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The press release has a popular science background - https://www.nobelprize.org/uploads/2020/10/popular-physicsprize2020.pdf https://www.nobelprize.org/uploads

The press release has a popular science background - https://www.nobelprize.org/uploads/2020/10/popular-physicsprize2020.pdf https://www.nobelprize.org/uploads/2020/10/popular-physicspr... Highly recommend the illustrations on the press release for a quick overview Cross section of a black hole (pdf) - https://www.nobelprize.org/uploads/2020/10/fig2-phy-en-cross-section.pdf https://www.nobelprize.org/uploads/2020/10/fig2-phy-en-cross... The Milky Way - https://www.nobelprize.org/uploads/2020/10/fig3-phy-en-milky-way.pdf https://www.nobelprize.org/uploads/2020/10/fig3-phy-en-milky... Stars closest to the centre of the Milky Way - https://www.nobelprize.org/uploads/2020/10/fig4-phy-en-stars-closest.pdf https://www.nobelprize.org/uploads/2020/10/fig4-phy-en-stars...

frereubu 6y ago
An illustration in the press release contains this phrase: "When a massive star collapses under its own gravity, it forms a black hole that is so heavy that it captures everything that passes its event horizon. Not even light can escape. At the event horizon, time replaces space and points only forward. The flow of time carries everything towards a singularity furthest inside the black hole, where density is infinite and time ends." I enjoy reading passages like that because there's a point where I lose comprehension completely - after "Not even light can escape" - and the rest of it is enjoyably poetic gibberish to a non-physicist like me. It reminds me of the beginning of The Four Quartets by TS Eliot: Time present and time past Are both perhaps present in time future, And time future contained in time past. If all time is eternally present All time is unredeemable. What might have been is an abstraction Remaining a perpetual possibility Only in a world of speculation. What might have been and what has been Point to one end, which is always present.
- SiempreViernes 6y ago
  Honestly, "time replaces space" is probably intentionally dramatic: I don't think anyone really means more than that the light-cone is so tilted it lies completely outside of where it started. In practice it just means that wherever you try to go you'll end up in the same place, basically you're going down a funnel and the exceptional thing is that the funnel is made out of spacetime itself.
  - Sharlin 6y ago
    Well, time does very concretely swap roles with one of the spatial dimensions, namely the radial one. They change signs in the metric, making the radial dimension timelike and the old temporal dimension spacelike.
    - SiempreViernes 6y ago
      I think there is more to the special status of time than just the sign convention used, so I find this mathematical detail about as interesting as the singularity on the event horizon.
- konschubert 6y ago
  I’m a Physicist (Not Astrophysicist, but still. ) I can assure you that this is also gibberish to me. These kind of popular science translations are like one-way hash functions. If you really understand the science, you can probably recognize where they are coming from. But by themselves they contain 0 information.
  - abdullahkhalids 6y ago
    As someone who understands hash functions, I understand where you are coming from and got non-zero information from your comment.
  - mturmon 6y ago
    Not only that, but in this case, given that we don't have a theory of Quantum Gravity yet, the notion of "what happens" at the singularity is inevitably mystical. The press release is glibly going from "science mode" to "mystical mode" and acting like it's all known by physics, which it's not. (I'm not really complaining ... it's a press release, after all.)
  - Bodell 6y ago
    That's because the black hole sucked all the information out of it. Haha.
  - tyre 6y ago
    Look, if it gets us phrases like “… where density is infinite and time ends.” then I’m here for them. I cannot wrap my mind around what it means, but it’s a savage description.
- sharpneli 6y ago
  Non poetic but hopefully bit more understandable explanation of what it tries to say: After crossing the event horizon the radial direction becomes like time. And what used to be time becomes like space. What this means that you will inevitably travel to the center, just in the same way as you travel into the future in normal life. Inside the event horizon the center is not at any place that you can see, instead it is in your future.
  - psychoslave 6y ago
    To be fair, the universe will never confront you to such a puzzling situation, as it will kindly squash you under heavy gravity before you come close to any object so massive.
    - kryptiskt 6y ago
      Not necessarily, a supermassive black hole can have quite bearable gravity at the event horizon (as the event horizon radius depends linearly on the mass and the gravity declines quadratically with distance). You still wouldn't be able to communicate your experiences though.
      - ckosidows 6y ago
        Doesn't an event horizon imply a gravitational pull so strong not even light can escape? Isn't the effect of gravity the same at the event horizon for all sizes of a black hole? I thought the size only affected the "acceleration" of the gravitational pull based on the distance from the singularity? A supermassive black hole means you will take longer to be spaghettified, but it will still happen and it will happen before you cross the horizon, won't it?
        radioactivist 6y ago
        A uniform force doesn't do anything harmful to you. You get stretched into spaghetti by the difference in force between the ends of your body. In large black holes that difference can be small even as you pass through the horizon (where the total force is large).
- uHuge 6y ago
  That is a misunderstanding and a simplistic depiction of the inner structure inside the event horizon sphere. True is we have no observations of the internals but time ending is in contradiction to the cones of particles ejected from the "hole", observed by astronomers.
  - Sharlin 6y ago
    Black hole jets do not originate from beyond the event horizon. They are made of matter in the accretion disk surrounding the black hole that spirals inward but is deflected and ejected by the black hole's magnetic field.
- tannhaeuser 6y ago
  Worth noting that the "BH so massive even light can't escape" meme, a staple of popular science, wouldn't make sense since photons don't have mass. What's happening is that space is skewed (according to Schwarzschild if I got it right). It can be better groked with a modern depiction of a BH such as in eg "Interstellar" where the far end of the accretion disk is observed as a second disk.
  - Sharlin 6y ago
    Light has mass-energy, and mass-energy both affects and is affected by the gravitational field. Indeed it is theoretically possible to make a black hole out of nothing but photons [1]. [1] https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics) https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)
  - tzs 6y ago
    > Worth noting that the "BH so massive even light can't escape" meme, a staple of popular science, wouldn't make sense since photons don't have mass. Even worse, it is frequently explained with an analogy to escape velocity. You have a certain escape velocity at the surface of the Moon, the analogy starts, and your rocket needs to exceed that to get out. Gravity is stronger at the surface of Earth, so escape velocity there is higher, and rockets need to go even faster. At the event horizon, gravity is strong enough that escape velocity is the speed of light, and so nothing can get out because you can't go faster than light. Great--except the escape velocity thing only applies to trying to get out ballistically. (Current rockets are essentially ballistic because they expend most of their fuel while still deep in Earth's gravity well). Escape velocity explains why someone inside the event horizon can't throw things out of the black hole using a catapult, or using a rocket that expends all its fuel before reaching the event horizon. It doesn't explain why something with continuous thrust could not get out. It doesn't explain why someone inside couldn't build a ladder that extends past the event horizon and simply climb out. It doesn't explain why someone outside could not lower a tether in and pull someone out.
- baxtr 6y ago
  I wonder what happens if you inject parts of that into GPT-3... maybe we solve some mysteries with that
- me_me_me 6y ago
  https://www.youtube.com/watch?v=mht-1c4wc0Q https://www.youtube.com/watch?v=mht-1c4wc0Q I hope it helps. I think this is the cleanest explanation with actual visual representation. Edit: Sorry this one is even better. How Time Becomes Space Inside a Black Hole | Space Time https://www.youtube.com/watch?v=KePNhUJ2reI https://www.youtube.com/watch?v=KePNhUJ2reI
- T-A 6y ago
  Here's a simple explanation, with pictures: http://visualrelativity.com/LIGHTCONE/schwarzschild.html http://visualrelativity.com/LIGHTCONE/schwarzschild.html And here's a more technical one: https://en.wikipedia.org/wiki/Penrose_diagram#Black_holes https://en.wikipedia.org/wiki/Penrose_diagram#Black_holes
- gizmo686 6y ago
  In some sense, nothing particuarly interesting happens at the event horizon of a black hole. For a sufficiently large black hole, the space at the event horizon is essentially flat [0]. The time and space swapping weirdness is entirely an artifact of the coordinate system being used. If you think of spacetime as a 4 dimensional geometry, there is no particularly reason to pick out any specific shape of the "time" coordinate. For a given interval in space-time, there is notion of "proper time" that is invariant to coordinate system transformations, so a given observer does have an "ideal" coordinate to use for time. The "proper time" of a given observer could be the space axis of another coordinate system. Assuming you have enough background in math, what I think is a reasonably understandable explanation is here: https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be&list=PLpGHT1n4-mAvcXwzOIz3dHnGZaQP1LEib&t=4090 https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be... Once he gets through explaining the hyperbolic coordinate sytstem, you can skip ahead to https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be&list=PLpGHT1n4-mAvcXwzOIz3dHnGZaQP1LEib&t=5247 https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be... Space is time line: https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be&list=PLpGHT1n4-mAvcXwzOIz3dHnGZaQP1LEib&t=5478 https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be... A somewhat clarifying picture of it taking "infinite" time to cross the event horizon, without anything interesting happening near the event horizon: https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be&list=PLpGHT1n4-mAvcXwzOIz3dHnGZaQP1LEib&t=5767 https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be... [0] As with any gravitational object, there are tidal forces. However, due to the increasing radius of the event horizon, the strength of the tidal forces at the event horizon decrease as the mass of the blackhole increases.
- pfortuny 6y ago
  I cannot but disagree with you on Eliot. It is a christian image and he is talking about God’s view of History. The waste land is at times gibberish, though, in his own words.
potiuper 6y ago
The PR seems like a double dig on Hawking. "Nothing, not even light, can escape." except Hawking radiation?
- SiempreViernes 6y ago
  Hawking radiation is emitted from the outside, if you start beyond the barrier it's usually not counted as an escape.
  - melling 6y ago
    i thought that a black hole could eventually disappear through Hawking radiation. Eventually being a really long time.
    - pas 6y ago
      Yes, it could, and yes, it theoretically [in some models] contains/radiates information. But the "radiation" happens right at the event horizon, the particles that get emerge have been "created" on the outer side. https://www.youtube.com/watch?v=XT_iZ7QEit8 https://www.youtube.com/watch?v=XT_iZ7QEit8
      - pbhjpbhj 6y ago
        This seems as good a place as any to ask: when the particle-antiparticle pairs are made at the event horizon, one falls in, the other is emitted as radiation. Why don't the p & ap produced then pair up with and annihilate with other ap and p created in the vicinity such that it wouldn't really be detectable over ordinary vacuum activity. This could happen both inside and outside the horizon. It seems like Hawking radiation (if I've understood correctly) could be produced but would be almost impossible to detect as it would all annihilate immediately? What have I missed?
        a1369209993 6y ago
        The particle []or[] antiparticle (only one avoids falling in) produced usually does pair up and annihilate with another (anti)particle, but that happens above the event horizon, so the photon resulting from that annihilation sometimes is pointed away from black hole and escapes. It's only very small black holes where the pair-production particles themselves have sufficient height and speed to escape.

frereubu 6y ago

An illustration in the press release contains this phrase: "When a massive star collapses under its own gravity, it forms a black hole that is so heavy that it captures everything that passes its event horizon. Not even light can escape. At the event horizon, time replaces space and points only forward. The flow of time carries everything towards a singularity furthest inside the black hole, where density is infinite and time ends." I enjoy reading passages like that because there's a point where I lose comprehension completely - after "Not even light can escape" - and the rest of it is enjoyably poetic gibberish to a non-physicist like me. It reminds me of the beginning of The Four Quartets by TS Eliot: Time present and time past Are both perhaps present in time future, And time future contained in time past. If all time is eternally present All time is unredeemable. What might have been is an abstraction Remaining a perpetual possibility Only in a world of speculation. What might have been and what has been Point to one end, which is always present.

SiempreViernes 6y ago
Honestly, "time replaces space" is probably intentionally dramatic: I don't think anyone really means more than that the light-cone is so tilted it lies completely outside of where it started. In practice it just means that wherever you try to go you'll end up in the same place, basically you're going down a funnel and the exceptional thing is that the funnel is made out of spacetime itself.
- Sharlin 6y ago
  Well, time does very concretely swap roles with one of the spatial dimensions, namely the radial one. They change signs in the metric, making the radial dimension timelike and the old temporal dimension spacelike.
  - SiempreViernes 6y ago
    I think there is more to the special status of time than just the sign convention used, so I find this mathematical detail about as interesting as the singularity on the event horizon.
konschubert 6y ago
I’m a Physicist (Not Astrophysicist, but still. ) I can assure you that this is also gibberish to me. These kind of popular science translations are like one-way hash functions. If you really understand the science, you can probably recognize where they are coming from. But by themselves they contain 0 information.
- abdullahkhalids 6y ago
  As someone who understands hash functions, I understand where you are coming from and got non-zero information from your comment.
- mturmon 6y ago
  Not only that, but in this case, given that we don't have a theory of Quantum Gravity yet, the notion of "what happens" at the singularity is inevitably mystical. The press release is glibly going from "science mode" to "mystical mode" and acting like it's all known by physics, which it's not. (I'm not really complaining ... it's a press release, after all.)
- Bodell 6y ago
  That's because the black hole sucked all the information out of it. Haha.
- tyre 6y ago
  Look, if it gets us phrases like “… where density is infinite and time ends.” then I’m here for them. I cannot wrap my mind around what it means, but it’s a savage description.
sharpneli 6y ago
Non poetic but hopefully bit more understandable explanation of what it tries to say: After crossing the event horizon the radial direction becomes like time. And what used to be time becomes like space. What this means that you will inevitably travel to the center, just in the same way as you travel into the future in normal life. Inside the event horizon the center is not at any place that you can see, instead it is in your future.
- psychoslave 6y ago
  To be fair, the universe will never confront you to such a puzzling situation, as it will kindly squash you under heavy gravity before you come close to any object so massive.
  - kryptiskt 6y ago
    Not necessarily, a supermassive black hole can have quite bearable gravity at the event horizon (as the event horizon radius depends linearly on the mass and the gravity declines quadratically with distance). You still wouldn't be able to communicate your experiences though.
    - ckosidows 6y ago
      Doesn't an event horizon imply a gravitational pull so strong not even light can escape? Isn't the effect of gravity the same at the event horizon for all sizes of a black hole? I thought the size only affected the "acceleration" of the gravitational pull based on the distance from the singularity? A supermassive black hole means you will take longer to be spaghettified, but it will still happen and it will happen before you cross the horizon, won't it?
      - radioactivist 6y ago
        A uniform force doesn't do anything harmful to you. You get stretched into spaghetti by the difference in force between the ends of your body. In large black holes that difference can be small even as you pass through the horizon (where the total force is large).
uHuge 6y ago
That is a misunderstanding and a simplistic depiction of the inner structure inside the event horizon sphere. True is we have no observations of the internals but time ending is in contradiction to the cones of particles ejected from the "hole", observed by astronomers.
- Sharlin 6y ago
  Black hole jets do not originate from beyond the event horizon. They are made of matter in the accretion disk surrounding the black hole that spirals inward but is deflected and ejected by the black hole's magnetic field.
tannhaeuser 6y ago
Worth noting that the "BH so massive even light can't escape" meme, a staple of popular science, wouldn't make sense since photons don't have mass. What's happening is that space is skewed (according to Schwarzschild if I got it right). It can be better groked with a modern depiction of a BH such as in eg "Interstellar" where the far end of the accretion disk is observed as a second disk.
- Sharlin 6y ago
  Light has mass-energy, and mass-energy both affects and is affected by the gravitational field. Indeed it is theoretically possible to make a black hole out of nothing but photons [1]. [1] https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics) https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)
- tzs 6y ago
  > Worth noting that the "BH so massive even light can't escape" meme, a staple of popular science, wouldn't make sense since photons don't have mass. Even worse, it is frequently explained with an analogy to escape velocity. You have a certain escape velocity at the surface of the Moon, the analogy starts, and your rocket needs to exceed that to get out. Gravity is stronger at the surface of Earth, so escape velocity there is higher, and rockets need to go even faster. At the event horizon, gravity is strong enough that escape velocity is the speed of light, and so nothing can get out because you can't go faster than light. Great--except the escape velocity thing only applies to trying to get out ballistically. (Current rockets are essentially ballistic because they expend most of their fuel while still deep in Earth's gravity well). Escape velocity explains why someone inside the event horizon can't throw things out of the black hole using a catapult, or using a rocket that expends all its fuel before reaching the event horizon. It doesn't explain why something with continuous thrust could not get out. It doesn't explain why someone inside couldn't build a ladder that extends past the event horizon and simply climb out. It doesn't explain why someone outside could not lower a tether in and pull someone out.
baxtr 6y ago
I wonder what happens if you inject parts of that into GPT-3... maybe we solve some mysteries with that
me_me_me 6y ago
https://www.youtube.com/watch?v=mht-1c4wc0Q https://www.youtube.com/watch?v=mht-1c4wc0Q I hope it helps. I think this is the cleanest explanation with actual visual representation. Edit: Sorry this one is even better. How Time Becomes Space Inside a Black Hole | Space Time https://www.youtube.com/watch?v=KePNhUJ2reI https://www.youtube.com/watch?v=KePNhUJ2reI
T-A 6y ago
Here's a simple explanation, with pictures: http://visualrelativity.com/LIGHTCONE/schwarzschild.html http://visualrelativity.com/LIGHTCONE/schwarzschild.html And here's a more technical one: https://en.wikipedia.org/wiki/Penrose_diagram#Black_holes https://en.wikipedia.org/wiki/Penrose_diagram#Black_holes
gizmo686 6y ago
In some sense, nothing particuarly interesting happens at the event horizon of a black hole. For a sufficiently large black hole, the space at the event horizon is essentially flat [0]. The time and space swapping weirdness is entirely an artifact of the coordinate system being used. If you think of spacetime as a 4 dimensional geometry, there is no particularly reason to pick out any specific shape of the "time" coordinate. For a given interval in space-time, there is notion of "proper time" that is invariant to coordinate system transformations, so a given observer does have an "ideal" coordinate to use for time. The "proper time" of a given observer could be the space axis of another coordinate system. Assuming you have enough background in math, what I think is a reasonably understandable explanation is here: https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be&list=PLpGHT1n4-mAvcXwzOIz3dHnGZaQP1LEib&t=4090 https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be... Once he gets through explaining the hyperbolic coordinate sytstem, you can skip ahead to https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be&list=PLpGHT1n4-mAvcXwzOIz3dHnGZaQP1LEib&t=5247 https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be... Space is time line: https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be&list=PLpGHT1n4-mAvcXwzOIz3dHnGZaQP1LEib&t=5478 https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be... A somewhat clarifying picture of it taking "infinite" time to cross the event horizon, without anything interesting happening near the event horizon: https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be&list=PLpGHT1n4-mAvcXwzOIz3dHnGZaQP1LEib&t=5767 https://www.youtube.com/watch?v=yv2-KPagCQs&feature=youtu.be... [0] As with any gravitational object, there are tidal forces. However, due to the increasing radius of the event horizon, the strength of the tidal forces at the event horizon decrease as the mass of the blackhole increases.
pfortuny 6y ago
I cannot but disagree with you on Eliot. It is a christian image and he is talking about God’s view of History. The waste land is at times gibberish, though, in his own words.

potiuper 6y ago

The PR seems like a double dig on Hawking. "Nothing, not even light, can escape." except Hawking radiation?

SiempreViernes 6y ago
Hawking radiation is emitted from the outside, if you start beyond the barrier it's usually not counted as an escape.
- melling 6y ago
  i thought that a black hole could eventually disappear through Hawking radiation. Eventually being a really long time.
  - pas 6y ago
    Yes, it could, and yes, it theoretically [in some models] contains/radiates information. But the "radiation" happens right at the event horizon, the particles that get emerge have been "created" on the outer side. https://www.youtube.com/watch?v=XT_iZ7QEit8 https://www.youtube.com/watch?v=XT_iZ7QEit8
    - pbhjpbhj 6y ago
      This seems as good a place as any to ask: when the particle-antiparticle pairs are made at the event horizon, one falls in, the other is emitted as radiation. Why don't the p & ap produced then pair up with and annihilate with other ap and p created in the vicinity such that it wouldn't really be detectable over ordinary vacuum activity. This could happen both inside and outside the horizon. It seems like Hawking radiation (if I've understood correctly) could be produced but would be almost impossible to detect as it would all annihilate immediately? What have I missed?
      - a1369209993 6y ago
        The particle []or[] antiparticle (only one avoids falling in) produced usually does pair up and annihilate with another (anti)particle, but that happens above the event horizon, so the photon resulting from that annihilation sometimes is pointed away from black hole and escapes. It's only very small black holes where the pair-production particles themselves have sufficient height and speed to escape.