The multiverse has been proposed as a way to understand strange quantum behavior.
VICTOR DE SCHWANBERG/SCIENTIFIC PHOTO LIBRARY
This year a physical experiment was published that claimed to measure A single photon in two places at once – and thereby discrediting the idea of a multiverse – has drawn pushback from many skeptical physicists, but the scientists behind the demonstration stand by their claim.
In May, Holger Hofmann from Hiroshima University in Japan and colleagues reported results from a modified version of the famous double-slit experiment that showed that individual photons are “delocalized,” or cannot be contained in one place.
original experimentfirst performed in 1801, demonstrated that when light hits a screen through two thin slits, it creates a wave-like interference pattern. This pattern holds true even when photons are passed through one at a time, which many physicists consider evidence that even individual photons behave like waves. But there has been, and still is, a lot of debate about what actually happens to a single photon and what exactly we are measuring.
When quantum particles are said to have a wave-like shape, it usually refers to the particle's wave function—a mathematical description of all the possible places the particle could be.
These possibilities are superimposed on each other, forming a so-called superposition, until they are measured. Most physicists argue that this measurement causes the wave function to collapse from a superposition into a single value.
One way to understand this is to assume that there is a superposition of many possible universes on top of each other, each with photons moving in different paths, and that photons from different universes can somehow interfere with each other. This is known as the “many worlds” interpretation.
But Hofmann and his team say their experiment provided direct evidence that the photon passes through both slits, indicating that the wave function is not just a mathematical tool but a guide to what's really going on. So this is evidence against the idea of a multiverse.
However, many physicists disagreed with the team's approach, arguing that repeated statistical measurements cannot be used to determine particle properties. “I think you can't make statements about a single photon with this,” Andrew Jordan at Chapman University in California said New scientist in our original story.
The claim that fundamental questions in quantum mechanics could be solved experimentally was met with “a lot of skepticism,” Hofmann says, in part because their experimental measurement technique was partly new, he says.
“We're stepping on a few people's toes,” Hofmann says. This is because most interpretations of quantum mechanics assume that the quantities you measure and their mathematical interpretation represent the real world. “The many-worlds interpretation is simply the most extreme manifestation of this assumption,” says Hofmann.
Instead, their work shows that the mathematical wave function is not real, and the only reality is what can be measured,” says Hofmann. “Superpositions make it appear as if the state is described by such hypothetical measurements, but actual experimental data contradicts such over-interpretations,” he says.
Although Hofmann and his team struggled to get the paper published in the journal, they were invited to talk about the work of other research groups and continue to take the work further. “I fully expected some resistance. In fact, it would hardly be worth doing this work if it were easy. You have to change consciousness, and that takes a lot of time,” says Hofmann.
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