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In Search of a Wormhole

A star called S2 is intriguingly placed, orbiting around the supermassive black hole thought to be at Sgr A*, the bright, compact radio source at the center of the Milky Way. S2 has an orbital period of a little over 16 years and a semi-major axis in the neighborhood of 970 AU. Its elliptical orbit takes it no closer than 120 AU, but the star is close enough to Sgr A* that continued observations may tell us whether or not a black hole is really there. A new paper in Physical Review D now takes us one step further: Is it possible that the center of our galaxy contains a wormhole?

By now the idea of a wormhole that connects different spacetimes has passed into common parlance, thanks to science fiction stories and films like Interstellar. We have no evidence that a wormhole exists at galactic center at all, much less one that might be traversable, though the idea that it might be possible to pass between spacetimes using one of these is too tempting to ignore, at least on a theoretical level. At the University at Buffalo, Dejan Stojkovic, working with De-Chang Dai (Yangzhou University, China and Case Western Reserve University), thinks the star S2’s behavior may offer a way to look for wormholes.

Image: An artist’s concept illustrates a supermassive black hole. A new theoretical study outlines a method that could be used to search for wormholes (a speculative phenomenon) in the background of supermassive black holes. Credit: NASA/JPL-Caltech.

Note that the authors are not saying they find such an object in the existing datasets on S2 (the object has only been monitored since 1995 at UCLA and at the Max Planck Institute for Extraterrestrial Physics). Rather, they’re arguing for using the behavior of objects near black holes, where extreme astrophysical conditions exist, to see whether they exhibit unusual behavior that could be the result of a wormhole associated with the black hole. So this is a methodological approach that advances a proposed course of observation.

You may remember that a 1995 paper from John Cramer, Robert Forward, Gregory Benford and other authors including Geoff Landis (see below) went to work on this question, though not using a star near the Milky Way’s center (see How to Find a Wormhole, a Centauri Dreams article from the same year). Cramer et al. argued for looking for an astrophysical signal of negative mass, which would be needed to keep a wormhole mouth open. Let me quote from something Geoff Landis told me about the paper:

“If the wormhole is exactly between you and another star, it would defocus the light, so it’s dim and splays out in all directions. But when the wormhole moves and it’s nearer but not in front of the star, then you would see a spike of light. So if the wormhole moves between you and another star and then moves away, you would see two spikes of light with a dip in the middle.”

That’s an astrophysical signature interesting enough to be noted. And from the paper itself:

“…the negative gravitational lensing presented here, if observed, would provide distinctive and unambiguous evidence for the existence of a foreground object of negative mass.”

Back to Stojkovic, whose new paper notes a property we would expect to exist in wormholes. Let me quote his paper on this:

The purpose of this work…is to establish a clear link between wormholes and astrophysical observations. By definition, a wormhole smoothly connects two different spacetimes. If the wormhole is traversable, then the flux (scalar, electromagnetic, or gravitational) can be conserved only in the totality of these two spaces, not individually in each separate space.

Interesting point. An example: A physical electric charge on one side of the wormhole would manifest itself on the other side. There, where there is no electric charge, an observer would notice the electric flux coming from the wormhole and assume that the wormhole is charged. There is, in fact, no real charge at the wormhole, but the flux is strictly conserved only if the entirety of both spaces connected by the wormhole is considered. And as the paper goes on to state, a gravitational source like a star orbiting the mouth of the wormhole should be observed as gravitational perturbations on the other side.

The message is clear. Again, from the Stojkovic paper:

As a direct consequence, trajectories of objects propagating in [the] vicinity of a wormhole must be affected by the distribution of masses/charges in the space on the other side of the wormhole. Since wormholes in nature are expected to exist only in extreme conditions, e.g. around black holes, the most promising systems to look for them are either large black holes in the centers of galaxies, or binary black hole systems.

By now it should be clear why S2 is an interesting star for this purpose. Its proper motion orbiting what is believed to be a supermassive black hole at Sgr A* could theoretically tell us whether the black hole harbors a wormhole. The extreme gravitational conditions make this the best place to look for a wormhole, and minute deviations in the expected orbit of S2 could indicate one’s presence. That means we need to assemble a lot more data about S2.

Stojkovic doesn’t expect to find a lot of traffic coming through any wormhole we do find:

“Even if a wormhole is traversable, people and spaceships most likely aren’t going to be passing through. Realistically, you would need a source of negative energy to keep the wormhole open, and we don’t know how to do that. To create a huge wormhole that’s stable, you need some magic.”

In the absence of magic, we can still put observational astronomy to work. We may be a decade or two away from being able to track S2 this closely, and in any case will need a lot more data to make the call, but the scientist cautions that even deviations in its expected orbit won’t be iron-clad proof of a wormhole. They’ll simply make it a possibility, leading us to ask what other causes on our own side of the presumed wormhole could be creating the perturbations. And any wormhole we do come to believe is there would not necessarily be traversable, but if the effects of gravity from a different spacetime are in play, that’s certainly something we’ll want to study as we untangle the complicated situation at galactic center.

The paper is Dai and Stojkovic, “Observing a Wormhole,” Phys. Rev. D 100, 083513 (10 October 2019). Abstract / preprint). The Cramer et al. paper is “Natural Wormholes as Gravitational Lenses,” Physical Review D (March 15, 1995): pp. 3124–27 (abstract).

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{ 18 comments… add one }
  • Alex Tolley October 29, 2019, 14:22

    If the BH at the center of our galaxy was also a worm-hole, it would certainly make for some interesting SF stories of the type Stephen Baxter writes (Xeelee series).

    While gravity anomalies are the detection model in this post, if there is material traversing the worm-hole, is it also escaping from the BH on our end too, or just at the other end? If not, are there detectable “white-holes” in galaxies that are connected to the BH worm-holes in other galaxies? If that is teh case, does that imply that material lost to a BH also holding a worm-hole will not gain mass, as that mass passes through the worm-hole to another point in spacetime? If there is -ve mass in the universe, is there any possibility that its presence in our galaxy affects net gravitation sufficiently to account for the hypothesized dark matter effect on stellar motion?

    • Eric Heim November 4, 2019, 16:42

      Love Baxter’s mind stretching fiction. I take it you’ve read Exultant? I find him a much better short story author than a novelist. Still full of fascinating ideas and descriptions of exotic things!

  • Harry R Ray October 29, 2019, 16:11

    “…continued observations may tell us whether or not a black hole is really there.” A black hole IS REALLY THERE! We know already because the Event Horizon consortium has flat out stated that they ALREADY have an image of its shadow and are in the process of enhancing it to the point where it is as good as the one of M87’s shadow so they can submit it to a scientific journal for peer review.

    • Bruce D. Mayfield October 31, 2019, 10:03

      That line questioning the reality of the SMBH at our galactic core took me aback too Harry. I’m not near as up to date as you are on new findings, but this consensus thought about Sgr A*:

      “Sagittarius A* (pronounced “Sagittarius A-Star”, abbreviated Sgr A*) is a bright and very compact astronomical radio source at the center of the Milky Way, near the border of the constellations Sagittarius and Scorpius about 5.6° south of the ecliptic.[6] It is likely the location of a supermassive black hole,[7][8][9] similar to those generally accepted to be at the centers of most if not all spiral and elliptical galaxies.

      Observations of a number of stars orbiting around Sagittarius A*, most notably the star S2, have been used to provide evidence for the presence of, and produce data about, the Milky Way’s hypothesized central supermassive black hole, and have led some scientists to conclude that Sagittarius A* is beyond any reasonable doubt the site of that black hole.[10]

      What else could it be if it isn’t a black hole?

  • Geoffrey Hillend October 29, 2019, 17:13

    A concentration in space of negative energy would cause the light waves to diverge instead of converge. The problem is there appears to be no way to have a large concentration of negative energy to occur in space naturally. Black holes have only positive energy density. The Hawking radiation around a black hole is the only place there negative energy can occur, but not inside a black hole. Hawking radiation is based the excitation of virtual particles of quantum vacuum zero point energy near the event horizon of a black hole. Just as many virtual particles of positive energy density fall into a black hole as virtual particles with negative energy. I don’t see how there can be a local concentration of negative energy. It may be that local concentrations of negative energy are not or can’t be made naturally, but only be artificially man or made with some kind of electronic device. The details of how a black hole makes negative energy are not given.

    A graviton has a spin of 2 so if we reverse the spin it would be an anti-graviton or negative energy. I am not saying not to look for natural worm holes, but I don’t know how there could be any natural local concentrations of negative energy.

  • JH October 30, 2019, 18:40

    I like science fiction as much as anyone, but I don’t think wormholes exist in the real universe. As other have noted, if wormholes exist then shouldn’t there be “white holes” to correspond with black holes? And yet dozens, maybe hundreds, of black holes have been discovered but no white holes. Although this is my admittedly lay opinion, it seems to me that wormholes are a lot like aliens. If the universe is full of them, why haven’t we found any?

    I recall a article in Scientific American from a few years ago, where the author suggested that at the center of a black hole quantum effects were strong enough to counteract gravity. Once again, I’m not a physicist so I might be remembering the article wrong, and I can’t provide a link. But the author’s point was that maybe black holes don’t shrink into nothing after all. He suggested there is still something real at the center.

    Also the Einstein-Rosen bridge idea that allows for wormholes is just a math equation. It doesn’t necessarily describe reality like the more famous E=Mc2. For example if the math describing wormholes was solid, you would think the math would predict where in the universe the other end of a given wormhole could be found. And yet, when scientists talk about wormholes they leave it vague where the other end might be.

    So when it comes to wormholes, I’m from Missouri, the “show me” state.

    • Brett Bellmore October 31, 2019, 6:06

      “But the author’s point was that maybe black holes don’t shrink into nothing after all. He suggested there is still something real at the center.”

      As long as it shrinks at least as far as the event horizon, it’s kind of academic whether or not it keeps shrinking, you’ll never see any difference. And for large black holes, the average density out to the event horizon isn’t even particularly high, so there’s no reason to expect odd effects to keep the matter from reaching it.

      In the (Excellent!) SF novel “Disporia”, by Greg Egan, a future civilization puts a huge amount of work into constructing a transverseable wormhole, only to discover that the distance through it was exactly equal to the outside distance.

      I’ve always wondered why it’s assumed wormholes, if they really existed, would be *shortcuts*. Perhaps it’s just a hangover from their use in SF?

      • Alex Tolley October 31, 2019, 12:12

        I’ve always wondered why it’s assumed wormholes, if they really existed, would be *shortcuts*. Perhaps it’s just a hangover from their use in SF?

        The usual image is of a curve in space that folds back on itself, so that the wormhole distance is shorter. But what if one or more the space dimensions are compressed in the wormhole? Alternatively, what if physics is changed inside the wormhole so that inertia is lost, or light is not constrained to the velocity in normal space so that higher velocities are possible? The problem with any of these is that all sorts of paradoxes can occur, just as with FTL velocities, which makes me suspicious of their likelihood. But as the saying goes “The universe is not only stranger than we imagine, it is stranger than we can imagine.”.

      • Mike Serfas October 31, 2019, 18:12

        See https://arxiv.org/pdf/1608.05687.pdf and the associated news story about the talk: https://phys.org/news/2019-04-wormholes.html I certainly haven’t checked the math, but apparently it prohibits FTL travel via wormhole… and no negative mass is required for it.

    • hiro October 31, 2019, 18:08

      It’s similar to heavy elements 10x and 11x are unstable and they simply don’t exist in stable-state in nature for thousands or millions of year. I think the existence of natural stable wormholes only exists in SF; the huge amount of exotic energy to stabilize giant wormholes so that we could observe them from our telescopes requires artificial engineering because mother nature doesn’t do charity in a certain sense.

  • Geoffrey Hillend October 30, 2019, 19:23

    One still needs negative energy hold open the worm hole.

    • Al Jackson October 31, 2019, 20:59

      Off the top of my head I think non-traversable wormholes can still exist… these are the ones that go back to 1935 , Einstein-Rosen bridges. These are the ones that Carl Sagan wanted to use in Contact but found out, probably from Kip Thorne, that Fuller and Wheeler showed that tese were non-traversable, one single photon down the throat would cause the worm hole throat to pinch off, no info could be transmitted that way.
      R. W. Fuller and J. A. Wheeler, “Causality and Multiply-Connected Space-Time,” Phys. Rev. 128(919) (1962).

      Thorne and Morris came up with a solution to this:
      Morris, Michael S. & Thorne, Kip S. (1988). “Wormholes in spacetime and their use for interstellar travel: A tool for teaching general relativity”. American Journal of Physics. 56 (5): 395–412.

      It is never been clear how ‘natural’ wormholes might form, I can’t say that is well pointed out in this article.

  • ljk October 31, 2019, 11:27

    In 2007, scientists said we can make artificial wormholes:

    https://www.wired.com/2007/03/artificial-worm/

    In 2015, scientists claim to have made an artificial magnetic wormhole:

    https://phys.org/news/2015-08-trio-artificial-magnetic-wormhole.html

    Any progress updates since then?

    • Ron S. October 31, 2019, 14:44

      Neither item is about gravitation.

  • Geoffrey Hillend October 31, 2019, 16:29

    I agree with the opinions of JD and Alex Tolley. Just because I wrote about the energy conditions necessary for worm holes does not mean I believe in them or promote that idea. In fact, in 2010 I already came to the same conclusions that I thought that worm holes and Einstein-Rosen bridges were more like mathematical curiosities more than physical realities or they were to imaginary like science fiction which is why I have been only studying the ideas about warp drives.

    From what I recall reading from an older astronomy book, the white whole idea was it was not inside a black hole, but in another universe. One had to open up a worm hole inside a black hole and travel through the outer boundary of our universe and through the inner boundary of another universe and through white hole into that alternate universe. The white hole looks like a Quasar or active galactic. Today, this idea seems to me more like science fiction. The idea that we can open up a worm hole inside a black hole seems impossible. Also one has to believe in the multiverse and multiple worlds or many worlds theory in order for white holes to work which I don’t believe for many reasons including Occam’s razor: “You shouldn’t multiply hypothesis when you don’t need them.”

  • Mike Serfas November 2, 2019, 20:52

    For a review of the negative space concepts, see http://www.madore.org/~david/math/kerr.html#course.negspace . See the Carter-Penrose diagram of a Kerr-Newman black hole here for example: https://cerncourier.com/a/physics-in-the-multiverse/

    These ideas do seem audacious … what amazed me most about the concept is that throwing a single electron or proton into a black hole could change it from Kerr to Kerr-Newman or back again … which would seem to imply that a single electron has the capability to open, or close, whatever kind of “gate between positive and negative space” these models describe. Yet in the recent descriptions I’ve been hearing about Susskind’s ideas ( https://www.youtube.com/watch?v=pY5D7ZgWuXc ) make it sound like any two entangled particles could represent a wormhole. Who really knows?

  • Gary Wilson November 3, 2019, 15:01

    A Pluto orbiter is a great idea but surely well down the list of priorities. We need to get orbiters out to several of the gas giant moons including Enceladus, and Europa. These missions would require much shorter voyage times, shorter communication pathways to Earth, and would provide communication relay points for landers (hopefully). Any of these missions if done well will be enormously expensive. A lander, to be effective would need the ability to penetrate kilometers of ice and deploy a submersible ROV of some sophistication. All of these missions would extend our capabilities in space greatly. Let’s work our way outward in a systematic manner.

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