Or maybe it would be fairer to say that our universe is a vast Holodeck.

In a detailed Scientific American article, physicist Jacob D. Bekenstein describes how our universe could be a holograph "painted on the edge" of a higher-dimensional universe:

Using anti-de Sitter spacetime, theorists have devised a concrete example of the holographic principle at work: a universe described by superstring theory functioning in an anti-de Sitter spacetime is completely equivalent to a quantum field theory operating on the boundary of that spacetime [see box above]. Thus, the full majesty of superstring theory in an anti-de Sitter universe is painted on the boundary of the universe. Juan Maldacena, then at Harvard University, first conjectured such a relation in 1997 for the 5-D anti-de Sitter case, and it was later confirmed for many situations by Edward Witten of the Institute for Advanced Study in Princeton, N.J., and Steven S. Gubser, Igor R. Klebanov and Alexander M. Polyakov of Princeton University. Examples of this holographic correspondence are now known for spacetimes with a variety of dimensions.

This result means that two ostensibly very different theories--not even acting in spaces of the same dimension--are equivalent. Creatures living in one of these universes would be incapable of determining if they inhabited a 5-D universe described by string theory or a 4-D one described by a quantum field theory of point particles. (Of course, the structures of their brains might give them an overwhelming "commonsense" prejudice in favor of one description or another, in just the way that our brains construct an innate perception that our universe has three spatial dimensions; see the illustration on the opposite page.)

For all my Matrix and Holodeck language, it's important to note that Bekenstein seems to be talking about a mathematical relationship that would exist naturally. But I'm not sure he addresses the issue directly. Sure a universe *can *be holographically painted on the edge of a different kind of universe occupying different dimensions, but *how *would this happen?

Who did the painting?

Maybe that's just how universes work. Perhaps the higher-level universe is just the first in an infinite series of turtles' backs.

Or maybe somebody made it happen. Perhaps some intelligence in a 5-D anti-de Sitter universe looked "up" (we're talking five dimensions, here, so I have to be cautious when talking about directions) and said to one of her associates, "Say, did you ever notice that we could put a whole little universe right there on that boundary? Wouldn't that be neat?"

And so here we all are. Not the Holodeck, not the Matrix. Just a sort of cosmological equivalent of the paint job my wife and I did on our bedroom over the weekend. To be fair, I guess putting our universe in place would have been more like installing an aquarium than like painting a room, but you get the idea.

I don't mean to be flippant. And I don't mean to suggest that it was easy. (Actually, have you ever *tried *to put in an aquarium?) The technology to paint a universe holographically on the edge of our own universe is far beyond our current capability. We're only coming to terms with the idea that such a relationship between universes is possible. Moreover, it might not be something that you can do from within a given universe. Maybe the ability to holographically project a 4D universe onto a 5D universe is only available in, say, a 9D universe.

For some reason, this whole idea reminds me of Roger Zelazny's
The Chronicles of Amber. In the Chronicles, there was one real world, Amber, which cast an infinite number of parallel-universe "shadows." Our own universe was one of the shadows. Now, we all tend to think of our universe as being *real.*

I mean, obviously.

But the Amberites didn't see it that way. Shadows were just shadows; some were more like Amber than others, and were therefore more real. Others tended off in the direction of Chaos, and were therefore less real.

Perhaps that's how the higher-dimensional interior designers would view us. Interesting, even amusing, but not really real.

(via GeekPress)

Posted by Phil at July 22, 2003 10:36 AM | TrackBackComments