Some time ago in my pursuit of time travel, I discovered that I often ran across stories that might well have had time travel based on reviews that I’d read or the title of the story or even that most dreadful of deceits: an author deceiving the poor reader! But in the end, many such stories contained no real time travel. Of necessity, The Big List of Time Travel Adventures rejected such stories for membership, and that was no problem.
However another problem did occur: In my dotage, I kept coming back to these Pretenders, forgetting that they had already been cast aside. In order to avoid wasting valuable List-Creation Time, I decided to catalog the rejects in a separate list of their own, and that separate list appears after the end of the real time travel list.
And yet, even after many discussions of these points with my Grandpa, both of us kept struggling with A Christmas Carol. It’s not hard to see why. Clearly there was a trip to the past: 
They walked along the road, Scrooge recognising every gate, and post, and tree; until a little market-town appeared in the distance, with its bridge, its church, and winding river. Some shaggy ponies now were seen trotting towards them with boys upon their backs, who called to other boys in country gigs and carts, driven by farmers. All these boys were in great spirits, and shouted to each other, until the broad fields were so full of merry music, that the crisp air laughed to hear it! 
Now if that’s not time travel, what is? Ah . . . “Not so fast!” says Ghost!
“These are but shadows of the things that have been,’ said the Ghost. “They have no consciousness of us.”
Even Ghost Himself admits there’s no interaction with the past. Observation is permitted, but not interaction. They might as well be watching a movie! In general, if you can’t interact with the past and the past can’t see you, then that’s not time travel.
Fair enough, but what about Future Ghost? Isn’t He bringing information from the future to Scrooge? Transfer of information from the future to the past may be boring compared to people-jumping, but it is time travel, so A Christmas Carol must be granted membership in the list after all, don’t you think?
Ah, not so fast again! At one point, Scrooge asks a pertinent question:
“Before I draw nearer to that stone to which you point,” said Scrooge, “answer me one question. Are these the shadows of the things that Will be, or are they shadows of things that May be, only?”
The answer is critical to whether time travel occurs. The difference between things that May Be and things that Will Be is like the difference between Damon Knight and Doris Day: Both are quite creative, but (as far as I know) there’s only one you go to for time travel.
The scary Future ghost never answers the question, and moreover, Scrooge appears intent on not having the future he sees come true. So, I want to say that Scrooge saw only a prediction or a prophecy or a vision of a possible future—none of which are time travel.
For many years, I stuck by my guns: Viewing the past is not time travel. Visions of a possible future are not time travel. Scrooge was not a time traveler. And yet, Dickens’ planted a seed wherein a major character seemed to go backward or forward in time and even more(!) return to the present, and that seed grew into the industry we now call time travel. For this reason and more, Scrooge and Marley and Tiny Tim, too, have earned their place on The Big List of Time Travel Adventures. So in my old age, perhaps wondering when my ghosts shall visit, I have new guidelines:
- Reconstructing the past from data that is readily available in the present is not time travel. But if a noninteractive vision of the past is presented with even the barest feeling of time travel, then such a story is awarded a spot on the Big List.
- Similarly, it’s possible to construct a prediction of the future from data in the present. If we lived in the pre-quantum world of classical physics, we could even strengthen the word prediction, claiming that we have computed what Leibnitz called “the possibility to calculate everything . . .” And yet, once again, I find that noninteractively viewing the future (or a possible future timeline) is sufficiently chrono-atypical that in the absense of any explicit calculating machinery, such stories are now liberally allowed on the Big List.
If these shadows remain unaltered by the Future, the child will die.
Charles Dickens, Master Traveller
Given the evolution of my understanding of time travel described above, Dickens has sentenced me to many happy hours of additional work as the keeper of the Big List, for which I offer my thanks and now officially cite him as an undisputed Master Traveller.