Physicists Built a Wormhole for Magnets
The metal sphere lets one magnetic field pass through another undetected, which could lead to improvements in medical imaging
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Wormholes are science fiction staples that can send travelers across galaxies without having to worry about 1,000-year trips or cosmic roadblocks. Predicted by general relativity, such objects are still just theoretical—unless you’re a magnet.
A trio of scientists at the Universitat Autònoma de Barcelona has built a device that functions as a kind of wormhole for magnetic fields. If the device is put inside an applied magnetic field, it is magnetically undetectable. And if another magnetic field travels through the wormhole, it appears to leave space altogether, only showing up at either end.
This magnetic wormhole won’t teleport anything to another star system, but it could offer a path to building magnetic resonance imaging (MRI) machines that don’t involve putting patients in a claustrophobic tube.
According to theory, a wormhole wrinkles the fabric of space-time so that two distant places become connected, and traveling through the tunnel takes no time at all. Wormholes aren't absolutely forbidden by physics, as they show up in certain solutions of Einstein's relativity equations, but there is lively debate among physicists about whether they are possible in our universe. At the same time, previous studies showed that it might be possible to build a simplified wormhole in the lab that would allow electromagnetic waves to travel through an invisible tunnel.
To make their model wormhole, physics professor Alvaro Sanchez and his team started with a 3.2-inch sphere of copper, yttrium, oxygen and carbon–a common alloy for commercial superconductors. They surrounded it with a layer of plastic, and covered that with another thin layer of ferromagnetic material.
"We surrounded it with a carefully designed 'metasurface' to cancel the field," says Sanchez.
The layered sphere had a hole in it, and through that the researchers put a rolled-up metal tube that was also magnetized—effectively, a skinny dipole magnet. The team turned on a magnetic field and put the whole apparatus inside, using liquid nitrogen to cool the sphere and maintain the superconductivity of the metal alloy.
Ordinarily, the magnetic field lines surrounding a magnetized superconductor will bend and become distorted—not unlike the distortion of space-time caused by intense gravity. That didn't happen. Instead, the surrounding magnetic field simply passed right by the sphere as though nothing was there.
The last step was testing the wormhole. The magnetized cylinder showed two poles until it was sent into the sphere. As it moved through the device, the cylinder's field seemed to wink out, only showing at the mouths of the wormhole. While the cylinder wasn't traveling faster than light, it was moving unperturbed and unseen between two regions of space, invoking the image of a classical wormhole.
And as the cylinder emerged from the other end of the sphere, only the pole that was sticking out could be seen, creating the illusion of a magnetic monopole—something that does not truly exist in nature.
Matti Lassas, a mathematician at the University of Helsinki who has studied magnetic cloaks, says that even though this monopole is an illusion, it could still offer insight into the ways theoretical monopoles might behave. "It is a way of fooling the equations," he says.
From a practical standpoint, the demonstration shows that you can shield magnetic fields so they don't interfere with each other, Sanchez says. This is where the application to MRI machines comes in.
The human body is mostly water, which contains hydrogen atoms made of smaller particles called protons that each spin on an axis. Normally these spins are randomly aligned. An MRI works by generating a strong magnetic field, which makes the protons line up like iron filings. The machine then beams pulses of radio waves at the area to be imaged, knocking the protons out of alignment. As they swing back to re-align with the magnetic field, the protons give off radio waves, and the body's tissues "glow" in those wavelengths.
To direct a strong magnetic field at the body, current MRI machines involve putting the patient inside a giant magnetic coil cooled to cryogenic temperatures. These machines are basically coffin-like tubes, which many patients find cramped and anxiety-inducing. Instead, stretching the sphere into a wire shape might make it possible to direct a strong, uninterrupted field at any part of the body you want without encasing the patient, Sanchez says.
In addition, the shielding effect might allow engineers to build an MRI that uses multiple sensors, using different radio frequencies and looking at different body parts all at the same time—without interference. The various frequencies could be used to more clearly image parts of the body that are harder to see when the patient is lying prone with their arms at their sides.
Being able to shield magnetic fields, especially if one can do it in small areas, could also help with imaging while doing surgeries, says Lassas. He notes that usually you have to remove any metal from the vicinity of an MRI—there have been cases of injuries as unsecured metal objects went flying across the room. More than that, metal interferes with the imaging.
"You bring something small, and it spoils the image," he says. "So that now if you have this magnetic wormhole, you have a tube and you can pass things through without disturbing the image. Maybe one could get an image and do surgery at same time."
Such applications are a ways off, though, and some experts in the field are still skeptical that the device will be useful for more than theoretical modeling. "They don't give many details of their [device] design, so I am a little hesitant to endorse their conclusions," says Sir John Pendry, a professor of physics at Imperial College London and co-director of the Centre for Plasmonics & Metamaterials.
"That said, it is true that by manipulating the permittivity and permeability, some extraordinary topological distortions of space can be simulated, at least as far as electromagnetic fields are concerned."