It sounds like something drunk physicists might consider after a long night at the university pub: What if the universe was nothing more than a hologram? But, interestingly enough, this idea is a serious one that scientists have had a difficult time ruling out. At least, until now.
A team of researchers at Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, have performed an experiment that they say rules out the hologram theory once and for all, reports Science.
The so-called "holographic principle," if true, would mean that the universe actually exists in only two dimensions, and that the third dimension is an illusion in the same way that holograms present the false impression of a third dimension. The theory has some proponents among string theorists, because the holographic principle would also imply that the total amount of information in the known universe is finite. It would assist string theorists in formulating their grand "theory of everything" that melds the theories of gravity and quantum mechanics.
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Since we would perceive the world the same regardless of whether it actually existed in three dimensions or as a two-dimensional hologram, the idea is difficult to test. But Fermilab theorist Craig Hogan had an idea. He reasoned that if the universe was a hologram, then something called "holographic noise" should make it extremely problematic to measure directions — forward-backwards, up-down, left-right — with the same precision. This is because in a holographic universe, there are only really two dimensions.
Using a device called an interferometer, which is essentially a system of lasers and mirrors, Hogan checked to see if precise measurements of lasers pointed in different directions were difficult to come by. If the universe was a hologram, then the lasers should "jiggle" ever-so-slightly.
Turns out, no jiggle.
Hogan therefore declared that the holographic principle was falsified, but his results have stirred up controversy. Not all theorists are convinced that the holographic principle entails the existence of noise that would cause a measurable jiggle, meaning that Hogan's experiment might not make for an adequate test.
Even so, the controversy has at least generated discussion about exactly what would test the holographic principle, which is a step forward for the science behind the theory.
"At least he's making some effort to make an experimental test," said Yanbei Chen, a theorist at the California Institute of Technology. "I think we should do more of this, and if the string theorists complain that this is not testing what they're doing, well, they can come up with their own tests."
So the world might still be a hologram, might not. For now the question is still up in the air, but proponents of the holographic principle have some extra work to do to explain Hogan's results. And that's how science begins to move forward.