A Texas Tech University chemical physicist has developed a new theory of quantum mechanics that presumes not only that parallel worlds exist, but also that their mutual interaction is what gives rise to all quantum effects observed in nature.

The theory, first published by Professor Bill Poirier four years ago, has recently attracted attention from the foundational physics community, leading to an invited Commentary in the physics journal, Physical Review X.

According to Poirier's theory, quantum reality is not wave-like at all, but is composed of multiple, classical-like worlds. In each of these worlds, every object has very definite physical attributes, such as position and momentum. Within a given world, objects interact with each other classically. All quantum effects, on the other hand, manifest as interactions between "nearby" parallel worlds.

The idea of many worlds is not new. In 1957, Hugh Everett III published what is now called the "Many Worlds" interpretation of quantum mechanics. "But in Everett's theory, the worlds are not well defined," according to Poirier, "because the underlying mathematics is that of the standard wave-based quantum theory."

In contrast, in Poirier's "Many Interacting Worlds" theory, the worlds are built into the mathematics right from the start.

Does this prove anything definitive about the nature of reality? "Not yet," says Poirier. "Experimental observations are the ultimate test of any theory. So far, Many Interacting Worlds makes the same predictions as standard quantum theory, so all we can say for sure at present is that it might be correct."

Poirier first arrived at the idea unexpectedly, in the pursuit of a much more practical goal. "I didn't just sit down one day and say 'gosh, let's invent a crazy new quantum interpretation with interacting parallel worlds.' I was trying to develop an efficient computational method using something called quantum trajectories, when it suddenly hit me how you could get everything from the trajectories (i.e. the worlds) themselves, without actually needing any wave."

Poirier published both the new mathematics and the new interpretation in a 2010 Chemical Physics paper, leading to a collaboration with mathematician Jeremy Schiff at Bar-Ilan University. This in turn led to a 2012 publication in the Journal of Chemical Physics which -- with over 20,000 downloads -- is one of the most downloaded papers in that journal's history. More recently, this work has garnered the attention of the broader community. "We are very pleased that other physicists and even philosophers are now getting involved," says Poirier.

One such researcher is Australian physicist Howard Wiseman of Griffith University in Brisbane. "I am very glad to have met Bill," says Wiseman, adding that Poirier is "taking literally this idea that you have an ensemble of particles…rather than just an individual one." Wiseman and coworkers recently submitted their first article on Many Interacting Worlds to Physical Review X, which was published together with Poirier's Commentary. Wiseman's approach is a discrete version, for which "there is a finite but extremely large ensemble of particles…well, ensemble of worlds, I should say," he explains.

Regarding the mathematical developments in Wiseman's article, Poirier says, "These are great ideas -- not only conceptually, but also with regard to the new numerical breakthroughs they are almost certain to engender. Our group offered the foundational physics community a new interpretation of quantum mechanics; in effect, they have now returned the favor, by offering us a promising new computational method."

Bill Poirier is Chancellor's Council Distinguished Research Professor and also Barnie E. Rushing Jr. Distinguished Faculty Member at Texas Tech University, in the Department of Chemistry and Biochemistry and also the Department of Physics.