5 ms·

https://en.wikipedia.org/wiki/Old-fashioned_(short_story) https://en.wikipedia.org/wiki/Old-fashioned_(short_story) An Asimov story about stranded astro-miners

• Mistletoe 4y ago
  Sorry for a stupid question but I’ve seen it repeated on the internet many times that we can never observe anything actually falling into a black hole because it takes forever to actually fall in due to time lengthening the closer it gets. Is that true? It has never made sense to me, since we see effects of black holes all the time.
  • dotancohen 4y ago
    The object falling in has its time dilated to forever - it will never actually experience the "getting there". Outside observers, on the other hand, will observe the "getting there" just as if the black hole were any other large mass. Or do I have that backwards...
    • birdiesanders 4y ago
      Backwards
      • dotancohen 4y ago
        Thank you!
    • WrtCdEvrydy 4y ago
      Yes, the outside observers can see the item falling into the blackhole while the object experiences more and more time dilation. If you were falling into a wormhole, you would die of old age before getting there while outside observers would see you fall in quickly.
      • alonmower 4y ago
        You would be ripped apart instantaneously while everyone outside of the black hole would see the light you emit as you’re crossing the event horizon frozen in time. It’s an optical effect, nothing magical is happening to you as you fall into the enormous mass
      • OkayPhysicist 4y ago
        Like the comment you were responding to, you have that backward.
    • OkayPhysicist 4y ago
      You have that backwards. The person falling into the black hole falls straight towards the singularity as if it was any other massive object, straight through the event horizon without noticing anything change. The far away observer sees the falling one infinitesimally approach the event horizon, but never cross.
      • he0001 4y ago
        This ”never cross” statement bends my mind. Doesn’t it also mean that if we are observers, observing a black hole, we should not see an actual blackness as we should only see things that are slowly falling into the hole? Regardless of how much time that has been spent from the beginning of time? I mean the event horizon is the boundary but that never happen?
        • cthalupa 4y ago
          The light is increasingly redshifted, so for practical purposes it disappears from view quite quickly. The more sensitive the instrument, the longer you can observe, and this doesn't really have a limit - as sensitivity approaches infinity, so does the length of time you could continue to observe the object. But for practical purposes, we would not see a black hole as some sort of weird psuedo-magnet with all sorts of junk stuck to the edge of the event horizon.
        • OkayPhysicist 4y ago
          Because of time dilation, light emitted (or reflected off of) objects very near the event horizon end up getting spaced out over (almost infinite) amounts of time. For example, lets say you dropped a beacon that flashes every second into a black hole. As it approached the event horizon, you'd see the flashes only happen every 2 seconds, 4 seconds, minute, hour, decade, etc. Meanwhile, the length of those flashes are getting longer at the same rate, while producing the same number of photons, so the light gets dimmer and dimmer.
          • he0001 4y ago
            Another factor, that other things are falling into the whole, wouldn’t that mean that the event horizon, relatively, gets closer to an earlier object? Meaning an object may reach the event horizon faster than it would originally or is that constant relatively where the object exist in its descend?
  • plonk 4y ago
    https://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html https://math.ucr.edu/home/baez/physics/Relativity/BlackHoles... > So if you, watching from a safe distance, attempt to witness my fall into the hole, you'll see me fall more and more slowly as the light delay increases. You'll never see me actually get to the event horizon. My watch, to you, will tick more and more slowly, but will never reach the time that I see as I fall into the black hole. Notice that this is really an optical effect caused by the paths of the light rays. > This is also true for the dying star itself. If you attempt to witness the black hole's formation, you'll see the star collapse more and more slowly, never precisely reaching the Schwarzschild radius. I don't understand everything but it seems that the falling guy tends towards the event horizon, getting slower and slower relative to the observer, and never reaching it from the observer's point of view? Edit: this applies when observing something falling into the black hole. It doesn't apply to faraway objects that deviate because of the black hole's gravity well, so we can observe most of a black hole's effects.
    • Mistletoe 4y ago
      Yes they say this but how do we see the jet in the original linked article haha?
      • plonk 4y ago
        No source now, but I think I've read that the jet is matter that's far enough from the black hole to escape it, accelerated during its rotation. The wiki page isn't very clear about how the jet is created: https://en.wikipedia.org/wiki/Tidal_disruption_event https://en.wikipedia.org/wiki/Tidal_disruption_event
      • dcminter 4y ago
        As I understand it (based entirely on pop sci books and articles) they're purely from the accretion disk i.e. nothing inside the event horizon. I don't think the exact mechanism is agreed upon beyond that.
      • wholinator2 4y ago
        The types of highly visible bright lights coming from black holes are not actually coming from inside the black hole. The gravitational potential of the well is so incredibly high that objects falling through it gain immense amounts of energy, thus giving of very high energy radiation, i.e. x-rays.
  • monocasa 4y ago
    The effects aren't limited to just falling in. Once you pass the event horizon it's game over, but remarkably little matter from, say a star falling in, will actually reach the event horizon. For one example, a lot of particles get swept up in the magnetic maelstrom surrounding spinning black holes and are shot away from the poles at near the speed of light. That's what we're seeing here.
  • lisper 4y ago
    > Is that true? Probably. We don't know for sure because quantum effects might change things, and we don't yet have a theory of quantum gravity. The event horizon of a black hole is pretty much the one place in the universe where the effects of quantum gravity are most likely to manifest themselves, so one should hedge one's bets when making predictions in their vicinity. > It has never made sense to me, since we see effects of black holes all the time. Falling into a black hole is different from falling into a regular gravitational field. All kinds of weird shit happens before you reach the event horizon. Among other things, tidal forces rip you apart, heat you up, and turn you into a plasma. That plasma emits radiation, and that is what you see (because all that happens outside the event horizon).
    • bmitc 4y ago
      It all depends on the size of the black hole. HUGE black holes have weak tidal forces.
      • lisper 4y ago
        True, but the hole under discussion here is not one of those. (And it's important to note that big holes have weak tidal forces at the event horizon. They still probably have pretty significant tides close to the singularity, but God only knows what actually goes on in there).
        • libraryofbabel 4y ago
          > but the hole under discussion here is not one of those. That’s not correct: It’s a supermassive black hole at the center of a galaxy; the tidal forces will be weak at the event horizon.
          • lisper 4y ago
            Yeah, I know that's what the news reports say, but I'm pretty sure they got it wrong. A galactic hole doesn't emit radiation (except perhaps Hawking radiation) because its tidal forces are too weak.
  • rssoconnor 4y ago
    FWIW, I asked my physicist friend this question one time. He said while an outside observer would never see a "massless test particle" enter the event horizon due to time dilation effects, real particles have mass and their own gravitational field, and thus due to complicated stuff they can eventually been seen passing through or otherwise somehow merging with the event horizon.
  • BurningFrog 4y ago
    So an observer near the black hole would see an eternally accumulating number of objects falling towards it, but crawling to a halt near the event horizon?
    • MattPalmer1086 4y ago
      And the light getting increasingly red shifted until you can't really see it anymore.
      • BurningFrog 4y ago
        I see. Another way to think of "redshift" is "lower energy", so these things will disappear from sight another way.
        • deleted 4y ago
          [deleted]
    • cthalupa 4y ago
      It depends on the sensitivity of the instruments. For human eyes looking out the window of a spaceship, they would be redshifted away to invisibility pretty quickly.
  • waltbosz 4y ago
    https://en.wikipedia.org/wiki/Spaghettification https://en.wikipedia.org/wiki/Spaghettification I think spaghettification is my favorite word, maybe it's tied with defenestrate.
  • cthalupa 4y ago
    You'll never directly see them fall in, but you will see them "disappear" pretty quickly as the light is redshifted past the point of visibility, etc. The more sensitive whatever tool you are using to detect the photons is, the longer you can watch, and something that approaches infinite sensitivity would be able to see you for a time period that also approaches infinity, but outside of the realm of the theoretical, anything falling in to the black hole will wink out of existence in a fairly large hurry once it reaches the event horizon. But things like accretion disks and these relativistic jets are happening outside of the event horizon, so they're not subject to these same concerns to begin with. For example, the accretion disk of Sagittarius A*, the supermassive black hole at the center of our galaxy, has an accretion disk that is roughly 1/100th of a light year, or about 25 times the size of our solar system. The event horizon, however, is only about 16 million miles - or a roughly 1/6th the distance between the sun and the earth. (These numbers are based on our current best estimates - and those estimates have changed frequently over the past 20 years as we get better data, but the general scale should be quite accurate)
    • szundi 4y ago
      AFAIK you never see it falling in as it just slows and turns into more red, but slowly.
  • rirze 4y ago
    There's a difference between objects falling into the black hole versus material accreting on the black hole's horizon that can generate high energy beams.
  • bmitc 4y ago
    The visible effects we see for black holes are things from well outside the event horizon, where black holes behave as just another gravitational object. Things, i.e. gas, can rotate and swirl around them. Since the black hole can be rotating and the gas being slung around violently, it can emit radiation. If I understand correctly, the jets for supermassive black holes can extend out to sizes comparative to the containing galaxy’s diameter. Here’s a nice simulation showing this in action (article in description): https://youtu.be/g1aW8TDOm4A https://youtu.be/g1aW8TDOm4A The YouTube channel Kurzgesagt also has some pretty good illustrations and animations.
  • cryptonector 4y ago
    It is and it isn't true. Light from the falling object will be red-shifted, and eventually you won't be able to see it, but if you could see extremely long wave-length light, and if you could observe it for a really long time, you'd see light from that object asymptotically approach the universe's size as its wavelength, and you'd never see the object go over. But obviously it's not possible for humans to observe extremely long wavelength light, so you'd just see the object disappear when light from it red-shifts beyond the range you can observe. The object, meanwhile, does fall in from its perspective.
  • at_a_remove 4y ago
    Once a black hole -- a collapsar -- forms, and you want to toss something into it, it is best to imagine two timelines. From the point of view of the object being hurled into the black hole, things proceed more or less normally: you accelerate as you fall, but light behind you becomes curiously more blue and brighter. You eventually reach the event horizon, which ought to be called EH-sub-0, because it is only the first event horizon. It might be helpful to think of a black hole's interior as infinitely layered event horizons, event horizons "all the way down." You'd note a restriction of movement -- "up" (away from the black hole) is no longer a possibility; every direction is some variation of down, perhaps down and to the left, down and east, whatever, but always down. Eventually tidal forces take over depending on the size of the thing -- you might notice them before or after the outmost event horizon, and "spaghettification" occurs even as you are pummeled with X-rays and gamma radiation from behind (millennia of impacting photons blueshifted and jammed into a smaller timeline). From the outside, however, your astronaut or thrown Cylume lightstick becomes more and more red, and dim, slowly approaching that event horizon but you'll never see it get there as it now emits infrared and not much of that. You switch on your FLIR and you can see it, for a while, but it grows dimmer and eventually disappears off of that. Eventually it emits very weak radio waves, and you lose track of the thing, but even if you spent a million years building longer and longer antennae, you'd never see it hit. The effects you see of a black hole are 1) gravitational lensing (photons bending in their trajectory around the exterior of a black hole, just above the outermost event horizon), 2) the formation of an accretion disc (as matter swirls into it, growing hot from friction and compression), 3) absolute blackness if you managed to get a "transit" of something particularly large across a light path, 4) other knock-on gravitational effects, like disturbed orbits.
    • wizzwizz4 4y ago
      > You'd note a restriction of movement -- "up" (away from the black hole) is no longer a possibility; every direction is some variation of down, perhaps down and to the left, down and east, whatever, but always down. You'd notice if you were doing calculations as you fell. Locally, nothing particularly special happens at the event horizon, as far as I understand; just, past that point, all future directions lead to the centre of the black hole. (Plenty of past directions still point outwards, so you wouldn't even see anything particularly special unless you were paying close attention to, say, the apparent shape of the black hole.)
  • ars 4y ago
    You are correct, and it means black holes can never actually form, because it would take an infinite amount of time for them to form. > since we see effects of black holes all the time. We do not, we see super massive objects, or black holes in progress, but no actual black holes.
    • cthalupa 4y ago
      >You are correct, and it means black holes can never actually form, because it would take an infinite amount of time for them to form. This is incorrect. They necessarily do not have an event horizon that light cannot escape until they are a black hole, so as they have finished forming into one by the time we can no longer observe past the event horizon. We can also still witness the black hole growing even after that point. [1] 1. https://www.forbes.com/sites/startswithabang/2020/01/11/ask-ethan-does-a-time-stopping-paradox-prevent-black-holes-from-growing/?sh=5935cf297b83 https://www.forbes.com/sites/startswithabang/2020/01/11/ask-...
      • ars 4y ago
        I appreciate you finding me this link, but I have MAJOR issues with the explanation. It basically say that yes, it will take an infinite amount of time, but because the mass is able to arrive at the black hole before it becomes a black hole, it can first arrive at the black hole, and then after that the event horizon will grow to encompass the new mass. I'm sorry, but that's just ..... I don't even know how to respond. The mass arriving and the black hole changing mass happen at the exact same time, as the mass arrives, the time dilation of the pending black hole increases, and the mass never actually arrives. These things don't happen sequentially, they happen simultaneously.
        • cthalupa 4y ago
          There's a couple of things here. 1) Again, it cannot have this event horizon until it becomes a black hole. That is one of the defining features of a black hole. We will be able to see photons escaping through the collapse period until it is a black hole, and once photons can't escape, it is already a black hole. 2) Time does not flow universally with a single reference frame. It appearing to take infinitely long for something to fall into the black hole from our point of view does not mean that it does so for the thing falling into the black hole or for the black hole itself. Time flows normally for the observer, and if they are falling into, say, a supermassive black hole with limited tidal forces, and in a spaceship that can protect from the radiation, etc. from the accretion disk and everything else, they will not notice anything particularly different about the low of time as they fall. In fact, for black holes of sufficient size and with sufficient charge or rotational velocity, there's actually a second event horizon past the first that could even potentially support stable orbits, even those of planets or entire solar systems. It's likely only a theoretical thing - we don't know a mechanism that would generate enough rotational velocity or charge for a black hole large enough for there to be enough room to push this second event horizon out far enough from the singularity to make this practical. But time flows differently for both parties, and the increase in mass in the black hole is immediate for the black hole itself, as is the increase in the event horizon's radius, as it would be for anything falling into it.
• monkeycantype 4y ago
  I tried to perform a frequency domain analysis of the recorded signal but it's returning HTTP 419 Never Gonna Give You Up