A New Way of Thinking About Spacetime That Turns Everything Inside Out
One of the weirdest aspects of quantum mechanics is entanglement, because two entangled particles affecting each other across vast distances seems to violate a fundamental principle of physics called locality: things that happen at a particular point in space can only influence the points closest to it. But what if locality — and space itself — is not so fundamental after all? Author George Musser explores the implications in his new book, Spooky Action At a Distance.
When the philosopher Jenann Ismael was ten years old, her father, an Iraqi-born professor at the University of Calgary, bought a big wooden cabinet at an auction. Rummaging through it, she came across an old kaleidoscope, and she was entranced. For hours she experimented with it and figured out how it worked. “I didn’t tell my sister when I found it, because I was scared she’d want it,” she recalls.
As you peer into a kaleidoscope and turn the tube, multicolored shapes begin to blossom, spin and merge, shifting unpredictably in seeming defiance of rational explanation, almost as if they were exerting spooky action at a distance on one another. But the more you marvel at them, the more regularity you notice in their motion. Shapes on opposite sides of your visual field change in unison, and their symmetry clues you in to what’s really going on: those shapes aren’t physical objects, but images of objects — of shards of glass that are jiggling around inside a mirrored tube.
“There’s a single bead of glass that’s being redundantly represented in different parts of the space,” Ismael says. “If you focus in on the larger embedding space, the physical description of the three-dimensional kaleidoscope, you’ve got a straightforward causal story. There’s a piece of glass, the piece of glass is being reflected along the mirrors, and so on.” Seen for what it really is, the kaleidoscope is no longer mysterious, though still pretty awesome.
Decades later, while preparing a talk on quantum physics, Ismael thought back to the kaleidoscope and went out to buy a fancy new one, a shiny copper tube in a velvet case. It was, she realized, a metaphor for non locality in physics. Maybe particles in an entanglement experiment or galaxies on the farthest reaches of known space act strangely because they’re really projections — or, in some other way, secondary creations — of objects existing in a very different realm.
“In the kaleidoscope case, we know what we have to do: we have to see the whole system; we have to see how the image space is created,” Ismael says. “How do we construct an analogue of that for quantum effects? That means seeing space as we know it — everyday space in which we view measurement events located at different parts of space — as an emergent structure. Maybe when we’re looking at two parts, we’re seeing the same event. We’re interacting with the same bit of reality from different parts of space.”
She and others question the assumption, made by nearly every physicist and philosopher from Democritus onward, that space is the deepest level of physical reality. Just as the script of a play describes what actors do on a stage, but presupposes the stage, the laws of physics have traditionally taken the existence of space as a given. Today we know that the universe has more to it than things situated within space. Nonlocal phenomena leap out of space; they have no place in its confines. They hint at a level of reality deeper than space, where the concept of distance ceases to apply, where things that appear to lie far apart are actually nearby, or perhaps are the same thing manifested in more than one place, like multiple images of a single shard of kaleidoscopic glass.
When we think in terms of such a level, the connections between subatomic particles across a lab bench, between the inside and the outside of a black hole, and between opposite sides of the universe don’t seem so spooky anymore. Michael Heller, a physicist, philosopher, and priest at the Pontifical Academy of Theology in Krakow, Poland, says: “If you agree that the fundamental level of physics is not local, everything is natural, because these two particles which are far apart from each other explore the same fundamental nonlocal level. For them, time and space don’t matter.” Only when you try to visualize these phenomena in terms of space — which is forgivable, because it’s hard for us to think in any other way — do they defy comprehension.
The idea of a deeper level seems natural because, after all, it is what physicists have always sought. Whenever they can’t fathom some aspect of our world, they assume they must not yet have gotten to the bottom of it all. They zoom in and look for the building blocks. How mysterious it is, for example, that liquid water can boil to steam or freeze to ice. Yet these transformations make perfect sense if liquid, vapor and solid are not elemental substances, but distinct forms of a single fundamental substance.
Aristotle took the states of water to be diverse incarnations of so-called prime matter, and the atomists — presciently — thought they were rearrangements of atoms into tighter or looser structures. En masse, the building blocks of matter acquire properties that, individually, they lack. Likewise, space might be built of pieces that are not themselves spatial. Those pieces might also be disassembled and reassembled into non spatial structures such as the ones that black holes and the big bang are hinting at.
“Spacetime can’t be fundamental,” says the theorist Nima Arkani-Hamed. “It has to come out of something more basic.”
This thinking completely inverts physics. Nonlocality is no longer the mystery; it’s the way things really are, and locality becomes the puzzle. When we can no longer take space for granted, we have to explain what it is and how it arises, either on its own or in union with time.
Clearly, constructing space isn’t going to be as straightforward as melding molecules into a fluid. What could its building blocks possibly be? Normally we assume that building blocks must be smaller than the things you build out of them. A friend of mine and his daughter once erected a detailed model of the Eiffel Tower out of popsicle sticks; they hardly needed to explain that the sticks were smaller than the tower.
When it comes to space, though, there can be no “smaller,” because size itself is a spatial concept. The building blocks cannot presume space if they are to explain it. They must have neither size nor location; they are everywhere, spanning the entire universe, and nowhere, impossible to point to. What would it mean for things not to have positions? Where would they be? “When we talk about emergent space-time, it must come out of some framework that is very far from what we’re familiar with,” Arkani-Hamed says.
Within Western philosophy, the realm beyond space has traditionally been considered a realm beyond physics — the plane of God’s existence in Christian theology. In the early eighteenth century, Gottfried Leibniz’s “monads” — which he imagined to be the primitive elements of the universe — existed, like God, outside space and time. His theory was a step toward emergent space-time, but it was still metaphysical, with only a vague connection to the world of concrete things. If physicists are to succeed in explaining space as emergent, they must claim the concept of spacelessness as their own.
Einstein foresaw these difficulties. “Perhaps… we must also give up, by principle, the space-time continuum,” he wrote. “It is not unimaginable that human ingenuity will some day find methods which will make it possible to proceed along such a path. At the present time, however, such a program looks like an attempt to breathe in empty space.”
John Wheeler, the renowned gravity theorist, speculated that space-time is built out of “pregeometry,” but admitted that this was nothing more than “an idea for an idea.” Even someone as irrepressible as Arkani-Hamed has had his doubts: “These problems are very hard. They’re outside our usual language for talking about them.”
What keeps Arkani-Hamed going is that he and his colleagues have found just the sort of methods Einstein said they’d have to — ways to describe physics in the absence of space, to breathe in the vacuum. He has put these efforts into historical perspective: “For 2,000-plus years, people asked about the deep nature of space and time, but they were premature. We’ve finally arrived at the epoch where you can pose the questions and hope for some meaningful answer.”
Excerpted from Spooky Action at a Distance by George Musser, published in November 2015 by Scientific American/Farrar, Straus and Giroux, LLC.
Top image: Steve Ball/Shutterstock.
Source: http://gizmodo.com/a-new-way-of-thinking-about-spacetime-that-turns-everyt-1741498475
