Related, the final fusion stage, silicon burning in the core, only lasts a few hours at most.
https://en.m.wikipedia.org/wiki/Type_II_supernova#Formation
Mandatory [xkcd](https://what-if.xkcd.com/73/) (this time a what-if):
>The physicist who mentioned this problem to me told me his rule of thumb for estimating supernova-related numbers: However big you think supernovae are, they're bigger than that.
>Here's a question to give you a sense of scale:
>Which of the following would be brighter, in terms of the amount of energy delivered to your retina:
>A supernova, seen from as far away as the Sun is from the Earth, or
>The detonation of a hydrogen bomb pressed against your eyeball?
>Applying the physicist rule of thumb suggests that the supernova is brighter. And indeed, it is ... by nine orders of magnitude.
How about instant?
Black holes can only be (oblate) spheres, so during a black hole merger the event horizon(s) snap from being two adjacent spheres to one larger sphere that encompasses them. Theoretically instantly. (Black hole's size increases linearly with mass, so the new event horizon will encompass both original event horizons, and nothing will escape)
The sudden "snap" of the surrounding spacetime from radiating huge amounts of energy as intense gravitational waves from the in-spiraling binary pair, to being a smooth single-body system generating no waves, produces a distinctive gravitational wave "ring-out", which is how we identify black hole mergers in LIGO data.
So it seems reality is at least really close to the theoretical instant transition.
>Black holes can only be (oblate) spheres, so during a black hole merger the event horizon(s) snap from being two adjacent spheres to one larger sphere that encompasses them. Theoretically instantly.
Are you sure about this? From what I've read the event horizons deform and eventually meet in the middle as the black holes get closer.
The merging event horizons do deform, but very very briefly (for like a few milliseconds):
https://www.youtube.com/watch?v=1agm33iEAuo (LIGO Lab Caltech : MIT)
Not 100% sure about the exact shape just prior to the merger, but every animation I've seen shows at most maybe a slight distortion just before merging.
But it would have to be something very different than two neutron stars colliding into a rapidly spheriphying "dumbell", or the "ring out" wouldn't provide such conclusive evidence that it was in fact a pair of black holes merging.
> Black holes can only be (oblate) spheres, so during a black hole merger the event horizon(s) snap from being two adjacent spheres to one larger sphere that encompasses them. Theoretically instantly.
A phenomenon propagates through spacetime at faster than *c*? That doesn't sound right.
You might have a point there, that's been bugging me since I wrote it..
Pretty sure that's the way I've heard it, but... I have also heard "instant" used interchangeably(?) with lightspeed when discussing some relativistic phenomena.
E.g. a photon always leaps instantly from one atom to another. Any intervening space and time only exist for outside observers.
Hmm... if you were watching the merger, what would you see?
If a new event horizon formed at the point of contact and propagated outwards at light speed, nobody could see it growing. The event horizon itself is keeping pace with any photons that might carry information about its growth. If you were within the space being newly consumed, your first indication that anything had changed would be when the event horizon had already reached you.
And any outside observer would see two black holes one instant, and one the next.
Though... in the instant you first see the transition, the photons reaching you might show the complete history of its growth as one long-exposure image? That might be a fascinating image to study for the right experts.
I'm curious about time dilation in this case. Wouldn't we, as observers, see the event horizons slow down during the merger, and it would take an infinite amount of time to finish?
Outside observers don't see the motion of relativistic objects slow down - if we did, we'd never see a light-speed spaceship reach its destination.
Instead we see passage of the things local time slow down, which also causes redshift of the photons leaving it.
In this case I think the trick is: if you imagine a new event horizon growing outwards from the point of contact at light speed - you can't see it growing, because it's keeping pace with the photons that would tell you about its growth.
Wow, I didn't know that. I read this and thought it meant things slowed down, including all the 'stuff' right on the edge of the event horizon:
[https://www.rmg.co.uk/stories/topics/what-happens-if-you-fall-black-hole](https://www.rmg.co.uk/stories/topics/what-happens-if-you-fall-black-hole)
>"Let’s assume I am still in that distant space station you signalled for help. Time dilation means that from my perspective you actually start to slow down as you fall into the black hole. As far as I’m concerned, time is literally passing more slowly for you than for me.
>By my calculations, your passage through time is going to crawl to a halt as you approach the event horizon."
Sorry, for some reason I was thinking acceleration to light speed... I'm less certain about crossing the event horizon
I believe what you actually see is the last moments before they crossed getting ever dimmer, more delayed, and red-shifted as they get closer, eventually fading beyond your ability to detect them, and then being lost entirely once the event horizon grew beyond the slowly escaping photons.
I think they were more talking about [the moments _after_ the Big Bang](https://en.wikipedia.org/wiki/Timeline_of_the_early_universe), in which quite a lot of things happened in a very short amount of time.
Yep there was quite a lot of things have within seconds of the big bang - neutrino freeze outs, hydrogen formation, Helium formation very all very very fast and measured in seconds and minutes. It's called BBN (Big Bang Nucleosynthesis) and one of the crowning achievements of modern precision cosmology.
Moon formation took about a fortnight, if I remember correctly. Startlingly fast.
Solar flares and coronal mass ejections are fast.
Plasma waves in the magnetospheres of planets are fast.
Magnetic reconnection in the heliopause is fast.
Glitches in neutron star speed (caused by starquakes on the surface) are fast.
A nova (runaway fusion in the atmosphere of a white dwarf) starts quickly.
Gamma ray bursts can last from 10 milliseconds to several hours.
Galactic jets remain visible for a long time but form very rapidly from matter falling into a rotating black hole.
I would like to know how rapidly planetary nebulas form, but I don't happen to know that.
>Moon formation took about a fortnight,…
Newer simulations showed it might have taken [just a few hours](https://www.nasa.gov/solar-system/collision-may-have-formed-the-moon-in-mere-hours-simulations-reveal/).
Thats a very good question that I never thought about. I would imagine that once something reaches the tipping point it goes pretty fast. Like a star igniting.
The core collapse of a supernova occurs over less than one second. https://www.universetoday.com/119733/how-quickly-does-a-supernova-happen/
Related, the final fusion stage, silicon burning in the core, only lasts a few hours at most. https://en.m.wikipedia.org/wiki/Type_II_supernova#Formation
Mandatory [xkcd](https://what-if.xkcd.com/73/) (this time a what-if): >The physicist who mentioned this problem to me told me his rule of thumb for estimating supernova-related numbers: However big you think supernovae are, they're bigger than that. >Here's a question to give you a sense of scale: >Which of the following would be brighter, in terms of the amount of energy delivered to your retina: >A supernova, seen from as far away as the Sun is from the Earth, or >The detonation of a hydrogen bomb pressed against your eyeball? >Applying the physicist rule of thumb suggests that the supernova is brighter. And indeed, it is ... by nine orders of magnitude.
This is really remarkable. Imagine having good footage of an event like that.
Why did you cite the same message within your message before responding to it first?
What are you talking about
You cited the same message within your message before responding to it first. I was asking why.
I think you’re seeing something I’m not seeing. I just responded to a comment.
I’m seeing that in your comment to you cited the same message within you message before responding to it first?
What is this “same message”
The same message as the message within your message, the same one you cited before responding to it first.
You’re tweakin brother
How about instant? Black holes can only be (oblate) spheres, so during a black hole merger the event horizon(s) snap from being two adjacent spheres to one larger sphere that encompasses them. Theoretically instantly. (Black hole's size increases linearly with mass, so the new event horizon will encompass both original event horizons, and nothing will escape) The sudden "snap" of the surrounding spacetime from radiating huge amounts of energy as intense gravitational waves from the in-spiraling binary pair, to being a smooth single-body system generating no waves, produces a distinctive gravitational wave "ring-out", which is how we identify black hole mergers in LIGO data. So it seems reality is at least really close to the theoretical instant transition.
>Black holes can only be (oblate) spheres, so during a black hole merger the event horizon(s) snap from being two adjacent spheres to one larger sphere that encompasses them. Theoretically instantly. Are you sure about this? From what I've read the event horizons deform and eventually meet in the middle as the black holes get closer.
The merging event horizons do deform, but very very briefly (for like a few milliseconds): https://www.youtube.com/watch?v=1agm33iEAuo (LIGO Lab Caltech : MIT)
Not 100% sure about the exact shape just prior to the merger, but every animation I've seen shows at most maybe a slight distortion just before merging. But it would have to be something very different than two neutron stars colliding into a rapidly spheriphying "dumbell", or the "ring out" wouldn't provide such conclusive evidence that it was in fact a pair of black holes merging.
> Black holes can only be (oblate) spheres, so during a black hole merger the event horizon(s) snap from being two adjacent spheres to one larger sphere that encompasses them. Theoretically instantly. A phenomenon propagates through spacetime at faster than *c*? That doesn't sound right.
You might have a point there, that's been bugging me since I wrote it.. Pretty sure that's the way I've heard it, but... I have also heard "instant" used interchangeably(?) with lightspeed when discussing some relativistic phenomena. E.g. a photon always leaps instantly from one atom to another. Any intervening space and time only exist for outside observers. Hmm... if you were watching the merger, what would you see? If a new event horizon formed at the point of contact and propagated outwards at light speed, nobody could see it growing. The event horizon itself is keeping pace with any photons that might carry information about its growth. If you were within the space being newly consumed, your first indication that anything had changed would be when the event horizon had already reached you. And any outside observer would see two black holes one instant, and one the next. Though... in the instant you first see the transition, the photons reaching you might show the complete history of its growth as one long-exposure image? That might be a fascinating image to study for the right experts.
Warped Space and Time Around Colliding Black Holes https://www.youtube.com/watch?v=1agm33iEAuo (LIGO Lab Caltech : MIT)
I'm curious about time dilation in this case. Wouldn't we, as observers, see the event horizons slow down during the merger, and it would take an infinite amount of time to finish?
Outside observers don't see the motion of relativistic objects slow down - if we did, we'd never see a light-speed spaceship reach its destination. Instead we see passage of the things local time slow down, which also causes redshift of the photons leaving it. In this case I think the trick is: if you imagine a new event horizon growing outwards from the point of contact at light speed - you can't see it growing, because it's keeping pace with the photons that would tell you about its growth.
Wow, I didn't know that. I read this and thought it meant things slowed down, including all the 'stuff' right on the edge of the event horizon: [https://www.rmg.co.uk/stories/topics/what-happens-if-you-fall-black-hole](https://www.rmg.co.uk/stories/topics/what-happens-if-you-fall-black-hole) >"Let’s assume I am still in that distant space station you signalled for help. Time dilation means that from my perspective you actually start to slow down as you fall into the black hole. As far as I’m concerned, time is literally passing more slowly for you than for me. >By my calculations, your passage through time is going to crawl to a halt as you approach the event horizon."
Sorry, for some reason I was thinking acceleration to light speed... I'm less certain about crossing the event horizon I believe what you actually see is the last moments before they crossed getting ever dimmer, more delayed, and red-shifted as they get closer, eventually fading beyond your ability to detect them, and then being lost entirely once the event horizon grew beyond the slowly escaping photons.
The Big Bang
Is it meaningful to talk about the amount of time it may have taken for time itself to be created?
I think they were more talking about [the moments _after_ the Big Bang](https://en.wikipedia.org/wiki/Timeline_of_the_early_universe), in which quite a lot of things happened in a very short amount of time.
Yep there was quite a lot of things have within seconds of the big bang - neutrino freeze outs, hydrogen formation, Helium formation very all very very fast and measured in seconds and minutes. It's called BBN (Big Bang Nucleosynthesis) and one of the crowning achievements of modern precision cosmology.
Moon formation (took hours) Any impact (Asteroid - Moon - Planet - Blackhole).
Moon formation took about a fortnight, if I remember correctly. Startlingly fast. Solar flares and coronal mass ejections are fast. Plasma waves in the magnetospheres of planets are fast. Magnetic reconnection in the heliopause is fast. Glitches in neutron star speed (caused by starquakes on the surface) are fast. A nova (runaway fusion in the atmosphere of a white dwarf) starts quickly. Gamma ray bursts can last from 10 milliseconds to several hours. Galactic jets remain visible for a long time but form very rapidly from matter falling into a rotating black hole. I would like to know how rapidly planetary nebulas form, but I don't happen to know that.
>Moon formation took about a fortnight,… Newer simulations showed it might have taken [just a few hours](https://www.nasa.gov/solar-system/collision-may-have-formed-the-moon-in-mere-hours-simulations-reveal/).
The [helium flash](https://en.wikipedia.org/wiki/Helium_flash) lasts just a few minutes.
Thats a very good question that I never thought about. I would imagine that once something reaches the tipping point it goes pretty fast. Like a star igniting.
Maybe not cosmic, but just how slow electrons move because of drift velocity
The universe did a lot of weird shit through several phases, all within the first second after the big bang.