Why Time Travel would be difficult?

I know that all of us have asked this question, not to anyone else, but to ourselves.. "What if, I have had ______". Depending upon how happy you are in your life at this particular moment of time, number of times might be different, but don't lie, all of have asked this question, in multiple variations. What if I have had come to office on that day, what if I have had responded this way to that question, what if I have had asked that girl/boy out on that day, what if I didn't do that on that day...? So, in a way we all are waiting for the most, THE MOST, awaited invention/discovery of like ever. Time Machine.

So, this article is just to tell you not to hold your breath for that, it's going to be difficult, because it's going to REALLY difficult. Let me start by telling you why it might actually be possible, though difficult to a degree of the impossibleness, but possible nonetheless.

According to Einstein's very old idea in his fabled 'General Theory of Relativity' , if space is uniformly filled with some invisible energy, then gravity generated by this mist would be repulsive in nature, not the attractive force that we are used to imagine gravity as. This is called as Dark Energy. You remember the Red Shift observed due to Hubble's Law? Where Edwin Hubble discovered that everything in the space is actually expanding, moving away from each other at an ever increasing rate. Which means our universe is expanding, not just at a constant speed, but at increasing speed. This kinda blew physicists apart, but then idea of Dark Energy answers that. What if there is a repulsive energy which actually is pushing everything apart, at higher speeds. Now I don't want to bore you about how science proved Dark Energy exists, but trust me, we did. Not only the proof of it's existence, but also how much of it exists. According to some of the most accurate calculations like 27% of our universe is made up of Dark Matter, 68% is made up of Dark Energy, and then just 4% is actually the visible universe.

When astronomers worked out how much of Dark Energy has to be infused in the space to cause the speed up that we have observed, the answer is breathtaking, it's 1.38 x 10 ^ -124, that is 1.38 x 10 to the power of -124. This is ridiculously precise.

Now, String Theory (or hypothesis, whatever you want to say, depending your own degree of affiliations) talks about the more fundamental particle than atoms, protons, neutrons and quarks, that is Strings. It says that at fantastically small space, everything is fundamentally created from a vibration of strings. And the vibration itself determines everything, mass, strengths of forces etc. But then math of String theory proves that there has to be atleast 11 dimensions, and these dimensions combine to create millions of shapes of the dimensions and hence millions of universes (we just happen to live in a universe with 3 dimensions). And since all these universes will have different shapes of different dimensions, the amount of Dark Energy, might be different in each of these universes. And here comes the sledgehammer, if the amount of Dark Energy deviates by an infinitesimal small amount, galaxies would never form, which means, no stars, no planets, no life, as we know it.

What does this mean? It means that at the multiverse level, if there is a universe where there are even one more dimensions, like ours is the one with 3 dimensions, there is a universe with 4 dimensions, 4th one being time, that universe will never have the this form of life that we are having right now. Are you still with me? Hope you are. Which means, that if there is a way that we travel the 4th dimension of time, that would probably be done through a higher dimensional universe, maybe through a portal or something, we won't be there in that universe. Wow, how sad it suddenly becomes, right? String theory on one hand gives us a way, shows us a light, that there might be a universe where Time Travel might be a reality, but then that universe in all probabilities, won't be for us.

This is regardless of the paradoxes that you might have already heard about:

1. Grandfather's Paradox
2. Butterfly Effect
3. Bootstrap Paradox

At this point of time, you should be asking me, but Kunal, we aren't sure that String theory is correct, so, negating the possibility of something as big as Time Machine to create a Utopian universe, on the basis of a theory which has not been proven yet in more than a decade, is not fair. And my friend, point taken. Which brings me to my next point, the problem of reference.

So, think again, what we want to achieve, in the picture above, as earth is revolving around Sun, in anticlockwise fashion, to go back in time by 6 months, we want to go from position B to position D, when earth was at location D. And here's the challenge, nothing is fixed in the universe that we are in. So, whenever we are trying to find location, it's always in reference to something. For example, the positions A, B, C and D are in reference to the location of Sun. But then we know for a fact that Sun is also moving, in reference to our solar system. Then our solar system itself is moving in reference to center of our galaxy, which by itself is moving in reference to the universe itself. Now, when we want to go from B to D, where exactly is that place in the absolute spatial terms? We have no idea about it, none, zilch, nada. Do you remember the plant of the earlier Planet of the Apes movie? Remember when Mark Wahlberg actually reached planet earth by moving through time line, he lands on the earth of probably some different universe, at a different time line. Because there is no way in hell that we can know the absolute position of earth at a particular time to reach there, in future or past.

Then again, why should it even be a surprise to us about if there is a possibility of us existing in different universes? Didn't Quantum theory proved that particles can exist in more than one place at one point of time? And like everything else, even we are made up of the same particles, so can't we inherit the same properties of those particles and exist in different universes at the same time? I know it really rips apart the threads of common sense, but yeah, there is a possibility for sure.

This begs the question, so, does it mean that it would never happen the way we want it? Can we never travel back in time to do something that we want to do, not another version of us, but us, ourselves? We don't really know the answer to this question, only thing we know is that it seems that even if it happens, we will not just travel time, but we will travel universes as well. We will have to travel a dimension which will split our timeline to get us in a universe which was created for that particular timeline itself. Or maybe this is something that has already happened. Maybe this is how Einstein and Newton came into our world to help us understand the concepts that still seem almost dizzying to us. The universe that both of them explained to us, with the kind of accuracy and predictability, is unreal. We are still discovering how well they explained everything with their simple equations, while sitting in front of their fireplaces, with a notebook and a pencil in hand, without the kind of tools that we are having right now. Maybe they were the beings who came from future to tell us about things that we might not have ever discovered. So, guys, yeah, there's a hope, just don't hold your breath on that.