I'm an encyclopedia researcher and editor and I've been researching time travel at work. To say that it's been interesting would be an understatement.
Here are some things I've learned about time travel:
It meshes with the laws of physics. In fact, Einstein's theory of relativity supports the possibility of time travel!
Many people think that time travel is impossible due to logical flaws. This is not true!! For example, there is the grandfather paradox. If Helga traveled backwards in time and killed her grandfather in his crib, she would not exist so it would be impossible for her to have done that. Many people would use this example to completely dismiss the possibility of time travel. They are wrong!
The Butterfly Effect
Even the slightest alteration to an earlier point in the timeline could change the whole future.
...They are wrong because logic is based on the forward linear progression of time, so we can't use logic to dismiss the idea of moving backwards in time. For example, one basic rule of logic is that "If x = y, then x and y are the same." This is true for most purposes... But time destroys that logic. If x = Helga as a toddler and y = Helga as an old woman, then x = y but x and y are very different.
Logic is a manifestation of how our brains are wired to process spacetime in a consistent manner that we can swim through. Using logic to judge the possibility of time travel is in itself logically flawed.
The theory of the multiverse could solve the grandfather paradox. Maybe Helga goes back in time and her arrival at that previous point in time sprouts a new branch of the future. This would explain why there aren't hoards of people coming to visit from the future.
It is possible that closed timelike curves (CTC's) are how humans will travel through time in the future. A CTC would be made by a time machine. The time machine would be made by a wormhole. The wormhole would be made by the concentration of a massive amount of energy, or by negative energy. In a CTC, the time traveler could only go as far back as when the time machine was created. This would also explain why we don't have billions of travelers from the future waltzing around.
The possibility of a real CTC is supported by the rules of logic and by the laws of physics. Many, including Stephen Hawking and Nobel Prize winning physicist Kip Thorne, agree that this would be possible if our society became advanced enough!
some of my notes:
