General relativity Essay Example for Free

General relativity Essay For many years time travel was the stuff of science fiction. This was all just part of the worlds imagination until recently. Scientists now believe that the current laws of physics allow us to travel though time. They believe that we can now travel back to see our founding fathers sign the declaration of independence. We could travel to 2999 to witness the birth of the next new millennium. Such travel would require a machine capable of withstanding great pressures and incredible amounts of speed. The act of actually traveling though time is for the most part, agreed upon, but the implications of such travel is not so decided upon. Many different theorists have different views of what could happen and some go, as far as to say that if we did travel to the past, we would end up in a different universe that is a replica of this one. One of the most basic concepts is that of Dilation, a stretching of something. Some scientists believe that the main gateway to the past or future is a wormhole. Einsteins general relativity theory explains about universal constants, this is important to understand the concepts of travel at light speed. Traveling to the past could create problems if someone tried to change something. This is a paradox. A few of these paradoxes are explained through the use of quantum mechanics. Sailing though the cosmos at the speed of light with no time passing us by, moving throughout time to witness the ancient Egyptians create their masterpieces. This is an exciting concept that we could actually formulate and make happen. Before the time of Einstein, Newton and other great investigators thought of space as an infinite expanse in which all things exist (Hewitt 213). We are in space and we live in it along with all of the planets and stars. It was never clear if the universe exists in space or space exists in the universe. Dose space exists outside the universe or only within the bounds of it. The similar question, does the universe exist only in time or does time only exist in the universe? Was there time before the universe, and will there be time after it ceases to exist? Einsteins answer to this is that time and space only exist within the universe. There is no time or space ? outside. (Hewitt 213) Einstein said that space and time are two separate parts of a whole called space-time (Hewitt 213). To understand this, consider our present knowledge. We move though time at the rate of 24 hours per day. This is only half the story though. To get the other half we have to convert our thinking from moving though time to moving though space-time (Hewitt 213). When we move, we not only move through space, we move though time. This is the idea of space-time. If a person were to stand still, they would be moving only though time. If they moved a little bit, they would be moving though space a little bit, but still mostly though time. If one were to travel at the speed of light, what changes would they experience in time? The answer is simple; they would be traveling through space, with no travel though time (Hewitt 214). They would be as ageless as light, for light travels though space only (not time) and is timeless. The frame of reference of a photon, a particle of light, a trip across the universe would take no time at all (Hewitt 214). To understand how traveling though time would work, we must first understand how time and space can be stretched. Motion in space affects motion in time. Whenever we move through space, we to some degree alter our rate of motion in time. This is known as time dilation, a stretching of time that occurs ever so slightly for everyday speeds, but significantly for speeds approaching the speed of light. If we were to attempt to travel to the nearest star, Alpha Centauri, which is 4 light years away, even traveling at the speed of light would take 8 years round trip (Hewitt 228). The center of our galaxies is something like 30000 light years away and at the speed of light would take 30000 years to get there. We could not possibly survive that long. These arguments fail to take in to account of time dilation though. Time for a stationary observer on earth and for an astronaut on a spaceship of high velocity is different. A persons heart beats to the rhythm of the realm it is in. One realm of time seems the same as any other to the person in the realms, but not to an observer outside that realm that can see the difference. As an example, astronauts traveling at 99% the speed of light could make a trip to the star Procyon that is 11. 4 light-years away in 23 earth years round trip (Hewitt 229). Because of time dilation, it would seem that only 3 years passed for the astronauts, there clocks would be 3 years older; they would be biologically only 3 years older (Hewitt 229). It would be the mission control people that would appear to be 23 years older. The question is why dose this happen. Lets say that we are in our hometown, looking at the grandfather clock that is in the center of town. The clock reads 12:00 noon. Light from the sun bounces off the face of the clock and hits our eyes. We then turn our head and the light misses us and travels off into space. In space, there is a space ship that is traveling at the speed of light. An astronaut looks out his passenger-side window and sees the reflection of the clock. It reads 12:00 noon. As he continues to move at the speed of light, he keeps up with the reflected face of the clock. In the space ship time would pass as normal, but time in the universe would have seemed to stop. This might sound like cosmic bologna but the idea has been proven. In 1975 Professor Carl Tllie of the University of Maryland tested this theory using two synchronized atomic clocks (Brian par2). One clock was placed on a plain and flown for several hours while he other clock stayed on the ground. Upon landing, the clock on the plain was a little slower than the one on the ground. This was not due to experimental error, for the same test was done several times and each time yielded the same results. Because of time dilation travel in to the distance future is a definite possibility. The only problem lies in propelling a craft to such speed at which light travels. Carl Sagan wrote a science fiction novel about a fictional device that allowed his character to travel great distances across the universe. Those faster than light speeds are not achievable; he also knew there was a common convention in science fiction that would allow a gimmick of a shortcut through ? Hyper space as a means around this problem( par2 ) . Sagen turned to Kip Thorne for help for hyperspace connections through space-time( par2). A black hole always has two ends, a property ignored by everyone except a few mathematicians until the mid-1980s. Thorne was sufficiently intrigued to set two of his Ph. D. students, Michael Morris and Ulvi Yurtsever, the task of working out some of the details of the physical behavior of what the relativists know aswormholes. By starting out from the mathematical end of the problem, they constructed a space-time geometry that matched Sagans requirement of a wormhole that could be physical traversed by human beings. Sagan was right; hyperspace connections do at least in theory provide a means to travel to far distant regions of the universe without spending thousands of years putting around in an ordinary spacecraft. Since the 30s scientists have speculated that wormholes exist. Einsteins theory combines 3 dimensional space with time to create a 4 dimensional space (Brian par3). Wormholes are gateways between two different parts of the universe made by linking two black holes. Wormholes are in the fabric of 4 dimensional space that are connected, but which originate at different points in space and different times. By connecting the two holes they provide a quick path between two different locations in space and time. Distortions in space cause the point separated by the gap to bulge out and connect. This forms a wormhole through, which something could instantaneously travel to a far away place and time. This is basically the 4dinensial equivalent of a folded sheet of paper, to make contact from one edge of the paper to the other. One could build a craft strong enough to withstand the intense force of the gravity towards the center, and pass right through like opening a door of a house and stepping outside, except the space travelers outside could be light-years away and centuries before the current time. If the traveler enters one side he would exit in the opposite side in a different place and time. The difficulty of doing this is in keeping the hole open till the travel gets through otherwise it would collapse and the traveler would not be seen again. The trip is not impossible just extremely difficult. It is believed to be possible to create our own wormhole. To actually make one, two identical machines consisting of 2 parallel metal plates charged with unbelievable amounts of energy would need to be constructed. When the machines are placed in close proximity of each other the enormous amounts of energy, about that of an exploding star, would rip a hole in the space-time continuum and connect the two machines via a wormhole. This is possible and the beginnings of it have been illustrated in the lab by what is known as the Casimir effect. The next step would be to put one of these machines on a space ship and send it off at near light speed. The ship would take the machine on a journey while being connected to the other on earth via the wormhole. A step in the hole would take us to where the other machine is, but that would be in a different time. Its use would be somewhat limited because we could not travel to a time before the machine was created. However if we were to utilize wormhole technologic we would have to be so advanced that we could master the energy within blockhouse. Space-time consists of portraits or events that represent a particular place at a particular time. Your life forms sort of a worm in space-time. The tip of the tail is your birth and the head is your death. And everything that is the body is your life, otherwise called your world line. In three-dimensional space, a rocket that is not accelerating is stationary, but in four-dimensional space the ship is moving along is world line. Einsteins law states simply that the world line of every object is a geodesic in the continuum. A geodesic is the shortest distance between two points but in curved space is not generally a straight line. If an objects world line were to be distorted, so much of form a loop connected with a part on itself that represented an earlier place in time it would create a corridor to the past. Picture a loop to loop that runs into it as it comes around. This closed loop is called a closed time like curve. These curves could be used to travel into our own history. All the clams made about time travel are consequences of the basic scientific laws and standard Quantum Mechanics. Wormholes and closed time like curves appear to be the main way to travel to the past. The aforementioned theories do fine in expelling how to we would go about traveling through time, but they do little to explain what it would be like traveling through them. Quantum mechanics can be used to model possible scenarios and yields the probability of each possible output. In the context of time travel, it has a so-called many universe interpretation. First pursed by Huge Evertt III in 1957. This means that if something can physically happen it does in some universe. Everett says that our reality is only one of the many equally valid universes. There is a collection of these universes called a multiverse. Every multiverse has copies of every person, structure and atom. For every possible event every possible outcome is said to be played out in a different universe. This interpretation of Quantum Mechanics is quite controversial, but it does suggest that it may be impossible to travel backward in it to our own dimension, but quite possible to travel back in time to an alternate dimension. Such an idea of linking parallel universes has been suggested in science fiction novels and in some television shoes such as Sliders. In the television series Sliders, a sliding machine creates a wormhole that links 2 parallel dimensions. Each week a group of these sliders jump into the wormhole and emerge in the same place and time, but in a different dimension. They can run into there own selves and experience a society vastily different than their own. The stuff of science fiction stems from existing Physical theories. So now that we know travel through time is theoretically possible, what would it be like? What would traveling at light speed be like? It would be similar to driving our car at 60 mph. You could not really tell the difference, Einstein says that you can not tell the difference in uniformly moving vessels. According to Einsteins laws of special relativity sight speed travel is not achievable. For any object to attain light speed, an object must be massless, such as a photon. Any object with mass would require an infinite amount of energy to accelerate to light speed. As we know, everything has mass so it would be impossible for any human to achieve these speeds. Another barrier on our traveling the speed of light, is the fact that light is pure energy, if we were to travel at that speed, we would turn into energy blobs. What happens when we actually travel back in to time? What happens if we change something, or try to commit suicide or to invent something from the future that we take for granted? The future from that point could be drastically changed. This argument is commonly called the Chronology principal. This principal states that the time travel could bring information to the past that could be used to create new ideas or products. If Pablo Picaso, the most influential and successful painter of the 20th century were to travel back in time to meet his younger self, assuming he stayed in his correct universe, he could then give himself a portfolio of all his work. His younger self could reproduce the paintings and profoundly and irrevocably affecting the future of art. This would involve no creative energy by the inventor. The reproductions would exist because they are copies from the original and the originals exist because they are copies of the reproductions. No creative energy would ever have to be put forth to create these masterpieces. Because of the chronology principal time travel, by some, has been ruled out. The cosmos await us, and the history of our world is at our fingertips. Would we use this great power for good, bad, and wealth? All we have to do is get in our spaceship, set sail for the nearest wormhole, and hope for a little luck, and we can witness things only told in stories. Only the traveler can decided what he or she wishes to go back for. The theories today state that traveling through time is possible, however they do not say what could be the repercussions of our actions. This great frontier awaits us; we have the knowledge, and are slowly but surly developing the technology. Only time will tell when time itself no longer rules our lives as one of the chief amendments of the universal constitution.