7 ms·

The Unraveling of Space-Time

90 points by nsoonhui 2y ago

ninacomputer 2y ago
Just in passing, Quanta magazine has been excellent lately!
- dist-epoch 2y ago
  It was also excellent in the past! It's excellent in general
- nuancebydefault 2y ago
  It was observed as excellent in your universe, in our universe...
soup10 2y ago
My understanding of black holes is rather straightforward, gravity is so strong it prevents light and matter from escaping it's orbit. That does not mean that nothing is there or that all physics as we know it breaks down. Simply that our instruments can't observe what's there directly.
- marcyb5st 2y ago
  Not so simple. If there is no collapse into a singularity, what happens to the matter? Theoretically speaking, we have no clue to what happen to matter beyond neutron stars levels of degenerate pressure. Specifically, what happens to fermions once all the quantum states are filled and they are still constrained by all the other fermions around them? We have no idea (and everything seems to point to a collapse into a singularity). If, instead, there is an actual singularity (which has infinite density) it means that the curvature of space time is infinite, which our current theories can't cope with. Additionally, if singularities have infinite density, how is it that black holes can have different masses? A singularity can only be characterized by its position in spacetime since it has no size and so there is no space/surface for it to have any other property and yet we see that there are black holes with different masses. Another thing we can't explain with our theories. So yeah, black holes mess with our theories in a fundamental way because as soon as you start pondering what happens inside them we discover that general relativity or quantum mechanics or both break down and so they must be incomplete. Spacetime, being a construct of general relativity is therefore also an incomplete description of the real fabric of space time.
  - soup10 2y ago
    Ok, but in my mind it's a lot like a mystery box, there's a lot of speculation about what's in the box, but without new instruments or new observation techniques, if the light/information from inside isn't reaching us we'll probably not be able to prove what's going on in the box one way or the other. One can claim "space-time breaks inside the mystery box" all you want, but I haven't heard of any testable theories.
    - wanda 2y ago
      Perhaps, but in terms of getting things done and making progress, it isn't very useful to suppose that it is simply a mystery box and that's that. Because if we just accept that, what do we do then? We just sit and wait for some new astronomical observation to give us a clue? that could take forever, and we'd be banking that we have the tech to observe this magic hint. Better to suppose that the theories we have comprise an accurate approximation or partial model of reality, and from there strive to find a better model. The process of doing so will either refine/entrench our current model and our conviction, or it will result in actually finding a better model. Win-win, and all the while, we can still have our telescopes and detectors on for the magic hint we'd be sat waiting for anyway. When things break down into singularities, it can be a pretty good indicator that we've got something wrong. Not necessarily, but in this case, I think we missed something.
      - soup10 2y ago
        Sure, I just think it might have a more "boring" answer than people are hoping for. E.g. behind the veil is something extremely high mass and energy, but it's more akin to a new class of Star rather than something where space, time, mass and energy lose all meaning.
        cruffle_duffle 2y ago
        I mean based on the well tested theories we have now regarding general relativity… it isn’t just gonna be a new class of star. Unless general relativity is flat wrong, which it isn’t. That isn’t to say general relativity is the end all of our understanding of the universe—black holes are a perfect demonstration of where our understanding breaks down completely. Clearly there is a lot more going on than we currently can explain. For it to just be a super dense “new class of star” would first require you to explain why general relativity is completely wrong. And that is the problem. Black holes are weird because they break the well tested equations we currently use to describe what we observe in the universe. If you want my opinion, figuring this shit out (including what we are calling “dark matter”) is gonna unlock a whole new realm of cool stuff for humanity. I suspect there is a reason why we haven’t solved the Fermi paradox and it is because most “intelligent life”, as we imagine it, is living outside our current understanding of the universe. To get into the “cool aliens club”, our understanding of the universe will need to change.
- tiborsaas 2y ago
  If you deepen your understanding it suddenly stops being rather straightforward. Here's a good playlist to warp your head around the subject. https://youtube.com/playlist?list=PLsPUh22kYmNBl4h0i4mI5zDflExXJMo_x&si=CG47O0MFQd7rzMy7 https://youtube.com/playlist?list=PLsPUh22kYmNBl4h0i4mI5zDfl...
psychoslave 2y ago
If there are experiments that can be tried to challenge my own current perspective on the matter, I’m interested. Because to my mind, anything that is said to emerge implies that the dimension we usually refer to as time is already an implicit hypothesis of this anything being able to emerge. And if there is something out of time, then by its very definition it can’t interact with time: - either there’s a connection with time and then at some point there is a change to that thing that can no longer be considered an absolute static thing as there is a before and after event that this thing is attached to, - or this thing is without any relation to time and thus can not be something that engender time itself. To be clear, I think there is still large room for interpretation anywhere formal mathematical means can give us great insights that would be unreachable without them. Agreeing with equations is not agreeing on the interpretation to give to the equations at a larger epistemological picture, and even less on ontological genesis.
- winwang 2y ago
  Consider an unchanging singly-linked list as a universe. Time (or perhaps "the passage of time") in the intuitive sense does not exist for this universe, but it does exist in the sense that there is a global ordering of values. But does the ordering of the values come from the edges or the nodes? The ordering requires both. Or, more humanly(?), a film reel. At least, this is how I would think of it if required to give a simple-but-possibly-off-base answer for a possible way time could be emergent (would love it if someone more educated could correct me). This is also known as the Einstein block universe model. Otherwise, since my physics education is far below the actual bar needed to understand quantum gravity stuff, I think back to thermodynamic microstates and macrostates, and how temperature is emergent.
- guy234 2y ago
  I feel like someone could describe foam emerging from the sea without implying that it is a process in time. It could be thought of as a process relating to the properties of seawater, wave agitation, sand etc. It is possible for a picture, not a video, to depict foam emerging from the sea. Also, there need not be a before or after, or even quantifiable extrinsic changes.
- 2y ago
IAmGraydon 2y ago
Doesn’t spacetime emerge from dimension? In other words, first there was a dimensionless point. Something interacted with this and from that point arose dimension. From dimension, spacetime emerged.
ackbar03 2y ago
Does anyone have a good recommendation for an introductory book on these concepts? I read a bit of The Fabric of Reality but had trouble progressing too far with that one. The author talks about the quantum slit experiment, somehow arrives at the explanation of parallel universes, and then claims anyone who disagrees with this conclusion must have faulty logic. A huge chunk of reasoning behind parallel universes seems to be skipped and I have trouble taking it seriously every time it is brought up.
- sandgiant 2y ago
  Sean Carroll (professor of physics, quoted in the article) has a highly-rated book titled "Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime" [1] which discusses exactly these topics. I haven't read it, but it's on my list. I also highly recommend his podcast "Mindscape" where he discusses this and a range of other topics in science and philosophy. [2] [1] https://www.preposterousuniverse.com/somethingdeeplyhidden/ https://www.preposterousuniverse.com/somethingdeeplyhidden/ [2] https://www.preposterousuniverse.com/podcast/ https://www.preposterousuniverse.com/podcast/
- codethief 2y ago
  > A and then claims anyone who disagrees with this conclusion must have faulty logic. A huge chunk of reasoning behind parallel universes seems to be skipped and I have trouble taking it seriously every time it is brought up. I think your scepticism is generally warranted. There is a reason the many-worlds interpretation is called an interpretation, just like the Copenhagen interpretation and others. The interpretations cannot be logically deduced from the experimental evidence we have. They are attempts to try to make sense of the results. As for book recommendations, I have really liked Tim Maylin's "Philosophy of Physics: Quantum Theory" because of the precision and clarity he brings to the discussion. I should mention, though, that I've got a physics degree.
  - mikhailfranco 2y ago
    Tim Maudlin
bbor 2y ago
A) I like cute scroll effects, but maybe we should consider making them additive rather than completely ephemeral (when screen size permits)? The intro is beautiful on mobile, I'm sure, but it's just kind of irritating on desktop. B) Thanks so much for posting, I had skimmed a few of these articles but didn't realize it was part of a cohesive series. For others, since it's not really obvious at first: the whole series is built to setup the three articles at the bottom, where Charlie Wood examines three competing research groups. Quanta is on fire these days... This is an amazing evolution upon 2020's What is a Particle?, which is an article I've been bringing up in like every other conversation b/c it's so fascinating and accessible. C) Other than the initial complaints about the intro, the article itself is downright groundbreaking webdev-wise. And I called it when I started this comment -- the rest is additive! The way the text deforms around the sliding divs (but quick enough that it probably won't interrupt you since you haven't gotten to it yet) is just beautiful, I don't think I've seen that before. The dynamic, freeform cutouts fit perfectly with the theme, and the background is bold (how many sites are purple??) but indescribably perfect. Of course, the star of the show is the animated "thought experiment" page, even if the transitions are atomic (can't be reversed halfway through by scrolling back up). And the final summary + animation is worth scrolling to the bottom for, even if you don't read the rest of it. Well done Quanta web team, you're seriously raising the bar with this article, IMHO. Inspiring stuff. Is there any magazine ~~article~~ "series" (issue?) that even approaches the beauty and cohesiveness of this one? I'd love to proven wrong by the experts on here ;) [ETA: wow everyone hates the UX, I'm shocked. Why, in particular...? At the end of the day the linked page is just a list of links that appears right near the top, I don't understand the ubiquitous hate! What am I missing?] D) I'm pretty far from critically evaluating the physics surveys themselves, but I certainly found them helpful. Some quotes that are just insanely insightful, the kind of simple, boring statements that edge on superstition through their pure profundity alone: In periods when we are looking for new theories, physics has always become philosophical. Our natural perspective as beings with locations separated by space sticks out as a mathematical oddity. “It’s a reminder that the laws of physics that we perceive in our world don’t seem to be random,” said Sean Carroll (opens a new tab), a physicist at Johns Hopkins University. “They seem to be specific.” “AdS/CFT is an insane suggestion that should be stupid,” said Geoff Penington, a physicist at the University of California, Berkeley who studies holography. “But then you try all these things, and it all ends up being consistent.” For his part, he feels that holography isn’t radical enough. It shows how one dimension of space could emerge, but otherwise all the familiar ingredients of quantum theory are there from the start: some space, locality, and a clock to mark time. Arkani-Hamed feels that all of those elements should emerge together from something more primitive — as they do in surfaceology. It might seem like I’m interested in lots of different things, but I’m not sure if they’re really all that disconnected. At least within math, it is kind of true that sufficiently beautiful things tend to be connected with one another. E) Any friendly experts around to explain what a "lower dimension" representation of a black hole would look like? What's a periodically-repeating 2D manifold, given that circles (flattened spheres) don't pack? I guess it warps to pack nicely? This is a core example they use to explain the broader thesis--which I thought I understood--but I don't really understand in the topological shape of what they're describing, so it ended up confusing me more. In particular I'm commenting on this: So the key to black holes’ underlying structure exists on their surface. “People began to think,” Law said, “that maybe whatever microscopic theory describes black holes lives in a space-time with one lower dimension.” F) Even more fundamentally, can someone explain why we can't just assume that there isn't spacetime inside black holes? If everything's pointing towards their contents being entirely contained within their infinitely-thin surface, why can't we just embrace that? In other words, that whatever determinations make up the universe are undetermined in those places? That the diameter of every black hole is 0, when considered from the inside? I'm assuming the answer is "complicated math says no", but I'm failing to confirm that. Sorry for the spam, won't mind if this is deleted -- it's just terribly helpful to write as I go. If you're scrolling by, I highly recommend bookmarking this series in full! And if you work at Quanta and are reading this: you're awesome.
dang 2y ago
[stub for offtopicness]
- leetrout 2y ago
  I really am over the stupid scroll hijacking sites.
  - MathMonkeyMan 2y ago
    Fucked up my phone jeez.
  - king_magic 2y ago
    Seriously. This page looks and interacts like shit on my iPhone. Gave up and went to reader mode. Still sucks.
  - bmitc 2y ago
    Agreed. Quanta has great content, but man alive, this particular "article" (?) is completely unbearable. I wish they'd just release these special issues as actual print magazines. I'd love to have them in the flesh, but Quanta very rarely publishes their stuff on paper.
  - jazzypants 2y ago
    It's just gonna get worse now that it's easy to implement with CSS. https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_scroll-driven_animations https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_scroll-...
    - leptons 2y ago
      Firefox and Safari don't support it. https://caniuse.com/mdn-css_properties_animation-timeline_scroll https://caniuse.com/mdn-css_properties_animation-timeline_sc...
      - jazzypants 2y ago
        That link mentions that Firefox already supports it if you change a setting, and Apple is literally currently implementing it. https://lists.webkit.org/pipermail/webkit-dev/2020-June/031228.html https://lists.webkit.org/pipermail/webkit-dev/2020-June/0312... https://github.com/WebKit/WebKit/pulls?q=Scroll+animations https://github.com/WebKit/WebKit/pulls?q=Scroll+animations
SvenL 2y ago
Quantamagazine is pretty amazing. The content, the visualizations, no ads, it’s loading pretty quick - I think this is how the web should be
- mikhailfranco 2y ago
  Completely failed to load with Brave on laptop. Loaded in Chrome. Various effects were annoying. Right click - load in new tab didn't work for linked articles. And no changed link colors to show which articles I'd read before. Fancy graphics break web conventions.
nyc111 2y ago
Spacetime in physics has always been an imaginary mathematical construct. Spacetime is not something that exists in reality. Take the deflection of light equation used to compute the deflection of light in General Relativity: alpha = (4GM)/c^2*r This equation contains no terms for something called “spacetime”. This equation does not say that the light is bent by spacetime or that this observation is done in spacetime. But physicists write a fictional story over this equation and pretend that spacetime bends the light. The equation doesn’t say that, physicists do. And now physicists decided that spacetime does not really exist, it is emergent etc. Just a few years back people who said these things in forums would be dubbed crackpots by physicists.
- mr_mitm 2y ago
  It's a bit more involved than that. That simple equation you quoted has been derived from the geodesic equations. Geodesics are the equivalent of straight lines on curved manifolds, which is a mathematical object. The shape and geometry of the manifold in question, which in turn influences the shape of the geodesics, is given by the matter distribution, or more specifically the energy stress tensor. The relationship between the manifold and the energy stress tensor is described by the Einstein field equations. We gave that manifold the name "spacetime".
  - raattgift 2y ago
    Couple minor additions: geodesics are physical in that (i) they are the paths taken by objects in free-fall and (ii) light (massless waves, etc etc) in free space is always in free-fall: all allowable null curves are null geodesics. Massive objects and light may be accelerated (the direction part of the velocity vector changes with scattering even if the magnitude part does not) and during acceleration will not be bound to a geodesic because they aren't in free-fall. Even though I agree with the way you put it, I'll say it's probably a bit too strong to write that stress-energy is the (sole) source of curvature given the extremely curved spacetime of our expanding universe. However, Einstein was OK with Schrödinger taking that view <https://arxiv.org/abs/1211.6338 https://arxiv.org/abs/1211.6338> (a super-interesting bit of science history), and we don't know enough about the cosmological constant vs dark energy, nor cosmic inflation.

90 points by nsoonhui 2y ago

ninacomputer 2y ago

Just in passing, Quanta magazine has been excellent lately!

dist-epoch 2y ago
It was also excellent in the past! It's excellent in general
nuancebydefault 2y ago
It was observed as excellent in your universe, in our universe...

soup10 2y ago

My understanding of black holes is rather straightforward, gravity is so strong it prevents light and matter from escaping it's orbit. That does not mean that nothing is there or that all physics as we know it breaks down. Simply that our instruments can't observe what's there directly.

marcyb5st 2y ago
Not so simple. If there is no collapse into a singularity, what happens to the matter? Theoretically speaking, we have no clue to what happen to matter beyond neutron stars levels of degenerate pressure. Specifically, what happens to fermions once all the quantum states are filled and they are still constrained by all the other fermions around them? We have no idea (and everything seems to point to a collapse into a singularity). If, instead, there is an actual singularity (which has infinite density) it means that the curvature of space time is infinite, which our current theories can't cope with. Additionally, if singularities have infinite density, how is it that black holes can have different masses? A singularity can only be characterized by its position in spacetime since it has no size and so there is no space/surface for it to have any other property and yet we see that there are black holes with different masses. Another thing we can't explain with our theories. So yeah, black holes mess with our theories in a fundamental way because as soon as you start pondering what happens inside them we discover that general relativity or quantum mechanics or both break down and so they must be incomplete. Spacetime, being a construct of general relativity is therefore also an incomplete description of the real fabric of space time.
- soup10 2y ago
  Ok, but in my mind it's a lot like a mystery box, there's a lot of speculation about what's in the box, but without new instruments or new observation techniques, if the light/information from inside isn't reaching us we'll probably not be able to prove what's going on in the box one way or the other. One can claim "space-time breaks inside the mystery box" all you want, but I haven't heard of any testable theories.
  - wanda 2y ago
    Perhaps, but in terms of getting things done and making progress, it isn't very useful to suppose that it is simply a mystery box and that's that. Because if we just accept that, what do we do then? We just sit and wait for some new astronomical observation to give us a clue? that could take forever, and we'd be banking that we have the tech to observe this magic hint. Better to suppose that the theories we have comprise an accurate approximation or partial model of reality, and from there strive to find a better model. The process of doing so will either refine/entrench our current model and our conviction, or it will result in actually finding a better model. Win-win, and all the while, we can still have our telescopes and detectors on for the magic hint we'd be sat waiting for anyway. When things break down into singularities, it can be a pretty good indicator that we've got something wrong. Not necessarily, but in this case, I think we missed something.
    - soup10 2y ago
      Sure, I just think it might have a more "boring" answer than people are hoping for. E.g. behind the veil is something extremely high mass and energy, but it's more akin to a new class of Star rather than something where space, time, mass and energy lose all meaning.
      - cruffle_duffle 2y ago
        I mean based on the well tested theories we have now regarding general relativity… it isn’t just gonna be a new class of star. Unless general relativity is flat wrong, which it isn’t. That isn’t to say general relativity is the end all of our understanding of the universe—black holes are a perfect demonstration of where our understanding breaks down completely. Clearly there is a lot more going on than we currently can explain. For it to just be a super dense “new class of star” would first require you to explain why general relativity is completely wrong. And that is the problem. Black holes are weird because they break the well tested equations we currently use to describe what we observe in the universe. If you want my opinion, figuring this shit out (including what we are calling “dark matter”) is gonna unlock a whole new realm of cool stuff for humanity. I suspect there is a reason why we haven’t solved the Fermi paradox and it is because most “intelligent life”, as we imagine it, is living outside our current understanding of the universe. To get into the “cool aliens club”, our understanding of the universe will need to change.
tiborsaas 2y ago
If you deepen your understanding it suddenly stops being rather straightforward. Here's a good playlist to warp your head around the subject. https://youtube.com/playlist?list=PLsPUh22kYmNBl4h0i4mI5zDflExXJMo_x&si=CG47O0MFQd7rzMy7 https://youtube.com/playlist?list=PLsPUh22kYmNBl4h0i4mI5zDfl...

psychoslave 2y ago

If there are experiments that can be tried to challenge my own current perspective on the matter, I’m interested. Because to my mind, anything that is said to emerge implies that the dimension we usually refer to as time is already an implicit hypothesis of this anything being able to emerge. And if there is something out of time, then by its very definition it can’t interact with time: - either there’s a connection with time and then at some point there is a change to that thing that can no longer be considered an absolute static thing as there is a before and after event that this thing is attached to, - or this thing is without any relation to time and thus can not be something that engender time itself. To be clear, I think there is still large room for interpretation anywhere formal mathematical means can give us great insights that would be unreachable without them. Agreeing with equations is not agreeing on the interpretation to give to the equations at a larger epistemological picture, and even less on ontological genesis.

winwang 2y ago
Consider an unchanging singly-linked list as a universe. Time (or perhaps "the passage of time") in the intuitive sense does not exist for this universe, but it does exist in the sense that there is a global ordering of values. But does the ordering of the values come from the edges or the nodes? The ordering requires both. Or, more humanly(?), a film reel. At least, this is how I would think of it if required to give a simple-but-possibly-off-base answer for a possible way time could be emergent (would love it if someone more educated could correct me). This is also known as the Einstein block universe model. Otherwise, since my physics education is far below the actual bar needed to understand quantum gravity stuff, I think back to thermodynamic microstates and macrostates, and how temperature is emergent.
guy234 2y ago
I feel like someone could describe foam emerging from the sea without implying that it is a process in time. It could be thought of as a process relating to the properties of seawater, wave agitation, sand etc. It is possible for a picture, not a video, to depict foam emerging from the sea. Also, there need not be a before or after, or even quantifiable extrinsic changes.
2y ago

IAmGraydon 2y ago

Doesn’t spacetime emerge from dimension? In other words, first there was a dimensionless point. Something interacted with this and from that point arose dimension. From dimension, spacetime emerged.

ackbar03 2y ago

Does anyone have a good recommendation for an introductory book on these concepts? I read a bit of The Fabric of Reality but had trouble progressing too far with that one. The author talks about the quantum slit experiment, somehow arrives at the explanation of parallel universes, and then claims anyone who disagrees with this conclusion must have faulty logic. A huge chunk of reasoning behind parallel universes seems to be skipped and I have trouble taking it seriously every time it is brought up.

sandgiant 2y ago
Sean Carroll (professor of physics, quoted in the article) has a highly-rated book titled "Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime" [1] which discusses exactly these topics. I haven't read it, but it's on my list. I also highly recommend his podcast "Mindscape" where he discusses this and a range of other topics in science and philosophy. [2] [1] https://www.preposterousuniverse.com/somethingdeeplyhidden/ https://www.preposterousuniverse.com/somethingdeeplyhidden/ [2] https://www.preposterousuniverse.com/podcast/ https://www.preposterousuniverse.com/podcast/
codethief 2y ago
> A and then claims anyone who disagrees with this conclusion must have faulty logic. A huge chunk of reasoning behind parallel universes seems to be skipped and I have trouble taking it seriously every time it is brought up. I think your scepticism is generally warranted. There is a reason the many-worlds interpretation is called an interpretation, just like the Copenhagen interpretation and others. The interpretations cannot be logically deduced from the experimental evidence we have. They are attempts to try to make sense of the results. As for book recommendations, I have really liked Tim Maylin's "Philosophy of Physics: Quantum Theory" because of the precision and clarity he brings to the discussion. I should mention, though, that I've got a physics degree.
- mikhailfranco 2y ago
  Tim Maudlin

bbor 2y ago

A) I like cute scroll effects, but maybe we should consider making them additive rather than completely ephemeral (when screen size permits)? The intro is beautiful on mobile, I'm sure, but it's just kind of irritating on desktop. B) Thanks so much for posting, I had skimmed a few of these articles but didn't realize it was part of a cohesive series. For others, since it's not really obvious at first: the whole series is built to setup the three articles at the bottom, where Charlie Wood examines three competing research groups. Quanta is on fire these days... This is an amazing evolution upon 2020's What is a Particle?, which is an article I've been bringing up in like every other conversation b/c it's so fascinating and accessible. C) Other than the initial complaints about the intro, the article itself is downright groundbreaking webdev-wise. And I called it when I started this comment -- the rest is additive! The way the text deforms around the sliding divs (but quick enough that it probably won't interrupt you since you haven't gotten to it yet) is just beautiful, I don't think I've seen that before. The dynamic, freeform cutouts fit perfectly with the theme, and the background is bold (how many sites are purple??) but indescribably perfect. Of course, the star of the show is the animated "thought experiment" page, even if the transitions are atomic (can't be reversed halfway through by scrolling back up). And the final summary + animation is worth scrolling to the bottom for, even if you don't read the rest of it. Well done Quanta web team, you're seriously raising the bar with this article, IMHO. Inspiring stuff. Is there any magazine ~~article~~ "series" (issue?) that even approaches the beauty and cohesiveness of this one? I'd love to proven wrong by the experts on here ;) [ETA: wow everyone hates the UX, I'm shocked. Why, in particular...? At the end of the day the linked page is just a list of links that appears right near the top, I don't understand the ubiquitous hate! What am I missing?] D) I'm pretty far from critically evaluating the physics surveys themselves, but I certainly found them helpful. Some quotes that are just insanely insightful, the kind of simple, boring statements that edge on superstition through their pure profundity alone: In periods when we are looking for new theories, physics has always become philosophical. Our natural perspective as beings with locations separated by space sticks out as a mathematical oddity. “It’s a reminder that the laws of physics that we perceive in our world don’t seem to be random,” said Sean Carroll (opens a new tab), a physicist at Johns Hopkins University. “They seem to be specific.” “AdS/CFT is an insane suggestion that should be stupid,” said Geoff Penington, a physicist at the University of California, Berkeley who studies holography. “But then you try all these things, and it all ends up being consistent.” For his part, he feels that holography isn’t radical enough. It shows how one dimension of space could emerge, but otherwise all the familiar ingredients of quantum theory are there from the start: some space, locality, and a clock to mark time. Arkani-Hamed feels that all of those elements should emerge together from something more primitive — as they do in surfaceology. It might seem like I’m interested in lots of different things, but I’m not sure if they’re really all that disconnected. At least within math, it is kind of true that sufficiently beautiful things tend to be connected with one another. E) Any friendly experts around to explain what a "lower dimension" representation of a black hole would look like? What's a periodically-repeating 2D manifold, given that circles (flattened spheres) don't pack? I guess it warps to pack nicely? This is a core example they use to explain the broader thesis--which I thought I understood--but I don't really understand in the topological shape of what they're describing, so it ended up confusing me more. In particular I'm commenting on this: So the key to black holes’ underlying structure exists on their surface. “People began to think,” Law said, “that maybe whatever microscopic theory describes black holes lives in a space-time with one lower dimension.” F) Even more fundamentally, can someone explain why we can't just assume that there isn't spacetime inside black holes? If everything's pointing towards their contents being entirely contained within their infinitely-thin surface, why can't we just embrace that? In other words, that whatever determinations make up the universe are undetermined in those places? That the diameter of every black hole is 0, when considered from the inside? I'm assuming the answer is "complicated math says no", but I'm failing to confirm that. Sorry for the spam, won't mind if this is deleted -- it's just terribly helpful to write as I go. If you're scrolling by, I highly recommend bookmarking this series in full! And if you work at Quanta and are reading this: you're awesome.

dang 2y ago

[stub for offtopicness]

leetrout 2y ago
I really am over the stupid scroll hijacking sites.
- MathMonkeyMan 2y ago
  Fucked up my phone jeez.
- king_magic 2y ago
  Seriously. This page looks and interacts like shit on my iPhone. Gave up and went to reader mode. Still sucks.
- bmitc 2y ago
  Agreed. Quanta has great content, but man alive, this particular "article" (?) is completely unbearable. I wish they'd just release these special issues as actual print magazines. I'd love to have them in the flesh, but Quanta very rarely publishes their stuff on paper.
- jazzypants 2y ago
  It's just gonna get worse now that it's easy to implement with CSS. https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_scroll-driven_animations https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_scroll-...
  - leptons 2y ago
    Firefox and Safari don't support it. https://caniuse.com/mdn-css_properties_animation-timeline_scroll https://caniuse.com/mdn-css_properties_animation-timeline_sc...
    - jazzypants 2y ago
      That link mentions that Firefox already supports it if you change a setting, and Apple is literally currently implementing it. https://lists.webkit.org/pipermail/webkit-dev/2020-June/031228.html https://lists.webkit.org/pipermail/webkit-dev/2020-June/0312... https://github.com/WebKit/WebKit/pulls?q=Scroll+animations https://github.com/WebKit/WebKit/pulls?q=Scroll+animations

SvenL 2y ago

Quantamagazine is pretty amazing. The content, the visualizations, no ads, it’s loading pretty quick - I think this is how the web should be

mikhailfranco 2y ago
Completely failed to load with Brave on laptop. Loaded in Chrome. Various effects were annoying. Right click - load in new tab didn't work for linked articles. And no changed link colors to show which articles I'd read before. Fancy graphics break web conventions.

nyc111 2y ago

Spacetime in physics has always been an imaginary mathematical construct. Spacetime is not something that exists in reality. Take the deflection of light equation used to compute the deflection of light in General Relativity: alpha = (4GM)/c^2*r This equation contains no terms for something called “spacetime”. This equation does not say that the light is bent by spacetime or that this observation is done in spacetime. But physicists write a fictional story over this equation and pretend that spacetime bends the light. The equation doesn’t say that, physicists do. And now physicists decided that spacetime does not really exist, it is emergent etc. Just a few years back people who said these things in forums would be dubbed crackpots by physicists.

mr_mitm 2y ago
It's a bit more involved than that. That simple equation you quoted has been derived from the geodesic equations. Geodesics are the equivalent of straight lines on curved manifolds, which is a mathematical object. The shape and geometry of the manifold in question, which in turn influences the shape of the geodesics, is given by the matter distribution, or more specifically the energy stress tensor. The relationship between the manifold and the energy stress tensor is described by the Einstein field equations. We gave that manifold the name "spacetime".
- raattgift 2y ago
  Couple minor additions: geodesics are physical in that (i) they are the paths taken by objects in free-fall and (ii) light (massless waves, etc etc) in free space is always in free-fall: all allowable null curves are null geodesics. Massive objects and light may be accelerated (the direction part of the velocity vector changes with scattering even if the magnitude part does not) and during acceleration will not be bound to a geodesic because they aren't in free-fall. Even though I agree with the way you put it, I'll say it's probably a bit too strong to write that stress-energy is the (sole) source of curvature given the extremely curved spacetime of our expanding universe. However, Einstein was OK with Schrödinger taking that view <https://arxiv.org/abs/1211.6338 https://arxiv.org/abs/1211.6338> (a super-interesting bit of science history), and we don't know enough about the cosmological constant vs dark energy, nor cosmic inflation.