Wormholes make for great science fiction because they get us around the speed-of-light conundrum. Taking a shortcut through spacetime, they connect one part of the universe to another, though where and when you would come out if you went in a wormhole would be an interesting experiment, and not one for the faint of heart. But do we have any evidence that wormholes exist, and if they did, what could we look for that might reveal their presence?
Perhaps it’s time to revisit a fascinating 1994 paper called “Natural Wormholes as Gravitational Lenses.” The authors are a compendium of names known to anyone with an interest in the physics of interstellar flight or its depiction in science fiction: John G. Cramer (whose columns in Analog set high standards for science writing); Geoffrey A. Landis (Mars Crossing and innumerable short stories); Gregory Benford (whose bibliography of novels is too long to list); Robert Forward (the leading proponent of interstellar studies) and two other physicists whose work deserves a wider audience: Michael Morris and Matt Visser.
It was Visser (Washington University, St. Louis) who suggested a possible configuration for a wormhole that frames it with ‘struts’ of exotic material, the struts having a negative mass density that could result in an interesting object indeed, what the paper describes as ‘…a flat-space wormhole mouth framed by a single continuous loop of exotic cosmic string.’
Geoffrey Landis calls cosmic strings ‘flaws in geometry,’ but you can also think of them as flaws in the structure of spacetime itself. They’re quite useful in imagining wormholes because to preserve a primordial wormhole formed at the beginning of the universe, you need to wrap it in negative energy, and a negative mass cosmic string could do the trick. There are plenty of conditions here, but Landis put it this way in an interview I did with him back in 2003: “If one of these hypothetical negative mass cosmic strings got wrapped around a hypothetical primordial wormhole, you could have a hypothetical stable primordial wormhole, one that could still exist.”
Detecting such an object becomes a fascinating exercise in itself. We know how to look for the signature of gravitational lensing, as in imagery of a distant galaxy that has been shaped by the gravitational influence of an intervening galaxy. A wormhole should show a negative mass signature that, instead of focusing light, does the opposite. The signature of that ‘defocusing’ is characteristic. Landis again:
“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.”
As theoretical as all this sounds, it’s actually quite useful. As the authors of the wormhole paper put it: “…the negative gravitational lensing presented here, if observed, would provide distinctive and unambiguous evidence for the existence of a foreground object of negative mass.” It makes sense, then, given the interest among astronomers in observing normal gravitational lensing with positive mass objects, to keep open the possibility of finding such a signature, which would provide our first solid evidence of wormholes.
And it also corresponds with how science works today. Much of the analysis of the voluminous data collected by our instruments is performed by computer software. And the value of a paper like this one, beyond its purely scientific interest, is that it identifies a pattern that such software should be written to recognize among all the other patterns that clue researchers in to interesting findings. It would be absurd to have solid evidence of a wormhole in data that was never analyzed in precisely the right direction.
As for that wormhole itself, an ancient one from the earliest days of the cosmos wouldn’t be of much use from a transportation perspective — you have to get to it first, after all, and it might be millions of light years away. And then there’s that problem of figuring out where it comes out on the other side. But it may be that a Kardashev Type II civilization, able to use all the energies of a star, could create artificial wormholes using negative energy, and if that is the case, the universe may have shortcuts galore through the Einstein barrier.
The paper is John Cramer, Robert L. Forward, Gregory Benford et al., “Natural Wormholes as Gravitational Lenses,” Physical Review D (March 15, 1995): pp. 3124-27, also available on the arXiv site (and thanks to Gregory Benford for forwarding a copy). Be sure to read Robert Forward’s novel Timemaster for his fictional take on negative energy and many other ideas from the outer limits of science. In addition to being a fascinating speculative romp, it’s a rich and funny book.
Astrophysics, abstract
astro-ph/0610441
From: Alexander Shatskiy Dr. [view email]
Date (v1): Sun, 15 Oct 2006 07:10:28 GMT (370kb)
Date (revised v2): Sun, 24 Dec 2006 09:59:40 GMT (370kb)
Astrophysics of Wormholes
Authors: N.S. Kardashev, I.D. Novikov, A.A. Shatskiy
Comments: 15 pages, 5 figures
We consider the hypothesis that some active galactic nuclei and other compact astrophysical objects may be current or former entrances to wormholes. A broad mass spectrum for astrophysical wormholes is possible. We consider various new models of the static wormholes including wormholes maintained mainly by an electromagnetic field. We also discuss observational effects of a single entrance to wormhole and a model for a binary astrophysical system formed by the entrances of wormholes with magnetic fields and consider its possible manifestation.
http://arxiv.org/abs/astro-ph/0610441
General Relativity and Quantum Cosmology, abstract
gr-qc/0701133
From: Francisco Lobo [view email]
Date (v1): Wed, 24 Jan 2007 18:02:33 GMT (12kb)
Date (revised v2): Tue, 6 Mar 2007 17:38:14 GMT (12kb)
A general class of braneworld wormholes
Authors: Francisco S. N. Lobo
Comments: 6 pages, Revtex4. V2: comments and references added, to appear in Phys. Rev. D
The brane cosmology scenario is based on the idea that our Universe is a 3-brane embedded in a five-dimensional bulk. In this work, a general class of braneworld wormholes is explored with $R\neq 0$, where $R$ is the four dimensional Ricci scalar, and specific solutions are further analyzed. A fundamental ingredient of traversable wormholes is the violation of the null energy condition (NEC). However, it is the effective total stress energy tensor that violates the latter, and in this work, the stress energy tensor confined on the brane, threading the wormhole, is imposed to satisfy the NEC. It is also shown that in addition to the local high-energy bulk effects, nonlocal corrections from the Weyl curvature in the bulk may induce a NEC violating signature on the brane. Thus, braneworld gravity seems to provide a natural scenario for the existence of traversable wormholes.
http://arxiv.org/abs/gr-qc/0701133
Millimetron Space Observatory to Search for Astro-engineering
Artifacts and Wormholes in the Universe
http://www.dailygalaxy.com/my_weblog/2008/01/russias-millime.html
Russia has a new space mission in preparation that can be
used for the search for extraterrestrial intelligence. The
project Millimetron is a millimeter and sub-millimeter space
observatory with a 10 meter diameter mirror, very sensitive
receivers for single dish mode and will be used for orbiting
VLBI (Very Long Base Interferometer). This telescope would
be convenient for a very sensitive all sky survey with the
possibility of constructing images of sources with a very
high angular resolution. The mission will be useful for the
search for astro-engineering constructions in the universe.
The goal of the project is to construct a space observatory
operating in millimeter, sub-millimeter and infrared wavelength
ranges using 12-m cryogenic telescope. The observatory will
provide possibility to conduct astronomical observations with
super high sensitivity (down to nanoJansky level) in a single
dish mode, and observations with super high angular resolution.
The space-based observatory will also make it possible to
look for the signatures of wormholes at the center of large
galaxies.
An ordinary black hole focuses light rays passing close to
it as if it were a giant concave lens – an effect known as
gravitational lensing. A wormhole’s negative mass of
phantom matter would have the opposite gravitational
lensing effect to normal matter, making any light passing
through the wormhole from another universe or point in
space-time diverge, and emerge from it as a bright ring.
Meanwhile, any stars behind it would shine through the
middle.
“It is an interesting attempt to actually think of what a
real signature for a wormhole would be, but it is more
hypothetical than observational,” says Lawrence Krauss at
Case Western Reserve University in Cleveland, Ohio.
“Without any idea of what phantom matter is and its
possible interactions with light, it is not clear one can
provide a general argument.”
Millimetron Project is included into the Space Research
Program of Russian Federation for 2015. The launch date
for the first spacecraft is planned for 2016.
Posted by Casey Kazan.
If worm holes exist with orifices in this space-time, one would wonder on their conduit stability and their location stability. Another option for detection would be to exploit regular energy signals within the universe such as pulsars. With worm holes, pulsar signals would have a conventional path to an earth observatory as well as the unconventional path to earth via a worm hole. Therefore, with one worm hole, there would be two observable energy sources, the actual pulsar and the worm hole orifice. Assuming a relatively stable location and with two energy sources, a scalar interference pattern would be generated revealing the pulsar’s location as well as the worm hole orifice’s location.
Regarding worm hole stability, Dr. Thorne of Cal Tech theorized the use of negative energy to stabilize the mouth of the worm hole. Could the Casimir effect be useful at generating this negative energy using double wall carbon nanotubes? Once a microscopic worm hole is captured and stabilized, can the energy of the dimensions through which the worm hole passes be exploited as well?