In this section, addressed to all public, we discuss the more common paradoxes which arouse time travels. As we all know, travelling towards the future supposes no contradictions; paradoxes appear travelling towards the past.

In previous section we demonstrated the theoretical possibility of performing time travels to the past; therefore, we can wonder if they make sense. First of all, we have to point out that the theoretical results obtained in the previous section do not solve these paradoxes. However, with everything we know about the fourth dimension –which is time-, we are ready to discuss the more common paradoxes, using non very rigorous arguments but straightforward enough to get a intuitive understanding.

If the time travel was really possible, the following situation, which appears frequently in the science fiction movies, could happen: if I perform a time travel of 10 years towards the past, would I meet myself 10 years younger?

To answer this question, we are going to use the video from Carl Sagan in this section: what is time? In particular, in the part in which the square is pushed by the apple from the ‘flat’ world into the third dimension, to return immediately. The ‘flat’ colleagues of the square see that the square disappears from one place and appears magically in other. Nevertheless, both for the apple and the square the trip happens through a third dimension and what happens has not any magic.

Let’s think in a similar way. Let’s admit that time is the fourth dimension we don’t see. If I travel ten years to the past, my contemporary from ten years ago would observe that I disappear suddenly from one place and, then, I appear suddenly in another, because I moved through the fourth dimension that is invisible for them. Therefore I wouldn’t meet with my ‘another me’ ten years younger, because for my contemporary ones this ‘another me’ disappears when my ‘real me’ appears ten years before. The existence of an invisible fourth dimension allows that to happen. As a consequence, my contemporary ones would see that suddenly I get older 10 years.

Despite anybody could point out, what would happen if in these 10 years you had fattened some kilograms? Then, my contemporary would see that the excessive molecules had to be disappeared, suddenly, from the place they were in that moment and would appear in my body at the same time. What if I had got thinner? In this case, part of my mass had been left behind in my way and had disappeared.

What if I did go back in time until before my birth? Then, it would be something similar because all my molecules would disappear from the place they were in that moment and would appear immediately in my body. For my contemporary, in this new reality, I would never be born; rather apparently I would appear from the nothingness, or they would think I’m coming from one unknown place. That is what they would think because they didn’t see the part of my trip through the fourth dimension that I did.

What if I did go back further and kill my great grandfather? The paradox is in that if I kill my great grandfather I would never be able to go to the past to kill him, since I have yet to be born. In this case, I don’t disappear suddenly because, as we said before, for my contemporary, in this new reality I will not be born, but one day I appeared from the nothingness. So if my great grandfather dies, I will continue my existence and there is not a paradox.

All of that can be better understood if we look at the movement in the three dimensions of the space. In order to go from one place to another we can follow different ways. In each way we see different things. The same happens with time travel. Once I finish the trip to the past I continue a different way to the original. That is the reason there can be different ways, realities o temporal lines when I move through the time.

It is important to highlight that all these apparent paradoxes arise in the three-dimensional universe we are stuck to, and if we want to explain them we have to admit unearthly situations as the one described. For a fourth-dimensions being there are not exist paradoxes and all is pretty clear… aren’t they?


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