10 things you should know about black holes

[@WhySoitanly]

The more I watch Sabine the more I learn.

[@bobhoven3959]

Nice that I can vissit your older u tube movie,s thanks I will use it as back up learning 🎯👍💖

[@Mikey-mike]

That is the best compliment one can pay a teacher.

[@NoizyInSeattle]

One of those very rare Sabine videos where I can say "I knew that."

[@nosuchthing8]

That's why she made it perhaps..To let us join in

[@devilyn76]

What happens at the horizon, stays at the horizon...

[@will2see]

That's why from our point of view nothing happens at the event horizon because it hasn't happened yet, but it will inevitably happen in the infinite future.

[@devilyn76]

Because of time dilation. Time slows as you approach the Event Horizon. And it slows more the closer you are. Technically, if black holes didn’t evaporate, you can never reach the black hole itself. From an outside view, you would fall forever. However, from your point of view, you would watch the universe age faster and faster. To you, you would reach the event horizon fairly quickly. But, you would see the entire life of the universe and see it die before you reached it...

[@will2see]

When you fall into a black hole (you are about to cross the event horizon) you see and experience things very differently than when somone observes you falling into the black hole. But don't worry about it too much...

[@user-hr8pz6lh5w]

Except for implicit randomness.

[@Rancid-Jane]

@@devilyn76 "But, you would see the entire life of the universe and see it die before you reached it..." Not quite as fun as being at The Restaurant at The End of The Universe, but still incredibly interesting.

[@lindsayforbes7370]

Apologies Dr S. In my enthusiasm to ask this question I forgot to congratulate you on this video. The content of course is spot on and as I've said before, the presentation style is clean and does not overpower the message. More please.

[@kidnuke2]

Hi Sabine, I am an internal medicine physician who cares for the elderly. I really enjoy your vignettes on physics! Thanks for making such an abstruse topic accessible to the lay public.

[@JiveDadson]

I am the elderly, and I enjoy them too.

[@shevonsilva]

What I admire most of her is her presentation of science in a very honest way. Best wishes.

[@johnrendle1303]

You are simply fabulous. Such a pleasure to watch your videos. Concise, informative and delivered with a wicked sense of humour. One of the best educational channels out there. Bravissima!

[@smokinjoe9415]

It must be cold in her studio! Gets me excited!

[@rouhihossein]

Hi Sabine, I just discovered your excellent KZbin channel. A question which is in my mind for a long time, knowing that my understanding of physics is limited, I must have been miss understanding something: so if an observer in orbit around a black hole watches another observer moving in the direction of the black hole, the falling looks slower and slower, until it "freezes" and never reaches the horizon. The 2nd observer just keeps falling in his own referential and passes "normally" the horizon. Ok so this comes from general relativity if I understand correctly. So my question is: how is it that we see black holes evolve, merge, etc. if from our point of view nothing never passes the horizon? It's a bit confusing! Maybe you've already answered this question in your video, I've not watch it entirely yet! Thank you for this high quality channel. Hossein

[@bearcb]

We don't see the black hole or anything inside it, just the effects it has on the surroundings: star trajectories, gravitational lenses, gravitational waves. There is even a photo taken recently of a star being sucked into one, stretching like pasta!

[@LuisMailhos]

Happy birthday, SH! By the way, great video.

[@Tripskull]

Hypothesis and collapse... I just love your accent lol Keep up the good work. You're so important to humans with the work you do...thank you for your contributions

[@daffidavit]

I love this new Channel which I've recently subscribed to. What amazes me is how things have not changed so much since 1966 when the TV series Star Trek season one Epd. 20 on Netflix entitled "Tomorrow is Yesterday" written by my alma mater Dorothy C. Fontana and produced by Gene Roddenberry referred to a "black hole" as a "Dark Star" in the episode. The "Dark Star" as renamed by the scriptwriters presumed the "Black Hole" had such a high gravitational pull that even the Enterprise had to use all of it's warp engines in reverse just to escape the "black star's" gravitational pull. It is clear that Gene Roddenberry hired scientists, some from NASA to explain the events for the science fiction in the series back in the day. Even back in 1966 the term "Black Hole" was met with resistance. Similar to what Dr. John Wheeler met when he invented the term "Black Hole" for a paper he published which coined the term. The publisher initially opposed the term "Black Hole" but finally yielded to it for publication purposes. The term was considered derogatory in its nature at the time and still was as of 1966 when the TV series "Star Trek" had to call it a "Dark Star" instead. To this day, the term "Black Hole" offends some people. John Wheeler had to fight for the right to use the term in his famous paper, but he won. Dr. Wheeler was later quoted as saying, "black holes have no hair". Wow, what a thing to say back in the day. Was it another insult? No it was not. What John Wheeler was really trying to say was that "Black Holes" are completely "clean" at their "event horizons" . In the above video by Dr. Hossenfelder this is acknowledged. A Black Hole's event horizon has "no hair" according to Dr. John Wheeler. The event horizon is a place where there are no distinguishing waypoints. There is not point of demarcation from on inch before nor one inch after a black hole's event horizon. That is what John Wheeler was trying to say. If I have to cite my sources, I guess I can go back and look at all the audiobooks I've read this from, but anybody who knows anything about black holes knows that Dr. John Wheeler wrote about and said these things.

[@diqweezle9751]

You want black hole questions? Here are some black hole questions: What does the evaporation of a black hole ultimately look like? Does it emit Hawking radiation until the point at which it has decreased to zero mass, or does Hawking radiation stop before then? Does a black hole's density decrease as it emits Hawking radiation over time? If so, can a black hole theoretically lose the requisite gravitational pressure for continuing its existence as a black hole (e.g. can it "unfold" into something like a neutron star or some other dense glob of matter before it evaporates completely)? Love your videos, Sabine!

[@antoniomaglione4101]

Very clearly stated information, I appreciated it. You made a truly great video. I recommended this video to a non physicist friend. He said to me: "They say at the beginning the black hole is black because the gravity is so intense that even the light can't leave from beside the horizon; but at the end of the video, they say the black hole emits a thermal radiation (he meant the Hawking radiation), so what gives? It is black or not?" I explained the discovery of the radiation happened at a much later time, while the name had already stuck, and this radiation is emitted *after* the horizon. May be repeating this detail (from where the Hawking radiation is emitted) later can eliminate any confusion.

[@iVardensphere]

THANK YOU for NOT saying "nothing can escape... not even light".

[@hipphipphurra77]

may be se forgot to say "nothing can escape, not even light"

[@hadesdescent6664]

Nothing but radiation? Is radiation faster than light, and wouldn't it be pulled back into the black hole? The scientists only speculate, and don't know nothing with certainty! Too many conflicting ideas....

[@iVardensphere]

@@hadesdescent6664 think of light as radiation. It is a part of the electromagnetic spectrum. And yes, it could certainly fall into a black hole. My OP was to thank the speaker for not using the same phrase uttered in nearly every single description of a black hole influence.

[@iVardensphere]

Oh... and Radiation is not faster than light

[@hadesdescent6664]

@@iVardensphere I understand that, thanks for answering, but that Hawking radiation would eventually nullified the black hole is absurd to me. Black hole is constantly eating, and that loosing radiation is greater than amount of what is falling inside is doubtful at best. How come that beyond visible universe, expansion of space is faster than light? And quantum physics vs General relativity is in conflict. I'm not competent enough to understand many of those things in physics, astronomy etc... But, it's a mess of pure speculation and theories of all sorts!

[@d36williams]

your videos are great, I really appreciated especially your explanation on what it means for black holes to lose information, and why that is an issue

[@MurderCraw]

I looooove the strangeness of black holes. When I heard we detected their gravity and then got an image of one, I cheered so loud.

[@packetcreeper]

I can't think of anything in the entire universe that I am more interested in than black holes. I appreciated your video immensely, and hope to see more like it in the future.

[@victorpaesplinio2865]

Wow! I found your channel while searching for science and I loved it!

[@cutepuppyneo]

Firstly, I'd just like to say thank you for making these videos. You're a real inspiration, and the work you're doing on group think etc is so valuable to the scientific community and scientific progress. I am so grateful for this. OK, so I have a question about black holes: If time runs slower as the gravitational effect increases in strength, wouldn't this prevent a true singularity from forming, as it it would take infinitely long for one to actually form, and instead wouldn't it be more accurate to say that it 'tends' towards a singularity but it is actually just 'extremely dense'?

[@fjbayt]

The time runs slower for the observer outside, the image of someone falling into a blackhole is redshifted in the horizon and freezes, for the one falling time ticks like always, so the individual clocks of the matter that fall into making one never stops from their perspective thus time doesnt stop the singularity from happening. Althouh the singularity is the name of something that is not yet explanable.

[@ThePinkus]

@@fjbayt That is the answer given by certain solutions to GR, maybe we can call them as "proper theoretical BH" solutions in that they extends geometrodynamics inside the horizon up to the singularity. What Marc Bali is asking can be stated as if those solutions are the physically relevant ones. The reason his question can be reworded like this is that the GR solution is determined by the energy-matter distribution: solutions resulting from all energy-matter accumulating on this side of the horizon are different than those for which energy-matter ends up inside the horizon. I think, and I might be wrong, that in a region void of energy-matter GR has no unique (well defined?) solution (yep, that region is sort of contradictory, surely looks suspect). The scenario where energy-matter wholly accumulates on this side of the horizon is that of a sort of gemetrodynamical cavitation rather than that of a "sink hole". In this scenario gemetrodynamics does not extend to the inside of a horizon (so that that suspect region is not actually there), perhaps no more than it extends to an hypothetical embedding geometry of the curved space-time. In this sense there would be no singularity. Also, in this scenario, there is clearly no information loss.

[@pedrolmlkzk]

@@fjbayt that's not really accurate, although their time would never stop someone that falls in to a black whole would suffer from extreme time dilation to the point that to reach the singularity he'd need to travel an infinite amount of time

[@onbored9627]

When I stopped watching quantumn woo videos in favor of "actual physics" videos I was so amazed by the difference... then I found this channel. Where Sabine makes other physicists feel like woo doctors in comparison. I can't tell if I'm happy about this or not. Yet, I can't stop watching.

[@adram3lech]

Could you elaborate on what you said about collider blackholes? How come in order for them to exist there should be higher dimensions?

[@Bigalldone]

Thanks for all your work Sabine. Wondering if the "spooky action at a distance" would work if you place one part of an entangled pair into a Black hole.

[@antonystringfellow5152]

There are various interpretations of "spooky action at a distance", one of which is not really spooky at all. However, regardless of which interpretation is correct, the answer to your question is, "Yes", since this effect is not governed by distance (space) or time. Light, like all massless energy, travels at the speed of causality. It would be just as correct to refer to this speed as the speed of gravity, since gravity waves, having no mass, also travel at the speed of causality. This speed is the limit at which cause and effect can propagate through space. This is why no event that occurs beyond the event horizon can have any effect outside of it.

[@amandayorke481]

@@antonystringfellow5152 that sounds really interesting. As I'm a cultural historian I only have the beginnings of a terribly basic understanding of scientific and mathematical formulae and language. At various times I've heard carefully slow explanations of general relativity in English and briefly been able to follow them, but they've all focussed on why nothing can exceed the speed of light; what I've never heard before is what the speed of light itself represents. But of course I suppose the phrase "speed of causality" is actually the same thing turned around and examined from a different angle.

[@AurelienCarnoy]

@@antonystringfellow5152 hello Antony. I wanted to ask you a question: if in the middle of a hypothetical hollow planet one experience zero gravity, then the same would apply at the singularity of a black hole. It would feel like zero gravity like in space. Am i missing something? Thank you.

[@NothingMaster]

Let’s forget about the black holes for a minute; that black shirt looks so elegant on you; specially against that starry sky background. 👍🏻

[@MaoDev]

@ilkldme lmao

[@paulbush1497]

You are the brightness of my mind , your words touch my thirst and desire . For clear understandable knowledgeable knowing.

[@le13579]

Thank you for this video. they're properties of black holes at dinner (!) and your video ("Let's see what Sabine says...") has resolved the arguments. My idea to use the event horizon of a small black hole in the kitchen as a pasta maker has been addressed. In a similar vein, my idea to use a black hole instead of a rubbish bin in the kitchen has also been addressed. (I'm sure everyone has been thinking of this application since black holes were first theorised.) I guess our family can now go back to quality time talking about prince harry.

[@maddhopps]

Regarding #10, I think we wouldn’t get much warning from the effects on the outer planets if the black hole approached somewhat perpendicularly to the orbital plane.

[@heliomartins6681]

Thank you, Sabine, great video!

[@BrettCaton]

At the moment, it seems clearly impossible to go faster than light. However, imagine there was a spaceship that could manage the trick. It approaches a big black hole, so big that it is not torn apart as it approaches the event horizon. Perhaps the galactic core one. It turns back and moves to a safer distance. a) How much time dilation does the crew face compared to an observer, roughly? I think the answer is "not much"? Now it returns, passes the event horizon, uses its drive to escape again, and returns to that safe spot. b) How much time dilation does the crew face compared to an observer, roughly? I think the answer is "infinite"? Or at least that they would be flung into a distant future, where the stars might be burning out, or worse, a big rip is happening? Or is the answer simply "unknown"?

[@hjs6102]

a) it depends from the time they spend there and the distance to the horizon, from a fraction of a second to millions of years, all is thinkable b) impossible, that's why you get a contradiction "infinite"

[@michaelseely378]

Just subscribed! Found you on a night I cant sleep and have been watching youre videos for the last few hours, I watch and read alot of info on the topics you discuss but you have a way making my feeble mind wrap around it a bit easier. Hello from Boston.

[@xlnt2new]

This happens to me more often than i like to admit (to my cardiologist mostly) - Hello from Sofia.

[@amtep]

What I still can't figure out is how black holes can exist if (from our point of view) nothing ever falls into them. Same for collisions of black holes.

[@Jopie65]

That's a good question. Purely intuitively I'd say that all mass of the bh seen from us, lives at the horizon. So there is no 'inside' it from our perspective. But what about seen from someone falling into a bh? My intuition says that that person would see the bh shrink. Because when there's time dilation, there's also length contraction. So from that person's point of view he'd also never reach the horizon cause eventually it's become a single point. But I never hear about that. And that's what I don't get. Why is length contraction never considered? It would solve all those questions about where the information is and what is inside a bh.

[@istvanszennai5209]

then you didn’t listen to the video. As she said the most common black holes are formed from depleted stars. Things don’t have to ‘fall in’.

[@hjs6102]

@@istvanszennai5209 Well, it is in deed not so easy. You are free to choose an observation point within the collapsing star. At which point the first horizon appears? Does it grow? You have to be very careful, from which point of view you start your calculations and care about not to change the view without transposing all the coordinates in space and time.

[@istvanszennai5209]

@HJ S: 😑 the star uses up all its fuel, explodes into a supernova, then it _might_ collapse into a black hole. You ask ‘at which point’; it depends on the star to begin with...the point is, that the Schwarzschild solution predicted it, and today we have definite proof. End of story.

[@hjs6102]

@@istvanszennai5209 You misunderstood what i meant. I wanted to say, that if you have an event horizon at some location and time and then you go back in time, does the horizon shrink towards zero or popped it into existence instantaneously exactly with the given radius. And this timeline has to be viewed from an outside observer and an observer inside the later event horizon. What would the observers see?

[@jean-francoisguilbo7833]

Information loss paradox: either the random frequencies of the Hawking radiation contains the information, but we don't know how to decypher it or either (but less likely) it is gone in another baby universe, the blackhole been a gateway or either (more likely) we think we know all about information loss, but in fact we have made huge confusions when applying couple of theorems and obviously, they don't work for blackhole.

[@juanausensi499]

I think information does really disappear in the black hole, and if quantum mechanics have a problem with that, then, well, it's time to do some revisions.

[@jorgepeterbarton]

Is not possible black hole will eat us up . 2020: ok, we'll see.

[@brookscarpenter8327]

Agreed. We still have time.

[@thefaboo]

The only catastrophe we managed to dodge 😂😭

[@janosmadar8580]

Excellent video! But I have a little problem when I compared this video to your other excellent video: "Solutions to the black hole information paradox". In this video, you said at 2:19: “... but from outside it takes like it [to fall into black-hole and cross the horizon] take forever. On the other hand, one of the subject of that video is that if an object felt into black-hole (see 10:35 in this video too), then it’s information content must come out when the black-hole is still large / latest when it is evaporated. I.e. an outside observer must wait endlessly until an object falls into a black-hole (cross the event horizon) but the black-hole will evaporate within finite time from viewpoint of this outside observer (theoretically if the Universe just expanding forever). So, If the black hole is destroying itself before anything can fall into it, then why we ask what will happen the information of this object when it is felt into black-hole? Does it make sense? Or maybe I have caught your explanation in the wrong way.

[@Kapomafioso]

Couple of questions: 1) if black hole is "everything with radius smaller than the event horizon corresponding to the object's mass", then isn't every stable, free elementary particle a black hole on its own? If not, what is the radius of an electron? If yes, how come every elementary particle black hole doesn't evaporate immediately and leave a trace of stuff behind? 2) what is the kinetic energy distribution of the particles coming out of the black hole? I'm looking for something like S (E), similar to S(nu) for a black body. Is it spherically symmetric? Does it follow Lambert's cosine law? 3) if an observer outside of a black hole sees something falling in slowing down, seemingly taking forever, could we ever observe a black hole to grow due to infalling matter? How can we possible observe it, if all infalling matter suddenly slows down and takes forever (from our perspective) to fall in? 4) what is the position vs. time function of a photon, directed exactly at the event horizon from inside of a black hole? If it cannot ever escape, that means it has to "slow down" (in order to never get past the event horizon from the inside), but we know, that photons have a constant speed (in a vacuum - does it mean inside of a black hole horizon is not considered vacuum?) Or, since c dt - dr = 0 for a photon, then if dr has to slow down, then photon's time should slow down to keep this consistent.

[@andrewc9643]

Dr. Sabine. Firstly, I loved all the videos that you have made, that I have seen! So far, I have heard a lot of references to Einstein. This one references Hawking. Could you do a video just on Hawking and some commentary on his work. I think that would be great!

[@brothermine2292]

Two questions: 1. What percentage of supermassive black holes was originally dark matter that fell in? 2. Since distant observers see that it takes infinite time for an infalling object to reach the event horizon, why is there a paradox problem accounting for the quantum information the object contained? The info can't be lost if it never reaches the black hole.

[@nosuchthing8]

A blessing for a black hole... "May God bless and keep black holes...far away from us!"😬

[@kathieroper-ericson3964]

If an outside observer watching something fall into a black hole sees the object freeze in time , then why don't we see everything that ever fell in frozen in time?

[@hjs6102]

That is the case. For the outside observer the light from the falling thing becomes a redshift (the waves will become longer and longer and so weaker and invisible) but the object never crosses the horizon.

[@Jopie65]

Yes, so all stuff off the black hole lives on the surface of the event horizon. So, what is inside it then, you may ask? My conclusion is, there is no inside of a black hole. I'm also trying to make a case that someone falling in a black hole, will also never cross the horizon. Because that person would see it shrink as he nears the horizon.

[@DrunkenUFOPilot]

@@Jopie65 No, the infalling tourist sees the horizon, the black hole, widen more then expected for approaching a typical spherical object. All that is visible that's not the BH, shrinks into a little spot, becomes very bright, very blue shifted. I think. I admit, I haven't actually tried to see for myself yet!

[@Jopie65]

@@DrunkenUFOPilot The reason that I think the tourist would see the bh becoming smaller is because, I think, seen from outside the (not so lucky) tourist begins to look bigger. Here's why: Imagine the tourist bringing Einsteins light clock. Every photon bounce between 2 mirrors counts as a tick. When the tourist nears the BH horizon, the external observer would see it's clock slow down until it (almost) stops at the horizon. Here's the thing: light has a constant speed in every reference frame. For the clock to tick slower, the mirrors need to be further apart! Eventually so much that they are wrapped around the horizon multiple times. Poor tourist merges with the surface of the BH. Seen from the tourist however, his clock doesn't run slower. But the clock of the BH starts to run quicker once he nears the horizon. Hence the horizon must become smaller. Follow my reasoning? Could you point me to a mistake?

[@keithrowley5520]

Excellent - lucid. As I, in my limited way, understand it, Hawking radiation arises from the spontaneous appearance in vacuum of particle pairs as a function of 'uncertainty' - i.e. quantum fluctuations in energy level. In the vicinity of a black hole, one of these particles, the 'anti-particle' falls into the black hole, releases its energy and reduces the mass of the black hole. The other particle, being short-lived, 'vanishes' again or 'hangs about'. (This all sounds like magick to me, but I have some faith in the math and empirical evidence). So the issue now is of conservation of information. Forgive my limited understanding, but at a classical level, we can write differential equations that play backwards and forwards in time. In principle, if we had infinite accuracy in the variable coefficients of our equations, we could replay the whole universe backwards and forwards (as Laplace thought). I practice, we do not have that exactitude and so chaos reigns - but in principle, no information is ever lost. I 'think' you are saying that the same applies at the tiny quantum level? So the problem is that we cannot ever recover information beyond the 'horizon' of a black hole. Now here's what puzzles me - why do we relate Hawking radiation to the processes and information inside a black hole at all? The particle pairs are created in vacuum throughout the universe (are they not?), So what is the connection between the absorption of one particle of a pair into a black hole and the information already in it? Are you saying that the absorption process itself destroys information? Pardon my poor understanding Dr, Hossenfelder - I'm an engineer, not a physicist and it's a privilege being able to as you these questions.

[@SabineHossenfelder]

The problem with information loss is not that the information in the radiation is lost. It's that the radiation causes the black hole to shrink, so that the information about what else is inside the black hole is ultimately destroyed. It is not the horizon that causes the problem. The horizon is merely the location where information becomes disconnected. What causes the problem is the singularity that ultimately destroys whatever touches it.

[@keithrowley5520]

@@SabineHossenfelder Thank you sincerely. Now I must go away and think!

[@adrianconstantin1132]

I believe Hawking radiation says the particle pairs that get separated by the horizon (after the spontaneous formation) can no longer re-combine, and so the remaining particle does not vanish back, but remains, and that is what makes the ratiation. I also believe there is no empirical evidence for this, it is just as thought experiment

[@FighterFred]

Yes, they're a bit scary. Did my thesis on accretion disk variability so I know a bit about them. A few comments; 1. the time delay effect for far observers when matter crosses the horizon may be observable, if the huge gravitational Doppler shift can be compensated for or very long wavelengths being used. 2. the Hawking radiation has zero practical influence as you mentioned, 3. one should not ignore the rotational energy of BHs, since that may become the only energy source in the far future when all stars have ended their evolution, 4. staying close to the horizon without getting killed may one day be used as a one way time machine into the far future. The question is what purpose such an adventure would have.

[@herwighuener3256]

Way back in the eighties I bought the book of Misner Thorne and Wheeler "Gravitation". I think it is still the best textbook around - or has something better come up since? Also, in this book it is shown that many things in relativity can be explained by simple diagramms. What spacetime does is not that complicated, and for understanding things one can mostly ignore the tensor calculus. Why is this so? If you walk through a curved landscape (mountaineering), you also do not need math in order to understand how to go from A to B. - However, knowing some math does not hurt - beautyful or not.

[@SabineHossenfelder]

MTW is still one of the best references, simply because it covers pretty much everything relevant in GR. I myself also use it. (Though I want to complain it's starting to fall apart. The binding is miserable.) It is of course out of date now as with the cosmological data and so on.

[@herwighuener3256]

The first volume of "Berkeley Physics Course" is also a good reference for beginners. I mention that because the media tell, at this moment, that Charles Kittel is dead at 102. His books about Solid State Physics and Thermodynamics were, for me, essential in understanding physics. RIP - If physicists are admitted to heaven, that is.

[@toddq6443]

@@herwighuener3256 Nicely stated, I agree. TNQ

[@toddq6443]

@@SabineHossenfelder At least we all still appreciate the value of wonderful, useful texts. Each time I have had to move into a new home I question my sanity at having to relocate my massive library.....but then I select a volume, open it at random, take a deep inhale and begin to read.....suddenly all of the effort seems well worthwhile (even those with tattered bindings are a blessing). I have a 1955 Larousse Enclyopedia of of Astronomy in near mint condition which I value like a beloved pet! :) TNQ

[@sbkarajan]

So called stellar black hole, which started this entire black hole farce series, is impossible to begin with, as the sun is not really a hydrogen plasma ball. The black hole itself, where the definition is being continuously shifting to make common sense these days, probably don't exist after all. Think about this, about the closest star, and how little we know about it. 1. The density of the sun is 1.4 g/cc. The density of SOLID H and He are 0.076 g/cc and 0.2 g/cc respectively. The sun is probably not made of H or He. 2. The pressure and temperature of the sun's core is "modeled" to nearly equal, or exceed those of Hydrogen bomb's. If that's the case, H and He cannot exist in plasma state in the core any long term. Moreover, all of H in the core should have fused into He instantly when such pressure and temperature was reached billions of years ago. Yet' it's slowly and surely fusing H into He all this time.... Nope. 3. The radiation from the sun is that of blackbody. H and He plasma don't do that, they emit lines of spectrums, like neon sign does. 4. Looking at the solar activity close up from the telescope, they are not that of some gas or plasma, but of some magma... Did you know that even the clouds in the sky or smokes from chimney are mostly solid particles like water ice or shoot? Gases are very thin and mostly invisible. 5. Some stars repeat supernova explosions, again and again, never disappears, have you looked at such news? If not, google it.

[@eytansuchard8640]

Thank you for the lecture. 1) All we know about black holes will collapse if we detect electromagnetic emission from black hole mergers or observe episodes of energy emissions not from an accretion disk or from matter that falls in. 2) We assume that matter is destroyed in a black hole. That would imply a zero Einstein tensor and only a non zero Weyl tensor. It is not sure if it is even possible though I personally like the idea. 3) QFT relies on particle fields via spinors. An alternative approach is torsion operators and Geometric Chronon Fields where the building blocks are not particles but realization events of space-time. We don't know about particles but about their interaction events. In the Geometric Chronon approach, matter appears where these realization events or Causal Sets are misaligned. In mathematical terms, it is where the Reeb vectors of the gradients of the Geometric Chronon Field are not zero and thus prohibit geodesic motion. Gravity in this case is simply the controlling response of space-time.

[@NaRhala]

re: 3) w h a t but also v e r y i m p r e s s i v e

[@eytansuchard8640]

@@NaRhala The results of this model are more impressive. It allows unexpected gravity and anti-gravity by electric charge. That means Alcubierre - White warp drive is within reach !!!

[@jonathancamp7190]

How about a video titled, 10 things you should know about Sabine Hossenfelder. Your choice of what 10 things you want to tell us about yourself.

[@solariss.3743]

Dear Mme Hossenfelder, may I kindly ask you 3 questions about BH in german language? 1) Warum weist die gekrümmte Raumzeit eines SL nicht die Tendenz auf sich wieder zurückzustülpen so wie sich auch die Raumzeit um die Erde oder die Sonne wieder abflacht nachdem der Körper vorbeigezogen ist? Die Masse ist ja in der Singularität "verschwunden" und kann somit nicht mehr die SL-Raumzeit in ihrer Verkrümmtheit fixieren. Vielleicht hat die Raumzeit eine fixe Sollbruchstelle und ist nur begrenzt elastisch? 2) Wie kann es sein, dass SL unterschiedliche Massen, Größen haben wo doch alle ein und dieselbe Singularität aufweisen? Wie kann sich hineinfallende Materie auf die "äussere" Beschaffenheit des SL auswirken wo doch alles in der Singularität "verpufft"? 3) Kann es sein, dass im SL-Zentrum nicht Singularität auftritt sondern nur Raum der aber absolut frei von Quantenfluktution ist? Vielen Dank für Ihre so stark vermittelnde Art Physik zu erklären, sodass auch bei nicht Initiierten wie ich das Licht ab und an in der Laterne angeht ;-)

[@toddq6443]

In your opinion Sabine, what combination of instrumentation and/or observations is required for us to find definitive answers to these questions re Black Holes? Any experiments that you are aware of on the horizon which may provide us with satisfaction? Is the human mind really capable of coming to terms with Infinities.....given that any kind of cosmological Infinities even exist at all? TNQ

[@denisrobert36]

Sabine, some people still think a black hole is a hole. Can it be mentioned clearly by a scientist that a black hole is not an empty hole but physically a spherical object like any stars, except that its mass is so dense that it doesn't permit even light to escape.

[@DavidBruno]

How did this only get 4K likes? Was much more understandable than spacetime.

[@RickSeeger]

Is our universe the inside of a supermassive black hole? There seem to be many parallels: black hole accretion/universe expansion, black hole formation/inflation, the horizon could contain enough information to describe a 3D universe inside via the holographic principle, etc; Is there a way to prove this is not the case?

[@piotao]

What about firewall at the event horizon? There has to be light trapped exactly there, how does it influence hawking radiation?

[@supercommie]

I prefer the explanation that says a black hole is a region where all paths lead to the center. It's a relativistic explanation, and when I first heard it it blew my mind.

[@DavidBeaumont]

It's explained really well in: kzbin.info/www/bejne/gZazf5uLf5elm6s Space becomes "time like" and time becomes "space like". In the same way that outside a black hole, the direction of time is "forward only", inside a black hole, space is "forward only".

[@WorldStreetOmaha]

Here's a question that our group of four has had for more than ten years: If from the perspective of the outside observer, the person traveling to the black hole or anything else never crosses the event horizon because time becomes nearly infinitely slow from our perspective, then we observers should never observe black holes growing in mass. For instance, instead of observing super massive black holes, it seems that we should instead observe these black holes only as small black holes (as when they first came into existence) with enormous amounts of matter frozen just outside the event horizon. Even if a BH has collided with a neutron star, not enough time has passed (from our perspective) for the neutron star to have passed the event horizon. What are we missing?

[@michaelsommers2356]

Because you are far from the black hole, it does not matter whether the mass is inside the black hole or just outside it; you still feel the same gravity. You could think of all the mass of the black hole being in a spherical shell, or in a solid ball, or in a single point, and get the same gravity in each case.

[@WorldStreetOmaha]

@@michaelsommers2356 Thanks for the reply. It's interesting to think about how all the matter acquired by every black hole would just be at the edge of the event horizon.

[@georgeemil3618]

What I understand is that 1) to an observer watching someone approach the event horizon, his time slows down so much thst eventually it stops totally. From his point of view looking out at us, our time is speeding up to the point where everything and every event has happened all at once including the conclusion of the universe. Again, from an outsider's pov, the travellor actually never enters past the event horizon. 2) One doesn't enter into a black hole. One enter into the event horizon and after that you'll see all his molecules, atoms and subatomic particles shedding off to surround and join all the other particles compressed at the black hole. The black hole is actually all the subatomic particles gathered and compressed together so that there is no space between any of them. That is, all the quirks, quarks, strange, charm and muons are touching each other and you are intermingled in them. So there really is nothing to see in the black hole as everything is compressed together with no gap. What you do get to see is what happens after crossing the event horizon.

[@Quickacts]

Okay but are black holes just compressed matter ? Like if i try to touch it what will i feel

[@Alexander-dt2eq]

Why do black holes vanish? Given the fact that black holes evaporate over time, wouldn't they just become some dark dense object which does not have enough mass to be a black hole any more and therefore stops evaporation at some point in time (in mass).

[@SabineHossenfelder]

Well, that's one of the possible solutions to the black hole information loss which have been proposed. The problem is that since nothing can come out of a black hole, the horizon cannot vanish as long as general relativity remains valid. For that to happen, stuff that was previously inside would have to be able to then be outside. You can do it if you change something about general relativity.

[@fattyz1]

I love her teaching style and everything else about her. I got lost about how does anything go the wrong way out of the black hole and read the wiki. Magic, if you can't do the math. Ok. Maybe it'll make sense when gravity gets figured out

[@lindsayforbes7370]

I read that the biggest neutron star 2.16 stellar mass is 20 kilometres across and the smallest black hole 3.8 stellar mass is 24 kilometres across its event horizon. The densities of these two bodies are the same +/- 2%. Is it possible that as a neutron star gets bigger that the the radius of the event horizon simply exceeds its physical radius? In " The pressure distribution inside the proton", coauthors V. D. Burkert, L. Elouadrhiri, and F. X. Girod show that the the average peak pressure, near the center of the proton, comes out to 10^35 pascals: a greater pressure than neutron stars experience anywhere. Is this reason to believe that stellar black holes are just large neutron stars?

[@SabineHossenfelder]

If the radius of the event horizon becomes bigger than the actual radius of the star, then the matter can no longer be stabilized and it will inevitably collapse.

[@toddq6443]

I really admired this thought provoking question Mr Forbes. TNQ

[@adrianconstantin1132]

Neutron stars formation indeed requires a star of a size up to, but not quite, that of a black-hole forming star. Neutron star or not, as soon as an object size fits inside the diameter of the black hole corresponding to its mass, the black hole is created. So neutron stars always have a radius larger (but still close to) then that of the corresponding black hole of the same mass. Neutron stars can be observed (by telescope), black holes can not, so there is no confusion between them, not visible nor conceptual (theoretical). They are totally different.

[@amedeofilippi6336]

What makes me feel “ strange “ is that if ithink about densities of a BH , I see that the larger they are the less dense they become. M87 Supermassive BH has about 0.6 kg per cubic meter, much lighter than water while a 3.8 Solar mass BH has the tremendous density of about 4*10^24 kg per cubic meter. Believe that I would prefer to fall in a supermassive BH after all!

[@gyro5d]

Blackholes are Counterspacial sinks. When stars die they become iron. This iron becomes coherent and produces an enormous gauss. "The higher the gauss, the smaller its field." The Counterspacial Sink's gauss is so strong it can't leave its Inertial plane. Leaving Mass without Magnitude/Magnetism.

[@sparhopper]

Perhaps it only _appears_ that Black Holes do _not_ have a surface (6:49), because the light given off by the collision lies well within the horizon of the Black Hole (since the surface itself lies well within the horizon) and that light is unable to escape?

[@AkamiChannel]

sparhopper I think physicists would have worked that out

[@sxdrujandis]

Nice, more enjoyable than most blackhole vidues due to more accurate and recent theory. I'd suggest that a simple explanation for not understanding how some blackholes get so large, would probably make more sense if the 'big-bang' theory is changed with universe is constant theory. Too many factors point to that the universe age theory is not realistic, ancient blackholes might offer more proof to that end..

[@happyhome41]

Beautifully done. I feel as though I slept at a Holiday Inn last night. Thank you.

[@yukterez]

Does the black hole lose positive mass, or does it gain negative mass? In the second case the material should remain, only the gravitation should cancel out.

[@SabineHossenfelder]

What "material" are you speaking of?

[@yukterez]

the material that is supposed to evaporate

[@ThomasJr]

I love that she recognizes that the inside of a BH is not understood because GR doesn't work in such a scenario (and a few others). But it seems Penrose/Hawking theorems affirm that BHs need to have singularities. Should we trust Penrose theorems? Or are those only valid if GR also applies to BH?

[@ISK_VAGR]

AMAZING...! A question: the center of a black hole is a singularity, then hypothetically a white hole center is a Ubiquity, i.e. everywhere in the space out of the black whole? If this is true, can the particles created during quantum fluctuations the same particles that passed through the black hole singularity? Thanks....!

[@333STONE]

White whole would push and not pull. I think a black whole is the Reciprocating precessional hyperboloid gone over the limit of oscillation or spin and starts divergence and convergence in the form of the White Whole the inhale and exhale inhale=black exhale=white There is an intermediate blackhole in the sword of Orion in the middle is the trapezium open star cluster where the 5 stars form a cross the top of which is a binary . Now that's where the barnards loop starts. Which curiously looks like a fibonacci spiral, and if one follows said loop trajectory it leads to our solar system. That's probably why orions nebula is so important to ancient cultures the eye in the triangle

[@zzzoldik8749]

When gravity make thing shrink, it happen in moving reference frame or non moving reference frame or for all reference frame? Could you answer this question please

[@offeratzitz8329]

Hey Sabine, question about black holes and special relativity. If I have a high velocity (outside of the milky way), and I see space more compact - will I observe that the milky way span over a smaller volume of space? If so - will I also observe the milky way having less mass? If not - is there a certain velocity in which I will observe the milky way has a large mass compacted in a relatively very small volume, and observe it as a black hole? Is it possible that we are actually moving at a high velocity and what we observe as black holes are actually regions of matter moving much slower than us and we only observe them as black holes? Also - in case an object have higher velocity - its observable universe will actually contain more space than an object having lower velocity, so it is possible that objects inside a slowly moving region of space will not be able to observe other far away objects while the far away objects *will* be able to observe them due the difference in their perception of space-time? So what we observe as the event horizon of a black hole is the limit of the observable universe from "inside" the black hole?

[@Jean-Pierre-PETIT]

Sabine Hossenfelder is very talented and composes wonderful songs. But she is also a scientist who in 2008 laid the foundations for a cosmological model where the universe is made up of a mixture of positive and negative masses. It is then described not, like Albert Einstein's model which is summarized by a single field equation, but by a system of two coupled field equations. From this angle Sabine is therefore the successor of Albert Einstein. But she could not build from her model elements that could be compared with the observations. In France, we developed in 2014 a system also based on similar equations that we have exploited with great success by showing a dozen points where it matches observational data. Sabine accused us of plagiarizing her own model. But these two systems are not identical. So we looked at how our model could be considered a special case of her model, which would not bother us at all. But we were unable to show it. Sabine may hold the key to this case. Under these conditions she should, as we have asked her several times, publish an article showing this and we would be happy if this story could be cleared up in good faith because this accusation of plagiarism, formulated in the emails she sends to correspondents, puts us in a very unpleasant situation. Jean-Pierre Petit and Gilles d'Agostini, from France

[@netherby4335]

Have 'black holes' been observed that couldn't instead be explained by dense plasmids viewed end on? Is there in fact any way to tell if an object is a black hole and not a plasmid, since they should appear to be the same thing when viewed from a fixed position?

[@BrunoKramm]

Liebe Sabine, was passiert eigentlich in dem Moment indem aus einer Masse ein schwarzes Loch wird? Ich meine wenn das zeitintervall immer kleiner wird auf den Moment hin, wenn die Region die Singularität wird. Davor kann Licht aus dem höchstwahrscheinlich noch sehr heißen Zentrum in allen Wellenlängen entweichen. Danach aber nicht mehr. Kann man sich das so vorstellen wie bei der chaostheorie, wenn alles streng deterministisch auf einen Punkt zu läuft nachdem man keine Aussage machen kann, wie die Endposition aussieht, also streng chaotisch? Aber eigentlich ist ein schwarzes Loch ja ein sehr geordneter Zustand, da ja nichts mehr raus kann sondern alles nur reinfâllt. Und von außen sieht ja das Reinfallen in das schwarze Loch extrem langsam aus. Bevor es ein schwarzes Loch ist, jedoch nicht. kann man sich das dann wie einen seltsamen dopplereffekt vorstellen? Viele Grüße, Bruno Kramm PS: Danke für Deine inspirierende Arbeit

[@MegaRooikat]

Thanks Sabine - love your work - As a person is falling towards the event horizon their 'clock' will slow down to zero from an outside observer's point of view. From the viewpoint of the person falling what would they see happening? Would they not see time flowing by quicker and quicker until 'all of time' flicks by in an instant when they hit the event horizon?

[@DavidBeaumont]

PBS SpaceTime talks about this. See: kzbin.info/www/bejne/gZazf5uLf5elm6s Short answer, no. The person falling into the blackhole might not even experience anything special at the event horizon.

[@Jopie65]

@@DavidBeaumont I saw that one too. But consider this: Suppose someone could really cross the horizon. Since the only path for light and any other thing inside a bh is towards the center, how can this person still see, or be aware of his feet when inside a bh? And if he can't, why then say that he would not be able to tell her crossed the horizon? I think a person could never cross it, cause from his point of view, the horizon shrinks. People seem to forget: When there is time dilation, there's also length contraction.

[@matnelen1724]

It slows down but the photons eventually stop coming right? Any new reflected light wouldn't get to you either, so wouldn't you fairly quickly just fade out once you cross the horizon? So it wouldn't look like you're falling slowly, it would look like you disappeared? Am I confused?

[@jonathanillert2808]

As a observer from the outside time is slower when something gets closer to a black hole. But how much? is it possible that nothing has reached the singulariety of a black hole so far? could that be the reason why we get no information out of black holes sinc to get information something has to reach the center and come out first?

[@singingphysics9416]

I have a question: since for us, anything falling into the black hole takes literally forever to fall in (since time stops at the horizon), how can a black hole grow (from our frame of reference)?

[@hillstrong715]

Another question is if during the generation of the black hole, time dilation is occurring as a consequence of increasing collapse or other effects then from our perspective we should see the entire process slow down to the extent of it effectively stopping as far as we are and the rest of the universe in concerned and so how would the black hole ever form in the first place? The alternate question is what would an observer see happening in the outside universe as they fall towards the event horizon?

[@dwinsemius]

Regarding QM not allowing any information loss: Please comment on the situation of a light source emitting a photon that passes through a two slip apparatus with a screen detector. The position of the "detected" photon is random to a degree (modulo the interference pattern) but I would say that the process is not really reversible, at least as I understand the terms.

[@n0ccca]

Sabine talks like a German John Battman. I'm riveted. I love it.

[@rogerman65]

Why is the surrounding temperature hotter around a small black hole? And is a supermassive black hole smaller than a regular black hole?

[@jjdigitalvideosolutionsllc5343]

Can the black hole evaporate to a point when it is no longer dense enough to be a black hole, changing to something less dense like a neutron star? Can other bodies evaporate in similar fashion?

[@BeefGold]

I just checked the other channel. I watched Talk to Me. Not less confused. I'm gonna stay here.

[@bernard3690]

My question is whether the existence of Hawking radiation can be deduced as follows: Since a black hole is a region of space which we are unable to observe energy and matter are therefor allowed to emanate from it because such emanations do not violate any law of nature for the simple reason that we are unable to observe those laws being violated. To violate a law of nature presumably assumes that we can observe those laws being violated which of course within a black hole we can not. Therefore radiation from a black hole can not be forbidden which presumably means that it must exist.

[@gyro5d]

Negative Hologram. Area is the Horizon. (Imformation) Volume is the Blackhole/Counterspacial Sink. Counterspacial Sinks are Aether's Hyperboloid's, Inertial Plane, into Counterspace, Stars are into Space. Andrea Getz, after the Nobel Prize, said, The Blackhole is rotating backwards. Not if the Blackhole is a Counterspacial Sink, Aether's Hyperboloid. Would be rotating backwards in Counterspace. The Aether Hyperboloid rotates in one direction. Looking into one vortex CW, looking into the other/opposite vortex CCW. Opposite rotation.

[@williamburke1882]

I have watched several of these and find them fascinating even though I don't get much of it. Thank you for making them short and interesting (I have a very short ...what was I saying? oh yeah, attention span.) I would like to make one small suggestion however and that is that there is more than one picture of Stephen Hawking out there.

[@travisray2934]

Maybe a dumb question, as I don't grasp even the simplest explanations of relativity or physics of any sort, but if you could bend space time, like with a warp drive (which Im sure I also misunderstand the mechanics of) could you in theory flip a black hole inside out? And if so, what would happen?

[@kloassie]

3:03 "if the black hole is massive enough, you can cross the horizon without noticing what just happened" Does that mean that if the black hole is massive enough, your heart would still be able to pump your blood _all_ around in your body just after you crossed the horizon? Cause otherwise, you _would_ notice something. And if the heart would still be able to pump the blood to the outer regions* of the body, then would it also be able to do so when only half of your body has crossed yet? Cause otherwise, it would not be logical the heart would suddenly be able to do so again once your complete body has crossed. And if the heart would be able to do that once you only crossed half yet, then basically the heart would pump part of the blood _out_ of the black hole's horizon again -> meaning that _that_ part of the blood would (temporarily) escape the black hole's grasp again Sure, one could and might counterargue that the heart most likely wouldn't be able to pump around (completely) anymore even _before_ you reach the horizon, but in that case I'd say two things: 1. Apparently the black hole hasn't been imagined large enough to bring up this counterargument 2. The you-person in which the heart is pumping blood around is just an example. One might just as well replace it for a sturdy robust concrete industrial hydrolic pump, blowing something as light as helium just back and forth 3. (As a bonus) Sabine wouldn't mention "you can cross without noticing" if the not-noticing would be due to the event in which you already died from a heart-pumpage failure **)* Outer region = the part further away from the black hole's center

[@juanausensi499]

The more massive the black hole, the larger the radius of the event horizon. That also means that the event horizon if further away from the black hole, so this horizon is further away of strange black-hole phenomena, like extreme tidal forces. Keep in mind that the event horizon is only a location, not a thing.

[@kloassie]

@@juanausensi499 yet also with large black holes there _is_ an event horizon. There _is_ a point in time and space which the crossing of it makes escape impossible. And if the black hole is large enough, you _will_ cross it _consiously_ (assuming that you do cross it in the first place in a vehicle that has working life support systems). If you cross it consiously, that means your body will still be more or less intact. Including an intact enough blood flow. An intact human body is larger than a point. Hence, the body will not cross the event horizon completely in just one instant of time. Let's say you drift in head first. Then at some point in time your head and torso have crossed the event horizon, however your legs not yet. So your blood pumping heart already has crossed the event horizon. If that heart would pump blood to the direction of your legs (which are still 'outside') then that would mean your heart would be pumping 'out of the event horizon', so out of 'the point of no return'. Thereby it would violate the laws of physics, which obviously is impossible. Conclusion: the heart would *not* be able to pump blood to the direction of your legs. Now about that conclusion, I don't know about you of course, but my guess is that I myself _would_ notice something if my legs would become deprived of blood.

[@juanausensi499]

​@@kloassie There is no discontinuity or rupture of space or the laws of physicis in the event horizon. It's just a distance. Imagine a river ending with a waterfall, with the water going faster the closer you are to the waterfall. A boat is in that river, floating obliviously to its doom. Let's say the maximum speed of the boat is X, and that the speed of the water far from the waterfall is less than X and close to the waterfall larger than X. That river would have a 'event horizon', a distance from the waterfall that is the exact point of no return for that specific type of boat. Before that point, it's possible for the boat to scape the waterfall, after that point, it's not. But looking at the river, there is nothing special about that point, it's just water accelerating continuously. This horizon tells more about the boat that about the river. Continuing the metaphor, people on the boat can run along the boat just fine, before the horizon, and after the horizon.

[@jamesruscheinski8602]

When matter become denser inside black hole, does some of the density leak into another area or dimension as gravity?

[@EGarrett01]

Good video. It seems like when people discuss black holes, they never seem to properly emphasize that this isn't abstract made-up nonsense, these things are REAL and they are examples of how space and time as we understand it is only a subset of what is possible, a black hole is, literally, a place where gravity is so strong that *reality itself* literally breaks, and we can't even do math to figure it out, nor look inside it because nothing can ever come out. It's the perfect example of "truth is stranger than fiction" and "there are more things in heaven and earth than are dreamt of in your philosophy."

[@martinstubs6203]

Your forgot to add "... and nothing can ever get in either." See my comment below.

[@Jone952]

2:00 You say from the outside it looks like it takes forever to fall through the event horizon. Does it literally take infinite time?

[@tripleceas]

Johnny Schmegma i wonder this too. Scientists have observed objects (i believe stars) falling into black holes and matter being ejected on the other side. How is this possible if it takes 'forever' from the outside viewer to watch an object fall into a black hole?

[@hjs6102]

@@tripleceas Well, the press writes "into" because the writer hasn't understood the physics, or they simplify, to not confuse the readers with complicate details. If a star falls "into" a BH, we only see what happens to the star before reaching the event horizon.

[@hjs6102]

@@se7enTse7en Well I am not a scientist, so I can't answer this question, sorry.

[@WylliamJudd]

I would love to see what you think about Magnetospheric eternally collapsing objects.

[@timjackson3954]

An observer falling through an event horizon is said to be unaware of its presence. Suppose he she or it is on a trajectory grazing the horizon, and pokes it with a stick. The fact that the end of the stick won't come back is a bit of a giveaway isn't it? Wouldn't the effects on the view of the 'outside' universe be noticeable too. As I understand it the angle of view should be reduced and the incoming light blue-shifted. For example, what would time compression do to the cosmic equilibrium temperature in that place?

[@betaneptune]

At 6:59 you say "falling through a horizon and then just vanishing." But you told us earlier in the video that we never see anything cross the horizon. So which is it?

[@Grimebucket]

I'm not a physicist so take anything I say with a grain of salt. From my understanding, the reason things vanish from our view is not because we see them pass through the horizon but because the light emitted from them becomes more and more redshifted until they become invisible.

[@betaneptune]

@@Grimebucket Yes. That is the standard explanation. But how can a black hole grow if nothing makes it to the event horizon (form the viewpoint of a distant observer)? Clearly the black hole collision that produced the gravitational waves observed by LIGO completed. The ringing of the completion of the merger was observed, so it must have happened, even in our frame of reference. So I think as mass accumulates on the surface of a black hole, its corresponding Schwarzschild radius must also grow, which I think would mean that we would actually the hapless astronaut cross the event horizon, except the view would be ruined by the extreme redshift. Thank you for your reply.

[@prosoporific]

Umm question.. if we was in a black hole and that then bumped into a other one what would it do to things inside..

[@sansdomicileconnu]

we can t calcul it with escape velocity?

[@mauriziorvt]

I have a question: if matter falls into a BH and we can see it falling for an infinite time, what happens to the light emitted by the falling matter that prevents us from continuing to see it? Can it be the Red Shift? Thank you.

[@michaelsommers2356]

It does get red-shifted.

[@ThomasJr]

Sabine, what is the actual surface of the BH mass? Does it exist like in planets? Is it the even horizon?

[@paulkohl9267]

Unless I missed it, noticed no mention of AMPS? In 2019, how can you not mention the Firewall when going over things to know about bh's? Btw, what if the firewall has the quantum data spread out on it (like 2-brane)? In such a case subatomic particles would be black hole quanta and there would be no information paradox, as there is no loss of quantum data.

[@sadderwhiskeymann]

in the event a black hole would come to eat us all up, are there any theories on how to avoid it?

[@ERICHOEHNINGER]

a spaceship that drags our sun out of the way. or it's time to leave your house.

[@garyproffitt5941]

The amazing mysteries of life Sabine.

[@dennisr1683]

Love your presentations. In theory, could antimatter black holes exist? If so, what would happen if an antimatter black hole encountered a normal matter black hole?

[@istvanszennai5209]

in theory yes; in practice no, as antimatter vanished in the early stages of the universe. There’s another interesting thing tho: dark matter black hole. While the dark matter theory is controversial, it was shown in recent studies, that dark matter clumps together just like ordinary matter.

[@dennisr1683]

@@istvanszennai5209 Many thanks for the reply. My thought about the antimatter black hole was sort of a crazy thought experiment about how you might be able to convert the mass of a black hole into energy. Again, just in theory, the idea was by combining a normal matter black hole with an antimatter black hole would the combined masses convert to pure energy reducing the mass and gravity or would the gravity hole be too deep and somehow convert the energy back to matter and gravity? I don't really expect an answer but it did seem like a interesting concept. Also - thanks for addressing the idea of dark matter and black holes!

[@istvanszennai5209]

@Dennis R: I think it’s not a wise idea to merge a regular and antimatter black hole; the resulting radiation would be catastrophic to the surroundings (I know it’s sci-fi, but if you watched Stargate Atlantis, Rodney destroyed an entire solar system by similar means).

[@hjs6102]

@@istvanszennai5209 As mass is equivalent to energy, it doesn't matter. If antimatter and matter collides inside a BH, the resulting radiation would stay inside, because it wouldn't change the gravity. But I think, if there is matter or antimatter within a BH it would become radiation anyways because of the strong gravitation tides.

[@istvanszennai5209]

@HJ S: then you misunderstand relativity. Anyway this is a hypothetical thought as we don’t know what happens inside a black hole.

[@dineshsadhwani3717]

2:18 I would not look this happy falling into a black hole

[@michaelseely378]

One more question (cant sleep) if the final parsec problem is indeed true, would the gravity waves moving at each other cancel each other out or have some sort of bounce? Im thinking back to the double slit experiment when particles behave as waves and dont the troughs cancel each other out? Thanks

[@benbooth2783]

I have a big issue with the proclamation that Black holes exist, it's way more subtle than that. A black hole is an exotic astrophysical object that was first predicted to exist by the theory of General Relativity. All properties and physics that we associate with a black hole are predicted by two theories that are incompatible with each other (QM and GR). Nobody has been close to an object that we call a black hole and conducted experiments to verify our predictions. Really, all we can say for certain is that we have found some exotic objects in space and the only thing we can think of that could explain our observations is the blackhole - one of our most extreme predictions which is made in regimes where the physics that made those predictions fail. To then confidently state that these objects are blackholes (as described in our theories) contradicts one of fundamental concepts in science - scepticism.