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Humanly Traversable Wormholes
- Analemma_ 6y ago> An even bigger problem seems to be producing the wormhole in the first place. It would be interesting to understand whether they can be produced in the RS model. Since they require topology change, this seems difficult. Has there been any serious (or at least semi-serious) thought given to this? I've perused some literature on wormholes, and it seems like even if you can somehow handwave away the GR energy conditions, the causality violations, etc., when talking about wormholes, everyone's always stuck on the issue of getting one to begin with. Do we know anything about whether the topology of spacetime can be changed?
- grawprog 6y agoA few results from a quick search on changing the topology of spacetime. There was a bunch more. It seems to be an area of research anyway. https://arxiv.org/abs/1212.3000 https://arxiv.org/abs/1212.3000 https://arxiv.org/abs/hep-th/9311186 https://arxiv.org/abs/hep-th/9311186 http://adsabs.harvard.edu/full/1997BASI...25..571B http://adsabs.harvard.edu/full/1997BASI...25..571B
- zamalek 6y agoSo far as changing the topology of spacetime, NASA is (or was) investigating it as part of Alcubierre/Warp drive research[1]. That being said, a warp bubble is a far simpler goal than a wormhole. > According to White, these results showed a vanishing but non-zero difference between charged and uncharged states after signal processing, but this difference remains inconclusive due to external interference and limits in the computational processing. [1]: https://en.wikipedia.org/wiki/White%E2%80%93Juday_warp-field_interferometer https://en.wikipedia.org/wiki/White%E2%80%93Juday_warp-field...
- enchiridion 6y agoIsn't that changing the geometry, not the topology?
- qubex 6y agoThe Alcubierre Drive does not change topology (number of shortest paths), only geometry (lengths of the shortest path).
- 6gvONxR4sf7o 6y agoFollow up question: When a black hole is created, is that a change in spacetime topology?
- techdragon 6y agoTopology basics would tell me that fundamentally at least as far as a simple overview goes... a “black hole” doesn’t imply a topological change however a “wormhole” does imply a topological change. One “punches through” the otherwise “flat” space time, creating another “opening” in the surface and increasing the complexity of that space time surface. To use the proper topology related words... The presence of a wormhole would make a region of space time that contained both ends of that wormhole, non-homeomorphic with that same region of space time without the wormhole. A black hole would not affect how homeomorphic the two regions of space time are, therefore it’s not really a change in the “topology” of the space even if the black hole would definitely change the geometry of that space quite drastically.
- qubex 6y agoA highly nontrivial issue connected with the change of topology associated with wormholes is whether passing through a wormhole reverses chirality or not.
- imglorp 6y agoIf there are any naturally occurring wormholes, would they have different external properties as compared to black holes?
- yazaddaruvala 6y agoAt the least light should escape a wormhole, and we should "see" what is on the other side. Otherwise I'm not sure how it'd be possible to detect any difference between a wormhole and a blackhole.
- gizmo686 6y agoThats the question. Even if wormholes exist, the Universe is under no obligation to make them observable to us. If they are always on the other side of a black hole event horizon, then there would be no way for us to detect them, even in principle.
- Johnjonjoan 6y agoWould we not be able to infer their existence by finding a white hole? I do see how calling that a detection could be a stretch.
- nine_k 6y agoActually, GR describes white holes, along with black holes, but no ideas how a white hole would form in the real universe apparently exist.
- deleted 6y ago[deleted]
- maxcan 6y agoIt is true no physical law obligates the universe to make them observable to us. But, this is the same universe that gave rise to Star Trek, Firefly, and especially The Expanse making so many of us dream of interstellar travel. So, I’d say ethically it’s pretty damn obligated to make them observable :) /s (Sort of.. not really)
- aaron695 6y agoI thought this was simple. You can't go faster than light. If you go through a wormhole (Or just send information) you go faster than light (Ignoring Hollywood's incorrect movie Event Horizon where you just bend paper), so you go back in time. So it's not possible. Because you can kill you father (or something mathematical with information) which is a paradox. End of story.
- mpalmer 6y agoI think that might be stretching what it means to be fast. Wormholes seem to be about warping space. Rate of motion doesn't enter into it.
- briga 6y agoWhat's to say we live in a world without paradoxes?
- rd07 6y agoWell, wormhole is not about how to travel faster than light, but about creating a shortcut between 2 points in a certain dimensional space by using a higher dimensional space. The most used explanation is using a piece of paper, the shortest route to travel between 2 points in a piece of paper is a straight line. But, we can shorten it by folding that paper and create a hole that connect the 2 points through the 3th dimension.
- yellowapple 6y agoI don't understand why "faster than light" automatically implies "go back in time". If it takes me 10 seconds to travel 10 lightyears, then that means I should still be traveling forward in time (specifically by 10 seconds), no? Like, it might apply on a "moving through local space faster than light" sense because physics is weird like that, but the whole idea behind wormholes is to shrink the actual distance traveled (from the traveler's point of view).
- ikeboy 6y agoBecause of relativity, you can have locations A and B in spacetime and a frame of reference such that A happens before B and a different frame such that B happens before A. So, if you're at A, you can travel faster than the speed of light and arrive before B happens. Then, after B happens, you can travel back to before A happens.
- yellowapple 6y agoI know this is immature, but... > We now change the geometry of the throats by connecting them to each other so that the geometry of the deep throat region is given by
- refulgentis 6y agoedit to empty, please
- klyrs 6y agoIt sounds like things falling into wormholes accelerate terribly -- a natural particle collider? Should we be able to see the detritus?
- dimastopel 6y agoWould a wormhole enable escaping our local group, in theory? From what I understand the current assumption is that we will never be able to travel beyond our local group because of the accelerated universe expansion.
- raducu 6y agoIf the wormhole is somehow artificially made, no, because, as far as I understand, you have to drag the exit hole through space, and thus you are limited by the speed of light. As to naturally occurring wormhole, I don't think there is any accepted and likely ocurring phenomenon that creates a wormhole, let alone across galaxies. So most likely, no.
- simonh 6y agoThe only example I can think of is a wormhole created by quantum fluctuations in the early universe, stabilised by a negative energy cosmic string, then cosmic inflation expanded it to macroscopic size and flung the two ends far apart. But of course the various features of that aren't universally accepted and are not likely to occur, so eh.
- fastball 6y agoIf we ever figure out FTL travel then presumably we could escape the local group, no?
- andyljones 6y agoDid a double-take seeing Maldacena's name on this. He's better known for discovering AdS/CFT, which is the foundation of a lot of modern work on quantum gravity. https://en.wikipedia.org/wiki/AdS/CFT_correspondence https://en.wikipedia.org/wiki/AdS/CFT_correspondence
- newsbinator 6y agoI was curious how we'd go about detecting wormholes: https://www.sciencedaily.com/releases/2019/10/191023135913.htm https://www.sciencedaily.com/releases/2019/10/191023135913.h... > In the new paper, scientists write that if a wormhole does exist at Sagittarius A, nearby stars would be influenced by the gravity of stars at the other end of the passage. As a result, it would be possible to detect the presence of a wormhole by searching for small deviations in the expected orbit of stars near Sagittarius A. I assume that would be a rather large worm hole, for us to detect the gravitational effects on stars that exist on the other side. I wonder if there's any approach to detecting micro-wormholes closer to our own star? Perhaps by setting up tens of thousands of micro-satellites around (Starlink), blasting radio waves in all directions, and seeing which ones don't make it to the receiver?
- ben_w 6y agoThis also makes me wonder: would accelerating end A of a wormhole have the same effect on the environment around end B of the wormhole as holding end A stationary in a gravity field? Motivation: Can there be in-universe traversable wormholes which can never be time machines? Caveat: no I have not studied GR, so if I’m asking the physics equivalent of a CompSci fresher asking how to pass the Turing test, tell me.
- marcinzm 6y ago>Motivation: Can there be in-universe traversable wormholes which can never be time machines? There was a paper(?) that noted that specific configurations of wormholes (basically tree shaped, no loops) do not allow time travel. I think it or another paper postulated some mechanism for wormholes collapsing if they violate that property.
- Akronymus 6y ago> I assume that would be a rather large worm hole, for us to detect the gravitational effects on stars that exist on the other side. Would the size of the wormhole actually affect the amount of gravity bleeding through? And how do we even define the size of a wormhole?
- kklisura 6y ago> Interestingly, they are allowed in the quantum theory, but with one catch, the time it takes to go through the wormhole should be longer than the time it takes to travel between the two mouths on the outside[a] > [a] This also implies that they can not be converted into time machines This doesn't seem like "classical" wormhole, right?
- JoachimS 6y agoBut it could still be useful. As a source of energy, propulson for example. Sink one end into a star and put the other where you need power.
- qubex 6y agoI can’t believe I’ve never thought of that... wow, what a ‘blast’! Wouldn’t it cause the core to collapse inwards though, as it would basically provide a “safety valve”-type release (though I presume if you were to place it on the edge of the fusing core, it would basically replace a patch of pre-existing surface area at the expense of convection and radiation pressure above taking a nose-dive).
- samus 6y agoIf the wormhole travels all the way to the core, then it will relocate about half of the star to the other end. If the wormhole can be closed, then it would act as a giant pizza cutter for stars. Potentially very useful to defuse supernovas. Or to utterly annihilate your enemy's stronghold... What would happen is more complicated to answer if the wormhole stays open. The star would effectively have double the surface area, but apart from that, the consequences for the star's future development elude me right now.
- bausano_michael 6y agoThis reminds me of a great hard sci-fi book, Greg Evanses Diaspora.
- m_a_g 6y agoAny suggestions on what to learn so that I can understand this paper? I would love to be able to fully comprehend this paper.
- messe 6y agoThe following assumes you are comfortable with Linear Algebra, Calculus, and Basic Physics (Newtonian Mechanics and Thermodynamics) at an early undergraduate level. Start with the Lagrangian and Hamiltonian formations of classical mechanics (Landau & Lifshitz - Mechanics). Then, study Quantum Mechanics (R Shankar - Quantum Mechanics). Statistical Physics while not key here, will be useful for building up an intuition (Landau & Lifshitz - Statistical Physics is good). Classical Field Theory, i.e. Electromagnetism should now be learned (J.D. Jackson). Then, I'd recommend learning Calculus on Manifolds (Spivak) and Differential Geometry (I can't remember a good textbook on this right now). If you're at this point you will now have a solid understanding of the maths needed to know GR and QFT. Zee has two good pedagogic books for these "Einstein Gravity in a Nutshell" and "QFT in a Nutshell". Once you know QFT, read a textbook on the standard model. That'll get you most of the way there. Strictly speaking, you could do possibly learn a lot less to understand this paper, but to be able to pick and choose which parts of the above are actually needed would require a significant amount of work in itself.
- pa7x1 6y agoThere might be better or more modern references for Differential Geometry but I enjoyed Barrett O'Neills' book. https://www.elsevier.com/books/semi-riemannian-geometry-with-applications-to-relativity/oneill/978-0-12-526740-3 https://www.elsevier.com/books/semi-riemannian-geometry-with... Also Misner-Thorne-Wheeler and Wald's book on General Relativity.
- fractionalhare 6y agoGreat suggestions. I would add that Calculus on Manifolds might be sufficient for differential geometry. One note on expectations - each of the domains you mentioned is typically an upper level undergraduate course (except for the first three). These courses usually progress at a rate of maybe 10 - 15 pages per week (~200 pages of a textbook covered in 16 weeks). It's genuinely hard to absorb this material in that amount of time, and unless you're exceptionally capable you should assume it will take you even longer under self-study. If you proceed with doing this, make sure you work through at least a few of the exercises at the end of each chapter of each book, and try to compare your solutions against solutions you find online. This is not to discourage anyone - studying all of this will probably be very rewarding! It's just a lot of work. It takes a massive amount of effort to get to the point where you can understand all the prerequisites needed to follow a research paper in modern math or physics.
- wrkronmiller 6y ago> Using them, one could travel in less than a second between distant points in our galaxy. A second for the observer that goes through the wormhole. It would be tens of thousands of years for somebody looking from the outside. Unless the energy requirements are lower, it sounds like this isn't much better than just traveling close to c (assuming you had adequate shielding).
- Filligree 6y agoHowever, with a wormhole you can step back through it. Which, yes, in this case would send you back in time. No problems there; it isn't a causal loop.
- chmod775 6y agoThe stepping back in time would make it a causal loop if you were able to observe something happening in the past (light traveling from the source) from the exit side, then go back through the wormhole to change this. To prevent this, the observed wormhole traversal time would need to be slightly faster than the speed of light, because then you also couldn't go back far enough to change something you already observed (assuming the "time" here is symmetrical to the time it takes going in the other direction). However there are other problems: What happens when I have 2 matching wormhole pairs, each exit being located to the entry point of the other. If I step back through the exits again and again can I go back in time as far as I wish?
- bollu 6y agoNot sure I understand, why is it not a causal loop?
- Filligree 6y agoThe wormhole sends you back in time, but not far enough back to arrive at your point of origin before you left. If you could treat the wormhole like a magic door that takes you across space, then two people looking at each other through the door wouldn't see anything unusual. One would be in the distant future, by the galaxy's clock, but not by the wormhole's. So going through in one direction takes you into the future, and the other takes you into the past, but it's a constant offset. The size of the offset depends on how you moved the other end to where it is. It's true that with multiple wormholes you could try to create a loop, though. That would probably fail due to virtual particular loops.
- edna314 6y agoBro, what's negative energy?
- m3kw9 6y agoCounter productive way to travel as it takes longer to use this worm hole to get to point B using conventional travel. But it seems like a good way to travel to the future. Just skip to point 4 in the doc.
- qubex 6y agoIt’s pretty clear why we’re all fascinated with faster than light travel (it makes the Universe feel accessible on our comparatively tiny timescales), but it’s also a sheer display of narrative obstinacy on our part that we continue to try to find loopholes in the rules of the Universe to allow something that so patently ain’t meant to be. Just build ‘em dormant A.I. probes, set ‘em off on their long lonely drifts, and let the magic of self-reproducing Von Neumann automata take hold once they arrive in a star system with suitable resources!
- aeternum 6y agoUnfortunately probes just don't capture the human imagination like manned exploration does. Perhaps a reason to invest in tech like neuralink? If we eventually merge with AI, perhaps each of those probes will ultimately feel like an appendage that is just slower to respond.
- aeternum 6y agoUnfortunately probes just don't capture the human imagination like manned exploration does. Perhaps a reason to invest in tech like neuralink? If we eventually merge with AI, perhaps each of those probes will ultimately feel like an appendage that is just slow to respond.
- boxed 6y agoI disagree. http://localroger.com/k5host/pitv.html http://localroger.com/k5host/pitv.html I have re read that dozens of times. It's a striking and powerful vision of a possible future.
- aeternum 6y agoSo the machines put them on a barren planet in the middle of interstellar space with no source of natural light? Seems like a pretty desolate end for humanity. I'd rather merge my consciousness with the probes and explore, something like this: http://www.skyhunter.com/marcs/GentleSeduction.html http://www.skyhunter.com/marcs/GentleSeduction.html