[HN Gopher] What is spacetime made of?
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What is spacetime made of?
Author : nyc111
Score : 44 points
Date : 2022-11-23 06:08 UTC (1 days ago)
(HTM) web link (www.scientificamerican.com)
(TXT) w3m dump (www.scientificamerican.com)
| satvikpendem wrote:
| Why, luminiferous aether of course!
| akomtu wrote:
| If we're talking about aether, then it's worth mentioning that
| the seven elements have been traditionally earth, water, fire,
| air, aether (magnetic field), space (aka the emptiness) and
| consciousness.
| signalToNose wrote:
| Site down?
| WastingMyTime89 wrote:
| This article is framed in a way I find epistemologically suspect.
| It confuses observations, models and truth. Some of its
| intertitles are meaningless like "Will we ever know the real
| nature of space and time?".
|
| The article is actually about models in which spacetime is an
| emergent property of more fundamental structures: string theory
| and loop quantum gravity. Both face a lack of experimental
| evidences validating their predictions.
| saeranv wrote:
| I don't think this criticism is fair. For example, the article
| in the section quoted below clarifies that string theory hasn't
| been proven experimentally, and is being investigated
| mathematically, here:
|
| > But string theory is difficult to understand--it lives in
| mathematical territory that has taken physicists and
| mathematicians decades to explore. Much of the theory's
| structure is still uncharted, expeditions still planned and
| maps left to be made. Within this new realm, the main technique
| for navigation is through mathematical dualities--
| correspondences between one kind of system and another.
| Koshkin wrote:
| But the question, then, is: is there reality behind the model
| (or, rather, how close to reality the model is)? The answer
| lies in how _accurate_ the model is. This is all we can know in
| this regard.
| pyinstallwoes wrote:
| No matter how good a model is, a simulacrum is still a
| simulacrum.
| WastingMyTime89 wrote:
| But knowing if there is reality behind the model is not a
| scientific question. There is no tool in science which can
| answer that. The only thing that matters is how well the
| model predicts what we observe.
|
| One can believe that's a form of truth but people should be
| conscious that it is merely a belief.
| edgyquant wrote:
| Of course not all these models are is a description of the
| mammalian brains tooling to make prediction. There is not a
| single reason to believe it's the real nature of "reality,"
| whatever that is supposed to mean.
| JakeAl wrote:
| Scientific American was once like reading well illustrated
| research journal paper. Today it's the "science" equivalent of
| People magazine.
| pyinstallwoes wrote:
| > It confuses observations, models and truth.
|
| Succinctly describes the global zeitgeist.
|
| Perhaps modern idioms are to blame with relation to the copula.
| We seem to say things are what they are without a qualifier on
| what type of existence it has.
| awinter-py wrote:
| sigh
|
| not sure why you'd try explaining LQG to a layperson without
| 'background independence' as a motivating concept
|
| would rather see pop sci invest in explaining the actual concepts
| to laypeople, rather than their philosophical implications
|
| like give me an interactive intro to witten diagrams as a way
| into ads-cft + holography
|
| or like make lie groups interesting somehow please
|
| the theoretical physicist they interview in the first paragraph
| has videos about her specific work (kozsul duality) which go
| deeper into the concepts
| https://www.youtube.com/watch?v=VW87-4t-Fsg
| swayvil wrote:
| Probably emotions. An endless torrent of the stuff. Like your
| favorite song, minus the words and notes.
|
| Which is then interpreted as sights, sounds, smells, thoughts (we
| love those), feelings, time, space, things, pizza, money, etc.
| kordlessagain wrote:
| Spacetime is the Ether, in my opinion. This was tested, but never
| proved/disproved:
| https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_exper...
|
| Here's a paper on it:
| https://www.researchgate.net/publication/283669822_Connectio...
|
| The upshot is a charged shell will modify the
| acceleration/inertia of particles inside the shell, according to
| Weber's Electrodynamics:
| https://en.wikipedia.org/wiki/Weber_electrodynamics
| [deleted]
| hdjjhhvvhga wrote:
| Well, the concept of ether/aether had many forms and some of
| them were definitely disproved. The wiki link you gave
| basically confirms the absence of aether at increasingly
| smaller scales.
| duozerk wrote:
| > Spacetime is the Ether, in my opinion. This was tested, but
| never proved/disproved
|
| Am I missing something ? because you just linked an article
| that clearly disproves your first assertion.
|
| ... and followed it by what looks like a poorly written
| research article by a self described "independent physicist"
| (https://nitter.net/tavi_balaci) with only three published
| articles and all kinds of red flags.
| kordlessagain wrote:
| Yeah, I hear you.
|
| > After all this thought and preparation, the experiment
| became what has been called the most famous failed experiment
| in history.
|
| We accept Maxwell's equations as the truth, not Weber. I'm
| not saying this alternate approach is true, it's just my
| opinion we missed something, collectively.
|
| The paper is likely poorly written, but it's something I
| found while researching this a few years ago. Just sharing it
| for others to see. Again, my comment isn't claiming one way
| or the other...
| TEP_Kim_Il_Sung wrote:
| Your'e missing Phlogiston. It surrounds us and penetrates us.
| It binds the galaxy together.
| dimensionc132 wrote:
| college_physics wrote:
| these folks are doing their best to combine and extrapolate
| mathematical principles to extremes (an approach which, nota
| bene, did prove spectacularly successful in explaining huge parts
| of the universe earlier on) but the results of this exercise has
| been exceedingly poor for almost half a century now.
|
| at some point we must give up or admit that the nature of the
| game has changed. In a sense even the tiniest piece of
| experimental evidence that probes (or at least remotely reflects)
| the _actual_ inner workings of "quantum" spacetime would be
| worth more than this enormous cumulative effort to infer what is
| happening on the basis of abstract symmetries and what not.
| zachf wrote:
| You might be excited by [0]. The idea there is to study a novel
| phenomenon in strongly-coupled quantum systems that is very
| complex to see ordinarily, but becomes easy to understand when
| you look at the same physics from the gravitational
| perspective. That would be a nontrivial experimental check of
| AdS/CFT duality. It's effectively a novel form of "quantum
| teleportation" wherein an excitation is transmitted between
| systems using the quantum equivalent of a gravitational
| wormhole [1].
|
| [0] https://arxiv.org/abs/1911.06314
|
| [1] https://arxiv.org/abs/1608.05687
| awinter-py wrote:
| there were cool things that came from pure math in the early
| quantum + relativistic era -- lasers + black holes were math
| constructs before we thought to build them / look for them in
| the sky
|
| I think (as an outsider to this field) the 'probing' now has
| fallen to the quantum computing people. their day job is
| basically making houses of cards out of entangled particles; if
| there are tricks to be learned about entanglement, they may be
| the ones to find them
| ngcc_hk wrote:
| And superposition. The other part like quantization of field
| and the wave function ... decoherence.
| thriftwy wrote:
| Are there any formulas supporting this or that composition of
| spacetime? Until there's math it's a simple handwaving.
| zachf wrote:
| One of the most important papers in this field is [0]. (As is
| common in science, it built on a long history of nearby ideas,
| e.g. [1].) An important calculation done around this idea is
| presented in [2], in which remarkable progress is made on
| Hawking's black hole information paradox. All of these papers
| have some amount of mathematical backing, but you'll find
| plenty of formulas and calculations in [2]!
|
| [0] https://arxiv.org/abs/1306.0533
|
| [1] https://arxiv.org/abs/1005.3035
|
| [2] https://arxiv.org/abs/1908.10996
| thriftwy wrote:
| > General relativity contains solutions in which two distant
| black holes are connected
|
| I can see these as artifacts of insisting to work in 3D
| coordinates and dealing with artifacts of projection where it
| breaks down, instead of working in honest 4D coordinates
| where formulas are much simpler and everything is smooth.
|
| How would two connected black holes look like in Kruskal-
| Szekeres coordinates? Where's the firewall in case of
| Kruskal-Szekeres coordinates? Where's the firewall at all if
| the event horizon seemingly moves away from you as you
| approach the wormhole?
| zachf wrote:
| The existence of those solutions is independent of a choice
| of coordinates. (Nothing in GR is ever allowed to depend on
| coordinates, in the end!) The existence of the second
| asymptotic region is easiest to see from the Penrose
| diagram of the Schwarzschild black hole. A derivation of
| this that uses Kruskal coordinates is in [0], see Figure
| 3.3 for the result.
|
| [0] https://scholar.harvard.edu/files/yshi/files/physics_21
| 1r_-_...
| thriftwy wrote:
| Thank you for this insightful link. I'm still not sure
| why one would need to explain that (such as an "ERP
| pair") instead of just the topology of space being what
| it is in this specific case. As far as I know these
| models fail to produce any interesting prediction and
| even explain all the known facts in their terms.
|
| One would need to find out which stellar evolution paths
| would lead to black holes being linked by a wormhole.
| This assumes no magic happening beyond the event horizon
| and the evolution of matter inside it following already
| known laws.
| [deleted]
| ogogmad wrote:
| Scientific American's reputation is in the toilet:
| https://www.math.columbia.edu/~woit/wordpress/?p=13152
|
| I don't recommend wasting your time.
| butMebbe wrote:
| Middle management idiocracy has taken over to "create jobs"
| everywhere.
| Akronymus wrote:
| Dont they kinda have to, to avoid falling into problems with
| the DEI crowd?
| TEP_Kim_Il_Sung wrote:
| ad majorem Dei gloriam
| zachf wrote:
| Peter Woit has strong opinions but they're often not
| representative of the physics community as a whole. In my
| opinion, which as a physicist myself I think matters as much as
| Woit's (i.e. not much), Scientific American is variable in
| quality, but I wouldn't dismiss the article before reading it.
|
| This article does a pretty good job of summarizing a range of
| modern ideas about spacetime. I see that it introduces laymen
| to some of the important names in the field, including van
| Raamsdonk and Maldacena, and presents their important and
| influential work in an accessible way.
|
| No paywall version:
| https://web.archive.org/web/20221124171006/https://www.scien...
| ogogmad wrote:
| There's also nonsense like this:
| https://www.scientificamerican.com/article/physicists-
| need-t...
|
| https://scottaaronson.blog/?p=6202
|
| https://www.scientificamerican.com/article/nasa-needs-to-
| ren...
| zachf wrote:
| Is this what the kids call "cancel culture"? I'm judging
| the quality of the OP article, not the sum total of
| everything that they've ever published. The politics of the
| editors of Scientific American may not align perfectly with
| my own, but it's still worth engaging with their content
| when it's thoughtful, and I think this article is an
| example of that.
|
| Edit: actually that's not true, I just wrote that SA's
| overall quality is "variable". So yes, I already conceded
| not everything they publish is a winner. And for what it's
| worth, I agree that the piece they published on E. O.
| Wilson was in very poor taste.
| swayvil wrote:
| At some point in the past SA contradicted some point of
| dogma. Now their output is forever picked over for
| evidence supporting a case for, yes, "cancelling them".
|
| That's how they do it these days.
| ogogmad wrote:
| No, it's not "cancel culture". If you're not an expert in
| the area, you need to know how trustworthy the
| publication is. As it stands, there are indicators that
| it's not trustworthy.
|
| [edit] Sure, the article might have some value. I can
| accept that. Thank you.
| zachf wrote:
| I have a PhD in physics. I gave my assessment of the
| article in the first reply above. You're welcome to
| disagree, but since it seems you're mostly interested in
| rejecting the article on the basis of who published it
| instead of the content, perhaps this is a dead end.
|
| Edit: appreciate the edit :)
| api wrote:
| It's what the kids call click bait of the subspecies
| known as "trolling for controversy." It comes in two
| flavors: "woke" and "anti-woke." In all cases the goal is
| to get you to click so someone can sell ads.
| [deleted]
| mikewarot wrote:
| Non-majority opinion/Guestimate of reality follows:
|
| I think that spacetime is an emergent phenomenon of something
| that has no dimensions. Imagine RAM in your computer, inherently
| there's an address dimension when the CPU needs to read/write
| data, but the actual physical location doesn't matter (other than
| latency).
|
| How correlated two bits of matter/energy/spacetime are is a good
| proxy for distance, except when it isn't. A photon leaves a star,
| then strikes your eye a billion years later, and those events
| _could_ be entangled, as far as the photon is concerned, they
| happened at the same instant in time.
|
| However the laws of physics work, I don't see how there can be
| any direct mapping between what we see, and the underlying
| quantum phenomenon, as long as light and quantum superpositions /
| entanglement, are things.
| spiantino wrote:
| I think what you're describing is nonlocality? It's well-
| described by quantum mechanics, which sits on top of regular
| old continuous spacetime. Is that not the direct mapping you're
| talking about?
| LanceJones wrote:
| "I think that spacetime is an emergent phenomenon of something
| that has no dimensions."
|
| I actually think that's a helpful statement. If you read/watch
| Bernardo Kastrup or Don Hoffman, this is in line with how they
| present their primary argument about consciousness being
| fundamental.
| colechristensen wrote:
| This kind of terminology soup speculation isn't helpful. Don't
| muddy the waters when you don't know enough to add anything of
| value.
| Koshkin wrote:
| The article itself isn't much better:
|
| _If space is made of entanglement, then the puzzle of
| quantum gravity seems much easier to solve: instead of trying
| to account for the warping of space in a quantum way, space
| itself emerges out of a fundamentally quantum phenomenon._
| zachf wrote:
| I have a PhD in a closely related field and I'm not sure
| what you mean--this sentence is well-formed and basically
| correct, if slightly simplified to appeal to laymen.
| lachlan_gray wrote:
| Stephen wolfram is working on something like this, he wants to
| model the laws of physics entirely with recursive graph
| rewiring. I haven't looked into it, but he says that space and
| time turn out to be emergent quantities when you look at it
| like that. He also has things to say about quantum and
| relativistic effects
|
| https://m.youtube.com/watch?v=CLXyDCISsUY&themeRefresh=1
| tombakt wrote:
| > A photon leaves a star, then strikes your eye a billion years
| later, and those events could be entangled, as far as the
| photon is concerned, they happened at the same instant in time.
|
| If a photon does not experience time then I find it challenging
| to imagine that it could have a perspective at all.
| TEP_Kim_Il_Sung wrote:
| I once read somewhere that if you swap time in spacetime with
| gravity, then the universe turns crystalline, and lots of
| stuff makes more sense.
|
| In that way, perhaps photons experience other stuff.
| dreamcompiler wrote:
| It gets worse. Not only do photons not experience time, they
| don't experience space either. From a photon's point of view,
| it's always every "where" it needs to be. Which means there's
| no distinction between places. Which means space doesn't
| exist, from a photon's POV.
| Razengan wrote:
| Memory addresses?
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