Book where people are continually slipping between "close" parallel alternate worlds/paratime without realizing it?

Question

Only clear recollection from the book is an example along the lines of:

Experience: I know I put my keys on the table next to the door, but when I went back they weren't there. Looked all around the house, happened to pass by that table again - and there they were.

Reason: the person had slipped into a near-identical parallel-ity in which the keys had not been left on the table, and then slipped back again into the previous reality - or at least into another one which had the keys on the table.

Perhaps a person or a team became aware of this, and some story took off from there.

Almost certainly 1985-2005-ish. English. Read in USA. Probably a stand-alone novel. Almost certainly more sci-fi than fantasy. Thought it sounded like a James P Hogan, but couldn't find one like it among the paperbacks at hand here. And - at least with the search terms tried - couldn't find a match by a web search.

Answer 1

Possibly Worlds of the Imperium by Keith Laumer.

The plot involves parallel worlds. The protagonist is recruited to assassinate and replace his double on another world, where he is a ruthless dictator. Does that sound familiar?

Here's a part that is similar to what you recall.

Winter went on talking while I tried to assemble his fragmentary information into a coherent picture. A vast spider web of lines, each one a complete universe, each minutely different from all the others;
...
"As to the very close lines, theory now seems to indicate that there is no actual physical separation between lines; those microscopically close to one another actually merge or blend. It's difficult to explain. One actually wanders from one to another, at random, you know.
....
"So we're all shifting from one universe to another all the time without knowing it," I said skeptically.

"Not necessarily all of us, not all the time," Winter said. "But emotional stress seems to have the effect of displacing one. Of course with the relative positions of two grains of sand, or even of two atoms within a grain of sand being the only difference between two adjacent lines, you'd not be likely to notice. But at times greater slips occur with most individuals. Perhaps you yourself have noticed some tiny discrepancy at one time or another; some article apparently moved or lost; some sudden change in the character of someone you know; false recollections of past events. The universe isn't all as rigid as one might like to believe."

You can read the whole novel for free on Project Gutenberg.

If correct it's a duplicate of this and this.

Answer 2

John Barnes' Finity might fit the bill. In it, proximity to quantum computers cause people to switch between alternate universes, often without realizing it. This review discusses it

Lyle Peripart, an American expatriate who teaches astronomy in 21st-century New Zealand, takes for granted that his world was shaped by the triumph of Hitler's nuclear-armed forces over Allied resistance in the 1940's. Then he learns from a Delphic billionaire named Geoffrey Iphwin that widespread use of quantum-based computer chips is breaking down the barriers between the Many Worlds, so that calling on a cell phone or taking a ride in an automated taxi can catapult you into a reality with a radically different past.

Peripart joins a group of adventurers out to discover why, in all the worlds they visit, there is no sign of life from the North American territory of the former United States. The cast of characters, who change in subtle and not so subtle ways as their pasts mutate, are engaging enough to hold our attention; along with the pathos and puzzlement inherent in their situation, they manage to find humor and several varieties of love before the narrative reaches as much of a conclusion as is possible in the endlessly malleable universe they inhabit.

Answer 3

This isn’t Larry Niven’s “All the Myriad Ways,” is it? It’s been a while since I read it, and I can’t find my copy to check, sorry.