So, what does sci fi have to do with the Kennedy assassination?

In a recent novel by Stephen King (also now a mini series on Hulu), the protagonist  is told about an accidentally discovered time portal in his home town. Without going into too many details or spoiling the ending, he is urged to go back in time to stop the assassination of President Kennedy.

First of all, can we have such a portal? Many authors have discussed possibilities for time travel, one being Michio Kaku in his Physics of the Impossible. We can indeed have such a portal in the case of a wormhole. A wormhole is essentially a short cut through time and space. However, there are problems. They can only be made of exotic matter that has negative mass. We can’t immediate conjure up negative mass so this seems potentially problematic.another issue is that the side of the portal that’s in the past must already be there. That is, we can’t truly create a portal to the past unless part of it is already there. So, in all there are problems, but the concept is possible.

There remains a grander difficulty. Many physicists believe that time travel to the past is fundamentally impossible because of the logical conundrums that are introduced, such as the famous Grandfather a Paradox (if you can backward time travel,you can potentially kill an ancestor thus preventing your own existence; however, that would prevent you from going through the time portal to begin with).

However, this falls short of all of us physicists declaring that time travel to the past is logically, physically and technologically impossible.