Top 10 Theories and Paradox of Time Travel

Albert Einstein believes that time is an illusion. It is relative, which means time can vary for different observers depending upon the subject’s speed through space. In other words, time either slows down or speeds up. Time travel, on the other hand, is defined as a movement of a subject from different points in time.
Time travelling has been a very popular topic in most debates and researches, a project we all hope to become a reality. Why not? Everyone wish they could go back in time to escape present regrets, death, and grief or for whatever reason they hold. Alleged proofs of the idea of time travelling, in fact, are circling in the internet. A lot of articles attempts to explain time travelling theories and paradox, videos claiming that there are real time travelers, we’ve watched it all happen in movies, but can it be in real life?
Scientifically speaking, according to Einstein’s Theory of Relativity, it is possible to travel in time – going forward. But going back to the past, it’s a lot more complicated than said. It’s going to need an infinite source of energy, faster than the speed of light. There is nothing faster than the speed of light, which means time travelling is a no, not a chance.
Hypothetically stating, according to Quantum Physics, there’s this strange-but-true phenomena such as quantum nonlocality, where particles instantly teleport across vast distances, would probably give way to make time travelling a dream come true.
And if time travelling were to come true, what would it be like? Are there endless possibilities to what you can do with it?
Here we got 10 theories and paradox of time travel that hopefully, might be proven.

1. Predestination Paradox.

It is when a time traveler went back in the past, tries to alter an event, but instead of preventing the tragedy, he or his action caused it to happen. And then, he would go back, try a different method, option or action, and still it ended up the same way as it is to be.
Or how about this, you decided to travel back in time to kill Adolf Hitler. But whatever you do, it just won’t happen. So you decided to travel further back in time, just when he is about to be born. You took him and replaced him with a different baby, who then grew up to be Adolf Hitler, and you came back to the present only to find out that the kid who grew up to be Adolf Hitler still caused devastation and sorrows. Now it seems that you contributed largely to the tragedy, but no.
Predestination paradox simply suggests that what happened must happen and will happen.

1. Bootstrap Paradox.

Also known as Ontological Paradox, whereas ontology is a branch of philosophy concerned with the nature of being, or existence.
So, this type of paradox merely implies that any object, person or piece of information sent back in time will be in an infinite loop wherein the object will not have any discernible origin, and exist without ever been created. It will be in an infinite loop because, that object sent back in time, might or would cause the same event to happen again and again.
For example, if a traveler goes back in time, had an affair, goes back to his present without knowing that his partner is pregnant, had a time travelling son, went back in time, had an affair and the same event happens again and again. It’s an infinite loop.

1. Grandfather Paradox

This paradox is considered as ‘self-inconsistent’. Why? Because your very own existence is at risk. Let’s say you have an ancestor, your grandfather perhaps or the father of your grandfather, who rebelled against the country, killed a lot of innocent people or caused you and your family to be in the pit of shame. This made you so angry that you wanted to go back in time and kill him. But think about this, if you try to kill your grandfather for whatever reason, your father will not be born and your family including you will not exist.

Though some physicist and scientist that there are two things that could happen if you attempt to assassinate your own grandfather:

Either a Time Line Protection Hypothesis, in which you won’t be able to kill your grandfather. You approached him, point a gun at his head, the gun won’t shoot. It jammed. Point a gun at the other direction, Bang! Point back at him and it still won’t fire. You might try other weapons, a knife perhaps and other strategies but all these would end to another failure.

Or Multiple Universes Hypothesis, when you succeeded to kill your grandfather and then goes back to the present but everything about you does not exist. You have no history, family, friends; no one knows you or anything about you. It’s either you arrived at a parallel universe or your action caused an alternate timeline for you to exist without an origin.

1. Let’s Kill Hitler Paradox

It has a similarity with the Grandfather Paradox, although this paradox has a much bigger consequences.
We all know why most people want Adolf Hitler dead because he is responsible for the injustice death of millions of Jews. Imagine you have access to a time machine, and you thought you will go back in time to kill Hitler yourself. You found him; point a gun at his head, Bang! If you did successfully assassinated him, a part of history would be erased, History classes will not teach students about a guy named Adolf Hitler and how much he has done, you and everyone else will never know him which means you will not have any motive to travel in time.

1. Polchinski’s Paradox

A time paradox scenario, in which a billiard ball enters a wormhole, comes out in the past just in time to stop the younger version of the ball from entering the wormhole. This is proposed by an American theoretical physicist named Joseph Polchinski.

1. Through the wormhole

You probably have heard of the term ‘wormhole’ from movies like Zathura: A Space Adventure and from science fiction books like A Wrinkle in Time (Madeleine L’Engle, 1963) and Bright Moments (Daniel Marcus, 2011). A wormhole is a theoretical passage through space-time that could create shortcuts for long journeys across the universe. It has two openings each from a different region and/or universe, making time travel a possibility.

Einstein’s Theory of Relativity suggests the possible existence of wormholes and since it was first theorized in 1961, there hasn’t been any discovery of a real existing wormhole. And even if there really is, it wouldn’t be easy to make use of it as a time machine.

The size of a wormhole is said to be so small that a ship is impossible to fit nor a human. Plus, no one can tell the stability of a wormhole and whatever exotic matters are in there. It’s a very huge risk.

1. Infinite Cylinder

Also known as Tipler Cylinder where a collection of matter 10 times the mass of the sun is squeezed and rolled into a very long and dense cylinder. This mechanism is a solution to the equation of General Relativity by Willem Jacob Stockhum (1936) and Komel Lanczos (1924) but wasn’t recognized until Frank Tipler analysis showed in his 1974 paper.

The Tipler Cylinder, in order to work, shall spin along its longitudinal axis a few revolutions per minute. This should create a frame-dragging effect. A ship following a specific spiral course shall find itself in a ‘closed time-like curve’. There are problems though. For this to work the Tipler’s Cylinder has to spin infinitely long, this is to make sure that the portal will be stable until the ship which has to be steered carefully and professionally, will hopefully arrive at its destination. Furthermore, there’s no assurance that the ship will not encounter exotic species during time travel.

1. Black Holes

Our universe is filled with mystery yet to be solved and one of these is the existence of black holes. A black hole is a place in space where gravity pulls so much that even a single light cannot get out. Because no light can get out, we can’t see them without special tools used to detect these black holes.

While wormholes aren’t yet discovered physically, black holes are and some says these can be used to time travel. If a ship moves rapidly around a black hole to artificially create that condition with a huge, rotating structure, the ship and its crew will be travelling through time. The speed has to be as fast the speed of light and/or faster. But, according to Physicist Amos Iron at the Technion-Israel Institute of Technology in Haifa, Israel, there is a fault in this theory because the machine to be use to rotate around a black hole might fall apart before it is able to rotate the black hole at the required speed.

And even if someone did manage to enter a black hole, there is no assurance that he will live because when an object enters a black hole, the gravity inside it will stretch every atom in the body and look like spaghetti.

1. Cosmic Strings

Back in 1991, a physicist named J. Richard Gott introduced the idea of Cosmic Strings. As the name implies, cosmic strings are string-like energy stretched across the entire universe, thinner than an atom and under immense pressure.

According to the Anderson Institute, some scientist believes cosmic strings can be used to . Theoretically, if two parallel cosmic strings are pulled closely together or just one plus a black hole, this would create arrays of “closed time-like curves” making time travel a possibility.

1. Time Machine

To be able to travel back and forth in time, it is generally known that it requires a certain device – a time machine.
Time machines, as we’ve seen in movies, varies from a small room, head devices, manmade portals to time travelling cars and with a few clicks and pulls, you’re off to go to the past or future. It’s more than just that. The machine will need loads of negative energy density, if such exist, to be able to travel in time because of its potential possibility to create a portal from one point in time to another in the past.

However, there are researches that suggest a time machine can be without the needs of exotic matters. Using normal matters to create a doughnut shaped vacuum and inside this space-time could get bent upon itself focused on gravitational fields to form closed time-like curve.

To summarize, there are many researches, theories, suggestions about making time travel a reality. There are improvements and so are limitations. Even so keep in mind that all of these are not yet proven but who knows? Sometimes the great inventions are discovered by accidents.

References:
http://www.astronomytrek.com/5-bizarre-paradoxes-of-time-travel-explained/
https://topdocumentaryfilms.com/through-the-wormhole-is-time-travel-possible/
https://www.space.com/21675-time-travel.html
http://wizzed.com/10-mind-bending-theories-about-time-travel/
http://theweek.com/articles/445007/4-scientific-theories-actual-time-travel
https://www.livescience.com/33730-science-fiction-fact-wormhole-space-travel.html?_ga=2.120512904.1804306231.1510705699-1205273022.1510705699
http://www.andersoninstitute.com/tipler-cylinder.html
https://www.space.com/20881-wormholes.html
https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-black-hole-k4.html
http://www.andersoninstitute.com/cosmic-strings.html