5 ms·

I've always wondered if the "horizon" metaphor in event horizon was more apt than we expected - just like when you approach the earth's horizon, you don't get f

I've always wondered if the "horizon" metaphor in event horizon was more apt than we expected - just like when you approach the earth's horizon, you don't get flattened or fall off, you just reveal more geography - I've always wondered if it were possible that as you approach an event horizon you don't get "squashed into spaghetti" but just reveal more space which is just as "normal" as the space before you approached the horizon. But caveat - i have no real reason to actually believe this is true - I'll assume for now it's just poetic.

jerf 4y ago
The "squashed into spaghetti" occurs in "normal space" before you get to the black hole, for most black holes. It is not an effect of anything special about black holes, it's just plain ol' normal tidal effects, turned up to eleven, then turned up until the knob breaks, then turned up some more. Neutron stars will give you a bad day with tidal effects too long before you reach their surface. Very large black holes turn out not to have this, though it's going to be a long time cosmologically before there are any large black holes also quiet enough for you to get anywhere near.
- syllablehq 4y ago
  To an outside observer it would look like you were torn apart by tidal forces, but would it feel that way to you? Or would you feel normal? If it's just space being curved, would you feel nothing just like you feel nothing in freefall? I'm sure this question is wrong...
  - yencabulator 4y ago
    The "tidal effect" here is due the difference in gravity experienced by parts of you at different distances from the gravity source. Imagine your feet pulled downward hard enough that your bones stretch and/or snap, while you are squished in from the sides. And then more. You'd become a long thin strand of matter, no longer in the shape of a human and no longer feeling anything. It's not "just a ride down" where things feel locally normal, and it's not a phenomenon about black holes, as some stars can do that to you too. https://en.wikipedia.org/wiki/Spaghettification https://en.wikipedia.org/wiki/Spaghettification
    - deleted 4y ago
      [deleted]
    - deleted 4y ago
      [deleted]
  - jerf 4y ago
    Position is relative, velocity is relative, acceleration is actually absolute. Tidal forces are not relative, they are agreed upon by all observers, who would all agree that you got torn apart by those forces. You can remember this by considering the effect acceleration has on objects; there is no trajectory an object can take in which it will observe the surface of the earth being at 25G and consequently everything being crushed on it. They'll still see 1G, they just won't agree about the velocities being modified and in sufficiently extreme cases, won't agree about how long the forces were applied for, but they'll still see 1G. Being able to witness varying accelerations would actually be a very strange theory, having instead a twin paradox in which one astronaut takes off and comes back home to a twin (and civilization) crushed to death, whereas the stay-at-home twin sees his twin take off, get crushed to death, and never return home at all. The YouTube videos trying to explain this universe would certainly be epic. Again, this all happens in normal space too; the black-hole-ness of the black hole is not in play yet. Non-black hole objects can "spaghettify" too.
- selfmodruntime 4y ago
  What? Any reading material on the last part?
  - jerf 4y ago
    I don't have a specific link. But the larger the black hole, the lesser the tidal forces at the event horizon. Tidal forces are created by gravity gradients, the differences, and the differences become less extreme as the black hole sizes up. You can see it just by thinking about how the gravity field changes around an object as it gets larger; think about where the 1G line as you make the Earth denser and denser, and note how quickly the field is changing at that point. Hypothetically, a large black hole would permit you to actually survive entry into the event horizon. It's still hypothetical because the environment around any such black hole in the current era is still far too violent for you to get that close, and it will be for cosmologically-meaningful periods of time.
yencabulator 4y ago
> you just reveal more geography Technically true, according to current theories. The slope of spacetime gets steeper and steeper and you traverse through that spacetime as you go. (Due to the gravity, you won't be whole to experience it.) https://youtu.be/8-xODPI1OFg?t=253 https://youtu.be/8-xODPI1OFg?t=253
deleted 4y ago
[deleted]
zackmorris 4y ago
The tricky part with black hole spaghettification is that the slope of the gravity gradient (tidal force) can be pictured as exceeding 90 degrees within the event horizon, because there is no speed limit for the flow of space. This doesn't violate physics because Einstein's speed of light limit only applies to matter moving within space. This idea has been embraced by astrophysicists to explain inflation at the start of the Big Bang. Why this matters is that when something spaghettifies, the particles at the end can never catch up to the ones at the beginning. The space between the ends of the spaghetti grows. Which also means that the spaghetti can never reach the pit at the center of the black hole, because the pit is farther ahead in its journey. So our intuition that falling into a black holes means that we'll collide with the center is incorrect. If we could survive the journey, we'd see ourselves falling forever towards something growing infinitely farther away. Like trying to catch up with a falling elevator that's moving faster than we are. From the outside, we see anything falling in as becoming 2D on the surface, red shifting as it accelerates away from us, becoming time dilated until it appears to freeze, never quite reaching the speed of light from our frame of reference. So even though it's being stretched along the radial axis and perspective should make it look smaller over time as our separation grows, it appears to stay the same size to us as it was when it entered the event horizon. So a black hole can be thought of as an infinitely long tunnel to.. somewhere. I prefer to think of it as a bubble which only grows internally. So in a very real sense, a whole universe is being birthed inside. Unfortunately the math breaks down near the singularity, so maybe the particles do see themselves colliding with a pit. For example, the sun is 8 light minutes from Earth, so even if it was heavy enough to collapse into a black hole, it should still take 8 minutes to reach the center for a particle falling towards it, from its frame of reference. But I don't think that's how it works. I think that the space flowing in faster than the speed of light overcomes spaghettification, creating a maximum strain inversely proportional to the mass of the black hole. Hawking hinted at this when he thought about what would happen to a human falling into a billion solar mass black hole whose tidal forces are weak enough that they're survivable. -- edit: this paragraph is wrong, the universe behind also red shifts, which I realized after considering that the object's watch and ours are synchronized during free-fall -- Probably what happens is that the object sees the universe behind it speed up faster and faster as it blue shifts, until it ends in a white-hot flash the number of light-seconds away that the object began falling. Meanwhile the space ahead appears to expand in the same way as inflation, creating a pocket universe containing the mass which has already fallen in. Except that the universe behind appears to also red shift, due to the increasing distance between the object and anything behind. The expansion and contraction probably balance to create a microwave background at a temperature inversely proportional to the age of the universe inside. So the background inside might be hotter than ours since the black hole is smaller than the parent universe. ---- Also if nothing more falls into the black hole and it starts evaporating, matter inside will see previously fallen matter growing away from it. Just like how we see stars and galaxies moving away from us faster than the speed of light when their distance times the Hubble constant exceeds the speed of light, causing our universe to grow lighter and expand faster, which we perceive as dark energy. So matter inside would eventually see the perimeter rushing towards it faster and faster as the black hole loses its mass, with its internal Hubble constant growing larger and larger until the expansion of space rips the matter apart as energy, back into the parent universe as its mass falls beneath a few solar masses. Which has implications for our universe, where instead of heat death, we re-experience spaghettification as the rate of the expansion of the universe keeps increasing until we explode. Or maybe the expansion only applies outside of our gravitationally-bound galaxy. So eventually the universe would only be our galaxy. But, I tend to think that evaporation still occurs, so even our galaxy would eventually be torn apart. But it would probably have already gone down the drain into the Milky Way's supermassive black hole, Sagittarius A*. In other words, the falling probably never ends. Which implies that maybe the universe is infinite, although we can never reach the parts moving away from us faster than the speed of light. Until we invent warp drive or meet aliens or something. Just so everyone knows, I completely made all of this up, starting from first principles after watching a lot of PBS Space Time and How the Universe Works. But that's ok since astrophysicists don't have a reference to point to that disputes my unfounded claims yet: https://jila.colorado.edu/~ajsh/insidebh/schw.html https://jila.colorado.edu/~ajsh/insidebh/schw.html Also, my description doesn't consider the quantum aspect of spaghettification, or how particles might behave inside gravitational barriers: https://en.wikipedia.org/wiki/Particle_in_a_box https://en.wikipedia.org/wiki/Particle_in_a_box https://en.wikipedia.org/wiki/Quantum_tunnelling https://en.wikipedia.org/wiki/Quantum_tunnelling I haven't found a clear summary yet for how the wave function behaves in a gravity gradient or under extreme time dilation, or when space is moving near or faster than the speed of light. Shoot, I just realized something after writing this out. Two particles in free-fall without external forces should have synchronized watches. The object falling into the black hole may not actually lose synchronization with us. Does anyone know if that's correct? https://en.wikipedia.org/wiki/Synchronous_frame https://en.wikipedia.org/wiki/Synchronous_frame https://www.physicsforums.com/threads/question-regarding-time-dilation-inertial-motion-and-acceleration-due-to-gravity.477834/ https://www.physicsforums.com/threads/question-regarding-tim... If the clocks stay synchronized until the lead object reaches the pit, what happens if the pit is never reached?

jerf 4y ago

The "squashed into spaghetti" occurs in "normal space" before you get to the black hole, for most black holes. It is not an effect of anything special about black holes, it's just plain ol' normal tidal effects, turned up to eleven, then turned up until the knob breaks, then turned up some more. Neutron stars will give you a bad day with tidal effects too long before you reach their surface. Very large black holes turn out not to have this, though it's going to be a long time cosmologically before there are any large black holes also quiet enough for you to get anywhere near.

syllablehq 4y ago
To an outside observer it would look like you were torn apart by tidal forces, but would it feel that way to you? Or would you feel normal? If it's just space being curved, would you feel nothing just like you feel nothing in freefall? I'm sure this question is wrong...
- yencabulator 4y ago
  The "tidal effect" here is due the difference in gravity experienced by parts of you at different distances from the gravity source. Imagine your feet pulled downward hard enough that your bones stretch and/or snap, while you are squished in from the sides. And then more. You'd become a long thin strand of matter, no longer in the shape of a human and no longer feeling anything. It's not "just a ride down" where things feel locally normal, and it's not a phenomenon about black holes, as some stars can do that to you too. https://en.wikipedia.org/wiki/Spaghettification https://en.wikipedia.org/wiki/Spaghettification
  - deleted 4y ago
    [deleted]
  - deleted 4y ago
    [deleted]
- jerf 4y ago
  Position is relative, velocity is relative, acceleration is actually absolute. Tidal forces are not relative, they are agreed upon by all observers, who would all agree that you got torn apart by those forces. You can remember this by considering the effect acceleration has on objects; there is no trajectory an object can take in which it will observe the surface of the earth being at 25G and consequently everything being crushed on it. They'll still see 1G, they just won't agree about the velocities being modified and in sufficiently extreme cases, won't agree about how long the forces were applied for, but they'll still see 1G. Being able to witness varying accelerations would actually be a very strange theory, having instead a twin paradox in which one astronaut takes off and comes back home to a twin (and civilization) crushed to death, whereas the stay-at-home twin sees his twin take off, get crushed to death, and never return home at all. The YouTube videos trying to explain this universe would certainly be epic. Again, this all happens in normal space too; the black-hole-ness of the black hole is not in play yet. Non-black hole objects can "spaghettify" too.
selfmodruntime 4y ago
What? Any reading material on the last part?
- jerf 4y ago
  I don't have a specific link. But the larger the black hole, the lesser the tidal forces at the event horizon. Tidal forces are created by gravity gradients, the differences, and the differences become less extreme as the black hole sizes up. You can see it just by thinking about how the gravity field changes around an object as it gets larger; think about where the 1G line as you make the Earth denser and denser, and note how quickly the field is changing at that point. Hypothetically, a large black hole would permit you to actually survive entry into the event horizon. It's still hypothetical because the environment around any such black hole in the current era is still far too violent for you to get that close, and it will be for cosmologically-meaningful periods of time.

yencabulator 4y ago

> you just reveal more geography Technically true, according to current theories. The slope of spacetime gets steeper and steeper and you traverse through that spacetime as you go. (Due to the gravity, you won't be whole to experience it.) https://youtu.be/8-xODPI1OFg?t=253 https://youtu.be/8-xODPI1OFg?t=253

deleted 4y ago

[deleted]

zackmorris 4y ago

The tricky part with black hole spaghettification is that the slope of the gravity gradient (tidal force) can be pictured as exceeding 90 degrees within the event horizon, because there is no speed limit for the flow of space. This doesn't violate physics because Einstein's speed of light limit only applies to matter moving within space. This idea has been embraced by astrophysicists to explain inflation at the start of the Big Bang. Why this matters is that when something spaghettifies, the particles at the end can never catch up to the ones at the beginning. The space between the ends of the spaghetti grows. Which also means that the spaghetti can never reach the pit at the center of the black hole, because the pit is farther ahead in its journey. So our intuition that falling into a black holes means that we'll collide with the center is incorrect. If we could survive the journey, we'd see ourselves falling forever towards something growing infinitely farther away. Like trying to catch up with a falling elevator that's moving faster than we are. From the outside, we see anything falling in as becoming 2D on the surface, red shifting as it accelerates away from us, becoming time dilated until it appears to freeze, never quite reaching the speed of light from our frame of reference. So even though it's being stretched along the radial axis and perspective should make it look smaller over time as our separation grows, it appears to stay the same size to us as it was when it entered the event horizon. So a black hole can be thought of as an infinitely long tunnel to.. somewhere. I prefer to think of it as a bubble which only grows internally. So in a very real sense, a whole universe is being birthed inside. Unfortunately the math breaks down near the singularity, so maybe the particles do see themselves colliding with a pit. For example, the sun is 8 light minutes from Earth, so even if it was heavy enough to collapse into a black hole, it should still take 8 minutes to reach the center for a particle falling towards it, from its frame of reference. But I don't think that's how it works. I think that the space flowing in faster than the speed of light overcomes spaghettification, creating a maximum strain inversely proportional to the mass of the black hole. Hawking hinted at this when he thought about what would happen to a human falling into a billion solar mass black hole whose tidal forces are weak enough that they're survivable. -- edit: this paragraph is wrong, the universe behind also red shifts, which I realized after considering that the object's watch and ours are synchronized during free-fall -- Probably what happens is that the object sees the universe behind it speed up faster and faster as it blue shifts, until it ends in a white-hot flash the number of light-seconds away that the object began falling. Meanwhile the space ahead appears to expand in the same way as inflation, creating a pocket universe containing the mass which has already fallen in. Except that the universe behind appears to also red shift, due to the increasing distance between the object and anything behind. The expansion and contraction probably balance to create a microwave background at a temperature inversely proportional to the age of the universe inside. So the background inside might be hotter than ours since the black hole is smaller than the parent universe. ---- Also if nothing more falls into the black hole and it starts evaporating, matter inside will see previously fallen matter growing away from it. Just like how we see stars and galaxies moving away from us faster than the speed of light when their distance times the Hubble constant exceeds the speed of light, causing our universe to grow lighter and expand faster, which we perceive as dark energy. So matter inside would eventually see the perimeter rushing towards it faster and faster as the black hole loses its mass, with its internal Hubble constant growing larger and larger until the expansion of space rips the matter apart as energy, back into the parent universe as its mass falls beneath a few solar masses. Which has implications for our universe, where instead of heat death, we re-experience spaghettification as the rate of the expansion of the universe keeps increasing until we explode. Or maybe the expansion only applies outside of our gravitationally-bound galaxy. So eventually the universe would only be our galaxy. But, I tend to think that evaporation still occurs, so even our galaxy would eventually be torn apart. But it would probably have already gone down the drain into the Milky Way's supermassive black hole, Sagittarius A*. In other words, the falling probably never ends. Which implies that maybe the universe is infinite, although we can never reach the parts moving away from us faster than the speed of light. Until we invent warp drive or meet aliens or something. Just so everyone knows, I completely made all of this up, starting from first principles after watching a lot of PBS Space Time and How the Universe Works. But that's ok since astrophysicists don't have a reference to point to that disputes my unfounded claims yet: https://jila.colorado.edu/~ajsh/insidebh/schw.html https://jila.colorado.edu/~ajsh/insidebh/schw.html Also, my description doesn't consider the quantum aspect of spaghettification, or how particles might behave inside gravitational barriers: https://en.wikipedia.org/wiki/Particle_in_a_box https://en.wikipedia.org/wiki/Particle_in_a_box https://en.wikipedia.org/wiki/Quantum_tunnelling https://en.wikipedia.org/wiki/Quantum_tunnelling I haven't found a clear summary yet for how the wave function behaves in a gravity gradient or under extreme time dilation, or when space is moving near or faster than the speed of light. Shoot, I just realized something after writing this out. Two particles in free-fall without external forces should have synchronized watches. The object falling into the black hole may not actually lose synchronization with us. Does anyone know if that's correct? https://en.wikipedia.org/wiki/Synchronous_frame https://en.wikipedia.org/wiki/Synchronous_frame https://www.physicsforums.com/threads/question-regarding-time-dilation-inertial-motion-and-acceleration-due-to-gravity.477834/ https://www.physicsforums.com/threads/question-regarding-tim... If the clocks stay synchronized until the lead object reaches the pit, what happens if the pit is never reached?