The film draws in at least four important additional time travel tropes: suspended animation, a single nonbranching, static timeline (with the corresponding inability to go back and change it), experiencing the passage of time at different rates, and a trip to the far future. And according to the SF Encyclopedia, the film was originally conceived as a sequel to the 1960 film of The Time Machine.
Warning: The first publication of the story in that ultimate anthology (Final Stage: The Ultimate Science Fiction Anthology) was “cut to shreds” by a ham-handed editor at Charterhouse, so your best bet is to read it in one of Silverberg’s later collections.
After Smith’s death in 1966, the story was completed by his wife, Genevieve Linebarger, and sold to Harlan Ellison’s The Last Dangerous Vision, but that anthology was endlessly delayed. So in 1987, a translated version of the story was published in a French collection of Smith’s stories, and that was the first published version (although we’ve listed it as an English story, since that’s how it was written). The English version was finally published in Smith’s 1993 complete short science fiction collection by NESFA. By then, Ellison’s rights to the story had expired, although that didn’t stop him from suing NESFA.
I recognized the theory—it’s the one on which time travel is based, even though we’ve never discovered time travel, at least not in any useful way, and researchers all over the universe discourage experimentation in it. They prefer the other theory of time travel, the one that says time is not linear, that we only perceive it as linear, and to actually time travel would be to alter the human brain.
But what Squishy is telling me is that it’s possible to time travel, it’s possible to open small windows in other dimensions, and bend them to our will.