Believe it or not, Doc Brown never could have gone back to the future… or the past… or really have ever gotten his DeLorean up to 88 miles an hour because the vehicles had notoriously terrible engines. But that is not the topic of this paper, we will explore the possibility of time travel and the philosophical along with ethical problems that could and would arise from it. But before this continues we need to understand a few the principles that make up ways of how time travel could work.
Our first principle is the Universe’s speed limit, an overall maximum speed of matter. Currently, this known speed is the limit for anything that contains mass or information, light is able to move at this speed because it is made of photons. Photons are massless particles that are emitted as electromagnetic radiation when light is produced. Light like anything moving can be slowed down when it collides with another particle or some kind of object, even space dust, air, and water can slow it down because it requires more work, work is the amount of energy transferred over a distance by another force. In layman’s terms if your going to move a cup then you have got use your hand to push it once this is done you have produced work.
Light has to move through these particles and this action requires work which leads it to lose some energy and changes lights velocity. Moving onto the second principal energy, whenever mass moves it expends some kind energy no matter how small the change in position or direction it requires energy. The first law of Thermodynamics states this essentially, that energy cannot be created or destroyed, the second law can be summed up that whenever energy is transformed or moved it takes energy to make that transfer.
Energy is known to be finite, we cannot have an infinite or unlimited amount of it. For an infinite amount of energy to be achieved we would need to invent a perpetual motion machine, there are several different kinds but for time traveling we would need one which does work without energy, this breaks the first law of thermodynamics through producing work without expending energy. These two ideas are extremely important to remember during this paper where you will be introduced to several types of real and theoretical. Time travel is a very real thing and has been studied before but this kind of time travel is not the conventional kind you would think of involving Flux capacitors, a Blue telephone booth, or a flash of red and yellow lightning before they disappeared. The direction you go, past or future is usually dependant on the method you choose to travel, some forms only allow a one-way trip and others you can go both ways.
The first kind of time travel we will look at is known as time dilation. Time dilation was theorized and first written by Albert Einstein in a paper published on June 30, 1905, ON THE ELECTRODYNAMICS OF MOVING BODIES, where he described that an observer at rest experiences time different than an observer in motion. An example of this phenomenon can be seen in the 24 GPS satellites that rotate Earth 24 hours a day, these satellites move at speeds of 14,000 km/h (8,700 mph) and due to their speed they require special clocks to sync up with the time is on Earth’s surface because the satellites experienced 7200 nanoseconds (0.0072 milliseconds) less in 24 hours than we did on Earth. This number seems extremely small but as an object accelerates closer to c it experiences time exponentially slower than space outside of itself. Time travel is possible through this kind of dilation, because of this if a human could be sent away from Earth at near the speed of light and travel any distance, they would experience a significant amount of less time than people on Earth.
They could travel away from Earth for 1 year moving near c and return 50 years or even 500 years in the future all thanks to time dilation around them. But to achieve this kind of time travel we would need a massive amount of energy, and a ship that could carry enough fuel to move at near speed of light speeds. This feat is not currently possible with the technology available because fuel is extremely heavy when used in rockets and expending that fuel takes energy, to move even more fuel requires a bigger rocket, and that requires more energy. To achieve a fraction of this or it as a whole would be a titanic and near impossible effort. The fastest a human has ever traveled was the Apollo 10 Lunar-Module upon re-entry of Earth’s atmosphere on May 19th of 1969 it reached speeds of 39,897 km/h (24,791 mph) as stated by NASA, to put this speed in perspective they are only moving one 27,051st of c. But that is not to say we have never made an object move at speeds near c, the Large Hadron Collider a machine built to accelerate and study the effects of particles moving extremely fast is able to move a proton at 0.999999990 c, or about 11 km/h (6.
8 mph) slower than c which is an amazing feat. To summarize that, if something accelerates close to c it begins to experience timeless then something observing it. There is one more form of time dilation that allows for time travel to the future, called gravitational time dilation, first theorized by Albert Einstein in his papers on his theory of relativity and later confirmed it with tests using general relativity.
This form of time dilation can be described as clocks at different points of a gravitational mass would experience time slower than an observer. If person 1 with an atomic clock in their hand and stands on Earth’s surface, and person 2 floats at Earth’s Exosphere (the outermost part of the atmosphere) the clock on the surface of the Earth would tick nanoseconds faster than the one in the exosphere, which would slow down. This method is also a one way trip to the future, but to make any substantial change in the time it would require being extremely close or next to something with a massive amount gravity.Now it is time to dive into a more theoretical approach to time travel through wormholes. First theorized in 1921 by a physicist named Hermann Weyl, when he proposed “one-dimensional tubes” void of any space or energy, inaccessible and infinite in length. This was later expanded by Albert Einstein and Nathan Rosen who connected the idea first had by Weyl back to Einstein’s theory of general relativity and described “bridges” between two points of spacetime. Wormholes can be explained as a compression of spacetime to imagine this think of a piece of paper and fold it into a half, then take a pencil and shove it through the piece of paper. Theoretically, these would connect millions or billions of light years, down to a few meters, or even different periods of through a tunnel that links the two sides together.
While in theory, it would definitely allow for a sort of time travel if the wormhole leads to it, but that presents a few problems. The first is wormholes are not necessarily transversable and their hypothetical size varies from the smallest unit in existence known as a planck, to macroscopic size, the size at which something can be viewed by the human eye. These sizes are all depending on the kind and the method used to create them and the physicist proposing the method. Creating them is another problem, many physicists such as Stephen Hawking, and Kip Thorne argue not only the means to make them but whether they exist at all naturally in our Universe. Wormholes would even allow for time travel to the past, or the future but traveling to the past cannot go further than the creation of the wormhole itself. These were are some of the few known both real and hypothetical ways to time travel, beyond these things it gets more and more hypothetical and complex to understand the intricate ways time flows and how to flow with it. Time is always flowing backward, forwards, and it has a path because time is always going to happen. Every single event in history is built on an event preceding itself and stopping one event will just lead to another to substitute it.
If someone went back in time and changed an event based on size it would create ripples that change the future in both short term and long term. For example, if you went back in time and took Einstein’s calculator and smashed it in half, it might delay the publish date of some of his work but he would just go out and buy another calculator. This is on a small scale, but if you went back in time and burned all of Einstein’s unfinished papers, it could set him back years or he may go back to working in a patent office. But the direction you move in time has varying consequences as the future has little to no effects on the continuum of the present or past but moving to the past presents something of a problem. A future objects very presence at a time it’s never participated in would break something known as causality.
Every action has an equal and opposite reaction which means this presence would send ripples through the timeline, small and minute but the effect of these ripples are currently unknown some believe it is impossible to go backward in time but hypothetically some of those who believe in it think it would create another parallel world. In 1957 Hugh Everett a renowned American physicist who proposed a theory that would later be renamed the Many-worlds interpretation. The theory went on to state that every single outcome that is ever possible is an entirely separate Universe that exists.
These can all lead to small but snowballing outcomes that affect the timeline for years to come. Changes to the timeline all branch off and create entirely new realities where everything is just as real and genuine as our own, but those events can lead to small and large changes in the future. There’s another theory that any change to the timeline the moment something from the future interacts with the past will create a new timeline that replaces the previous one before it. A good example is in the movie Back To The Future where the protagonist Marty McFly almost erases his own birth, throughout the film he uses a polaroid of him and his siblings where he is slowly fading in and out of existence more and more until he saves himself in the end by reuniting his parents.
Aside from all of problems that creates, if Marty interfered in any sort of way or fashion with his parents meeting he wouldn’t have time to save himself, if his parents went on a path to never meet and he existed in the same period as them he’d be a living paradox or he’d be immediately erased from existence. One of the two is very likely to happen. Paradoxes are an interesting thing that plays an integral part in time travel in both fact and fiction, by definition they’re something that concludes in a self-contradicting or illogical way. The understanding of paradoxes in time travel acts as a set guide of rules to follow if someone ever went back.
For example, imagine we send your great grandfather’s pocket watch back in time. From the 1st of January 2018 to the same date of 1918 the person who receives it gives it to your great grandfather who passed it down the family line to you, and then on 1st of January 2018 you send it back in time. Who had the pocket watch first? This sounds like no big deal but, when this happens we create a paradox without a discernible beginning or end, this is known as a Causal loop where the events origin is not possible to be found much like Marty McFly in the example, he would exist with no beginning or end. There are dozens of paradoxes all with different causes and effects which render them completely unique compared to one another, another known as the Bootstrap paradox is similar but drastically different to a Casual loop. The Bootstrap paradox involves sending information from the future to the past for this imagine George Lucas went back and time and gave the script of the movie Star Wars to himself, how can the script exist if it was never created?