How Can We Travel Through Time?

The concept of 'time travel', popularized by H.G. Wells's book 'The Time Machine', is a scenario that many of us dream about from time to time. Going to the beginning of humanity and meeting the first human, meeting someone you idolized from history, going back and changing the moments you regret, maybe even killing your grandfather and destroying your existence...

So how possible is that? First of all, we need to know that the subject of time travel can cause some paradoxical problems. The most well-known in this regard is the 'Grandfather Paradox'. According to this paradox, if you go back in time and kill your grandfather, your father will never be born, so you will not exist. Here the paradox begins. If you never existed, there would be no one who went back and killed your grandfather. So you will exist again and be stuck in a loop.

Considering such a scenario, we can mention three possible situations for travel to the past. Either it will not be possible to go back to the past because the past cannot be changed. Either the timeline we change will create a parallel universe. Or you can go to the past but only as an observer who cannot interfere with anything. Then it wouldn't be logically impossible to go back in time, would it?

When it comes to time travel, I think it's easier to go to the future than to look at go the past. It's even proven mathematically. The twin paradox is the simplest example of this situation. Let me briefly explain this paradox.

In the twin paradox. Two siblings of the same age adjust their clocks to each other. While one of these brothers stays on Earth, the other is sent into space by a ship moving at close to the speed of light. When the brother in the spaceship returns to Earth, he remains young as if almost no time has passed, while things seem not to be the same for the other brother. Decades have passed for the rest of the world, and he is now much older than his brother, with whom he was once the same age. This is because time flows faster on Earth than on a spaceship. In other words, time passes more slowly in objects moving at a speed close to the speed of light. This means that one minute for the brother on the spaceship is equivalent to years on earth.

According to this paradox, when the twin sent to space returns to earth, he is actually teleported to the future. Of course, there is no timeline formed on the world, and there is no way back, that's beside the point. After all, there seems to be a way to go into the future. But is this enough? Not really. If we can't go back, if we can't choose the time we want, if we can only reach the future of the world instead of our own, this is not enough for us.

No matter how much time travel seems like a fictional scenario, the scientific world takes it very seriously and continues to produce theories on it. Let's take a look at what these theories are. The first theory comes from Einstein. As we just mentioned in the twin paradox, according to the 'Theory of Relativity', if we move at a speed close to the speed of light, time will slow down for us. The closer we are to the speed of light, the farther we can travel in time. However, for this, we need a very advanced space shuttle so that we do not get crushed in the shuttle during our trip. Otherwise, we will have to end our journey with the hope of seeing the future because of serious physical problems.

Another way out of Einstein's Theory of Relativity is to use gravity. The more gravity is, the slower the time flows… So we need very high gravity like black holes to teleport into the future. The danger here arises from the possibility of not being able to escape the gravity of the black hole, and possibly even being drawn into it. And it is still unknown what our fate will be after falling into the black hole. Still, it looks like we can at least slow down time using the gravitational pull around black holes.

It would be a shame if we skip mentioning 'Wormholes' while talking about black holes. Wormholes, proposed by Albert Einstein and Nathan Rosen, are said to be shortcuts in the universe. As I mentioned in my article "How can teleportation be possible", it is thought that there is a black hole on one side of these short-path tunnels and a white hole on the other. We can also argue that this path, which I think can be used in teleportation, can also be used to go forward or backward in time by bending spacetime. Why not, if there is a solution to the problem that holes can close involuntarily and we cannot find our way inside?

Another effect similar to the bending of spacetime by the massive gravity of black holes comes from 'String Theory'. According to this theory, the universe consists of threadlike structures called strings. These strings vibrate to form different particles, just like the strings of a musical instrument vibrate and produce different sounds. Although it is not certain whether they exist yet, they have been proven mathematically. It is known that these filamentous structures exert a very high gravity around them. Now that we know the tricks of high gravity, we can say that putting two strings together can bend spacetime.

Is that all? No… Next is the 'Tipler Cylinder'. The Tipler cylinder is so identified with time travel that it is also called the Tipler Time Machine. The logic of the Tipler Cylinder is the bending of spacetime as a result of an infinitely long, massive cylinder spinning around its axis at a speed close to the speed of light. It is said that if you walk around the cylinder in one direction, you can go back in time, and if you walk in the opposite direction, you can go forward. Of course, this is just a theory for now… But still, the idea of traveling in time just by walking is very nice. Moreover, this time it is two-way.

Another theory, similar to the Tipler cylinder proposed by the American physicist Ron Mallet, is to bend spacetime with a rotating cylinder of light. A substance that enters turbulence begins to drift in space and time, which provides an opportunity for time travel. Mallet is still trying to find funds for his experiment. If successful, it may open another door to time travel. Good luck Mallet!

The last method I will talk about is a little different from the others. This time we stop our own time without bending space-time. With this method, known as 'suspended animation', biological functions are slowed down or stopped. In a 2005 study, American scientists tried this process on a mouse. With a small amount of hydrogen sulfide, which binds to the same receptor as oxygen, they slowed the mice's metabolism and lowered their body temperature to 13°C. After six hours, the mice could be awakened without any health problems. Unfortunately, the same practice failed with sheep and pigs. In other words, it cannot be said that it offers much hope for living things with larger structures. Studies continue. There is still hope to wake up in the world of the future.

Of course, all this is not an obstacle to freezing people. Hundreds of people have already been cryopreserved. This method is applied in the form of stopping the biological activity at temperatures below -130 °C. Liquid nitrogen is used at this stage. The freezing medium usually contains a protein source and cryoprotectant. The freezing process is applied to people who are considered legally dead. Whether they can be re-awakened is a mystery. If you want to try your luck despite all the uncertainties, you can put your name on the waiting list in the USA and Russia.

To sum up, you can quickly travel to a time in the future by freezing yourself or jumping on a spaceship. But if you want to have a time machine and shuttle back and forth in time, you need to find a way to bend space-time. For this, you must build a time machine that can move at a speed close to the speed of light, withstand high gravity, and protect you against all external influences and gravity. As difficult as it may seem, it is theoretically possible. Of course, we still do not know how likely it is to change the timeline. But at worst, I think we have a strong chance of going as a spectator.