The physics blogosphere is buzzing about a new paper by cosmologist Craig Hogan — the subject of a long feature by Ron Cowen in Science News — proposing that our universe is a hologram, made up of pixels of spacetime. The so-called holographic principle has been around since the 1990s: it basically holds that the 2D surface area enclosing a 3D volume of spacetime pretty much encodes all the information contained within that volume — just like a standard hologram.
Holograms are 3-D images that have been projected and captured on a 2-D surface. The most common ones are found on things like credit cards, designed to foil potential forgers. but with the right tools, it's possible to create your own holograms at home: all you need is a laser (red is best), lenses to spread out the beam, mirrors to direct the beam to the desired locations, a beam splitter, and holographic film, which has a finer grain than regular film and thus can record light at much greater resolution. Oh, and you'll also need these handy instructions, courtesy of How Stuff Works.
Basically, you point the laser at the beam splitter, dividing the beam into two part. You will have carefully placed your mirrors in such a way to direct those beams of light to their targets. The targets: two lenses that serve to diffuse the narrow beams of coherent laser light. One beam (the object beam) reflects off whatever object you're imaging — say, Princess Leia recording an urgent message for Obi-Wan Kenobi in Star Wars — and lands on the holographic film, while the second (reference) beam hits the film directly, without reflecting off the object.
Hogan is suggesting that something similar happens in the fabric of spacetime, which might be far more "grainy" and uneven than scientists have thought to date, generating scarcely detectable "noise." (They're already dubbing it "Hogan's Noise.") And that graininess (noise) becomes larger (louder) when it is observed across a great distance, much like a movie projected onto a big screen is magnified or playing your iPod through a speaker amplifies the sound waves. As Cowen puts it:
It's a tantalizing notion but there is plenty of reason to be skeptical. Cowen outlines the caveats in more detail, but basically, (1) Hogan's hypothesis violates a tenet of special relativity known as locality, which holds that something happening in one region of spacetime can only affect what happens in an adjacent region; (2) Hogan's analysis is primarily conceptual, rather than presenting a rigorous mathematical theory; and (3) the tiny pixels of spacetime are so small (at the Planck length), they cannot be detected directly by any experiment.
Actually, that last caveat might not hold true. There's a machine in Hannover, Germany called GEO600 that is designed to search for the ripples in the fabric of spacetime known as gravitational waves. It has yet to find any, but about a year ago, the detector recorded a signal that contained some unexplained noise.
Could it be Hogan's Noise? It currently seems unlikely, since the sources for much of that noise have now been accounted for, but there is just enough uncertainty in those results to leave open the possibility. In fact, GEO600's team of scientists are now analyzing higher frequencies in search of the "jitter" Hogan's hypothesis predicts. Even if they succeed, more evidence will be needed. A new experiment currently being built at Fermilab might have just enough sensitivity to detect this fuzzy holographic spacetime at an unprecedented tiny scale.
And who knows? Maybe there are violations of special relativity at the quantum scale. It would certainly make pursuit of a quantum theory of gravity a tiny bit easier for physicists if they could toss out that pesky locality limitation, and assume that two areas of spacetime can influence each other even if they are separated by vast distances. That's the potentially grander impact of Hogan's Noise: it could give rise to revolutionary advance in quantum gravity research and get us that much closer to a theory of everything that merges quantum mechanics and relativity.