international group of theoretical physicists

We are the international group of theoretical physicists assembled in Stockholm to work on the paradoxes of black holes, hawking radiation, and the deep mysteries of the Universe. Ask us anything!

We’re here at the Nordic Institute for Theoretical Physics (NORDITA) ready to take your questions.

We spent this past week working on some of the most challenging questions in theoretical physics. Last Tuesday, our colleague Stephen Hawking presented to us his latest idea to solve the growing paradoxes of black hole physics. We discussed this, and many other ideas, that may light the path towards a deeper understanding of black holes… and perhaps even point us towards the holy grail of physics. The so-called, “Theory of Everything”!

Could black hole Hawking Radiation be a “super-translation” of in-falling matter? Why does the Universe conserve information? Is “information” a physical object or just an idea? Do collapsing black holes bounce and become a super slow-motion white holes? Can black holes have an infinite amount of charge on their surfaces? Or, could black holes not exist and really be “GravaStars” in disguise? We’re trying to find out! Ask us anything!

Special thanks to conference organizers Nordita, UNC-Chapel Hill, The University of Stockholm, and facilitation by KTH Royal Institute of Technology.

AMA Participants so-far:

  • Malcolm J. Perry
    String Theorist
    Professor of Theoretical Physics, Cambridge University
    Chief Collaborator with Stephen Hawking and Andy Strominger on new idea involving super-translations in Black Hole physics.
  • Katie Freese
    Director of The Nordic Institute of Theoretical Physics
    George Eugene Uhlenbeck Professor of Physics at University of Michigan
    Founder of the theory of “Natural Inflation.”
    Author of first scientific paper on Dark Stars.
    Author of “The Cosmic Cocktail: Three Parts Dark Matter.”
  • Sabine Hossenfelder
    Assistant professor for high energy physics and freelance science writer
    The Nordic Institute for Theoretical Physics (Nordita)
    Blogs at
  • Paulo Vargas Moniz
    Chair of department of Gravitation and Physics
    University of Beira Interior, Portugal
    Author “Quantum Cosmology” Vol I, Vol II.
    Author of “Classical and Quantum Gravity”
  • Carlo Rovelli
    Theoretical Physicist
    AIX-Marseille University
    Author “7 Brief Lectures in Physics”
    Co-founder of Loop Quantum Gravity.
  • Leo Stodolsky
    Emeritus Director
    The Max Planck Institute
    Originator of methods for detecting dark matter in Earth-based laboratories
  • Francesca Vidotto
    NWO Veni Fellow
    Radboud University Nijmegen
    Author of “Covariant Loop Quantum Gravity.”
    Author of the first scientific paper proposing Planck Stars
  • Kelly Stelle
    Professor of physics
    Imperial College of London
  • Bernard Whiting
    Professor of Gravitational and Quantum Physics
    University of Florida
  • Doug Spolyar
    Oskar Kelin center fellow of cosmology
    Co-author of first paper on Dark Stars
  • Emil Mottola, particle cosmologist
    Los Alamos National Laboratory
    Author of first paper on GravaStars
  • Ulf Danielsson
    Professor of Physics
    Uppsala University
    Leading expert of String Cosmology
    Recipient of the Göran Gustafsson Prize
    Recipient of the Thuréus Prize
  • Yen Chin Ong
    Theoretical Physicist
    Nordita Fellow
  • Celine Weimer
    The Un-firewalled
    Queen of the Quark-Gluon Plasma, the CMB Anisotropies, and of the First Baryons
    Queen of Neutrinos
    Khaleesi of the Great Universal Wave Function
    Breaker of Entanglement
    Mother of Dragons
    KTH Royal Institute of Technology
  • Tony Lund
    “Through the Wormhole: With Morgan Freeman”

Proof: Director and Conference Organizer Katie Freese: Science Writer Tony Lund:

If you could rename “black holes” based on what we currently know about them what would you call them? And why?

[Tony Lund] Based on what I’ve heard this week…

  • If Malcolm is correct: “Confounding Sasquatch Spheres.”
  • If Emil is correct: “Super Heavy GraviStars”
  • If Francesca is correct: “Quirky Flippy Bouncy Whitey Blacky Ball”
  • If Jim is correct: “Cosmic Oreo.”
  • If Stephan is correct: “Black Holes — stop worrying about it.”
  • If Joe is correct: “Fiery Death Ball”
  • If Samir is correct: “Deadly Fuzz Ball.”

There are more… I’ll try to think of them!

Someday, I hope each of these will get their own movie poster!

[Emil Mottola] Well, one of the possibilities we discussed this past week is that ‘black holes’ might not be ‘holes’ at all, in the sense of a singularity or ‘sink’ into which everything would be infinitely squeezed out of existence. I proposed (with my collaborator Pawel Mazur) that there might be a non-singular interior condensate surrounded by a thin shell, membrane or phase boundary instead of an event horizon. This non-singular configuration we call a gravitational condensate star or gravastar.

[Katie Freese] An interesting question. It made me think, and in the end I decided I like the name “black hole.” It really does capture the immense gravitational pull of these objects, that on the whole prevents things from escaping.

It is true that Stephen Hawking showed that “black holes aren’t black.” What is meant by that: Before the 1970s, it was thought that anything entering the black hole would be lost forever. More accurately, anything getting closer than the “Event horizon” would never be able to get back out, even if it were moving with light speed. The event horizon is the point of no return. However, then Stephen discovered Hawking radiation. At the event horizon of the black hole, pairs of particles and antiparticles are created. One of them falls back into the black hole but the other emerges. Because of this radiation coming out of the black hole, black holes eventually evaporate. It takes some time for this to happen: a black hole weighing as much as our Sun takes 1075 years to evaporate.

“Black” usually means nothing can get back out, yet because of Hawking radiation, it does. So in that sense “black holes aren’t completely black.” But I still like the name.

[Malcolm Perry] The name black hole was first coined by John Wheeler in 1967 to describe a region of spacetime into which one cannot see. Nothing has changed between then and now. I think black hole is still a perfect time description since Hawking radiationcomes from near the black hole and not ffor either inside it or its surface. Black holes are still regions of spacetime you cannot see into, or if you are inside one they are regions of spacetime you cannot escape from.

[Francesca Vidotto] A black hole is defined mathematically by an “event horizon” that, once is formed, stay there forever. Physicist are working on the notion of an horizon that forms, stay there for a while and then disappears: the technical term for this is “trapped surface”. So what is a black hole with a trapped surface instead of an event horizon? Maybe I will call it just a “quantum black hole”, because are quantum-gravity effects that transform the horizon into a trapped surfaces. Fir myself, depending on what I like to emphasize, I may call it “Planck star” or “exploding black hole” or “bouncing black hole”… but that’s my taste!

Can you explain some of what you’re doing in laymen’s terms?

[Bernard Whiting] Gravity explains how heavenly bodies, such as stars and planets, hold together, while quantum mechanics explains what are the properties of ordinary matter. We are trying to understand how these two theories can work together when stars become very compact and collapse to form a black hole. So far, our understanding suggests that black holes should not remain black, but should eventually evaporate. This leaves us with a puzzle about how information of what formed the black hole can still be preserved after the end of the evaporation. That is the puzzling problem we have been discussing all week.

Why is it important that the information is preserved after a black hole evaporates? What exactly is this information?

[Bernard Whiting] As Francesca Vidotto explained in answering another question, a theory in which information is not preserved is usually considered to be problematical from a physics perspective. Normally, quantum mechanics does preserve information very well, but there is a potential problem when black holes are introduced. In 1976, Stephen Hawking described this problem in a paper entitled “Breakdown of predictability in gravitational collapse” published in Physical Review D. Ever since then, there has been a quest to discover a theory in which this breakdown would be absent. That topic was the focus of our meeting here at Nordic this week.

[Doug Spolyar] The information we are concerned about with black holes is what goes into making a the black hole in the first place. Classically, There is no way to know whether a black hole was made of TVs, Anti-Matter, or more conventionally a collapsing star. Quantum Mechanics suggest the information of the initial state can not be lost. If the information is indeed lost then Quantum Mechanics breaks down.

It could be matter or energy. You can’t just make information disappear out of the universe, it has to go somewhere.

[Bernard Whiting] Yes, you cannot just make information disappear. It takes some some energy to do a calculation and create a piece of information. In her talk at this conference, Fay Dowker showed how to replace some of our usual energy arguments by arguments about entropy instead. Nevertheless, energy and entropy are not the same thing.

So here is one of the problems we used to help us understand all this. Suppose you write a message on a piece of paper, and then burn the paper with the message on it. We would argue that all the information in the message must be contained in the motion of the molecules and heat radiated from the burning paper. But you need never fear that someone would be able to gather the molecules and heat photons and reconstruct your message, so the information in your message would be effectively lost, and even safely lost if that is what you intended.

So what are some theories – once again in layman’s terms (as much as possible) that you’ve been discussing, if you’re allowed to share?

[Tony Lund] One of the ideas presented that I quite enjoyed was Carlo and Francesca’s theory that when a star collapses, it does not form a black hole. It actually ‘bounces’ over a VEEEEEERRRRYY long period of time (we’re talking 10 followed by 50 zeroes or higher, depending on the mass of the initial star. It’s a very speculative theory, and based primarily on ideas found in “Loop Quantum Gravity” which is also speculative) However, I found this idea compelling because it challenges us to consider the possibility that the Universe is playing a trick on us! What we think is one thing, may actually turn out to be another in disguise.

Another excellent talk argued that Black Holes are actually “GravaStars” — in essence, an EXTREMELY dense star.
(I may also be biased because Emil’s math was entirely classical and I didn’t have to pretend to understand it ;))

[Bernard Whiting] It is surprisingly simple to name those theories, namely Einstein’s theory of gravity and the theory of quantum mechanics, which explains the properties of ordinary matter, such as tables and chairs. At their core, these theories are both rather complicated. Nevertheless, the reason you fall down toward the ground (and not just float as if in free fall) is due to the influence of gravity, the lasers in your CD player were developed through our understanding of quantum mechanics. And there is one more thing. Stephen Hawking’s discovery that black holes can evaporate meant that they could also be described as having a temperature. Temperature and entropy (which measures information loss) are both notions in thermodynamics, which is believed to apply to all physical systems. So that too is always part of our discussions. Your AC or heat exchanger work by using thermodynamical principles and, of course, energy.

What tools could help in your analysis? That is, how could more relevant data be collected regarding the nature of black holes and anything else related the the question? Satellites or probes with particular sensors? More powerful telescopes? The LHC?

[Bernard Whiting] Well, our discussions are rather theoretical, and the main tools we use are quite mathematical. As mentioned in another answer, the Event Horizon Telescope is an observational instrument that help us verify that the physical properties of black holes are as we think. And if they are not, that would be very exciting for us to attempt to understand.

[Kelly Stelle] There are a number of ongoing and upcoming observational programs that can shed very important light on the nature of black holes. For one thing, gravitational radiation has not yet been directly observed. There is an ongoing search for this in a series of gravity wave observatories: LIGO (Hanford WA an Livingston LA in the USA). GEO 600 in Germany, the Virgo Interferometer in Italy and a number of upcoming labs are actively involved in this. Gravitational radiation has been indirectly observed in the binary pulsar (Hulse & Taylor got the Nobel Prize for this, see, e.g. But direct observation of gravitational radiation would be extremely important.

Another observational program of importance for understanding black holes will be the Event Horizon Telescope (, which will be designed to observe the shadow cast by the horizon of the black hole Sagittarius A*.

How can we demonstrate that our entire universe is not part of a black hole?

[Francesca Vidotto] This is indeed a studied possibility. Or better: we study the horizons for black holes, but we know that in an expanding universe there is a cosmological horizon. Understanding the properties of black holes horizons can help us to understand cosmological horizons.

What are some of the most important physics concepts that you think people should know about?

[Katie Freese] There are four forces that describe everything in nature: electromagnetism (the most important one in our daily lives); strong interactions that keep our nuclei from falling apart; weak interactions that are responsible for some types of radioactivity; and gravity which makes you fall off cliffs. We understand all of them except gravity. That is why black holes and cosmology are such important testing grounds to learn from… gravity entirely dominates there! There is a good classical theory of general relativity describing gravity but we don’t know how to merge it with quantum mechanics. Quantum gravity is the big unsolved problem of theoretical physics. If Einstein couldn’t get it, then … can we?

Does that final concept of “if Einstein couldn’t do it…” Have some discernible impact on the effort to understand something he couldn’t?

[Francesca Vidotto] Yes, it does! Einstein had a fantastic sense for physics, understanding where there were the real problems. So if Einstein thought that something was valuable to struggle to understand, we have to take it seriously… that’s why we have to follow the path of Einstein and try to build a theory of quantum gravity! I like to think that Einstein would have liked what we are doing in Loop Quantum Gravity 🙂

[Kelly Stelle] Less than one might think. Einstein spent the last years of his life trying to develop a unified theory of gravity and electromagnetism. The problem was that he didn’t know enough at the time to make this a reasonable thing to try. One needed to know about the relations between electromagnetism and the weak nuclear interactions to set the pattern the became what is now known as the “Standard Model”, which successfully unifies electromagnetism and the weak interactions. Nowadays, we have a much deeper understanding of that stage of unification, and can look forward to attempts to bring in the strong nuclear interactions. (Weak interactions are involved in relatively slow processes like neutron decay; strong interactions are what bind protons and neutrons together into atomic nuclei.) So the current approach is much more hierarchical. Einstein was extraordinarily good at abstract thinking, and he managed to create the general theory of relativity largely by pure thought and calculation. That is what we call the “top down” approach, and indeed, it is one of the ways that theorists try to make progress. But pretty much everybody realizes that one can’t get all the way to a fully unified theory including gravity just by pure thought. One also needs the “bottom up” approach, working from the details of what is known about the various fundamental interactions of particle physics. So most theorists recognize that some combination of the “top down” and “bottom up” approaches is going to be needed. That combination would be rather un-Einsteinian.

Were most of the discussions at the conference were about the notion of “information”?

[Francesca Vidotto] In the past century you would have heard physicists saying “everything is energy”, now you are more likely to hear them saying “everything is information” or as the good old Wheeler would have said: “it from bit”. Well: it is not really that information makes up things, in the same way that energy does not make up things… but they are extremely useful concepts to describe reality. For instance, in the relational interpretation of quantum mechanics, the theory can be reconstructed by starting from just two principles about information. When discussing the physics of black holes, most of the problems can be phrased in terms of understanding how information behaves. A black hole is characterized by a horizon, behind which information get lost. A theory that does not preserve information is not well defined, so we need to understand how to recovered the information. But this require a theory of quantum gravity 🙂

As someone working to get the word out about scientific discovery, what are the biggest challenges you see of reconciling complex science and the understanding of the common person?

[Tony Lund] Ah, yes. It can be quite hard sometimes because some of the most beautiful ideas in cutting physics are difficult to explain in less than 20 minutes.

I tried once to explain the Anti-De Sitter Conformal Field Theory Duality (“Ads/CFT”) to my Mother’s kindergarten class. I think one of them got it, but she may been just been eagerly staring at the cookie jar.

What’s so pleasurable about attending conferences like these, is that Physicists use the same neurological tools as laymen to try to understand the mysteries of the Universe… our brains are very good at understanding concepts related to motion, so Physicists often discuss new ideas by describing how imaginary particles, or mathematical objects, or even calculations themselves, “move” in an abstract space. For example, its useful to think about equations “going to infinity” rather than resulting in infinity.

So, the layperson uses the same regions in their brain to understand complex processes, they just don’t have the massive lexicon of terms and concepts that these cats do.

So, when I’ve only got 2 minutes to explain”Ads/CFT” on TV, I always try to think about what’s literally moving in that space, and how to visualize it.

What would be the real world implications should a “theory of everything” be developed? Are you hopeful of it ever becoming a reality?

[Katie Freese] I just did a BBC radio interview on exactly that question last Sunday! Here is the podcast link.

To a physicist, the “theory of everything” is the unification of the four forces I described a minute ago. We know the Universe is expanding from a very hot early Big Bang. So, if we look backwards in time, it’s like going to hotter temperatures. The forces start to unify. First electromagnetism and weak interactions unify to electroweak (this is tested up the wazoo in particle accelerators and lots of people got Nobel Prizes for this one). Then as you look farther back in time to hotter temperatures, we are pretty sure there is a Grand Unified Theory (takes GUTs) that brings in the third force, strong interactions.

OK but what about gravity? That is the tough one. In fact that is what defines the Big Bang… the limitations of science as we know it. We don’t know how to unify gravity along with all the other three. Sure, we will get it someday — the unification of all four forces. Right now String Theory is the best bet (but it would be nice if there were one single prediction). Anyhow there will definitely be a “Theory of Everything” as defined in this physicsy ways someday. I wish my computer would stop trying to fix my typing. Yes I do mean Physicsy.

Next question: what is it good for? WE SHALL SEE. It will change your life. That’s why we are paid to think. Because somebody will definitely find some application that will blow your mind. I can give plenty of examples of serendipitous discoveries, like Bell Labs funded fundamental science that had nothing to do with telephones and what came out of that? the transistor. Imagine life without the toy you are on right now (the computer). OK ‘nough said. BTW on the subject of getting paid: “I think, therefore I am paid.” Did you catch the reference to Descartes?

How do physicists determine whether information escapes black holes or not?

[Leo Stodolsky] Good question. That’s what we’ve been arguing about all week. It’s complicated by the fact that there’s no simple general definition of “information”, like there is, say, for energy.

[Malcolm Perry] In our present state of knowledge, one is really talking about thought experiments rather than practical measurements. The laws of quantum mechanics say the time evolution of a system can never involve information loss. Yet if a black hole forms and then completely evaporates, then nobody has till now been able to convincingly demonstrate how information can be preserved in this process. THe discovery of super translation hair for black holes may well provide such a mechanism.

[Yen Chin] To add on to what Malcolm has replied: The information loss problem is, at least so far, a discussion about whether information is lost in principle. Consider, for example, the burning of a book. All the information within is seemingly lost, and it would be practically impossible to actually recover the information. However no one really thinks that information is really lost in such a process. The question for black hole physics is whether an evaporating black hole is like a burning book at all. In classical general relativity, a neutral non-rotating black hole is only characterized by its mass. So if one starts with a hydrogen gas cloud that collapses to form a black hole, and compares it with another black hole formed from some other stuff— the two black holes would be exactly the same [if they have the same mass]. Information loss means that unlike the burning book, we could not recover the initial state of the holes, even in principle. However, even if information is not loss, but is encoded in the Hawking radiation, it would be scrambled beyond recognition — we may need to collect all the Hawking radiation and try to decode the information — not an easy thing to do (just like recovering information of a burning book!) It may take a time scale far longer than the lifetime of the black hole to do this (see, e.g. the work by Harlow and Hayden)].

What about something like Shannon entropy?

[Leo Stodolsky] Yes entropy is a traditional measure of “information”. The trouble is here we’re looking for something where we can say it’s in this or that place or space-time location. The usual entropy is not in a definite place–it’s not ‘local’. But General Relativity, which is what we’re dealing with in the Black Hole problem, uses exclusively local quantities.

When do you guys think an exciting breakthrough may happen the average joe would understand? I’m thinking along the lines of Star Trek warp drive, replicators, transporters. In short, I’d love to see some cool stuff before I die, please make that happen.

[Yen Chin] I’d also love to see some cool stuff like hyperdrive and wormhole travel. However, it is not likely that these would actually happen in our life time, sorry 🙁 It is not even clear that these are even possible at all — these faster-than-light travels typically requires very exotic material to make them stable and so on, and there are many mathematical results that make this very unlikely. A nice popular science book you may want to read is “Time Travel and Warp Drives: A Scientific Guide To Shortcuts Through Time And Space” by Everett and Roman.

[Bernard Whiting] We think the detection of gravitational waves would be cool. They are predicted by Einstein’s theory of gravity but, so far, their effects have only been seen indirectly, such as in the slow spiral of two neutron stars towards each other as energy is carried away by the gravitational waves. Next month, the upgraded LIGO gravitational wave detectors will begin taking science data again. We look forward to their success.

At our conference, we are looking forward to another breakthrough. For forty years we have understood that black hole horizons can have an entropy, and we have thought of this in terms of them hiding the information about how the black hole was formed. At out meeting, Stephen Hawking and Malcolm Perry proposed a new way for how the black hole horizon might encode that information. We will consider it a great achievement if we can explain how that information may be carried away from the black hole (and hence not lost) as the black hole evaporates. That’s the really cool result all of us at the conference trying to understand.

Could time be cyclical?

[Doug Spolyar] Maybe the Universe is cyclical if you are Paul Steinhardt

[Malcolm Perry] One theory of cyclic universes has been proposed by Neil Turk at the Perimeter Institute and Paul Stein hard at Princeton University. A description of their theory can be found at on the Wikipedia under the entry “Cyclic Model”

From my limited understanding a black hole forms from the supernova of a very massive star, how are the supermassive black holes that are putatively at the core of all galaxies formed (theoretically)? From a ‘galactic collapse’? Or are they a different object from normal black holes (beyond being huge).

[Katie Freese] The Universe is full of supermassive black holes, and we are not sure how they form. This is known as “The Big Black Hole Problem.” Every galaxy has one at its center; for example there is a black hole weighing four million Suns at the center of our Galaxy (the Milky Way). More surprising is the fact that there are even more enormous BH (weighing ten billion Suns) soon after the beginning of the Universe.

So how do these form? There are competing theories. The first stars may be responsible for the progenitors of these big beasts. Once these early stars die, they collapse into black holes; then these black holes could merge together to make ever bigger ones. In the standard picture of first star formation, however, the stars are just too small to get this to work. It’s hopeless to try to get them to merge quickly enough to explain the very early supermassive BH.

So my collaborators and I had a new idea: Dark Stars. In fact, one of my collaborators is sitting in this room at Nordita right now also answering questions. Dark stars are stars that are made up almost entirely of ordinary hydrogen, but the power source is dark matter annihilation instead of the usual hydrogen burning fusion.

That leads me to the dark matter problem. Most of the mass in the Universe is NOT ordinary atoms. Instead, it is something not yet identified. We have known of the existence of dark matter for 80 years (from the way it pulls gravitationally on other objects) but we don’t know what is. I don’t want to go too far afield in this answer, but it is this dark matter that could power the first stars, instead of fusion. These Dark Stars can grow to be supermassive themselves, up to ten billion Suns, so that they will eventually collapse to supermassive black holes.

Right now the idea of Dark Stars is still speculation, but I’m excited to say that the James Webb Space Telescope (JWST), which is NASA’s $10 billion dollar sequel to Hubble Space Telescope, will launch in 2018 and I’m hoping they find these early Dark Stars.

[Emil Mottola] This is a very interesting question, which is a subject of active research. We now know that just about every galaxy (where we can tell) has a supermassive object at or near its center (which may or may not be a ‘black hole’). This challenges our understanding of structure formation in cosmology, since there doesn’t seem to be a way to grow such enormous objects–billions of solar masses in some cases–from the ‘seeds’ produced -it is presumed-by inflation. There isn’t enough time in the age of the universe to grow something that large unless (perhaps) they were produced some other way. But how? We don’t know the answer to that puzzle yet.

Has there been any progress made towards the resolution of the firewall paradox?

[Francesca Vidotto] Physicists love paradoxes: these are where fun becomes! More precisely: paradoxes, that in physics often arises as an infinity that takes away predictability from our equations, show as the limitation of the theory we are using; therefore some new theory should take place before the old theory breaks down. For firewalls, this means that quantum gravity should take place before they appear. And we know exactly the time when they appear: it is about the time of half of the time of Hawking evaporation. The idea of Planck stars is that an effect from non-perturbative quantum gravity takes place before we reach that time. So no firewalls there!

I noticed the title “Through the Wormhole” within the post description. Does this mean that teleportation is a real possibility?

[Francesca Vidotto] I think we have to distinguish the two things… Yes, teleportation is real! We do realize teleportation using entanglement, one of the basic features appearing in quantum mechanics. Well: we do it just for a qbit (a unit of information), not for Mr Spock… but yet we are doing great experiments, like the one between the observatory in one island and another in another island in the Canaries, or maybe soon with the instruments sent in space. For wormholes, the story is different. Wormholes were postuled on the basis of general relativity by Einstein and Rosen, and the idea was later developed by Thorne. General relativity may allow it, but not necessarily… I personally tend to think that wormholes are not realized in nature, but stringy physicist like to use wormholes to describe the quantum properties of spacetime…

Would it be possible for any of you to explain the concept of super-translation and how it plays into the physics of black holes?

[Carlo Rovlie] Here is a zero-level version of what a “super translation” means. Take a big sphere and imagine many clocks on it, say all beating at the same time. Now make one of the cocks miss a bit. So now that particular clock is a bit later than all the others. Well, this change is (an elementary version of) a “super translation”. It is a “translation” because it is like “translating in time”. But it is a “super” translation because it does not translate all the clocks (like normal time translation would), but only some of them. Now it turns out out, or at least so suggest Malcolm and Stephen, that the “super translations” might code the information about how things fall in a black hole…. but Malcolm can certainly explain this part better…

[Malcolm Perry] The original idea of a super translation relates to how to detect gravitational radiation. Imagine a collection of satellites orbiting the earth. As you look into the sky, these satellites will formake a fixed pattern. Now suppose that a burst of gravitational radiation passes through the system. The pattern the satellites makes will change. The mathematical description for this change is called a super translation. What is new is the discovery that can extend the idea of a super translation to the horizon of a black hole. Then the super translation will give information about what has fallen into a black hole. In this way, one can determine what goes to make up the black hole and hence resolve (or perhaps help to resolve) the black hole information paradox

Do you guys have links to all the talks from the conference?

[Malcolm Perry] Look at the Nordita website next week;

What is one big breakthrough you think might come up in the field of theoretical physics in the next couple of years?

[Emil Mottola] This is always hard to guess. Surprises can come from anywhere–the LHC or astrophysics being the most likely. In our universe there are a lot of very high energy events (like gamma ray bursters) that are not well understood. The nature of dark matter and dark energy are still unknown, but detectors keep getting better and observations keep going deeper, so a breakthrough is possible in a number of areas, including what really are ‘black holes’?

How can we say that earth is not at the center of the universe,when we haven’t yet found the boundaries of the universe?

[Leo Stodolsky] Will answer your question with a question. Which city would you say is the centre of the (surface of the) planet?

[Katie Freese] It’s very reasonable to imagine that the Universe is infinite. That means that, no matter direction you go, there is always more stuff. Then there cannot possible be a center.

If I follow that thread… if the Universe really is infinite, then everything possible is happening somewhere out there. Way out there is another Earth that is exactly like this one, with another person exactly like you, but that one didn’t ask the question you just did. It’s a strange thought! Check out Brian Greene’s book Hidden Reality which gives a beautiful description of all types of parallel universes.

[Doug Spolyar] Actually, we might be at the center of the universe! One possible explanation of the Dark Energy is that we live in a LTB Universe, but Data more or less rules out the possibility due to constraints from the CMB…Copernicus wins again!’dovich_Effect_Power_Spectrum

Could there exist another, smaller universe inside the event horizon of a BH? Like if our Universe started with some massive BH, that is continually is getting fed by a higher level universe, would that not explain the energy paradox and explain “dark energy”?

[Yen Chin] I don’t have any comment about the dark energy part of your query, but… yes, it is possible that there is another universe inside a black hole. In fact, it does not have to be small at all! Due to nontrivial spacetime curvature, it is possible to have a very large space inside a relatively small black hole. That is to say, you can’t infer the volume of a black hole from how big it looks from the outside. However, it is not clear if this helps with resolving the information loss issue at all — need more research!

[Emil Mottola] There have been speculations of that kind, but no one has been inside an event horizon of a BH –or been to one at all. So no one knows for sure what’s inside.

What is the most far out theory that really could be plausible?

[Doug Spolyar] I think actually its data that makes us go after plausible theories…New Weird phenomena is actually the source. Quantum mechanics goes against our common sense understanding of the universe, but data forces us to accept quantum mechanics…So the adage is True: Fact is weirder than fiction.

Is “information” a physical object or just an idea? Could you expand on this more? My first thought was along the lines of: “well its information if it can be measured, which would mean it must be physical” Also, I recently graduated with my B.S. in Astronomy and B.A. in physics. What are some of the best sources to learn more about this?

[Emil Mottola] It’s a confusing subject. If you have a B.A. in physics you might have taken a first course in quantum mechanics. Then you know that there is such a thing as a Hamiltonian and a unitary operator of time evolution. In a black hole singularity the evolution is apparently non-unitary. This is inconsistent with basic quantum theory. That is what people mean by loss of information.

So the ending of interstellar… probably would not have gone down like that huh?

[Emil Mottola] Probably not. A good representation about time dilation though–with Cooper leaving while is daughter is young and returning when she’s an old lady.

If nothing can escape the gravity of a black hole, how do they emit radiation?

[Yen Chin] Hawking radiation comes from the quantum field outside the black hole, not from the inside.

I’ve been reading through this thread and seeing phrases like, “everything is information,” and, “information can’t escape a black hole.” Could you explain a little bit some of the distinctions you mean when talking about information vs just energy or mass? Can you quantify information?

[Emil Mottola] This is a good question. If you write a note on a piece of paper, then burn the paper, where has the ‘information’ in the message gone? According to standard physics taught in textbooks, it isn’t really ‘lost’ but contained in the way the smoke or ashes are arranged finally, so practically impossible to retrieve, but not lost in principle. In the BH case the puzzle seems to be that there is no way even in principle to get anything out of a singularity.

What were all of your undergraduate majors? Were any of you interested in something nonscientific when you first went to university?

[Yen Chin] I was first interested in biology/life sciences when I was in high school, and contemplated various majors including forensic pathology, entomology, and zoology! Then I found out that I wasn’t that good in chemistry… I ended up with a major in mathematics. Initially I wanted to go into pure mathematics (math is beautiful!), but my childhood interest in astronomy caught up and so I changed to [astro]physics during my PhD. At one point in high school I also seriously considered going into Chinese study or something like that, instead of the sciences. I think it is good to explore various interests — the universe is so big, and life is so short, it is a bit of a waste not to try somewhat different things at least once 😉

What can regular folks do to help convince politicians to increase funding for scientific research?

[Kelly Stelle] Vote for scientifically literate politicians. In the US, there are very few members of Congress or the Senate with a scientific background. Rep. Rush Holt (now CEO of the American Association for the Advancement of Science) was one of just two physicists in the House of Representatives. Support for science did not use to be a partisan issue — in the past, Republicans used to be even more supportive of scientific research than Democrats. But in the current highly polarized situation, that no longer seems to be the case.

Do you guys ever be like- “Aghh! It’s very difficult to explain complex stuff to the general people” ? If so what do you guys do?

[Katie Freese] It is true that mathematics is a language (like Swedish) and if you know it, it opens up new worlds. But once we have found results, we can usually find ways to explain the ideas in words. IN fact, it’s our responsibility to communicate what we are doing with everybody. Artists put paintings in museums, and we write books or give lectures or do an AMA to put ideas out there to the public. It’s important. That is why we are all gathered here today.

Considering there is no actual proof that suggests string theory is the actual world model, what do you say to those that claim that what you guys are proposing is based more on faith than science?

[Katie Freese] Science must be testable! Right now string theory has beautiful theoretical motivation in that is does allow unification of quantum mechanics and gravity. But it makes no predictions yet. That is NOT acceptable in the long run but for now people are pushing forward the theory in the hopes that we can test it down the road.

In the 1980s everybody expected that there were would be a unique string theory and by now we would have tested it. What happened instead is that it turns out there are 10500 or so different vacua of string theory, and in principle our Universe could be in any of them. This leads to the multiverse theory, where there are large numbers of universes. However we couldn’t exist in most of these universes, because their properties aren’t compatible with human life. So now people use an “anthropic” principle to try to figure out what fraction of these universes look like ours.

I am not a fan of the multiverse. Physicists have major disagreements about that. There are very smart people on both sides of the argument. To me, it becomes philosophy and we are reneging on our jobs as scientists, which is to find physical laws that make testable predictions for the real world.

Since image can be captured only if light is emitted back, how posibbly you are taking the picture of the black hole?

[Emil Mottola] One can look at light (meaning radiation at any wavelength) is refracted or bent around a black hole. If there is an interior different from what is generally believed on the basis of classical general relativity, then light might possibly even pass through. Obtaining such images at sub-mm wavelengths may be possible in the next few years with the Event Horizon Telescope.

If an anti matter black hole and a matter black hole collide, what will we see? Another black hole?

[Kelly Stelle] The distinction between matter and antimatter relies on a symmetry that is not respected by black holes. So when matter or antimatter fall into a black hole, the black hole grows a bit, but otherwise there is no difference between the two cases. This answer refers to the original absorption of matter into a black hole. Just what happens after eons of time and the black hole evaporates is another question: is there a memory of the original stuff being matter or antimatter. The discussion on that topic is an important part of the current discussions in the field.

Can you help me understand how elementary particles come together to form objects? I’ve always been very interested in theoretical physics, but I simply don’t understand how particles with no mass can come together to form objects — let alone how something with no physical presence can exist.

[Kelly Stelle] Massless particles travel at the speed of light, and basically describe phenomena that we call “forces”. Light, whose particle aspect is called the photon, is an example. Particles that clump together to form “objects” basically need to have mass. They may be acted upon by forces, described by massless particles, however, so the forces binding massive particles together need to be taken into account as well. The high-energy protons at the LHC are an example. They are, in one picture, composed of three massive quarks (up, up & down). But they are also bound together by the strong nuclear force, which in particle physics is described by a massless gauge particle theory. The strong force quanta are called “gluons”, so protons are really a bound state of quarks with the binding done by massless gluons. The whole package, the proton, gets its mass from a combination of the masses of the quarks plus the mass equivalent of the gluons’ energy.

If quantum entanglement happens over vast distances, does this violate general relativity? If so, how does string theory solve this?

[Emil Mottola] Quantum entanglement does not violate General Relativity in that it could have been prepared in the past not violating causality. But Gen. Rel. is still a classical theory in which quantum physics is not really taken into account. String theory is a quantum theory but does not tell us much about spacetime or black holes (at least not yet).

If time dilation is infinite at the event horizon of a black hole, then how does anything get past it? shouldn’t everything that falls into a black hole be stuck at the even horizon?

[Tony Lund] Time dilation is a Relativistic phenomena, so the flow of time changes relative to the observer.

Suppose Mathew Mcoughney is sitting in his space and he’s getting real tired of Matt Damon’s shit. So, he throws Matt Damon into a black hole. If you’re Matt Damon, you just float along into the black hole and nothing special happens… eventually, you get deeper and deeper and gravity becomes so intense that you rip apart.

But Mathew, sitting outside the BH, sees that time is getting slower and slower for Matt as he approaches the event horizon. It gets so slow that Matt appears to be “stuck” on the Event Horizon.

Is it possible that the matter pulled into a black hole can never evaporate because there will never be enough time? Theoretically the matter would be pulled at close to the speed of light, so it would almost freeze in time?

[Celine Weimer] The mass of black holes is too large for it to evaporate in our time. For a black hole with the mass of our sun the evaporation time is about 1075 seconds.

If one would consider the so-called primordial black holes instead which can have significantly lower mass it is possible for it to evaporate in our time 🙂

As some of the world’s most educated people, what sort of improvements would you like to make to the education system? What changes could we make that would produce more folks to advance science in the next generation?

[Bernard Whiting] I think it is very important to cultivate, and even stimulate, curiosity in students throughout their entire education. Everything around you right now has physical, chemical and perhaps even biological, properties, many of which you could easily understand. When students are curious about these things, they get very excited by learning how we actually do understand them. Science news curiosity.

Do you believe we are in any way close to developing free energy? Is understanding gravity key in its development, or is it purely an electromagnetic engineering issue?

[Tony Lund] “free energy” is usually used as pseudo-science term for perpetual motion or ‘something for nothing’ that could give us power (electric or mechanical) without the consumption of any kind of fuel. There is no chance in hell of this ever happening, because it violates just about every law of physics that’s succeeded in describing the Universe how we observe it.

For example, the total energy of the Universe is ZERO! Believe it not, the Universe is the only “free lunch” that we know of.

So, I suppose, if you found a way to create your own Universe in your basement, and inflationary cosmology holds true, you could have free energy… but you’d have to jump into your new Universe and you’d never be able to get back out. See Alan Guth’s paper “How to Build A Universe in your Basement.”

Black Holes, however, may turn out to be a free “Garbage Disposal” If Emil is correct, you can, in essence, just through stuff onto the Black Hole (truly a “GraviStar”) and it will stick there forever, never to be un -stuck.

More relevant to your question is the idea of “VERY VERY VERY INSANELY CHEAP Energy.” Now THAT is possible!

Last year, fusion scientists at NIF in Berkely were able to demonstrate “Alpha Heating” in their fusion reactor… the data show that they are only a factor of 3 away from achieving nuclear fusion. So, they’re experiment is $4 billion dollars. If you built an experiment 3 times larger, we’d be in the age of nuclear fusion power…

…and we could provide electric power for a city with 1 million people for day with a bottle of water and produce zero emissions or toxic byproducts.

If someone were at the point in his life where he is about to go to university in a year or two, what tips would you give him if he wanted to become a theoretical physicist and work on the same problems as you do?

[Tomas Lothman] Learn and study for the absolute long term. Rote learning and cramming might get you through the next exam, but you are as likely to forget it in a week or two, and do not confuse familiarity with a subject for true understanding or learning. You will start to understand a subject when you can state the key ideas and assumptions in your own words without need for reference, and see how it all fits together. Don’t be afraid of testing yourself; see if you can solve problems, redo calculations, and derive results and theorems on your own, and not just while studying but through time. Even if you find it hard, the fact that you put the effort in by trying for yourself will make sure you will remember it once you look up the solution or solve it.

Another point is that even if you are primarily interested in modern theoretical physics, you should not discard the classical areas of physics (such as classical mechanics, electrodynamics, and thermodynamics). Not only do these topics form the foundation of later theories, they also serve to elucidate the practice of physics. A lot of students are so eager to get to the good stuff that they forget to do the ground work in the beginning courses. By the same token, the importance of linear algebra is hard to overstate.

It is also a good idea to start programing; not only are you likely to use it later on, but it will also be a good exercise in logic and abstraction which is also likely to help you later on. Python is a good starting point as there are a lot of good resources.

I can also recommend the guide by Gerard ‘t Hooft:

But in the end it is about not losing one’s passion for the subject, and continuing to ask questing and striving for answers.

If space travel were to ever become a reality, if we came across a blackhole in space would it be visible? Would the gravity be too powerful and there be no escape even if you could see one?

if you came across a typical black hole (and let’s say ‘classical’ black holes… so nothing new and exotic like the stuff we’ve been talking about at this conference.) out there in the cosmos, a couple of things would happen, depending on how how big the black hole is and what’s going on around it.

  1. You’d fry — Raiders of The Lost Ark Style
  2. You wouldn’t see anything out of the ordinary.
  3. You’d mistake it as a dying star stuck in time.

When black holes are really small, or feeding, they’re super bright. If nothing’s going on, you’d see a large black void (a sphere) that bends the light coming from behind it.

Ever want to know what it would look like if you jumped in??

You can!