4 ms·

If I got BH theory right, each particle of the ship entering the event horizon will almost fully stop, while the next particles entering will still slightly mov

If I got BH theory right, each particle of the ship entering the event horizon will almost fully stop, while the next particles entering will still slightly move, compressing the whole ship into a thin shell or crust that, due to atomic mechanics, won't function as normal matter, so the crew won't know what happened to them. The entering ship will redshift until it dissapears. Their particles will "spacetime-travel" far far away into the future until the compressed crust bounces back to space as radiation. Did I get it right?

pierrec 2y ago
Ignoring the "atomic mechanics" and "spacetime travel" parts, what you're describing is roughly what might be seen by an external observer, far from the black hole. From the ship's point of view, passing the event horizon happens (and in the case of a large-enough black hole, could be quite uneventful). This puzzle is all about reconciling those two points of view, and exploring intermediate points of view. If you're trying to describe things from a single authoritative point of view, of course, there is no such thing (although here's the disclaimer: I am also not an astrophysicist)
- readyplayernull 2y ago
  Granted. Thinking twice, BHs move in space really fast, for example when they orbit other BHs. Meaning their mass is not frozen in time, otherwise these will elongate or rip apart. So the time dilation wouldn't be have such big effect, and atoms might not be compacted too much?
  - raattgift 2y ago
    BHs move in space pretty slowly! Singleton black holes from collapsed stars move in their galaxy about the same as uncollapsed star: on the order of 200 km/s or so (faster towards the middle but still in the disc where motion is roughly circular around the galaxy's centre, slower in the bulge where motion is randomly around the galaxy's centre). Really unusually high-velocity stars move about 65-100 km/s faster than these, which is still not that fast, and "hypervelocity stars" (we've seen some twenty, compared to the 100 billion or so stars in our galaxy) move about only five to ten times faster still, but we're still at only about a thousandth of the speed of light. Black hole binaries can be arbitrarily wide, even up to many thousands of light-years, taking hundreds of thousands of years or more to orbit each other, possibly at speeds comparable to those of stars in galaxies. MEERKAT just announced its pulsar timing array results which focuses on orbital periods of some tens of years ("nanohertz gravitational waves"), which means not moving very fast. Here's a nice cartoon: https://physics.aps.org/articles/v16/116 https://physics.aps.org/articles/v16/116 LIGO is sensitive to much higher frequencies, once a black hole binary's mutual orbit has shrunk considerably - at the final chirp, they are moving at double-digit percentages of the speed of light and the orbital periods are in the milliseconds. In that regime black hole horizons do have bumps raised on them: https://www.youtube.com/watch?v=Y1M-AbWIlVQ https://www.youtube.com/watch?v=Y1M-AbWIlVQ The black holes can't rip apart though: everything inside stays inside. I'm afraid I can't figure out what you're talking about in terms of frozen in time, time dilation, or atoms compacting.
mtdewcmu 2y ago
Let's see if I can state this properly. The atoms of the ship will pass right through the event horizon like nothing. To see the ship, though, photons have to travel from the ship to your eyes. As the ship goes deeper into the black hole's gravity, the photons will "appear to" be getting slowed down by the black hole's gravity well, each photon more than the last. So, an outside observer would have to wait longer and longer to get the next photon. In fact, he'd have to wait an infinitely long time to get all of them. It's like an optical illusion, except that a real physicist would say it's not an optical illusion; it's time dilation, etc.

pierrec 2y ago

Ignoring the "atomic mechanics" and "spacetime travel" parts, what you're describing is roughly what might be seen by an external observer, far from the black hole. From the ship's point of view, passing the event horizon happens (and in the case of a large-enough black hole, could be quite uneventful). This puzzle is all about reconciling those two points of view, and exploring intermediate points of view. If you're trying to describe things from a single authoritative point of view, of course, there is no such thing (although here's the disclaimer: I am also not an astrophysicist)

readyplayernull 2y ago
Granted. Thinking twice, BHs move in space really fast, for example when they orbit other BHs. Meaning their mass is not frozen in time, otherwise these will elongate or rip apart. So the time dilation wouldn't be have such big effect, and atoms might not be compacted too much?
- raattgift 2y ago
  BHs move in space pretty slowly! Singleton black holes from collapsed stars move in their galaxy about the same as uncollapsed star: on the order of 200 km/s or so (faster towards the middle but still in the disc where motion is roughly circular around the galaxy's centre, slower in the bulge where motion is randomly around the galaxy's centre). Really unusually high-velocity stars move about 65-100 km/s faster than these, which is still not that fast, and "hypervelocity stars" (we've seen some twenty, compared to the 100 billion or so stars in our galaxy) move about only five to ten times faster still, but we're still at only about a thousandth of the speed of light. Black hole binaries can be arbitrarily wide, even up to many thousands of light-years, taking hundreds of thousands of years or more to orbit each other, possibly at speeds comparable to those of stars in galaxies. MEERKAT just announced its pulsar timing array results which focuses on orbital periods of some tens of years ("nanohertz gravitational waves"), which means not moving very fast. Here's a nice cartoon: https://physics.aps.org/articles/v16/116 https://physics.aps.org/articles/v16/116 LIGO is sensitive to much higher frequencies, once a black hole binary's mutual orbit has shrunk considerably - at the final chirp, they are moving at double-digit percentages of the speed of light and the orbital periods are in the milliseconds. In that regime black hole horizons do have bumps raised on them: https://www.youtube.com/watch?v=Y1M-AbWIlVQ https://www.youtube.com/watch?v=Y1M-AbWIlVQ The black holes can't rip apart though: everything inside stays inside. I'm afraid I can't figure out what you're talking about in terms of frozen in time, time dilation, or atoms compacting.

mtdewcmu 2y ago

Let's see if I can state this properly. The atoms of the ship will pass right through the event horizon like nothing. To see the ship, though, photons have to travel from the ship to your eyes. As the ship goes deeper into the black hole's gravity, the photons will "appear to" be getting slowed down by the black hole's gravity well, each photon more than the last. So, an outside observer would have to wait longer and longer to get the next photon. In fact, he'd have to wait an infinitely long time to get all of them. It's like an optical illusion, except that a real physicist would say it's not an optical illusion; it's time dilation, etc.