SOMETIMES, perceiving something as real doesn鈥檛 cut it. With the shimmering image of a hologram, the illusion is clear enough. That 3D representation is a trick of the light, a projection of information encoded in just two dimensions. But it would be a bit of a shocker if we found out that the entire universe were made that way.
We鈥檙e not close to proving that, still less working out the implications. But a groundswell of work in theoretical physics suggests it鈥檚 a distinct possibility.
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The story really begins in the 1990s. Physicists were struggling to tame the intractable mathematics of string theory 鈥� our best stab at forcing gravity to play nicely with the other three forces of nature 鈥� when they discovered a cunning trick. Under certain circumstances, by subtracting one from the number of dimensions in the universe you were dealing with 鈥� in other words, treating it like a hologram 鈥� gravity could be made to disappear.
The best-researched instance of this 鈥渉olographic principle鈥�, known as the AdS/CFT correspondence, only works in a complex 5D space-time bent back on itself rather like the surface of a Pringle. The trick has proved surprisingly useful, not just in string theory but also to elucidate the workings of practical things like superconductors, and explain such stubborn problems as why particles have mass.
鈥淩ealising that one of our dimensions is an illusion will take humanity a century to digest鈥�
But this year, Daniel Grumiller of the Vienna University of Technology in that the principle also applies in a 鈥渇lat鈥� space-time akin to our own universe 鈥� albeit with two spatial dimensions, . 鈥淭his is non-trivial evidence in favour of flat-space holography, but far from being a proof,鈥� he says.
Craig Hogan, a physicist at Fermilab near Batavia, Illinois, is out to get that proof. If the holographic principle applies in a flat universe like ours, space-time itself should start to look fuzzy at a certain scale, like a hologram viewed too close. He and his colleagues have built a device at Fermilab, known as the Holometer, to scout for this 鈥渉olographic noise鈥�. It ramped up to full power last year.
Any evidence for the holographic principle would be revolutionary, he thinks. 鈥淚t is fundamental because it will go beyond the same basic ideas of geometry we have used for over 2000 years, since before Euclid.鈥�
How will it change us? Practically, perhaps not much: we鈥檒l still perceive what we call three dimensions, and the phenomenon we call gravity will still hurt us if we hurl ourselves off a cliff. But Grumiller thinks it could spark a sea change akin to the one started by Copernicus 500 years ago 鈥� plus, eventually, a similar puzzlement about how we were fooled for so long. 鈥淔or the way we picture the universe and ourselves as part of it, the realisation that one of our dimensions and gravity are 鈥榠llusions鈥� is very profound,鈥� he says. 鈥淚 estimate it will take at least a century for humanity to digest it.鈥�
Explore more in this series: 鈥�10 discoveries that would change everything鈥�
This article appeared in print under the headline 鈥淲hat if 鈥� The universe is an illusion?鈥�
