If wormholes big enough to fit a human or a spaceship exist, telescopes should be able to detect any wavering starlight the space-time shortcuts cause while moving in front of a distant star.

Star brightness would fluctuate from a wormhole because of gravitational lensing, caused when a massive object (such as a galaxy) warps the fabric of space and bends light around it. The effect, which resembles the distortion of objects behind a thick lens, exaggerates with increasingly massive objects.

When it comes to wormhole hunting, said Nagoya University astrophysicist Fumio Abe, looking for the distant signatures of smaller gravitational lenses, called microlenses, is the way to go.

“Gravitational microlensing in stars has already been observed, but the variation of the brightness by a wormhole would be different from any ordinary star,” said Abe, whose wormhole-detecting methodology appears Dec. 10 in The Astrophysical Journal.

Wormholes are yet-to-be-observed warpings of space and time so extreme that they connect one point to another through a tunnel-like throat. Such connections may be able to transport something – a photon of light or a spaceship – to another galaxy, the edge of the universe, another universe entirely or possibly backward or forward in time.

“Wormholes can be a very uncomfortable subject for scientists who study general relativity because they make it possible to create time machines and travel faster than light,” said John G. Cramer, a University of Washington experimental physicist who was not involved in the study.

Albert Einstein's theory of general relativity implied the existence of gravitational microlensing, an effect proven to exist in 1919 when the sun’s gravity shifted the apparent position of a star during a total solar eclipse. There are now more than a dozen efforts underway to study the phenomenon.

“We already have lots of data on gravitational lensing, so we can study the existence or nonexistence of wormholes simply by reanalyzing the data,” Abe said. “We can find wormholes if they exist or set some kind of limit on their abundance.”

Physicists from around the world are intrigued by and supportive of the proposal, but all of them, Abe included, emphasize the words “if” when it comes to pondering wormhole existence.

“This is a neat calculation showing that, if wormholes are out there, this would give us a fighting chance to see them,” said Matt Visser, a theoretical physicist at Victoria University of Wellington in New Zealand (also not involved in the study). “But wormholes are speculative stuff. A lot of work has been done with them, but primarily as a theoretical tool to stretch Einstein’s ideas to their limits, to break them and see what drops out the other end.”

Einstein and physicist Nathan Rosen proposed the existence of wormholes in 1935, dubbing them Einstein-Rosen bridges. Decades later, the objects were mathematically shown to be unstable: Before even a piece of light could have a chance to fly through, the throat of the wormhole would close up for good.

More recent work by Michael Morris and Kip Thorne, however, suggests that highly exotic negative mass and energy – thought to behave counter to gravity – could prop open a wormhole's throat long enough for a courageous human to sneak through.

Nevertheless, the challenges to create wormholes in the lab are enormous.

“For a wormhole about 1 meter across, big enough to fit a person, you’d need a Jupiter’s worth of negative mass converted into negative energy – think E = mc2 – to hold the throat open and hope it remains stable," Visser said. "That’s an incredible amount.”

Alien technology advanced enough to collect negative energy and create a wormhole is a more likely than a natural scenario, said Cramer and Visser, but not much can be ruled out because our knowledge is purely theoretical.

“Some say wormholes may have formed at a very early stage of the universe, right after the Big Bang," Abe said, noting that the energy density then may have been extreme enough to both pop wormholes into existence and stabilize them.

Such large and traversable Ellis wormholes, as they're called (among other names), are the kind Abe’s method may find if they're lurking in the nearby cosmos and pass in front of a star.

“On a graph (see below), the star’s changing brightness would look something like some bump at the center, but with gutters on both sides of the peak,” Abe said. “Gravitational lensing by ordinary stars does not show the gutters.”

With minor tweaks to telescope software, a couple of instruments could look for Abe’s distinctive light signatures and confirm or constrain the existence of wormholes within a few years, Abe said. One is the Microlensing Observations in Astrophysics telescope, and the other is the Optical Gravitational Lensing Experiment telescope.

“If the wormhole exists, it shows some possibility of a traveling or time machine. But practically, using them in this way is almost impossible because they’re likely very distant from Earth, probably at least 10,000 light-years,” Abe said. “It may not make sense to go through a wormhole because it would take such a long time to travel to one.”

What many scientists would be excited about is the potential to reconcile conflicting ideas about gravity on both universe and quantum scales.

“If they do turn out to exist, I’ll be ecstatic,” Visser said. “In the meantime, they’re great props for science-fiction novels and movies.”

Images: 1) A Shanghai subway tunnel. Credit: Flickr/Stuck in Customs

2) The massive galaxy cluster Abel 2218, some 2 billion light-years away, distorts light from galaxies behind it and serves as a prime example of gravitational lensing. Credit: NASA/Andrew Fruchter/Sylvia Baggett/Richard Hook/Zoltan Levay

3) Light curves caused by gravitational microlensing. Wormholes with different throat sizes (thick red lines) stand out compared to microlensing light curves of more typical objects such as stars (thin green lines). Credit: The Astrophysical Journal/Fumio Abe

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