If this depiction of space is correct, then like any computer, there is an inherent limit to the universe’s data storage and processing capacity.
Laser beam array as part of the Holometer experiment. Image: Fermilab
If a friend told you that we were all living in a giant hologram, you'd probably tell him to lay off the kush. But incredibly, physicists across the world are thinking the same thing: That what we perceive to be a three-dimensional universe might just be the image of a two-dimensional one, projected across a massive cosmic horizon.
Yes, it sounds more than a little insane. The 3D nature of our world is as fundamental to our sense of reality as the fact that time runs forward. And yet some researchers believe that contradictions between Einstein's theory of relativity and quantum mechanics might be reconciled if every three-dimensional object we know and cherish is a projection of tiny, subatomic bytes of information stored in a two-dimensional Flatland.
"If this is true, it's a really important insight," Daniel Grumiller, a theoretical physicist at the Vienna University of Technology, told me over the phone. Grumiller, along with physicists Max Riegler, Arjun Bagchi and Rudranil Basu, recently published the very first study offering evidence that the so-called "holographic principle"—that certain 3D spaces can be mathematically reduced to 2D projections—might describe our universe.
[In our podcast, the Motherboard staff talks to Craig Hogan, the Fermilab scientist who is actually performing these experiments.]
"If you asked anyone twenty years ago how many dimensions our world has, most of us would answer 'three spatial dimensions plus time,'" he said. "The holographic principle would mean that this is actually a matter of perspective."
The holographic principle was first postulated over 20 years ago as a possible solution to Stephen Hawking's famous "information paradox." (The paradox is essentially that black holes appear to swallow information, which, according to quantum theory, is impossible.) But while the principle was never mathematically formalized for black holes, theoretical physicist Juan Maldacena demonstrated several years later that holography did indeed hold for a theoretical type of space called anti-de Sitter space. Unlike the space in our universe, which is relatively flat on cosmic scales, anti-de Sitter space as described by mathematicians curves inward like a saddle.
If this depiction of space is correct, then like any computer, there is an inherent limit to the universe's data storage and processing capacity.
"Anti-de Sitter space is not directly relevant to our universe, but it allows us to perform calculations that would otherwise be very difficult if not impossible," Grumiller said.
Within this theoretical space, Maldacena showed that two sets of physical equations mapped perfectly onto each other: The equations of gravitational theory, and those of quantum field theory. This correspondence was totally unexpected, because while gravity is described in three spatial dimensions, quantum field theory requires only two. That the laws of physics produced identical results two or three dimensions pointed to anti-de Sitter-space's holographic nature.
"This was the first instance where somebody explicitly showed how holography works," Grumiller told me. "But given that our universe is not anti-de Sitter space—it's approximately flat at large scales—it's interesting to ask whether the holographic principle applies to flat space, as well."
To demonstrate that our universe can indeed be seen as a hologram, physical quantities would have to be calculated using both quantum field theory and gravitational theory in "flat" space, and the results would have to match. Grumiller decided to see whether one key feature of quantum mechanics—quantum entanglement—could be replicated using gravitational theory.
When two quantum particles are entangled, they cannot be described individually, but instead form a single quantum "object," even if they're far apart. There is a measure that describes how entangled a quantum system is, known as the "entropy of entanglement." After several years of work, Grumiller and his colleagues managed to show that this entropy takes on exactly the same value when calculated in gravitational theory and quantum field theory for spaces like our universe.
"This calculation affirms our assumption that the holographic principle can also be realized in flat spaces," said Riegler in a press release. "It is evidence for the validity of this correspondence in our universe."
If the holographic principle does indeed describe our universe, it could help resolve many inconsistencies between relativistic physics and quantum physics, including the black hole information paradox. It would also offer researchers a way to solve some very tough quantum problems using relatively simple gravitational equations. But before we can be sure that we're living in the Matrix, there's still a lot of work to be done.
"We did this calculation using 3D gravitational theory and 2D quantum field theory, but the universe actually has three spatial dimensions plus time," Grumiller said. "A next step is to generalize these considerations to include one higher dimension. There are also many other quantities that should correspond between gravitational theory and quantum field theory, and examining these correspondences is ongoing work."
Beyond the theoretical considerations, there's the entirely different matter of pulling back the illusion and experimentally observing the holographic nature of reality. As it happens, physicists at the Department of Energy's Fermilab are now trying to do just that.
As Motherboard reported last year, Fermilab Center for Particle Astrophysics Director Craig Hogan recently hypothesized that our macroscopic world is like a "four-dimensional video display" created from pixel-like bits of subatomic information 10 trillion trillion times smaller than atoms. To our macroscopic eyes, everything around us appears three-dimensional. But just as moving your face toward the TV screen will cause pixels to come into focus, if we stare deeply enough into matter on a subatomic level, the bitmap of our holographic universe might reveal itself.
So. If this depiction of space is correct, then like any computer, there is an inherent limit to the universe's data storage and processing capacity. What's more, that limit should bear telltale signatures—so-called "holographic noise"—that we can measure.
As Hogan explained to Motherboard's Jason Koebler, if we are indeed living in a hologram, "the basic effect is that reality has a limited amount of information, like a Netflix movie when Comcast is not giving you enough bandwidth. So things are a little blurry and jittery. Nothing ever just stands still, but is always moving a tiny bit."
Reality's bandwidth fuzz, if you will, is exactly what Hogan's lab is now trying to measure, using an instrument called the Holometer, which is basically a really big and powerful laser pointer.
"We are specifically trying to determine if there is a limit to the precision with which we can measure the relative positions of large objects," postdoctoral researcher Robert Lanza told me in an email. "This would represent a fundamental limit in the actual information that the universe stores."
The actual experiment that will decipher this involves measuring the relative positions of large mirrors separated by 40 meters, using two Michelson laser interferometers with a precision 1 billion times smaller than an atom. If, as according to the holographic noise hypothesis, information about the positions of the two mirrors is finite, then the researchers should ultimately hit a limit in their ability to resolve their respective positions.
"What happens then?" Lanza said. "We expect to simply measure noise, as if the positions of the optics were dancing around, not able to be pinned down with more precision. So in the end, the experimental signature we are looking for is an irreducible noise floor due to the universe not actually storing more information about the positions of the mirrors."
The team is currently collecting and analyzing data, and expects to have their first results by the end of the year. Lanza told me they are encouraged by the fact that their instruments have achieved by far the best sensitivity ever to gravitational waves at high frequencies.
"The physics of gravitational waves is unrelated to holographic noise, however, the gravity wave results demonstrate that our instrument is operating at top notch science quality, and we are now poised to experimentally dig into the science of holographic noise," Lanza said.
So, it seems that for now, we'll have to wait for the physicists doing the hard math and shooting the lasers to tell us whether our lives are just a very sophisticated illusion. In the meanwhile, the big question on my mind is, how the heck will such a revelation affect us?
"This knowledge won't impact our everyday lives, in the same way that knowing about the Big Bang or other galaxies does not change our everyday lives," Grumiller said.
"But in the same way that knowing that the universe started with a Big Bang has profoundly changed our view of the universe, knowing that the universe is like a big hologram is a profound insight."
Lanza agrees. "It would force us to fundamentally alter our perception of reality, in a way that many of us, myself included, would have a hard time wrapping our heads around," he said.
Indeed, it sort of untethers the definition of "simulation" entirely. If we are living in a giant hologram, can we really say that all the sim worlds and MMOs we've built aren't as real as our universe's planets, star clusters and galaxies, all of which boil down to quantum dots on a cosmic bitmap?
Perhaps the only thing we can say with any certainty is this: If our universe is a simulation, it's probably as close to a perfect one as we can ever hope to achieve. In that sense, living in the Matrix doesn't sound so bad, after all.
Perfect Worlds is a series on Motherboard about simulations, imitations, and models. Follow along here.
Despite being perceived as an extreme optimist, Ray Kurzweil is the first to admit that this technology could very quickly bring an end to the world as we know it. Watch Motherboard's 2009 documentary The Singularity of Ray Kurzweil.