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Traversable Wormholes

  1. Jun 5, 2008 #1
    First off, I'm curious about the accuracy of this paper:


    I don't know nearly enough about GR to understand the math of the paper. It seems legit to a layman like me, but it IS posted on a hard sci-fi website, not any academic institution. To summarize, the paper claims that the exotic matter requirement for a traversable wormhole of arbitrary size can be placed easily within the realm of quantum effects (like the Cassimer effect). This has something to do with changing the limit from asymptotically flat to increasingly flat. I know what asymptotically flat means, but not increasingly flat, or weather or not that is feasible.

    Second, I'm wondering about what traversable wormholes would actually look like. I've seen simulations of the visual effects created by black holes, but I'm not sure traversable wormholes would look in any way similar. For one, I wouldn't expect any redshift, because I assume that would also imply time dilation and probably extreme tidal forces. Also, I would of course expect to see light from the other side of the wormhole, which obviously is not considered in any visual simulations of black holes.

    And third (yes, I'm really going that far) I have a question about the actual formation of a traversable wormhole. What basically is the process for creating one? I know there are various models, so there may not be a universal explanation. I know the original proposal was an exotic matter shell surrounding a concentration of mass, although this wouldn't allow passage. In any case, my most pertinent question about this is where the other end of the wormhole would end up? Would it start at the same point, and separate? Or would it open up in some random region of space? Or (probably most likely) do we just have absolutely no idea?

    Okay, that was a lot of questions so I don't blame anybody for not answering all of them. Any little bit would be helpful. Thanks.
  2. jcsd
  3. Sep 18, 2008 #2
    To answer your question, we would probably need a quantum theory of gravity to really answer such questions. Unfortunately, we don't know the details of such a theory yet.

    In particular, to form a wormhole we need to change the topology of the universe (in this case, create a 'handle' in it ... like going from a cup to a coffee mug). Nothing in GR describes processes that could change the topology (except I guess singularities, but that is where the theory fails to describe what happens anymore and a quantum theory should fix this). So all papers I've seen (I admit I haven't bothered to read the one you linked) necessarily focus instead on what matter distribution would be required in such a universe that already has such a topology ... or asks questions about the stability of wormholes (they could close off to singularities on each side).

    If you COULD change the topology, in order to not violate causality, it would have to be a local process. So yes they would open by each other, and then you'd need to drag one side of the hole to where-ever you wanted it. Hmm... but if a worm-hole could pinch off, the reverse must be allowed in the theory as well. I guess even trying to use causality here isn't very guiding. We will have to wait for a quantum theory of gravity to really know, but my impression (from current candidates for such a theory), is that we probably won't be able to change the topology like that.

    I hope that helped.
    Last edited by a moderator: Sep 20, 2008
  4. Jun 14, 2011 #3
    1. You can safely ignore any physics paper posted on a science fiction game site. Now from what I've read there is nothing "easy" about using the Casimir effect to hold open a wormhole. And any wormhole geometry that is not asymptotically flat, i.e. one that does not become flat space at arbitrarily great distances from the wormhole's throat, is no good. It wouldn't be consistent with nature. [To have a wormhole geometry that is "increasingly flat", the wormhole's matter would have to be spread throughout all of space and carefully arranged so that its density decreases with distance from the throat of the wormhole.]

    2. I found a wormhole FAQ that seems to have informative entries:

    What would a wormhole look like?
    A wormhole would likely appear to be a bubble or window through which unfamiliar stars are visible. If the wormhole is massive, dense, rotating, and in the proximity of luminous matter -- such as that found in stellar atmospheres -- it could be surrounded by a visible “accretion disk” much like those surrounding black holes.

    What would it be like to travel through a wormhole?
    As you enter a deep spherical wormhole, you will see stars concentrated in a sphere directly ahead. After awhile you peer out of your spaceship’s port window. You will notice another ship on a parallel course off in the distance. Upon inspecting it with your telescope, you will notice that it looks exactly like the starboard side of your spaceship. That’s because it is. Looking through your starboard window similarly reveals a distant port view of your ship. The sky will show relatively few stars in directions at right angles to your inward trajectory. The more forward your angle of view, the more stars you will see, until you see the aforementioned spherical concentration straight ahead. As you approach this concentration -- the wormhole’s throat -- you will notice that the parallel image of your ship is much closer. You wave and, after a momentary delay, can (through your telescope) see yourself waving. As you pass through the throat, you will find yourself gazing upon a normal sky of unfamiliar stars. The parallel image of your ship will recede and soon vanish. In contrast to this experience, traveling through a maximally benign Visser (thin-shell) wormhole would be just like stepping through a doorway. You could even straddle this doorway and be at once in two universes or vastly separated regions of the same universe.

    3. Again, two entries from the same FAQ:

    How difficult would it be to create a wormhole?
    The ability to create a traversable wormhole is well beyond current human technology. It would require the enlargement of one of the many submicroscopic quantum wormholes believed to exist within any volume of space. The process would likely require an intense, ultra-high frequency negative energy source -- something we have no idea how to produce.

    How could an advanced civilization ensure that the mouths of their intra-universe wormholes are in desired locations?
    They would proceed as follows. Step 1: At the desired location of the first mouth, enlarge a virtual wormhole extracted from the spacetime foam. Step 2: Determine the location of the second mouth by traversing the newly enlarged wormhole and studying the sky from the vantage point of the second mouth. Step 3: If this location is undesirable, return through the wormhole, collapse it, and begin again at Step 1. Otherwise, continue to Step 4. Step 4: Charge the second mouth by showering it with charged particles. Step 5: Use electrostatic attraction to precisely position the second mouth by suitably dragging it.

    The FAQ is an excerpt from a recent book on wormholes. The front cover seems to have some sort of artist's conception of a wormhole that seems to match the description above.
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