Time Travel Possibilities
Pre Einstein era, astronomers heavily relied on physics' laws to understand and explain the working of the universe. Astronomers leveraged on the laws proposed by Isaac Newton, the first law which states that objects will always be in motion or at rest unless compelled to act otherwise by external forces. The second law states that a body will accelerate towards the direction of the net force inducing the motion. Lastly, the third law which states that for a body subjected to force(s) there exists equal and opposite reactions. For years before Einstein, physicists had begun to understand limitations and pose challenges to Newton's theory. These fundamental theories of physics help us gain insight into the possibility of time travel taking place. Several scientists have proposed the options of time traveling taking place and how it can take place. This paper will look into the works and theories of famous scientists who have tried to establish the possibility, paradoxes, and troubles associated with the issue of time travel.
James Clerk Maxwell, a Scottish physic scientist, was able to demonstrate how light is a wave that exhibits both magnetic and electric properties. The initial understanding was that light was only compelled to be transmitted via a medium known as ether. However, advanced research in optics has demonstrated that ether is not required. Additionally, in space, light travels in a vacuum. After Maxwell's findings, the theory of the luminiferous ether serving as a medium of propagating light was discussed. Central to this discussion was the question of the earth's motion in this medium. This hypothesis was in response to whether or not the luminiferous ether is incorporated within moving matter. According to the second variant of this claim, relative motion exists, an indication that the speed of motion defines the speed of light (Stanford Encyclopedia of Philosophy, 2018) .
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Morley, a renowned physicist, made significant developments in his respective field elaborating on this claim. Morley's research firstly revolved around questions that required a specific and precise establishment of density and atomic weights of gasses, primarily oxygen. His findings attracted scientist Michelson, and together they have established what we coined the Michelson-Morley experiments, which aimed to measure the movement of the earth in respect to the ether itself. These Experiments failed to detect any ether drag effect on the speed of light in various directions relative to planets motion. Lorentz finally dispelled any theory of ether drag. This great debate stimulated the inception of Einstein’s of special relativity.
The special relativity theory leverages on geometry to explain how time and space of objects in a straight line with consistent speed are linked. A key deliverable in understanding the feasibility of time traveling is the ability of objects to move with the speed of light. A famous equation E=Mc^2 that was formulated by Albert Einstein demonstrates the interchangeability between mass and energy. If the mass is converted to energy, it then follows that the magnitude of energy produced is the equivalent of the energy that was residing in the object’s mass. From the Einsteins equation, it can be deduced that there exists a directly proportional relationship between the energy and the product of mass and the speed of light squared. The increase of mass with speed serves as a vital tool in understanding how fast objects can be able to move within the universe. Presently, the fastest speed that has been recorded is the speed of light, and if the speed of an object nears that of light, its mass will exponentially approach infinity and this will dictate that an infinite amount of energy will be needed to power this motion. This signifies why there is a limit on objects ultimate speed. Einstein puts it that as objects approach light speed, their mass approach infinity, and at that limit, it gets difficult for an object to travel faster than light’s speed. Einstein developed special relativity theory in 1905 and became the ground his idea of general relativity (Stanford Encyclopedia of Philosophy, 2018) .
A major shortcoming that has riddled Einstein's theory is that it only takes into account effects relative to an observer in constant speed motion. From one perspective it can be deduced that motions characterized by consistent speeds occur at specific instances. However, reality has it that moving objects change speed with time. There were attempts by Einstein to generalize his Special relativity theory to suit the view of people accelerating relative to others. At the initial stages, Einstein was not specific on how he would employ Universal gravitation law proposed by Isaac Newton. According to Newton across space, bodies with mass pull each other. From his analysis, gravity between two objects is obtained by finding the product of the object's masses and dividing it through by the square of the distance separating the two objects. According to the computations by Isaac Newton and owing to the fact that gravity is proportional to the square of the distance between two objects, it consequently follows that gravity is strong within shorter distances as opposed to the gravity existing when objects far apart.As per Hans(2001), Newton had the erroneous assumption that the actions of the force of gravity were instantaneous.From his theory Einstein had alluded that no object could travel at speeds higher than the speed of light, in this case, not even gravity could do travel at infinite speed, on the other hand, Newton propagated the idea that the interaction of masses purely generated gravity. Finally, Einstein was able to demonstrate that the ability of mass being inherent in virtually every energy forms; it then follows that the masses had gravity.
Einstein's groundbreaking idea was that gravity was not a force but was indistinguishable from acceleration. He called this the Equivalence Principle. He showed that if he were to fall freely in a gravitational field, he could not feel his weight. The influence of gravity also creates an effect called time dilation. Einstein predicts that the closer a body is to a large mass, with a tremendous gravitational pull, the slower time runs for it. It seems that gravity is pulling on time slowing its effect. Time dilation raises one of the first theoretical possibilities for time travel.
A clock best explains time dilation in Einstein's particular relativity theory. This experimented clock slows down as perceived by an individual who exhibits motion relative to that clocks. Non-accelerating observers can determine which activities are bound to happen simultaneously.It is worth noting that an observer moving concerning a stationary one, they will disagree on whether the events that elapsed happened simultaneously. In the case of the clock, there are two parties involved, an observer that runs with a clock and one stationary with a clock, and it has been documented that the time elapsed as per the clock of both parties is different.The reason for this is that the one who was running with a clock his time was less compared to the stationary one. This example was one of the first ideas regarding the change in time and key to future philosophies regarding time travel feasibility. This philosophy stimulated the twin’s paradox phenomenon.
One of the most challenging experiments in special relativity is the twin’s paradox. It is characterized by twins, and one goes to space on board a high speed rocket and the other remains on earth. It gets puzzling when the one who went to the area comes back to earth to find the other twin having aged more than him, and yet they both observed each different moving. A rational explanation for this paradox can be explained by using the stationary and moving clocks ideology, and it occurs that the twin traveling to space with a high speed space capsule was moving slower as opposed to the inertial frame of his earthbound twin (Hans, 2001) . According to a false application of special relativity, each twin should have paradoxically found that the other has aged less. However, the solution of this paradox can be within the confines of special relativity.it is worth noting that The trajectory for the traveling twin’s is made up of two separate and independent frames of inertia namely :the frame for space voyage and the one to descend from space, and because of this, space-time paths symmetries between the twins do not exist. From the information obtained, the twin’s paradox ceases to be a paradox but rather a logical contradiction.
Einstein took these thought experiments from special relativity and felt that he could use these experiments, but this time with light. He used a similar operation to get new results that exhibit fundamental importance needed when carrying out same approach for light's ray. The experiment compels one to have an imagination of a lonely astronaut that floats through one empty void. The astronaut then decides to send an SOS signal emanating from his built-in laser pointers suit. As he beams the signal, a spacecraft flies past the astronaut and hopes those on board the spaceship will capture his SOS signal. From the astronaut's view, the signal he sent traveled straight ahead, and as the spacecraft flies by, the message inform of light strikes the window. In the process of the light signal making its way via the spaceship, the ship continues to accelerate. At the point that the signal strikes the ship, the signal informs of light hits on the lower spot from the ship's entrance. Instead of being curved, the beam the astronaut saw travels on a straight line. Previously it was demonstrated that the validity of acceleration similar holds when it comes to analyzing gravity. Unlike the astronaut, passengers in the ship saw the SOS signal as a curved arc making its way to the ship. With SEP, Einstein was able to realize the ability of gravity to bend light. More specifically, gravity warps space around itself. It turns out that gravity is nothing more than curved four-dimensional space-time. This thought experiment led to Einstein’s General Theory of Relativity (Stanford Encyclopedia of Philosophy, 2018) .
The idea of space-time curvature being able to be determined by energies and matter distributions within themselves stimulated the flourishing of the general theory of relativity. It can be described as R=GE a complex mathematical equation where G denotes gravitational constant, whereas R symbolizes a descriptor of space-time distortion. From the equation, we can deduce that gravity is not a pull but a disturbance of space and time.
Now that we understand the physics and history relevant to time travel, we can dive a little deeper into some of the physics as well as the thought experiments that raise questions on the possibilities of traveling back in time.
Scientists have argued that for time travel to occur, a loop either open or closed must exist. However, Monton believes that time travel can occur even in the absence of a loop. He presents to us two types of loops that is the casual open loop and the occasionally closed loop (Monton, 2009) . A rarely closed loop is one where event a leads to event b than to c and back to event a. The casual open loop, on the other hand, is a case where event g leads to event k but k also has another cause that is not an event. In typical time travel stories, the loops that are usually involved are the open loops. One of the arguments that Monton presented proves which try to demonstrate time traveling can occur in the absence of loops is the case where time travel occurs in distant lands that lack loops. The world where time travel occurs without involving loops is a world where there is no metaphysical difference between the past and the present.
In the article, The Paradoxes of Time Travel David Lewis analyzes his view on space-time and how it relates to a time traveler. Lewis aspouses to vehemently defend the likelihood of time traveling against those scientists’ state that time travel is impossible. Lewis is strongly condemned these lines of thought:
P1. Time travel gives rise to paradoxes.
C1. If time travel is possible, then paradoxes would be possible.
P3. Paradoxes are not possible
C2. Time travel is not possible
Lewis’s objective is to demonstrate that P1 is false, and time traveling should not give rise to contradictions. (Hanley, 2004) .
Lewis starts by characterizing time travel, as having a stable connection among existence. "What is an ideal opportunity to travel? Unavoidably, it includes a disparity among time and time". As per Lewis, by withdrawing and after that touching base at one's destination, the difference between the season of flight and time of entry gives us the passed time, which is fundamentally the adventure's length time. He poses the inquiry, "how might it be that two unequal measures of time isolate a similar two occasions, his flight, and his landing?" A few rationalists guarantee that there must be two free time measurements; that for time travel to be conceivable, it must not be a line on the plane. In any case, with the end goal for this to happen, at that point, a couple of occasions may have different partitions that are unequal on the off chance that they are isolated more in one of the time measurements than in the another. To explain, Lewis says that the life of a typical individual possesses a straight askew line over the plane of time at a steady rate. The presence of a time traveler, in any case, involves a twisted way with a differing slant. At the point when taken a gander at intently, the record does not give us the cutting edge origination of time travel. Lewis, at that point, poses the inquiry "when the voyager returns to the times of his youth will his mates be there to meet him?" Lewis says no since he has not landed at the piece of the plane where the mates are found. The reason is that the voyager is never again isolated from them along with two elements of time, yet he is as yet separated from them alongside the other.
Our reality and the universe of a time traveler is a complex of occasions with four measurements. Time is one of the four measurements and the spatial analyses aside from that among time and the others segregate among time and the others between different time-like measurements. Time stays one-dimensional since not two occasions such as measurements are symmetrical. He proceeds to guarantee that suffering thing like a period streak is openings that are comprised of various brief parts found on multiple occasions and places. Possibilities, along these lines, are subjective contrasts between different worldly parts having the option to persevere through some comparable things which are equivalent to changing the view from East to West. This is a subjective distinction between various scene spatial pieces of this His case from this investigation of room time is in the event that we should take the likelihood of time travel as valid, there will be a distinction of assessment between two diverse worldly pieces of the peruser toward the start of the article and the ensuing phase of the finish of the article, something we consider in our examination.
Lewis proceeds by attesting that if a change is a subjective contrast between transient parts than what doesn't have worldly elements can't change for example numbers or occasions of the time. A time traveler like every other individual is a line through space-time and is an entirely made of different dimensions which are situated on various occasions and places. If he goes once again into the past, the streak he displays is a crisscross, and on the off chance that the voyager goes towards the future, at that point, his line will be extended into a straight line. If he ventures whichever way quickly with no in the middle of the stage between his flight and entry, his term is zero, and he is a streak that is broken.
At the point when examined concerning how it is conceivable that two unequal measures of time isolated a similar two occasions, Lewis answered saying that time has two autonomous measurements. He instead responds to this inquiry by recognizing time itself, outside time, from the individual time of a specific time travel what is estimated by the voyager's wristwatch. The precedent given was if his voyage takes roughly an hour of his own time, which his wristwatch records an hour later at entry than at takeoff (Lewis, 1976). In outside time, the landing time has been exhibited to surpass the takeoff by over 60 minutes, if the time traveler goes to the future or touches base before the flight the person in question will head out to the past.
Lewis proceeds to state that the estimations by his watch are regularly in conflict with the outer time, anyway, he isn't a time traveler and what his dysregulated wristwatch estimations are neither one of the personals time or time itself. "That which is estimated by my wristwatch regularly can't help contradicting outside time, yet I am no time traveler; what my misregulated wristwatch measures are neither time itself nor my own time." Rather than an operational definition, he says, there should be a meaning of individual time that is practical. Only time can be characterized as that component occupying specific jobs in the type of occasions endangering the life of the time traveler. For example, if you somehow managed to take average individual's dimensions, they display explicit expected regularities custom fitted to outer time. "Properties will undoubtedly persistently change as one moves along generally and in a way that is commonplace."
Phil Dowel gives a possible objection to Lewis’s views. He says in The Case for Time Travel that one popular anti-time travel sentiments revolving around traveling back to the past always includes contradicting statements that more than one distinct temporal views separate two events. The example he uses to familiarize the reader with this objection was written by Willaim Grey in The Case for Time Travel and is as follows. “A time traveler's departure in 2000 will be separated from her arrival in 1960 by the time of her trip (2 hours, say) and the external time interval, minus 40 years. We need some explanation of this chronological discrepancy." David Lewis, according to Dowel, answers this problem by distinguishing between a time travelers personal time measurements by their watch, and the external time measurements by reasonable means. On the other hand, Grey responds to this paradox by merely moving on to discussing other objections and concludes his claims by stating that "without further explanation, it is surely reasonable to suppose that there is only one time series, that of physical time and that this also is the time of our experience."
Dowel says, “the answer to time paradox demur, which is that chronological discrepancies are countenanced under the theories of relativity, and in fact, they are demonstrated through experiments.” (Grey, 1999) . Future time Traveling, includes a chronological mismatch and therefore stimulates contradictions as per the time mentioned above paradox. Time paradox reasoning must be incorrect since this idea has been proved by experiment.
Grey responds to Lewis, claiming that the arising of chronological discrepancies that are connected to the special theories of relativity is benign, whereas time travel is not. The reason he gives is that these hypotheses don't provide space for the explorer to return before he left. On the off chance that this case is right, given that the speed of light confines the paces, the strategy expressed above can't bring you into the past. Then again, this case is the thing that we have to show that the time travel mystery thinking must be inaccurate since it supplies such logical inconsistency of time interims between two occasions. The measure of logical contradiction for this situation between two hours and twenty years is equivalent to there are in instances of in reverse time travel Overall there are different types of temporal discrepancies in modern physics that Grey is unaware off. Space-time that involves closed timelike curves gives room for traveling into the past. Kurt Gödel was one of the first to show that solutions to the general theory of relativity are there. Most recently, there are many investigations it the possibilities of closed timelike curves (Sklar, 1984) . The easiest to grasp is the idea of a where a wormhole which brings together two space-time points together such that an individual can travel into the future and in the past. In these types of spacetimes, especially by using the wormhole, there are temporal discrepancies existing which according to Grey are not limited by specific physics metrics. “In The Case for Time Travel by Phil Dowel, He discusses the “times paradox” that Lewis touched upon.”
A vital objection to the chances of traveling back in time is the Grandfather paradox. This paradox seems best described by Nicholas Smith. The description is as follows that for time travel to be admissible logically, is because an individual could go back in time and destroy the wormhole and get rid of the young age (Stanford Encyclopedia of Philosophy, 2018) . But if this were the case then the condition that is necessary, for the time travel to take place, would be eliminated and we would conclude that the time travel did not take place. To reply to this, it is only right to establish that the time traveler can’t alter the past in this way, is a petite principle. One would ask the reason behind time traveling being constrained and what mysterious force causes suicidal rage?
To put, the idea is that traveling back in time is impossible because if it did occur, the travelers might choose to adopt a destructive personality such as killing their grandfather or their young selves. We have a conception that changing the past in some way, by trying to kill the younger person is impossible. There is nothing that can stop these things from happening. If we were somehow able to get to a point where a time traveler comes face to face with his grandfather with a way to kill him, then there is nothing available to stopping the impossible from occurring . Therefore we must extend the timeline and state that it must be impossible for someone to get into this situation at all, and that is saying in fact that time travel is impossible.
To defend the chances of time traveling, there is a need to explain that time travel does not rhyme with a way of doing impossible things. In scenarios where a time traveler travels to the past, and he or she faces the hurdle of killing his grandfather, what could stop them from dying? David Lewis pondered this idea and came up with a possible objection that would show time travels impossibilities. Lewis goes to say that He or She would fail for some common reason". Stanford Encyclopedia of Philosophy claims that an idea like this would be that the time traveler’s gun fails or slip on banana peels and fall etc. Furthermore, a common occurrence is needed in stopping the time traveler from committing murder. The above objection is dismissed because traveling in the past is not characterized by the existence of practically impossible events
In conclusion, several scientific theories have been proposed in support of time travel. Scientists such as Lewis and Einstein claim that time travel is possible, and they have backed up their thoughts using various thought experiments.
On the other hand, there exists a group of a scientist such as Grey and Phil Dowel who oppose the issue of time travel. According to them, time travel is impossible, and they have backed up their position with scientific evidence. More research needs to be done to come to a common conclusion on whether time travel is possible or impossible.
References
Grey, W., (1999). Troubles with Time Travel. Royal Institute of Philosophy , 55-70.
Hanley, R., (2004). NO END IN SIGHT: CAUSAL LOOPS IN PHILOSOPHY, PHYSICS, AND FICTION. Synthese, Vol. 141 , 123-152.
Hans. (2001). Special relativity: a modern introduction. Lakeville: MN: Physics Curriculum and Instruction.
Lewis, D., (1976). The Paradoxes of Time Travel. American Philosophical Quarterly , 145-152.
Monton, B., (2009). Time Travel without Causal Loops. The Philosophical Quarterly , 54-67.
Sklar, L., (1984). Comments on Malament's "'Time Travel' in the Godel Universe." Philosophy of Science Association , 106-110.
Stanford Encyclopedia of Philosophy . (2018, March 23). From https://plato.stanford.edu/entries/time-travel/
