I've watched this at least 50x, and still learn from it, as it takes awhile to mentally process. Darn interesting, and thanks for creating this content.
Absolutely brilliantly explained. What I love is that you take your time explaining things. Channels like Arvin Ash, Science Asylum, PBS Space Time, ParthG, etc are all great but they cram in complex physics topics in 8 or 15 minute videos. Hardly enough time to absorb what they're saying. I love your feature length videos. You explain things that the non expert can understand, yet detailed enough for those with a rudimentary understanding of physics to still find massively helpful. I've only just discovered your channel. Please carry on the good work.
The part about space time itself flowing into the black hole does an excellent job in my mind at explaining why the light speed coming out from the gravitational area outside of the event horizon is slowed down. It's the speed of light minus the speed of gravitational attraction. That's super cool.
...for more than 3 years, RUclips waited to send me your way. I'm so glad it did! Near college level lectures explained just simply enough for most average folks to be awed while going in deep enough into the math and physics to still teach space nerds like myself :)
Interestingly enough these were college lectures. They were just the college lectures for an Honors introductory astronomic class. They would of course have to be modified for classes in a major. But they are relatively advanced for an introductory class
@@JasonKendallAstronomer then all my keeping up with and constant intake of information hasn't been for naught! While I don't understand the math, I can see the visuals of the physics working in my head. I'd love to properly go through college, but I don't have the patience or resources to deal with the system, so I teach myself what I can when I can. Thank you for expanding my knowledge faster than infalling matter during a core collapse
Jack will never make it to the singularity. He (or whats left of him) will stay just below the event horizon while time rushes "above" him. Eons will pass in an instant, and eventually he will be ejected in form of hawking radiation, or be flung out at the definite "end of times" when enough mass has evaporated from the black hole, when the outward pressure wins over gravity. I have absolutely nothing that supports this, just a gut feeling. ;)
Hawking radiation doesn't work like that. Radiation doesn't come from beyond event horizon. Virtual particles emerge out of nothing and sort of lend the energy from universe, which is given back when they vanish. Black hole evaporates because sucked in other virtual particle changes into negative -
First thing to say is beyond the event horizon reminds me of the first rule my economics teacher pounded into my head. You cannot use micro rules to solve macro problems! If space/time is the thing that every thing else is a Feature of, then when the denominator ( Time ) becomes zero all bets are off.. If the event horizon is in fact time equaling zero then there should be a thin shell ( Plank length or 2 ) of stuff falling at zero speed. Anyway thks Jason for taking the time to try and teach us, and forgive our assumptions.
Well, you're assuming a simple algebra and assuming economic principles. I knew it was a Dark Art, but this is the darkest corner to apply its principles!
Curious: everything being torn apart by tidal forces as it falls into a black hole. Is this true of fundamental particles too? Do single electrons experience tidal forces?
Well is than alright to assume that probably singularity is the most luminous object in the universe but in a region around it its gravity puls with such speed that exceeds even speed of light?
I wonder wether, at least for rotating massive stars, the constant angular momentum could lead , during the shrinking of the star, to a certain balance between increasing centrifugal force and gravitational force before reaching the Schwarzschild radius thus avoiding BH formation.
That’s a good physics question. I’m sure someone has a paper on arxiv.org to that effect. You’ll hunt long for the answer and it’ll be a brutal bit of GR. also, it’ll involve degenerate states of matter, since the postulated spinning would allow for the matter to settle, however briefly, into a bizarre state.
I liked the analogy of spacetime flowing like water if you consider that with spacetime being flat rather than the usual depiction of it being curved. And this flow shows the direction of gravitational flow. One question I have is that can you have negative mass that changes this direction of flow? Or if you consider your typical spacetime picture of concave troughs caused by large masses, why don't we see convex peaks? Could such phenomena push spacetime flow as to account for the universes expansion attributed to dark energy?
I like this question! The spacetime metric of the universe as a whole is very different than that of a black hole. The Schwarzschild Metric for a black hole is defined by a distant observer and not a near one. If you fall into a black hole, you don’t perceive your own clock running slowly. But a distant observer would measure your clock essentially stopping as you approach the event horizon. The spacetime metric for the universe is the Robertson-Walker metric. It is homogeneous and isotropic. That means all observers inside the particle horizon see the universe expanding uniformly from all locations. This results in no location being special compared to any other region. So there is no time dilation for any observer.
If mass is converted into a length and space is "longer" near massive objects, then how would you apply this concept to black holes? Also, if mass is the thing toward which spacetime is flowing, then what kind of spacetime flows (i.e. curvatures) are being produced by any given black hole? There must be some terminal point to a given black hole, albeit an immense distance (but not infinite), correct? Further, if space(time) flows faster than the speed of light, as suggested, since it is not a "thing" (without mass?), then spacetime is pure energy? Dark energy? And since black holes convert mass into energy (gravitational waves), then mass/matter is not lost to a black hole (nor lost to the universe) but is converted into a form of energy (i.e. the gravitation waves)?
Jason love you're lectures! They are rad although I'm not quick enough to understand or visualize ALL material! Still fun, on this lecture I was at wonder if Jack would not "feel" the gravitational tide ripping him apart. Wouldn't the gravity prevent the electrical pain signals also be torn towards singularity, never reaching his brain?
I think that the signals would travel faster than the stretching, so yeah, he'd feel it.... But one's body would likely not survive to the point where spaghettification would happen. It'd be quite a bouncy ride.
Something ive always wondered about: Just beyond the event horizon, space becomes time, and time becomes space, (because relativity) so what do you think it would be like, if space-time became time-space?
Interesting thought, but the odd way to state it is that the future is "right below your feet", literally. That means that the direction of "down" is always unseeable. It "is" the Future. That's why, even inside the black hole, you see the event horizon below you....
I really don't like physicist saying, "pass neutron degeneracy pressure the star will collapse all the way to a singularity". How do we know there isn't another stage, for example quark degeneracy or even Higgs pressure? Even better what if they DO assume it's at some finite radius and work a GR and QFT theory from that, does that help?
I don't like 'infinite' anything either, doesn't seem to fit with reality, but fine mathematically. I'm wondering if stretching space-time also affects things like the universal constants, especially the planck length. Could be a single high energy particle, rather than a 'singularity', sitting in there. (particles being enough energy stuck in a field in one spot).
If the gravitational energy density is high enough for spontaneous particle creation at the Schwarzschild radius, then this must also occur at smaller distances. Does this connection between massive energy density's and particle creation have any implications on the beginning of our universe?
Thank you for this. I have watched and continue to watch countless videos on black holes and the holographic universe... Everything quantum. It's no wonder I don't sleep at night 🤷❤️🙏🌒🌕🌘
And to jack, as he approaches the blackhole, if he looks up the universe will appear to be blueshifted more and more. He will eventually go blind, or get cancer, from just this light. So if the blackhole doesnt kill you (which it will) then you would be blinded and killed by the blueshifted light, as it will become more than deadly gamma radiation.
Million ways to die.... Actually, the photons would pack so much energy from the blue shifting that they would create ever more energetic particles. Those particles would bombard you with great energy, tearing you and themselves apart....
enjoying the videos Jason, thanks! so in this one, there seems to be a discrepancy in the equivalency principle, maybe just in the example. say there's Jill's lab free-floating in space. then there's Jack's identical lab free-falling towards an event horizon. wouldn't physics then be actually different in Jack's lab, so he could tell "uh oh, gravity gradient detected! lab falling into a black hole!," because Jack would start to feel being stretched before his imminent spaghettification?
You are correct. Jack will, strictly speaking, as he gets closer to the hole, see some effects as you say, especially if the hole is stellar mass, because of the non-uniform field near the EH. The point of the example is, of course, to show that we can choose a small enough lab frame so that even in a stellar mass black hole, the effects wouldn't be seen. That is the basic idea of all GR. But yes, if Jack's falling spaceship were miles high and wide, like the final episode of Doctor Who (number 12), then effects would be extremely apparent.
Well why do we see the bright accretion discs near the event horizon of a black hole, if the light coming from the infalling matter is so incredibly redshifted?
There a couple of reasons for this. The first is that it doesn’t spiral all the way to the event horizon at some point which is called the smallest stable orbit it’s simply plunges in. The other is that the x-ray radiation of the innermost accretion disk happens pretty far outside of the Schwarzschild radius.
@@JasonKendallAstronomer Oh Thank you! So we see only the accretion disc and it't processes but we can't ever seen the "spiralling down" actually. So therefore many artificial pictures do suggest quite false impressions.
@@kalles8789 i think about that sometimes just how fucking crazy it would be to look down into space just dropping to a bottomless hole like if there was no accretion disc and it was a small enough bh so that you can entirely see the actual fabric of space dropping and then riding the most insane rollercoaster hill drop ever, obviously not possible but still nuts, the idea of space being a fabric that distorts from mass but we cant see the actual fabric like wtf is it like how does something hold shit up and you cant see it but you move through it exist mind boggling
So a neutron star, while it is weird, it is certainly possible according to known physics. A black hole though, it seems to be 'impossible', Because the idea suggests that stuff can just disappear.
Didn't watch it , but I think blackholes make stuff not visible to the eye. The stuff however is still notable in other ways (gravity). But may be I should listen to the lecture first...
47:30 'that funny thing' ? 1:09:00 Hawking radiation is fact. Spontaneous particle creation/annihilation at the event horizon is a consideration worthy of thought. perhaps the anti-particle survived falling into the singularity and this presented as a loss of mass in the whole system, a reduction in the system as a black hole. Oh to see inside! Me wanna know.
Nope, Hawking Radiation is not fact, as any physicist will acknowledge. We have no working theory of quantum gravity and Hawking Radiation, according to theory, is of so weak intensity that it might never be measured.
I fail to see how anything that is a 'real' particle falling in would do anything other than increase the mass, unless you have some negative mass particle. I'd guess you can't warp space-time enough to stop light getting out completely, just extremely red shifted to long radio wavelength. If you could warp space-time that much, surely you'd have some sort of 'barrier' / 'break' that nothing could actually cross (anything has to travel through space-time, including light) and you'd be sort of pulling it inside out in a way (hard to visualise or describe in 3d), I like to think of it of an extremely steep sided hole (rubber sheet analogy with exteme stretch) but where the sides aren't quite at 90 degrees, but very close and ending at an extremely small point (but not quite infinitely small), with the 'hole' being very narrow. I'm probably way out, though.
This is what I don't understand. If all of the light from the universe shines into the black hole at infinite blue shift (so infinite energy) and light carries energy, and energy and mass are equivalent, then why doesn't the black hole increase in energy (and mass) infinitely quickly to become the size of the entire universe? Obviously this doesn't happen, so either my thought process is totally out of whack, or light energy can't convert into 'real' mass (no amount of light can convert into additional mass - shining light into a black hole, no matter the energy level, can't deposit additional energy inside, somehow). This seems to go against some sources that say mass is just 'confined' energy.
First just to be clear there is not an infinite amount of light that is shining on a black hole. It’s an extremely small surface area compared to the universe so only a very small amount of light actually hits the black hole horizon. Most light that goes towards a black hole actually misses the event horizon and is scattered away on odd looping paths determined by the Schwarzschild metric.
The error comes from thinking that a black hole sucks up everything. The Earth has a much bigger cross section as a target than a black hole. But it’s not getting infinitely hit due to sucking up light. Also The Sun is shining by light and it’s not much smaller than stellar mass black holes.
@@JasonKendallAstronomer I'm misunderstanding what you mention around 43:00 then. Not surprising as I, like probably many others just can't, as you say, get their heads around something so complex.
i wonder why the size difference of the (black hole sun = 3km) and the (black hole earth 0,8cm) is so much bigger than compared to the normal state? (Sun diameter = 1,391.000km) / (Earth = 12.700km). So in the normal state the earth would fit 110 times across the diameter of the sun but when we compare the black hole size, the black hole earth would fit in the black hole sun 375.000 times ( 3000m / 0,8cm) Why is that difference so big?
The main reason is that the Earth and Sun now have different states of matter, and different compositions. The Earth and Sun have almost the same exact atomic composition. They were formed from the same cloud of gas and dust. However, Earth was not massive enough to hold onto the primordial hydrogen and helium, so they stayed in gaseous form and did not collapse down. Earth was formed from dust and rocks, but the the gas (mostly H and He) was centered on the young proto-Sun. At the end of formation, the Sun contained most of the mass of the Solar System, and nearly all the H and He. This means the Sun's state of matter is a classical ideal gas all the way down, so pressure, temperature and volume are well described by that throughout the Sun. The Earth, though, is a solid. Solids have complex relationships between temperature, pressure and volume, and resist compression in different ways than the Ideal Gas Law. To wit: you can compress air with just your mouth or clapped hands, but you can't compress a table or chair. You can break it, but you have a really hard time compressing it. Even a trash compactor mostly folds and removes structural spaces to reduce size. You can expand and contract metals by heating them, though, and this is more like what I am saying. In any event, the Earth doesn't get much smaller due to the way solids resist compression. The Sun, as a gas, compresses quite well. Now, a black hole isn't anything but mass and spacetime. It isn't a gas or solid, and asking what its equation of state is, is meaningless, since the composition of it is just "mass" and "spin" and maybe "charge". That's it. Nothing more. You use relativity to describe a black hole, and you use solid state physics to describe the Earth, and you use a gas law to describe the Sun. These all lead to very different relationships between mass, composition, volume, temperature and pressure.
@@JasonKendallAstronomer I understand that the properties/composition of earth and sun are different. But to calculate the size of a black hole you only need to know the mass of a object right? I want to visualize my thoughts to you. Reality: Volume (Earth could fit 1.300.000 times in the sun) Mass (Sun has the mass of 330.000 earths) Black hole scenario (diameter): Sun (2,96km) or 296.000cm Earth (8,8mm) or 0,88cm The difference between those two scenarios is ridiculous. A 0,88cm (Black hole / earth marble) could fit in a (Black hole Sun /2,94km) trillion x trillion x trillion....times. Imagine you would compress 330.000 individual earths (wich is equal to the mass of the sun) into a 0,88cm black hole each. And than merge all the mini black holes together. would a 2.96km black hole arise? It would only be true if you line up those mini black holes in a line. 330.000 x 0,88cm = 296.000cm But the black hole is a sphere right? so you cant just add up the diameter of the black holes. You have to add the Volume of each mini black hole right? Volume black hole (earth) Diameter: 0,88cm Volume: 0,357cm´3 330.000 x 0,357cm´3 = 118.000cm´3 = Diameter: 60,85cm -> this should be the size of the black hole sun when the volumes are calculated together and not just the diameter
The difference arises because the BH radius are depending only on the mass of the two bodies and reflect the ratio between the mass of sun which is 2*10^30kg and that of earth which is about 6*10^24 kg
... and the moral of the story is... DON'T be like Jack and Jill... One little argument and Jack is ripped to shreds... In the meantime, Jill has to live with his final image for eternity!
As matter crosses the event horizon wouldn’t it freeze in that orbit as time slows to near zero? Wouldn’t that prevent mass from continuing to “fall” to the center of mass of the BH? So then would BHs be uniformly “solid” as matter it stuck at the radius it crossed the EH?
Interesting syllogism! But your conclusion doesn’t follow from the two statements above it. This is because the Schwartzschild metric is mathematically equivalent to another metric without a coordinate singularity at the EH. The EH is merely where infalling matter starts to fall faster than the speed of light. Thus, no signal can return. No chemical bond or atomic bond or nuclear bond can stand up to the effect of this falling so anything that survives passage through the EH is torn apart.
You missed a huge point to make about Jack and Jill and next time get rid of the stupid laser pointer out of the thought experiment and give them a rope. It's just a thought experiment so make the rope infinitely long. Just a quick question Jason. Remind me again, what is the maximum speed of an object falling in an infinitely long gravity well?
The idea of an infinitely long rope and and infinitely long gravity well, are not really too realistic. Thought experiments are geared to actually be experiments that could be done if you had the money, resources, technology and materials. One cannot get an infinite rope, so your first statement has a real-world result. The rope would break, no matter what, it would dangle straight in from about 1.5 R_schwarzschild. Anything holding the rope would orbit no matter what. Your second statement assumes the Newtonian potential. Things are different in the strong regions inside 3 R_s of the event horizon. There is a maximum orbital speed in the ergosphere of a rotating black hole. And, of course, the maximum speed of "falling" would be the speed of light. Nothing goes faster than, or equal to, light speed if it has mass. No infinities except at the singularity....
If the intense gravity near the event horizon slows down time, then why in every rendering of a black hole I’ve seen in these types of lectures show the matter closest to the horizon moving quickly and white hot? Shouldn’t it be redder and slower than matter farther away from the horizon? The bathtub drain visual model where matter is spinning faster near the horizon needs to be retired.
Awesome video, many many thanks!!! I finally got a lot of answer regarding black holes and especially regarding the singurlarity, why light can’t escape anything from within the Event horizzon. Jason Kendall have a fantastic way of simplefying the advanced language. Thanks to this video, l got some answers and l feel physical lighter in my body. I have used a lot of brainpower nagging about the whole thing about the concept of singularity and that it actually have a surface. Ten-twenty-or more-hours of drowning myself in fantastic videos of the universe, was’nt able to make me understand this, before now…finally! A lot of thanks and looking forward to study more of your videos👌
So does jack always see the blackness below him or does he see it envelop him ? It can't be both . Either the black hole is always below him or it is all around him as he looks up . Which one ?
@@JasonKendallAstronomer but what I mean is , if the black hole always stands off below him , then how does his view of the universe become a shrinking circle above him. I was lead to believe that his view of the universe should become a compressed blue shifted ring around him. Not an ever shrinking circle above him. I have seen this explained both ways but I think the correct answer is it forms a compressed ring around him as he approaches the singularity.
Interestingly, this same thing was said to Newton as a public insult for using the word gravity to describe the phenomenon of things falling to Earth. They mocked him for saying that Nature has a heavy and sad disposition.
Great lectures and I really appreciate the NO commercial interruptions.
I've watched this at least 50x, and still learn from it, as it takes awhile to mentally process. Darn interesting, and thanks for creating this content.
Absolutely brilliantly explained. What I love is that you take your time explaining things. Channels like Arvin Ash, Science Asylum, PBS Space Time, ParthG, etc are all great but they cram in complex physics topics in 8 or 15 minute videos. Hardly enough time to absorb what they're saying. I love your feature length videos. You explain things that the non expert can understand, yet detailed enough for those with a rudimentary understanding of physics to still find massively helpful. I've only just discovered your channel. Please carry on the good work.
The part about space time itself flowing into the black hole does an excellent job in my mind at explaining why the light speed coming out from the gravitational area outside of the event horizon is slowed down. It's the speed of light minus the speed of gravitational attraction. That's super cool.
...for more than 3 years, RUclips waited to send me your way. I'm so glad it did! Near college level lectures explained just simply enough for most average folks to be awed while going in deep enough into the math and physics to still teach space nerds like myself :)
Interestingly enough these were college lectures. They were just the college lectures for an Honors introductory astronomic class. They would of course have to be modified for classes in a major. But they are relatively advanced for an introductory class
@@JasonKendallAstronomer then all my keeping up with and constant intake of information hasn't been for naught! While I don't understand the math, I can see the visuals of the physics working in my head. I'd love to properly go through college, but I don't have the patience or resources to deal with the system, so I teach myself what I can when I can. Thank you for expanding my knowledge faster than infalling matter during a core collapse
@thetobi583 agreed. This is a great gift of public outreach education! Thanks Jason.
Jack will never make it to the singularity. He (or whats left of him) will stay just below the event horizon while time rushes "above" him. Eons will pass in an instant, and eventually he will be ejected in form of hawking radiation, or be flung out at the definite "end of times" when enough mass has evaporated from the black hole, when the outward pressure wins over gravity.
I have absolutely nothing that supports this, just a gut feeling. ;)
Hawking radiation doesn't work like that. Radiation doesn't come from beyond event horizon. Virtual particles emerge out of nothing and sort of lend the energy from universe, which is given back when they vanish. Black hole evaporates because sucked in other virtual particle changes into negative -
First thing to say is beyond the event horizon reminds me of the first rule my economics teacher pounded into my head. You cannot use micro rules to solve macro problems! If space/time is the thing that every thing else is a Feature of, then when the denominator ( Time ) becomes zero all bets are off.. If the event horizon is in fact time equaling zero then there should be a thin shell ( Plank length or 2 ) of stuff falling at zero speed. Anyway thks Jason for taking the time to try and teach us, and forgive our assumptions.
Well, you're assuming a simple algebra and assuming economic principles. I knew it was a Dark Art, but this is the darkest corner to apply its principles!
Great series of videos, thank you very much!
Thanks!
the photon shell of a blackhole would certainly shine a bright lighjt in your face kinda like a kilonova at nose distance
Curious: everything being torn apart by tidal forces as it falls into a black hole. Is this true of fundamental particles too? Do single electrons experience tidal forces?
Wonderful Sir.very important and informative .thank you
Well is than alright to assume that probably singularity is the most luminous object in the universe but in a region around it its gravity puls with such speed that exceeds even speed of light?
I love these series ❤
Fantastic videos!
I wonder wether, at least for rotating massive stars, the constant angular momentum could lead , during the shrinking of the star, to a certain balance between increasing centrifugal force and gravitational force before reaching the Schwarzschild radius thus avoiding BH formation.
That’s a good physics question. I’m sure someone has a paper on arxiv.org to that effect. You’ll hunt long for the answer and it’ll be a brutal bit of GR. also, it’ll involve degenerate states of matter, since the postulated spinning would allow for the matter to settle, however briefly, into a bizarre state.
I liked the analogy of spacetime flowing like water if you consider that with spacetime being flat rather than the usual depiction of it being curved. And this flow shows the direction of gravitational flow. One question I have is that can you have negative mass that changes this direction of flow? Or if you consider your typical spacetime picture of concave troughs caused by large masses, why don't we see convex peaks? Could such phenomena push spacetime flow as to account for the universes expansion attributed to dark energy?
Why wasn’t the gravitational time dilation of the universe infinite at the Big Bang? Seems like that moment should have taken forever.
I like this question! The spacetime metric of the universe as a whole is very different than that of a black hole. The Schwarzschild Metric for a black hole is defined by a distant observer and not a near one. If you fall into a black hole, you don’t perceive your own clock running slowly. But a distant observer would measure your clock essentially stopping as you approach the event horizon.
The spacetime metric for the universe is the Robertson-Walker metric. It is homogeneous and isotropic. That means all observers inside the particle horizon see the universe expanding uniformly from all locations.
This results in no location being special compared to any other region. So there is no time dilation for any observer.
If mass is converted into a length and space is "longer" near massive objects, then how would you apply this concept to black holes? Also, if mass is the thing toward which spacetime is flowing, then what kind of spacetime flows (i.e. curvatures) are being produced by any given black hole? There must be some terminal point to a given black hole, albeit an immense distance (but not infinite), correct? Further, if space(time) flows faster than the speed of light, as suggested, since it is not a "thing" (without mass?), then spacetime is pure energy? Dark energy? And since black holes convert mass into energy (gravitational waves), then mass/matter is not lost to a black hole (nor lost to the universe) but is converted into a form of energy (i.e. the gravitation waves)?
Jason love you're lectures! They are rad although I'm not quick enough to understand or visualize ALL material! Still fun, on this lecture I was at wonder if Jack would not "feel" the gravitational tide ripping him apart. Wouldn't the gravity prevent the electrical pain signals also be torn towards singularity, never reaching his brain?
I think that the signals would travel faster than the stretching, so yeah, he'd feel it.... But one's body would likely not survive to the point where spaghettification would happen. It'd be quite a bouncy ride.
Something ive always wondered about:
Just beyond the event horizon, space becomes time, and time becomes space, (because relativity) so what do you think it would be like, if space-time became time-space?
Interesting thought, but the odd way to state it is that the future is "right below your feet", literally. That means that the direction of "down" is always unseeable. It "is" the Future. That's why, even inside the black hole, you see the event horizon below you....
I really don't like physicist saying, "pass neutron degeneracy pressure the star will collapse all the way to a singularity". How do we know there isn't another stage, for example quark degeneracy or even Higgs pressure? Even better what if they DO assume it's at some finite radius and work a GR and QFT theory from that, does that help?
I don't like 'infinite' anything either, doesn't seem to fit with reality, but fine mathematically. I'm wondering if stretching space-time also affects things like the universal constants, especially the planck length. Could be a single high energy particle, rather than a 'singularity', sitting in there. (particles being enough energy stuck in a field in one spot).
If the gravitational energy density is high enough for spontaneous particle creation at the Schwarzschild radius, then this must also occur at smaller distances. Does this connection between massive energy density's and particle creation have any implications on the beginning of our universe?
It certainly does. Take a peek at my Module 11 videos on the Big Bang.
Thank you for this. I have watched and continue to watch countless videos on black holes and the holographic universe... Everything quantum. It's no wonder I don't sleep at night 🤷❤️🙏🌒🌕🌘
Just curious if you've watched my series on atoms and light. It describes a lot of QM.
And to jack, as he approaches the blackhole, if he looks up the universe will appear to be blueshifted more and more. He will eventually go blind, or get cancer, from just this light. So if the blackhole doesnt kill you (which it will) then you would be blinded and killed by the blueshifted light, as it will become more than deadly gamma radiation.
Million ways to die.... Actually, the photons would pack so much energy from the blue shifting that they would create ever more energetic particles. Those particles would bombard you with great energy, tearing you and themselves apart....
enjoying the videos Jason, thanks! so in this one, there seems to be a discrepancy in the equivalency principle, maybe just in the example. say there's Jill's lab free-floating in space. then there's Jack's identical lab free-falling towards an event horizon. wouldn't physics then be actually different in Jack's lab, so he could tell "uh oh, gravity gradient detected! lab falling into a black hole!," because Jack would start to feel being stretched before his imminent spaghettification?
You are correct. Jack will, strictly speaking, as he gets closer to the hole, see some effects as you say, especially if the hole is stellar mass, because of the non-uniform field near the EH. The point of the example is, of course, to show that we can choose a small enough lab frame so that even in a stellar mass black hole, the effects wouldn't be seen. That is the basic idea of all GR. But yes, if Jack's falling spaceship were miles high and wide, like the final episode of Doctor Who (number 12), then effects would be extremely apparent.
Well why do we see the bright accretion discs near the event horizon of a black hole, if the light coming from the infalling matter is so incredibly redshifted?
There a couple of reasons for this. The first is that it doesn’t spiral all the way to the event horizon at some point which is called the smallest stable orbit it’s simply plunges in. The other is that the x-ray radiation of the innermost accretion disk happens pretty far outside of the Schwarzschild radius.
@@JasonKendallAstronomer Oh Thank you! So we see only the accretion disc and it't processes but we can't ever seen the "spiralling down" actually. So therefore many artificial pictures do suggest quite false impressions.
@@kalles8789 i think about that sometimes just how fucking crazy it would be to look down into space just dropping to a bottomless hole like if there was no accretion disc and it was a small enough bh so that you can entirely see the actual fabric of space dropping and then riding the most insane rollercoaster hill drop ever, obviously not possible but still nuts, the idea of space being a fabric that distorts from mass but we cant see the actual fabric like wtf is it like how does something hold shit up and you cant see it but you move through it exist mind boggling
So a neutron star, while it is weird, it is certainly possible according to known physics.
A black hole though, it seems to be 'impossible',
Because the idea suggests that stuff can just disappear.
Didn't watch it , but I think blackholes make stuff not visible to the eye. The stuff however is still notable in other ways (gravity). But may be I should listen to the lecture first...
47:30 'that funny thing' ?
1:09:00
Hawking radiation is fact. Spontaneous particle creation/annihilation at the event horizon is a consideration worthy of thought. perhaps the anti-particle survived falling into the singularity and this presented as a loss of mass in the whole system, a reduction in the system as a black hole. Oh to see inside! Me wanna know.
Nope, Hawking Radiation is not fact, as any physicist will acknowledge. We have no working theory of quantum gravity and Hawking Radiation, according to theory, is of so weak intensity that it might never be measured.
I fail to see how anything that is a 'real' particle falling in would do anything other than increase the mass, unless you have some negative mass particle. I'd guess you can't warp space-time enough to stop light getting out completely, just extremely red shifted to long radio wavelength. If you could warp space-time that much, surely you'd have some sort of 'barrier' / 'break' that nothing could actually cross (anything has to travel through space-time, including light) and you'd be sort of pulling it inside out in a way (hard to visualise or describe in 3d), I like to think of it of an extremely steep sided hole (rubber sheet analogy with exteme stretch) but where the sides aren't quite at 90 degrees, but very close and ending at an extremely small point (but not quite infinitely small), with the 'hole' being very narrow. I'm probably way out, though.
This is what I don't understand. If all of the light from the universe shines into the black hole at infinite blue shift (so infinite energy) and light carries energy, and energy and mass are equivalent, then why doesn't the black hole increase in energy (and mass) infinitely quickly to become the size of the entire universe? Obviously this doesn't happen, so either my thought process is totally out of whack, or light energy can't convert into 'real' mass (no amount of light can convert into additional mass - shining light into a black hole, no matter the energy level, can't deposit additional energy inside, somehow). This seems to go against some sources that say mass is just 'confined' energy.
First just to be clear there is not an infinite amount of light that is shining on a black hole. It’s an extremely small surface area compared to the universe so only a very small amount of light actually hits the black hole horizon. Most light that goes towards a black hole actually misses the event horizon and is scattered away on odd looping paths determined by the Schwarzschild metric.
The error comes from thinking that a black hole sucks up everything. The Earth has a much bigger cross section as a target than a black hole. But it’s not getting infinitely hit due to sucking up light. Also The Sun is shining by light and it’s not much smaller than stellar mass black holes.
@@JasonKendallAstronomer I'm misunderstanding what you mention around 43:00 then. Not surprising as I, like probably many others just can't, as you say, get their heads around something so complex.
i wonder why the size difference of the (black hole sun = 3km) and the (black hole earth 0,8cm) is so much bigger than compared to the normal state? (Sun diameter = 1,391.000km) / (Earth = 12.700km).
So in the normal state the earth would fit 110 times across the diameter of the sun but when we compare the black hole size, the black hole earth would fit in the black hole sun 375.000 times ( 3000m / 0,8cm)
Why is that difference so big?
The main reason is that the Earth and Sun now have different states of matter, and different compositions. The Earth and Sun have almost the same exact atomic composition. They were formed from the same cloud of gas and dust. However, Earth was not massive enough to hold onto the primordial hydrogen and helium, so they stayed in gaseous form and did not collapse down. Earth was formed from dust and rocks, but the the gas (mostly H and He) was centered on the young proto-Sun. At the end of formation, the Sun contained most of the mass of the Solar System, and nearly all the H and He. This means the Sun's state of matter is a classical ideal gas all the way down, so pressure, temperature and volume are well described by that throughout the Sun. The Earth, though, is a solid. Solids have complex relationships between temperature, pressure and volume, and resist compression in different ways than the Ideal Gas Law. To wit: you can compress air with just your mouth or clapped hands, but you can't compress a table or chair. You can break it, but you have a really hard time compressing it. Even a trash compactor mostly folds and removes structural spaces to reduce size. You can expand and contract metals by heating them, though, and this is more like what I am saying. In any event, the Earth doesn't get much smaller due to the way solids resist compression. The Sun, as a gas, compresses quite well. Now, a black hole isn't anything but mass and spacetime. It isn't a gas or solid, and asking what its equation of state is, is meaningless, since the composition of it is just "mass" and "spin" and maybe "charge". That's it. Nothing more. You use relativity to describe a black hole, and you use solid state physics to describe the Earth, and you use a gas law to describe the Sun. These all lead to very different relationships between mass, composition, volume, temperature and pressure.
@@JasonKendallAstronomer I understand that the properties/composition of earth and sun are different. But to calculate the size of a black hole you only need to know the mass of a object right?
I want to visualize my thoughts to you.
Reality:
Volume (Earth could fit 1.300.000 times in the sun)
Mass (Sun has the mass of 330.000 earths)
Black hole scenario (diameter):
Sun (2,96km) or 296.000cm
Earth (8,8mm) or 0,88cm
The difference between those two scenarios is ridiculous. A 0,88cm (Black hole / earth marble) could fit in a (Black hole Sun /2,94km) trillion x trillion x trillion....times.
Imagine you would compress 330.000 individual earths (wich is equal to the mass of the sun) into a 0,88cm black hole each.
And than merge all the mini black holes together. would a 2.96km black hole arise?
It would only be true if you line up those mini black holes in a line.
330.000 x 0,88cm = 296.000cm
But the black hole is a sphere right? so you cant just add up the diameter of the black holes.
You have to add the Volume of each mini black hole right?
Volume black hole (earth)
Diameter: 0,88cm
Volume: 0,357cm´3
330.000 x 0,357cm´3 = 118.000cm´3
= Diameter: 60,85cm -> this should be the size of the black hole sun when the volumes are calculated together and not just the diameter
The difference arises because the BH radius are depending only on the mass of the two bodies and reflect the ratio between the mass of sun which is 2*10^30kg and that of earth which is about 6*10^24 kg
... and the moral of the story is... DON'T be like Jack and Jill... One little argument and Jack is ripped to shreds... In the meantime, Jill has to live with his final image for eternity!
Black hole as mobster murder scene.
As matter crosses the event horizon wouldn’t it freeze in that orbit as time slows to near zero? Wouldn’t that prevent mass from continuing to “fall” to the center of mass of the BH? So then would BHs be uniformly “solid” as matter it stuck at the radius it crossed the EH?
Interesting syllogism! But your conclusion doesn’t follow from the two statements above it. This is because the Schwartzschild metric is mathematically equivalent to another metric without a coordinate singularity at the EH. The EH is merely where infalling matter starts to fall faster than the speed of light. Thus, no signal can return. No chemical bond or atomic bond or nuclear bond can stand up to the effect of this falling so anything that survives passage through the EH is torn apart.
You missed a huge point to make about Jack and Jill and next time get rid of the stupid laser pointer out of the thought experiment and give them a rope. It's just a thought experiment so make the rope infinitely long.
Just a quick question Jason. Remind me again, what is the maximum speed of an object falling in an infinitely long gravity well?
The idea of an infinitely long rope and and infinitely long gravity well, are not really too realistic. Thought experiments are geared to actually be experiments that could be done if you had the money, resources, technology and materials. One cannot get an infinite rope, so your first statement has a real-world result. The rope would break, no matter what, it would dangle straight in from about 1.5 R_schwarzschild. Anything holding the rope would orbit no matter what.
Your second statement assumes the Newtonian potential. Things are different in the strong regions inside 3 R_s of the event horizon. There is a maximum orbital speed in the ergosphere of a rotating black hole. And, of course, the maximum speed of "falling" would be the speed of light. Nothing goes faster than, or equal to, light speed if it has mass.
No infinities except at the singularity....
A blackhole has nothing from our own universe inside.
If the intense gravity near the event horizon slows down time, then why in every rendering of a black hole I’ve seen in these types of lectures show the matter closest to the horizon moving quickly and white hot? Shouldn’t it be redder and slower than matter farther away from the horizon? The bathtub drain visual model where matter is spinning faster near the horizon needs to be retired.
Awesome video, many many thanks!!!
I finally got a lot of answer regarding black holes and especially regarding the singurlarity, why light can’t escape anything from within the Event horizzon.
Jason Kendall have a fantastic way of simplefying the advanced language.
Thanks to this video, l got some answers and l feel physical lighter in my body. I have used a lot of brainpower nagging about the whole thing about the concept of singularity and that it actually have a surface.
Ten-twenty-or more-hours of drowning myself in fantastic videos of the universe, was’nt able to make me understand this, before now…finally!
A lot of thanks and looking forward to study more of your videos👌
So does jack always see the blackness below him or does he see it envelop him ? It can't be both . Either the black hole is always below him or it is all around him as he looks up . Which one ?
Correct. Jack always sees the hole below him. There is no timeline curve/path from below up to him
@@JasonKendallAstronomer but what I mean is , if the black hole always stands off below him , then how does his view of the universe become a shrinking circle above him. I was lead to believe that his view of the universe should become a compressed blue shifted ring around him. Not an ever shrinking circle above him. I have seen this explained both ways but I think the correct answer is it forms a compressed ring around him as he approaches the singularity.
Gravity is a social construct.
Just kidding, I'm not crazy lol.
Interestingly, this same thing was said to Newton as a public insult for using the word gravity to describe the phenomenon of things falling to Earth. They mocked him for saying that Nature has a heavy and sad disposition.