traveler knows about the past there would have to be some kind of an anti-paradox force of nature to stop the tampering of history. Also if you could travel into your past to a place and time where there were no time travelers your mere arrival would be a paradox in a single timeline.
One main paradox is the grandfather paradox also known as the autonomy principle10. This paradox is created when a time traveler goes back in time to meet his grandfather. Upon their introduction the time traveler could change the course of events leading to your grandfather and grandmother being wed. The traveler could tell his grandfather a family secret to convince that he is who he says he is and his grandfather in turn tell his soon to be wife. His soon to be wife doubts the sanity of the traveler's grandfather and commits him. The time traveler's grandparents would have never gotten married so his mother wasn't born and the time traveler was created through autonomy. This paradox would rule out time travel, yet the laws of physics do not forbid it.
A way to solve a paradox is the multiple universes concept. Hugh Everett III proposed the multiple universe theory in 1957. Everett said, "that our reality is only one of many equally valid universes." Within every multiverse there are copies of every person, structure, and atom. Every possible event and outcome are said to be played out on a different universe. Some scientists think that these universes could be linked through time travel.
In conclusion time travel is possible but things like the bucket factor and the different outcomes can make time travel very dangerous. Someone could easily destroy the universe or change the time line and create a paradox. So in the end time travel is best left undiscovered. We just shouldn't be messing around with time.
Time Travel Essay
Time travel is feat thought by most to be impossible. After all time travel is what many science fiction movies are made of. Let us not forget such movies as “Back to the Future” or “The Time Machine.” Yet unlike those movies time travel is not necessarily fiction. “We are in our own time machines, our hearts are pumping blood, we're breathing, we are existing through time (at least until our own personal time machines seriously malfunction).” (Need help citing this!) Still surrounding this topic is a series of theories, and surrounding these series is a number of flaws. Theories and flaws that need to be explained to fully understand the idea of time travel. First things first we must state the basics.
To begin with throw away whatever you thought you ever knew about time travel. There is no such thing as working time machines, you can’t go back in time by falling into a black hole, and sitting in a tub of water is not going to change you molecular structure and send it back in time by having you float through a wormhole. Time travel is achieved through speed; theoretically you must reach close to light speeds to go forward in time and faster than light speed to go back in time, according to Einstein’s theory of relativity mind you. Einstein’s theory of relativity is the basis of all time travel theories (Davies 1), “The essence of his prediction is that time is not absolute and universal but depends on the observer’s state of motion.” (Davies 1) States Paul Davies of the University of Adelaide in Australia, and writer for Sky & Telescope Magazine. “This implies that two observers moving at different speeds, say, will measure different time intervals between the same two events.”(Davies 1) For example say there are two people, Bob and Bobette, if Bob is traveling at x speed and Bobette is traveling at a speed of 2x, the amount of time passing would differ between Bob and Bobette. So what does this have to do with anything? Well I’ll tell you. Now this is pure fiction it is being used to show a point. Say we are traveling to Andromeda, which is 2.2 million light years away (help). We first set the acceleration to 1g (the gravitational field of the earth) because if we could accelerate to infinity we would be smashed to the size of an atom (help). So at 1g we should reach our maximum speed (the speed of light) in 354 days (help). After that it would take no time to get there at all since the time to get there would have shrunk to zero (help). So assuming we go there just to come back, it should take us a little under two years to get there and back. So we would have only aged two years, while the earth would have aged 2.2 million years. Thus us theoretically we would have travelled to the future. ...
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