In new research, physicists have discovered a way to look for wormholes across the universe and, more importantly, distinguish them from black holes.
When it comes to making predictions, Albert Einstein’s theory of general relativity is pretty much unbeatable, at least in physics. The theory says that objects of mass “warp” the very fabric of spacetime, and that this warp gives rise to the force of gravity. The theory also led to the suggestion of a multitude of phenomenons, events, and objects that astronomers and physicists would eventually discover in the cosmos. Yet one major cosmic object still hasn’t been found: a wormhole.
Unlike black holes, wormholes remain purely hypothetical. If they exist, they have remained undetected. But physicists have just discovered a promising new way to possibly find them.
Predicting the Existence of Wormholes
General relativity predicted black holes as objects of tremendous mass so densely packed they create a region of space with such intense gravity that not even light is fast enough to escape them, well before astronomers ever saw hints of such regions. General relativity also foresaw tiny ripples in spacetime created by accelerating objects of mass, which we now call “gravitational waves” and can detect with huge, highly sensitive laser interferometers.
The prognosticating power of Einstein’s crowning achievement further predicted that the warping of spacetime by objects of great mass would also bend light, sometimes magnifying it or even making distant single objects appear at multiple points in space. Astronomers now use this magnification of light, known as “gravitational lensing” or sometimes “microlensing,” to spot distant objects such as galaxies that existed in the early universe.
Solutions of the field equations of general relativity suggest that events similar to black holes could exist that form the entrances and exits of “tunnels” or “bridges” that could connect two distant regions of space.
What Is a Wormhole, Exactly?
Technically called an “Einstein-Rosen bridge,” these tunnels through space—and maybe even time—are more commonly known as wormholes. Enticing prospects to scientists, wormholes may offer the possibility of crossing vastly separated areas of the universe effectively faster than light could travel between those points.
To picture this, imagine all of space as a flat sheet of paper curved like a saddle. Conventional travel through space is like traveling from one dot on the paper to another, passing over the surface of the paper. A wormhole caused by so-called exotic matter with a negative mass would be like a metal straw pushed through the paper connecting the top half to the bottom.
A conceptual illustration of a wormhole.
Just as the straw would allow travel from one side of the paper to the other without traversing the surface of the paper, wormholes could allow passage from one side of the universe to the other without traveling the distance across space by which those points are physically separated.
Scanning the Universe
Physicists have suggested that if wormholes do exist, they would be so massive that they would also have a light-bending “gravitational lens” effect just like black holes do, and this could be one way to glimpse them. The difficulty is, how would astronomers tell the difference between the gravitational lensing caused by black holes and the same phenomenon created by wormholes?
“The observations of wormholes are very hard since current techniques cannot distinguish between the lensing effects of black holes and wormholes,” Lei-Hua Liu, a physicist at Jishou University in China, and lead author of the research paper published in Physical Review D, tells Popular Mechanics. “To be more precise, the observations of a black hole and a wormhole would be almost the same. These objects are very comparable.”
Lei-Hua led a team of researchers from several institutions in China, that built a simulation of an electrically charged, spherical wormhole and looked at the effect on the universe around it. This model suggested that if wormholes do exist, they not only could be spotted using gravitational lensing effects on light but also that this effect would be different for wormholes and black holes.
The team calculated that wormholes may magnify light by a staggering 100,000 times, a gravitational lensing effect much stronger than that seen around even black holes. In addition to this, the team discovered a feature in this lensing effect for wormholes that black holes don’t possess. And those factors could be key to finally finding wormholes and telling them apart from black holes.
“We used the gravitational lensing effects of general relativity to explore the observational effects of wormholes,” Lei-Hua says. “Our investigations showed that the magnification of background images after the bending of light by a wormhole will cause magnification of that light by a factor of 100,000.”
This is the first image ever taken of a black hole, known as Sagittarius A*, taken by the Event Horizon Telescope in 2022. One day, astronomers might finally prove the existence of wormholes as well.
Lei-Hua explained that by plotting the shape of this magnification not only could astronomers spot wormholes, but they could also distinguish these tunnels through spacetime from their general relativity cousins.
“There will be two peaks for the magnification caused by wormholes, a high peak, and a gentle peak,” Lei-Hua says. “The magnification caused by black holes when plotted has only one peak, which is the maximum value of magnification.”
That massive magnification factor and the shape of that magnification when plotted aren’t the only gravitational lensing factors discovered by the team that could separate wormholes and black holes, however.
Seeing Triple With Wormholes
When light from a background source like a galaxy travels past a strong lensing object, let’s say a black hole, often the light takes a different path past that object. Some light is weakly lensed, while light passing closer to the lens has its path more strongly diverted. As a result, light from the background object appears to an observer at different times and thus at different points in a single image.
Lei-Hua explained that the calculations made by the team regarding the gravitational lensing and the bending of light created by wormholes also showed that these tunnels in space should create triple-repeated images of background light sources. These triplicate images will also take on distinguishing characteristics that point to their origins.
“There will be three images after bending the light by the wormhole, in which one is very bright, and the other two images will be much weaker in comparison,” Lei-Hua says.
Of course, confirming the theory put forward by Lei-Hua and the team would mean observing more gravitational lensing events in the universe, and hunting for the features that they suggest are indicative of wormholes.
“If we can observe more microlensing events in the near future and make a more precise plot of the magnification they cause, we could compare these observations with our theoretical calculations,” Lei-Hua says.
The team also intends to look for more features in the gravitational lensing of light that could be unique to wormholes.
“Generally speaking, our research aims to provide some possibilities for distinguishing wormholes and blackholes,” Lei-Hua says. “By doing this, in some sense, we can finally test the existence of wormholes.”
