Ten thousand videos online about "what would happen if somebody fell inside a black hole" all say the exact same thing, but YOU PRESENT ENTIRELY NEW MATERIAL THAT ABSOLUTELY NONE OF THOSE OTHER VIDEOS DO! Thank you!
I've been watching your channel for years and this is the first time I think I fully understood such a complicated topic all the way through the video. Very well done.
@@ArvinAsh- Hi there! Re. only seeing a narrow beam of light from the direction you fell from when you're inside the event horizon... wouldn't you also see light from a vast region around your direction of origin that hit the blackholes at an angle and got bent into your trajectory? This might represent light that was emitted further back in time than your origin light for similar distances maybe, so you might see a weird hyperbolic panoramic view in all directions that includes a time gradient as you look away from the direction of origin
In relativity, it is required that all identical clocks tick away at the same rate, everywhere, and under all circumstances of motion. There is no such thing as "time stopping".
@@aaaa8130 Excellent question. The first step fundamentally is experimentally determining if the gravitational field is a metric field (measurements of Local Position Invariance, Local Lorentz Invariance, Weak Equivalence). A metric field does not affect matter with such effects as differences in elapsed proper time being due to geometry (clocks traversing different spacetime distances). All measurements to date are consistent with the gravitational field being a metric field. Once the experimental data is established the rate at which time lapses is given by the norm of the vector tangent to a world-line. Given a world-line expressed in arbitrary spacetime coordinates, X(τ), with tangent vector U=dX/dτ, the rate is then g(U,U)=1, which is a constant.
Oh yes! This is the episode I had been waiting for, I have heard talks about what happens inside a black hole from Neil De Grasse Tyson, Sean Carroll, Brian Greene and Janna Levin but I know for sure Arvin Ash would answer all of my questions on this topic.
@@tomorowsnobodys Dialect is really interesting because he goes out of his way to challenge the TH-cam physics community quite bluntly!😂 But his stuff is really good too. I always wonder who he is as he does not say.
ur channel brought me through my covid infection, i had fever dreams while sleeping listeing to ur videos. almost transendential. love u man. and as always. and never ending. its coming up. RIGHT NOW.
This has got to be your best video yet!!! Absolutely well done and easy to understand and follow along! I've always wondered what it would look like falling into the singularity, now I know! Fantastic job to you and the rest of the staff
It's bizzare to imagine the scenario where everywhere (left, right, up, down) you look there is the singularity even though technically it is a core of a "sphere" and only along one direction
But that's how we are now with time. Every second that passes, is one second in the "forward direction". There is no going back in time, or sideways, etc. (yes, I am aware of time dilation, but that is still going only forward, just at different rates relative to other observers, still no going backwards or sideways).
@@destructionman1 true, but that's a temporal direction... The commenter is saying that the spatial directions will all look the same. No matter how much GR says that space and time are equivalent, they aren't experienced that way by humans... We absolutely experience time and space differently. So it is wild that you'd always be seeing the center
Black holes illustrate the need for a unified theory incorporating quantum gravity, as they are where extreme gravity appears to 'crush' matter down to infinitesimal scales. However, I believe we can make progress if we look at it in the following terms: 1The singularity should be góregarded not as a location in space at all, but as a future point in time, thus its omnipresence regardless of which way an infalling observer looks. 2. In Relativity, mass is not a measure of 'stuff', of 'matter', which can be 'converted' into energy; it IS confined energy. 3. The singularity therefore represents energy at an incredible degree of confinement at a point in the future, a point towards which spacetime is flowing faster than the speed of causality/light.
13:05 This is such an interesting property of massive black holes, and produces some truly mind boggling sci-fi options, like the Birch World, a Dyson-Sphere-esque construction built around supermassive black holes that provides virtually limitless living space.
This wasn't actually the sort of content I was in the mood for, but I've such respect for Arvin that when the algorithm suggested it, because it was him, I knew it would be good...
Great show. The tilted light cone was a really cool way of looking at it. I have a simple question with (to me) far out implications. If we were to observe the astronaut approaching a black hole, I'd assume that as the red shift increased it would to continue to the infra red, and on out into long radio waves. But would it ever stop wiggling entirely? If not, it seems to me to imply that the astronaut (in our reference frame) never quite reaches the event horizon, from which it would follow that in our frame of reference, nothing not there before its formation has ever pierced the event horizon of a black hole.
You are correct. The interior of a bh is in our infinite future. I studies these thing under Kip Thorne, and my conclusion is that curved space is hard to grasp, but doable, and curved time is a major mind fuxk. But your comment is spot on.
If I understand your question correctly, yes you are generally right -- every object a black hole has ever absorbed, would to our perspective still be absorbing it and we would still see photons being emitted from the object, albeit rarely. So e.g. say a black hole absorbed an object that emits 1 photon per second (relative to the object itself), we may still see that object, but it (relative to us) is emitting 1 photon every 10 seconds, and that photon is red-shifted (lower energy to us than the energy it had as seen from the object itself). Something like that. It is hypothesized that we can in principle see a few photons from very very long ago this way. So say a black hole forms 1 second after the big bang and absorbs something then - we can, in principle, see this object (albeit dimmer and red-shifted, as described). Imagine seeing an image of a dinosaur on the rim of a black hole in the milky way? Obviously not gonna happen, but physics does allow it. Mind boggling stuff. And although we don't actually see the objects that a black hole absorb get absorbed, we can observe the black hole increase in mass (and electrical charge, and change its angular momentum, etc.) and therefore increase in radius. Needless to say, this universe is fascinating :)
@@DrDeuteron Thanks Dr. Deuteron! So we hear from time to time of black holes merging. But in our reference frame (RF) they will never pierce one another's event horizon, since nothing would ever enter a black hole in our RF. So black holes cannot merge from the point of view of anyone outside. They just circle, I'd assume faster and faster until the relativistic effects take over, then slower and slower. In the end I suppose that by gravitational lensing you'd conclude that in our RF the two black holes were next to each other forever. Is that what we "see"?
@@DrDeuteron Also. I just thought about another cool implication that would seem to be a logical consequence: Take any black hole. In a very long time, we are told, it will disburse its mass through Hawking Radiation until it reappears, I suppose as a Neutron Star. But then for anyone falling in to a black hole, as soon as they reach the event horizon, an infinite amount of time will have passed in our RF, so the Hawking radiation and reappearance of a star will occur before they fall into the black hole. Hence no one, even in their own RF could ever get beyond the event horizon. I know it doesn't sound right, but it seems to me a consequence. I wonder where my error is. Maybe along the lines of the relativity of simultaneity though I'm not sure how.
What about the edge case of a neutron star just shy of being a black hole? What if I add just one gram of matter to it? Would the inside morph into a singularity instantly?
This is a great question that I have also pondered. I imagine there will be "nucleation sites" where microscopic black holes (probably the size of the Planck distance) form and then grow and merge with others. How fast this happens will depend on how quickly all the particles falling into these black holes can shed their momentum, remember they have to somehow go from their current momentum to zero at the singularity. Conservation of momentum says that this energy cannot just disappear, so it has to be radiated as light, gravitational waves etc. and transfer to other particles that will escape the overall gravity well at very high speed probably. This is what I can never understand about these animations: What happens to the momentum of the infalling astronaut?
@@ebenolivier2762 >Conservation of momentum says that this energy cannot just disappear Nigga please, redshifted photons lose their energy to nothingness
@@ebenolivier2762 It is simpler than that, the momentum is just energy so once it is inside the growing event horizon (imagine some matter falling towards the centre of the neutron star, 'nucleating' a single black hole near the centre and then pulling the rest of the neutron star towards that central black hole) it will just become part of the black hole mass. Probably all of that will happen in a microsecond.
Penrose drew a diagram of core collapse in his famous paper. The horizon forms at a mid radius, before the singularity, and as matter crosses it, it grows to the final radius. Regarding the mass limits, the neutron star runs out of degeneracy pressure before it’s a blackhole, so it starts to collapse before there is a horizon. The radius at the limit is around 12 km, and the final horizon is around 7.5 km…so there is a no man’s land. Not sure how fast the collapse is, tho. All I heard was less than second Lots of uncertainty in the equation of state of nuclear matter….unlike white dwarfs, where we pretty much know how electrons behave.
@@tonywells6990Yes, but if the energy becomes part of the BH mass it is forever cut off from the rest of the universe since nothing can escape a BH. This will violate conservation of energy/mass won't it?
The exploration of such fascinating ideas pushes the boundaries of our understanding and drives scientific progress. Keep the curiosity alive - the future might hold some incredible revelations that could change our understanding of space, time, and the potential for traversing the continuum in ways we can’t yet imagine!
Kudos to Arvin for pointing that the unphysical nature of the swapping of the time and space (radial coordinate only) in Schwarzschild coordinates. Nicely done.
@@DrDeuteron It's unphysical because it doesn't exist. There is nothing that happens upon crossing the horizon and all world-lines are necessarily future-directed. The space/time switching nonsense comes about from Schwarzschild-Droste coordinates which is an exterior solution. In any other coordinate system there isn't any switch. Curious, what do you even think gets switched in Schwarzschild-Droste?
@@kylelochlann5053 the signs of g_tt and g_rr, which means future light ones point to smaller radii. My understanding is that shwarzschild is exterior to spherically symmetric mass, exactly by Beckensteins theorem, so the horizon isn’t a problem. If it were, why go to other coordinates to removed the coordinate singularity?
I've watched this documentary called Interstellar where a guy enters a black hole and finds himself behind a bookshelf in his home on Earth. He is able to push individual books out of the shelf and he can see his daughter on the other side of the shelf but for some unclear reason, he cannot exit from behind the shelf into the room. All this happens after he drove his car at a high speed (with a flat tire), smashing full grown corn plants in a corn field,, while there's a famine and there's a road like ten meters away.
What blows my mind thinking about this is, gravity becomes so strong that your light cone only points to the singularity. Anything beyond the event horizon is your past. All your possible futures only lead to the singularity.
It always amazes me how stable black holes appear to be (high entropy, Hawking radiation), it’s already collapsed, but yet it feels like iblack holes are like dark stars in principle.
Black holes if they are not piddlingly pico, femto or atto scale, i.e. smaller than an electron and comprised of several thousands to a few hundred thousands of tons of mass, effectively act like memory devices, near-perfect spacetime capacitors, that only leak "spacetime charge" slowly, like a near perfect capacitor, via Hawking radiation until they are piddling, then they flame out brilliantly like a big bang singularity?! Look at black holes, the matter disappears into curved spacetime past the event horizons of the near perfect spheres, but the universal acceleration or gravity of the disappeared fermions etc. is remembered and projected outward at the constant speed of light; we'd still orbit our black hole sun if it collapsed to a singularity right now, but darn it we'd get pretty cold after 8 minutes or so? We'd orbit that sun for a very long time, until it got sucked into a larger memory sphere far into the future? Not to worry, thank Schwarzchild, Chandresekar, Albert and Oppenheimer for the future memories?! Like Dali showed, it's persistent?! As Frank & Furter sang, let's do the time warp again?!
15:42 I'm concerned that you carried forth with this incorrect assumption that the view of the universe would concentrate into a point behind him when you've been including clips in this video of simulations that disprove this exact assumption. The assumption only works with a static observer, but there is no static observer beyond the event horizon. An observer in freefall will never see the black hole shadow take up more than 180 degrees of his field of view.
Very well made video, but I think there is a mistake at the end : after crossing the horizon, the light behind you wouldn't become highly blueshifted, it would instead be redshifted, and it wouldn't be concentrated into a beam but still occupy a whole hemisphere behind you. This can be seen in the simulation by Andrew J S Hamilton which was briefly shown in the video.
@@ActionReplay91 No, ingoing null geodesics look kind of like logarithmic spirals below the Schwarzschild horizon (globally), they are not all falling radially inwards in general. Therfore, they can 'hit you from the sides' as well. In simpler terms, it looks like this bc. of gravitational lensing (as it was successfully quoted from Andrew Hamilton at 12:00 in this video, yet messed up somehow at the end). The relativistic beaming/aberration only happens when you try to maintain a constant Schwarzschild r coordinate (as pointed out by ScienceClic).
@@DavidGoldgruber just a question - let's hypothetically supposed a that an observer is under acceleration due to gravity (before hitting the singularity), and will that observer be able to distinguish the two light rays? The ones radially falling directly inwards Vs. The ones spiralling towards the centre?
@@ActionReplay91 Please do not use the word 'acceleration' in this context. The astronaut is a free faller. Free faller means timelike geodesic motion. On these wordlines, proper 4-acceleration is 0 by def. I am not entirely sure that I understand your question properly, but yes, oc. he can estimate/tell the difference, if he knows how the background stars would look like without the lensing effect of the black hole. (It helps very much of course if he is familiar with GR and raytracing.)
@@DrDeuteronActually, the reason a bh can’t be escaped is due to the gravity preventing anything from doing so. The past is always the past. I can go into my home, when the outside could be considered the past, as it’s where I came from. But I can exit said house because no FORCE is preventing me from doing so. Nothing to do with time. The notion that the past is always outside and the future always inside the eh is merely consequential, but it isn’t what is physically preventing anything from exiting. The spacetime curvature is too high, that’s what prevents escape, but frame dragging also adds to the difficulty of departure.
Thanks Arvin! Titling the light cone was a very effective graphic. And I like the casual dropping of a “BS” in there. I like when education channels (Dr Becky does it too) are reflective of their audience and common parlance used today. Makes things more casual and relatable. Society is changing
What a wonderful movie! Thanks a lot ❤Arvin Ash 1:17 ... and time from our perspective far away from the black hole appears to come to a complete stop here at the event horizon. But this region within the black hole unlike the singularity at its center is not completely mysterious. General relativity does describe what happens inside it. And what happens inside is some of the weirdest stuff that you might not even be able to imagine. It's a region where space and time behave in bizarre ways and our intuitions about reality are challenged. We are going to take a journey that we could never take in real life, and survive to tell it. We are going to go inside a black hole and describe both graphically and visually what would happen and what we would see. 1:54 ... 4:46 But presuming the mass is concentrated in a tiny volume inside what we would have between this singularity and the edge of the black hole, also called its event horizon, is mostly empty space. It may contain things that have fallen through, but if the black hole is not very active, that is, if thing are not falling into it, then there would be just empty space inside. But this empty space would not be anything like the empty space that astronauts see far away from from earth. 5:14 it would have some bizarre properties. First while black holes are black when we look at them from the outsie, you wouldn't see all balck on the inside. It would be lit up from all the light that's falling into it. And everything would be falling towards the singularity. And this singularity would appear to be locate in all directions. No matter which way you moved, you would be moving towards it. There would be no other path. 5:38 ... This might not seem intuitive, but it starts to make sense when you dive into the physics of it. And the pphysics says that space and time would get twistd. What does this mean? To better understand what happens to space and time inside a black hole, let's start by briefly reviewing hw we describe movement in spacetime graphically. 5:55 ... 8:38 ... This tilting becomes more pronounced as the gravity of the object increases. And in the presence of a black hole, the gravity is so pronounced that the light cone continues to tilt until at the edge of the event horizon, it tilts a complete 45% towards it. This means that no object including photons have anyworld lines away from the black hole. Everything falls insider once it 9:18 ... enters the event horizon. There is no turning back at this point. It's a point of no return. ... 9:55 at this point you might say wait a minute this is all bullshit becaue the astronaut could never be inside a black hole it would either take forever, because time stops at the event horizon, or he would be pulled apart, that is , spaghettified on his way due to the high gravitational pull. Thiese are legitimate objects. But let me address how the issues of time dilation and spaghettification can be overcome. 10:16 Regarding time dilation, you may have heard that time slows down in a gravitational field. This is correct. And you may have heard that time comes to complete stop at the event horizon. 🕕This is not quite correct. 🕕If you are observing the astronaut falling in the black hole from somewhere far away, it would appear to you that he never enters the black hole, even if you watched him for eternity. This is because his photons can never reach you from the edge of the event horizon because all photons at the edge can only go inside. The gravitational well is so strong there that any photons there cannot escape to the outside. So the last photons you will see are highly redshited photons from just above the event horizon. You will never actually see him go insde. But from the Astronaut's perspective, 🕧time would tick normally as he fell into the black hole 🕜and he would simply just go right on through to the inside. This is just something that you can never observe from far away. If he were to look back towards you, well he wouldn't actaully see any visible light because most of the light near the event horizon would be so highly blue shifted that it would be in the x-ray part of the light spectrum, so he could not really see this light with his eyes. Infrared light and teh cosmic microwave background light now would be in the visible spectrum so the astronaut might see these. 11:37 ... 13:38 ... now the astronaut has made it inside the event horizon, what does he see now? First let's look at what happens to our light cone inside. We know that it was 45 degree 【 C = light speed, the first universal speed limit. 】 at the edge of the event horizon 【No 3d object exists there: 3d(3τ)||(t3)δ3 ---> 2d(2τ)1δ(1t)||(τ1)d1(τ2)δ2 , e.g. an electron (up-spin) plunges into Dirac sea, merging with its quantum field in the form of the equivalent energy. 】. As you might imagine it continues to tilt more and more al the way to the singularity. It goes from 45 degrees at the event horizon, all the way to 90 degrees at the singularity. Some characterize this 90 degree 【 D = dark speed, the second universal speed limit i.e. the maximum rate of spacetime expansion in the second inflationary epoch. 】 shift as a "switching" of place between time and space 【Supposedly the light cone is 90 degree at the singularity of an edge of another event horizon on which Dirac sea sits, in terms of the cosmological model of Bible, the singularity is a geometric point of the cosmological buffer zone from 54 C-QUANTA-R5, the stage of Dirac sea, which plays an important role in generating an electron (down-spin) as long as Dirac sea gets an input of an equivalent energy elsewhere back to Planck world.】This is not an accurate characterization. One of the hallmarks of general relativity is that the choice of coordinate system really makes no difference in the characteristics of spacetime. One could choose a coordinate system where no such switch occurs. But it would describe the same spacetime inside the black hole. The singularity, if it exists, is really every where in the sense that its gravitational well will be felt in everydirection, whether he goes sideays or backwards, NO matter which way eh astronaut would try to move, he would will still be moving towards the singularity. Since time can only flow one way, it means that all future events lie at the singularity. The singularity now becomes an inevitable moment in time. 14:46
Einstein said: “To those of us who believe in physics,” he wrote in 1955 to the family of a friend who had recently died, “this separation between past, present, and future is only an illusion, if a stubborn one.” It's always the Present everywhere in the Universe. Time doesn't flow. It is Entropy that accounts for change. Travelling to the Past is not possible because the Past has "no location." The configuration that is called the Past been undergoing constant transformation and its current configuration is what we call the Present. At least, that what I think.
Thank you! The widespread saying of space and time switching inside a black hole never made sense to me. It always feels more like space gains some time-like property as in it becomes directional towards the singularity. Good to have this verified by your video!
Error: 11.29. Light falling into the black hole is RED-shifted, not blue-shifted to the in-falling observer. Upon crossing the horizon the in-falling light is stretched to twice its emitted wavelength.
In fact, you're right no matter how fast it's going your reference point is slower than you and you're running away from it or it's going away from you, so it goes red like what we perceive with telescopes and call Hubble constant!
This is a really nice video about cosmology, thanks Arvin, great! A lot of people try to explain the functionality of black holes with a vacuum cleaner, and that's a bit superficial in my opinion. There are different categories of black holes (primordial, normal, massive, supermassive and the powerful variant, the quasar) from galaxy rotor to matter converter and galactic power house, it really has it all. But one thing is certain: without them our universe could hardly function!
There’s only one single type of bh, what you describe as different “types of bh’s” are actually all the exact same thing, just that some are heavier/more massive than others. But that certainly has no effect whatsoever on the type of bh. You might sub-categorise bh’s with electric charge and those with angular momentum, but even those are STILL the exact same type of physical phenomena as all other bh’s. That’s the very definition and meaning of the famous quote, “bh’s have no hair”.
12:51 That's incorrect, because the "r" coordinate is not a physical distance, it is only a coordinate ( that is spacelike outside the horizon and timelike in the interior). Actually, in GR textbooks , the "r" coordinate is usually called " the areal radius" , because it is defined by the surface area of cocentric spheres. The reason why tidal forces are weaker near the horizon for more massive Black Holes is that they're inversely proportional to r^3 {~M/(r^3)}. The so called " surface gravity" ( this is a GR technical term, it's not the "gravitational force" on the horizon!) is κ= 1/4M ( for the simple non rotating, non charged BHs), where M is the total mass of the Black Hole.
And R_schwarz goes a M, so the tidal “force” at the horizon falls as mass to the fourth….and for a ten million solar mass black hole, the forth power is….big.
The craziest thing about the journey into the black hole is similar to when people die and return(NDE) They say they feel like they are falling one way or another, and they see light from around them and above them and then a deep blacker than black hole below them... I really believe that the mind is a reflection of the universe...
See light? As I understand it, if you are at the event horizon you wont be seeing anything for long as your eyeballs will be far away from the rest of the parts of your body and they will soon follow.
13:08 How could the event Horizon ever have the same gravitational pull as the Earth? Wouldn't that mean that light could escape, as light is definitely strong enough to escape our Earth? I've always took the "large BH are safer than small BH" to mean that the *change* in gravity at the EH is minimal...but the overall gravity is still massively high. Meaning, your head and feet wouldn't feel much difference (thus no spaghettification), but overall your body would still be under extreme gravity
The gravitational pull of all black holes and the Earth are identical - they're all equal to zero. But yes, I think Arvin (who hasn't studied relativity) is referring to tidal acceleration. The proper acceleration needed to hold an object at constant coordinate position goes to infinity upon approach to the horizon.
Wow, that's exactly how I was imagining it. Some internet physicist was arguing with me that you can see in front of you while looking at the singularity behind the event horizon.
A really simple way to look at it is, once you cross the event horizon, that point in space now becomes an event in your past to which you can never return. This is what is meant by time and space switching places.
I think it’s cool that with a super massive BH, assuming no firewall, you could survive for some time inside the BH but never come out and probably eventually meet a nasty end.
My understanding of black holes you would see nothing but light near the event horizon and it is physically impossible to go into a black hole without Quantum tunneling. To get into a black hole’s space it would require an infinite amount of energy to get inside a black hole’s space which should contain a massive object that I suspect is extremely radioactive. Light takes the path of least resistance and becomes deflected on the other side of the black hole. Like climbs, the Higgs force barrier and is eventually expelled from the black hole depending on its deflection. Black holes are a focal point of all light sources within our galaxy. This light concentration from our galaxy creates this halo-like ring of light. The shape of the higgs field doesn't allow normal interaction within the event horizon. If we sent something into a black hole it would end up mostly on the other side or a paraboloid based vector. To break this higgs field barrier you would have to quantum tunnel into a black hole. My research and understanding of this cosmos is that if we accelerate in a specific direction there is a chance to end up in the other parallel universe on the opposite side like in a Penrose Diagram.
This, and other videos like it who base their presentations on the latest theoretical work, are profoundly important to the accurate, popular understanding of science. Since black holes are so ridiculously far away we will _never_ be able to send a probe or a human to examine them. Thus, this theoretical work is what we will base _all_ of our science on. Kudos to Prof. Ash! 😊
I was born with many difficulties in my life. Although I am not fully educated, I have a strong love for science and the universe. Thank you for bringing it to me. Love you
If mass just bends space, why light doesnt turn back on its initial path after exiting curved space grid? If grid is bended, its bended on all sides, so on exit path light must get back on his track?
The rate of curvature depends on the distance from the black hole, and a photons path can curve back on itself at the right distance and they can enter a circular orbit of the black hole at twice the event horizon distance.
13:10 "For a sufficiently massive blackhole, its *surface gravity* at the event horizon can be as small as it is on earth." I believe you meant the tidal force rather than gravitational acceleration.
While that is the focus of the statement, what he said is perfectly true and implies that the tidal forces are negligibly small. A black hole of 1.6E12 solar masses would have a "surface gravity" of about 9.5m/s^2. Of course that black hole would be about a light year in diameter and the only way you could feel the gravity would be to have an insanely large orbital ring.
the most intriguing is, the infalling observer also thinks you are in a black hole since for thr infalling observer the universe is shrinking into a singularity once he reaches the photon sphere and he also thinks, you are in timespace...just like you think about him, as well
Finally a good explanation without that erroneous mantra that a black hole is a place from which light cannot escape as if the light had somewhere to run by propagating through space time😉 I really liked it when the Astronaut falls towards the singularity and sees only blue light Who is less and less and eventually escapes the fonts themselves It reminds me very much of the situation of visible and invisible space that is, the acceleration of distant galaxies 😊 After all, our universe emerged from a singularity. ♾
He's using the 1939 definition of a singularity... Maybe in a few centuries the public will learn about relativity of the 1960s and maybe thousands of years to update the public on where we're at today.
Finally I unstand why A bigger black hole has less gravitational pull. It essentially has two equations in effect! More details than Sabine's video! I gave u a thumb up for that!
masterfull once again my friend! though, neill de grasse tyson would probably disagree, he recently spoke out that he figures the possibilty for a black hole to actually create an entire new universe inside it with its own tick of time. much like i hypothesised a couple years ago but my intuition tells me i'm wrong, or at least a whole new set of rules in physics would apply
At 13:38, it is said the person can cross the event horizon feeling no significant change. I don’t understand this- if your legs cross the event horizon before your head, would you not lose all causal contact from feet to head at that point. How can you still feel your feet (below the horizon) if your head is above it?
For you the horizon passes by at light speed exactly, so signals from your feet can reach your head without problems even though they don't move "up" relative to the BH. Your head follows fast enough to catch them.
Brilliant review, professor Ash. I have a question about what you say at 10:30... If the light appears to stay there forever as we watch the astronaut fly into the black hole, then we should be able to see the redshifted light of everything that's ever fallen into the black hole. I must be missing something.
The unperturbed radially outgoing light at the horizon remains forever. We of course can't see it (unless we fall in behind the astronaut) as it never escapes into the exterior spacetime. That said, you are correct that there are photons in photon rings outside a rotating black hole that contains the history of what fell in.
I think Kip Thorne has the best hypothesis of the singularity, that matter/energy in the quantum sense transforms into space/time energy. This solves virtually all of the problems of the singularity because the matter/energy is being transformed into something that is not infinitesimally small.
11:40 that's only true if you hover in place above the event horizon, using thrusters to accelerate to offset the black hole's gravity. Then you get all these relativistic light effects such as blueshift and beaming - because acceleration causes it, not gravity. If you free fall into it, the event horizon seems like it stretches into an infinite plane as you approach the singularity, but there are no other visible effects.
@@kylelochlann5053 That's only true if you use propulsion to fight against gravity. If you free fall in, you accelerate at the same rate as the light gets blueshifted, and it cancels out.
@@michaelbuckers No, you have it backwards. The in-falling traveler sees the light redshifted which is easily calculated by taking the inner product of the 4-frequency with the observer world-line. It is the stationary shell observer that sees the blue-shifted light. You can find a rigorous derivation on the arXiv pre-print server: arxiv:0712.2154
@Arvin - How about Higgs field switched off inside the black hole? And all infalling particles (dust) will be massless. And singularity can be visualized as a ball of massless particles occupying a single state.
Nothing has ever made to the singularity so far, the time that takes to go from event horizon to the singularity is absurd because of how warped spacetime is in a black hole. If everybody in the cosmos throw themselves in a black hole, in different times in history, they would reach the singularity at almost the same time. Mind blowing physics
If the singularity is in every direction when you cross the event horizon, in which direction would you get spaghettified then? Seems like you won't because if singularity is everywhere, then you are pulled everywhere with an equal force, and thus not pulled anywhere?
Thanks Dear Arvin Sir for your detailed explanation videos related to science and universe. Would you please make a detailed video regarding quantum fluctuations and how these fluctuations give rise to space time matter and energy. Anyways I had enjoyed all your videos and they were great. Lots of love ❤ and wishing you a longer prosperous life ahead. Love from INDIA 🇮🇳.
Assuming you enter a dormant supermassive black hole, you still die immediately. While the gravitational gradient at the event horizon is small, and you aren't spaghettified, all the atoms in your body can only move in one direction. Your blood will only move in one direction. Your lungs will only expand in one direction, expanding on one side, contracting on the other, and then never changing. The electrochemical signals in your nerves and brain cannot travel in any direction other than down. It's a nice thought experiment, but humans can't live in what is essentially a 1 dimensional space.
All your particles will only move "down" but it doesn't mean you die - when you travel on a train they also move in one direction, there's no problem there.
@@thedeemon I don't think you understand. On a train, you can walk forward or backward. In a BH, there is no backward. There is only one direction, down to the singularity. Falling feet down, the blood could travel to your feet, but never travel back up. Blood would never go up to your brain because there is no up. Not even light can move up in a BH. That's why it's black.
@@someguy-k2h Relative to the ship you can still walk back and forward, because relative to the horizon you'll still be falling down, towards singularity. It's the "no drama" principle, as Susskind describes it. You're in free fall and in locally flat space, nothing special happens to you locally.
There would be some comfort in knowing that by the time I died in the black hole, everyone I knew will have died thousands of years prior and I wouldn't be leaving anyone behind
1:12 that's actually the black hole's shadow, it's approximately 2.5 times bigger than the event horizon. It's due to the fact that light bends around the black hole and takes quite a bit of orbital distance before it straightens out and enters your eyes eventually. If the event horizon surface had globe lines and you could see them, the shadow would mostly look like inverted ball; you could see 100% of its surface, most notably both poles, and some of it - several times over.
13:05 I may be wrong, but I see a contradiction here. If the event horizon is the distance from the singularity (radius) where light cannot longer escape black hole’s gravitational pull, how can this gravitational pull be equal to the one on earth at the horizon of a supermassive black hole? Edit: I think the author meant gravitational gradient (ie the rate of change of gravitational pull between the head and toes of the astronaut, or any two arbitrary points) instead of gravitational pull. For supermassive black holes this gradient indeed is similar to that on earth.
One thing I didn't understand: how can the gravity at the event horizon be strong enough to block the exit of photons but not strong enough to spaghettify the astronaut?
As you stated in this video, the 2D space and 1 dimension of time light cone applies in a flat space (or Euclidian space). What happens to the shape of a light cone in Euclidian space when space-time begins to curve or distort due to gravity? For example a 45 degree angle in Euclidian space is no longer 45 degrees in non-Euclidian space
You cant actually fall into a black hole. Either the black hole is large enough to have an accretion disc, in which case you would be obliterated by the plasma whipping around at roughly 0.5 C. OR The black hole is too small to have an accretion disc, in which case the tidal forces would spaghettify you long before you reach the event horizon.
I've watched so many of these videos on theory and this is probably the best one yet... where is your video on time travel? I don't see it in the description
I may be way off, but I'm thinking about the spacetime diagram. We always remove a spatial dimension to make it easier to visualize the time dimension and the worldine looks like a 3 dimensional cone. But I think about adding that other dimension back into the diagram and what would that look like. Obviously we can't visualize 4 dimensions, but it seems like it would still appear to expand outward, but in every direction simultaneously since we can't observe a fourth spatial dimension. That sounds a lot like Hubble's law. Everything in the universe is moving. Maybe the expansion of the universe is just the universe moving through time. Is that a thing, or am I way off? Maybe he addressed this in the video, I was too busy typing this.
If you were in a non inertial reference frame looking out light would be blueshifted but if you were in an inertial reference frame that same light is red shifted.
The term "surface gravity" in this line is misleading: "As a consequence, for a sufficiently massive black hole, its surface gravity at the event horizon can be as small as it is on earth." I think the correct term would be tidal force.
Ten thousand videos online about "what would happen if somebody fell inside a black hole" all say the exact same thing,
but YOU PRESENT ENTIRELY NEW MATERIAL THAT ABSOLUTELY NONE OF THOSE OTHER VIDEOS DO! Thank you!
Brilliance is the ability to fully explain the seemingly unexplainable; Arvin does this in spectacular fashion. Nice trip!
Inexplicable.
My thoery--Black holes aren't holes at all. They are black spheres made of pure dark matter.
Yes, he is the best
I think we call this "imaginative".
As in, having an active "imagination" 😏
Amen!
I've been watching your channel for years and this is the first time I think I fully understood such a complicated topic all the way through the video. Very well done.
Great to hear!
@@ArvinAsh- Hi there! Re. only seeing a narrow beam of light from the direction you fell from when you're inside the event horizon... wouldn't you also see light from a vast region around your direction of origin that hit the blackholes at an angle and got bent into your trajectory? This might represent light that was emitted further back in time than your origin light for similar distances maybe, so you might see a weird hyperbolic panoramic view in all directions that includes a time gradient as you look away from the direction of origin
Thanks!
If a person falls inside and dies, can the spirit escape?
Even the spirit is spaghettified.
In relativity, it is required that all identical clocks tick away at the same rate, everywhere, and under all circumstances of motion. There is no such thing as "time stopping".
@@aaaa8130 Excellent question. The first step fundamentally is experimentally determining if the gravitational field is a metric field (measurements of Local Position Invariance, Local Lorentz Invariance, Weak Equivalence). A metric field does not affect matter with such effects as differences in elapsed proper time being due to geometry (clocks traversing different spacetime distances). All measurements to date are consistent with the gravitational field being a metric field.
Once the experimental data is established the rate at which time lapses is given by the norm of the vector tangent to a world-line. Given a world-line expressed in arbitrary spacetime coordinates, X(τ), with tangent vector U=dX/dτ, the rate is then g(U,U)=1, which is a constant.
Oh yes! This is the episode I had been waiting for, I have heard talks about what happens inside a black hole from Neil De Grasse Tyson, Sean Carroll, Brian Greene and Janna Levin but I know for sure Arvin Ash would answer all of my questions on this topic.
Yeah, he is the best. So many concepts are explained so well and easily.
Niel Degrasse Tyson is a hack who's full of more hot air than a balloon.
Also check out Dialect and PBS.
@@creativesource3514i forgot about dialect! Thank you!
@@tomorowsnobodys Dialect is really interesting because he goes out of his way to challenge the TH-cam physics community quite bluntly!😂 But his stuff is really good too. I always wonder who he is as he does not say.
ur channel brought me through my covid infection, i had fever dreams while sleeping listeing to ur videos. almost transendential. love u man. and as always. and never ending. its coming up. RIGHT NOW.
What a wonderful video, Professor.
Your research, script, presentation and animated graphics were fantastic! (As always)
Thank you so much 😊
This has got to be your best video yet!!! Absolutely well done and easy to understand and follow along! I've always wondered what it would look like falling into the singularity, now I know! Fantastic job to you and the rest of the staff
It's bizzare to imagine the scenario where everywhere (left, right, up, down) you look there is the singularity even though technically it is a core of a "sphere" and only along one direction
But that's how we are now with time. Every second that passes, is one second in the "forward direction". There is no going back in time, or sideways, etc. (yes, I am aware of time dilation, but that is still going only forward, just at different rates relative to other observers, still no going backwards or sideways).
@@destructionman1 true, but that's a temporal direction... The commenter is saying that the spatial directions will all look the same. No matter how much GR says that space and time are equivalent, they aren't experienced that way by humans... We absolutely experience time and space differently. So it is wild that you'd always be seeing the center
Black holes illustrate the need for a unified theory incorporating quantum gravity, as they are where extreme gravity appears to 'crush' matter down to infinitesimal scales. However, I believe we can make progress if we look at it in the following terms: 1The singularity should be góregarded not as a location in space at all, but as a future point in time, thus its omnipresence regardless of which way an infalling observer looks. 2. In Relativity, mass is not a measure of 'stuff', of 'matter', which can be 'converted' into energy; it IS confined energy. 3. The singularity therefore represents energy at an incredible degree of confinement at a point in the future, a point towards which spacetime is flowing faster than the speed of causality/light.
13:05 This is such an interesting property of massive black holes, and produces some truly mind boggling sci-fi options, like the Birch World, a Dyson-Sphere-esque construction built around supermassive black holes that provides virtually limitless living space.
This wasn't actually the sort of content I was in the mood for, but I've such respect for Arvin that when the algorithm suggested it, because it was him, I knew it would be good...
Arvin Ash is one of those fine channels you can confidently click the up-thumb before the video starts :)
Great show. The tilted light cone was a really cool way of looking at it. I have a simple question with (to me) far out implications. If we were to observe the astronaut approaching a black hole, I'd assume that as the red shift increased it would to continue to the infra red, and on out into long radio waves. But would it ever stop wiggling entirely? If not, it seems to me to imply that the astronaut (in our reference frame) never quite reaches the event horizon, from which it would follow that in our frame of reference, nothing not there before its formation has ever pierced the event horizon of a black hole.
funny thing is that the black hole itself is that. It is the collapsed star falling towards the singularity, hence, a frozen star
You are correct. The interior of a bh is in our infinite future. I studies these thing under Kip Thorne, and my conclusion is that curved space is hard to grasp, but doable, and curved time is a major mind fuxk. But your comment is spot on.
If I understand your question correctly, yes you are generally right -- every object a black hole has ever absorbed, would to our perspective still be absorbing it and we would still see photons being emitted from the object, albeit rarely. So e.g. say a black hole absorbed an object that emits 1 photon per second (relative to the object itself), we may still see that object, but it (relative to us) is emitting 1 photon every 10 seconds, and that photon is red-shifted (lower energy to us than the energy it had as seen from the object itself). Something like that.
It is hypothesized that we can in principle see a few photons from very very long ago this way. So say a black hole forms 1 second after the big bang and absorbs something then - we can, in principle, see this object (albeit dimmer and red-shifted, as described). Imagine seeing an image of a dinosaur on the rim of a black hole in the milky way? Obviously not gonna happen, but physics does allow it. Mind boggling stuff.
And although we don't actually see the objects that a black hole absorb get absorbed, we can observe the black hole increase in mass (and electrical charge, and change its angular momentum, etc.) and therefore increase in radius.
Needless to say, this universe is fascinating :)
@@DrDeuteron Thanks Dr. Deuteron! So we hear from time to time of black holes merging. But in our reference frame (RF) they will never pierce one another's event horizon, since nothing would ever enter a black hole in our RF. So black holes cannot merge from the point of view of anyone outside. They just circle, I'd assume faster and faster until the relativistic effects take over, then slower and slower. In the end I suppose that by gravitational lensing you'd conclude that in our RF the two black holes were next to each other forever. Is that what we "see"?
@@DrDeuteron Also. I just thought about another cool implication that would seem to be a logical consequence: Take any black hole. In a very long time, we are told, it will disburse its mass through Hawking Radiation until it reappears, I suppose as a Neutron Star. But then for anyone falling in to a black hole, as soon as they reach the event horizon, an infinite amount of time will have passed in our RF, so the Hawking radiation and reappearance of a star will occur before they fall into the black hole. Hence no one, even in their own RF could ever get beyond the event horizon. I know it doesn't sound right, but it seems to me a consequence. I wonder where my error is. Maybe along the lines of the relativity of simultaneity though I'm not sure how.
Exceptionally accurate and clear, clearing up some of those maybe fun but incorrect sci-fi myths. Perfect! 👏👏👏
What about the edge case of a neutron star just shy of being a black hole? What if I add just one gram of matter to it? Would the inside morph into a singularity instantly?
This is a great question that I have also pondered. I imagine there will be "nucleation sites" where microscopic black holes (probably the size of the Planck distance) form and then grow and merge with others. How fast this happens will depend on how quickly all the particles falling into these black holes can shed their momentum, remember they have to somehow go from their current momentum to zero at the singularity. Conservation of momentum says that this energy cannot just disappear, so it has to be radiated as light, gravitational waves etc. and transfer to other particles that will escape the overall gravity well at very high speed probably. This is what I can never understand about these animations: What happens to the momentum of the infalling astronaut?
@@ebenolivier2762 >Conservation of momentum says that this energy cannot just disappear
Nigga please, redshifted photons lose their energy to nothingness
@@ebenolivier2762 It is simpler than that, the momentum is just energy so once it is inside the growing event horizon (imagine some matter falling towards the centre of the neutron star, 'nucleating' a single black hole near the centre and then pulling the rest of the neutron star towards that central black hole) it will just become part of the black hole mass. Probably all of that will happen in a microsecond.
Penrose drew a diagram of core collapse in his famous paper. The horizon forms at a mid radius, before the singularity, and as matter crosses it, it grows to the final radius.
Regarding the mass limits, the neutron star runs out of degeneracy pressure before it’s a blackhole, so it starts to collapse before there is a horizon. The radius at the limit is around 12 km, and the final horizon is around 7.5 km…so there is a no man’s land.
Not sure how fast the collapse is, tho. All I heard was less than second
Lots of uncertainty in the equation of state of nuclear matter….unlike white dwarfs, where we pretty much know how electrons behave.
@@tonywells6990Yes, but if the energy becomes part of the BH mass it is forever cut off from the rest of the universe since nothing can escape a BH. This will violate conservation of energy/mass won't it?
The exploration of such fascinating ideas pushes the boundaries of our understanding and drives scientific progress. Keep the curiosity alive - the future might hold some incredible revelations that could change our understanding of space, time, and the potential for traversing the continuum in ways we can’t yet imagine!
Kudos to Arvin for pointing that the unphysical nature of the swapping of the time and space (radial coordinate only) in Schwarzschild coordinates. Nicely done.
Timestamp? What’s unphysical about it?
@@DrDeuteron It's unphysical because it doesn't exist. There is nothing that happens upon crossing the horizon and all world-lines are necessarily future-directed. The space/time switching nonsense comes about from Schwarzschild-Droste coordinates which is an exterior solution. In any other coordinate system there isn't any switch. Curious, what do you even think gets switched in Schwarzschild-Droste?
@@kylelochlann5053 the signs of g_tt and g_rr, which means future light ones point to smaller radii. My understanding is that shwarzschild is exterior to spherically symmetric mass, exactly by Beckensteins theorem, so the horizon isn’t a problem. If it were, why go to other coordinates to removed the coordinate singularity?
I've watched this documentary called Interstellar where a guy enters a black hole and finds himself behind a bookshelf in his home on Earth. He is able to push individual books out of the shelf and he can see his daughter on the other side of the shelf but for some unclear reason, he cannot exit from behind the shelf into the room. All this happens after he drove his car at a high speed (with a flat tire), smashing full grown corn plants in a corn field,, while there's a famine and there's a road like ten meters away.
“Documentary” 🤣
What blows my mind thinking about this is, gravity becomes so strong that your light cone only points to the singularity. Anything beyond the event horizon is your past. All your possible futures only lead to the singularity.
And on top of that - the singularity is not a point in space, but point in time…. Space becomes time and time becomes space… awesome)))
It always amazes me how stable black holes appear to be (high entropy, Hawking radiation), it’s already collapsed, but yet it feels like iblack holes are like dark stars in principle.
Black holes if they are not piddlingly pico, femto or atto scale, i.e. smaller than an electron and comprised of several thousands to a few hundred thousands of tons of mass, effectively act like memory devices, near-perfect spacetime capacitors, that only leak "spacetime charge" slowly, like a near perfect capacitor, via Hawking radiation until they are piddling, then they flame out brilliantly like a big bang singularity?!
Look at black holes, the matter disappears into curved spacetime past the event horizons of the near perfect spheres, but the universal acceleration or gravity of the disappeared fermions etc. is remembered and projected outward at the constant speed of light; we'd still orbit our black hole sun if it collapsed to a singularity right now, but darn it we'd get pretty cold after 8 minutes or so? We'd orbit that sun for a very long time, until it got sucked into a larger memory sphere far into the future?
Not to worry, thank Schwarzchild, Chandresekar, Albert and Oppenheimer for the future memories?! Like Dali showed, it's persistent?! As Frank & Furter sang, let's do the time warp again?!
the astronaut falling into the blackhole looks really high. It must make his experience extra special.
Came to the comment section for this lmao
I can only conclude observing this astronaut that the solution to unifying quantum mechanics and general relativity is DMT
15:42 I'm concerned that you carried forth with this incorrect assumption that the view of the universe would concentrate into a point behind him when you've been including clips in this video of simulations that disprove this exact assumption. The assumption only works with a static observer, but there is no static observer beyond the event horizon. An observer in freefall will never see the black hole shadow take up more than 180 degrees of his field of view.
Is there a video that better presents an observer's perspective inside a blackhole?
Very well made video, but I think there is a mistake at the end : after crossing the horizon, the light behind you wouldn't become highly blueshifted, it would instead be redshifted, and it wouldn't be concentrated into a beam but still occupy a whole hemisphere behind you. This can be seen in the simulation by Andrew J S Hamilton which was briefly shown in the video.
Why would it be a hemisphere? Shouldn't it be a funnel (cone like structure) as all lights rays tends to convergence towards the singularity?
@@ActionReplay91 No, ingoing null geodesics look kind of like logarithmic spirals below the Schwarzschild horizon (globally), they are not all falling radially inwards in general. Therfore, they can 'hit you from the sides' as well. In simpler terms, it looks like this bc. of gravitational lensing (as it was successfully quoted from Andrew Hamilton at 12:00 in this video, yet messed up somehow at the end). The relativistic beaming/aberration only happens when you try to maintain a constant Schwarzschild r coordinate (as pointed out by ScienceClic).
@@DavidGoldgruber just a question - let's hypothetically supposed a that an observer is under acceleration due to gravity (before hitting the singularity), and will that observer be able to distinguish the two light rays? The ones radially falling directly inwards Vs. The ones spiralling towards the centre?
@@ActionReplay91 Please do not use the word 'acceleration' in this context. The astronaut is a free faller. Free faller means timelike geodesic motion. On these wordlines, proper 4-acceleration is 0 by def. I am not entirely sure that I understand your question properly, but yes, oc. he can estimate/tell the difference, if he knows how the background stars would look like without the lensing effect of the black hole. (It helps very much of course if he is familiar with GR and raytracing.)
Just wanted to thank you, Arvin, for content that always intriguing and fascinating. Well done.
If time appears to come to a complete stop at the event horizon, then does that imply that the event horizon is infinitely far away?
Yes. The reason you cannot leave a bh is that outside is the past, and you can’t go to the past. Curved time is just really weird.
@@DrDeuteronActually, the reason a bh can’t be escaped is due to the gravity preventing anything from doing so. The past is always the past. I can go into my home, when the outside could be considered the past, as it’s where I came from. But I can exit said house because no FORCE is preventing me from doing so. Nothing to do with time. The notion that the past is always outside and the future always inside the eh is merely consequential, but it isn’t what is physically preventing anything from exiting. The spacetime curvature is too high, that’s what prevents escape, but frame dragging also adds to the difficulty of departure.
@@aaronperelmuter8433 I’ll go with Kip Thorne’s explanation over yours.
Arvin you're the best my friend
Thanks Arvin! Titling the light cone was a very effective graphic. And I like the casual dropping of a “BS” in there. I like when education channels (Dr Becky does it too) are reflective of their audience and common parlance used today. Makes things more casual and relatable. Society is changing
Yeah that caught me off guard in the most pleasant way.
I like how you explain things and break things down
What a wonderful movie! Thanks a lot ❤Arvin Ash 1:17 ... and time from our perspective far away from the black hole appears to come to a complete stop here at the event horizon. But this region within the black hole unlike the singularity at its center is not completely mysterious. General relativity does describe what happens inside it. And what happens inside is some of the weirdest stuff that you might not even be able to imagine. It's a region where space and time behave in bizarre ways and our intuitions about reality are challenged. We are going to take a journey that we could never take in real life, and survive to tell it. We are going to go inside a black hole and describe both graphically and visually what would happen and what we would see. 1:54 ... 4:46 But presuming the mass is concentrated in a tiny volume inside what we would have between this singularity and the edge of the black hole, also called its event horizon, is mostly empty space. It may contain things that have fallen through, but if the black hole is not very active, that is, if thing are not falling into it, then there would be just empty space inside. But this empty space would not be anything like the empty space that astronauts see far away from from earth. 5:14 it would have some bizarre properties. First while black holes are black when we look at them from the outsie, you wouldn't see all balck on the inside. It would be lit up from all the light that's falling into it. And everything would be falling towards the singularity. And this singularity would appear to be locate in all directions. No matter which way you moved, you would be moving towards it. There would be no other path. 5:38 ... This might not seem intuitive, but it starts to make sense when you dive into the physics of it. And the pphysics says that space and time would get twistd. What does this mean? To better understand what happens to space and time inside a black hole, let's start by briefly reviewing hw we describe movement in spacetime graphically. 5:55 ... 8:38 ... This tilting becomes more pronounced as the gravity of the object increases. And in the presence of a black hole, the gravity is so pronounced that the light cone continues to tilt until at the edge of the event horizon, it tilts a complete 45% towards it. This means that no object including photons have anyworld lines away from the black hole. Everything falls insider once it 9:18 ... enters the event horizon. There is no turning back at this point. It's a point of no return. ... 9:55 at this point you might say wait a minute this is all bullshit becaue the astronaut could never be inside a black hole it would either take forever, because time stops at the event horizon, or he would be pulled apart, that is , spaghettified on his way due to the high gravitational pull. Thiese are legitimate objects. But let me address how the issues of time dilation and spaghettification can be overcome. 10:16 Regarding time dilation, you may have heard that time slows down in a gravitational field. This is correct. And you may have heard that time comes to complete stop at the event horizon. 🕕This is not quite correct. 🕕If you are observing the astronaut falling in the black hole from somewhere far away, it would appear to you that he never enters the black hole, even if you watched him for eternity. This is because his photons can never reach you from the edge of the event horizon because all photons at the edge can only go inside. The gravitational well is so strong there that any photons there cannot escape to the outside. So the last photons you will see are highly redshited photons from just above the event horizon. You will never actually see him go insde. But from the Astronaut's perspective, 🕧time would tick normally as he fell into the black hole 🕜and he would simply just go right on through to the inside. This is just something that you can never observe from far away. If he were to look back towards you, well he wouldn't actaully see any visible light because most of the light near the event horizon would be so highly blue shifted that it would be in the x-ray part of the light spectrum, so he could not really see this light with his eyes. Infrared light and teh cosmic microwave background light now would be in the visible spectrum so the astronaut might see these. 11:37 ... 13:38 ... now the astronaut has made it inside the event horizon, what does he see now? First let's look at what happens to our light cone inside. We know that it was 45 degree 【 C = light speed, the first universal speed limit. 】 at the edge of the event horizon 【No 3d object exists there: 3d(3τ)||(t3)δ3 ---> 2d(2τ)1δ(1t)||(τ1)d1(τ2)δ2 , e.g. an electron (up-spin) plunges into Dirac sea, merging with its quantum field in the form of the equivalent energy. 】. As you might imagine it continues to tilt more and more al the way to the singularity. It goes from 45 degrees at the event horizon, all the way to 90 degrees at the singularity. Some characterize this 90 degree 【 D = dark speed, the second universal speed limit i.e. the maximum rate of spacetime expansion in the second inflationary epoch. 】 shift as a "switching" of place between time and space 【Supposedly the light cone is 90 degree at the singularity of an edge of another event horizon on which Dirac sea sits, in terms of the cosmological model of Bible, the singularity is a geometric point of the cosmological buffer zone from 54 C-QUANTA-R5, the stage of Dirac sea, which plays an important role in generating an electron (down-spin) as long as Dirac sea gets an input of an equivalent energy elsewhere back to Planck world.】This is not an accurate characterization. One of the hallmarks of general relativity is that the choice of coordinate system really makes no difference in the characteristics of spacetime. One could choose a coordinate system where no such switch occurs. But it would describe the same spacetime inside the black hole. The singularity, if it exists, is really every where in the sense that its gravitational well will be felt in everydirection, whether he goes sideays or backwards, NO matter which way eh astronaut would try to move, he would will still be moving towards the singularity. Since time can only flow one way, it means that all future events lie at the singularity. The singularity now becomes an inevitable moment in time. 14:46
I could not find l mathematical symbol tile on my keyboard 🎹 on my smartphone TCL
Einstein said: “To those of us who believe in physics,” he wrote in 1955 to the family of a friend who had recently died, “this separation between past, present, and future is only an illusion, if a stubborn one.”
It's always the Present everywhere in the Universe. Time doesn't flow. It is Entropy that accounts for change. Travelling to the Past is not possible because the Past has "no location." The configuration that is called the Past been undergoing constant transformation and its current configuration is what we call the Present. At least, that what I think.
Hi. This was amazing!! Never ever found out anything clearer and better explained ❤❤❤❤ thank you so much ❤❤❤❤
Thank you! The widespread saying of space and time switching inside a black hole never made sense to me. It always feels more like space gains some time-like property as in it becomes directional towards the singularity. Good to have this verified by your video!
Error: 11.29. Light falling into the black hole is RED-shifted, not blue-shifted to the in-falling observer. Upon crossing the horizon the in-falling light is stretched to twice its emitted wavelength.
In fact, you're right no matter how fast it's going your reference point is slower than you and you're running away from it or it's going away from you, so it goes red like what we perceive with telescopes and call Hubble constant!
this video is full of misconceptions, errors and popular myths, it's wrong
@@trucker-lolwhere's your video with the correct interpretation and math
nothing stops at the point of no return
@@tylermcnally8232lol he don't have one
Always awesomely explained 🙂
These are among the best science videos on TH-cam.
This is my favorite Arvin video, to date !!!!!
This is a really nice video about cosmology, thanks Arvin, great!
A lot of people try to explain the functionality of black holes with a vacuum cleaner, and that's a bit superficial in my opinion.
There are different categories of black holes (primordial, normal, massive, supermassive and the powerful variant, the quasar) from galaxy rotor to matter converter and galactic power house, it really has it all.
But one thing is certain: without them our universe could hardly function!
There’s only one single type of bh, what you describe as different “types of bh’s” are actually all the exact same thing, just that some are heavier/more massive than others. But that certainly has no effect whatsoever on the type of bh. You might sub-categorise bh’s with electric charge and those with angular momentum, but even those are STILL the exact same type of physical phenomena as all other bh’s. That’s the very definition and meaning of the famous quote, “bh’s have no hair”.
@@aaronperelmuter8433 "category" was the world, sorry I am not English or Northamerican, the perfect translation sometimes fail...
@@thekingofmojacar5333 my apologies, your English is excellent, by the way. Better than many people who only speak English.
12:51 That's incorrect, because the "r" coordinate is not a physical distance, it is only a coordinate ( that is spacelike outside the horizon and timelike in the interior).
Actually, in GR textbooks , the "r" coordinate is usually called " the areal radius" , because it is defined by the surface area of cocentric spheres.
The reason why tidal forces are weaker near the horizon for more massive Black Holes is that they're inversely proportional to r^3 {~M/(r^3)}.
The so called " surface gravity" ( this is a GR technical term, it's not the "gravitational force" on the horizon!) is κ= 1/4M ( for the simple non rotating, non charged BHs), where M is the total mass of the Black Hole.
And R_schwarz goes a M, so the tidal “force” at the horizon falls as mass to the fourth….and for a ten million solar mass black hole, the forth power is….big.
The craziest thing about the journey into the black hole is similar to when people die and return(NDE) They say they feel like they are falling one way or another, and they see light from around them and above them and then a deep blacker than black hole below them... I really believe that the mind is a reflection of the universe...
Just awesome Arvin loved it … please bring up more !!
Great stuff, another home run, hooray Arvin!
See light? As I understand it, if you are at the event horizon you wont be seeing anything for long as your eyeballs will be far away from the rest of the parts of your body and they will soon follow.
13:08 How could the event Horizon ever have the same gravitational pull as the Earth? Wouldn't that mean that light could escape, as light is definitely strong enough to escape our Earth? I've always took the "large BH are safer than small BH" to mean that the *change* in gravity at the EH is minimal...but the overall gravity is still massively high. Meaning, your head and feet wouldn't feel much difference (thus no spaghettification), but overall your body would still be under extreme gravity
the event horizon id a boundary of space where the vacuum is accelerating at faster than light speed towards a singularity
The gravitational pull of all black holes and the Earth are identical - they're all equal to zero. But yes, I think Arvin (who hasn't studied relativity) is referring to tidal acceleration. The proper acceleration needed to hold an object at constant coordinate position goes to infinity upon approach to the horizon.
correct, the vacuum acceleration straight before a singularity is at infinite rate
Wow, that's exactly how I was imagining it. Some internet physicist was arguing with me that you can see in front of you while looking at the singularity behind the event horizon.
Aww sweet nighttime upload! Great vid too. Light moving equally in time and space is astounding
It's a convention, a choice of units where "speed of light" = 1. Astounding is that it is the same for all observers.
i like how you deskribed the singulaity so much
A really simple way to look at it is, once you cross the event horizon, that point in space now becomes an event in your past to which you can never return.
This is what is meant by time and space switching places.
Excellent as uaual. Thanks Arvin
This is so far the best explanation of what happens when you go to a black hole video.
I think it’s cool that with a super massive BH, assuming no firewall, you could survive for some time inside the BH but never come out and probably eventually meet a nasty end.
Arvin. I have so enjoyed this video chapter. I leaned something here. Thank you Mr Incredible. You're keeping us informed.
My understanding of black holes you would see nothing but light near the event horizon and it is physically impossible to go into a black hole without Quantum tunneling.
To get into a black hole’s space it would require an infinite amount of energy to get inside a black hole’s space which should contain a massive object that I suspect is extremely radioactive.
Light takes the path of least resistance and becomes deflected on the other side of the black hole. Like climbs, the Higgs force barrier and is eventually expelled from the black hole depending on its deflection. Black holes are a focal point of all light sources within our galaxy. This light concentration from our galaxy creates this halo-like ring of light.
The shape of the higgs field doesn't allow normal interaction within the event horizon. If we sent something into a black hole it would end up mostly on the other side or a paraboloid based vector.
To break this higgs field barrier you would have to quantum tunnel into a black hole. My research and understanding of this cosmos is that if we accelerate in a specific direction there is a chance to end up in the other parallel universe on the opposite side like in a Penrose Diagram.
what an awesome video, great job.
This, and other videos like it who base their presentations on the latest theoretical work, are profoundly important to the accurate, popular understanding of science.
Since black holes are so ridiculously far away we will _never_ be able to send a probe or a human to examine them. Thus, this theoretical work is what we will base _all_ of our science on.
Kudos to Prof. Ash! 😊
We do observe them
I was born with many difficulties in my life. Although I am not fully educated, I have a strong love for science and the universe. Thank you for bringing it to me. Love you
"Oh my God, It's full of stars!"
First time I understand your video fully
If mass just bends space, why light doesnt turn back on its initial path after exiting curved space grid? If grid is bended, its bended on all sides, so on exit path light must get back on his track?
This actually does happen, read up about the photonsphere around a BH.
The rate of curvature depends on the distance from the black hole, and a photons path can curve back on itself at the right distance and they can enter a circular orbit of the black hole at twice the event horizon distance.
Astounding explanations !
“Wait a minute. This is all bullshit.” Caught me off-guard with that one. 😂 9:52
I really enjoyed this one. Entertaining and informative, thank you 🙏🏻
13:10 "For a sufficiently massive blackhole, its *surface gravity* at the event horizon can be as small as it is on earth." I believe you meant the tidal force rather than gravitational acceleration.
While that is the focus of the statement, what he said is perfectly true and implies that the tidal forces are negligibly small. A black hole of 1.6E12 solar masses would have a "surface gravity" of about 9.5m/s^2. Of course that black hole would be about a light year in diameter and the only way you could feel the gravity would be to have an insanely large orbital ring.
the most intriguing is, the infalling observer also thinks you are in a black hole since for thr infalling observer the universe is shrinking into a singularity once he reaches the photon sphere
and he also thinks, you are in timespace...just like you think about him, as well
Awesome Arvin
Finally a good explanation without that erroneous mantra that a black hole is a place from which light cannot escape as if the light had somewhere to run by propagating through space time😉 I really liked it when the Astronaut falls towards the singularity and sees only blue light Who is less and less and eventually escapes the fonts themselves It reminds me very much of the situation of visible and invisible space that is, the acceleration of distant galaxies 😊 After all, our universe emerged from a singularity. ♾
He's using the 1939 definition of a singularity... Maybe in a few centuries the public will learn about relativity of the 1960s and maybe thousands of years to update the public on where we're at today.
Finally I unstand why A bigger black hole has less gravitational pull. It essentially has two equations in effect! More details than Sabine's video! I gave u a thumb up for that!
masterfull once again my friend!
though, neill de grasse tyson would probably disagree, he recently spoke out that he figures the possibilty for a black hole to actually create an entire new universe inside it with its own tick of time.
much like i hypothesised a couple years ago but my intuition tells me i'm wrong, or at least a whole new set of rules in physics would apply
Love the out of nowhere "Bullshit" @ 09:53!!!
Out of character, Arvin! Jk, you're the man👍
This space-time bending thingy is mind bending. While I find it fascinating, I can never really wrap my mind around it.
At 13:38, it is said the person can cross the event horizon feeling no significant change. I don’t understand this- if your legs cross the event horizon before your head, would you not lose all causal contact from feet to head at that point. How can you still feel your feet (below the horizon) if your head is above it?
For you the horizon passes by at light speed exactly, so signals from your feet can reach your head without problems even though they don't move "up" relative to the BH. Your head follows fast enough to catch them.
This is the best video, I want to hear more about that last bit of inner and outer event horizons
Brilliant review, professor Ash. I have a question about what you say at 10:30... If the light appears to stay there forever as we watch the astronaut fly into the black hole, then we should be able to see the redshifted light of everything that's ever fallen into the black hole. I must be missing something.
That redshifted light has an undetectable long wavelength, so we can't see it!
The unperturbed radially outgoing light at the horizon remains forever. We of course can't see it (unless we fall in behind the astronaut) as it never escapes into the exterior spacetime. That said, you are correct that there are photons in photon rings outside a rotating black hole that contains the history of what fell in.
You’re correct. Curved time is weird.
This was so good! Thank you so much!
Beautiful explanation. Thank you.
Super fascinating! Love it!
I think Kip Thorne has the best hypothesis of the singularity, that matter/energy in the quantum sense transforms into space/time energy. This solves virtually all of the problems of the singularity because the matter/energy is being transformed into something that is not infinitesimally small.
11:40 that's only true if you hover in place above the event horizon, using thrusters to accelerate to offset the black hole's gravity. Then you get all these relativistic light effects such as blueshift and beaming - because acceleration causes it, not gravity. If you free fall into it, the event horizon seems like it stretches into an infinite plane as you approach the singularity, but there are no other visible effects.
The astronaut sees the in-falling light as redshifted due to the classical Doppler shift. The redshift at the horizon is exactly z=2.
@@kylelochlann5053 That's only true if you use propulsion to fight against gravity. If you free fall in, you accelerate at the same rate as the light gets blueshifted, and it cancels out.
@@michaelbuckers No, you have it backwards. The in-falling traveler sees the light redshifted which is easily calculated by taking the inner product of the 4-frequency with the observer world-line. It is the stationary shell observer that sees the blue-shifted light. You can find a rigorous derivation on the arXiv pre-print server: arxiv:0712.2154
@@kylelochlann5053 This bears the implication that gravity affects photons and hadrons differently, and thus doesn't strike me as valid.
@@michaelbuckers There is no such implication whatsoever.
Love your work 😊😊😊
@Arvin - How about Higgs field switched off inside the black hole? And all infalling particles (dust) will be massless. And singularity can be visualized as a ball of massless particles occupying a single state.
Nothing has ever made to the singularity so far, the time that takes to go from event horizon to the singularity is absurd because of how warped spacetime is in a black hole.
If everybody in the cosmos throw themselves in a black hole, in different times in history, they would reach the singularity at almost the same time.
Mind blowing physics
If the singularity is in every direction when you cross the event horizon, in which direction would you get spaghettified then? Seems like you won't because if singularity is everywhere, then you are pulled everywhere with an equal force, and thus not pulled anywhere?
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Thanks Dear Arvin Sir for your detailed explanation videos related to science and universe.
Would you please make a detailed video regarding quantum fluctuations and how these fluctuations give rise to space time matter and energy. Anyways I had enjoyed all your videos and they were great.
Lots of love ❤ and wishing you a longer prosperous life ahead. Love from INDIA 🇮🇳.
Assuming you enter a dormant supermassive black hole, you still die immediately. While the gravitational gradient at the event horizon is small, and you aren't spaghettified, all the atoms in your body can only move in one direction. Your blood will only move in one direction. Your lungs will only expand in one direction, expanding on one side, contracting on the other, and then never changing. The electrochemical signals in your nerves and brain cannot travel in any direction other than down.
It's a nice thought experiment, but humans can't live in what is essentially a 1 dimensional space.
Exactly. And not just humans, nothing can.
@@ebenolivier2762 Sorry, I was being spiciest. No chemical based or energy based life existing in our 4 dimensional spacetime would survive.
All your particles will only move "down" but it doesn't mean you die - when you travel on a train they also move in one direction, there's no problem there.
@@thedeemon I don't think you understand. On a train, you can walk forward or backward. In a BH, there is no backward. There is only one direction, down to the singularity.
Falling feet down, the blood could travel to your feet, but never travel back up. Blood would never go up to your brain because there is no up. Not even light can move up in a BH. That's why it's black.
@@someguy-k2h Relative to the ship you can still walk back and forward, because relative to the horizon you'll still be falling down, towards singularity. It's the "no drama" principle, as Susskind describes it. You're in free fall and in locally flat space, nothing special happens to you locally.
There would be some comfort in knowing that by the time I died in the black hole, everyone I knew will have died thousands of years prior and I wouldn't be leaving anyone behind
1:12 that's actually the black hole's shadow, it's approximately 2.5 times bigger than the event horizon. It's due to the fact that light bends around the black hole and takes quite a bit of orbital distance before it straightens out and enters your eyes eventually. If the event horizon surface had globe lines and you could see them, the shadow would mostly look like inverted ball; you could see 100% of its surface, most notably both poles, and some of it - several times over.
❤ Very good 👍🏼
13:05 I may be wrong, but I see a contradiction here. If the event horizon is the distance from the singularity (radius) where light cannot longer escape black hole’s gravitational pull, how can this gravitational pull be equal to the one on earth at the horizon of a supermassive black hole?
Edit: I think the author meant gravitational gradient (ie the rate of change of gravitational pull between the head and toes of the astronaut, or any two arbitrary points) instead of gravitational pull. For supermassive black holes this gradient indeed is similar to that on earth.
Right, that surface gravity computation is not descriptive, proper acceleration there is still infinite.
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Fascinating video.
One thing I didn't understand: how can the gravity at the event horizon be strong enough to block the exit of photons but not strong enough to spaghettify the astronaut?
As you stated in this video, the 2D space and 1 dimension of time light cone applies in a flat space (or Euclidian space).
What happens to the shape of a light cone in Euclidian space when space-time begins to curve or distort due to gravity?
For example a 45 degree angle in Euclidian space is no longer 45 degrees in non-Euclidian space
Fascinating I love to learn about blackholes, to rap my head around blackholes I like to think of them in 2D and 3 Dimensions
Thanks Arvin
You cant actually fall into a black hole.
Either the black hole is large enough to have an accretion disc, in which case you would be obliterated by the plasma whipping around at roughly 0.5 C.
OR
The black hole is too small to have an accretion disc, in which case the tidal forces would spaghettify you long before you reach the event horizon.
I've watched so many of these videos on theory and this is probably the best one yet... where is your video on time travel? I don't see it in the description
I may be way off, but I'm thinking about the spacetime diagram. We always remove a spatial dimension to make it easier to visualize the time dimension and the worldine looks like a 3 dimensional cone. But I think about adding that other dimension back into the diagram and what would that look like. Obviously we can't visualize 4 dimensions, but it seems like it would still appear to expand outward, but in every direction simultaneously since we can't observe a fourth spatial dimension. That sounds a lot like Hubble's law. Everything in the universe is moving. Maybe the expansion of the universe is just the universe moving through time. Is that a thing, or am I way off? Maybe he addressed this in the video, I was too busy typing this.
If you were in a non inertial reference frame looking out light would be blueshifted but if you were in an inertial reference frame that same light is red shifted.
The term "surface gravity" in this line is misleading: "As a consequence, for a sufficiently massive black hole, its surface gravity at the event horizon can be as small as it is on earth."
I think the correct term would be tidal force.