“We’ve made a prediction on the basis of our best theories, and it is wrong, wildly wrong,” says Sean Carroll, a theoretical physicist at the California Institute of Technology. “That means we don’t just tweak a parameter here and there; we really have to think deeply about what our theories are.”
Even if no one knows where the energy of empty space comes from or why it has the value it does, there is now no doubt that it exists. And if there is energy to be had, there is inevitably somebody out there thinking of how to exploit it. The notion of limitless energy from empty space has inspired legions of wannabe physicists who dream of developing the ultimate perpetual-motion device, a machine that would solve the world’s energy problems forever. A quick Internet search for the words free energy and vacuum turns up pages and pages of schemes for tapping the vacuum’s energy. I ask John Baez if such efforts are as hopeless as previous perpetual-motion machines. Are they equally crazy and doomed to failure?
“Perhaps not as doomed as trying to prove the world is flat,” Baez says. “One thing I can say is that I sure hope it doesn’t work, because if you could extract energy from the vacuum, it would mean that the vacuum is not stable. For normal physicists,” he adds with a laugh, “the definition of the vacuum is that it’s the lowest-energy situation possible—it has less energy than anything else.” In short, Baez says, while we may be able to get energy from the vacuum, success “would mean the universe is far more unstable than we ever dreamed.”
The reasoning goes like this: If the vacuum is not at the lowest energy state possible, then at some point in the future, the vacuum could fall to a lower state, pulsing out energy that would threaten the very structure of the cosmos. If some clever engineer were ever to extract energy from the vacuum, it could set off a chain reaction that would spread at the speed of light and destroy the universe. Free energy, yes, but not what the inventors had in mind.
So maybe we won’t be pulling energy from the vacuum, but we might soon get some different benefits from empty space: confirmation of a 40-year-old theory and, with any luck, some radically new physics.
This fall the Large Hadron Collider (LHC) begins slinging protons at 99.99 percent the speed of light in opposite directions along a circular, 17-mile course. In the debris of the collisions that follow, physicists expect to find evidence of yet another strange component of empty space, one that would explain why particles have mass. Besides virtual particles and dark energy, theorists believe that the universe contains something called the Higgs field. Like dark energy, the Higgs field is thought to permeate all of space. But unlike the discovery of dark energy, which was completely unexpected and is still inexplicable, the detection of the Higgs field won’t surprise physicists at all. They have been hunting it ever since Peter Higgs, a physicist at the University of Edinburgh, proposed its existence in 1964.
Higgs wanted to explain why matter has mass, and more specifically why every particle has a different mass. He theorized the existence of an invisible field filling all of space and argued that particles acquire mass by interacting with this field. What we interpret as a particle’s mass is really the strength of its interaction with the Higgs field. For a very loose analogy, think of pushing a marble through syrup: The stickier the syrup, the harder it would be to push it.
If the Higgs field does exist, the LHC should find a previously unseen particle called the Higgs boson. Just as light, which is an electromagnetic field, is transmitted by particles called photons, physicists expect that the mass-endowing effect of the Higgs field is ferried by Higgs bosons.
The discovery of the Higgs boson would answer one of the most basic puzzles of our reality, and yet physicists seem oddly blasé about the prospect. “If it’s found, that would actually not be that exciting,” Baez says. “It would be a relief, maybe. Well, it would be exciting, but only in the same sense as if you lose your keys and then you find them again. Someone would certainly win a Nobel Prize for it, but after the initial excitement, particle physicists would become grumpy because it would just mean that what we thought was true is true, and all the things we don’t understand we still don’t understand, and there is still no new evidence.”
Some researchers, though, expect the LHC to turn up evidence of something very new indeed—extra dimensions of space. According to M theory—the latest, most audacious attempt to explain the fundamental workings of physics—the space around us may be made of as many as 11 dimensions. M theory proposes that the ultimate building blocks of the universe are not particles but tiny vibrating loops of energy, or strings, as physicists call them. For complicated mathematical reasons, those loops need 11 dimensions in which to vibrate; otherwise the theory doesn’t work. We experience only four dimensions (three of space and one of time) in everyday life because the other seven are supposedly so small that we do not notice them. They become evident only on the subatomic scale.
One way to picture this is to imagine a tightrope walker on a high wire. To the tightrope walker the wire is essentially one-dimensional, a line pointing in one direction. But an ant crawling on the wire would see it as a three-dimensional object; the ant could crawl completely around the wire, experiencing a dimension that is inaccessible to the tightrope walker. String theorists would say we’re like the tightrope walker, except that our “rope” is an 11-dimensional space, of which we are able to perceive only four dimensions.
Advocates of M theory have had a tough time convincing some of their colleagues about the reality of all those extra dimensions, but the LHC might win some converts. If extra dimensions really exist, some of the particles produced by the collisions inside the big accelerator may slip away into other dimensions, and particles from higher dimensions could spill into our four-dimensional world. So if physicists notice a shortfall or a surplus in their particle tallies at the accelerator, it might be the first evidence of the wild new physics to come. “Probably whatever is true will in fact be crazy, because historically the truth in physics always seems to be more far-out than anything you could have imagined,” Baez says.
Some physicists like to think that M theory will form the basis of what they call a theory of everything, a set of laws that will completely describe the universe in all its strangeness, where dark energy, quantum theory, extra dimensions, and magazine readers will all fit into one tidy package. But in the end, the key to cosmic truth may well come from another window on reality, the looming void. A good theory of nothing just might be the theory of everything physicists have sought for so long.