[HN Gopher] No, we didn't accidentally create a warp bubble
___________________________________________________________________
No, we didn't accidentally create a warp bubble
Author : russfink
Score : 154 points
Date : 2021-12-15 14:57 UTC (8 hours ago)
(HTM) web link (bigthink.com)
(TXT) w3m dump (bigthink.com)
| Exendroinient wrote:
| Sounds like a normal day in the science journalism. The same case
| was with the ""earth-like planets"" headlines even though some
| were unconfirmed and the only data known about them was their
| orbit, mass to a certain degree and star, which in most cases was
| small and very active. In the media outlets there weren't any
| information about the host star and the fact that most of those
| planets were tidally locked. Besides all of that, they were still
| calling them earth-like planets.
| koheripbal wrote:
| The reality is that Earth like planets probably exist in great
| numbers, but we lack the technology to see them since they are
| small and relatively far from their host star.
| tsimionescu wrote:
| Why do you think this is 'probable'? It's certainly possible,
| no doubts about that, but why do you believe there is a
| greater than 0.5 probability of it?
| Sohcahtoa82 wrote:
| A quick Google says that there are an estimated _two
| trillion_ galaxies, each with an estimated _100 billion
| stars_ on average, with an average of 1 planet per star.
|
| That means there's an estimated 200 _trillion billion_
| planets.
|
| Don't you think it's incredibly improbable that our Earth
| is the only one?
| tsimionescu wrote:
| I think that's impossible to estimate, at least for some
| definitions of "Earth-like".
| Sohcahtoa82 wrote:
| It's impossible to estimate a total number, for sure, but
| I think it's perfectly reasonable to believe that there's
| at least 1 other Earth-like planet in the universe.
| stakkur wrote:
| Zefram Cochrane will settle all this in 2063.
| webmaven wrote:
| Yeah, I found the original hype overblown. The claims made were
| also for a configuration that was odd, at best. Intuitively,
| there are any number of geometries that ought to produce greater
| 'negative energy densities' while being easier to manufacture and
| test than the sphere-in-a-cylinder one if the proposed effect
| isn't just a mathematical artifact.
| PaulHoule wrote:
| Every solution I've seen for the Alcubierre drive is static.
|
| To really make it work you have to start out in normal flat
| space, turn it on, and then turn it off.
|
| You have to do this without being killed. I suspect you'd face
| hazards like the hazards you'd have falling into a black hole.
| (Personally I think you die when crossing the event horizon and
| never make it to the classical singularity, not just because you
| got killed at the event horizon, but there is nothing that looks
| like the classical singularity.)
|
| I think the Alcubierre drive doesn't violate the censorship
| principle because practically it doesn't create closed timelike
| curves. You can't see outside, you can't get into it, you can't
| get around it. You might be moving faster than light in some
| sense but you can't interact with the universe and communicate
| messages from here to there.
| monocasa wrote:
| The whole shtick is that nothing is really moving FTL in an
| Alcubierre drive in the way that breaks the censorship
| principle, not that any not being able to get out is what's
| helping the concept.
|
| There's no underlying reference frame beneath space time
| itself, so warping space time like this just creates shortcuts.
| The time element of the vector is still positive for all
| possible particles, so no closed timelike curves.
|
| For an example that can be seen naturally, it's thought that
| the galaxies on the edge of the observable universe are moving
| away from us faster than C because of the expansion of the
| universe and it's warping of space time. The same math works
| just fine with them moving faster than C towards us if the
| universe were shrinking.
| PaulHoule wrote:
| I think of it as being like one of those trivial "faster-
| than-light" things like a spot of light.
|
| You can easily swing a laser pointer fast enough that the
| beam would crosses Earth's Moon faster than light.
| Information is moving outwards, not sideways, so that speed
| doesn't matter.
| monocasa wrote:
| That's a different underlying cause. Nobody would say that
| a rail gun that shoots ball bearings at near C breaks FTL
| just because you turn it.
|
| This is more that space time isn't euclidean. You can see
| this in how gravitational lensing can create longer
| straight line paths between two points. Just because you
| could send light down one pathway and it ends up later than
| something moving less than C, doesn't mean that you went
| FTL in a way that breaks causality. An Alcubierre drive is
| 'just' dynamically modifying the shape of space time to
| make more useful pathways.
| PaulHoule wrote:
| I don't think you can really use the paths.
| monocasa wrote:
| Why not? If you can bend space time into the bubble in
| the first place, why can't you bend it back?
|
| The main issue I've heard with 'popping' the bubble isn't
| that you cut yourself off from the rest of space
| permanently, it's that there's a collection of everything
| that would have been along your path time dilated sitting
| right at the edge of the bubble that flies into the
| bubble all at once and is pretty nasty for anything in
| the bubble.
| neltnerb wrote:
| The scientist being discussed in the article didn't even find a
| new solution.
|
| Article (very end):
|
| ---
|
| ...there's an enormous difference between what teams working on
| Casimir cavities do experimentally and the numerical
| calculations performed in this paper. That's right: This isn't
| an experimental paper, but rather a theoretical paper, one with
| a suspiciously low number (zero) of theoretical physicists on
| it. The paper relies on the dynamic vacuum model -- a model
| typically applicable to single atoms -- to model the energy
| density throughout space that would be generated by this
| cavity. They then use another technique, worldline numerics, to
| assess how the vacuum changes in response to the custom Casimir
| cavity.
|
| And then it gets shady. "Where's my warp bubble?" They didn't
| make one. In fact, they didn't calculate one, either. All they
| did was show that the three-dimensional energy density
| generated by this cavity displayed some qualitative
| correlations with the energy density field required by the
| Alcubierre drive. They don't match in a quantitative sense;
| they were not generated experimentally, but only calculated
| numerically; and most importantly, they are restricted to
| microscopic scales and extremely low energy densities. There's
| a lot of speculation and conjecture, and all of it is unproven.
| lumost wrote:
| Which is fine for a certain category of paper - in particular
| this opens the door to explicit measurements and manipulation
| of the curvature of space at extremely small scales. Further
| work is required to see if there is something real here or
| not.
| donkarma wrote:
| im a big fan of the idea that anyone who uses FTL with the
| intent of sending messages back in time has it not work
| mrfusion wrote:
| I think you're describing this?
| https://en.m.wikipedia.org/wiki/Novikov_self-
| consistency_pri...
| AnIdiotOnTheNet wrote:
| I've actually thought a lot about this, in particular
| because I had a dream involving Novikov self-consistency
| principle. I think the base idea behind self-consistency
| principle is that it prevents grandfather paradoxes but
| allows bootstrap paradoxes. In other words, stable time
| loops are allowed but unstable ones aren't. I submit that
| it is possible to have _meta-stable_ time loops such that
| all grandfather paradoxes are ultimately meta-bootstrap
| paradoxes.
|
| Assume that if time travel is possible, then changing the
| course of events must be also be possible just as directing
| future events by our decisions in the present is. If one
| goes back in time and kills their own grandfather, they
| have altered the future such that they are never born in
| order to time travel in the first place, a grandfather
| paradox. However, since time travel must have existed in
| order for this situation to occur, then undoubtedly someone
| else at some future date within this timeline will seek to
| change history as well. To keep this scenario simple,
| imagine that this person travels back in order to kill you
| before you are able to kill your own grandfather, thus
| restoring your original timeline in which you travel back
| to kill your own grandfather. This is a meta-stable time
| loop employing a meta-bootstrap paradox. Each timeline
| exists and is dependant on time travel from the other.
| Arbitrarily complex structures are possible involving
| arbitrarily many timelines, which in an infinite meta-time
| universe suggests the possibility that all time travel
| _must_ resolve in this way.
|
| I came up with this years ago, but have only ever seen
| something like it explored once: in the TV show 'Dark'.
| [deleted]
| YeGoblynQueenne wrote:
| [SPOILERS]
|
| If I remember correctly Dark to some extent relied on
| time travel to have time travel in the first place, i.e.
| Claudia Tiedemann needed to go back in time to hand H. G.
| Tannhaus the blueprints for the time machine that she
| used to go back in time with. That, in one of the
| alternate timelines- in the original timeline Tannhaus
| presumably made a time machine from scratch, or there
| would be no alternative timelines. In the end Jonas
| Kahnwald and Martha Nielsen go back in time to alter the
| course of the original timeline, thus eliminating their
| own. This is much like you say, except that in the end
| the original timeline is restored to the point before any
| time travel could happen, or had a reason to happen. And
| maybe that's a simpler way to eliminate any paradoxes: no
| time travel allowed [edit: yeah, sorry, that's Novikov].
|
| Sic mundus creatus est :P
| tshaddox wrote:
| How do meta-stable loops work for time travelers visiting
| themselves in the past? How is it that moments before
| entering the time machine they don't remember ever being
| visited by a future version of themselves?
| AnIdiotOnTheNet wrote:
| Because that happened in a different timeline. If A0 was
| not visited and later A1 and decides to travel back to A0
| and visit, that splits the timeline. Eventually some
| actor in that timeline (or another created by time travel
| from that timeline) will alter events such that they
| prevent A1 from visiting A0, restoring the original
| timeline and acting as the final piece of the meta-stable
| structure.
| tshaddox wrote:
| But if traveling back in time forks that timeline you
| don't have to worry about the self-consistency or
| bootstrap paradox at all, right?
| godot wrote:
| > I came up with this years ago, but have only ever seen
| something like it explored once: in the TV show 'Dark'.
|
| Doraemon, a Japanese children's cartoon (1970s to 1990s),
| created by Fujiko F Fujio, who is actually very well-
| versed in physics and science, has used something like
| this as a plot point in several different
| chapters/episodes and some movies. It doesn't actively
| call them "meta-stable time loops", since its target
| audience is children, but the idea and concept is there.
| Growing up watching and reading this series, I've learned
| more and more from it as I rewatch/reread old
| chapters/episodes, every time. I absolutely love it.
| mrfusion wrote:
| That's a great way to think about it. It reminds me of
| the Temporal integrity division in the 29th century in
| Star Trek.
| [deleted]
| Jenk wrote:
| Doesn't FTL make time slow for the travelling party? Or does
| it flip when you velocity is greater than C?
| roywiggins wrote:
| You'd end up returning to your own past if you took a round
| trip to Alpha Centauri faster than light, so more or less,
| yeah.
| doliveira wrote:
| Fermi paradox: advanced civilizations discover time travel
| and generate paradoxes that erase the timelines that led to
| their creation
| GolfPopper wrote:
| This is explicitly the background for SF author C.J.
| Cherry's _Morgaine Cycle_ , although the destruction isn't
| complete and leaves fragments scattered across space and
| time. (The reaction of a interstellar human civilization to
| discovering the fragmented network of space-time gates is
| "shut it all down and bury it".)
| EarthLaunch wrote:
| That sounds fascinating, I'll read that. C.J. Cherryh is
| one of the authors I somehow didn't pick up as a child,
| even though I was reading C.S. Friedman and the like.
| Maybe it was the covers.
| doliveira wrote:
| Wow, here's to me thinking I had had an original idea...
| But that book sounds fascinating, I'll be sure to check
| it out
| GenerocUsername wrote:
| Dark matter is obviously latent gravity acting across the time
| axis
| BrazzVuvuzela wrote:
| I'm not a physicist so take this with a huge grain of salt, but
| from what I understand, this proposed warp bubble would use the
| casimir effect. But the casimir effect works by creating a gap so
| narrow it excludes wavelengths of energy larger than it. So even
| if the math were all correct and you actually built one of these,
| wouldn't it be too small to actually send a signal through? And
| if nothing can fit through it, is there any point?
| colechristensen wrote:
| No, it would be a few micrometers across, hundreds of times
| larger than features on advanced microchips.
|
| And if it is effectively a warp bubble, it wouldn't have any
| immediate useful application, but for teasing you could send
| electrons or photons through it and measure effects. This is
| not a wormhole, the likely effect is either nothing or a slight
| signal timing change.
| Randor wrote:
| Well,
|
| I think journalism is getting worse as the years go by. Like
| everybody else I noticed the title and clicked on it a few days
| ago. Reading the paper revealed that the team was simply
| interpreting/speculating what the math was showing about some
| hypothetical energy density structures.
|
| Of course the sensationalized title propagated all over the net
| ignoring the facts.
| anonGone73 wrote:
| Journalism is getting worse, because the market has
| changed/evaporated. It is another race to the bottom.
|
| There are more journalists in prisons than ever before.
|
| Attention is a currency and we are easily distracted.
| Sohcahtoa82 wrote:
| > There are more journalists in prisons than ever before.
|
| In Russia or China, I can believe this. But in the USA and
| most of Europe, I'm going to need a citation before I believe
| that.
| sovnade wrote:
| It sounds like journalism is achieving its goal - getting more
| clicks. Like you said, everyone clicked it and read it.
|
| Not sure what the solution is when the only way for these
| outlets to stay afloat is to get more and more clicks.
| scythe wrote:
| A deeper problem is: how do you create an "open" discussion
| forum for paid subscription content?
|
| Everyone bemoans ad-financing, but everyone loves aggregators
| (including _Hacker News_ ), and aggregators and paywalls
| generally don't mix.
| skyechurch wrote:
| The market is responding to its incentives and producing an
| optimized product, line goes up and all is right with the
| world.
| sillyquiet wrote:
| Honestly, I think this has always been how most journalism has
| been, we're just noticing it more.
|
| But to be fair and I think to support your point, the bastions
| of so-called 'real' journalism do seem to have gotten fewer and
| fewer.
| likpok wrote:
| Journalism about physics has always been like this. The
| Alcubierre drive is 25 years old, even before that there were
| widely-publicized discussions of the same kind of idea: invert
| the equations and come up with interesting results.
|
| The realities of space travel are kind of grim: months to visit
| even nearby uninhabitable planets and decades to get anywhere
| interesting. Relativity has always been a huge and ever-
| increasing impediment to that, and the ways in which it is have
| percolated out. There's also the demand for hard science
| fiction with space battles (I personally am a fan!) that
| similarly runs aground on "you can't have a galactic empire
| where it takes a hundred years to reach the next province
| over".
|
| So there's lots of demand for "hey this thing makes FTL travel
| possible" and not as much demand for "scientists publish paper
| but everything still sucks".
| Randor wrote:
| Well,
|
| About a week ago this topic was widely in the news under
| variations of the title:
|
| "DARPA and NASA Scientists Accidentally Create Warp Bubble"
|
| That's the context of my response here in this thread. I am
| not sure if everyone reading this thread knows that. The new
| title "No, we didn't accidentally create a warp bubble" was
| the NASA engineer attempting to fix the misinformation
| generated by the journalists.
|
| Absolutely agree with you about physics journalism. I enjoy
| science fiction books too, I have no problem with the
| theoretical FTL topic.
| belly_joe wrote:
| The dynamic sort of of reminds me of the "market for lemons" in
| that the bad drives out the good.
|
| Not really quite the same though. The question is what the
| production function for articles looks like from the
| publisher/journalist perspective. If it's easier to produce
| clickbait articles than "real" articles then I think this
| effect is what we see in the market for news. But from another
| angle, it seems more labor intensive for a journalist to spin a
| weak finding into a strong finding than to simply report an
| exciting finding directly.
|
| https://en.wikipedia.org/wiki/The_Market_for_Lemons
| Randor wrote:
| Yeah,
|
| It makes me sad to think that I contribute to this process. I
| have to admit... that I probably do read alot of those
| clickbait articles giving them more views.
|
| It makes me even more sad when I think about the platforms
| that are removing the ability to downvote
| incorrect/misleading information.
| kuraudo wrote:
| This epidemic of "No, ..." titles needs to be cured.
| dang wrote:
| Good point, and it looks like something that can easily be
| scraped out. I'll add it to the list. Thanks!
| Semiapies wrote:
| Maybe we should use some machine learning solution that
| recognizes phrases that look too much like _titles_.
| dang wrote:
| The HN title dataset is public. If anyone can come up with
| software (ML or otherwise) to detect baity titles and/or
| debait them, we'd certainly be interested.
| TigeriusKirk wrote:
| It's one of the clickbaitiest title formulations around. It
| works amazingly well on a certain type of mindset.
| ravenstine wrote:
| _... Here 's why._
|
| :D
| [deleted]
| teawrecks wrote:
| Man.....I wish Feynman were still around today.
| pwdisswordfish9 wrote:
| It seems the warp bubble bubble just burst.
| dr_dshiv wrote:
| Oh boo hoo, we didn't solve the warp drive in the first attempt?
| The paper made some interesting but handwavy claims? This is what
| science actually is--incrementalism.
|
| Unless the guy lied, I say god bless him for finding something
| relevant to publish towards our multi-galactic future.
| juancampa wrote:
| The original paper states:
|
| > This qualitative correlation would suggest that chip-scale
| experiments might be explored to attempt to measure tiny
| signatures illustrative of the presence of the conjectured
| phenomenon: a real, albeit humble, warp bubble.
|
| The key word here is "conjectured". He didn't say he created a
| warp bubble.
|
| I'm okay with publishing conjectures. If you think there's
| something interesting, let the world know.
|
| Disclaimer: I'm not a scientist by any means.
| at_a_remove wrote:
| I only managed a BSc in Physics, although I did get to take grad-
| level G&R. My stance is the following: I do not care what your
| proposed method is for FTL, tell me how the paradoxes allowed by
| closed timelike curves will be resolved. No, just bundling all of
| it into a black-box general AI "cosmic censor" is not sufficient,
| that's just an abstraction saying not to worry about it.
|
| Yes, it ruins most of our fun space opera. Oh well.
| AnIdiotOnTheNet wrote:
| A bunch of nonsense thought from someone who reads too much
| sci-fi:
|
| > https://news.ycombinator.com/item?id=29569437
|
| In other words, it's perfectly ok to change the past and the
| universe doesn't so much self-censor as timelines always
| ultimately loop in some kind of meta-time back into each other.
|
| Another way to think of it is that it self-censors in the way
| that a delayed choice quantum eraser experiment does. The
| timelines which do not ultimately form part of a stable meta-
| loop structure destructively interfere with each other.
|
| Feel free to point out all the ways in which this is nonsense
| by the way. I love this sort of education through correction of
| ignorant armchair supposition.
| ben_w wrote:
| Well, QM allows superposition and entanglement, why not just
| have you and your grandfather be in an entangled superposition
| of |alive> and |dead> corresponding to each part of the
| sequence in the classical eponymous paradox?
|
| That said, I read a plausible claim that a CTC would have an
| unstable buildup of energy in the form of the wavefunctions of
| virtual particles self-reinforcing, so I suspect it's more
| likely that _trying_ to build a time machine would instead
| result in unbounded energy, and that being a possibility is
| generally considered a sign that somebody made a mistake.
| voldacar wrote:
| This article could have been 2 or 3 sentences but instead I had
| to wade through paragraphs of fluff
| johnhenry wrote:
| "This isn't an experimental paper, but rather a theoretical
| paper, one with a suspiciously low number (zero) of theoretical
| physicists on it."
| jerf wrote:
| I would say another problem with the underlying paper is that it
| uses quantum mechanical principles to compute its results, which
| we're then supposed to accept as something we can just inject
| into general relativity.
|
| However, we know those theories don't go together very well, and
| I would certainly consider trying to create "warp bubbles" as an
| extremal condition for the combination of the two, so we
| shouldn't take such a combination too seriously. Not necessarily
| unseriously simply on the basis of this one thing... I believe
| Hawking's initial computations for black hole radiation plays a
| _bit_ fast and loose with this distinction, albeit in a somewhat
| principled way, so it 's not an _immediate_ disqualifier. But it
| 's definitely a Spock-eyebrow-raise and a "hmmmmm?"
|
| Personally, I wouldn't be surprised that when we get the real
| theory of quantum gravity, if we ever do, that a lot of these
| "oh, look at this solution for general relativity!" obscurities
| go away, like wormholes, cosmic strings, the place in the Kerr
| metric that seems to lead to a new universe or some other exotic
| thing [1], singularities in general, and quite possibly, warp
| bubbles and other crazy solutions. This is the Occam's Razor,
| most parsimonious solution to the question "why is it that we
| look out in the universe and the craziest general relativity
| thing we see is black holes?"... the rest of these things are
| artifacts of the approximation that is general relativity.
|
| [1]:
| https://en.wikipedia.org/wiki/Kerr_metric#Kerr_black_holes_a...
| sam0x17 wrote:
| > Personally, I wouldn't be surprised that when we get the real
| theory of quantum gravity, if we ever do, that a lot of these
| "oh, look at this solution for general relativity!" obscurities
| go away
|
| In particular, I've thought dark matter is in this category of
| "bad theory rounding error" since I learned about general
| relativity and quantum mechanics in high school.
| wongarsu wrote:
| "We just don't understand gravity well enough" is one of the
| top approaches physicists try to solve the mystery about dark
| matter, but so far it doesn't seem overly likely. Especially
| galaxies without dark matter [1] are hard to explain without
| labeling the majority of dark matter as some kind of particle
| or field.
|
| 1: https://www.nasa.gov/feature/goddard/2021/mystery-of-the-
| gal...
| random314 wrote:
| Why did you think that? How does dark matter invalidate
| general relativity?
| sam0x17 wrote:
| Because I was taught at a young age to assume everyone is
| fallible and question assumptions, and it seemed an awful
| lot like a rounding error to me at the time.
|
| As people have mentioned, there is apparently now more
| substantial support for it, but back then it was posited
| based on equations only, and seemed a lot more like trying
| to explain away a theory not fully matching reality
| rmah wrote:
| Um, as I understand it, dark matter was not posited by
| equations but by how observations differed from the the
| equations. And essentially, this is still the state of
| things. To wit, the standard model doesn't match
| observation unless there is this "dark matter" out there.
| We have no idea what it is. It's just what we call a
| particular type of ignorance. Current work is either a)
| assume that the theory is correct and that "dark matter"
| actually exists so they try to figure out what it is or
| b) assume that current theory is wrong and so try to come
| up with a better theory. Or c) a combination.
|
| And essentially the same thing for "dark energy".
| sam0x17 wrote:
| I recall that back in the day my thought was that "Or our
| model of gravity is just wrong and what we're observing
| is correct (as in, visible matter is causing this
| behavior), we just don't understand how gravity works at
| massive scales because there are variables we aren't
| taking into account" but honestly it's been so long I
| forget all the basic info on this.
| manwe150 wrote:
| I think they mean the reverse: since dark matter gives a
| possible solution to some of the unexpected observations
| resulting from the current theories, so if the theories
| later change, they are hoping the dark matter/energy terms
| will vanish. I likely have about the same physics knowledge
| as them, so I don't speak from authority. But dark energy
| is not just a small fudge factor, so current theories seem
| unlikely to change by that much. As mentioned in the
| article, we have some measurements now also consistent with
| the existence of dark energy being pervasive, not just the
| appearance of it in theories.
| doliveira wrote:
| Nah, dark matter is the real deal. It's got way more evidence
| for it, and even the alternatives like MOND (which is
| something closer to a layman would argue as "maybe we
| understand the theory wrong") do need dark matter to explain
| some measurements.
|
| Dark energy, on the other hand...
| thereddaikon wrote:
| Dark matter isn't really a theory, its the name of an
| observation. Not sure how it can be any more or less legit.
| The name doesn't try to explain what's happening. Its just
| describing the weirdness of the observations.
|
| One thing that annoys me is the common description of dark
| matter as a single coherent theory of extra matter that
| can't be detected. Even wikipedia makes this mistake at the
| very beginning. But there are a lot of theories that try to
| explain it. None of which actually work yet. Once a theory
| that stands up is formed then the name will change.
| gizmo686 wrote:
| Dark matter is not merely an observation. It is a class
| of theories to explain that observation. Specifically, if
| your explanation for the underlying observation is of the
| form "there is some matter-like stuff with mass that is
| causing the observed effects through standard G.R.
| gravity. We haven't otherwised observed it because X",
| then you have a dark matter theory. Typically X involves
| week to non-existant interactions through other forces.
|
| If your explanation for the observation involves saying
| "General Relativity is wrong", or positing the
| modification or addition of some other force, it may
| account for the observation behind dark matter; it may
| even be correct; but it is not a dark matter theory.
|
| Assuming some dark matter theory is proven correct, we
| will _probably_ stop calling it dark matter when it is
| discovered. Although we still call nuclearly bound
| protons and neutrons with electrically bound electrons an
| "atom", even though we have since disproven the
| hypothesis that such objects are atomic.
|
| If the answer ends up not being a dark matter theory, we
| will probably just call it "gravity".
| Maursault wrote:
| Dark matter is not a theory, to be sure. It is a
| hypothetical.
| thereddaikon wrote:
| No its not a hypothetical. The measurements are there.
| Something unexpected is happening and nobody knows for
| certain what.
|
| The problem is someone picked the misleading name "Dark
| Matter" and then pop science, and actual scientists
| talking to laymen did the massive disservice of wording
| the explanation in such a way as to make it sound like
| there is a real theory that proposes there is some matter
| that interacts with gravity yet is invisible and
| undetectable in literally every other way called dark
| matter.
|
| I only learned the distinction in college when another
| student pointed out that dark matter as described was
| unscientific because it was an unfalsifiable, not to
| mention generally useless anyways. That led to patient
| explanation that it wasn't a hypothesis or theory and it
| was just what they called the observations. Would have
| been nice if anyone had bothered to start with that.
|
| There are a lot of hypothesis about what it really is.
| Neutrinos, WIMPS, SIMPS (heh), MOND etc etc.
|
| Personally I lean towards the got gravity wrong bit
| although not any specific explanation. I'm not a
| physicist but history and logic would suggest that while
| relativity is a pretty good explanation its far from
| complete. And I see no reason why forces necessarily have
| to work the same on the small scale and grand.
| ben_w wrote:
| Dark matter is a set of observations; we have a dozen or
| so hypotheses to explain those observations that we
| cannot yet rule out.
| GuB-42 wrote:
| The problem with dark matter is that it is a bit too easy
| to predict where it is. That's why so many people are
| looking for galaxies without dark matter. We sometimes find
| them, but I am not sure if there is an instance where we
| have confirmed that it is not a fluke of observation.
|
| The reason why it is a problem is that if you can reliably
| predict where dark matter is, then you can turn these
| predictions into equations and get away with dark matter as
| a form of matter. That's the idea behind modified gravity.
| Bocanova wrote:
| >> obscurities go away, like wormholes, cosmic strings, the
| place in the Kerr metric that seems to lead to a new universe
| or some other exotic thing [1], singularities in general, and
| quite possibly, warp bubbles and other crazy solutions.
|
| Buzz kill.
|
| Edit- You can find your own ride to the next WorldCon.
| curiousllama wrote:
| We want wormholes! We want wormholes!
| jerf wrote:
| _What do we want?_
|
| WORMHOLES!
|
| _When do we want them?_
|
| NOWYESTERDAYC'THULUTOMORROWUNDEFINED!
| nostromo wrote:
| I don't get the excitement for the Alcubierre drive.
|
| It requires _negative mass_ , something that doesn't exist. (It's
| not like dark matter, something we know exists but don't
| understand -- it is something that we have no evidence for its
| existence at all.)
|
| I feel like they were just playing with models, entered a
| nonsensical value (negative value for mass), and discovered a
| warp drive. If you're going to do that, just enter negative time
| and invent time travel while you're at it.
| JumpCrisscross wrote:
| > _negative mass, something that doesn 't exist_
|
| We don't know this. And this isn't a "can't prove a negative"
| argument. The origin of mass is frontier physics.
|
| More directly, one can explore why negative mass is needed, and
| whether there are other phenomena that produce that effect.
| Worst case: the math is interesting.
| WJW wrote:
| It's not so strange to understand the excitement when you think
| about how many people would really REALLY like FTL travel to be
| possible. Not only does it invoke romantic ideas about
| exploring the stars and lets people dream about becoming
| captain of their own starship on day, it also helpfully
| distracts from having to confront the extremely difficult
| social issues that hinder saving the Earth from it's myriad
| problems. Without FTL you take all those dreams away, so it's
| no wonder people are extremely interested in anything that even
| looks like a "solution".
| otrahuevada wrote:
| It does not need /negative matter/ or energy, though.
|
| What is needed, in the original, non-scammer-friendly version
| by Alcubierre is /something/ that can push spacetime in the
| opposite direction that mass and energy do.
|
| At least the original Alcubierre solution, he basically lays
| out the mechanism and says, paraphrasing: "hey, the numbers do
| work out. We just need something that doesn't make sense, or
| something that makes /the thing/ happen" We
| see then that, just as it happens with wormholes, one needs
| exotic matter to travel faster than the speed of light.
| However, even if one believes that exotic matter is forbidden
| classically, it is well known that quantum field theory permits
| the existence ofregions with negative energy densities
| in some special circumstances (as, for example, inthe Casimir
| effect [4]). The need of exotic matter therefore
| doesn't necessarily eliminate the possibility of using a
| spacetime distortion like the one described above for hyper-
| fast interstellar travel.
|
| https://arxiv.org/pdf/gr-qc/0009013.pdf
|
| The excitement here is partly due to the fact that this is both
| a trekkie thing and one that was previously not even supposed
| to numerically make sense.
|
| It's likely this "not requiring any specific fringe-physics
| thing" is what is causing the idea to catch on and continue to
| be ellaborated, because having specificed this mechanics well
| enough, then maybe and only maybe it might be possible to cause
| at least an analogue of it to exist and that'd be awesome.
| dogma1138 wrote:
| We don't know that Dark Matter exists other than we know there
| is (a lot of) mass missing which is needed to reconcile our
| observations (or we need to modify our theories around gravity
| which is where things like MOND come into play).
|
| Dark Matter is just a placeholder term for that missing mass
| with a lot of candidates ranging from normal (baryonic) matter
| to more and more exotic things.
|
| Negative mass does not contradict existing theories such as the
| standard model in fact it's somewhat built into them.
|
| But overall yes we haven't found any evidence of it actually
| existing we know that anti matter (probably one of the best
| candidates for it) has positive inertial mass from
| experimentation we didn't experimentally proven that it's
| gravitational mass is also positive but it most likely is as if
| it isn't it would be probably the most interesting discovery
| since it would violate the equivalence principle.
|
| In general you'll find people getting excited about any
| possibility for an FTL means of transport since otherwise we
| are unlikely to ever be able to explore the universe with
| anything other than telescopes.
|
| I fore one hope that we do find a way around the pesky speed
| limit because if not it seems that it's quite a bit of waste of
| space otherwise.
| Maursault wrote:
| > It's not like dark matter, something we know exists but don't
| understand
|
| No one _knows_ that dark matter exists, as it is only
| hypothesized. It is quite possible that dark matter does not
| exist.
| zionic wrote:
| Does it require negative _mass_ or negative space-time
| compression?
|
| We know gravity waves exist, so space time can oscillate
| between 0 and N where N is positive right? Are we so sure there
| is not a -N < 0 < N?
|
| Not even close to an expert in this stuff.
| mabbo wrote:
| They explain part of that in the article
|
| > Today, however, it's recognized that what's needed isn't
| necessarily negative mass or negative energy; that was simply
| the way that Alcubierre recognized one could induce the needed
| "opposite type" of curvature to space from what normal mass or
| energy causes.
|
| There's other options, and also we aren't 100% certain negative
| mass/energy can't exist (but probably not...)
|
| Edit: changed my tone because I was being a snarky jerk.
| q-big wrote:
| > No, we didn't accidentally create a warp bubble.
|
| ... we consciously did.
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