No doubt you have seen many movies and stories about time travel. And you have even come across topics that are claimed to be time travellers. For example, the picture above shows a man dressed in modern clothes, but in an old photo.

Or the image above shows a lady who is talking on a cell phone in Charlie Chaplin's 1928 film Circus.

• 

---

Or the photo above that belongs to one of Mike Tyson's boxing matches in 1995. The image is said to show a time traveler filming the race with a smartphone.

Of course, there are many of these cases, and perhaps the most recent of these cases is related to this 15-year-old Swedish girl named Greta Thunberg, who has been in the headlines of the media this year. She even made Trump react. In fact, she spoke out against global warming, and then the University of Washington found this photo in the university archives, which dates from 1898. As you can see, the girl in the photo is very similar to Greta. But beyond that, physicist Stephen Hawking hosted a party for time travellers on June 28, 2009. It seems that Tesla also has a role in the story of time travel. Perhaps the Philadelphia experiment in 1943, when the USS Eldridge disappeared, is his most important role in the story of time travel.

What you read is actually a very small part of the topics that have been claimed about time travellers or time travel and of course have never been confirmed. For example, in second photo, the person may have only a normal camera in his hand. The camera that existed at that time. Or The lady in the Circus movie may be listening to a regular radio. Because the radio was first built in 1920. Or that no one went to Hawking's party, but he believed that one day it would be possible. But despite this, is it really possible to travel in time? Scientists answer yes. But what does this mean?

---

To understand time travel, we must first become familiar with the concept of time While most people consider time to be fixed, the eminent physicist Albert Einstein proved that time is relative. For Einstein, space is described as a three-dimensional realm that provides coordinates - such as length, width, and height - as well as time as a "fourth dimension," which only moves forward. Let me explain simply: One-dimensional world that has neither deep nor height. A 2 dimensional world made up of infinite 1D lines. The 3 dimensional world is made up of 2D plates that make up the entire 3D space. And the 4 dimensional world, with time as the fourth dimension. The 4 dimensional world is made up of multiple 3D universe, each existing in a different instant of time. Each cube represents and instant of time and every next cube is the next instant of time This theory says that time and space are related. Einstein also said that our universe has a limit speed. That is, nothing can move faster than the speed of light at 300,000 kilometres per second. In fact, we all travel in time! For example, we travel for a year from this birthday to next birthday. And we all move at a certain speed in time: 1 second per second. But what does this theory mean for time travel? Well, according to this theory, The faster we move; Time is getting slower. Scientists have shown by experiments that this theory is correct.

Consider a person sitting in an airplane and moving fast. And at the same time his twin is on the ground. The person in plane grows old later than his twin because he actually travels in the time. In October 1971, Joseph C. Hafele, a physicist, and Richard E. Keating , took four atomic clocks aboard commercial airliners. They flew twice around the world, first eastward, then westward, and compared the clocks against others that remained at the United States Naval Observatory. The clock in the direction of the earth's rotation moved faster than the clock on the earth, while the clock that flew westward, moved slower than the clock in the earth. Therefore, the plane clock was moving slower than 1 second per second. According to Einstein's theory of general relativity, gravity can bend time. But what does this mean: we said that space is the third dimension and time is the fourth dimension, and we said that the 4D world is made up of 3D worlds.

---

Now imagine space-time as a piece of cloth. When anything with mass sits on that piece of cloth, it causes space-time to deep or bend. The bending of space-time causes objects to move in a curved path, and the curvature of space is what we know as gravity. An example of a return to the past is the use of space telescopes. Telescopes help us see galaxies that are very far away. It takes a long time for the light of distant galaxies to reach us. So when we look at the sky with a telescope, what we see are a long time ago of those galaxies. However, when we think of the term "time travel", we usually think of traveling faster than 1 second per second.

So in order to be able to move forward or backward in time, we have to move faster than the speed of light. but how. According to scientists, wormholes are the key to this puzzle. In 1935, Einstein and Nathan Rosen, using the theory of general relativity, elaborated on an idea called "bridges" through space-time. According to this theory, these bridges connect two different places in space-time or theoretically create shortcuts that can reduce time and distance. These shortcuts are called the Einstein-Rosen Bridge or the wormhole. Wormholes contain two openings that are connected by a throat. But time travel by wormholes will not be so easy either. There are 2 general problems. The size of the wormholes is microscopic and they are not stable. Scientists say that we need exotic substances to fix a wormhole. Recent research has shown that a wormhole containing an exotic substance can remain open and unchanged for a long time. In fact, exotic matter violates the known laws of physics, like a particle having a negative mass. So if a wormhole contains enough exotic substance, it could theoretically be used as a way to send information or travellers through space. And of course, wormholes can not only connect two separate places in the universe, but wormholes can provide time travel. But there is another possibility about traveling with wormholes. A traveler entering a wormhole may find himself in a parallel world instead of traveling in time . But Professor Mallett, a professor of physics at the University of Connecticut, has built a machine that he hopes will allow humans to travel in time. In his method, lasers are first used to produce a beam of circulating light. He explains that the space inside this "ring laser" must rotate, or in other words, twist, "like stirring a cup of coffee." At this time, space changes, and since space and time are closely related; The timeline of the line in which we all live will also change. And if the space is twisted enough, this linear timeline becomes a loop. And if time suddenly turns into a loop; It allows us to travel to the past.