Space Time……….Can we really travel through time to the future or past?

Albert Einstein was the one who discovered that we can’t separate time from space, they are one thus the name space time. Einstein further disapproved his fellow scientists about the concept on time, I mean have you ever asked yourself this question, what is time? What is a second? Einstein said everybody have his own time, time is not universal throughout the universe.
Just still in this concept about space time, He said if travelling fast time slows down. That one the twin paradox explains……..The twin paradox says. Imagine there are two twins on earth and one of them have been appointed to go and explore another galaxy far away, going to that galaxy they will have to travel more than the speed of light, the other one will go but on returning to earth after the exploration depending on the time they took there, they will find Earth different in that the twin will be Old or would have died and the earth would have progressed and a new generation would be there…….Here is the explanation, from Einstein travelling fast slows down time than the normal one…..while travelling in the speed of light 2 yrs for them would mean 100 yrs on earth so on returning they were in the future where they couldn’t have reached

……Imagine our technology could be advanced more than that we see in Star wars or star trek where we can go next to a black hole and  even circle it and return to earth…they say next to a black hole time slows down due to the gravity……. actually from Einstein gravity is caused by the bending of space so black hole is a collapsed star but with so much gravity mire than that of even the sun……..So if we go next to a black hole without being sucked in and land to we don’t know where…your time will slow down, your 4 hrs will be even 200 yrs in earth is that not traveling to the future?

 ……………………..no one have tried it but that’s theory  I think that’s even why master Yoda in star wars lived for long because He was traveling a lot to different galaxies slowing down his time not forgetting Spock and captain and the crew they have lived for long, That’s in Star Trek.
Time is a one way traffic? Is that right? What do you think? If in case we could be able to travel to the past then we could be receiving visitors from the future maybe even in the year or let me use Star date just in Star Trek…. Star date 5050……That year the technology, I can’t imagine………. we could be receiving visitors telling has may be Ebola wiped 1/3 of the world population or some the moon will fall down, just kidding…..Time is inevitable imagine going back in the past and killing your grandfather meaning your father will not be born and also you would not be born. If you were not born nobody will go back and kill the grandfather meaning he lived and your father was born so as you, so it’s just like a loop, Edge of tomorrow die live repeat………
So to me we can travel to the future but not to the past……………what do you think..