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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Hosted by Matt O'Dowd
Written by Matt O'Dowd
Post Production by Leonardo Scholzer, Yago Ballarini & Stephanie Faria
Directed by Andrew Kornhaber
Associate Producer: Bahar Gholipour
Executive Producers: Eric Brown & Andrew Kornhaber
Executive in Charge for PBS: Maribel Lopez
Director of Programming for PBS: Gabrielle Ewing
Assistant Director of Programming for PBS: John Campbell
Spacetime is a production of Kornhaber Brown for PBS Digital Studios.
This program is produced by Kornhaber Brown, which is solely responsible for its content.
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[@THE-X-Force]

It's comforting to know that ancient PBS Space Time videos will still be around even when Sag A* meets its end.

[@LuisSierra42]

As quantum information

[@THE-X-Force]

@@LuisSierra42 I dunno .. sounds like Bob was watching the vintage originals lol

[@uggoldos]

Hopelessly scrambled

[@BrianOSheaPlus]

​@@uggoldosBob's star-sized Matrioshka brain computers can unscramble them.

[@uggoldos]

But can the Matrioshka overcome uncertainty? Seems like the same problem Star Trek's transporter technology would have.

[@Orillion123456]

I love the idea that a future mind-uploading device requires you to breakdance on top of it while it uploads you.

[@richardconway6425]

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 😜

[@John-jc3ty]

its part of the physic process. he breaks his neck to avoid having 2 bobs at the same time and breaking unitarity

[@gage11769]

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.

[@bmxerkrantz]

​​@@richardconway6425your comment spins me right round baby right round - dead or alive

[@richardconway6425]

@@bmxerkrantz yes, that too !! 🐸

[@_Mute_]

"Digital Ghosts in a Dead Universe" would make a great metal album name

[@Annathroy]

Band name too

[@unocoltrane2804]

DGIDU!

[@b.s.7693]

​@@Annathroyand the first single

[@WackoMcGoose]

I think it's also within the allowed length limit of a Dot Tumblr Dot Com, too...

[@whoshotashleybabbitt4924]

@@b.s.7693 nah, Unitarity is the first single.

[@purplenanite]

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

[@AM-gf7zv]

Staring at the last piece of ass he'll ever see... and desperately looking to reconstruct it for 10^74 years and more.

[@davestrider2045]

11:22 He knows that quantum mechanics and, perhaps, his own heart. Why did this slowly become a romance?

[@alazarbisrat1978]

@@davestrider2045 Alice and Bob have been together since the start, of course someone had to ship them. So why not on a spaceship?

[@Andrew30645]

She jumped into a black hole to get away from him. That puts things in a different light!

[@JuanEstrella-Martinez]

Oh man, you got Dereked!

[@TreesPlease42]

with wind chimes to boot

[@juanfromthecosmos]

I love this internet thing of getting "Dereked"

[@borttorbbq2556]

Thats so Derrick

[@victorbrueggemann8934]

Maximum Derek!!!

[@thebogsofmordor7356]

I fell asleep listening to that video last night. I thought I was having a weird dream dejavu until I read this comment.

[@mlee9734]

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.

[@sharpsheep4148]

They also exchange MANY messages that they would like to keep private. Presumably about their grand adventures. 😅

[@apmcx]

Spherical Bob best bob

[@w01dnick]

Don't forget they are also experts in cryptography, network protocols.

[@Ein_Kunde_]

They are invincible.

[@TheSaneHatter]

But where are Carol and Ted . . .?

[@JBonzo12]

"Bob waited 10^87 years, so a week isn't so bad. " I'm now dead in this timeline. 🤣

[@AricBlunk]

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.

[@fragly]

😂 very accurate

[@marcomoon6062]

Both of them go over my head sometimes 😅

[@cereal-killer4455]

@@marcomoon6062Spacetime is at a much higher level of science than veritasium although both are brilliant

[@marfmarfalot5193]

It is!

[@kylelochlann5053]

Absolutely not. PBS is explaining one line of speculative reasoning.

[@StormbringerMM]

Veritasium Entered the chat. PBS Spacetime: “I was camping your respawn a few days ago”.

[@ZoonCrypticon]

Veritasium lost his credibility after the Gates connection. In veritasio veritas non iam est.

[@User-jr7vf]

@@ZoonCrypticon wooosh how does that invalidates what he says about science?

[@mheermance]

​@@User-jr7vfI don't even understand what that means.

[@rogaldorn4759]

​@@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.

[@JJean64]

​@@ZoonCrypticon Bro's acting like as if Bill Gates have the ability to somehow change the laws of general relativity or something 💀

[@_haze__5684]

Pancakification will be a whole new section in our text books before long and you heard it here first, from one Matt O'Dowd.

[@RichWoods23]

At least we won't go hungry.

[@Anonymous-ow6jz]

@@RichWoods23 yes, we have pancakes and spaghetti!

[@bmxerkrantz]

​@@Anonymous-ow6jz sooooo, what's for lunch?

[@ArawnOfAnnwn]

@@Anonymous-ow6jz Human pancakes. So is that how Soylent Green is made?

[@cosmicraysshotsintothelight]

Yeah but their skillets are convex instead of flat like ours. So the pancakes would look like Quisp cereal.

[@GwEClanGaming]

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 😂

[@astrocoastalprocessor]

that sounds so plausible

[@allanhernandez6692]

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.

[@WhyneedanAlias]

@@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)

[@Deletirium]

​​@@WhyneedanAliasRelativity is so incredibly weird.

[@viliml2763]

@@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.

[@Subbestionix]

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

[@aaronhammond7297]

I noticed and I don't even speak German

[@Subbestionix]

​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.

[@dembro27]

I heard him say it the right way, but maybe my grasp of German pronunciation is just that bad.

[@pierreabbat6157]

I heard "degunken" (middle syllable /gəŋk/ like "gunk").

[@charlesrockafellor4200]

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).

[@ReformationRamblings]

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.

[@donnyjepp]

You about to turn into pasta 😂

[@TheWebsOfCorruptionNeverFail]

Bro must have seen every Vsauce, Veratasium, John Micheal Godier, Vlog Bros, Smarter every day and PBS episode ever by now...

[@chitlitlah]

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.

[@LuisSierra42]

I am the guy right in front of you, near the singularity

[@aididdat1749]

I might be in the black hole because I can see what you wrote.

[@stanmanlyman4550]

Alice saw the tesseract and taught bob how to decipher all the qbits

[@LuisSierra42]

And then she saw her daughter and started screaming her name: MUUUUUURPH!!

[@stanmanlyman4550]

beautiful movie though

[@Deletirium]

Lamest twist EVER, for an otherwise very well-made film.😖

[@GetterRay]

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.

[@louisfriend1]

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.

[@MarijnvdSterre]

I know! You either die or end up behind some bookshelves.

[@brothermine2292]

Or both. The blue-shifted rain of X-rays hitting you from above would be fatal.

[@badbadrobotrobot959]

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".

[@duprie37]

​@@badbadrobotrobot959 Jennifer Rush just entered the chat...

[@Soupy_loopy]

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?

[@cosmicraysshotsintothelight]

@@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".

[@Ana_Jantra]

Cool! Another black hole video

[@JorgetePanete]

BOT

[@JonCofer]

I don’t really know what you’re talking about in most of this episode, but I do like the way you say it

[@hereticpariah6_66]

_"Spinning, whirling_ _Still descending.._ _Like a spiral sea_ *_UNENDING!!!"_* .. Rush, _Cygnus X-1_

[@brothermine2292]

"Twirling, twirling, twirling into the future." -- Citizen Kang (Or was it Kodos?)

[@nessiecz2006]

I'm confused but I like it

[@CortanaCH]

I just can't watch enough videos about black holes. The most fascinating thing in space.

[@gabor6259]

This is by far the best love story I've ever witnessed on this channel.

[@demeurecorentin]

The animations are of impressive quality for a free educational video on KZbin, thank you PBS.

[@PaintballVideosNet]

Me: I'm smart! *Watches video* Me: I'm dumb!

[@kwokhardy2512]

- Being up at 4am for no reason - Sees new spacetime video notification

[@Graycy808]

Feel it too lol

[@a_mediocre_meerkat]

- see bob breakdance to upload his mind to a computer at 4:07am

[@pqrnr]

Same

[@the_algo_rhythm]

Gang.

[@fraserwilliams2414]

- Sparks blunt

[@theplanetrepairman9945]

"What Happens If You Jump Into A Black Hole?" ....To shreds you say?

[@inplainview1]

This comment hasn't gotten enough love.

[@cosmicraysshotsintothelight]

Two shreds.

[@simoncoweII]

Jumping into a black hole is the secret recipe to making the best spaghetti in the universe.

[@evangonzalez2245]

Nuclear pasta always comes out a bit dense 😉

[@bentationfunkiloglio]

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!

[@koponstanley4]

Big ask, Could you ask for me about the background music playlist?

[@Soupy_loopy]

Hey, would you please ask if they could change the name of black holes to dark meatballs? Speghettification and dark meatballs just go together.

[@mgancarzjr]

I predict that we won't be able to decrypt the messages sent between Alice and Bob.

[@thezipcreator]

they're using that qubit to generate their encryption key

[@JdeBP]

Bob's dual computer science achievements of developing a true artificial intelligence _and_ a method of reading consciousness are somewhat underrated, too. (-:

[@cosmicraysshotsintothelight]

The bits might be arriving at a very slow baud rate...

[@MrChipMC]

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! 🙏

[@Zeeraha]

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.

[@MrChipMC]

@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

[@deepdrag8131]

Thanks for this. I’m planning to jump into a black hole for my birthday and I’m wondering what to expect.

[@jonathanl8538]

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 :)

[@MrLeafeater]

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.)

[@kobayashimaru8114]

I really appreciate all of the clever visuals

[@cherryspades3440]

LOVING the editing and overall production on the newest episodes

[@willo7734]

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!

[@jamesdouglas5055]

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.

[@badroad1000]

If we eat all that we'll end up with a huge gedankedank.

[@mattwilcox8134]

As another merch idea, that black hole pin design would make an awesome phone case.

[@cosmicraysshotsintothelight]

Only if the black part gets painted with Vanta Black and actually appears like a hole.

[@kyleespinoza7201]

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...

[@Moon_Metty]

Alright, we know about Alice and Bob. But this still doesn't answer the most important question of all: Where is Waldo?

[@Soupy_loopy]

No way, you're not dragging me into this. I spent way too much time searching.

[@TooTRUEtoBeG00D]

I just watched new Veritasium video about black/white holes. What a time to be alive.

[@AricBlunk]

I just saw your comment and saw the video last night and agree with you.

[@mkk3a]

A "Two Minute Papers" easter egg?

[@TooTRUEtoBeG00D]

@@mkk3a It seemed appropriate. Shout out to Karol.

[@TooTRUEtoBeG00D]

@@AricBlunk LETS GOOOOOOOOOO!

[@linecraftman3907]

I was worried about Bob until the very end, glad it worked out in the end

[@RedDuke42]

Fantastic video once more. This channel perfectly fills the niche between more layman-oriented science shows like Veritasium, and full-blown physics lectures. ❤

[@Acid_Viking]

Thank you for talking me out of jumping into a black hole.

[@SayAhh]

Cool! Another black hole video!

[@567secret]

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?

[@tonywells6990]

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.

[@boringturtle]

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.

[@garethdean6382]

Where they do battle with their nemesis, Carol.

[@drdca8263]

@@garethdean6382as well as Evelyn and Malaroy

[@Kronzik]

Starting to see the vision for this arc of content, excited to see it all come together.

[@Gandalf-The-Green]

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

[@gabor6259]

Firework!

[@TripleOmega]

My first thought here was: Wouldn't Alice witness the end of the universe due to time dilation before crossing the event horizon?

[@d4mdcykey]

This was a brilliant presentation and quite thorough, very impressive job.

[@Vastin]

I do love these sorts of thought experiments and your presentation on this one was a lot of fun to follow.

[@Vastin]

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.

[@axle.student]

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 :)

[@allanhernandez6692]

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.

[@axle.student]

@@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 :(

[@Vastin]

@@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.

[@axle.student]

@@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 :)

[@victorpilgrim]

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

[@Xanaden]

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.

[@JCDAMV]

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!

[@jo_crespo11235]

Excellent video Matt, keep the hard work.

[@BytebroUK]

I just want to say that although the channel is a joy anyway, I completely love these deep dive sequences. Good work, people.

[@buttonsjr]

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"

[@cesaraugusto6083]

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!

[@thedeemon]

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.

[@GeneticFreak]

This video came out just days after Derek's video and such perfect timing! A whole week of black hole pondering!

[@robbabcock_]

I can't wait for next week!

[@davidf5609]

This episode smells of Leonard Susskind.

[@WeRemainFaceless]

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.

[@breezyx976]

Hence why the singularity itself cannot exist. Nice catch!

[@anywallsocket]

“A few thousand billion years” lmao ok

[@juliavixen176]

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.)

[@Andromedon777]

​@@juliavixen176but would the universe behind you age much faster to the point of seeing its "death", including that of the BH?

[@david21686]

@@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?

[@grasshopper-ln9us]

This was the 1st KZbin channel I subscribed to and it's still going strong

[@abhisheksingh1143]

Fantastic video. Thank you. Congrats!

[@claudiaarjangi4914]

How freaky-cool is it , that the event horizon is a "border" between now & the literal Far far far future. 😁🌏☮️

[@Quzga]

MUUUURPH

[@Infinite_Horizonsss]

Thank for the video 🎉

[@tomorowsnobodys]

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!

[@doggedout]

"....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.

[@binbots]

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.

[@andreaswiescher7196]

That's an interesting point of view

[@andreaswiescher7196]

Can we get that covered in the next episode please?

[@ab8jeh]

Isn't that the premise of loop quantum gravity?

[@Corvaire]

Please don't disturb the delicate balance of book sales. ;O)-

[@timhaldane7588]

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?

[@sLeeeTo]

this was such a great video

[@danillorippel]

This video is amazing!❤

[@KoZeroSM]

0:11 It's "Gedanken," not deganken or whatever that was

[@indinaut]

it's spaghetti time!

[@evgenijdenisov]

Or pancakes.

[@peteshively5552]

I like pancakes

[@Soupy_loopy]

It's peanut butter jelly time peanut butter jelly time peanut butter peanut butter peanut butter and a baseball bat!

[@kevinmarshall3198]

No matter how much research I do on black holes, it's still difficult to understand this anomaly. The scale of it is difficult to comprehend. Its truly a real life object that seems like science fiction.

[@d3sync777]

The animators definitely had a lot of fun making this episode

[@evilleagueofevil9049]

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?")

[@tonywells6990]

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.

[@drdca8263]

@@tonywells6990Must there be finitely many photons emitted? If they have smaller and smaller amounts of energy, couldn’t there be infinitely many?

[@tonywells6990]

@@drdca8263 No, the photons don't multiply in number. They are redshifted.

[@drdca8263]

@@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)

[@ChobThomas]

You die, saved you 20 minutes

[@joey_after_midnight]

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.

[@boneladders]

these black hole related episodes are my absolute favorite! 🖤

[@bigjermboktown6976]

Am I first?!

[@sully7593]

Nan

[@ptiwari2392]

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...

[@jacksawyer3626]

Outstanding Dr. Matt.

[@mastercontrolprogram82]

Massively interesting episode!

[@vladus..]

Nice explanation 💪🏻

[@jamesleatherwood5125]

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! :)

[@Veldrade]

There are a few things I don't understand : -If time accelerates to basically infinity when you get close to the event horizon, then shouldn't the black hole have evaporated entirely before you reach its horizon ? -If photons from the event horizon appear to have more and more energy as Alice accelerates towards the black hole, shouldn't she be disintegrated before reaching it ? -Why can light inside the black hole go towards its outside (like the light from the cube going towards Alice's eyes when both have crossed the horizon) ? Shouldn't things only be able to move towards the center of the black hole ? It feels contradictory because if things can't get out of the event horizon, then it should be even worse when you get closer to the center, right ?

[@petepanteraman]

Great job 👍👍 makes sense why it's been a wait, but worth it

[@petepanteraman]

Also KZbin won't let me like the video

[@eagleoftheearth]

Damn! What a cliffhanger😧 can't wait for the next episode 👏

[@JTheoryScience]

3 Million subs! Congratz!

[@Kohl293]

Off all the answers, the firewall is my favorite. Can’t wait to see how it breaks everything!

[@derbychang]

This gedankenexperiment tears my heart apart

[@user-or5ke5yn4w]

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.

[@thedeemon]

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.

[@machevellian79]

Great episode, feels like I am waiting near the event horizon for next week an eternity from my perspective.

[@caffedinator5584]

Love the breakdancing mind copier 👌

[@hcesarcastro]

From Bob's persepective, which would have happened first: Alice crossing the event horizon or the black hole evaporating?

[@corlisscrabtree3647]

Thank you 🙏

[@The_Silver_Lurker]

Good follow-up to the episode of Star Talk from a couple weeks ago!

[@user-hq9wl8xo2t]

Thank you for the great material - it kept me busy for a few days :) In my opinion, there is no paradox if we assume that Alice never crossed the event horizon. The paradox arises from extending the equivalence principle to areas we should never reach. It's like in Einstein's thought experiment, pondering too long whether we are falling in an elevator or floating in zero gravity - reaching the Earth's surface will solve the puzzle. Alice will perish in a fraction of a second, just before reaching the event horizon. In a sense, she will collide with matter suspended in 'timelessness' that forms the history of the BH, constantly falling but never reaching the event horizon. This will only happen if Bob starts the colossal task of shielding Sagittarius A* with a screen cooled almost to 0 K, shielding background radiation and other radiation sources quickly enough. He knows that if he doesn't do this quickly enough, from Alice's perspective approaching the EH will cause the flow of time of the universe she leaves by falling into the BH to accelerate beyond imagination - thus her back will absorb massive amounts of background radiation photons, which falling in the BH's gravitational potential will increase in intensity and energy as they approach the EH. I imagine that the EH is a mathematical construct where spacetime reaches the speed of light. Beyond this space, we lose the ability to interact. From the perspective of a distant observer, how can anything cross the boundary if time stops? In my view, as long as the falling object can somehow interact with the universe, it 'must wait' until the end of such a relationship before making the move to cross the event horizon - as if the universe with its possible influence on Alice's fate must first be resolved before she could cross the EH. I wonder if in some sense, falling spacetime near the EH does not stretch and millimeter-sized areas in one reference frame cannot be light-years deep, creating a volume for the matter above the EH to solidify - a true hologram. However, the most important thing that would influence the matter would be the gradient of time flow - I imagine that it could generate effects similar to pressure (similar to countless photons on Alice's back), but it is difficult to imagine being in a place where a second passes near the legs while years pass near the head. At the same time, I would like to see if someone has calculated and what the calculations of quantum effects look like for two areas with such different time flows, or if quantum tunneling could not explain the effect of black hole evaporation? Only what I just described is the opposite of the thesis that black holes have no hair... :| The above solution seems not to generate paradoxes, a problem arises elsewhere: we know that BHs can form in finite time, grow, and merge with each other. While the above scenario prevented crossing the EH. Wouldn't it be an elegant solution to assume that only spacetime can overcome the speed of light limits, thus wrapping falling objects near the EH? Additional mass of a box with an electron and Alice at some point in finite time will increase the EH, creating a disturbance spreading at the surface, pushing out the EH surface with submerged matter above it. Similar phenomenon to the surface tension of liquids. Unless, the BH evaporates with Alice before they merge with the EH. I would like to be able to calculate this. :) The disturbance of the event horizon as a result of merging BHs should also emit Hawking radiation - after all, spacetime curvature is its source - it would be nice if we someday had detectors near merging BHs :) It seems that the above description does not generate paradoxes - yet I have devised a thought experiment that still disturbs my well-being: above, I assumed that it is not possible to cross the EH in finite time - it only submerges the matter that would have fallen onto it. However, couldn't we create a black hole in a way that does not require crossing the EH? For example, placing Alice inside a large empty space. Then surround her with an amount of water that would fill the entire solar system. Do this in such a way that the water circulates on certain orbits, preventing too rapid a gravitational collapse and gentle experimental conditions. In such a situation, can we describe the process of BH formation from the center of mass (future singularity;) ) and the immediate cessation of future BH matter on itself, or do the equations indicate that the EH will form outside, cutting off its influence on the universe? Piotr Pyrka :)

[@user-hq9wl8xo2t]

The source of gravitational time dilation is the gravitational potential, so the formation of EH should start from the center of mass... so that it is possible that EH is simply the end of our universes, which nothing can reach in finite time...🤔

[@floatocean7059]

I did it!!!!! I worked out how to map Heisenberg's Uncertainty Principle onto the atom. We can consider the electron as a vector, it has a magnitude and direction, the exact same properties used to measure momentum. The electron can move in any direction all around the centre, and it has a magnitude, an excited electron will be found further away from the centre, and a more stable one will be closer to the centre. So we can see there should be perfect mathematical symmetry between the electron and momentum. In fact, it could be helpful to think of the electron as the force carrier particle for momentum. In the current model, the electrons appear to be stuck on ridges, discrete intervals of distance away from the atomic nuclei, today physicists call these levels of excitement. In my model, the wave function exists as a real physical entity exerting an actual force. electrons form due to the wave function reaching its maximum or minimum value which coincidentally happens at these discrete distances, causing a perturbation in spacetime, these are called virtual particles, and we have seen other examples of virtual particles that act strangely like electrons, popping in and out of existence. the electron is the force carrier particle for the wave function. Which means the wave function is the fifth fundamental force, which means it has a field, which is somewhat intuitive because no matter the size of the object, it always has some amount of wobble as it moves. All objects have to follow a wave function, including you and I when we walk. Location has mathematical congruence with the nucleus. It has a constant wobble, thus keeping the absolute location an unknown. Momentum, then, has translation symmetry with the electron, with the electron particles following along the wave function. Since Heisenberg's uncertainty principle states if we know location, we cannot know the momentum, and vice versa. We can map the electron perfectly onto the wave function, without fully knowing either one. Since these have absolute mathematical congruence, the electron is pulling the nucleus in some sort of Heisenberg's tug-of-war, so we'll say. However, we need to first map Schrodinger's equation onto a sphere, using 3D trigonometry and differential equations. We've established that the electron is the force carrier particle for the wave function, or wave force. In the new model, each atom has exactly two electrons, or an electron pair, which create equal amplitudes in opposing directions, thus resulting in the wave function as described in Schrodinger's equations. This is another amazing coincidence, as all atoms have even numbers of electrons. When, in reality, they have exactly 2 opposing electrons that follow the wave function, reforming continuously at the highs and lows of the wave function. The momentum of the electron makes the nucleus lag behind, giving the increased distances seen for excited particles, and why we see discrete levels, or ridges. The drawing of the atom will change, it will now look something more like a horse and carriage, with the nucleus being pulled by the two electrons. The faster the horse (the electron), the longer the rope that tethers the nucleus to them. This is also a convenient coincidence, that momentum itself would lead to higher excitement levels for the force carrier particle of momentum (defined by the wave function). Prediction 1: We will have a formula which can precisely tell us when and where an electron will form by wrapping Schrodinger's equation around the equator of the atom. Prediction 2: The wave function is the fifth fundamental force, it has an associated field, and the electron is the force carrier particle for it. Prediction 3: We can catch an electron. Increasing its pressure using magnets or light will increase its wobble, which will give us unlimited green energy. Squeezing a single electron can result in a flood of baryons, exotic particles, and complex particles. Prediction 4: The electron itself is the force carrier particle for the wave function. So, if we get enough electrons and energise them to all face the same direction, we can travel at relativistic speeds, or possibly faster than light. In fact, the double slit experiment shows the wave function itself is FTL. Prediction 5: that wherever a wave function exists, the weak nuclear force will be exerting effort on the particle in question, since we can see the electron being exchanged between quarks. I can show, that the wave function FORCE is what is actually keeping the quarks at the exact distances. This means there is no weak nuclear force, but instead baryon decay occurs by the 'weak nuclear potential energy', the same energy we'll be farming from the electron pressure chambers. This means we have something to test, and since it is testable, we have already fulfilled one the requirements of proof of concept. Data analyses on the perturbations in other particles, such as the photon, caused by a 3D Schrodinger's equation could indicate whether we have stumbled upon a monumental jackpot and wealth of understanding in physics. If someone maps the Schrodinger equation onto a 3D plane along the equator (this allows for directionally opposing electrons), then maps the already known 'excitement levels' from the older model onto the maximums and minimums of the wave function from my new model, then this is will become proof of a working concept. I'm leaving this comment here, knowing full well, when that happens, I will have hard evidence to point to, showing I am the first to solve for the atom using the Heisenberg Uncertainty Principle. award me the appropriate accolades as you must, Nobel prize notwithstanding. Duncan McKay . DOB 24/12/1987