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My previous #steemstem tagged post was about the greenhouse gases which those cause the global warming. I noticed that my followers were very much interested in my science-related posts. As I really love to share my knowledge about science and technology I am going on creating new science posts like this one. I have always been an astronomy and cosmology enthusiast. Apart from the fact that I'm a physicist, I everytime concerned closely about planets, stars, space and time since the childhood. Especially the time itself. I always read the books and watched the documentaries so far. But it is the first time for me to write a detailed writing including this subject. As this post ends, I want you to have an insight of what time really ( time-travel) is and is not.

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My leisure times are mostly filled with tv series. I really like to watch historical movies and series. But when I get to bed I think of being in those old times:

• I really wonder how it would feel like to be in the historical times.
• How were the people looking like those times? What do they like to eat or drink?
• If I could go over there, would I really understand their speech?
• What would they do to me? Could they understand me if I would put in the picture?

and so on...

All these dreams and fantasies are originated from a phenomenon which the humans have always thinking and desiring to experience from time immemorial... This is the phenomenon called "Time Travel!".

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CAN WE UNDERSTAND THE TIME?

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As I am a Physicist, I should ask you that "can we understand the time?" before telling you that "What the Time is". Of course, we can explain the time in terms of complicated entropy equations and some straightforward definitions. But the more important point here is to be elucidated not to narrate directly! Let's together try to understand what the time is! I can feel the time but I have difficulties in understanding it. I want to tell what I mean that way: From the first time period of my life to my adolescence period seemed to me very long such that as if it must take hundreds of years to be 15 years old whereas It was only 10 years of time to be passed on...

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There are some research papers related this "objective time perception" phenomena. The hypothesis is proposing some brain activities running as the neuro-psychological progress. If you're interested in further reading about this issue. You may check out this one , this one, and this paper to have more clarified explanation. After my puberty (let's say between 15 to 25 years old) I still couldn't understand exactly how those years passed by so quickly. After 25, every day is incredibly elapsing too fast. And I have nothing in my hand to stop or slow it down.

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In the conversations which were held with my grandmother recently lost (these were her last days), she was always kept telling me that the life is only 1 day. She told, " she had lived her life so fast as if it is fitting in a time period which she blinks in just one second!". I have no idea what she really lived in the last seconds of her life but most of you know it is told that someone who is about to die sees his/her life flashes before his/her eyes in one millisecond. No wonder, I'm not intended to fill you with melancholy with deaths, loss or something. But I want you to feel the point that how our perceptions of the time differ by getting older. We feel the time's passing by with different speeds in our various life periods. We can feel it goes by but we can't really understand it. This is my point which I'd like to touch on.

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FOR UNDERSTANDING...

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Different from feeling, comprehending the time isn't in the scope of any talk, philosophy or any paranormal activity. It is completely the subject of Physics. If we would like to understand it we should give our ears and try to size up what it says about this subject. The time itself seems like a non-physical thing and appears as it is not a thing you can see or hold it. It is nothing of the kind! The time is a measurable and experimental thing of this world exactly like the stone, the soil, or the heat. We should understand what the dimension is before we understand the time.

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The Dimensions

Now, look at the corner of the wall and ceiling intersection on the upper right side of the room where you sit. You will see that the three boundary lines cut (belonging to the walls) from one left, one right and one below, intersect at a single point. That's the three spatial dimensions. In fact, you see a 3D object (wall) that fills the space of 3 spaces. If it were not there (or any other object), you would never see those 3 space dimensions. By the way, if you ask "what are those spatial dimensions?" then, of course, you already know them; Length, Width and Height... It only shows that you can't perceive these 3 spatial dimensions unless that object (wall) is not found there. It doesn't mean that the spatial dimensions never exist there.

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Think about it like this: You know space is a huge emptiness. If you were in space, you would probably just float on and encounter nothing almost for tens of thousands of years. And as long as you go, you will see nothing there, But, even you are not seeing anything there, then it doesn't mean that the spatial dimensions are not there. Dimensions are always there. We only see their presence when they are filled and perceptible. Imagine that you look at a clothesline from any distance. You will see it as a single straight line. Thus, an ant on the clothesline is only able to move on that line to the right or left at most. According to your perspective, the ant's degree of the freedom is only 1 dimensional for her to move on since the line hasn't any depth or width.

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However, as you change your perspective or viewpoint, you will see that the rope gradually thickens as you get closer to that balcony/rope. That's meaning that the "width" is added to that 1D clothesline. It is 2 dimensional any more. From this point on, you will start to realize that the ant has actually 2 degrees of freedom for moving. If you go on getting closer fairly good, then you will perceive that one more 3rd dimension of the rope is just there. Actually, the rope is a three-dimensional world for the ant where he moves on it. But remember, when you look from a distance, you saw a 1-dimensional thing. 2 extra dimensions became involved in later!

Actually, what I want to sum up is that the awareness of the dimensions are determined by our perceptions but their existence is independent of our perceptions. In other words, they have always been there and will be. Alright, how many dimensions in the real world actually exist? Are there only 3 of them? In fact, there are many more of them. As the results of the mathematical expressions for the "String Theory" which many research has had conducted on it, there must be many more than 11 spatial dimensions.

Ok. What do they look like? How can we sense them? Frankly, answers to all those questions are another post's topic. So you could have asked that "what is the relationship between the time and the spatial dimensions?".The relationship is that the time is another dimension just like the spatial dimensions. You know that length, width and height are intricated in our lives. And the time is also! We can't discriminate the time against the spatial dimensions in no sense. As we move along a path, we are making the same move in the same way as we are displacing in the width, height and height dimensions.

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Everything Is In Motion In The Universe. So Is The Time...

Perhaps you will be choosing not to believe it but yes, everything moves on in the universe as Cosmology says to us. Nothing is ever absolute stationary. Atom, human, cars (even the mountains), the earth, solar system, Milkway Galaxy and, terrifyingly huge clusters of stars... All of them are relatively in a motion. Please pay attention to this point! The important clause here is relatively. "Relatively" stands for in comparison or proportion to the other one. Because an object which is looking like immobile from a point of view (it's called "reference frame") is absolutely in a motion from another point of view with a certain velocity and to a certain direction. The moon has a relative motion to the earth. The moon revolves around it. Also, the earth has a motion according to the moon. Mountains seem like they are standing still on the ground. But they are whirling around the sun along with the earth according to an observer on Mars. And they have a relative velocity against the observer. There is no need to go away that much. The molecules of the mountains are always moving on backward and forwards... I guess I could make an insight of this question for you in this paragraph.

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Any object propagating in the vacuum (space) also makes displacement in width, length and, height dimensions (and in the other spatial extra dimensions which I mentioned in the previous paragraphs).It moves forward-backward and left-right. It goes forward in time alike. Attention! I don't say that it goes up and down, or left and right! I say; it only goes forward. I am trying to explain why the objects those are subjected to the time dimension (everything is subjected!) can only go forward. In fact, when viewed from this aspect; when something moves along space, it also will go forward in time. It is actually the travel in time in other words.

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We Are Actually Travelling In Time Right Now!

Technically speaking, all of us are the time travelers who are tripping in the time as written in the paragraph above. This is not a philosophical inference, this is what Physics says to us. Now I want to talk about that time-space correlation a little bit more. Imagine a car is driven at a speed of 100 km/h. And a person is looking at this car. From the person's point of view, the car comes towards him with a speed of 100 km/h. If the car goes contrariwise, the person sees that the car is relatively going backward at a speed of -100 km/h. The person stands in his spot with no motion.

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Because he stands, all the speeds mentioned are at 100 km/h. But to exaggerate a little, let's say, the person goes towards the car with a speed at 50 km/h and then this means that the car approaches him with a speed of 150 km/h in his point of view. Likewise, if the person goes backward with a speed of 50 km/h while the car is approaching him, then the car is going towards him with a 50 km/h speed relatively. Most of you already know what I try to tell you here from your high school physics classes. But I add a different point to the subject here; I say that the time which the car is living in' also changes while it getting close to the observer. In fact, this is the point related our main topic. Faster the car goes, longer the time which car lives according to the observer.

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If you feel yourself getting muddled, let me clarify it for you with an example: Assume that the car has a huge window and there is a huge clock inside it. And suppose that the observer (or the person/man whatever you call it), is seeing that the car goes from left to right. If the car goes from left to right at a certain speed as "V", the observer will realize that the time on the clock is not ticking that different than his own clock's. Because the speed range of the car is in our daily life's scale. Even if the car gets too fast, this case doesn't give a different result that easy. However!!!, if the car would increase its speed in the vicinity of lightspeed (Note that the lightspeed is around 300.000 km/sec) and if the observer would be able to see the clock inside, then he could realize that the time of the clock is getting along extremely slow in this ultrarelativistic car. It is called "time dilation" according to the special relativity. If someone would be sitting in the car and also able to see the watch of the observer who is outside, then he could see that the time is rushing extremely. It literally flies by!!!

So Why Does The Time Dilate? Or Contract?

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This all about Einstein's Special Relativity Theory. In case I say that this theory could be explained by writing hundreds of equations, It wouldn't be a mistake. This is the real theory which explains the above-mentioned example. Time dilation phenomena come true near the speed of light only. I'll also tell you about the time in Black Holes and the General Relativity which is the brother of Special Relativity late in this post.

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For the speeding up to the speed of light example, we know that; the car is making displacement in the spatial dimensions while it goes from left to right. On the other hand, it moves across the time as well. There is a correlation of energy conservation between space and time dimensions. If the car slows down to our daily life speed levels, it transfers its 'condensed' energy to the spatial dimensions. If it speeds up to near speed of light, then it starts to transfer its energy to time dimension in order to make the balance between space and time. Velocity (speed of the car) is defined as Dx/Dt.

Velocity is the rate of change of position with respect to time.

The similar energy based relationship between the rate of change of position and the time is also valid for the velocity and the size of the object which fills the spatial dimensions. So there are special relativity laws here too. That is, if we were to look at a horizontal stick outside from the vehicle approaching the speed of light, we would observe that the size is very different. In fact, almost everything outside the car is actually a stick or sticks set. For this reason, we see a very strange, twisted, chaotic reality. Of course, all of these explanations are in full detail in the physics books that describe the special relativity (which you often hear as the law of relativity). The books describing this subject are based on light as they describe the event. These are all the consequences of the motion and behavior of particles called photons, particles of light.

Now I hear you saying "Oh no! How did we end up here from Space-Time and the vehicle to the photon!!".Just be patient and read on...

After all, if there is a speed of light, there is a photon in the work, and we can explain what happens here by the photon. But do not worry, I'm not going to go much deeper because it's just like

 Planck constant x the frequency of the electromagnetic splitter is equal or something.

What I want you to know here is that you do not leave your attention to the connection between energy and the space I have described above _{(Here you should consider the properties like the object's volume or the mass filling the space)} and energy. Many of you have already known since your childhood. This is Einstein's famous equation, even what most people call the "atom bomb" equation.; E=mc²!!

_Source

This correlation tells us that energy is essentially the same thing with matter (you have to think of it in terms of volume, mass). In fact, most do not know but there is another perturbative expansion of this equation and it goes away. Something like:

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I put these math things as a figure, which most of you probably would not like very much, I want you to see that energy and matter (and therefore space-time dimensions) are connected together in a way. This equation is very roughly telling us that the matter and energy are almost identical to each other in the vicinity of the speed of light. Just imagine that; ourselves, our tissues, our molecules and atoms, and the quarks leptons etc which ones actually makes us be. We are the waves and energy!

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Things Become Changed When Speed Of Light Reached

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The E = mc² equation you just read tells us that if you give any amount of energy to a matter, mass also has to increase in proportion to the square of the speed of light. Indeed, if you increase the mass, it tells you the increase in energy. So let's think about this too. You have a rocket and you want to send it away. There is also a fuel depot which can contain any amount. There is a pre-defined mass of fuel you can fill in this fuel deposit, and thus the energy it can give. When you ignite the fuel tank, the kinetic energy that the fuel can provide to the rocket can uplift the rocket for a limited distance and can make the rocket reach a limited speed corresponding to that much energy. But if you enlarge the fuel tank and put more fuel in it, the amount of energy that will provide more fuel will allow you to reach more speed. With even greater fuel storage and even more fuel, it is faster and easier to go further.

But,

Each time you enlarge the fuel tank and each time you add much more fuel in it, Additional Fuel which you fill is meaning that you add More Mass on your rocket. You have to add up more fuel (means more mass) for getting near the vicinity of the speed of light just by continuing to do so.But you will never reach the speed of light. Even if you can approach 999999.99999% of it, you will never reach the speed of light. Theoretically assuming that if you arrive, then you need to add ** In infinite quantity** of fuel, You have to have an infinite mass. In practice, you will never get exactly the speed of light because nothing ever can have infinite mass

Suppose That Our Car Has Reached The Speed Of Light ...

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Let's say, theoretically, the vehicle followed by our observer has reached the speed of light, and our observer has the chance to see the gigantic clock inside the vehicle; Now stand tight!

The observer sees the clock stopped!

Yes according to the observer, THE TIME HAS STOPPED in the car which goes with the speed of light. From this moment on, that vehicle became an object which has an infinite mass and which the time has stopped inside. Alright! So how does the observer in the car see himself and the people outside? Nothing is different for himself. He goes on his daily life. But when he looks outside, he will see a vaguely light mixture of a reality or a kind of null space maybe as we guess. And let that person revolves around the earth during one week with his car going at the speed of light. And at the end, he wants to stop his car and get out the vehicle and say to his fellow observer that "Hey pal! How have you been during last week?". But bad news. When he wants to get out of the car and go to the friend, he will have a shocking moment…

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The person inside the car will find no observers around the vehicle and no such a place where he left 1 week ago. Probably he will be seeing the view of that place after hundreds of years. The person who traveled by the vehicle spent one week at light speed. But in the place he landed he went to the future for hundreds of years.

Yes, it is impossible to go at the speed of light, as we say, but even if he was traveling at speeds close to the speed of light, it would still be a week or longer than he spent in the road. That means that this person's car is a time machine for him, dear friends. This is a time machine. And if you have not noticed, there is no going back. It is only possible to go forward.

Well. Is Going Backwards In Time Not Possible At All?

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This is theoretically possible in physics. But it's a very tricky thing! So, to go back, you need to take some of the other theoretical things apart from special relativity. For this, it is necessary to include some general relativity into the work. I will talk about this in a little while. But first I have to tell you something. The time is depending on an entropic flow directed from the past towards future. For entropy, we can briefly express that it is the universe's a tendency from the disordered to the ordered state. Everything in nature goes from an ordered state to a disordered state, including our bodies. For example, during the big bang that happened 13.7 billion years ago, everything in the was gathered together with a very high order, but today space has become dispersed and scattered over the time.

Think of a glass, this glass will shatter when it falls down from the table. This is something entropic. And for us, the history of the cup is the moment when the cup waits on the table in the unbroken state. The present state (or let's say it "the future") is that it is shattered on the ground. Our brain understands the timeline of the glass as that the glass fell down and fell into the pieces But never can understand that the broken glass goes up from the ground and its pieces unite back and become one body. There is no such thing. Because the entropic and psychological time-line is always flowing from the past to the future. Entropy dictates this. If there was the possibility to reverse processes in some way by using a kind of energy which cosmologists call "negative energy", it would have been possible to put together all parts of that glass in the same way. And thus we could have the possibility of reversing our processes in hand.

But we will never have a machine which we sit down and press the buttons and tell it to go back in time...... There will be no such device for at least 1 trillion years ... 🤣...

There Are Paradoxes Too!

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We have met with paradoxes about time travel stories or movies many times. The most noteworthy of these is the Grand Father Paradox. According to the Grand father's paradox, if you had somehow traveled to the past, you would somehow kill your grandfather before your father is born. Under normal conditions, you should not be there at all. But you are there and you are shooting your grandfather with your own hands ... How will this work? So many paradoxes tell you that your existence will not be possible because of the paradoxes like going past by using the methods such as entropy reversal or using negative energy. All those tales are in the Sci-fi category and they are almost impossible. The universe does not allow such paradoxes.

I mean, at least for now, try not to trust time-travelers thing from the future. 🤣

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General Relativity And The Time

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In the above paragraphs, I have talked a lot about Einstein's Special Relativity Law. General relativity is a theory that derives from it and is a twin of special relativity. General relativity tells us that gravity or the time-concept changes in places where gravity forces apply much more. Where are all these places with big gravity? Of course the stars and the black holes.

In black holes, gravity is so high that even the photons which don't have any mass can't escape from gravity. For this reason, black holes are "black". Imagine someone in the event horizon who is holding a clock in hand. And imagine another one who can see the event horizon from outside. This person outside will see the clock is stopped.

Because you are the one who patiently read this post up to here, you are most probably one of the people who relishingly watched the "Interstellar". The theme of the movie was all based on this subject. The astronauts who got there realize that the time plane of the planets which were in the orbit of Black Hole Gargantua was warped. Our heroes who landed on the planet with the oceans just stayed there for 5 hours. And when they got back to their main spaceship in the orbit, they witnessed that the black guy had lived 20 years on the ship. Actually, I still couldn't figure out how they were capable of escaping from that big gravity with only a little pod!.....Anyways!....Here is a typical time travel story based on general relativity theory.

As you'll remember, the movie was emphasizing that space and time dimensions could be completely warped, folded or twisted by using the theme of the gravity waves in which we saw that our hero could make a conversation in the black hole with his daughter.

My dear followers, as you see, I cannot write down all the things related that important and theoretical topic in only one single post. But I hope that I could give a few thoughts on time and time-travel concept as Science teaches us.

If I could go back in time to the period of the kings, I would probably understand what they speak. But they would not probably give me a chance to live because I would be clothed in a very weird fashion according to them. Of course, I could do some show off with my electronic devices. But this time, they would be accusing me of sorcery or something.

I hope you liked my post. Feel free to drop your comment below and don't waste your time...

Here are of some of my science and technology related posts which you could be interested in:

• The Gases Shaping Up Our Lives: The Greenhouse Gases And Their Effect On The Atmosphere
• What Is "Multiverses" Theory Telling Us?
• Love In Atomic Scale: Quantum Entanglement
• The Summary Of A Genius
• Materials Of The Future: 2D Nanomaterials

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If you are a science enthusiast, don't forget to follow me. And also follow #steemstem for more high-quality science-related posts on Steemit.

More information can be found on the @steemstem blog and on our discord server and in our last project report.

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HERE IS THE REFERENCE LIST

<sub>1. Time Travel
2. Time Travel: Theories, Paradoxes & Possibilities
3. Special Theory of Relativity: The Principles
4. Chapter 7. Einstein’s theory of Special Relativity
5. General Relativity
6. Time Dilation - Einstein's Equation Explained with Worked Examples
7. Time dilation/length contraction - HyperPhysics Concepts
8. Is time travel possible?
9. Russian Cosmonaut already lives in FUTURE – proving time travel IS possible
10.How Traveling Back In Time Could Really, Physically Be Possible
11.How Time Travel Works</sub>

Note: All the Images are directly linked to the sources!

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