FAQs + Go to ground.news/floathead to stay fully informed and access reliable information. Subscribe through my link to get 40% off unlimited access this month only. FAQs 1) Shouldn't the speed of light be 300,000 km/s and not km/hr? Yes, sorry! 2) You mean we can't OBSERVE things entering BH, right? The title is a click bait, right? No! There are no events beyond the event horizon. So, from the perspective of an observer outside the BH, the event of something entering a black hole cannot happen. So, the last ever event is reaching the event horizon. Nothing ever happens beyond that. 3) Wait, if nothing ever enters a black hole, then how do black holes grow? How do they 'suck' stars and stuff? I am glad you asked. Imagine a star of 1 solar mass falling into a 1 solar mass black hole. From the outside perspective, we get a black hole of 1 solar mass with 1 solar mass worth of stuff almost frozen near the horizon. This creates practically the same spacetime curvature outside as a 2 solar mass blackhole and hence for all practical purposes, the black hole has grown! As the mass approaches the BH, its event horizon would grow. So, the 1 solar mass BH + 1 solar mass stuff near the event horizon will also have a larger event horizon pretty much the same as what a 2 solar mass BH would have. And there you have it, for all practical purposes, we could model this as a new BH of 2 solar mass even though nothing ever crosses the horizon! 4) So, where is all the stuff? Close to the event horizon or at the singularity? Yes. 5) What about Hawking radiation and black evaporation? That's beyond the scope of this explanation. This explanation is for static black holes. (static event horizon that always existed). Yes, these are idealised BHs. Any more questions?
🗣️🗣️Wait so how does NASA take pictures of stars entering the black hole.Can we not think as black holes as Wormhole that bends the fabric of space time so much that you go to an another universe, my whole life of 9 years has been a lie about black holes😮. Btw thank you sir, you make this tensor calculus and general relativity so simple👏 And!! What about the swazchild radi!!!!!????!!??!!!
This is video is so wrong. An observer’s PROPER time does not stop at the event horizon, and an observer can pass through the horizon quite readily. It only APPEARS time stops there due to light getting trapped near the horizon. A basic reading of GR textbook will tell you how to calculate how much proper time it takes to fall into a black hole - and that time is quite finite. I’d suggest watching ScienceClic’s video for a much better breakdown of the problem.
@@se7964worse is how he keeps attributing things to Einstein that Einstein never said or did… this it what happens when you let random RUclipsrs believe they can master physics
I'm a huge fan and have watched many of your videos. I almost skipped this one because I *know* why nothing can escape a black hole. At 0:26 my jaw dropped. Then seeing how escape velocity is not the reason I literally slapped my forehead! I just love the deep, intuitive understanding your videos provide. Thank you!!
"... but Einstein..? Well Mahesh..!" Several of your videos in, I must tell you I find them immensely entertaining, and I learn so much. Many thanx for your work!
I am looking forward to the video in which Mahesh intuitively, understandably, explains how to move back in time, because the person who interviews Einstein and Newton for each of his videos probably knows this
Imagine Cooper's view of the rest of the universe as he approaches the event horizon. Time passes normally for him, but far away from him, time appears to be passing faster. When he is close to the event horizon, every second that passes for him equals millions of years passing for the rest of the universe. When he reaches the event horizon, time outside the black hole becomes infinitely fast and he witnesses the end of the universe. He cannot leave the black hole, because the universe outside it no longer exists from his perspective.
If Cooper sees the rest of the universe age,wouldn’t he know that in his frame of reference time has slowed down which contradicts the fact that time is passing normally for him?
To enjoy this view of infinitely fast universe he must stop falling somehow and stay at the horizon exactly, which is impossible for a massive body just like it's impossible to move at light speed. If he falls down, he doesn't see the universe accelerated so much, as light struggles to catch up with him.
@@thedeemonNo, I recon he would see the universe (If he would turn around and look "out") age faster and faster right up until he passes the horison and the universe ends.. Crazy.
You're a fantastic teacher. I've been hitting this material hard without formal schooling for about 6 years and you really knocked me into the next field ;)
I'm 37 years old, I am a passionate about science and physics, and I Ve saw so many videos and documentary's in my life about black holes, but this is the first time I've understand how they "work" ... And it was so simple and easy... Great job!
aways wondering about "why" in physics and your channel not only explains the why, but the how, when and where too. great content. An outsider sees a Black Hole as a region in space, the insider sees the Black Hole as a region in time. Best explanation (based on current understanding) of a black hole and makes sense to average Joe such as I. your Interstellar film disclaimer pop up was really funny, although had to rewind, slow the speed and pause to get the joke.
I love learning from your videos. The way you explain it is easier to understand. I love your enthusiasm when you are explaining, it’s great & refreshing.
Probably a stupid question, but; If, from my perspective, nothing ever enters a black hole, how can it gain mass? Or, for that matter, have mass in the first place?
Those things will be stuck at the event horizon from our outside pov. The whole thing (black hole + stuff being stuck at the event horizon) will be practically a solid sphere and from outside there will be no gravitational difference between that stuff being on the "surface" or inside the black hole, so all of those things entering from their pov will also add to the black holes mass from outside pov. Of course this geometrical approximation changes inside the black hole, but from that perspective things can enter
The way that I understand it is using e=mc^2. We know that mass is just energy confined in space, and binding energy makes up most of the mass. Since it can’t possibly escape the black hole, then it’s effectively contained in the space just like all the other mass/energy. So it is effectively adding to its mass by going back to what mass actually is; just energy contained in a space.
@17:30 a cool video segment here would be one of your paper models showing the light cones tilting so you can see the external space is indeed now in Cooper's past light cone.
So, when two black holes collide, they cannot merge together to form a single black hole; but freeze as a "double black hole" touching each other at their corresponding event horizons??
Good point. But then how come scientists say they've detected gravitational waves from two black holes merging billions of years ago? What are we missing?
But from our perspective why isn’t the collision perpetually in our future? Yet we can “hear” the ring down in the scale of seconds?? Mahesh please do the follow up for these questions!
Brilliant video again! You make those hard things so intuitive, it's genius to be able to do that. I wonder what's your take on this: I argue that even from the perspective of the falling person, he won't pass the horizon. Here's why: Suppose astronaut Bob throws Einsteins light clock towards the BH. When it nears the horizon the clock starts to tick slower. But light travels with the same speed in all reference frames. So for the light clock to tick slower, it must become bigger, seen from Bob. And since the clock almost stops ticking it is so big that it wraps around the BH multiple times. Now he himself jumps towards the BH to retrieve his clock, with a faster initial speed so he'll catch up. When he nears his clock he'll see it tick faster again since he enters its reference frame. But that also means it shrinks again. Like everything else that was already (almost) at the horizon. That would mean the BH appears to shrink until it becomes so small that he'll wrap around it multiple times, like his clock. This means the "singularity" inside the BH is actually the horizon but seen from a different perspective. QED 😜
The "event horizon" *is* a _coordinate singularly_ for any distant observer(s) far away from the black hole... but it's _not a physical singularly_ Spacetime is still continuously defined beyond the horizon, and when you switch to using, for example, the proper time of an inertial observer falling into the black hole (Gullstrand-Painlevé Coordinates) You can keep going all the way past the event horizon to the physical singularly at the black hole's center of mass.
Yea so that's what I'm trying to argue against 😅 In special relativity the coordinate system is relative to the observer, different observers with different speeds use different coordinates to describe the same position. You have to do lorentzian transformations. Why would it be any different for a BH horizon? Or to argue in another way: When Bob throws in his clock, from his perspective it never crosses the horizon. But when he waits an extremely long time, hawking radiation evaporated the BH before the clock crossed the horizon. Since the view seen from the clock must be consistent with the view from Bob, the clock could never have crossed it, even from its view.
@@Jopie65 Yeah, from clock point of view horizon shrinks to dot faster then he riched it. And this happens relatively fast(if clock survive unfrozen supernova explosion), but in outside world "trillions" of years will pass. about SR near BH -> hyperbolically accelerated reference frame/The Rindler horizon
This is a really nice explanation, you're easily my favourite teacher in GR, that enthusiasm is contagious :) Two things I still don't understand though, in the case of a real-world scenario: if an ouside observer 'sees' something fall into the black hole, it gets frozen in time near the event horizon, but if it's a feeding BH, it grows, so after some finite amount of time, that infalling object would be behind the event horizon from the outside perspective as the horizon would move past the point where that object was. And if Hawking radiation is real, then from the perspective of an infalling observer the BH would 'evaporate under them' as they keep approaching the event horizon, because if the BH evaporates in a finite time, it must happen before the infalling observer reaches the horizon.
It's just an after image, their last photon streams keep getting redder and redder, until it's invisible, going to the radiowave spectrum. If the BH keeps growing at time, foremost we wouldn't even be able to see anyone approaching it, due to the extreme brightness of it's accretion disk, but if could filter out most of that radiation, the growth you only speed up the fade.
@@linuxp00 I'm not talking about seeing the object in visible light, but rather if you track it in space. Then you would know its position in relation to the center of the BH and after some time, you would find out that it should be behind the event horizon.
The mass of Cooper is enough to enlarge the EH, so at some (finite) time he will merge with the BH, even from an external perspective. The larger the mass of Cooper, the sooner it will happen, that why we "see" BH mergers or merger of BH with neutron stars quite frequently.
@@Juni_Dingo I think there is a misconception given to a metaphor abuse. The image is not the object, it doesn't matter where the image is, just that it stops on the surface to an outside static frame, if you follow along the astronaut you not going to see any after image at all, so it's just an illusion.
@@linuxp00 But that is not what I'm talking about, not seeing the infalling object, I'm talking about tracking it in space. Not with light or whatever, you can calculate the trajectory etc etc. I'm not talking about light here. Just that the object will eventually end up inside the event horizon from the outside perspective in the case of a growing BH
I could not stop myself by watching this video because I was asking the same questions and giving same arguments to everyone but no one was getting convinced and I was thinking why they don't understand my words.
I think he explained everything very well. But the title of this video makes it more confusing than it needs to be. I think if it was titled "Why can't we OBSERVE anything entering a black hole in the first place", it would remove some ambiguity.
Love these videos! It's disappointing that there's so many scientific misconceptions around when things have be known for so long, your channel really helps to overcome that. Plus I loved your impression of the 'theory guy'.
Some 40 years ago, Dr Venkatavaradhan, the then director of Mumbai's famous Nehru Planetarium, gave a lecture at our college about Black Holes and the inevitable "why nothing can escape from it" story. It was new then and so very fascinating, and I have been hooked for life into topics of stars and gravitation and black holes. Great video, and thanks for the insight, but with due apologies to Einstein, I fell I will stay with old one for some more 'time' - at the edge of the horizon!
- So, I fell into a black hole. - Well, that sucks! - No, it doesn't! Watch this cool video for a better explanation while I lurk over there on the event horizon. - Won't you cross it? - Well, it's matter of perspective... (Okay, I'm leaving)
I have asked many people why we can’t escape with continuous thrust if we are just 1 metre inside event horizon. Finally found an answer 😊 I have one question though. From the perspective of Cooper, will he ever reach the centre or anywhere inside after crossing event horizon? Say the radius of event horizon is 20 km. From his point of view time is running normally. He is looking at his clock. Will 1 second ever pass on his clock since that means an infinite amount of time outside?
Thanks, I love your videos! Does "time not tick at all" 8:38 in a literal way, meaning complete halt, at the edge of the black hole from our perspective? Or is it rather SO, SO, SO very slow that we cannot measure the rate? Meaning that it has practically stopped, from our perspective. I'm thinking that if time comes to an absolute 0 rate from whatever perspective then it must also be 0 rate from Coopers perspective. But from Coopers perspective time does not stop, so it has some rate, it is just too slow from our perspective. Am I missing something?
I think one of the best compliments I can give your channel, and you.. is that you never fail to make me think. About the topic at hand but also further into the subject. Questions start arising almost from the moment you start to speak. For instance.. when falling into a black hole.. looking towards the way you came.. what would you see? Does gravity affect sight? I'm sure it will depend on the black hole to start. A massive black hole, less hectic at the event horizon might be best. Upon looking "back" would you see events evolving more quickly in relation to their distance from you? I understand something entering into the black hole will look to be stuck in time.. frozen. Not sure if I've seen reporting on the reverse? Ok, your jokes are great! Your general talks on relativity are special
I agree with you that he makes SOME people think. One thing how can a black hole grow if nothing can get into it? How can the space man continue when his time stands still. I agree that he may not know that time stands still but it does according to these explanations. In my opinion he is so convincing that he is dangerous. There are so many other physicists not agreeing with SR and GR that it is far from sure it is true. In my opinion SR and GR is partly true but only partly. It is conveniently using what fits for it's explanation and forget the rest and also makes up fanciful ones.
@@leonhardtkristensen4093 No scientist worth their salt disagrees with SR and GR. Every prediction made by both theories have been observed time and time again. What is true is that GR is considered incomplete; there are edge cases in relation to quantum mechanics where GR and QM disagree on what happens, and that must be reconciled. That is not the same as GR being wrong. Space man can continue because in his reference frame, nothing unusual happens. He and the outside observer do not share the same inertial system, and thus, the same rules apply to them with different outcomes. That is the "relative" in relativity. Observations and measurements between different inertial systems disagree, they are relative to the inertial system. There is no fundamental overarching "truth".
@@leonhardtkristensen4093 according to Susskind.. that's exactly how. Matter attaches to the perimeter.. increasing the perimeter. *remember I'm a RUclips physicist AT BEST!* so my interpretation and words used aren't the best. Leonard susskind is a hard listen but if you're into this stuff, he has some great lectures. Don't expect nothing like this channel whose main focus is US.. susskind speaks at Stanford (if I'm correct)
@@leonhardtkristensen4093 as for not agreeing.. that's science. Science isn't about what's known.. its what's provable. Trying to discredit SR & GR IS THE WORK! Every time an experiment falls by the wayside.. that's more credit to the theory! If you look at research papers.. ANYONE can put an idea forward, doesn't mean they will be accepted.. I'm trying to say.. science isn't stuck up. It WANTS to be discredited.. that's the nature of science. Every failed experiment or test is just as vital as a discovery. Without it we would still believe in witches
@@lucemiserlohn I am in no doubt that Time keepeng slows down with speed and probably with gravity too. I have the believe that it has to do with electro magnetic movement at the atomic level. It correspond with what I know about signal delay through electronic circuits. The actual reason we will probably not know until we work out what electric and magnetic signals really are. I also believe that it is the two way motion of the EM that is involved. I believe time keeping is an oscillation at the atomic level and there fore a two way motion. I believe this is a thing that probably happens in organic bodies too so people will probably have the same time dilation as atomic clocks but I am not sure that that has been proved. By the way has any body checked light being bend around the moon? Bending around any star could also be from an atmosphere or plasma being there. It may well be the "incomplete" in SR and GR that bothers me. Also I have the feeling that if we could work out how to detect EM one way then we may well come to that there is some thing absolute. EM of cause travel at c.
The y=1/x on your shirt really matches with the situation you have to go to infinity to see the graph touching x axis similarly as you have to wait for infinite amount of time to see the person toching the event horizon
From our point of view, Cooper never crosses the event horizon; it will always look like he's stuck there. But the black hole itself does not exist for an infinite amount of time: because of Hawking radiation, it slowly evaporates and the event horizon slowly recedes. So we should see Cooper tracking this recession, getting closer and closer to the center, but never crossing the shrinking horizon. Eventually, the event horizon will collapse into a point, and the black hole will dissipate, and we will have never observed Cooper crossing it. With nothing holding him back, we will just see him go on his merry way to the next adventure. Now, what's wrong with this picture?
(Cooper can not see the Hawking radiation while in free-fall.) You want to know what Cooper is experiencing... so you want to use a coordinate system based on Cooper's proper time (and no one else's clock)... that means you're using Gullstrand-Painlevé Coordinates, which are continuous all the way to the physical singularly at the black hole's center of mass. Cooper will arrive in a very breif amount of time (depending on the mass of the black hole, a few fractions of a second to a few days on Cooper's own clock.) The event horizon is empty space. There is nothing there in Gullstrand-Painlevé coordinates.
The question of what Cooper experiences is indeed very interesting (and I have thoughts about that), but what I was really curious about is how to resolve the contradiction I see between the assertions that, from our point of view, (a) Cooper never crosses the event horizon, and (b) the lifetime of the black hole itself is finite. This would seem to suggest that Cooper outlasts the black hole without ever having crossed its event horizon.
@@vanosaurAs someone else pointed out in another thread, Cooper and the black hole together have an event horizon that's slightly larger than that of the original black hole. In contrast to the original horizon, he can pass the combined event horizon in finite time.
Thanks for this. I've been saying that for years and never found a good explanation to contradict this idea. The logical conclusion is that the black hole itself can never form. Using a coordinate system relative to the black hole is irrelevant: if the black hole is never completed, this coordinate system is not in true free fall. There are no black holes, there are no singularities, the black hole is a limit behavior of spacetime that can't be reached due to quantum fluctuations. What we observe are quadi-black holes that will never complete their collapse.
From our perspective I don't think we ever see anything happen. The event horizon cannot shrink from our point of view because it would take time to do so and there is no time. From our point of view there is no singularity either (whatever that actually means as matter cannot exist in a state that compact) and I would think Hawking radiation (that I have too many problems with) may only apply in coopers/black hole's frame of reference as cooper and the horizon are pretty much stuck in our frame. Now from its frame, perhaps its already 'evaporated', but I don't see how we'd ever see that. Cooper is dead but not, black hole is there but not. Makes perfect sense.
In the isolated case of the "static" black hole and one "participant" (+ the observer who's resting compared to the black hole), this sounds valid, but what about a real scenario, where there is additional matter, and the event horizon is also increasing based on how much stuff is around it, and how close that stuff is. So we should be able to "see" Cooper close in on the horizon, let's say 1 cm away, and we should also be able to "see" the black hole's event horizon growing more than 1 cm in radius (from other matter getting close), both in finite times, which means that even though Cooper is technically not able to pass the horizon by himself, the horizon should be able to engulf him, making it possible to enter the black hole from the outside perspective, he just won't be able to reach the distance of the original horizon from the center, and this even looses meaning after the horizon engulfed him Also, what about the case where both Cooper and the black hole are moving towards each other from the observer's point of view to begin with? In that case the black hole should have no slowing down "issue", and should just go through Cooper like an eraser, because otherwise the observer would have to experience Cooper to basically be "pushed back" by the black hole, while he seemingly turns into a sculpture, which doesn't seem to be valid. However if he is indeed gets "ran over", then that implies, that the observer should be able to shift into a perspective where Cooper is swallowed, and back to one where he's not, since it was just a matter of perspective, thus making it possible to experience someone going into, and out of a black hole, which should be impossible So in summary, even though I though I understood it, I just got confused again :D
You’re right in the first part. The black hole’s event horizon does expand based on the objects that “fall into” it. It’s why black hole’s mass depends on surface area instead of volume. If both cooper and blackhole are travelling at the same speed in opposite direction, you can simply substitute that with initial condition for cooper travelling twice the speed relative to the black hole. The black hole doesn’t repel him. But drags him with it on the opposite direction to which cooper was travelling. Like a fly that hits a bus windshield, he is dragged along.
What about the point of reference from inside the event horrizon? Would they see him fall in? What about about the Hubble radius where the expansion of the universe outpaces the speed of light? Is that just another event horizon? Are we inside a black hole of sorts? 🤔 another extremely good video!
@kinitpatel1866 The gravitational waves are from the spacetime outside the black hole. The spacetime outside the b.hole is being pulled by each "piece" behind/ next to it, like a treadmill. So the gravity doesn't have to "get out" of it to keep travelling away, 😁🌏☮️
I've watched the 3 videos in succession which culminate in this one - and even though I understood these issues before, these are the best explanatory videos I've ever seen. There are a few analogies where you take some liberties (i.e. cones versus spheres), but generally this should be understandable from any thinking person's perspective. Really well done! :-)
Hello Mahesh shenoy !!!! Today i got your video in my recommendation section and i am so happy that i clicked it Your videos are amazing interesting and unique Btw i am gonna watch every video on this channel within a week 😂😅😅 Keep making videos ❤
GR does NOT rule out going to your own past. SR does that, but GR (alone) does not. It's not something you can do with rocket engines (probably) but the equations themselves to the best of our knowledge do not rule out closed time-like curves
Here he means not CTC, but just moving outside one's light cone, or in backward time direction. With CTC you go forward in time, but due to the loop end up in some earlier moment of your history, it's a different thing.
now my only question is... how does the star becoming a black hole even look like during that process? does the infinite curvature appear at some random point within the star? many points? and then what? is there already an event horizon at that point, where? does it grow? aren't things therefore "entering" the black hole as the horizon grows? how does it become black? is it instantaneous, or is it a gradual red shift until it's not visible anymore? to our point of view, is the star inside of the black hole, or is it eternally falling onto the horizon?
But, we have direct evidence of things entering into black holes on our timescale. We have black holes merging with black holes. So, something needs to be able to go through the event Horizon on our timescales because those mergers are spectacularly fast.
@@chadb9270 black holes aren't really "objects", they're regions of spacetime. a black hole "falling" into another isn't like an object falling there, it's further distorting the spacetime around both of them. to us there is nothing inside the black hole, so matter doesn't actually enter either of them.
@@CiaDora-us1tf yeah, like. i'm not sure, actually. if anything, this video suggests that all the matter of the star is still falling and will remain falling forever, before it reaches the horizon. now, the mystery to me is when exactly and where does the horizon actually appear.
@@CiaDora-us1tf in the very middle i'm not so sure. if you go there sure, but right now, from our point if view, there isn't, it would take infinite time for something to even cross the horizon, let alone reach the center.
no. nothing can enter. he didn't explain why even from Cooper's point of view he doesn't enter. black holes do not live forever in reality. they evaporate from Hawking radiation before he can fall in even though that is a very short amount of time from his perspective.
It’s not a clickbait! From the perspective of the outside observer, there are no events beyond the event horizon! (By definition). Something entering a black hole would be an event beyond the event horizon. So, that can’t be true.
@@Mahesh_Shenoy We'll I can't travel to the never existed past... If Blackhole is the event horizon, your premiere was the event beginning 😄. I've explained my 'Proper rest' in the other comment's reply. Kindly see it if you are seeing this.
I love your channel, your energy, your enthusiasm, and you are an outstanding teacher. That being said. The current understanding of black holes physics says you are very wrong about "nothing ever entering a blackhole". WE from OUR reference frame from outside the event horizon will never see a falling object cross the EH. That much is true. But from the perspective of the falling object/person, they go through no problem and like a bat out of hell. Black holes feed on matter, collide and coalesce with other black holes, their gravitational waves go insane when nearly touching, then ring out and dissappear when they fall and cross each other's EH. There is a plethora of phenomena that contradicts your stance. Science does not back you up this time. I recommend you browse PBS spacetime's channel for a robust resource on black hole physics. All that being said, let me insist, I love your channel and what you do. I hope you keep it up, you are an outstanding communicator and teacher. Thank you for what you do.
So from our perspective, one black hole will never enter the event horizon of another black hole. Meaning that they will never collide, but yet LIGO saw gravitational waves of black holes colliding. Now i am puzzled.
gravitational waves are a result of acceleration. Massive objects (black holes) are accelerating towards each other (doesn't matter if directly or in a spiral) and hence send those waves. The waves are the strongest just before the collision (from our perspective just before the time dilation becomes too strong and the waves are redshifted too much)
Hi sir My doubt: Suppose a person is falling in a black hole, From his perspective he is going in it via the event horizon and from our perspective (suppose a space station some what near the black hole but out of its visible influence) the observation are that the person is static. This is normal observation according to you and science. But what if the space station starts moving towards the black hole, will observation of the person will be the same i.e., static or that person is moving OR what kind of observation are found. Thank you for this video. It was really fun.
Great video, I love your channel! But I think this is actually incorrect! Things DO NOT slow down when they fall in a black hole, this is a common misconception, Einstein never said any of that. You DO see things falling in a black hole, at the speed of the gravitational acceleration, as simple as that. When you see something falling in a black hole, its speed does not slow down, it falls extremely fast. You just need to imagine a "Gravitational Light Clock" hovering above the event horizon. Light going up, slows down and redshifts, then it falls back down, at the speed of light and blueshifts to the original wavelength. This is the origin of the gravitational simultaneity. Only when you hover above the event horizon, resisting the gravity, you can look up and see the entire rest history of the universe. Gravitational/Acceleration relativistic effects take place only when something moves in relation to another thing, or when something hovers in a gravitational field.
It's not a misconception. Just look at Kruskal diagram, how lines of constant time go there, and when light from falling body near the horizon reaches (if ever) a static outside observer. Also look at Rindler horizon, how crossing it looks for the accelerated observer, same effect of visibly slowing down to infinity.
@@thedeemon It is a misconception. You can clearly see this in the Kruskal acceleration space time diagram which you mentioned, as something moves at a specific acceleration, a light ray coming from the back will never catch up to it, from the perspective of the accelerating body, the universe behind it would be black, there would be a horizon behind it, which is analogous to a gravitational horizon. In gravitation, something accelerating would be standing still, hovering above the black hole, and below the object there would be the black hole's event horizon, which is analogous to the Rindler horizon. In the acceleration space time diagram which you talked about, you can clearly see that the events in the object's part opposite to the direction of movement happen first, which is exactly what happens when something is accelerating and hovering above the event horizon of a black hole, events in the parts of the body facing the black hole happen first than the events in the parts of the object facing away, the Simultaneity is the same. Again, in the Gravitational Light Clock, light slows down only going up, and when it falls, it does so at the speed of light. If an object slowed down while it fell, so would light, and therefore Gravitational Simultaneity would not exist. Under the light of the Equivalence Principle. Without gravity, if something passes by you accelerating, it is going to pass by you extremely fast, as it gets close, it blueshifts, as it moves away, it redshifts. Therefore, the same thing happens in gravitation, as something falls in a black hole, it accelerates towards the black hole extremely fast, and the light coming out of it blueshifts as it gets close, then when it is closer to the black hole than the outside observer is, the light redshifts.
@@cai0_o It's like you're not even looking at the lines in those charts. Just track which moments of a free falling body going towards and through the horizon correspond to which moments of the accelerated external observer. You'll see how the last minute before crossing maps to basically infinite future of the accelerated external observer. So in that observer's perspective the falling body slows down and nearly halts.
Fantastic video, @Floatheadphysics, but it introduces a new misconception at 12:00. This debunks a huge misconception that is ubiquitous in even academically-rigorous black hole content. It does point out a new misconception though - even an infalling observer would never pass the event horizon. As anything falls towards the black hole, it’s time dilation increases arbitrarily, right? But we know black holes emit Hawking radiation and evaporate on finite timescales. 10^100 years for the infalling observer would go by in a flash as they watched the universe behind them speed up exponentially. This means that the infalling observer actually observes the event horizon shrinking right ahead of them, never reaching it. They would then (ignoring tidal forces) reach the midpoint of the black hole and experience the explosion that results from the runaway hawking radiation at the end of the black hole’s life. I would love if you could make a video on this interaction as well - it points to the fundamental realization that there is no interior of a black hole, and there is no event horizon, just layers on layers of apparent horizons. As Hawking stated, “there are no black holes”
8:10 at the very very edge your mass becomes part of the Schwarzschild radius calculation and the black hole _grows around you._ once inside mass must wait until hawking evaporation reaction nullifies it as the black hole shrinks. Time inside is slowed to stop and will last "forever" before time ticks forward, but the black hole itself has a finite life time.
This is an amazing video! I love the excitement in which you share knowledge. Though, I have one lingering question after watching. If nothing can ever enter a blackhole, then how does it gain more mass? Does it all just pile up at the surface from our perspective? I know its going into the blackhole from their own perspective but as far as the rest of the universe is concerned, the blackhole should never grow in size right?
Yeah it piles up... but there's not really an "inside" that stuff needs to be inside. "Gravity" is the (global) geometric shape of 4D spacetime ... I mean... you don't need to be "inside" the Earth to contribute to how much "gravitational force*" the Moon feels in orbit. From the Moon, the ISS is contributing to the Earth's gravity while not physically touching the ground. If you're a satellite in space at the L1 Lagrange point between the Earth and Moon, each feels your gravity contributing to the mass of the Moon and Earth.
The way I've heard it explained is that all paths lead to the singularity. There's also a theory that says you would see the singularity no matter which direction you look inside the black hole. Assuming the singularity is emitting light
Even if it was emitting light, that light couldn't go "up" to you, so you won't see it even if every available direction for you indeed leads to singularity. It's like here you can move in any direction and you're still heading towards next Monday, next Monday is in your every direction yet no light can come to you from it, you can't see it.
Hi Mahesh! I'm an engineer with a particular interest in General Relativity and Quantum Theory, kind of like a hobby of mine. I find your videos super intuitive and I love the way you find to explain complex stuff in simple terms and graphs. I have a question on this video, though. I find the explanation on why escaping a Black Hole (from the astronaut's perspective) is impossible since it would require to time travel to the past super intuitive and logical. However, here's the question: if the astronaut gets very very very close to the event horizon, its clock will slow down. Then, if he finds a way to get away from said black hole (super thrusters of whatever), he will be "kind of traveling to the past", since he will be older that, say, somebody who stayed far away (this is the twins paradox). Why is that "time travel" allowed, but the one after the event horizon is not? Going into the event horizon seems to be an extreme version of the twin paradox. Does my question make sense, or did I entangle myself?
Very well put. The interesting part is that in this scenario is not symmetrical: we see Cooper slowing down and he sees the rest of the universe accelerating up. Because it takes an infinite amount of time to reach the event horizon, Cooper will se the universe accelerate insanely. Before he reaches the event horizon (from his perpective), so much time will have passed that the black hole will evaporate (in the case the universe expands forever) or the universe will collapse and start again (in the case it is cyclic).
Not quite. From Cooper's point of view, nothing happens at all when he crosses the horizon. However, once he does, space and time now switch functions; space becomes restricted in movement, but time does not. This means that any movement now takes place in time, so Cooper can visit the past or the future at will, but whatever he does, he will end up at the (space) point of convergence, which is called the singularity. Note that the singularity is unavoidable, and (from out perspective) is in time, not in space.
@@lucemiserlohnIf you use Gullstrand-Painlevé Coordinates (i.e. use Cooper's own proper time) you don't need to do the time-space-swap trick to analytically continue past the log(0) curvature at the event horizon. By the way, Cooper does *NOT* observe the rest of the universe speed up behind him due to the abaration of light. In fact, everything "above" him will get more and more red-shifted. He can't (and won't) see Hawking radiation either while in inertial free-fall. And he will actually collide with the physical singularly at the black hole's center of mass in a really brief, finite amount of time. (Like, seconds to days.)
It's not symmetric. The light falling in behind him is spaghettified (red-shifted) and will eventually "freeze in time" too... after a very short duration of Cooper's own proper time.
It's essentially multiplication by the "imaginary" unit so that you can use the complex logarithm to get past the infinite log(0) curvature at the event horizon. Swapping around the first two rows of the metric tensor is the same as how complex numbers are 2×2 matrices and swapping the rows transforms "1" to "i".
This is the most sensible explaination I've ever seen of the time/space inversion that happens beyond the event horizon of a black hole. I heard about this phenomenon, but this was the first time it made sense. Quick question though -- hypothetically, if from the rest of the universe's persepctive, Cooper's clock would slow almost infinitely as he approached the event horizon, would that not mean that from Cooper's perspective, the universe's clock would speed up almost infinitely, allowing him to view the evolution of the universe from that point forward in seconds from his own perspective?
Simultaneity is relative. We pair our moments with Cooper's moments in one way, where 1 his second maps to minutes/hours/years of our timeline, but Cooper has a different frame of reference and he considers different pairs of our moments simultaneous to him, so in his perspective his 1 second corresponds to 1 second or less of our timeline, not hours or years. Different frames of reference, depending on how they move, pair events as simultaneous differently. Which means he doesn't see us sped up at all, unless he stops falling.
You are brilliant. Insanely good teaching :-) Unfortunately I still did not understand the following Question: If Cooper enters the black hole time will pass way more slowly for him compared to his twin on earth. The Cooper who entered the black hole does not registrate anything. Now the question: If the Cooper inside the black hole stays younger (because time goes slower for him) would'nt he have to travel in future to escape from the black hole? But the direction in time (future or past) he had to travel is not the main aspect of this problem, because the time travel itself is it. But why would the time travel be neccessary to escape? That's what I still did not understand. The event horizon is the edge from where the outside viewer does not see any proceeds any more. OK. This is caused by time delation and infinite red shift. But what causes the difference between a travel in space and the travel in time crossing the event horizon?
I might be too late to have this question answered but…what happens if Cooper has a jetpack attached to his torso, and he falls in feet first? There will be a point where his feet are below the event horizon, but the rest of him can still escape (from Cooper’s perspective). So if he lights his jetpack, will he be ripped in half? If yes, there would be seemingly no reason, no forces tearing him apart. And this can apply right down to the subatomic level…even chemical and nuclear bonds happen over some distance. So if his feet are causally disconnected from the rest of him, they can’t be physically connected either. How would he not notice this as he crosses the event horizon, even with no thrust forces involved???
Isn't that the beginning statement? If you had enough propulsion to counter the gravitational pull, you could "leave" even if your feet are behind the event horizon. No speed is enough to eject matter out of a BH on their own. But put a rope? Bring a pocketrocket? No problem at all. It may take a while tho!
I think this is solved by delta v, producing enough impulse to escape the black hole once near the event horizon would put so many g's of thrust on you that you'd disintegrate. Basically the amount of sudden thrust you'd need to put out would be so huge you'd immediately destroy yourself on subatomic level. It'd be like being a particle in a particle accelerator.
Another great explanation and intuitive animations Mahesh. I love your chats with Einstein. You're such good friends. 😄One thing I don't understand about black holes is why the spacetime curvature is infinite at the singularity if they are formed from a finite amount of mass. 🤔
That's just what GR equations predict. Once the black hole is formed, trajectories for mass inside all lead to singularity, and other equations say if all mass is concentrated in a point we get a lot of infinities there. Whether this actually describes what really happens we're not sure, it's just simple mathematical models.
Is there any distance constraint on event horizon? Does it have any thickness? If you went in feet first, there would be a point where your head would not see your feet inside. The blood from your feet would not be able to return to your heart. You would no longer feel your feet as the nerve signals could not come out.
You are the best teacher I ever had. . Though now I am a 38 year old parent of 2 kids watching this video . . though it's not related to my job or my kids age to understand it 😅
a) You can see an astronaut entering a black hole. Once he is very close, the region around the black hole becomes denser the Schwarzschild radius for that region, so the Schwarzschild radius of the black hole increases. You end up seeing the black hole increasing in radius and "eating" the astronaut. This is seen observationaly in black hole and neutron star merges (the neutron star is a fat astronaut). The final black hole just increases its radius a lot and we don't even see any meaningful red shift photons at all. b) In real GR solutions, according to what we see, we do see matter exiting a black hole coming from the future: all real black holes are extremely fast spinning and, according to Kerr Solution, the ring singularity is removable (not actually proved yet), but if mass passes its ring, it will enter another universe where time is inverted, that is, it will enter a white hole. But we don't know if this is physical or not, but the solution is there.
May you create a video that gives a more intuitive explanation of how the outside of the black hole becomes your past and the inside becomes your future, i understand that the spacetime metric's signature (of a blackhole relative to the free-falling observer) changes such that the space components become time-like and the time component becomes space-like when the observer passes the event horizon. Therefore causing the outside of the blackhole to become your past and the inside your future but the problem is that this is just math talk (it would be interesting to see what you can come up with explaining spacetime metric signature) and it would be interesting to have conversations about spacetime metric signatures, what they tell us about the "shape" of the universe and how space and time are connected. Great video as always and I wish you the best!!!
FAQs + Go to ground.news/floathead to stay fully informed and access reliable information. Subscribe through my link to get 40% off unlimited access this month only.
FAQs
1) Shouldn't the speed of light be 300,000 km/s and not km/hr?
Yes, sorry!
2) You mean we can't OBSERVE things entering BH, right? The title is a click bait, right?
No! There are no events beyond the event horizon. So, from the perspective of an observer outside the BH, the event of something entering a black hole cannot happen. So, the last ever event is reaching the event horizon. Nothing ever happens beyond that.
3) Wait, if nothing ever enters a black hole, then how do black holes grow? How do they 'suck' stars and stuff?
I am glad you asked. Imagine a star of 1 solar mass falling into a 1 solar mass black hole.
From the outside perspective, we get a black hole of 1 solar mass with 1 solar mass worth of stuff almost frozen near the horizon. This creates practically the same spacetime curvature outside as a 2 solar mass blackhole and hence for all practical purposes, the black hole has grown!
As the mass approaches the BH, its event horizon would grow. So, the 1 solar mass BH + 1 solar mass stuff near the event horizon will also have a larger event horizon pretty much the same as what a 2 solar mass BH would have. And there you have it, for all practical purposes, we could model this as a new BH of 2 solar mass even though nothing ever crosses the horizon!
4) So, where is all the stuff? Close to the event horizon or at the singularity?
Yes.
5) What about Hawking radiation and black evaporation?
That's beyond the scope of this explanation. This explanation is for static black holes. (static event horizon that always existed). Yes, these are idealised BHs.
Any more questions?
🗣️🗣️Wait so how does NASA take pictures of stars entering the black hole.Can we not think as black holes as Wormhole that bends the fabric of space time so much that you go to an another universe, my whole life of 9 years has been a lie about black holes😮.
Btw thank you sir, you make this tensor calculus and general relativity so simple👏
And!! What about the swazchild radi!!!!!????!!??!!!
Two way speed of light is 300,000 km/s. How do you explain quasars or blazars if one way speed of light is 300,000 km/s?
:)
This is video is so wrong. An observer’s PROPER time does not stop at the event horizon, and an observer can pass through the horizon quite readily. It only APPEARS time stops there due to light getting trapped near the horizon. A basic reading of GR textbook will tell you how to calculate how much proper time it takes to fall into a black hole - and that time is quite finite. I’d suggest watching ScienceClic’s video for a much better breakdown of the problem.
@@se7964worse is how he keeps attributing things to Einstein that Einstein never said or did… this it what happens when you let random RUclipsrs believe they can master physics
I had to harness the power of love to solve spacetime to pause that screen on time.
Unpopular opinion: such a stupid movie
@@gadelavega bro thinks this is reddit
i even had to go back in time to actually read it!!!
.25x and precision scrubbing
If you are on PC you can use the < and > keys to go frame by frame.
I'm a huge fan and have watched many of your videos. I almost skipped this one because I *know* why nothing can escape a black hole. At 0:26 my jaw dropped. Then seeing how escape velocity is not the reason I literally slapped my forehead! I just love the deep, intuitive understanding your videos provide. Thank you!!
"... but Einstein..? Well Mahesh..!" Several of your videos in, I must tell you I find them immensely entertaining, and I learn so much. Many thanx for your work!
This format is great
You learned nothing from this video since it is wrong. If you did 'learn' anything then you've been miseducated.
I am looking forward to the video in which Mahesh intuitively, understandably, explains how to move back in time, because the person who interviews Einstein and Newton for each of his videos probably knows this
Imagine Cooper's view of the rest of the universe as he approaches the event horizon. Time passes normally for him, but far away from him, time appears to be passing faster. When he is close to the event horizon, every second that passes for him equals millions of years passing for the rest of the universe. When he reaches the event horizon, time outside the black hole becomes infinitely fast and he witnesses the end of the universe. He cannot leave the black hole, because the universe outside it no longer exists from his perspective.
If Cooper sees the rest of the universe age,wouldn’t he know that in his frame of reference time has slowed down which contradicts the fact that time is passing normally for him?
To enjoy this view of infinitely fast universe he must stop falling somehow and stay at the horizon exactly, which is impossible for a massive body just like it's impossible to move at light speed. If he falls down, he doesn't see the universe accelerated so much, as light struggles to catch up with him.
Just came to the same conclusion.
@@thedeemonNo, I recon he would see the universe (If he would turn around and look "out") age faster and faster right up until he passes the horison and the universe ends.. Crazy.
@@notme2.o654He would see it but his body would just experience time passing normally.
Alright we want a 2 hour special on black holes. This left me unsatisfied 😂. Not because it wasnt good but i have more questions than answers now.
If you leave a lesson with more questions than answers thank your teacher. That's actually the best compliment you can give them.
same thing
You are my favourite youtuber...
You have made physics really interesting and thought driven...
Kudos to you.
You're a fantastic teacher. I've been hitting this material hard without formal schooling for about 6 years and you really knocked me into the next field ;)
I'm 37 years old, I am a passionate about science and physics, and I Ve saw so many videos and documentary's in my life about black holes, but this is the first time I've understand how they "work" ... And it was so simple and easy... Great job!
Great presentation, contagious enthusiasm and positivity - your videos are just perfect for fridays! Thank you for this.
aways wondering about "why" in physics and your channel not only explains the why, but the how, when and where too. great content. An outsider sees a Black Hole as a region in space, the insider sees the Black Hole as a region in time. Best explanation (based on current understanding) of a black hole and makes sense to average Joe such as I. your Interstellar film disclaimer pop up was really funny, although had to rewind, slow the speed and pause to get the joke.
Hint: you can use "," and "." to skip single frames backwards and forwards :)
I love learning from your videos. The way you explain it is easier to understand. I love your enthusiasm when you are explaining, it’s great & refreshing.
Probably a stupid question, but; If, from my perspective, nothing ever enters a black hole, how can it gain mass? Or, for that matter, have mass in the first place?
A doubt that's troubling me tooo.! !!
That is exactly what I was thinking when I was watching him say this.
I tried looking it up but I couldn’t find a convincing answer
Those things will be stuck at the event horizon from our outside pov. The whole thing (black hole + stuff being stuck at the event horizon) will be practically a solid sphere and from outside there will be no gravitational difference between that stuff being on the "surface" or inside the black hole, so all of those things entering from their pov will also add to the black holes mass from outside pov. Of course this geometrical approximation changes inside the black hole, but from that perspective things can enter
The way that I understand it is using e=mc^2. We know that mass is just energy confined in space, and binding energy makes up most of the mass.
Since it can’t possibly escape the black hole, then it’s effectively contained in the space just like all the other mass/energy. So it is effectively adding to its mass by going back to what mass actually is; just energy contained in a space.
18:12 I was missing that outro so much. Even if matpat wasn't the one doing it, at least someone did.
The legacy lives on!
@@Mahesh_Shenoy Or shall I say, it links on.
@@Mahesh_Shenoy didn't know u watched matpat lmao
This channel never lets me down! Once again an amazing video
Rick Astley also never lets you down!
You know what else doesn't let you down? Black holes (..well atleast from my perspective)
Bro please never stop teaching. You have a GIFT my man! Love every single thing you've posted!
Thanks Mahesh, I’ve been struggling with the concept of space and time reversing inside a black hole, this was a very helpful explanation 👍
@17:30 a cool video segment here would be one of your paper models showing the light cones tilting so you can see the external space is indeed now in Cooper's past light cone.
So, when two black holes collide, they cannot merge together to form a single black hole; but freeze as a "double black hole" touching each other at their corresponding event horizons??
Good point. But then how come scientists say they've detected gravitational waves from two black holes merging billions of years ago? What are we missing?
Actually they can collide, because from their perspective time doesn't freeze, just as from Cooper's perspective he can enter the black hole.
But from our perspective why isn’t the collision perpetually in our future? Yet we can “hear” the ring down in the scale of seconds?? Mahesh please do the follow up for these questions!
I am not fully sure but I think the waves (or what we "hear") is not due to the collision but the bodies spinning around one another
Its getting better with every video :D
Brilliant video again! You make those hard things so intuitive, it's genius to be able to do that.
I wonder what's your take on this: I argue that even from the perspective of the falling person, he won't pass the horizon.
Here's why:
Suppose astronaut Bob throws Einsteins light clock towards the BH. When it nears the horizon the clock starts to tick slower. But light travels with the same speed in all reference frames. So for the light clock to tick slower, it must become bigger, seen from Bob. And since the clock almost stops ticking it is so big that it wraps around the BH multiple times.
Now he himself jumps towards the BH to retrieve his clock, with a faster initial speed so he'll catch up. When he nears his clock he'll see it tick faster again since he enters its reference frame. But that also means it shrinks again. Like everything else that was already (almost) at the horizon. That would mean the BH appears to shrink until it becomes so small that he'll wrap around it multiple times, like his clock.
This means the "singularity" inside the BH is actually the horizon but seen from a different perspective.
QED 😜
The "event horizon" *is* a _coordinate singularly_ for any distant observer(s) far away from the black hole... but it's _not a physical singularly_ Spacetime is still continuously defined beyond the horizon, and when you switch to using, for example, the proper time of an inertial observer falling into the black hole (Gullstrand-Painlevé Coordinates) You can keep going all the way past the event horizon to the physical singularly at the black hole's center of mass.
Yea so that's what I'm trying to argue against 😅
In special relativity the coordinate system is relative to the observer, different observers with different speeds use different coordinates to describe the same position. You have to do lorentzian transformations. Why would it be any different for a BH horizon?
Or to argue in another way:
When Bob throws in his clock, from his perspective it never crosses the horizon. But when he waits an extremely long time, hawking radiation evaporated the BH before the clock crossed the horizon. Since the view seen from the clock must be consistent with the view from Bob, the clock could never have crossed it, even from its view.
@@Jopie65 Yeah, from clock point of view horizon shrinks to dot faster then he riched it. And this happens relatively fast(if clock survive unfrozen supernova explosion), but in outside world "trillions" of years will pass.
about SR near BH -> hyperbolically accelerated reference frame/The Rindler horizon
This is a really nice explanation, you're easily my favourite teacher in GR, that enthusiasm is contagious :)
Two things I still don't understand though, in the case of a real-world scenario: if an ouside observer 'sees' something fall into the black hole, it gets frozen in time near the event horizon, but if it's a feeding BH, it grows, so after some finite amount of time, that infalling object would be behind the event horizon from the outside perspective as the horizon would move past the point where that object was.
And if Hawking radiation is real, then from the perspective of an infalling observer the BH would 'evaporate under them' as they keep approaching the event horizon, because if the BH evaporates in a finite time, it must happen before the infalling observer reaches the horizon.
It's just an after image, their last photon streams keep getting redder and redder, until it's invisible, going to the radiowave spectrum. If the BH keeps growing at time, foremost we wouldn't even be able to see anyone approaching it, due to the extreme brightness of it's accretion disk, but if could filter out most of that radiation, the growth you only speed up the fade.
@@linuxp00 I'm not talking about seeing the object in visible light, but rather if you track it in space. Then you would know its position in relation to the center of the BH and after some time, you would find out that it should be behind the event horizon.
The mass of Cooper is enough to enlarge the EH, so at some (finite) time he will merge with the BH, even from an external perspective. The larger the mass of Cooper, the sooner it will happen, that why we "see" BH mergers or merger of BH with neutron stars quite frequently.
@@Juni_Dingo I think there is a misconception given to a metaphor abuse. The image is not the object, it doesn't matter where the image is, just that it stops on the surface to an outside static frame, if you follow along the astronaut you not going to see any after image at all, so it's just an illusion.
@@linuxp00 But that is not what I'm talking about, not seeing the infalling object, I'm talking about tracking it in space. Not with light or whatever, you can calculate the trajectory etc etc. I'm not talking about light here. Just that the object will eventually end up inside the event horizon from the outside perspective in the case of a growing BH
I love your channel so much that I pre liking and commenting. I already know I am going to love the video.❤
I could not stop myself by watching this video because I was asking the same questions and giving same arguments to everyone but no one was getting convinced and I was thinking why they don't understand my words.
I think he explained everything very well. But the title of this video makes it more confusing than it needs to be. I think if it was titled "Why can't we OBSERVE anything entering a black hole in the first place", it would remove some ambiguity.
@@albertjewell1963 It's not about observing. Nothing can objectively enter a black hole in your frame of reference except you :)
In black holes, spacetime is bent so much that all paths lead towards the center so there is no direction out.
All causal curves lead deeper into the interior. There are space-like that lead to the exterior.
It is explained as space and time flip their position
I wonder why we can see (perceive) the merger of two black holes? Why don't they freeze in each other's event horizon?
Love these videos! It's disappointing that there's so many scientific misconceptions around when things have be known for so long, your channel really helps to overcome that. Plus I loved your impression of the 'theory guy'.
I feel like my mind has become a black hole. But it was just blown. Awesome video, as always!
Good job on your narrative approach to these concepts, im loving it.
You've spelled _naïve_ wrong.
Some 40 years ago, Dr Venkatavaradhan, the then director of Mumbai's famous Nehru Planetarium, gave a lecture at our college about Black Holes and the inevitable "why nothing can escape from it" story. It was new then and so very fascinating, and I have been hooked for life into topics of stars and gravitation and black holes. Great video, and thanks for the insight, but with due apologies to Einstein, I fell I will stay with old one for some more 'time' - at the edge of the horizon!
- So, I fell into a black hole.
- Well, that sucks!
- No, it doesn't! Watch this cool video for a better explanation while I lurk over there on the event horizon.
- Won't you cross it?
- Well, it's matter of perspective...
(Okay, I'm leaving)
I have asked many people why we can’t escape with continuous thrust if we are just 1 metre inside event horizon. Finally found an answer 😊
I have one question though. From the perspective of Cooper, will he ever reach the centre or anywhere inside after crossing event horizon? Say the radius of event horizon is 20 km. From his point of view time is running normally. He is looking at his clock. Will 1 second ever pass on his clock since that means an infinite amount of time outside?
It should be 300.000 km/s in the Beginning of the Video ;-)
Ahhh.. Damn it! Thanks for pointing it out.
@@Mahesh_Shenoy No worries! Nice video as allways! You have a great way of making things, that are hard to understand, understandable! .-)
These are the mistakes every creator hates like hell...
299,792,458 meters per second
I think it was intentional to boost engagement. It's a common tactic online. Post incorrect Information and engagement goes Up
Thanks, I love your videos! Does "time not tick at all" 8:38 in a literal way, meaning complete halt, at the edge of the black hole from our perspective? Or is it rather SO, SO, SO very slow that we cannot measure the rate? Meaning that it has practically stopped, from our perspective. I'm thinking that if time comes to an absolute 0 rate from whatever perspective then it must also be 0 rate from Coopers perspective. But from Coopers perspective time does not stop, so it has some rate, it is just too slow from our perspective. Am I missing something?
I think one of the best compliments I can give your channel, and you.. is that you never fail to make me think. About the topic at hand but also further into the subject. Questions start arising almost from the moment you start to speak. For instance.. when falling into a black hole.. looking towards the way you came.. what would you see? Does gravity affect sight? I'm sure it will depend on the black hole to start. A massive black hole, less hectic at the event horizon might be best. Upon looking "back" would you see events evolving more quickly in relation to their distance from you? I understand something entering into the black hole will look to be stuck in time.. frozen. Not sure if I've seen reporting on the reverse? Ok, your jokes are great! Your general talks on relativity are special
I agree with you that he makes SOME people think. One thing how can a black hole grow if nothing can get into it? How can the space man continue when his time stands still. I agree that he may not know that time stands still but it does according to these explanations.
In my opinion he is so convincing that he is dangerous. There are so many other physicists not agreeing with SR and GR that it is far from sure it is true. In my opinion SR and GR is partly true but only partly. It is conveniently using what fits for it's explanation and forget the rest and also makes up fanciful ones.
@@leonhardtkristensen4093 No scientist worth their salt disagrees with SR and GR. Every prediction made by both theories have been observed time and time again. What is true is that GR is considered incomplete; there are edge cases in relation to quantum mechanics where GR and QM disagree on what happens, and that must be reconciled. That is not the same as GR being wrong.
Space man can continue because in his reference frame, nothing unusual happens. He and the outside observer do not share the same inertial system, and thus, the same rules apply to them with different outcomes. That is the "relative" in relativity. Observations and measurements between different inertial systems disagree, they are relative to the inertial system. There is no fundamental overarching "truth".
@@leonhardtkristensen4093 according to Susskind.. that's exactly how. Matter attaches to the perimeter.. increasing the perimeter. *remember I'm a RUclips physicist AT BEST!* so my interpretation and words used aren't the best. Leonard susskind is a hard listen but if you're into this stuff, he has some great lectures. Don't expect nothing like this channel whose main focus is US.. susskind speaks at Stanford (if I'm correct)
@@leonhardtkristensen4093 as for not agreeing.. that's science. Science isn't about what's known.. its what's provable. Trying to discredit SR & GR IS THE WORK! Every time an experiment falls by the wayside.. that's more credit to the theory! If you look at research papers.. ANYONE can put an idea forward, doesn't mean they will be accepted.. I'm trying to say.. science isn't stuck up. It WANTS to be discredited.. that's the nature of science. Every failed experiment or test is just as vital as a discovery. Without it we would still believe in witches
@@lucemiserlohn I am in no doubt that Time keepeng slows down with speed and probably with gravity too. I have the believe that it has to do with electro magnetic movement at the atomic level. It correspond with what I know about signal delay through electronic circuits. The actual reason we will probably not know until we work out what electric and magnetic signals really are. I also believe that it is the two way motion of the EM that is involved. I believe time keeping is an oscillation at the atomic level and there fore a two way motion. I believe this is a thing that probably happens in organic bodies too so people will probably have the same time dilation as atomic clocks but I am not sure that that has been proved.
By the way has any body checked light being bend around the moon? Bending around any star could also be from an atmosphere or plasma being there.
It may well be the "incomplete" in SR and GR that bothers me. Also I have the feeling that if we could work out how to detect EM one way then we may well come to that there is some thing absolute. EM of cause travel at c.
The y=1/x on your shirt really matches with the situation you have to go to infinity to see the graph touching x axis similarly as you have to wait for infinite amount of time to see the person toching the event horizon
Easter egg regarding 5 dim tesseract with power of love... was funny!
THANK YOU for this! The escape velocity thing always bothered me but I’ve never seen it addressed until I saw this video!
From our point of view, Cooper never crosses the event horizon; it will always look like he's stuck there. But the black hole itself does not exist for an infinite amount of time: because of Hawking radiation, it slowly evaporates and the event horizon slowly recedes. So we should see Cooper tracking this recession, getting closer and closer to the center, but never crossing the shrinking horizon. Eventually, the event horizon will collapse into a point, and the black hole will dissipate, and we will have never observed Cooper crossing it. With nothing holding him back, we will just see him go on his merry way to the next adventure. Now, what's wrong with this picture?
(Cooper can not see the Hawking radiation while in free-fall.) You want to know what Cooper is experiencing... so you want to use a coordinate system based on Cooper's proper time (and no one else's clock)... that means you're using Gullstrand-Painlevé Coordinates, which are continuous all the way to the physical singularly at the black hole's center of mass. Cooper will arrive in a very breif amount of time (depending on the mass of the black hole, a few fractions of a second to a few days on Cooper's own clock.) The event horizon is empty space. There is nothing there in Gullstrand-Painlevé coordinates.
The question of what Cooper experiences is indeed very interesting (and I have thoughts about that), but what I was really curious about is how to resolve the contradiction I see between the assertions that, from our point of view, (a) Cooper never crosses the event horizon, and (b) the lifetime of the black hole itself is finite. This would seem to suggest that Cooper outlasts the black hole without ever having crossed its event horizon.
@@vanosaurAs someone else pointed out in another thread, Cooper and the black hole together have an event horizon that's slightly larger than that of the original black hole. In contrast to the original horizon, he can pass the combined event horizon in finite time.
Thanks for this. I've been saying that for years and never found a good explanation to contradict this idea.
The logical conclusion is that the black hole itself can never form. Using a coordinate system relative to the black hole is irrelevant: if the black hole is never completed, this coordinate system is not in true free fall.
There are no black holes, there are no singularities, the black hole is a limit behavior of spacetime that can't be reached due to quantum fluctuations. What we observe are quadi-black holes that will never complete their collapse.
From our perspective I don't think we ever see anything happen.
The event horizon cannot shrink from our point of view because it would take time to do so and there is no time.
From our point of view there is no singularity either (whatever that actually means as matter cannot exist in a state that compact) and I would think Hawking radiation (that I have too many problems with) may only apply in coopers/black hole's frame of reference as cooper and the horizon are pretty much stuck in our frame. Now from its frame, perhaps its already 'evaporated', but I don't see how we'd ever see that. Cooper is dead but not, black hole is there but not. Makes perfect sense.
I don't know what to say, but this is the best video on the internet about blackhole! ❤
In the isolated case of the "static" black hole and one "participant" (+ the observer who's resting compared to the black hole), this sounds valid, but what about a real scenario, where there is additional matter, and the event horizon is also increasing based on how much stuff is around it, and how close that stuff is.
So we should be able to "see" Cooper close in on the horizon, let's say 1 cm away, and we should also be able to "see" the black hole's event horizon growing more than 1 cm in radius (from other matter getting close), both in finite times, which means that even though Cooper is technically not able to pass the horizon by himself, the horizon should be able to engulf him, making it possible to enter the black hole from the outside perspective, he just won't be able to reach the distance of the original horizon from the center, and this even looses meaning after the horizon engulfed him
Also, what about the case where both Cooper and the black hole are moving towards each other from the observer's point of view to begin with?
In that case the black hole should have no slowing down "issue", and should just go through Cooper like an eraser, because otherwise the observer would have to experience Cooper to basically be "pushed back" by the black hole, while he seemingly turns into a sculpture, which doesn't seem to be valid.
However if he is indeed gets "ran over", then that implies, that the observer should be able to shift into a perspective where Cooper is swallowed, and back to one where he's not, since it was just a matter of perspective, thus making it possible to experience someone going into, and out of a black hole, which should be impossible
So in summary, even though I though I understood it, I just got confused again :D
You are right.
I think he will be pushed, not sure about the math tho
Yep, it's all about perspective of particular frame of reference, and a fully static solution.
You’re right in the first part. The black hole’s event horizon does expand based on the objects that “fall into” it. It’s why black hole’s mass depends on surface area instead of volume.
If both cooper and blackhole are travelling at the same speed in opposite direction, you can simply substitute that with initial condition for cooper travelling twice the speed relative to the black hole. The black hole doesn’t repel him. But drags him with it on the opposite direction to which cooper was travelling. Like a fly that hits a bus windshield, he is dragged along.
One of the greatest explanations of all time ❤🎉
Brilliant video...very well explained. But man its mind bending!
Thank you!
Mahesh you may try to explain with light cones visually. it may be more clear.
If nothing can enter a black hole Then how black holes grow in size or two black holes merge
@@CiaDora-us1tf but that will happen infinitely in the future....
What about the point of reference from inside the event horrizon? Would they see him fall in? What about about the Hubble radius where the expansion of the universe outpaces the speed of light? Is that just another event horizon? Are we inside a black hole of sorts? 🤔 another extremely good video!
If nothing can enter a black hole from our perspective, how do we observe gravitational waves from black hole mergers?
@kinitpatel1866
The gravitational waves are from the spacetime outside the black hole.
The spacetime outside the b.hole is being pulled by each "piece" behind/ next to it, like a treadmill.
So the gravity doesn't have to "get out" of it to keep travelling away,
😁🌏☮️
0:26 hey isn't c=300,000km/sec?
Yes i was also going to point out that but you already did, appreciated
It is when you round
I've watched the 3 videos in succession which culminate in this one - and even though I understood these issues before, these are the best explanatory videos I've ever seen. There are a few analogies where you take some liberties (i.e. cones versus spheres), but generally this should be understandable from any thinking person's perspective. Really well done! :-)
Was waiting from morning after i saw the community post...
Hello Mahesh shenoy !!!!
Today i got your video in my recommendation section and i am so happy that i clicked it
Your videos are amazing interesting and unique
Btw i am gonna watch every video on this channel within a week 😂😅😅
Keep making videos ❤
11:49 what is there to do with frequency we want the wave length right if frequency is low then wave length is high that is it should be visible ????
GR does NOT rule out going to your own past. SR does that, but GR (alone) does not. It's not something you can do with rocket engines (probably) but the equations themselves to the best of our knowledge do not rule out closed time-like curves
Here he means not CTC, but just moving outside one's light cone, or in backward time direction. With CTC you go forward in time, but due to the loop end up in some earlier moment of your history, it's a different thing.
now my only question is... how does the star becoming a black hole even look like during that process?
does the infinite curvature appear at some random point within the star? many points? and then what? is there already an event horizon at that point, where? does it grow? aren't things therefore "entering" the black hole as the horizon grows?
how does it become black? is it instantaneous, or is it a gradual red shift until it's not visible anymore? to our point of view, is the star inside of the black hole,
or is it eternally falling onto the horizon?
But, we have direct evidence of things entering into black holes on our timescale. We have black holes merging with black holes. So, something needs to be able to go through the event Horizon on our timescales because those mergers are spectacularly fast.
@@chadb9270 was just about to say this, nicely put, i love the video but was left with that doubt in mind
@@chadb9270 black holes aren't really "objects", they're regions of spacetime. a black hole "falling" into another isn't like an object falling there, it's further distorting the spacetime around both of them. to us there is nothing inside the black hole, so matter doesn't actually enter either of them.
@@CiaDora-us1tf yeah, like. i'm not sure, actually. if anything, this video suggests that all the matter of the star is still falling and will remain falling forever, before it reaches the horizon. now, the mystery to me is when exactly and where does the horizon actually appear.
@@CiaDora-us1tf in the very middle i'm not so sure. if you go there sure, but right now, from our point if view, there isn't, it would take infinite time for something to even cross the horizon, let alone reach the center.
I'm officially MIND BLOWN from this (and I'm a physics geek): it's all about the perspective and relativity. Thank you , FloatHeadPhysics!
I think the video title is misleading. It should be “Why can an outside viewer never observe anything entering a Black Hole”
Its a click bait title, I don't hold it against him as its a good video
no. nothing can enter. he didn't explain why even from Cooper's point of view he doesn't enter. black holes do not live forever in reality. they evaporate from Hawking radiation before he can fall in even though that is a very short amount of time from his perspective.
It’s not a clickbait! From the perspective of the outside observer, there are no events beyond the event horizon! (By definition). Something entering a black hole would be an event beyond the event horizon. So, that can’t be true.
It’s almost as if the title’s interpretation is….relative
@Mahesh_Shenoy if space flip with time there must be many "times directions" in Black hole ?
you are amazing sir i will go to my dream iisc, iiser pune all because of you i love you and i love physics you are true Legend!
I am ur big fan
Sir I wanna know various science things but I am not getting a chance to do so. from which university have I graduated.
awesome as always
It's too dark.
astonishing, why you are making such a difficult concept/theory sooo easy to understand, ❤❤❤❤
i never thought the other perspective 😂😂😂
16:33 who would want to go to previous monday. I would go to sunday instead............if i could
Enjoyed that. Thanks! But these contradictions make it seem like we really don’t know and just apply our best guess 😂
1st comment?
Me second
I beat you to it 6 hours ago :D
@@Mahesh_Shenoy We'll I can't travel to the never existed past... If Blackhole is the event horizon, your premiere was the event beginning 😄. I've explained my 'Proper rest' in the other comment's reply. Kindly see it if you are seeing this.
We need a floathead video to make the switch from spatial direction to temporal direction at the event horizon more intuitive!
Love the interactive format of this video.
I love your channel, your energy, your enthusiasm, and you are an outstanding teacher.
That being said. The current understanding of black holes physics says you are very wrong about "nothing ever entering a blackhole". WE from OUR reference frame from outside the event horizon will never see a falling object cross the EH. That much is true.
But from the perspective of the falling object/person, they go through no problem and like a bat out of hell. Black holes feed on matter, collide and coalesce with other black holes, their gravitational waves go insane when nearly touching, then ring out and dissappear when they fall and cross each other's EH.
There is a plethora of phenomena that contradicts your stance. Science does not back you up this time. I recommend you browse PBS spacetime's channel for a robust resource on black hole physics.
All that being said, let me insist, I love your channel and what you do. I hope you keep it up, you are an outstanding communicator and teacher. Thank you for what you do.
For outside observer gravitational time dialation is in effect only if a body is accelerated near mass
9:07 I just realized why it's called the event horizon now
This is my favorite series on RUclips!
I just watched an 18 minute video on black holes, I'm confused if I'm a nerd or your way of explaining is so engaging. It's both.
It's not nerdy to enjoy space. It's a part of nature.
Great video! One's time can never be slowed down... that's good to remember.
So from our perspective, one black hole will never enter the event horizon of another black hole. Meaning that they will never collide, but yet LIGO saw gravitational waves of black holes colliding.
Now i am puzzled.
gravitational waves are a result of acceleration. Massive objects (black holes) are accelerating towards each other (doesn't matter if directly or in a spiral) and hence send those waves. The waves are the strongest just before the collision (from our perspective just before the time dilation becomes too strong and the waves are redshifted too much)
@@jukokobarinko wow. That is a nice and clear explanation. Makes sense. Thanks
Hey y'all, I just got back from the infinite future, and I gotta say, it is pretty cool watching everything fall through the EHs is a sight to behold!
Hi sir
My doubt:
Suppose a person is falling in a black hole,
From his perspective he is going in it via the event horizon and from our perspective (suppose a space station some what near the black hole but out of its visible influence) the observation are that the person is static.
This is normal observation according to you and science.
But what if the space station starts moving towards the black hole, will observation of the person will be the same i.e., static or that person is moving OR what kind of observation are found.
Thank you for this video.
It was really fun.
If nothing ever enters a black hole then how can the black hole be expanding.
Great video, I love your channel! But I think this is actually incorrect!
Things DO NOT slow down when they fall in a black hole, this is a common misconception, Einstein never said any of that. You DO see things falling in a black hole, at the speed of the gravitational acceleration, as simple as that.
When you see something falling in a black hole, its speed does not slow down, it falls extremely fast.
You just need to imagine a "Gravitational Light Clock" hovering above the event horizon. Light going up, slows down and redshifts, then it falls back down, at the speed of light and blueshifts to the original wavelength. This is the origin of the gravitational simultaneity.
Only when you hover above the event horizon, resisting the gravity, you can look up and see the entire rest history of the universe.
Gravitational/Acceleration relativistic effects take place only when something moves in relation to another thing, or when something hovers in a gravitational field.
It's not a misconception. Just look at Kruskal diagram, how lines of constant time go there, and when light from falling body near the horizon reaches (if ever) a static outside observer. Also look at Rindler horizon, how crossing it looks for the accelerated observer, same effect of visibly slowing down to infinity.
@@thedeemon It is a misconception.
You can clearly see this in the Kruskal acceleration space time diagram which you mentioned, as something moves at a specific acceleration, a light ray coming from the back will never catch up to it, from the perspective of the accelerating body, the universe behind it would be black, there would be a horizon behind it, which is analogous to a gravitational horizon. In gravitation, something accelerating would be standing still, hovering above the black hole, and below the object there would be the black hole's event horizon, which is analogous to the Rindler horizon.
In the acceleration space time diagram which you talked about, you can clearly see that the events in the object's part opposite to the direction of movement happen first, which is exactly what happens when something is accelerating and hovering above the event horizon of a black hole, events in the parts of the body facing the black hole happen first than the events in the parts of the object facing away, the Simultaneity is the same.
Again, in the Gravitational Light Clock, light slows down only going up, and when it falls, it does so at the speed of light. If an object slowed down while it fell, so would light, and therefore Gravitational Simultaneity would not exist.
Under the light of the Equivalence Principle. Without gravity, if something passes by you accelerating, it is going to pass by you extremely fast, as it gets close, it blueshifts, as it moves away, it redshifts. Therefore, the same thing happens in gravitation, as something falls in a black hole, it accelerates towards the black hole extremely fast, and the light coming out of it blueshifts as it gets close, then when it is closer to the black hole than the outside observer is, the light redshifts.
@@cai0_o It's like you're not even looking at the lines in those charts. Just track which moments of a free falling body going towards and through the horizon correspond to which moments of the accelerated external observer. You'll see how the last minute before crossing maps to basically infinite future of the accelerated external observer. So in that observer's perspective the falling body slows down and nearly halts.
Fantastic video, @Floatheadphysics, but it introduces a new misconception at 12:00. This debunks a huge misconception that is ubiquitous in even academically-rigorous black hole content. It does point out a new misconception though - even an infalling observer would never pass the event horizon.
As anything falls towards the black hole, it’s time dilation increases arbitrarily, right? But we know black holes emit Hawking radiation and evaporate on finite timescales. 10^100 years for the infalling observer would go by in a flash as they watched the universe behind them speed up exponentially. This means that the infalling observer actually observes the event horizon shrinking right ahead of them, never reaching it. They would then (ignoring tidal forces) reach the midpoint of the black hole and experience the explosion that results from the runaway hawking radiation at the end of the black hole’s life.
I would love if you could make a video on this interaction as well - it points to the fundamental realization that there is no interior of a black hole, and there is no event horizon, just layers on layers of apparent horizons. As Hawking stated, “there are no black holes”
I absolutely love this guy. You can NOT watch one of these videos without smiling, it would be easier to escape a black hole 😂
8:10 at the very very edge your mass becomes part of the Schwarzschild radius calculation and the black hole _grows around you._ once inside mass must wait until hawking evaporation reaction nullifies it as the black hole shrinks. Time inside is slowed to stop and will last "forever" before time ticks forward, but the black hole itself has a finite life time.
This is an amazing video! I love the excitement in which you share knowledge. Though, I have one lingering question after watching. If nothing can ever enter a blackhole, then how does it gain more mass? Does it all just pile up at the surface from our perspective? I know its going into the blackhole from their own perspective but as far as the rest of the universe is concerned, the blackhole should never grow in size right?
Yeah it piles up... but there's not really an "inside" that stuff needs to be inside. "Gravity" is the (global) geometric shape of 4D spacetime ... I mean... you don't need to be "inside" the Earth to contribute to how much "gravitational force*" the Moon feels in orbit. From the Moon, the ISS is contributing to the Earth's gravity while not physically touching the ground.
If you're a satellite in space at the L1 Lagrange point between the Earth and Moon, each feels your gravity contributing to the mass of the Moon and Earth.
The way I've heard it explained is that all paths lead to the singularity. There's also a theory that says you would see the singularity no matter which direction you look inside the black hole. Assuming the singularity is emitting light
Even if it was emitting light, that light couldn't go "up" to you, so you won't see it even if every available direction for you indeed leads to singularity. It's like here you can move in any direction and you're still heading towards next Monday, next Monday is in your every direction yet no light can come to you from it, you can't see it.
You are the master explainer. I love it. Thank you, sir!
Truly wonderful videos! Thank you
Hi Mahesh! I'm an engineer with a particular interest in General Relativity and Quantum Theory, kind of like a hobby of mine. I find your videos super intuitive and I love the way you find to explain complex stuff in simple terms and graphs. I have a question on this video, though. I find the explanation on why escaping a Black Hole (from the astronaut's perspective) is impossible since it would require to time travel to the past super intuitive and logical. However, here's the question: if the astronaut gets very very very close to the event horizon, its clock will slow down. Then, if he finds a way to get away from said black hole (super thrusters of whatever), he will be "kind of traveling to the past", since he will be older that, say, somebody who stayed far away (this is the twins paradox). Why is that "time travel" allowed, but the one after the event horizon is not? Going into the event horizon seems to be an extreme version of the twin paradox. Does my question make sense, or did I entangle myself?
Very well put. The interesting part is that in this scenario is not symmetrical: we see Cooper slowing down and he sees the rest of the universe accelerating up. Because it takes an infinite amount of time to reach the event horizon, Cooper will se the universe accelerate insanely. Before he reaches the event horizon (from his perpective), so much time will have passed that the black hole will evaporate (in the case the universe expands forever) or the universe will collapse and start again (in the case it is cyclic).
Not quite. From Cooper's point of view, nothing happens at all when he crosses the horizon. However, once he does, space and time now switch functions; space becomes restricted in movement, but time does not. This means that any movement now takes place in time, so Cooper can visit the past or the future at will, but whatever he does, he will end up at the (space) point of convergence, which is called the singularity. Note that the singularity is unavoidable, and (from out perspective) is in time, not in space.
@@lucemiserlohnIf you use Gullstrand-Painlevé Coordinates (i.e. use Cooper's own proper time) you don't need to do the time-space-swap trick to analytically continue past the log(0) curvature at the event horizon.
By the way, Cooper does *NOT* observe the rest of the universe speed up behind him due to the abaration of light. In fact, everything "above" him will get more and more red-shifted.
He can't (and won't) see Hawking radiation either while in inertial free-fall. And he will actually collide with the physical singularly at the black hole's center of mass in a really brief, finite amount of time. (Like, seconds to days.)
It's not symmetric. The light falling in behind him is spaghettified (red-shifted) and will eventually "freeze in time" too... after a very short duration of Cooper's own proper time.
"Elongated" 😂. You'd make the best physics teacher dude, thanks for the content 🙏🏾
I hope this video will have a follow up with some explanation on why space and time "switch place" inside it and such
It's essentially multiplication by the "imaginary" unit so that you can use the complex logarithm to get past the infinite log(0) curvature at the event horizon. Swapping around the first two rows of the metric tensor is the same as how complex numbers are 2×2 matrices and swapping the rows transforms "1" to "i".
Finally I can kind of get behind the idea of that near BH planet trip in the Interstellar movie. Thanks!
This is the most sensible explaination I've ever seen of the time/space inversion that happens beyond the event horizon of a black hole. I heard about this phenomenon, but this was the first time it made sense. Quick question though -- hypothetically, if from the rest of the universe's persepctive, Cooper's clock would slow almost infinitely as he approached the event horizon, would that not mean that from Cooper's perspective, the universe's clock would speed up almost infinitely, allowing him to view the evolution of the universe from that point forward in seconds from his own perspective?
Simultaneity is relative. We pair our moments with Cooper's moments in one way, where 1 his second maps to minutes/hours/years of our timeline, but Cooper has a different frame of reference and he considers different pairs of our moments simultaneous to him, so in his perspective his 1 second corresponds to 1 second or less of our timeline, not hours or years. Different frames of reference, depending on how they move, pair events as simultaneous differently. Which means he doesn't see us sped up at all, unless he stops falling.
You are brilliant.
Insanely good teaching :-)
Unfortunately I still did not understand the following Question:
If Cooper enters the black hole time will pass way more slowly for him compared to his twin on earth. The Cooper who entered the black hole does not registrate anything.
Now the question:
If the Cooper inside the black hole stays younger (because time goes slower for him) would'nt he have to travel in future to escape from the black hole?
But the direction in time (future or past) he had to travel is not the main aspect of this problem, because the time travel itself is it.
But why would the time travel be neccessary to escape?
That's what I still did not understand.
The event horizon is the edge from where the outside viewer does not see any proceeds any more.
OK. This is caused by time delation and infinite red shift.
But what causes the difference between a travel in space and the travel in time crossing the event horizon?
One of your best videos! loved the funny component of it.
I might be too late to have this question answered but…what happens if Cooper has a jetpack attached to his torso, and he falls in feet first? There will be a point where his feet are below the event horizon, but the rest of him can still escape (from Cooper’s perspective). So if he lights his jetpack, will he be ripped in half? If yes, there would be seemingly no reason, no forces tearing him apart.
And this can apply right down to the subatomic level…even chemical and nuclear bonds happen over some distance. So if his feet are causally disconnected from the rest of him, they can’t be physically connected either. How would he not notice this as he crosses the event horizon, even with no thrust forces involved???
Isn't that the beginning statement? If you had enough propulsion to counter the gravitational pull, you could "leave" even if your feet are behind the event horizon. No speed is enough to eject matter out of a BH on their own. But put a rope? Bring a pocketrocket? No problem at all. It may take a while tho!
I think this is solved by delta v, producing enough impulse to escape the black hole once near the event horizon would put so many g's of thrust on you that you'd disintegrate. Basically the amount of sudden thrust you'd need to put out would be so huge you'd immediately destroy yourself on subatomic level. It'd be like being a particle in a particle accelerator.
Another great explanation and intuitive animations Mahesh. I love your chats with Einstein. You're such good friends. 😄One thing I don't understand about black holes is why the spacetime curvature is infinite at the singularity if they are formed from a finite amount of mass. 🤔
That's just what GR equations predict. Once the black hole is formed, trajectories for mass inside all lead to singularity, and other equations say if all mass is concentrated in a point we get a lot of infinities there. Whether this actually describes what really happens we're not sure, it's just simple mathematical models.
Is there any distance constraint on event horizon? Does it have any thickness?
If you went in feet first, there would be a point where your head would not see your feet inside.
The blood from your feet would not be able to return to your heart. You would no longer feel your feet as the nerve signals could not come out.
You are the best teacher I ever had. . Though now I am a 38 year old parent of 2 kids watching this video . . though it's not related to my job or my kids age to understand it 😅
A truly great video! Love your explenations :D
a) You can see an astronaut entering a black hole. Once he is very close, the region around the black hole becomes denser the Schwarzschild radius for that region, so the Schwarzschild radius of the black hole increases. You end up seeing the black hole increasing in radius and "eating" the astronaut. This is seen observationaly in black hole and neutron star merges (the neutron star is a fat astronaut). The final black hole just increases its radius a lot and we don't even see any meaningful red shift photons at all.
b) In real GR solutions, according to what we see, we do see matter exiting a black hole coming from the future: all real black holes are extremely fast spinning and, according to Kerr Solution, the ring singularity is removable (not actually proved yet), but if mass passes its ring, it will enter another universe where time is inverted, that is, it will enter a white hole. But we don't know if this is physical or not, but the solution is there.
May you create a video that gives a more intuitive explanation of how the outside of the black hole becomes your past and the inside becomes your future, i understand that the spacetime metric's signature (of a blackhole relative to the free-falling observer) changes such that the space components become time-like and the time component becomes space-like when the observer passes the event horizon. Therefore causing the outside of the blackhole to become your past and the inside your future but the problem is that this is just math talk (it would be interesting to see what you can come up with explaining spacetime metric signature) and it would be interesting to have conversations about spacetime metric signatures, what they tell us about the "shape" of the universe and how space and time are connected.
Great video as always and I wish you the best!!!
Kruskal diagram to the rescue!
wow amazing explanation