11 ms·
Thought experiments that fray the fabric of space-time
- kelseyfrog 2y agoI still don't understand why a black holes needs an inside at all. If they are equivalent to their surface then why not dispense with having an interior and just be a surface?
- twiceaday 2y agoWhy isn't the surface smaller then? Probably something inside is pushing out? It's full? Also on the way to a black hole bodies clearly have insides. Do they somehow evaporate the moment a black hole forms? Edit: My understanding is that all bodies are the size that they are because the inner/outer pressure equalizes, and this has many equilibriums based on the makeup of the body. Black holes are the ultimate degenerate last-stand where the make up is basically raw "information" which cannot be compressed any further while allowing said information to be recovered, which seems to be a fact of our universe. And it just so happens that the amount of information is proportional to the surface area of the black hole rather than its volume, which is probably a statement about how efficiently information can be compressed in our universe. One dimension is redundant?
- crackez 2y agoSince when is the surface of the universe that of a hypersphere?
- enkid 2y ago"Pressure" as a concept doesn't apply to black holes. They are the size they are because of their mass. The bigger the mass, the larger area where their gravity is so great light can't escape. Scientists model black holes as only have a mass and a spin on the inside because that's all the external universe cares about. Information being inscribed on the exterior is an artifact of tike dilating as an object approaches a black hole, iirc.
- JumpCrisscross 2y ago> Why isn't the surface smaller then? Probably something inside is pushing out? The surface of space doesn't require something in a higher dimension pushing it out. That such an object may appear to have internal volume from our perspective doesn't need to be any more real than the apparent depth behind a mirror.
- naasking 2y ago> Why isn't the surface smaller then? Probably something inside is pushing out? Hoberman spheres expand and contract via forces that act only along the structures that make up the surface, and this is a simple classical object. I don't see why a more exotic physical object like a black hole couldn't only have properties defined by its surface.
- lisper 2y agoBecause if you free-fall into a black hole you can go past the event horizon.
- kelseyfrog 2y agoCan we? Is there a way to test this assumption? If not, then it's not science, right?
- mr_toad 2y agoIf you free fall into a black hole you are testing it. I don’t think that not being able to communicate your results makes it not scientific.
- kelseyfrog 2y agoI think the test involves communicating your results. It's the same thing with the afterlife
- amoss 2y agoPublish or perish made manifest.
- LargoLasskhyfv 2y agoMaybe it could be faxed back in time through a white hole?
- 1970-01-01 2y ago"Remember kids, the only difference between screwing around and science is writing it down."
- malaya_zemlya 2y agoThere's a theological doctrine called https://en.wikipedia.org/wiki/Eschatological_verification https://en.wikipedia.org/wiki/Eschatological_verification that claims that statements like "there's God" or "there's afterlife" are perfectly fine verifiable scientific statements, except that their verification come after death or Second Coming. Your comment reminds me of it.
- bongodongobob 2y agoA surface implies an interior, otherwise it's a just a point. A surface is a boundary, by definition there is another side, something that is being partitioned.
- kelseyfrog 2y agoI'm not a topological expert, but I'm pretty sure you can have a surface without an interior. A unit sphere would be a good example of a surface without an interior.
- bongodongobob 2y ago? It by definition has a radius of 1.
- krukah 2y agounit sphere != unit ball The former is the boundary, the latter is the interior + boundary. One of the great arbitrary naming conventions of math.
- magicalhippo 2y agoMinor nitpick, the ball might be closed or open, depending on whether the boundary is included or not, respectively.
- JumpCrisscross 2y ago> surface implies an interior, otherwise it's a just a point Space-time is not Euclidean geometry under GR.
- mr_toad 2y agoBut it is continuous, at least until you hit or pass through the singularity.
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- thebricklayr 2y agoAgreed. Couldn’t black holes warp spacetime to the extent that there is no such place as “inside”? Time dilation is infinite at the event horizon, after all. As you approach the event horizon, your frame of reference slows asymptotically to match that of the black hole while the universe around you fast-forwards toward heat death. I’d expect the hawking radiation coming out at you to blue shift the closer you got until it was so bright as to be indistinguishable from a white hole. You’d never cross the event horizon; you’d be disintegrated and blasted outward into the distant future as part of that hawking radiation.
- WantonQuantum 2y agoThe time dilation at the event horizon is infinite for an external observer. It appears that the person falling into the black hole slows down and never passes the event horizon. They redshift until you can't see them anymore. For the unfortunate person falling into the black hole, there is nothing special about the event horizon. The spacetime they experience is rotated (with respect to the external observer) in such a way that their "future" points toward the black hole. In a very real sense, for external observers there isn't really an interior of the black hole. That "inside" spacetime is warped so much that it exists more in "the future" than the present. Professor Brian Cox also says that from a string theory perspective there isn't really an inside of a black hole, it's just missing spacetime. I tried to find a reference for this but I couldn't find one. Perhaps in his book about black holes. I'm no physicist so happy to be corrected on any of the above!
- tsunamifury 2y agoYou know string theory is now generally considered a large scale fraud perpetrated by cox to maintain funding right?
- WantonQuantum 2y agoFound Sabine Hossenfelder's HN account! I am, of course, joking but she posts this sort of easy and empty clickbait.
- hoseja 2y agoBlack hole insides is another Penrose universe.
- mensetmanusman 2y agoWell stuff started on what seems like the inside, maybe space rips and everything floats to the shell?
- lisper 2y agoThere is an even simpler thought experiment you can do to reach this conclusion: consider what the result of measuring anything to an infinite precision could possibly look like. It would require somehow recording an infinite amount of information. How would you do that, particularly when you take into account that everything you can interact with to make an information storage device is subject to the Heisenberg uncertainty principle?
- oniony 2y agoIt would simply be written down on an infinitely long strip of paper.
- tonetegeatinst 2y agoMöbius strip for double surface area....I can practically see the cheese TV comercial
- __MatrixMan__ 2y agoYou could use a Turing machine tape for the job. I'm told they're stored in the parentheses mines beneath MIT, somewhere near the point masses.
- thfuran 2y agoThe shelving down there is frictionless, so they're often not so nearby.
- enkid 2y agoJust because you can't record something doesn't mean it doesn't exist.
- lisper 2y agoWho said anything about recording? What would the subjective experience of measuring something with infinite precision possibly be like?
- JohnMakin 2y agoPlease stop trying to present information in this style of webpage, I am begging you. Besides being an abysmal way to present scientific information, every time someone posts one of these it happens to be a topic I am extraordinarily interested in, but due to disabilities I have, I cannot read it even if I wasn't tremendously annoyed by it.
- pmontra 2y agoIt's really bad even for me on my phone. The text content fades away before I can scroll it completely into view. No reader mode available.
- not_a_bot_4sho 2y agoSame here. I gave up on reading it once the diagram animations made it near impossible
- selimthegrim 2y agoHow could it be made more accessible to you?
- JohnMakin 2y agoreader mode supported. sometimes they are sometimes no.
- smolder 2y agoI was disappointed to see reader mode wasn't available, and tried to find some other plugin to just show me the text. The couple plugins I tried could not parse it, nor could the text-only browser I downloaded called ViolonCello. (It only renders header and footer text.) It's very frustrating.
- oniony 2y agoThey could be regular web pages without the silly scroll animations, just like in the good old days.
- DiscourseFan 2y agoI’ve said this so many times now. Contemporary physics would greatly benefit from reading Kant. The extent of his influence on contemporary physics, especially with regard to space and time, is so great and the knowledge of his work so little in the scientific community of today. Almost all the great physicists of the 20th century were familiar with Kantian philosophy and were heavily informed by it.
- JumpCrisscross 2y agoWhat would Kant add to this discussion that the physicists in the article haven't considered? (Saying this as someone who's read Kant twice and agrees with most of what he claimed. Outside his taste in music.)
- 23B1 2y agoI too am wanting to know the answer to this question, sounds like an intriguing concept!
- DiscourseFan 2y ago>Saying this as someone who's read Kant twice I assume you mean the Critique of Pure Reason? Kant's Oeuvre is quite vast, though it wouldn't be unreasonable to have read the 3 critiques twice. >What would Kant add to this discussion that the physicists in the article haven't considered? Kant himself, I'm not sure, but its his model of the cosmos that we employ today, and spatio-temporality is a development out of his critical philosophy, especially his aesthetics. If you want to break space and time out of spatiotemporality it helps if you are familiar with the metaphysical undergirding of contemporary physics, since we have not treated them as separate since Einstein, even though Kant originally kept them as completely separate intuitions and did not seek to unify them but only to try and see what happens when they are set in relation. That is to say that spatiotemporality is, if we are being good Kantians, an entirely negative, transcendental view of space and time since it does not appear at the level of the senses but rather as an abstraction from them. But if we treat the second-level abstraction as real then we are bound to make errors about the empirical world, as returning to the critical project would, I believe, greatly help in re-evaluating our empirical methods.
- johnsanders 2y agoI remember as a kid asking how many possible speeds there are between 60 mph and 0 mph. Infinite right? So how does the car get from 60 to stopped when mom hits the brakes?
- transfire 2y agoZeno’s paradox.
- JumpCrisscross 2y ago> how does the car get from 60 to stopped when mom hits the brakes? The sum of an infinite series can be finite [1]. [1] https://www.mathcentre.ac.uk/resources/uploaded/mc-ty-convergence-2009-1.pdf https://www.mathcentre.ac.uk/resources/uploaded/mc-ty-conver...
- wzyoi 2y agoNot infinite if we take into the account that we have a physical car. Speed many but not infinite steps. Everything is infinite if we think this way.
- ruthmarx 2y agoThat you can split any finite length into an infinite amount does not equate to having to traverse infinite numbers.
- mensetmanusman 2y agoIn the same way a single second occurs.
- cloudking 2y agoThe car (and people) never truly stop moving, the earth is in orbit, spinning and rotating around the galaxy.
- AIorNot 2y agoBesides the silly, but inevitable HN complaints about the format of the webpage presentation, (great presentation btw) The fundamental challenges these experiments (and others) surface is a deep challenge to the traditional narratives of Materialism or 'Physicalism' as our understanding of what existence is. In essence science and human knowledge has lept forward technologigcally over the past 400 and esp the past 100 years because we started assuming the world was physical in nature, material and metaphysically, ie that it reduced to fundamentally physical things we could quantify and measure. Yet, the older I get the more inclined I am to believe in some form of Idealism.. Not only in Idealism but I'm leaning towards the belief that some kind of fundamental universal Consciousness is the only fundamental property or baseline to the universe or to existence. Time and Space is not fundamental. Locality isnt true.
- andrekandre 2y ago> I get the more inclined I am to believe in some form of Idealism.. Not only in Idealism but I'm leaning towards the belief that some kind of fundamental universal Consciousness is the only fundamental property or baseline to the universe or to existence. > Time and Space is not fundamental. Locality isnt true. thats interesting, but im curious what the basis for that thought comes from?
- deleted 2y ago[deleted]
- ur-whale 2y agoThe (what very much feels like an) assertion that "If a collision concentrates enough energy in a small enough region, the particles form a black hole" seems very much rabbit out of a hat. That supposes in particular that general relativity is still a valid theory at these minuscule scales, something that I believe has never been experimentally verified. If general relativity's equations do not work at the planck scale, we know strictly nothing about black hole formation.
- nyc111 2y agoBut physicists already made spacetime redundant by dividing it back to space and time. This was started by Dirac who restated general relativity with Hamilton formalism. The slicing of spacetime was completed in the sixties with ADM formulation. Also we know spacetime does not exist in practice because when we say "universe is expanding" we mean "space is expanding." It makes no sense to say spacetime is expanding.
- raattgift 2y agoYour comment is divorced from the coordinate freedom of general relativity. In any spacetime you care to do an ADM split on, there are an infinite number of real-valued smooth scalar fields whose gradient is everywhere non-zero and timelike available to serve as the coordinate time. In the standard cosmology the at-rest isotropic and homogeneous distribution of matter provides an obvious coordinate time function, but physics still has to work for other inertial and accelerated observers, so there is nothing preventing anyone from using a non-comoving observer's proper time in the ADM split. Nits: * Hamiltonian formulation of general relativity * ADM formalism The expansion is in the metric, and most visible (and most amenable to interpretation as an expansion of space) when using comoving coordinates. However, we are allowed to work in any system of coordinates, and when we do a general coordinate transform, we lose the interpretation of the metric expansion as an expansion in space. ("We see in both [Milne & de Sitter] cosmologies that the interpretation of redshift as an expansion of space is dependent upon the coordinates one chooses to calculate z." -- https://academic.oup.com/mnras/article/422/2/1418/1036317 https://academic.oup.com/mnras/article/422/2/1418/1036317 final sentence in §3.4 de Sitter space). The standard cosmology's FLRW spacetime (and also de Sitter space, where the vacuum constant positive scalar curvature makes for an easier-to-understand expansion history) is time-orientable. There are more points in spacetime in the future direction from an arbitrary point anywhere in the entire spacetime, than in that point's past. However, the real distribution of matter is in our universe lumpy, as is easily demonstrated right here on Earth. Standing on the ground you can tell that locally there is neither isotropy nor homogenity (you can see quite far up into the sky, but not so far into the ground). Moreover, there are differences in isotropic pressure, convection, heat conduction, and shear stresses between the air and ground, none of which are features of the perfect fluids in the FLRW model. So locally the FLRW metric is not suitable, and since the Earth is very much not vacuum de Sitter is even less suitable. Consequently it should not offend anyone to read that Manhattan isn't undergoing cosmological expansion. Most things within ten kiloparsecs of here are gravitationally collapsing. It requires coordinate contortions to interpret interplanetary or interstellar space in the Milky way as expanding, and switching to different systems of coordinates will blow up that interpretation. A "swiss cheese" universe with collapsing vacuoles in an expanding cosmology reflects that it's only when we go from ~kpc length scales to ~Gpc length scales that the distribution of matter behaves enough like perfect fluids to allow for an exact solution to the Friedmann equations. The collapsing vacuoles are usually modelled like Lemaître-Tolman-Bondi with a thin shell boundary; this results in a vacuole that time-orientable and has fewer spacetime points in the future direction. "Hole" time functions and "cheese" time functions must be different (hole clocks tick slower as they fall towards the centre).
- tsunamifury 2y agoAh yes a debate between scientists with theories which are so far removed from Science that it can’t be called anything other than fairy tails For those who aren’t in the know physics is in a crisis where huge portions of theoretical physics are turning out to be complete nonsense.
- deleted 2y ago[deleted]
- gcanyon 2y agoGood lord that was awful to read. Text popped into existence half-off the screen, disappeared just as it was entering the screen, etc. I'm operating on a 15" MacBook with a reasonable-sized window, and yet I had to scroll carefully back and forth to catch the text. And no reader mode with just the text.
- dang 2y ago"Please don't complain about tangential annoyances—e.g. article or website formats, name collisions, or back-button breakage. They're too common to be interesting." https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
- gcanyon 2y agoThe observational limits described here remind me very much (albeit that I read it 40 years ago) of Blood Music by Greg Bear. The ending (as I remember it) has nano-scale intelligences observing the universe so closely that the fabric of spacetime starts buckling under the strain.
- hoseja 2y ago>If a collision concentrates enough energy in a small enough region, the particles form a black hole and never reach a detector. Is this actually experimentally confirmed?
- simne 2y agoFortunately or not, largest artificial accelerators are still not powerful enough to produce artificial black hole. Sometimes from deep Universe, appear particles with much more energy than achieved at labs, and some theories say, their energy enough to create BH, but have not confirmation with decades observations, may be because scientific method need tens or better hundreds appearances in one place to confirm, but have less than half dozen.
- naasking 2y agoTo the extent that black holes are confirmed, sure.
- hoseja 2y agoI have major doubts there wouldn't be major weirdness at such an intersection of QM and GR.
- naasking 2y agoAny black hole should exhibit such weirdness around the event horizon and singularities though. If we had a reconciliation between GR and QM that resolved these issues for gigantic black holes, then arguably we'd also understand small black holes.
- hoseja 2y agoThat's what I'm doubting. There's no guarantee large-scale GR holds at microscopic scales.
- m3kw9 2y agoPlank length is our physical limit, a humans. Maybe another species smarter than us can prove deeper via some higher dimensions, exotic physics
- stared 2y agoI am not sure what the thought experiment is here — it is more like two facts, one about the Planck scale (and things break there) and the other about a black hole (its information is proportional to its surface). However, there are deeper things around. Seth Lloyd suggested that we use information density to derive general relativity from quantum theory: https://arxiv.org/abs/1206.6559 https://arxiv.org/abs/1206.6559
- yoaviram 2y agoNot only are these not thought experiments by most definitions, this is also not really an article by most definitions. It's as if the author had a few interesting yet unrelated thoughts, scribbled them down and covered up for the lack of depth with fancy illustrations and transitions.
- dentemple 2y agoThey're not unrelated thoughts. The author is describing current mysteries in physics related to the edges of what we could theoretically measure. The article actually seems clear and straightforward to me. I'd only add that I wish there were links at the end regarding what scientists are proposing right now for resolving those mysteries.
- mnky9800n 2y agoBut they are not thought experiments. That much is true.
- gibsonf1 2y agoReality is continuous and always changing. Space-time is just our human way of focusing on aspects of reality to understand it. Space-time is about human perception, not the reality we are trying to understand.
- rbanffy 2y agoOne of my favorites is a different interpretation of the events happening inside a black hole being inscribed in its surface: that there is no inside and the events happen at the surface, which seems totally normal because spacetime is so extremely stretched there things don't realize they look like a 2D surface from outside observers.
- wormius 2y agoDid quanta get bought by Forbes or something? I seem to recall they had a lot more informative articles than whatever this was. Further, there is no indication on how the first two postulates/statements force one to conclude the latter. Also? The whole format of the thing screams "LOOK AT ME". This is a very weird... thing (I hesitate to call it "article") coming from a site that previously had some interesting content (in the actual sense of the word, not the current colloquial sense) Is the problem the author can't let go of not understanding? That they need everything to be, for lack of a better term, quantifiable? That there must always be no boundary to our ability to measure? Do they demand an answer to why there is a limit to what we can see at the end of the universe (beginning/surface)? Is this something AI shat out for clicks? Did they fire actual writers at quanta? Did they smoke a bunch of DMT? Are you ok, quantamagazine? Do you need us to call for help? I'm a bit annoyed that I had to read that, thinking there would be some point, that the top thread was exaggerating, but they weren't.
- mnky9800n 2y agoI typically love quanta magazine but this particular page was very annoying to scroll through
- 1970-01-01 2y agoGood stuff for a sci-fi novel. Black holes become the spinning hard drive platters of the universe. To preserve the Earth from existential destruction, we must fling it into a black hole. This takeaway is a variation on an old theory. Perhaps we are already inside a black hole, and the expansion of spacetime is the rate of the black hole's growth in another universe.