Is time travel possible?

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What would you do if you can go back in time to the past or go far forward in the future? Time travel is a topic that no one is not familiar with it. We saw it in books and movies, particularly science fiction, where the characters can travel to a specific point in time using a hypothetical device known as a time machine. For at least 125 years, time travel has been a fantasy. H.G. Wells published The Time Machine in 1895, and it has been the subject of papers by physicists and philosophers for almost a century. But the real question is, can humans be able to travel through time?

Time travel is a term that is a staple to science fiction but explored in theoretical physics by scientists all over the world. The concept of time travel challenges our human logic and opens our minds to new possibilities. Before we fully grasp the phenomenon of time travel, we must first understand time itself. The concept of time has been a mystery for centuries, dating back to when troglodyte used small etchings on rocks to mark days. Who decided that a day is 24 hours long and a minute is 60 minutes long? It was us, the humans, who were responsible. We invented the time scale we use to express time. Extraterrestrial may have a different method for calculating time; hence time would have a different meaning.

Time is a social construct created by humans for humans; it is a concept we plot our lives around to have some sense of order, but we don't have control. The most fundamental aspect of time, according to Carlo Rovelli, is that it is an arrow that continues to flow without end. Time, unlike other physical rules, has only one direction of travel: forward. It means that no matter how hard we try, we will not live in the present because our present is constantly changing. When you read this blog, it takes some time for the text to reach your eyes. It indicates that you are reading in the past. It is a scientific confusion to tell what time it is. Einstein made one of these discoveries, which he published in his journal. He demonstrates that time is subjective rather than uniform or absolute. We also understand that time moves in no particular direction.

In H.G. Wells' The Time Machine, he was the first to combine these two seemingly ordinary terms to create something unique. Even as a theory, time travel took a long time to be discovered. It wasn't until after the industrial revolution that people started to speculate about the possibility of traveling through time. Einstein's theory of relativity gave time travel a backbone. In one seemingly simple equation, this theory connects space and time. It demonstrates that mass and energy are two sides of the same coin. The presence of mass-energy determines the curvature of the spacetime continuum. It has two main assumptions: all inertial frames of reference follow the same physical laws, and the speed of light in a vacuum is the same for all observers regardless of motion.

To continue, Hermann Minkowski, who inserted the notion of a 4th dimension, similar to the one used in H.G Wells' piece of fiction, was responsible for Einstein's crucial discovery. Surprisingly, a concept used for entertainment was becoming more and more a reality. Time is the fourth, and it is a mathematical model depicting spacetime as a continuum. It allows particles in the universe to shift and interact without considering gravity. Today, it explains special relativity. Large objects can warp and manipulate spacetime around them, forming curves, according to Einstein's theory of relativity. Since it states that the faster you go, the slower time passes, his theory is also the first step in our exploration of time travel. As a result, if you were moving at the speed of light, time would pass even more slowly for you, and you would only notice the effects when you returned to the stationary people you had left behind. They'll have aged much faster than you have.

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The theory of relativity, which is a recurrent theme, and the wormhole theory are the two theories that explain time travel. When working on solutions for Einstein's theory, Ludwig Flamm proposed the latter. He discussed the concept of a white hole, which is the complete opposite of a black hole and is an object that can't reach from the outside but allows energy to escape. A black hole is an area in which the curvature of spacetime and time dilation is infinite. Flamm also proposed that spacetime conduits could link the entrances to both black and white holes. Nathan Rosen elaborated his theory by introducing the concept of wormholes, which are spacetime shortcuts. Einstein's theory predicted the existence of wormholes mathematically. In 2006, a gamma-ray burst with atypical properties was discovered, leading many to assume it was the first discovery of a white hole. However, there was insufficient proof to back up this claim. Wormholes may cause matter to travel from one location to another in an instant. A wormhole's entrance would be a black hole, and its exit would be a white hole. Many people believe that wormholes function on a subatomic level, making them impossible to see and extremely difficult to replicate on a larger scale for human use, although unseen to date.

The theory may allow us to understand time travel. But flawed in practice; hence there are several risks associated with this form of time travel. Wormholes will never be wide enough for humans or even ants to pass through, and anyone who attempts to do so will almost certainly die, as the conditions needed to open a wormhole will be beyond for humans to endure. However, some argue that since the universe is expanding, some wormholes could expand to larger sizes. Another issue that arises is that Rosen theorized wormholes are unstable and can collapse very quickly. Exotic matter, described as any non-baryonic matter with unusual properties, will be the only way to keep these wormholes open for a long duration. The Casimir effect, a well-known physics phenomenon, could be able to manipulate wormholes. It refers to a force that operates between two uncharged plates, which results in temporary changes in the amount of energy contained within a point of the electric fields. However, it will increase the wormholes' instability and make them even more unstable. A photon generates an electron-positron pair in particle-antiparticle pair formation when used. Time travel involves significant risks, which everyone would expect when defying the laws of physics. The wormhole theory, in particular, is riddled with assumptions, and even the most measured methods can lead to death.

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Time travel is a contradiction in and of itself, full of paradoxes that make it seem impossible. Scientists use many of these paradoxes to argue against the idea of time travel. The grandfather paradox is the most well-known of the temporal paradoxes. It is a problem that would arise if you went back in time and killed your grandfather before he had children, preventing you from being born. You've effectively ended your life and thus would never have gone back in time to murder your grandfather in the first place. An inconsistent causal loop is a term for this scenario. Another example of this paradox is when people go back in time to kill Hitler; if they succeed, Hitler will no longer exist in the future, and there will be no need to go back in time in the first place. It is a problem because time travel cannot happen if these problems are present.

The Bootstrap paradox, also known as the ontological paradox, is another example of a paradox. It's when an item or piece of information is sent back in time, generating an endless loop in which we can't find the object's origin. Since Skynet would have wanted the T-800 cybernetic organism, which sent back in time to avoid John, the ontological paradox featured in the Terminator films. It is a closed-loop paradox, similar to the pedestrian paradox, in which we can't replicate the cause and effect until the point of origin is no longer distinct. The bootstrap paradox is consistent. However, it defies natural laws of physics like the law of causality: hence we can't use a past cause to predict a future event since it may be a future event that causes the occurrence in the past.

The pedestrian paradox is a temporal paradox in which traveling into the past causes an entity or individual to become involved in the events that they were most likely returning to avoid in the first place. Under this paradox, history must be written in advance and cannot be modified, so any effort to intervene would only help preserve past events. The final paradox in this blog is Polchinski's paradox. Joseph Polchinski established this through an unpublished letter to Kip Thorne. It notes that if a billiard ball is sent into the past through a wormhole and then collides with its former self, the billiard ball won't reach the wormhole in the first place. This paradox serves as a basis as scientific evidence that supports Einstein's theory, which makes it more reliable.

Time travel defies our logic and the fundamental laws of physics to the test. Due to the severe conditions needed for time travel to happen, there is no evidence of it. Einstein's relativity theory has been the primary advocate of time travel throughout history. When our velocity shifts drastically, the laws that govern our universe also start to shift. However, even with today's technology, the necessary speeds are not achievable. The physical laws may forbid exceeding the speed of light because it would necessarily require an infinite mass. The most realistic time travel model is the black hole theory, which, like the Tipler cylinder, allows a "ship" to travel quickly through a black hole and become trapped in a time loop. It is appealing since black holes do exist as to other theories, which ideas are hypothetical. However, we don't know what happens when one crosses the event horizon. The objects may perish, which negates the need for black holes in time travel.

Therefore, time travel is far from our reach. It is only theoretical and only happens on microscopic scales, but even the universe has limits that we will never surpass. With current technology, time travel is more of a distant dream. When we create objects that can endure the pressures of superluminal travel, time travel may be achievable.

References

1. Time travel for travelers? It’s tricky.
2. Is Time Travel Possible?
3. Time travel: fact or fiction. A study on the scientific, social and historical impacts of time travel.
4. Now Time Travel Can Be Paradox-Free, Thanks To Math
5. A Practical Understanding: Time Traveling Paradoxes
6. The Time Machine
7. The Time-Travel Paradoxes
8. Rules for Time Travelers
9. Classic time travel paradoxes