Time travel is one of the fascinating things for every science lover out there. All the sci-fi from "Doctor Who" to "Star Trek" and even "Avengers: Endgame" all add to various enthralling TIME TRAVEL theories but is it actually possible or are all these just made up.
To find answers we first need to understand what it all means scientifically.
WHAT IS TIME?
To understand this we need to go back to the foundation of Astrophysics. The most famous theory of Relativity. When Einstein was deriving this theory, he found out that time and space are actually relative. In fact, they are interwoven in a continuum. To understand this, picture the Space as a piece of cloth tied tightly from its corners. Now if we keep a Piece of mass on this cloth it tends to bend the piece and the time moving straight would now have to bend around it.
SO IF TIME CAN BE BENT, WHY CAN'T WE DO TIME TRAVEL?
It's not that easy to bend time for doing this, we would need an object with infinite mass so that the time around it would bend completely and form a time loop. Such constructs are often referred to as 'closed time-like curves' or CTCs in the research literature, and popularly referred to as 'TIME MACHINES'.
WHAT ARE SOME THEORIES THAT STATE TIME TRAVEL IS POSSIBLE?
One of the most popular theories amongst physicists is the wormhole theory. It states that if we use a wormhole, we might potentially be able to do time travel. However, with the current technology, it is impossible to create a wormhole and control it.
Another theory states that if we can move with the speed of light, The Time around us would stop because we are moving along the continuum of space-time, and then if we return we would potentially return back to the same point from where we had started even though we traveled to and fro from one point.
SO IS IT IMPOSSIBLE TO DO TIME TRAVEL?
Time travel right now with the technology we have is just theoretical however seeing the developments in the area of Quantum Physics, Nothing is as impossible as it seems. In theories, yes we can do time travel today also but practically it is still very tough to travel back and forth in time. We could possibly travel forward in time if we find something that travels at the speed of light but going back in time is nearly impossible because for that we would need something that travels faster than the speed of light and it is impossible to obtain that even in theories right now.