Where Does Matter That Falls into a Black Hole Go? ▸ KITP Public Lecture by Carlo Rovelli
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- čas přidán 3. 06. 2024
- There have been spectacular advances in our knowledge of the amazing objects in the sky that are the black holes during the last few years. Several Nobel Prizes have recognized this luminous moment for fundamental gravitational physics. All observations beautifully confirm our current theories. And yet, black holes remain utterly mysterious.
We observe a great amount of matter plugging into them. Where does it go? It is a simple question, but there is no consensus among scientists about the answer. Scientists are split into communities that follow different ideas and are often prey of fads and prejudices. The interior of a black hole is a strange place, whose space-time structure challenges our intuition. In this lecture, presented by the Kavli Institute for Theoretical Physics at UC Santa Barbara, Rovelli will describe what we know about the inside of a black hole, and current ideas to make sense of what we do not yet know about these most astonishing objects that fill the universe.
Carlo Rovelli is a theoretical physicist known for his work in quantum gravity. He was born in Italy, has worked in Universities in the United States, France and Canada. He heads the Quantum Gravity group of the Center of Theoretical Physics of the Aix-Marseille University. Rovelli is member of the Institute Universitaire de France, honorary professor of the Beijing Normal University, Honoris Causa Laureate of the Universidad de San Martin, Buenos Aires, member of the Académie Internationale de Philosophie des Sciences. In 1995 he has been awarded the Xanthopoulos Award for “the best relativist worldwide under forty”. He has written global best sellers among which are Seven Brief Lesson on Physics, translated in 44 languages, The Order of Time and the recent Helgoland, on quantum theory. Foreign Policy magazine included him in their 2019 list of the 100 most influential global thinkers.
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Can you please post the Q&A session for the talk? The Q&As are often the most interesting parts of these talks; I’d recommend appending these to the end of all your videos!
so happy I found this video! Thank you!!!!
Thank you.
The q&a would've been wonderful to hear
Nice talk. Thank you for sharing. Landau levels and time dilation factor. Degenerate matter reduced to plank size and quantum many body mixed shared state. Photosphere, neutrinoshpere, last possible stable orbit of an electron. Infalling particles on different paths that can collide. Some particles quantum tunneling through other particles.
But it gets to a question. Probability and predictability. Particle production from quantum foam and gravitational waves and given energy density regimes. Q.F.T. +G
I always believed there is a relation between curvature of gr and condensed matter phenomena. However i did not understand what the conclusions are.
When we say black hole, it seems like we are referring to 2D space. But when we say (sphere whirlpool), it seems like we are referring to 3D or 4D space.
LQG holds the secret of the singularity where the humongous mass is concentrated. Multidimensional singularity creates/emergent energy, mass and therefore gravity etc.
This is an interesting potential solution to the infamous black hole information problem.
As for dark matter, who knows?
Goes into even horizon.
Something spectacular (if not miraculous) happens here, a black hole is converting ordinary material into dark matter! That doesn’t seem to be a straightforward metamorphosis even in quantum gravity.
Depends on the observer - for an outside observer, nothing actually falls into a black hole due to time dilation. Time stops at the event horizon. So any object moving towards a BH will slow down infinitely. For the observer at the event horizon, other than the extreme bending of space time, nothing actually happens - the only direction any light can be received is from the narrow cone exactly opposite of the singularity and the observer falls right through and falls towards the center of the BH. BH is the collection of these mismatched events that never occur in the perspective of the outside observer
@Easwar Sankar - That cannot be quite right, because AT the event horizon, all matter must be moving AT the speed of light *BY DEFINITION*, but Relativity says _that means the particle mass-energy goes to infinity, even for a lone electron._ Since the black hole DOES NOT have infinite mass-energy, it cannot possibly confer infinite mass-energy TO ANYTHING, much less to EVERYTHING. Even if it could, that would mean the black hole mass-energy increased to infinity the first time anything fell in... which is obvious nonsense. Thus the original proposition is proved false. So... What IS the truth?
Assuming I understand what you are trying to say correctly...i would think the object crossing the event horizon is moving at the speed of light "by definition", but only relative to the outside observer. From the objects perspective light should still move at the speed of light even within the horizon relative to it's own frame. Would that mean that a objects mass-energy is also dependent on reference frame? In essence assuring it can never reach infinite density?
Also...time doesnt "stop" to the outside observer...only slow to 99.99...". Eventually the light "imprint" the object left behind will fade as the wavelength stretches to the infrared then on into undetectable ranges.
@@ej2796 Yes, or mostly yes. At the (Schwarzchild) Event Horizon, escape velocity = c, by definition, so it is not just about "outside observers" and their fast reference frame.
@@YodaWhat Objects need to move faster c only to escape the event horizon (impossible). For objects falling in, they can move as slow as you wish. The point I was making is that gravitational time dilation (according to general theory of relativity) would cause the outside observer to see that the clock of the falling object would slow down infinitely and also red shifted so much so that the outside observer would never see the object fall inside.
@@easwarsankar That interpretation is self-contradictory.
Seen from an outside observer all objects that are falling into a BH seem catching the surface of the EH in an infinite time thus all matter could well be distributed only on the surface of the BH and we could see kind of Black Spheres whose interior is empty of spacetime. No singularities .
Can we get to the subject of the video already please
according to Kip Thorne there is no matter in black hole, it is gone it is just curvature. but then how can a black holee have charge? only matter can have charge, or not? and if time does not exist at the singularity then how can it move through time? (let vertical black arrow at 21:11?)
Thorne is like everybody else with a big hammer: they all have nail blindness.
What if there is a sort of convection process that leads dark energy out of black hole.
When you calculate the mass of the Black Hole at the center of the Galaxy, are you calculating Black Hole plus dark matter mass? Or unknown how to tell them apart? Or no evidence of dark matter?
I would think one would calculate the mass based on the black hole’s gravitational attraction on other objects. You can’t see into the black hole, so I don’t think there would be anyway to tell the ratio of normal vs dark matter (thought there are probably ways to come up with a reasonable estimation).
@@timjohnson3913 If the dark matter falls inside the black hole’s event horizon, it can’t come out, so at that point does it matter? Also, shouldnt the center of the Galaxy have an accumulation of dark matter since gravity is only attractive and over time it should settle as the mass in the centern of the Galaxy grows
@@PeterTheSAGAFan Yes, I think it matters if dark matter falls into the black hole as the black hole itself would now have a stronger gravitational influence on objects outside of the black hole. Regarding your 2nd point, most (perhaps all?) of the dark matter is in “halos” that do not include the center the center of the galaxy. We know this because the speed of rotation of stars in the inner parts of galaxies is explained by the gravity of normal matter; it’s typically the stars in the outer ~2/3rds of the galaxy (from a radial perspective) that need the extra gravity from dark matter to explain why they are gravitationally bound to the galaxy.
@@timjohnson3913 yes, you are right about the halo distribution of dark matter. This is part of the reason I don’t believe in it and I suspect something is missing. But, of course, once dark matter is discovered as a particle, modification of gravity or something else, we will know for sure..
Remember how dark matter helped “seed” the galaxies? Yet, it has all migrated to the halo? I am not saying this did not happen. But I would like to see really good evidence that shows this is what happen and what we have..
See Birkhoff's theorem (in spirit, angular momentum spoils the exact relationship). Note that the Schwarzschild and Kerr solutions are *vacuum* solutions. There is no matter in a blackhole, and all the mass (energy) is contained in the curvature of space tip. As Kip Thorne says on youtube: it's a soliton, a stable object made entirely of spacetime.
This black to white hole transition avoids (as it seems) the formation of a Cauchy horizon:
The trapped surfaces of the black hole region below r=0 become anti-trapped above, in the white hole (assuming of course that QG physics allows for a smooth extension through the "Planck" region, near the spacelike hypersurface r=0), so Global Hyperbolicity is retained without the usual problems that Cauchy Horizons bring (instabilities etc).
Have you seen a white hole? I have not.
@@lepidoptera9337 Nobody ever saw a black hole evaporating, either, and, probably, nobody will ever see such a procedure in the foreseeable future.
Astrophysical black holes need a very long time to even start shrinking, so the only feasible confirmation of this (theoretically robust) prediction is to hope for a detection of a small primordial bh.
Until this happens, only analogue gravity experiments are doable.
My previous comment had to do with the plausibility of this proposal by C. Rovelli. Compared with the other solutions of the bh information problem (firewalls, fuzzballs, Euclidean wormholes/ "islands" and the like), it seems much more physically reasonable as an answer to what happens with unitary evolution in that cases.
@@dimitrispapadimitriou5622 But you do agree that black holes are confirmed by observation, I assume?
And what is it with all of you guys and unitary evolution? Your cup of coffee has unitary evolution. Does that make it anything else than an ordinary steaming cup of coffee? So what, in the world, should unitary evolution do to a black hole that it won't do to coffee?????
@@lepidoptera9337 Of course I agree about black holes! There is no doubt that there are millions of them in every galaxy, and if all is known about black hole thermodynamics is correct, then their gravitational entropy exceeds, by far, everything else's entropy in the universe!
About "unitary evolution":
The difference between ordinary processes and gravitational collapse/ evaporation is that black holes eventually shrink (both their mass and their Horizon area) and the Hawking radiation is thermal, so it does not contain any information about the collapsed stuff (besides the conserved quantities like angular momentum, mass, charge).
There are several options :
a) Gravitational Collapse/ evaporation is not unitary, at least for external observers. This option is advocated by Unruh, Penrose, Wald, Thorne and other GR experts.
Maybe they're right after all! In that case QM probably needs some modification.
b) Maybe information is conserved, although not for "external" observers. After all, we, apparently, losing stuff and information all the time as our universe is expanding due to Cosmological Event Horizons. This is the "Baby Universe" scenario.
c) Information is restored to long lived remnants (and, maybe is leaking out slowly).
Rovelli's proposal about black to white hole transition is quite similar,too.
d) Information is released, somehow, with the Hawking radiation, so unitarity is restored, at least for external observers. This last option is advocated, traditionally, by the Strings, Ads/CFT community.
Maybe you already know all these, so maybe you're aware of the difficulties each proposal has.
There are many pros and cons, controversies, and philosophical prejudices in all that, but it's kind of fun!
@@dimitrispapadimitriou5622 A cup of coffee shrinks within days when left alone. It literally evaporates. Now, please tell me why it is important that it evaporates unitarily rather then ordinarily. :-)
If you are so interested in black hole evaporation, then why are you not in the lab watching a cup of coffee all day long?
I can tell you why: because you already know that you can not learn _anything_ by doing that. From a physics point of view one also can't learn anything about gravitation from black hole evaporation. It's a purely theoretical speculation without any experimental or observational application. It's basically just a formula looking desperately for an application. Nothing more, nothing less.
To me that's boring and a ridiculous waste of paper. There are many things that one can learn about gravity by observation of black holes, but the unitary evolution thingumbob is not one of them. That's just "not even wrong" theory nonsense.
Matter falling into a black hole asymptotically approaches the event horizon and never actually enters the black hole because from the point of view of us, distant observers, the black hole never forms. In short, black holes only exist in the far infinite future but not in the present, so the information paradox simply does not exist as neither black holes
Well, the black hole exists. What is questionable is whether one can realistically talk about structure "below" the event horizon. For an outside observer a black hole is like a weakly radiating thin shell, as far as we know.
Neutron decay cosmology. The neutrons which invert at moment of neutron star collapse into black hole are transported via marangoni current to the lowest energy density points of space where they travel 14ish relativistic minutes then decay into amorphous atomic hydrogen. This decay causes a catastrophic volume increase of 10^14 times. This is expansion. This process is Lambda and why universe is in perfect balance. This amorphous hydrogen is much of dark energy. The galactic disk problem can be fixed I think w tweak to Friedmann matrix. Thixotropic fluid not perfect fluid.
The event horizon and associated gravity well are the photons trapped both at Planck frequency over their own gravity but trapped over the larger sphere that we see.
The other side of EinsteinRosen bridge is this universe
I have full topology worked out. Anyone wants to chat and help me out w this…… :)
OK that enough I don’t care about how many millions of copies of this and how many shades of gray if you can’t get to the subject that you’re supposed to be doing the video on you’ll get left behind by
No such thing as a black “hole”
A black hole (misnomer) is an collapsed highly dense star 🌟 which pulls everything into itself from all directions due to the intense gravitational force of the collapse…it is more like a highly dense black ball … the event horizon is where everything is pulled in…and Hawking radiation is the energy emitted from the intense collapse…we have two very proven dualities in physics: Space/time and Energy/mass…the latter is how black balls work
But why does one get singular solutions in general relativity? What prevents the matter from the further collapse in a "dense black ball"?
I see black holes as being multidimensional hypersurfaces...
@@waynedarronwalls6468 Black balls
The lack of a reasonable answer to the question would suggest that all the physical-mathematical model about BHs is flawed. Rovelli's witty proposal of white holes is clearly too extreme and unreasonable.
God might or might not play the roulette, but he certainly would not allow something or someone to weigh 1 billion solar masses, feed on 20 billion worth more of stars, and then forget what to do with all the stuff and allow it to just 'evaporate'.
So let's go back to the start and get a clean blackboard..
Rovelli is bullshitting again. He didn't answer the question where the matter goes. ;-)