What Happens To Quantum Information Inside A Black Hole?
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Meet Alice and Bob, famous explorers of the abstract landscape of theoretical physics. Heroes of the gerdankenexperiment-the thought experiment-whose life mission is to find contradictions in the deepest layers of our theories. Today our intrepid pair are jumping into a black hole. Again. Why? Well, to determine the fundamental structure of spacetime and its connection to quantum entanglement of course.
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Written by Matt O'Dowd
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I love the idea that a future mind-uploading device requires you to breakdance on top of it while it uploads you.
I think you'll find that you put the device on your head. For convenience, of course.
Remember, there is no up or down in space, just round and round ...
ratt 😜
its part of the physic process. he breaks his neck to avoid having 2 bobs at the same time and breaking unitarity
I loved that part so much lol. Just do a headspin on this device while it WHARGARBLS your brain into a digital copy and then just let your deceased body flop onto the ground.
@@richardconway6425your comment spins me right round baby right round
- dead or alive
@@bmxerkrantz yes, that too !! 🐸
It's comforting to know that ancient PBS Space Time videos will still be around even when Sag A* meets its end.
As quantum information
@@LuisSierra42 I dunno .. sounds like Bob was watching the vintage originals lol
Hopelessly scrambled
@@uggoldosBob's star-sized Matrioshka brain computers can unscramble them.
But can the Matrioshka overcome uncertainty? Seems like the same problem Star Trek's transporter technology would have.
Veritasium feels like a layman successfully reaching into the depths of science and bringing it back to us. PBS spacetime feels like a lifelong deep scientist successfully reaching out to the layman to explain things.
😂 very accurate
Both of them go over my head sometimes 😅
@@marcomoon6062Spacetime is at a much higher level of science than veritasium although both are brilliant
It is!
Absolutely not. PBS is explaining one line of speculative reasoning.
"Bob waited 10^87 years, so a week isn't so bad. "
I'm now dead in this timeline. 🤣
"Digital Ghosts in a Dead Universe" would make a great metal album name
Band name too
DGIDU!
@@Annathroyand the first single
I think it's also within the allowed length limit of a Dot Tumblr Dot Com, too...
@@b.s.7693 nah, Unitarity is the first single.
10:36 "(Bob) is looking for signs of the experimental qubit. But if we're being honest, he's also looking for signs of Alice."
awwww, that's so cute
Staring at the last piece of ass he'll ever see... and desperately looking to reconstruct it for 10^74 years and more.
11:22 He knows that quantum mechanics and, perhaps, his own heart. Why did this slowly become a romance?
@@davestrider2045 Alice and Bob have been together since the start, of course someone had to ship them. So why not on a spaceship?
She jumped into a black hole to get away from him. That puts things in a different light!
:) Forget about "Seven days too long"... THIS is true dedication!
People saying that Veritasium beat Space Time to the punch when literally everything in Derek's video had been covered by Space Time years ago.
And then there is kurzgesagt having addressed some topics months-years ahead.
But don't see it as a competition - since scope and presentation style are so different for those three.
@@nomansbrand4417 yeah, and different style. Veritasium is really more on the pop sci side. PBS tries to go a bit deeper and be a sort of middle ground
This is without doubt the most engrossing and informative description of both the information paradox and equivalence for the layperson I've ever watched. Thank you Dr O'Dowd, and a special thanks to Alice and Bob for their committment to science.
Alice and Bob are 2 unsung heroes of our time. They have been involved in so many experiments I can't ever count. The have been thrown into black holes, left drifting on space for years, put into the heart of a supernova, they have even been shot through the universe at the speed of light and left to experience all the negative affects from it. And they never ever complain.
They also exchange MANY messages that they would like to keep private. Presumably about their grand adventures. 😅
Spherical Bob best bob
Don't forget they are also experts in cryptography, network protocols.
They are invincible.
But where are Carol and Ted . . .?
In the three body problem series (book 2) some guy fell into a black hole accidentally and they refused to pay out his life insurance because he wasn‘t dead yet from their point of reference 😂
that sounds so plausible
I mean, they're right technically speaking! He hasn't fallen in yet! And even after a millennia has passed for everyone else, from his perspective hardly any time has passed at all!
That's the thing I don't fully get with these videos too. I fully understand that the person falling never experiences time slowing down (rather they would see the rest of the universe speeding up), but that doesn't mean that they actually cross the event horizon. That could only be true if black holes are actually eternal.
From their perspective, the hawking radiation taking place must speed up as well and the black hole would evaporate. The event horizon would shrink as they approach it and they would evaporate themselves before they ever cross.
@@allanhernandez6692 As far as I understood it, the person falling in would experience the universe speeding up to some degree, but not the entirety of the universes future would play out while crossing the event horizon. So for an outside observer it would take infinite time to see something cross the event horizon, but for a person falling the event horizon is no special location (if we keep the equivalence principle) so for them it would only take a finite amount of the outside universes time. So even for an evaporating black hole, stuff could fall in (from their own pov but not from an outside pov)
@@WhyneedanAliasRelativity is so incredibly weird.
@@WhyneedanAlias That is not the reason why Alice would not experience the universe speeding up to infinity. It is simply because the photons from the dying universe would not have time to catch up with her until she's practically at the singularity, at which point she'll be dead.
The animations are of impressive quality for a free educational video on CZcams, thank you PBS.
Me: I'm smart!
*Watches video*
Me: I'm dumb!
I'm in a superposition of smart and dumb at the same time.
Veritasium Entered the chat.
PBS Spacetime: “I was camping your respawn a few days ago”.
Veritasium lost his credibility after the Gates connection. In veritasio veritas non iam est.
@@ZoonCrypticon wooosh how does that invalidates what he says about science?
@@User-jr7vfI don't even understand what that means.
@@User-jr7vf
Agreed.
Now. If he had been shilling for the pharma, automobile or any other industry, tightly connected to systemic and abusive tendencies, I'd say:
It's time to raise yer pitchforks, and pass some judgement.
@@ZoonCrypticon
Bro's acting like as if Bill Gates have the ability to somehow change the laws of general relativity or something 💀
Thanks for the video. I’m currently falling past the event horizon of a black hole and I can confirm that it really do be like this.
You about to turn into pasta 😂
Bro must have seen every Vsauce, Veratasium, John Micheal Godier, Vlog Bros, Smarter every day and PBS episode ever by now...
My observations indicate that your approach to the event horizon has caused you to lose your grasp of the English language. Luckily, you should have crossed it by now so we won't have to hear it get worse.
I am the guy right in front of you, near the singularity
I might be in the black hole because I can see what you wrote.
My first thought here was: Wouldn't Alice witness the end of the universe due to time dilation before crossing the event horizon?
If time dilation is so intense that Alice can witness the end of the universe, wouldn’t the black hole have evaporated by the time she crosses the event horizon?
I am not ro on the matter, but all the stuff in the black hole past the event horizon over time, not witnessing all time until the end
For what it's worth, Alice and Bob are also the heroes of every computer security diagram. Their adventures are not limited to the textbooks of physics, computer science uses them too.
Where they do battle with their nemesis, Carol.
@@garethdean6382as well as Evelyn and Malaroy
And TV Tropes!
Oh man, you got Dereked!
with wind chimes to boot
I love this internet thing of getting "Dereked"
Thats so Derrick
Maximum Derek!!!
I fell asleep listening to that video last night. I thought I was having a weird dream dejavu until I read this comment.
I know! You either die or end up behind some bookshelves.
Or both. The blue-shifted rain of X-rays hitting you from above would be fatal.
Thank God that at least you can't come out of the black hole by moving faster than the speed of light because of "the power of love".
@@badbadrobotrobot959 Jennifer Rush just entered the chat...
Finally, someone else remembered the bookshelves. What's the point of jumping into a black hole if you're not going to check out the back of the bookshelves?
@@brothermine2292 How would they be moving faster than you to be "hitting" you? Or just make sure the helmet is lined with Brass. Gives a whole new meaning to "on the hat".
This is by far the best love story I've ever witnessed on this channel.
Yep, I came for science. Stayed for the love story!
Can't wait for the episode where Alice and Bob become entangled!
Jumping into a black hole is the secret recipe to making the best spaghetti in the universe.
Nuclear pasta always comes out a bit dense 😉
Pancakification will be a whole new section in our text books before long and you heard it here first, from one Matt O'Dowd.
At least we won't go hungry.
@@RichWoods23 yes, we have pancakes and spaghetti!
@@Anonymous-ow6jz sooooo, what's for lunch?
@@Anonymous-ow6jz Human pancakes. So is that how Soylent Green is made?
Yeah but their skillets are convex instead of flat like ours. So the pancakes would look like Quisp cereal.
Alice saw the tesseract and taught bob how to decipher all the qbits
And then she saw her daughter and started screaming her name: MUUUUUURPH!!
beautiful movie though
Lamest twist EVER, for an otherwise very well-made film.😖
This video demonstrates why PBS Space Time is the best science podcast in the known multiverse!
Super clear presentation and analysis that makes the most difficult concepts accessible to even us non-Phd mortals!
Big ask,
Could you ask for me about the background music playlist?
Hey, would you please ask if they could change the name of black holes to dark meatballs? Speghettification and dark meatballs just go together.
TL;DR if you fall into a black hole, the government will have to pay your pension for all eternity.
Dunno man, feels like the lawyer will say that since it is outside the boundary of the government, the contract obligation pauses until you return
Degankenexperiment 😂
For the non-germans: he pronounced the first two syllables of Gedankenexperiment (imaginary experiment, thought experiment) backwards - honestly not that noticeable or relevant, but had me smirk, so had to say it
I noticed and I don't even speak German
yeah xD
But I can see how non native speakers could mix up de and ge without having practice in German or knowledge of how German words are assembled
For the ones interested:
ge- is a common prefix of words that have some punctuality.
"Someone thought X" for example translates to "Jemand hat X gedacht", where "denken" is the stem of "to think".
In this case however "Gedanken" is not the past tense of "to think" but rather like "thoughts" or "in my mind".
It can also be more of a result of the thinking itself. It's like the entity of a thought or thoughts.
I heard him say it the right way, but maybe my grasp of German pronunciation is just that bad.
I heard "degunken" (middle syllable /gəŋk/ like "gunk").
I have little German, but mostly I come at it from an OCD and AS/HFA perspective, and being a geek means that I know that word intimately, so it leapt right out at me when he said it (though I was so surprised that I had to replay it a couple of times, and I still don't know how it got past the filming and editing crew).
I don’t really know what you’re talking about in most of this episode, but I do like the way you say it
Thanks for this. I’m planning to jump into a black hole for my birthday and I’m wondering what to expect.
Please make a episode about colliding blackholes and time dilation!
You are saying object is like "freasing" at the event horizon. So will we see how those blackholes approach each other and eventually collide or not?
Please explain! 🙏
Merger of two black holes has already been registered by LIGO. The black holes would collide in a way, that when close enough to each other, a new event horizon would appear because their masses are combined into the even stronger gravitational field. What is on the edge of event horizon is, by my view, frozen in time. What happens below it is another mystery. Example, towards the center of bodies, the gravity weakens, but the pressures are immense, thus time may pass within the black hole.
@Zeeraha exactly! I want to see the video like they did before about the monkey and observer near the blackhole , but this time about two blackholes
- Being up at 4am for no reason
- Sees new spacetime video notification
Feel it too lol
- see bob breakdance to upload his mind to a computer at 4:07am
Same
Gang.
- Sparks blunt
I just can't watch enough videos about black holes. The most fascinating thing in space.
I’ve watched most of the PBS spacetime episodes over the years and I can say this is my favorite one. Well done PBS spacetime!
As another merch idea, that black hole pin design would make an awesome phone case.
Only if the black part gets painted with Vanta Black and actually appears like a hole.
"What Happens If You Jump Into A Black Hole?" ....To shreds you say?
This comment hasn't gotten enough love.
Two shreds.
I predict that we won't be able to decrypt the messages sent between Alice and Bob.
they're using that qubit to generate their encryption key
Bob's dual computer science achievements of developing a true artificial intelligence _and_ a method of reading consciousness are somewhat underrated, too. (-:
The bits might be arriving at a very slow baud rate...
I propose after the geDunkin experiment is finished we all go out for geDonuts.
If we had completed a gedanken experiment instead we would all go out for fries because die gedanken sind frei.
If we eat all that we'll end up with a huge gedankedank.
LOVING the editing and overall production on the newest episodes
_"Spinning, whirling_
_Still descending.._
_Like a spiral sea_
*_UNENDING!!!"_*
..
Rush, _Cygnus X-1_
"Twirling, twirling, twirling into the future." -- Citizen Kang (Or was it Kodos?)
I'm confused but I like it
3:55 Thank you! For years I've wondered how to reconcile time freezing at the event horizon with actually crossing the horizon. How could anything cross if time slows down and ultimately "stops"? Wouldn't Alice see the whole future history of the Universe flash by, including seeing the black hole evaporate before she actually falls into it?
But I think this video's explanation did a good job putting these concerns to rest :)
You are correct that Alice sees all the stars go out as she falls through the event horizon. 4:43 Each second that passes for Alice is hundreds of thousands of times longer than the current age of the universe. Mind exploding
I really appreciate all of the clever visuals
This episode smells of Leonard Susskind.
It's in the name. Suss
I'm gonna compress all the videos I've watched, that explain this "experience", into a single video from which none of the constituent videos can escape or be decoded. I love black holes. (This is the most thorough of them all; I even learned a few things.)
Alright, we know about Alice and Bob.
But this still doesn't answer the most important question of all:
Where is Waldo?
No way, you're not dragging me into this. I spent way too much time searching.
I'm unreasonably glad that you gave Alice and Bob a 'happy' ending.
Fantastic video once more. This channel perfectly fills the niche between more layman-oriented science shows like Veritasium, and full-blown physics lectures. ❤
My intuition tells me that the quantum bit (and Alice, for that matter) isn't duplicated or deleted, but it being in the blackhole and emitted in Hawking radiation are different moments in time. I'm sure it's a gross oversimplification and me not fully understanding the math and physics, but i can't shake the feeling either.
Guess I'm waiting like Bob lol
Now that i think about it some time later, i wonder what digitized Alice would remember once Bob is done reassembling her. What was her subjective experience of it all? Would she remember falling past the event horizon? I wonder why or why not...
There is a reasonably straightforward resolution to this paradox, but it requires that we treat the horizon as a true horizon, not a coordinate horizon - and this seems logical if we consider the effect of length contraction on Alice's perspective of her own fall. She is after all, *approaching the speed of light* as she approaches the horizon, and her perspective of the black hole (if she could see through it) is that its depth is very rapidly diminishing, and as she gets even closer its width should likewise begin to contract rapidly until the entire horizon becomes a POINT OBJECT towards which she is falling.
By the time she 'reaches' the horizon, the diameter of the entire event horizon should only be a single Plank Length - the outer horizon has now *become* a singularity from Alice's perspective. All black holes have the same diameter of one Plank Length, regardless of their mass, though from a more distant perspective their Area and apparent diameter reflects their mass. Their density does NOT drop as they grow - they achieve Plank Density as the Beckenstein Bound is saturated, and their Area expands in lockstep with their mass to maintain Plank Density no matter how large or small they are. Whether a black hole is one angstrom wide, or a LY across, it has the same density, because it is now effectively a 2D sphere and its 'density' as a 2D object does not change as you add mass.
Unfortunately the implication this has for the tidal forces of the black hole are somewhat dire for Alice. She will be spaghettified because she is not approaching a black hole with a diameter of billions of km - she's approaching a black hole with a diameter of one plank length. She will then be pancaked as well, but she will NOT fall through a causal barrier where Bob can no longer observe her at all because she perceives no horizon at all, nor any space to fall 'into'. Alas Bob will receive very little information about her due to the time dilation she's experiencing in this 2-dimensional pseudo-singularity, which presumably will evaporate gradually via thermodynamic processes similar to how hawking radiation is currently described. He'll still have to go through the process of recording the Black Hole's entire evaporation process and reconstruct Alice's data, because she's been scrambled about as thoroughly as anything CAN be scrambled - reflecting the maximal entropy of the black hole.
Some interpretation similar to this is necessary to prevent violation of the Beckenstein Bound and prevent the formation of a true physical singularity of infinite density. In this case the surface of the black hole consists of a plank density shell of mass, with each element of it probabilistically 'smeared' across the entire horizon, as from the perspective of each particle they are in fact falling towards a singularity - though more accurately, they will see that singularity explode in their faces as they fall due to the fact that their perspective of the approach to the horizon now extends into the unimaginably distant future all the way to the point where they are re-emitted in very little pieces, their 'fall' concludes with them being blasted out into space and the infalling observer's experience would be far more akin to taking a nose-dive into a supernova than falling into a placid void.
Why do I think this is the case? I mean, quite frankly it's because I don't believe that beckenstein bound violation is acceptable, nor are physical infinities, and EVERY model of a black hole interior I've ever seen postulated clearly violates the Beckenstein Bound and describes a physical infinity - while this model prevents that. That's the entire reason. Make of it what you will.
Thank you. I am not a physicist but did follow most of what you said accept for a couple of labels. I currently have a deep fascination with the intersect of singularities and event horizons. Looking at the common Minkowski spacetime geometry with fore and aft light cones we have an intersect of the 3D event horizons at a singularity in the "Now" time event horizon. That illustration of the 2D plane that intersect the diagram appears to hold all of the infinite number of intersects in the 3D universe "across: that "Now moment. No singularity on that plane can be aware of any other singularity until some time later when the light cones of each singularity cross. Alternatively some of those singularities may be close enough to be touching in the time event horizon of "Now" and have a direct awareness of the other singularity .
So I am left with this mix of both local and non local singularities in every plank length in time. In some sense for me the entire universe feels like a kind of progression of infinite singularities in each "now" moment.
>
My focus is on this singularity intersect of all event horizons in each moment.
>
Sorry if I didn't explain my view well. It's complex in my mind and difficult to put into words in a short statement :)
This makes much more sense to me. I have always been frustrated by the black hole explanations which posit a crossing of the event horizon which makes no real sense given that black holes are not immortal, and even if the rest of the universe has an infinite amount of time to watch, the person falling will never cross.
Given that black holes evaporate, and the universe sees the black hole evaporate before the faller ever crossed the horizon, it can only make sense that the person falling must experience the corresponding rate increase of hawking radiation (from their perspective) as they approach the horizon until they themselves are emitted as hawking radiation.
@@allanhernandez6692 I am sitting here (again) struggling with the idea of red shift at the event horizon and light traveling away at 'c' from just above the event horizon. There is this frame of reference issue that keeps coming up for a photon suddenly shifting from a velocity of 'c' outward to zero velocity and then to a velocity of 'c' inward beyond the event horizon. I know different geometry explains this away by moving the direction of the photon sideways in time, but that zero velocity moment still weirds me out lol
>
[edit] The photon travels at 'c' in space and at 'c' in time and exist along the event horizon of the light cone already. I have to ask where we find the extra velocity or loose the velocity if 'c' is constant.. We can explain it a way with warped space, but then physics says space doesn't actually exist to warp in the first place. It's contradiction that I can't get past no matter what way physics explains it :(
@@axle.student There are a number of issues with the standard explanations of the event horizon. The problem seems to arise from an incomplete formulation of GR that postulates a crossable horizon in the first place - accepting that premise inevitably creates a host of paradoxical behaviors and contradictions. Because that's what our best math describes, that's the description most physicists accept for the time being - but looking at it in terms of logic and the fact that all our OTHER physics and math are violated once you take that step, it just seems like the least likely solution.
It really seems like in order to understand gravity and relativity better, they should be looking for ways to close off the horizon like this that maintain the logical consistency of the rest of physics, rather than playing with mathematical artefacts 'beyond' the horizon. While I see the appeal of that as a theoretician, it eventually loses its shine after the 'nth' iteration or so which fails to resolve any of these paradoxes.
@@Vastin Thank you. I appreciate your comments. Again not a physicist but well studied (non indentured) across a number of disciplines. It is the singularity and event horizon problem that has bugged me for as long as I can remember. I thew all the std constraints of physics out the window a few months back to jail break my mind and run some thought experiments. I focused upon the issues around the singularity and event horizon issues and gained myself some better insight by thinking outside of the box. I have nailed down some interesting perspectives around the 4D space-time geometry. I can see an entire working 4D universe abstractly in my head accept for the non locality link. Even gravity appears to become nothing more than an emergent expression or illusion of quantum and GR.
>
Lot of work to translate that from my head into words and graphics ahead. I have seen/encountered a number of physicists that appear to have been or are down a similar rabbit hole so I will look toward there work for some guidance. Maybe they have already tested it and no point my looking any deeper :)
I do love these sorts of thought experiments and your presentation on this one was a lot of fun to follow.
Excellent video Matt, keep the hard work.
Why can't Alice's perspective of falling into the singularity be equivalent to Bob's perspective of the hawking radiation emitted? Ie. the singularity is a projection of the inevitable future of the evaporation of the black hole by Alice's perspective? As I understand it this would make sense with what the spacetime diagram interior to the blackhole tells us?
Alice contains a lot more energy than that radiated as Hawking radiation which is why he has to wait a long time (10^100 years or so) for all of her information to come back out.
I just watched new Veritasium video about black/white holes.
What a time to be alive.
I just saw your comment and saw the video last night and agree with you.
A "Two Minute Papers" easter egg?
@@mkk3a It seemed appropriate. Shout out to Karol.
@@AricBlunk LETS GOOOOOOOOOO!
This was a brilliant presentation and quite thorough, very impressive job.
Fantastic video. Thank you. Congrats!
Cool! Another black hole video!
I was worried about Bob until the very end, glad it worked out in the end
I just want to say that although the channel is a joy anyway, I completely love these deep dive sequences. Good work, people.
Fantastic episode, Matt! Thank you!!
i think Alice never got pass the event horizon, falling down she starts to experience such a huge time dilation, that on her time scale the black hole starts to evaporate. I also think because of a such curved space the black hole (or is it the stuff that fell in? i feel like there's no difference, black hole is the stuff that fell into it) will start to glow. in that case black holes are frozen in time (for the outside observers) collapse, and that huge collapse is hidden by Einstein's squeezing of space to very thin slice of what we perceive as the event horizon. The crossable event horizon doesn't exist, instead it's a place where collapse of the black hole is happening, while the singularity is the moment in time to there they fall/when the black hole evaporates. This is the intuition i got from watching these wonderful videos for years
I thought the same thing. If it takes infinite time to reach the event horizon, then dark energy (expansion of universe) should make the distance to the event horizon infinite as well. and hawking radiation would cause the blackhole to vaporize before you pass the event horizon for the same reason.
This is only true when using Schwarzschild coordinates. Schwarzschild coordinates are very convenient for describing weak gravity fields, but they fail to describe a black hole event horizon.
There are alternative coordinate systems en.wikipedia.org/wiki/Schwarzschild_metric#Alternative_coordinates you can use to describe an event horizon without time becoming zero/infinite.
I think that is going to be explained in future videos!
Now do one about what an infinite universe with infinite mass and infinite energy would look like. PBS infinite series mentioned it in one of their last videos. The Mandelbrot set or another fractal pattern seems like it would immerge is such a situation due to infinite mass and energy requiring infinite black holes. I think the we could be inside of a black hole that is a part of a russian nesting dolls of black holes that is also part of a fractal of black holes and parallel universes and black holes could be the pathway to other universes.
It certainly makes more sense that "dark energy"
Starting to see the vision for this arc of content, excited to see it all come together.
I’ve ordered the black hole pin from your store! I happened to be shopping for pins today and wouldn’t you know it, one of my favorite channels uploaded an excellent new video and they happen to have a new pin depicting one of my favorite objects! How serendipitous for us both!
Six stars of the Northern Cross
In mourning for their sister's loss
In a final flash of glory
Nevermore to grace the night
- Rush
Firework!
Great video as always. But there's something that I've been wondering for a while and still haven't been able to find an answer.
Time dilation gets more and more extreme the closer you get to the event horizon as you mentioned, so in this case if Alice were to "hang around" close to the EH for a minute in her own relative time and then managed to get back to Bob far from it a way longer time would have elapsed for him and the "universe outside". That I understand.
But the problem is about her perspective as she goes through the event horizon. Wouldn't time dilation tend to infinite as she gets closer and closer?
If so, as soon as she were to cross it, her relative time dilation would be so extreme that any amount time she experienced inside the EH would be equivalent to a tremendous amount of time "outside"(maybe infinite?). And if so any time she spent there would mean that enough time outside had passed that the black hole would've evaporated, so she wouldn't ever be able to actually experience what it's like to be inside one, as all the space inside would get instantly smaller and she'd be crushed against the singularity before just "popping out of existence".
This has been leading to so many sleepless nights for me 😅. Please tell me what I've been doing wrong or missing. Thanks!
Time dilation is not just a function of position, it depends a lot on how you move. If you stay put, hover, then yes, time dilation near the horizon is very strong, and exactly at the horizon it's infinite, your clocks don't tick at all. But for that you need to stay put there, which is impossible for massive bodies. Very similar to moving at light speed - if you could go at speed of light, your clocks also wouldn't tick, infinite time dilation. But massive bodies can't do that. Event horizon is a "null hypersurface" - just like a light cone, staying there is equivalent to moving at light speed, crossing it outwards is equivalent to moving faster than light.
For a falling Alice things look differently, and her clocks keep ticking. She doesn't even see the outer universe sped up, unlike the staying put scenario. See how "proper time" is defined using the metric tensor, it's all about vectors in 4D spacetime, how you move there.
Outstanding Dr. Matt.
This video came out just days after Derek's video and such perfect timing! A whole week of black hole pondering!
MUUUURPH
How freaky-cool is it , that the event horizon is a "border" between now & the literal Far far far future.
😁🌏☮️
Massively interesting episode!
This was the 1st CZcams channel I subscribed to and it's still going strong
Love that you’re covering this topic. For most of my adult life I’ve pondered what would happen if you we’re to dive into a black hole (and survive the tidal forces/radiation etc).
I came to the conclusion that, theoretically, you’d never reach the “singularity”. By the time you reached the point in space that could be considered a singularity, the black hole would have dissipated and you’d find yourself back in normal space, albeit a few thousand billion years in the future.
Hence why the singularity itself cannot exist. Nice catch!
“A few thousand billion years” lmao ok
Using Gullstrand-Painlevé Coordinates (following the proper time of an observer in free-fall) you *will* actually reach the physical singularity at the black hole's center of mass in a finite amount of time. Pretty quickly too, from your point of view. (From seconds to days depending on the size of the black hole.)
@@juliavixen176but would the universe behind you age much faster to the point of seeing its "death", including that of the BH?
@@juliavixen176 What does that coordinate system say about how long it would take to reach the singularity in the reference frame of a distant observer? Would it be longer than the time it takes for the black hole to evaporate?
0:11 It's "Gedanken," not deganken or whatever that was
i have watched probable 40 videos on this topic and i just keep going
From Bob's persepective, which would have happened first: Alice crossing the event horizon or the black hole evaporating?
General relativity and quantum mechanics will never be combined until we realize that each individual observer is observing them both at different moments in time. Because causality has a speed limit (c) every point in space where one observes it from will be the closest to the present moment. When one looks out into the universe they see the past which is made of particles (GR). When one tries to look at smaller and smaller sizes and distances, they are actually looking closer and closer to the present moment (QM). The wave property of particles appears when we start trying to predict the future of that particle. It is a probability wave because the future is probabilistic. Wave function collapse is what we perceive as the present moment and is what divides the past from the future. GR is making measurements in the observed past and therefore, predictable. It can predict the future but only from information collected from the past. QM is attempting to make measurements of the unobserved future and therefore, unpredictable. Only once a particle interacts with the present moment does it become predictable. This is an observational interpretation of the mathematics we currently use based on the limited perspective we have with the experiments we choose to observe the universe with.
That's an interesting point of view
Can we get that covered in the next episode please?
Isn't that the premise of loop quantum gravity?
Please don't disturb the delicate balance of book sales. ;O)-
How do you reconcile this with experiments (and the entire field of quantum computation) that depend on keeping a system in superposition? What would it even mean for a system to be in superposition? Also, how would such a metaphysical explanation help to resolve mathematical infinities when attempting to combine the physics of GR and QM?
"....Bob can do this, because he has nothing but time on his hands."
Bob should have thought of that before he dropped Alice into an infinitely endless expanse of black nothing with a singularity at its center.
This video is amazing!❤
Thank you for this video!
it's spaghetti time!
Or pancakes.
I like pancakes
It's peanut butter jelly time peanut butter jelly time peanut butter peanut butter peanut butter and a baseball bat!
I'm confused. It seems to me like there is a simpler contradiction driving this weirdness, present without anything quantum (except Hawking radiation):
In Bob's frame of reference, Alice takes infinite time to cross the event horizon.
Also in Bob's frame, the black hole Hawking evaporates in finite time.
So, Alice never crosses the horizon in Bob's frame.
If we then ASSUME Alice crossed in her own frame, then of course the frames contradict.
I can't do the necessary math, but intuitively, Alice should never be able to cross, even in her own frame of reference. Time dilation would make it so the horizon shrinks away from her (via Hawking evaporation) before she reaches it.
The outro (15:28) says Alice not crossing would break the equivalence principle, so my question is, how?
(Is this the "firewall at the horizon?")
In Bob's frame Alice's photons that he receives do not take infinite time, since of course there are a finite number of photons emitted and Bob is of course at a finite distance. However, in Bob's frame Alice still passes the event horizon and actually increases the area of the event horizon and the radius of the black hole, which he can then measure a very short time later.
@@tonywells6990Must there be finitely many photons emitted? If they have smaller and smaller amounts of energy, couldn’t there be infinitely many?
@@drdca8263 No, the photons don't multiply in number. They are redshifted.
@@tonywells6990 Ah wait, we are only considering the periodic emissions of the gamma ones, and there is only a finite amount of Alice’s time that Bob sees (before she crosses horizon from her perspective) and it only flashes finitely many times,
Ok, I retract my previous point then.
(I was thinking about maybe possibly infinitely many infrared photons emitted from thermal radiation)
Loved the animations
3 Million subs! Congratz!
You die, saved you 20 minutes
Am I first?!
Nan
these black hole related episodes are my absolute favorite! 🖤
Nice explanation 💪🏻
wheres the new video dog
Awesome! :D Great episode. I have 2 questions:
1. I thought it was impossible to fly **directly** into a black hole? I was of the understanding that black holes are all “frame dragging” the space around itself in a sort of 3D whirlpool.
2. The fact that photons have to “struggle” out of the gravitational well was covered. So, shouldn’t Alice’s image have been red-shifted until she disappeared as she crossed the event horizon?
(**ASIDE:** BTW, not trying to nitpick! I just want to know if stuff I’ve learned elsewhere still holds. I know these _may_ have been omitted either by oversight or because it would needlessly overcomplicate the thought experiment.)
Thank you 🙏
Thank for the video 🎉
this was such a great video
Delighted by the addition of romance to the Alice and Bob thought experiment.
Love the breakdancing mind copier 👌
Good follow-up to the episode of Star Talk from a couple weeks ago!
Wow, Matt ending on a cliffhanger for once, what a pleasant surprise. Super cool episode, this is exactly the kind of stuff I wonder about sometimes (on a way lower level than this obviously). Something about the event horizon is so final, it would be a miracle if physics could find a way to peer past it. Maybe in a couple hundred years! or a couple thousand...
Great job 👍👍 makes sense why it's been a wait, but worth it
Also CZcams won't let me like the video
Off all the answers, the firewall is my favorite. Can’t wait to see how it breaks everything!
Now I think I'm starting to get it. When they tell that singularity is not a point in space but a moment in time - it means that you never reach the 'central point' of the black hole because time speeds up so fast that before you fall there, the black hole already evaporates. Hmmm... In some sense the center of a black hole doesn't exist then, as nothing ever reaches it.
Or even stricter idea - you can't actually pass through the horizon, because it starts shrinking right under your nose because of very fast time and Hawking radiation until it's just gone, and you find yourself at that same place without a black hole after it has evaporated, some 10^80 years later or so.
nope, the idea of singularity acting like a moment in time comes from analyzing a static solution where black hole does not evaporate and doesn't grow either. It's just about coordinates and spacetime geometry. See recent Veritasium video for more info and animated charts.
Didnt realize the thought experiment about falling into black holes had so many variations and variables based on perspective. My mind engine bes starting up and my thoughts be rumblin to life! Love it when videos do that! :)
an arrow on the surface of a torus pointed towards its empty center can travel endlessly around the circumference of the donut and always travel in a straight line that never reaches a singularlity, but forever travels towards it. It can appear a contradiction, but both situations can be true at the same time. To the rider of the arrow the Universe can seems to expand and contract while being static on the surface of the Torus.
Great episode, feels like I am waiting near the event horizon for next week an eternity from my perspective.
Matt thankyou so much! I have been dying for this series for years now! You are spot on! Cant wait for Bob and Alice to have a couple of blackhole mass sized piles of bell pairs 😉 I am AMPS…I mean AMPED for the next one!