Holograms Are Us
The closest physics has ever come to producing a bona fide ghost is probably the hologram, that eerily unreal object made entirely of light. Floating in space with no visible means of support, a holographic star ship can hover, a disembodied holographic face can turn to follow you, a holographic hand can wave in greeting.
Yet reach out to touch it, and it melts away like a cloud.
Once the exotica of science museums, holograms are now everyday objects, adorning books, credit cards, toys.
If physicist Leonard Susskind of Stanford University is right, holograms may be even more a part of our everyday existence than we think. In fact, the universe itself may be a kind of hologram.
That means that everything in it, including particles, stars, planets and people, is also a hologram. Holograms, if you like, are us.
How can the universe be a hologram?
In essence, a hologram is simply a three-dimensional image reconstructed in space from the information encoded on a two-dimensional surface. The hologram on a credit card, for example, appears to pop out like a solid object even though your fingers confirm that the plastic card is flat.
The way it works, roughly, is simple: Just as the grooves on an old-time phonograph record encode all the information needed to reproduce a sound, so all the information needed to produce the image in a hologram is encoded on a two-dimensional surface. When you put a needle on the record and hook it up to speakers, the original sound is reproduced. When you shine a light on or through a holographic plate, a three-dimensional image is produced.
In Susskind’s view, the universe is a hologram that is created from information (that is to say, the laws of nature) encoded entirely on a lower-dimensional boundary. For example, if the universe were a bowl of goldfish, the glass surface of the bowl would contain all the information needed to produce the fish, the sand, the water, the plants. In fact, the “real” universe would be the glass; the fish would be merely a holographic projection.
Susskind and his colleague Gerald t’Hooft came to this discovery by an unexpected route--exploring the treacherous territory around black holes. But now he thinks that through the holographic principle, they have discovered an entirely new way of looking at the laws of physics. Perhaps the only way. And at least a handful of other top physicists agree with him. Susskind and t’Hooft are two of most respected minds in the field.
“It’s not only a better description [of the physical world],” Susskind says. “It’s the only description; I’m absolutely convinced the holographic idea is right.”
At first glance, the notion seems utterly impossible. It appears intuitively obvious that a three-dimensional universe contains more information than a two-dimensional boundary around it. So how could you create the former from the latter?
Imagine, for simplicity’s sake, that the universe consists entirely of one kind of fundamental building block--say, a sugar cube. Say the universe is a large cube made out of smaller sugar cubes.
A cube with the dimensions 10 by 10 by 10 sugar cube units would produce a universe containing 1,000 fundamental bits. The base of the cube, however, would only contain 10 by 10, or 100 bits. How could you possibly encode all the information necessary to produce the 1,000-bit universe on a 100-bit surface?
Astonishingly, it turns out you can. A two-dimensional surface can contain all the information needed to reproduce a three-dimensional solid, or “bulk,” as the physicists call it. No one was more surprised by the result than Susskind himself. “This was something that was totally unexpected,” he said.
Lay readers shouldn’t worry if they can’t fully understand how this works. Even the physics community, Susskind admits, “is having trouble getting its head around this. It’s extremely puzzling and mysterious.”
The mathematics, however, is extremely solid. Worked out in detail by physicist Juan Maldecena of Harvard University several years ago, it’s now so convincing, said Susskind, that “most of us think it’s an absolute fact.”
What that means is: If you want to describe the universe and everything in it--gravity, particles, planets, newspapers and their readers--the correct equations to do that lie not on the three-dimensional “interior” we take to be the real physical world. Instead, they are written on a lower-dimensional surface. Like a hologram, the universe is a projection of the information on this boundary into space.
Or as Susskind puts it: “The bulk [that is, the real universe] is a completely derived concept.”
The Equations Work for Describing the Universe
Physicists are intrigued by the idea in part because the equations on the boundary make a lot more sense than they do in the interior. To go back to the sugar cube analogy, if you tried to figure out the rules of the sugar cube universe by looking at each of the 1,000 cubes, you would get lost in a labyrinth of information.
“It’s too confusing in there,” says Susskind, speaking of the “bulk” universe that physicists normally try to describe. “There are too many possibilities.”
The equations as they appear on the boundary seem to embody just the kind of sensible, consistent laws physicists have been seeking for decades.
Of course, there’s much more work to do. No one knows yet precisely how to decipher the code written on the boundary and project it to create the universe we experience and measure.
“We are far from knowing in detail how to translate back and forth between the surface to the bulk,” Susskind says.
Yet, even at this early stage, the idea has generated enormous excitement. “Future theories will be built this way,” Susskind says. “This is huge. This is a major paradigm shift.”
And where do the black holes come in? Susskind and t’Hooft fell into the holographic idea through trying to figure out what happens to the information that falls down a black hole. The short answer: It’s all retained on the black hole’s surface.
Any object--even a whole civilization or a whole galaxy--that falls down a black hole leaves indelible imprints on the black hole’s surface. Therefore, the surface must be able to contain all the information that’s contained in the “bulk.”
In fact, the physicists discovered that if someone tried to cram more information into a room than could be encoded on the room’s four walls, the room would become so massive it would collapse into a black hole. So there’s no getting around their conclusions.
And lest anyone think that these far-off corners of physics have nothing to do with their everyday lives, consider: According to Susskind, we could at this moment be inside of a black hole, or orbiting around its edge.
“There would be no way for us to know,” he said. “It could be true.”
