I think there's an argument that we don't entirely know the full nature of the changes Eckels has created in the timeline. Afterall, what we see at the end of the story is, more than anything else, the effects that have resulted from a much larger teleology, but we don't...
I think there's an argument that we don't entirely know the full nature of the changes Eckels has created in the timeline. Afterall, what we see at the end of the story is, more than anything else, the effects that have resulted from a much larger teleology, but we don't precisely see the process by which those changes have been shaped, or how this larger picture fits together. It's, in fact, a very limited window into an alternate present, but even from that limited vantage point, it is clear that Eckels has caused profound damage to the timeline.
When he first returns to the present, Bradbury writes:
Eckels stood smelling the air, and there was a thing to the air, a chemical taint so subtle, so slight, that only a faint cry of his subliminal senses warned him it was there. The colors, white, gray, blue, orange, in the wall, in the furniture, in the sky beyond the window, were... were... And there was a feel. His flesh twitched. His hands twitched. He stood drinking the oddness with the pores of his body.
In this description, one almost gets the sense of some kind of profound and fundamental change which Eckels himself cannot grasp. In returning to his world, he seems to have, in a sense, become an alien in it. In addition, there have been changes to spelling, as can be seen when he reads the Time Safari sign. At the story's opening, the English language operated by the same rules of spelling as it does in the real world, but not anymore. Thus, we read:
TYME SEFARI INC.
SEFARIS TU ANY YEER EN THE PAST.
YU NAIM THE ANIMALL.
WEE TAEK YU THAIR.
YU SHOOT ITT.
What I find particularly interesting, though, is not what has changed about the world, but in fact, what has remained constant. As we see, Time Safari still exists, with its time travel expeditions into the past. Additionally, we still observe two presidential candidates, named Keith and Deutscher, each (by all accounts) representing the same opposing set of ideological values. However, whereas originally Keith had won the election, now it is the authoritarian Deutscher that has won the election (and whereas the Time Sefari employee had originally supported Keith, now he is portrayed as supporting Deutscher instead).