One theme that has intrigued humanity for years has been whether it is possible to travel in time, either to the past or to the future. I bet you have ever questioned yourself in your life, and you would like to be able to make a trip in time, either to the past to correct some mistake, or to do something that you could but that for certain circumstances you did not. Maybe you want to go to the future to see how things will be. Whatever could be the reason, the theory of time travel is a very curious subject which can give much to talk about.

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Well, speaking of time travel, according to the numerous investigations, studies and tests, it is quite possible that we cannot travel to the past, to understand this in a simple way, I quote one of the most famous paradoxes that could be generated if we traveled to past. Suppose you get to a point in the past where your grandfather still does not know your grandmother and you kill him, if you do this then your father would never have been born and therefore you would not, so you could not have traveled to the past. However, this does not mean that a trip to the past is impossible at all.

On the other hand, scientists see the trip to the future much more likely. Albert Einstein, one of the most important scientists of all time developed a theory (of the most known by the way), called special relativity theory. In short, this theory tells us that space and time are a characteristic of a common object: Time-space. There is a limiting speed for any object traveling through space-time, 300.000 KMPS, it should be noted that light always travels at this speed.

Special Relativity also states that when relative velocity of an object (let's call it object 1) in comparison to another object (let's call this one 2), it is close to the speed of light; Time will slow down for object 1 than the object 2. 

It is also believed that there are other ways in which to make a journey through time would be possible; one of these ways could be through a shortcut, such as a wormhole (also known as "Einstein-Rosen Bridge.") In 1935, Einstein and Nathan Rosen proposed the existence of such holes, whose principle is to unite 2 different points of time space, being possible to transport matter through them. Many scientists have made their contributions to this theory. Unfortunately the existence of a wormhole has not been confirmed, it is just a theory.

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References

http://spaceplace.nasa.gov/review/dr-marc-space/time-travel.sp.html

https://hipertextual.com/2016/01/viajar-en-el-tiempo

http://es.gizmodo.com/viajar-en-el-tiempo-es-posible-te-explicamos-como-1655248853

https://es.wikipedia.org/wiki/Agujero_de_gusano

 (Note that the information of these websites it is on spanish, I did the translation for the info that I used on this post)