*Subjected To Terms & Conditions.
I wrote two posts in the past on time travel, one on how we see the past, and the other on how I think time travelling to the future is impossible. But despite telling you about the theoretical possibility of time travel in Relativity and String Theory, if I don’t tell you how to build one time machine to do so, what good is all that information, and in extension, this blog. So here I discuss how different types of time machines can be created, using the present ‘theoretical knowledge’ and some experimental knowledge. *Spoiler* This post doest not tell you how to construct a Plutonium powered DeLorean time machine like Dr. Browns, but nevertheless, more exotic versions.
One of the most well-known ways known to offer time travel. Einstein-Rosen bridges, or Wormholes, are portals in the space-time fabric. Many sci-fi movies have used the idea of wormholes for travelling in time. Wormholes are more like a tunnel, joining one point in space and time to another point in space and time(which might not be same as the first). Wormholes haven’t been observed yet, but come out as a solution of the equations of general relativity. We know that mass curls the fabric of space-time, and if a body is so heavy that when it curls space-time, two points in the fabric, otherwise distant, might come together, and a bridge is formed between them. Since, in this space-time fabric, time is also a parameter, it can so happen that the two points belong to different positions in time, and hence when you cross the bridge between the two locations, you are travelling between two points in time. The difficulty with wormholes is that they are so heavy and unstable that it might close even before you enter it, and if you indeed succeed in keeping it open, the severe radiations from it, because of its high energy, can kill you. On top of all this, you need ‘negative energy’ to create a black hole. Negative energy is very hard to create, and was first experimentally demonstrated by Casimir. He showed that even in a vacuum, between two plates, very close to each other, due to quantum fluctuations, matter-antimatter pairs emerge out of the blue and dissipate, and the statistically different amount of these particles between the plates compared to other sides, pulls the plates together, and this energy of vacuum is negative energy. But the amount is so small, that creating a wormhole is a humongous task. Opening a wormhole, the size of a man, is still more difficult.
Kurt Gödel showed that if our Universe is rotating, we can travel at speeds higher than its rotation, and when we go around it we can get back to a point in time before we started our journey. Since our universe is the space-time itself, going around it would mean not only going around in space but also in time. Whenever some astronomer visited Kurt, he would always ask them if they have seen any evidence that our Universe might be rotating, but to his disappointment, no such evidence has been found, the only thing about the movement of our Universe we are certain of is that it is accelerating outwards.
INFINITELY LONG ROTATING CYLINDER
Notice the movement of cream in your cup of coffee, whenever you stir it using a spoon, the rotations cause the whole coffee to swirl, and this curls up the surface of the liquid such that every point is dragged along with the spoon. This is a bit what happens in this mode of time travel. The Tipler Cylinder, is an infinitely long cylinder, which rotates along its longitudinal axis, when it rotates sufficiently fast, it drags the space-time with it. Oversimplifying the situation, I would say it creates closed timelike curves, paths in the space-time, which when you follow, you end up on the time before you started walking, and when a Tipler Cylinder rotates, this is exactly what it does, when it drags the different parts of space-time along with it. The difficulty apart from the near light speed angular velocity is that this cylinder needs to be infinitely long, and also requires huge amounts of negative energy.
While all the above mentioned methods emerge as solutions to the equations of general relativity, this here is an idea emerging from the String Theory. String theory which implies that all particles are nothing but different vibrations of strings, pictures the Universe as made of strings, ‘Cosmic Strings’ it self. If two cosmic strings were to collide, and you were able to move around them, calculations show that you would reach a point of time in the past. Though cosmic strings are almost the size of the Universe, or atleast galaxies, the have the advantage of not being infinitely long, or requiring negative energy. But they are really hard to find, and making two of them collide just the right way is another herculean task. Another disadvantage of cosmic strings is that they can take you just as much back in time where they were colliding, no more backward. These cosmic strings have energies of at least half of that of the solar system, and can form closed timelike curves when approach each other or a blackhole.
KERR BLACK HOLES
These were some of the most well-known scientifically proven ways that would allow you to travel in time. Another well known way could be to enter a rotating black hole, also called a Kerr Black Hole. Black holes have gravities so large that all the space-time fabric around them curls and bridges just like in wormholes, but unlike them, a rotating black hole is just a one way ticket, once you have entered the black hole, you cannot come back. It is hypothesized that there is a ‘white hole’ at the end of these black holes. White holes spew matter out of it, and so there is a one way bridge created through this black hole and white hole system, where matter enters from one end gets thrown out at the other end, in a different location in space as well as time. NO white hole has been observed yet, though we have seen a lot of Kerr Black Holes around in space.
Time Travel began as a topic of sci-fi, but with advances in physics and maths, it was understood that leaving time solely in the hands of writers would be unfair to science. Michio Kaku classifies time travel as a class II impossibility, meaning, though it is allowed by laws of physics, it will not be possible for atleast a thousand to million years, until we become a Type III Kardeshev Civilization. Steophen Hawking was one of the biggest deniers of time travel, asking “Where are the travellers from the future?”, and proposed a Chronological Protection Conjecture, a law that would preven time travel. Many scientists have tried, but no such law has been found. Recently Hawking went back on his stand and said Time Travel Could be Possible, but not Practical. So what are your views? If you are from the future, which of these methods did you use? Happy Reading, and Safe Travelling!
-The Cosmogasmic Person.