Of Particular Significance

A Quantum Gravity and Cosmology Conference

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 09/16/2013

I attended a conference this past week celebrating two great physicists (Steve Shenker and Renata Kallosh) whom I got to know pretty well during the early part of my career. Unlike most of the conferences I’ve attended in recent years, there were no talks at all about the Large Hadron Collider; the community of speakers was largely drawn from experts on quantum field theory, quantum gravity, string theory and cosmology.


Any one of the talks would require an extensive article, especially since the required background material isn’t currently explained on this website. So rather than get bogged down in details, I thought I’d try to give you more of the general flavor — reflective, perhaps, of the tenor of the field at the moment. I’ll cover a couple of the talks later, if time permits (though I’m a bit under the gun at the moment…)

If you like to put labels on people, you’d probably call most of the speakers “string theorists.” This is a useful label if you’re in a hurry and not very interested, or if you want to abuse people, but not so useful if you want to actually understand their research. Indeed, out of about 21 talks, there were 3 on string theory.  That said, many of the speakers have in the past done some research in string theory, and many of the talks owe a debt to lessons that have been learned from string theory.

So what were the talks about?  What are these people actually doing?

Quantum Gravity

A substantial number — everyone from the Nobel Prize winner Gerard ‘t Hooft to string theory expert Joe Polchinski to the calculator-par-excellence Zvi Bern — are trying to understand aspects of quantum gravity, in one way or another. This entails finding some way of reconciling the quantum world (central in the physics of particles and atoms and molecules and materials, and in quantum computers) with gravity (for which our best [but incomplete] description is Einstein’s theory of general relativity.)

Quantum Gravity and Black Holes

Many of the speakers (as well as Kallosh and Shenker themselves) have been drawn to the problem of black holes, because these objects, and the information stored within and around them, are a place where quantum and gravity meet head on. Since the 1970s, when Hawking and Bekenstein showed that quantum phenomena were important in understanding black holes properly, confusions and controversies have raged over how to think about these mysterious objects. Many great theorists have banged their heads on this problem, and arguably none have escaped unscathed.

Why has the controversy gone on so long? It is because the mathematics required to study these problems is simply too hard — no one has figured out how to simplify it enough to understand precisely what happens when black holes form, radiate particles, and evaporate.

You may wonder why so many experts spent some time working on string theory in the 1990s. The reason is that a sequence of conceptual and mathematical breakthroughs between 1995 and 1997 made a number of very difficult problems dramatically simpler. (You might enjoy my 3 short videos explaining the history.) It was learned how to use string theory to study the quantum properties of black holes, which had never been done before. (Note that these results do not depend on whether string theory is “right” — i.e., whether it is the correct theory of how quantum gravity works in nature. String theory in this context is a tool: it allows you to calculate things that couldn’t be calculated before.)

Unfortunately, despite Herculean efforts over 15 years to put them to use, it appears that the technical advances of the 1990s were insufficient.  The mathematics of black hole evaporation is still too complicated, and we still don’t have the methods necessary to answer the deepest puzzles of quantum gravity.  This, in part, is why the specifics of string theory are no longer at the forefront of current attempts, within the community at the conference, to answer these questions.

In fact, we heard this from none other than Lenny Susskind (famous for his efforts, along with those of ‘t Hooft and many others, to oppose Hawking’s view that black holes require no revision of quantum mechanics, but now himself deeply puzzled by the firewall problem — the failure of what Susskind called `complementarity’). Susskind stated clearly his view that string theory, as currently understood, does not appear to provide a complete picture of how quantum gravity works.  Well, various people have been saying this about string theory for a long time (including ‘t Hooft, and including string theory/gravity experts like Steve Giddings, not to mention various experts on quantum gravity who viscerally hate string theory).  I’m not enough of an expert on quantum gravity that you should weight my opinion highly, but progress has been so slow that I’ve been worried about this since around 2003 or so.  It’s remarkable to hear Susskind, who helped invent string theory over 40 years ago, say this so forcefully.  What it tells you is that the firewall puzzle was the loose end that, when you pulled on it, took down an entire intellectual program, a hope that the puzzles of black holes would soon be resolved.  We need new insights — perhaps into quantum gravity in general, or perhaps into string theory in particular — without which these hard problems won’t get solved.

Supersymmetric Versions of Gravity

Another area of interest at the conference concerns supersymmetric versions of gravity (“supergravity”). Now, why bother with supersymmetry? One reason people often work on supersymmetry is that the presence of superpartner particles with masses near 1 TeV/c² could perhaps resolve the naturalness problem of the Standard Model. (This possibility is looking increasingly doubtful, but is not yet excluded by the data from the Large Hadron Collider.) But there are several other reasons.

Just as string theory sometimes can be used as a tool to solve hard problems, the same is true of supersymmetry. Many problems that are currently too hard to solve in theories without supersymmetry can be solved if supersymmetry is included. If supersymmetry is part of nature, then these solutions may be directly relevant in nature. But even if it is not, the solutions to hard problems in supersymmetric theories may provide general insight into what the solution in the real, non-supersymmetric world may qualitatively look like.  There are a number of striking examples of success with this approach.

So there are at least two types of reasons to study supersymmetric versions of gravity.

  • Maybe quantum gravity is supersymmetric, in which case study of supergravity involves study of the real world.
  • Or maybe it’s not… but even so, supersymmetry makes it easier to study the problems of quantum gravity, and from these studies it may be possible to learn general lessons that apply in the real world.

Some speakers were therefore just interested in how supersymmetric gravity actually works, on its own merits.  There’s plenty of interesting mathematics, some of which might have implications for physics too.  Other speakers wanted to understand black holes, for reasons I’ve already described.

Cosmic Inflation

Another area of great interest is the era of cosmic inflation — the period, still conjectural but increasingly plausible, during which the universe is believed to have expanded, in a tiny tiny fraction of a second, by at least a factor of 1,000,000,000,000,000,000,000,000,000. [Yes. That’s right. Sounds insane, doesn’t it? Blame Einstein’s equations… they say it’s possible, and since they make many correct predictions, we’ve no choice but to take them seriously on this one too…] Experts on quantum gravity in general, and string theory in particular, often hope that somehow measurements of the properties of the early universe, specifically of inflation, will provide them a context in which to test their theoretical ideas… a long shot, but not impossible.

There were several talks on this subject, ranging from the implications of the most recent data on the cosmos to theoretical studies of the various possible causes of this extraordinary inflation, including a couple of new approaches with novel predictions that can be checked against future data. Advances in our observations of the universe are now so good that a number of possible forms of inflation are now ruled out; meanwhile, others are still in very good agreement with data.  This is definitely an exciting area to watch over the coming years.

Phases of Quantum Systems

There were also a few very important discussions of the physics of materials, and of other quantum systems. I found these so interesting that I think I’ll describe them in a post of their own… they had to do with the “phases” of quantum systems.  What’s a `phase’? In this context, it’s best described as a general state of being: the phases of water that we are all familiar with are ice, liquid water and steam.  More generally, the familiar phases of materials are solids, liquids and gases.  But materials can do many other things too.  They can be electrical conductors or insulators or superconductors; they can be magnets, of several different kinds; and there are many examples that won’t be familiar in ordinary life but play a big role in technology, or at least in forefront research.  Anyway — more on this soon.

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128 Responses

  1. He might try to convince you by giving you false promises
    about quality but do not be moved by it and do not sign any agreement also and neither
    should you give any advance. Mainly it covers the actual Microsoft windows
    and also the Microsof company servers. Wedding
    photo journalism is the motto and style for this

  2. Hi, My name’s Graham and an interested layman in all of this.
    As I understand it, general relativity says that massive bodies causes a warping of spacetime and that that is what we experience as gravity. So why is the graviton (ie a particle) needed?

  3. @ Stephen Tuck. In this day and age a diploma means everything, even if it isn’t and shouldn’t. No one will take you seriously without it, unfortunately. Just hang in there. I have sons and daughters with and without a degree, very often those without have more knowledge and common sense.

  4. “My natural, God-given intellectual ability has no human equal upon the face of the earth. Truthfully, I have corrected Einstein on both his theories, corrected the Dirac’s equation, and explained mysteries of Physics…”

    Yeah, unknown genius…

    1. I would rather be an unknown genius than apart of the conspiracy to suppress the knowledge of the universe from the whole of mankind. You can compromise your theoretical work so you don’t overturn your colleagues theories and maybe someday you will have a good enough theory and tenure to patch all the holes in the framework of Science to slow its sinking from the titanic weight of its errors. The truth is uncompromising and the truth will set you free. The evil one’s rulership of this world would like people to think that the Aether doesn’t exist because if people believed in subspace matter, they might believe in the existence of an eternal human soul. Then they might not be as corrupted by power and greed to sell their eternal salvation for earthly gain. You might not be aware of the evil forces at work trying to increase Godlessness and immorality throughout the world, but the Luciferian signs and secret societies have prolific control over the institutional power of the world. Mankind is still being deceived by the Tree of Knowledge. It isn’t the lie that if we eat of the fruit, we will be like God. If we are deceived from eating the fruit and we turn away from God (reveling in the sinfullness of Satan’s Science) then we may have temporary pleasure in sin, at the cost of our eternal salvation. I was an atheist that found the truth of God through Theoretical Physics. They say that when we have the Theory of Everything, we shall know the mind of God. I never knew that the unification of Gravity and the Electromagnetic Force would be the unification of true Science and Religion!

      1. @Stephen Tuck
        I am reading your back and forth arguments with other readers. I agree with others that your theories are far out and you should study lot of physics and math before you can make worthwhile contributions. The present method has worked reasonably well for last several hundred years. On the other hand I am sympathetic to your views on religion and science. Luckily my religion (Hinduism) has no conflict whatsoever with science. So I can comfortably participate in physics blogs and at the same time in religious and metaphysical discourses. Surely both science and religion as practiced today have limitations, and as far as I am concerned both are useful. But it is too early for both of them to approach each other as you are suggesting. Once science (or physics) understands consciousness then this relationship might be clear. In the meantime one should try for peaceful coexistence of both!! I certainly do not agree with tirades against religion by some prominent physicists.

        1. I have very extensive knowledge of Physics and mathematics. It should be quite apparent by seeing all my derived and integrated equations that I have great mathematical skills. I studied vast amounts of knowledge and data, found the flaws, corrected them, and moved on with further pieces of the puzzle. I did not begin with such a revolutionary theory, the equations guided my path. I have made some of the greatest discoveries in Physics and enjoyed doing it until I reached the point that the mechanics of the universe lost the romantic appeal of mystery. If you ask me, I would say that the amount of errors in Physics is shocking and that modern Physicists are doing an abysmal job of determining the truth. I believe that there are far crazier theories than mine. However, my ideas make perfect sense to me because I have such detailed knowledge from my equations. It would be impossible for my theory to be wrong because it explains too much, gives correct calculations, and has too many correlations.

  5. You don’t even define what is precisely “Space” for you, and what is its dimension. Space is not a quantity, or you consider it is a volume (L^3) ?

    You said :
    “Doesn’t it make more sense that Energy defined dimensionally is [M] [L]^2. Where does the [T]^-2 come from in E=mc^2? Isn’t [T]^-2 pretty strange? Frankly, I see E=m*c^2 as E = [M] [L]^2.”

    Simply, c is a velocity, that is the ratio of a length divided by a time, that is LxT^(-1).
    So, c² is L²xT^(-2). That is all. Hence E=mxc² iis MxL²xT^(-2).

    You can view that in aniother way :
    v is LxT^(-1). Acceleration is a velocity divided by a time, so LxT^(-2). Force is mass times acceleartion (F=ma), so MxLxT ^(-2). Work, which is a form of energy is Force x Length, so MxL²xT^(-2).
    All is coherent.

    Concerning my education, I have a PHD in theoretical physics, in the domain of particle physics.

    1. Okay Alain as a Ph.D. Particle Physicist, you might be interested in the Proton-Proton Collision. In it lies clues to what Space is and to what Matter is for all practical purposes. Your Science banished the Aether since Einstein even though all the major scientist’s mathematical work from Maxwell to Lorentz are based upon it. Now Quantum Physicists try to reconcile that with Quantum Foam. That collision is so energetic that scientists have said that it creates energy. However, according to the Conservation of Energy and 1st Law of Thermodynamics, “Energy cannot be created or destroyed, only transformed.” In fact, it is a consequence of something historically and histerically called the “Noether Theorem,” where the action of a physical system is the integral over time of a Lagrangian Function determined by the Principle of Least Action. It is so “elegantly done” (sarcasm) with Perturbations and everything. Don’t you find Purturbations a little perturbing? Well, I guess it fits in with your other mathematical parlor tricks like Renormalizations using Differential Equations that lead to all those Singularities and Infinities that are so nicely patched-over with all those extra spooky dimensions. Anyways, the extra energy obviously comes from a transformation of Space into Matter, which quite simply proves the existence of the Aether. You would probably have the fantastic job of seing that stream of electrons and positrons that comes from the breakdown of the Quark Substructure of a Proton in subspace (the Aether). Now if you can only see past that crazy Higg’s Mechanism of yours to see that it is the Lorentz Mechanism that gives rise to particle mass, you might could understand that Quarks consist of Electrons and Positrons bound together in a state of energy where their frequency energy converts into increased mass (wavelength; photonic-string length) yielding the higher mass of hadrons like Protons and Neutrons. Then you might even get an inkling that the central charge of the string of Electrons and Positrons determines whether the particles is a Proton or Neutron (the two most stable energy configurations). Of course, you would probably have to solve the fun little puzzle of what configuration yields Up-Quarks and Down-Quarks. Personally, I would go with a Y-shaped Chain of Electron and Positrons. However, I know you’ll be bored if I don’t give you something to do, so you can count-up the electron and positrons needed to account for their yield in the collision and correlate it to your needed Quark Configuration.

      For clarification, Space is quantitized. It is a particle field in an inverse state of energy to that of matter. It is where particle/anti-particle pairs are bound together spin-inducing themselves up to the speed-of-light, converting frequency-energy mass (wavelength; photonic-string length). Electrons are photonic-string manifolds (vibrating, rotating balls of photonic string). You should ask a String Theorist, “What is the String in String Theory?” to see if any of them know that it the photon. Mass is [L^3] and Space is an inverse state of energy. Both of them occupy a Volume as Space is merely Subspace Matter (Aether). Consider how a star forms higher elements of the Periodic Table by compressing matter into hadrons of Protons and Neutrons. In a black hole (collapsed star), you have the conversion of Matter into Space. Every galaxy has a black hole in its center and most astronomers agree that space seems to expand like we are in a bubble since the rate of expansion seems to vary accross vast distances of space.

      In your account of the Dimensional Analysis, you fail to realize that you are applying an acceleration with the misguidance of the fact that Time is consistently, incorrectly treated as a 4th Dimension or Spatial Coordinate on par with a Length. It is not exclusive, but rather inclusive within all Matter and Space. Einstein failed to treat Time as a separate variable and lumped it into a Continuum as Spacetime. The Continuum is actually the Electromagnetic Spectrum. The boundary of Time is Planck Length and the boundary of Space is Planck Mass. Now go from the shorter wavelength of high-energy (frequency) photons to the higher wavelengths (string-lengths of Matter and then Space). Do you see a correlation to how the Planck Constant was derived from Blackbody Radiation (the Space-component; black holes; Planck Mass)? My approach is just as consistent as yours, except mine yields much greater knowledge of the Quantum Mechanics of Matter and Space. My equations work and they yield a consistent framework between Quantum Mechanics and Gravitation. Why does your Gravitational Constant have a seasonal variation? Could it be that the Lorentz Mechanism causes a Mass-Increase when the velocity speeds up in its elliptical orbit? Come on, common sense dictates that Einstein should have unified Mass-Energy Equivalence with the Lotentz transformations of Mass-Increase and Time Dilation. I did just that and learned from the equation enough to unify Gravitation and the Electromagnetic Force by integration of Ampère’s Force Law with the right-hand side of Einstein’s Field Equation. Has your colleagues come up with a mathematically consistent unification? No they haven’t, nor can they without correcting all the mathematical inconsistencies that I have done in my Theoretical Physics Research.

      1. So, you didn’t take my advice… (Just enjoy the ride…) What a shame. You don’t have *any* chances (neither do I). We are like snowmen in hell 🙂 Your *only* chance is to build antimatter bomb based on your theory. It’s hard to argue with your theory at ground zero 😉

    2. So Alain, based upon your name and the information you provided, I have narrowed you down to 3 candidates:

      Alain Blondel – University of Geneva
      Department of Particle Physics

      Dr. Alain Bellerive
      Professor, Particle Physics
      Carleton ATLAS Group

      Dr. Alain Aspect
      French Physicist

      Of these candidates, I imagine that you are Dr. Alain Bellerive. My deductive reasoning was that you are fairly young and have a greater Internet presence. Also, Bellerive has a Ph.D. in the domain of Particle Physics. If correct, you would have been involved in the ATLAS Experiment that announced the discovery of the Higgs Boson in July 2012, where Peter Higgs and François Englert went on to win the prestigious Nobel Prize for their work in predicting the particle back in 1964. I bet y’all broke open some champaign bottles that day and congradulated each other’s ‘success.’ I had commented on the possibility of physicists finding something that they would mistake as the Higgs Boson a few months before the news. My mathematical equations definitively prove that the Higgs Mechanism is an incorrect theory. What does Spontaneous Symmetry Breaking explain? It is just smoke and mirrors for the fact that they could not explain the true underlying mechanics. Unlike the 13.25 billion dollars that it cost to find the ‘Higgs Boson,’ it did not cost taxpayers a penny for my research. I would love to hear your thoughts on this matter!

  6. My name is Stephen Tuck and I agree that insights are not useful if they don’t come with equations. However, I disagree that the mathematics is really all that difficult when you have a clear understanding of the underlying energy mechanics. It took me about 3-years to mathematically unify Gravitation with the Electromagnetic Force. It began with the theory that matter falling into a black hole converts into Space, causing the accelerated expansion of the universe. About 3 months later, I figured out that the c^2 in Einstein’s Mass-Energy Equivalence equation stood for the variables of Space and Time (both initialized by the c-constant) and linked it to the Lorentz transformations of Mass-Increase and Time-Dilation. I call it the Tuck-Einstein Equation:

    Energy = (Space * Mass * Time) / (1 – (v^2/c^2))^0.5

    I don’t know exactly why Einstein never mathematically finished his equation of Special Relativity, but this equation goes even farther because it correctly replaces the Dirac Equation of Quantum Mechanics. I figured that out when to integrate the two equations. I noticed that they were both wave-equations that are first-order in Space and Time and used forms of Quadratics. The Mass variable is really a pseudo-variable that acts as a scalar. Interestingly if you move the denominator to the left-hand side of the equation, you will see the Length Contraction Equation (except Length is replaced by the Energy variable, since Energy defines all dimensionally measurements). The Higgs Mechanism is incorrect since it is really what I call the Lorentz Mechanism that yields mass through an increase in photonic-string length. The equation seems to describe Electrons as a ball of string that vibrates and rotates (which I call Photonic-String Manifolds). I eventually figured out that the 8PI in Einstein’s Field Equation stands for Pi-Radians. A charged particle is equivalent to 2PI-Radians (1 full rotation). Atoms are naturally dipolar with protons always being paired with electrons. The simplest dipole would be equal to 4PI (proton and electron) and thus the interaction between them is the sum total of 8PI. This breakthrough finally allowed me integrate a variant form of Ampère’s Force Law with the right-hand side of Einstein’s Field Equation. I say variant form because I replaced the I (current variable) with the equation used in particle physics of I = (c * q). It took at least 20-steps to perform the integration but I ended up with what I call the Equation of Everything:

    ((F * 8*PI * (r / 6.33680e6)^2) / (q^2 * c^2)) = (((4*PI * m1) / 
    (Energy1 * (1 – ((v + 1.71941e6)^2 / c^2))^0.5)) + ((4*PI * m2) / 
    (Energy2 * (1 – ((v + 1.71941e6)^2 / c^2))^0.5)))

    The form above includes to non-essential modifications of allowing the radius to be specified in meters rather than unity to 1 average earth radius, and for the average velocity of the earth hard-coded (making here a deviation from earth’s velocity). I just did that because I like seeing the basic math parameters. See Earth’s gravity is equal PI^2 for a Perfectly Spherical Earth. The hills, valleys, and equatorial bulge hides that fact. Of course, the Lorentz Mechanism explains the seasonal variation in the Gravitational Constant since changes in velocity (due to an elliptical orbit) causes minor changes in the earth’s mass. The equation also points out artifacts in the Metric System because when I derived the Boltzmann Constant, I noticed it was off by 10^7, which is due to how the meter is defined for practicality. We can’t carry “Quarter-Meridian Stick” around with us so the did a decimal-shift of One Ten-Millionth. This came from the Inverse Form of the Equation that contains the Quantum Lorentz Force Equation and the Quantum Entropic Force Equation:

    ((F * r^2) / (2*PI * q^2 * c^2)) = 
    ((m1 / 
    (4*PI * Energy1 * (1 – (v^2/c^2))^0.5)) + 
    (m2 / 
    (4*PI * Energy2 * (1 – (v^2/c^2))^0.5)))

    Here is the Boltzmann Constant equation:

    kB = 1 / (((c^2 * PI) / (4 * gravity)) * 10^7)

    Anyways, I’ve got volumes of notes and discoveries. However, I just have a natural gift. I don’t have any college and it doesn’t look like I can afford such a luxury because of my circumstances in life. There is a lot of revolutionary knowledge to contend with like the fact that the speed-of-light is not constant, yet compliments Einstein’s Equations. The secret to the deriving the equation was through the Parameters of Space (which are also not constant). Einstein’s use of Riemann Geometry was wrong and Gravitational Time Dilation is actually Gravitational Refraction. Gravity is due to the transference of dipolar, rotational kinetic-energy through subspace (the Aether). Differential Equations are incomplete because they lack all the variables (unlike Multivariate Equations). If you want to know the truth, you must absolutely abandon the incorrect, popular mathematical frame-work of conventional Theoretical Physics!

    1. I stopped short of fully modeling the equations as Vector Matrices. There is still more work to do such as defining the Electron Perihelion to mathematically model the complexities of Electrodynamics, Fluid Dynamics, and Thermodynamics (which are all essentially different aspects of the equation dynamics). The Inverse Form links the the linear equations of Physics to the 3D-equations involved in Chemistry (and naturally Biochemistry). Chemistry just uses extra constants to linearize 3D-reactions (such as Avogadro’s Number and Boltzmann’s Constant). There was a reason that the “Pressure” component was found in Einstein’s Stress-Energy Tensor. I had hoped that my work would greatly benefit the technological advancement of mankind, but I believe that I was naive in placing such faith in the world. I see so much evil in control of the fate of mankind that I see the future as bleak. Right now they want to mess with the SI System of Measurement out of either ignorance or deliberate deception. I probably wasted my time with such efforts but it was a blessed distraction for me from the tremendous mental and emotional pain that I was experiencing. I also learned a lot about why Einstein was so brilliant and thus the root of my own curse/ability.

      1. Save your breath! Nobody won’t listen or care… been there, done that. Only if you can build antimatter bomb and blast it, you’ll be heard… by aliens in outer space 😉

        1. Kimmo, I totally agree. I had tried to formaly publish my first equation in Xavier Nuclear Physics B under the category of Special Relativity Mathematics. They replied saying that my work was outside the scope of their publication. Obviously, that’s not true for a Scientific Journal having such a category. However, they did indirectly hint at their decision as the referred me to the leading journal for “controversial matters in Physics.” I have arguments with “educated” guys that couldn’t find fault with my equations, but were in meritless opposition. Science today is a religion where you must be in agreement with their bible. I suppose you cannot expect a Theoretical Physicist to destroy their very profession by allowing the Theory of Everything to exist. Personally, I see Physicists today as Glorified Grant Writers. Today’s Science is not the noble, selfless undertaking that it is portrayed to be. I’m kinda afraid not only of the depth of my knowledge about the universe, but the possible consequences of having such knowledge. I don’t feel good within my soul about doing nothing, but I feel like their is really nothing that I can do!

    2. Your very first equation is evidently false :
      Energy = (Space * Mass * Time) / (1 – (v^2/c^2))^0.5

      Energy has dimension MxL²x(T^(-2), from E=mxc² for example. Here, you have MxT, so Space should be L²xT^(-3), this is incoherent with any definition of space. The reste of the equation (v²/c²…) is dimensionless.
      No wonder why your paper has been refused.

      Do you know what is called “dimensions equation” ? What are your diplomae in physics and mathematics ?

      1. First of all, my paper was not refused due to any inaccuracy. It was refused because the editirs of Xavier Nuclear Physics B were afraid to publish controversial material. Here is their response:

        Dear Mr. Tuck,

        The Supervisory Editors of Nuclear Physics B have now carefully considered your paper and they reached the conclusion that your work falls outside the scope of Nuclear Physics B. Therefore we regret to inform you that we are unable to publish your work in Nuclear Physics B. You are advised to submit your manuscript to a journal like Foundations of Physics.

        Thank you for giving us the opportunity to consider your work.

        Yours sincerely,

        Jeanette Bakker
        Journal Manager
        on behalf of the Editors of Nuclear Physics B

        Secondly, I have extensively analyzed my equation with Dimensional Analysis. It is not any old equation. It is not an equation, it is “the equation” that defines the very Systems of Dimensional Measurement (such as the SI System). This simple equation of Special Relativity defines all the dimensions of the universe. 

        Alright, let’s re-educate you Alain. In accordance with Maxwell Clerk’s Dimensional Analysis, Energy is defined as [M] [L]^2 [T]^-2. Now you said that this is coherent with E=mc^2. If you drop the Lotentz transformations in the denominator (that you say is dimensionless) you have E=(Mass x Space x Time), which is equivalent since I substituted (Space x Time) for c^2. I later even found where Einstein himself derived E=mc2/sqrt(1-v2/c2), which is the exact same equation except that he did not realize the c^2 substitution.

        Where Dimensional Analysis needs correction is that it adds the dimension of Time as [T]^-2 when it is already present in [L]^2 since c^2 stands for Space x Time. Since Space is initialized in my equation with the c-constant as well as Time, the energy constant c is the dimensional parameter of Length. Upon retrospection, this is why the Length Contraction Equation is found in my equation as E / (sqrt(1-v2/c2)) or E’ = (E / (sqrt(1-v2/c2))) if written in that syntax (since Energy replaces the Length variable). My typical convention is using ^0.5 for the representation of square-root since it is the mathematical equivalent in text form (that I use in equation editors like Formulaic). However, here I specified it as sqrt() for conciseness and added clarity.

        Doesn’t it make more sense that Energy defined dimensionally is [M] [L]^2. Where does the [T]^-2 come from in E=mc^2? Isn’t [T]^-2 pretty strange? Frankly, I see E=m*c^2 as E = [M] [L]^2.

        Interestingly, Maxwell said “If, as in the astronomical system, the unit of mass is defined with respect to its attractive power, the dimensions of [M] are [L^3 x T^-2]. Now, I have already stated that Mass is a scalar pseudo-variable of Space and Time (which are the boundaries of the Electromagnetic Spectrum). From my research, I know that c^3 is the range of the EM Spectrum. If you drop T^-2 as we did in above in E=mc^2, we get mass defined in respect to its attractive power is [L^3]. When you isolate mass in my equation, you get Mass = (E * (1 – v^2/c^2)^0.5) / (Space * Time), which is Energy divided by Space and Time. In the Lorentz transformation as Velocity increases, the Energy Multiplier decreases as Mass itself gains the energy through the Mass-Increase (as energy remains constant since it cannot be created or destroyed, only transformed). However, what is the total Energy being transformed? It is none other than the c-constant since it is the fastest velocity in the universe. The Lorentz math sets c^2 as unity within the Energy Multiplier and takes the square-root of that (sqrt(c^2) = c). With unity being equivalent to the value of 1 as a fractional whole, the Energy being transformed is equivalent to the c-constant. Therefore, mass defined with respect to its attractive power is [c^3] = [L^3]. There you have it, the c-constant is really an Energy Constant and Energy is equivalent to Length. The Energy is that of the Electromagnetic Spectrum, which directly maps to the equation. I think the c^3 EM Spectrum energy can best be seen below in how I derived the common form of the Planck Length Equation.

        Planck Length Equation Derivation:
        lp = (h / (2*PI * Mp * c))
        lp = (ℏ / (Mp * c))
        lp = ((G * Mp) / c^2)
        lp^2 = ((ℏ / (Mp * c)) * ((G * Mp) / c^2))
        lp^2 = ((ℏ * G) / (c^3))
        lp = ((ℏ * G) / c^3)^0.5

        Also Alain, there is no measured quantity in the universe that is dimensionless. Mathematicians are deluded to think that anything in the universe is dimensionless because energy defines the very systems of dimensional measurement within the universe and everything that exists is a form of energy. Just because you can cancel out units of dimension in mathematical equations or a constant is of unknown origin doesn’t make it dimensionless because if it were truly dimensionless, it wouldn’t exist.

        As for my diploma in mathematics and physics, I have none as I didn’t learn to parrot back the mindless flaws in Physics. Did you know that imaginary numbers are due to light-cone mapping, which is the incorrect treatment of Time as a spatial coordinate? That is something that mathematicians need to add to Number Theory. My natural, God-given intellectual ability has no human equal upon the face of the earth. Truthfully, I have corrected Einstein on both his theories, corrected the Dirac’s equation, and explained mysteries of Physics that were beyond the comprehension of Feynman (like that fact the Fine Structure Constant is a form of Coulomb’s Law for the photon). Isn’t it something how a person with no formal college education can outperform all the Ph.D.’s in Theoretical Physics? Only mankind would be ignorant enough to equate a person’s ability to a worthless piece of paper. A true genius needs no institution’s stamp of approval!

        1. You wrote :
          ” …since I substituted (Space x Time) for c^2″
          May I ask what allows you to substitute c² by (Space x Time) ? c² is a constant (c is one of the fundamental constant of Physics), so (Space x Time) must also be a constant.
          As I already said, c² has dimension L² x T^(-2), so “Space” should have dimension L² x T^(-3). What a strange “Space” !
          What is for you “Space” and “Time” ?

          Lets take the example of the electron :
          m = 9.109 x 10^(-31) kg
          c = 3 x 10^(8) m/s
          So the rest energy of the electron is :
          E = 9.109 x 10^(-31) x (3 x 10^8)^(2) ~ 8.198 x 10^(-14) J

          How do you compute the rest (v=0) mass of the electron with your formulae :
          E = Mass x Space x Time ?

          1. Alain, I don’t know whether my earlier answer sufficiently answered this question. I didn’t notice this reply until later and I would like to treat this as an interest in better understanding my work rather than a competition. I don’t have nearly the energy that I had before to argue, especially since I am facing many great difficulties in my life. Somehow I saw that Mass-Increase and Time-Dilation was a trade-off in energy and I think that my study in Dimensional Analysis allowed me to see that the c^2 represented Space and Time. I just know that I connected it with the Lorentz transformations and realized it was true. I didn’t know until much later that the c-constant wasn’t truly constant. I know my ideas sound wild, but they aren’t like other theories because I learned the truth by reading the equations. A mathematician might look at an equation and only see numbers and operations. I looked at the equation as a description of nature. I tried to see what the equations truly represented in physical reality. The c-constant isn’t really a constant because it depends on the Parameters of Space, which are the Permittivity of Space (the Electric Constant) and the Permeability of Space (the Magnetic Constant). I like calling the parameters because they are not constant either. The equation that defines the speed of light is:

            c0 = (1 / (μ0 * ε0)^0.5)

            One of Einstein’s principles of Special Relativity is that the speed-of-light is assumed constant, but there is no mathematical basis. Since the speed-of-light depends upon the Parameters of Space, you must see if they are variable. My philosophy is “Strength of Mind and Strength of Heart; Question Everything and Trust No-one.” Therefore I did not assume that even Einstein’s work was correct. I tested all knowledge for any inconsistencies. I learned that the Magnetic Parameter was arbitrarily set constant to the value 4π x 10^-7 v*s/(A*m). I also learned that Permittivity affected how fast light can travel through a medium and that the Permittivity affects Refraction, which causes the bending of light. These Parameters were also very important in Maxwell’s Equations. However, I think it became the most clear when I was able to integrate Ampère’s Law with the right-hand side of Einstein’s Field Equation through the Magnetic Parameter. The equation had symmetry and I saw that energy was exchanged through those parameters just like their counterparts of Space and Time. It became apparent that the same laws of Physics governed the bending of light around a massive object as that of the Refraction of light through a glass of water. Then I knew that Gravitational Time Dilation was really a form of Gravitational Refraction. There are many experiments showing that light can be slowed in mediums of matter. However, a lot of the physical and electrical properties of matter depend upon the Parameters of Space. Just like gravity is an attribute of mass, matter affects the variables of Space. This becomes much clearer when you see gravity is due to the transference of rotational kinetic-energy.

            Interestingly, I have this exact example calculation already set in my equation solver. Although, I do use the more accurate value of 2.99792e+08 m/s for the speed-of-light. You know, the photon’s mass is what slows it down to this speed rather than being 3e+08 m/s. I know because I was able to calculate the relativistic effect of mass (with my equation) against a theoretically massless particle having that speed. The Radiation Pressure of light is really due to the momentum of its mass. You must use the full equation for correct results:

            Energy = (Space * Mass * Time) / (1 – (v^2/c^2))^0.5

            Initializing Space, Time, and the c-constant to the previously mentioned value, setting velocity to 0, and mass to 9.10938e-31 kg, I get 8.18709e-14 J as the answer. This example is very easy since it does not use any of the relativistic capabilities of the equation. In order to see how Velocity affects Time-Dilation and Mass-Increase, you must use a special procedure to calculate the change in Energy, zeroing the Velocity, and then calculating the corresponding Mass and slowdown in Time after re-entering the Velocity. It is like solving two simultaneous equations at the same time within a single equation. It would be nice if equation solvers automatically had the capability to shift quantities between variables. However, I don’t know of any other equation requiring this functionality.

        2. When I wrote about Length Contraction, I meant E’ = (E * (sqrt(1-v2/c2))), but inadvertently used the division operator here. I’m sure that the context was clear for my intended meaning. When you move the denominator over to the left-hand side of my Tuck-Einstein Equation, you get the Length Contraction Equation with L replaced by E, since Length is due to Energy. I don’t like errors in my posts so I corrected it. The reason that my work is so correct is because I have always been first to admit mistakes or revise my work if it was wrong. I seek only perfection. This was only a typo but it signifies the level of my commitment for truth and righteousness.

  7. The current situation seems to be that the experts are not completely sure how to address this problem so as to bring it to a (knowledgable) conclusion. Besides, the experts can’t seem to agree on one single approach to this problem.

    There are at least two camps regarding this issue: on one side, we have Almheiri, Marolf, Polchinski, and Sully defending one position (Firewall), and on the other side, we have Maldacena and Susskind defending the entaglement/wormhole approach.

    This seems very much like a new front of the Black Hole Wars, or maybe a rehash.

    Kind regards, GEN

  8. F=P.M. A Where P is permeability of gravitoethertons we call ether or now dark energy. Universe is non isotropic whirl and swirl of dark energy. Let us revise the ideas of Einstein and Newton in the context of non isotropic varying soup density of gravitoethertons. Revised atomic model of Durgadas Datta gives us a residual mono magnetism due non existence of strong force and gravity push towards center of earth due to flow to c.g or a AVOGADROS LAW in enclosed gas on molecular way can be the basis of NEW PHYSICS and NOBEL COMMITTEE must not encourage the ideas of BIG BANG OR HIGGS BOSON NOW.

  9. @ E.S.:
    No my friend , F= ma is a relation among three real existing facts where each fact does not be realized by any other , but Einstein,s equations equate distributions with geometry not directly but thru an cause-effect mechanism ,so please just tell us :can any theory explain this physical mechanism which change the basic configuration of space.

  10. @Matt
    If going past the event horizon is in principle equivalent to exceeding the speed of light and then again nothing should exceed the speed of light therefore nothing should fall into a BH including a member of vacuum pair. This would imply no Hawking Radiation and no information is lost into the BH right?

    1. Concerning quantization a la Dirac. I have manage to apply this technique to spacetime quantization and discovered the graviton just as Dirac discovered the positron you can download my paper called Nexus: A quantum theory of Spacetime gravity and the Quantum Vacuum from http://www.scirp.org/journal/ijaa

  11. what is your views on loop quantum gravity as a candidate theory of quantum gravity in comparison to string/M-theory?

  12. @Shantanu:

    Alan Guth’s original proposal for Inflation was to find a way to “get rid of” the excess of Magnetic Monopoles that do not show up in our universe and did appear in some Big Bang theories.

    After this initial proposal was “thrown”, others realized that inflation could solve other “nuisances” of the models.

    Other cosmologists, like Linde and Kallosh, came to the idea of inflation from other initial approaches, and also found out that inflation does solve many “annoyances” of the BB models.

  13. Matt,
    Alan Guth himself has pointed out that inflation is not a theory, but a paradigm. However the problem is that its too broad a paradigm and given any set of observations one can easily construct any inflationary model.

  14. We really urgently need a highest caliber conference to study the primary fundamentals of nature where science reaches the frontiers of its capacity and where a clear cut border line is agreed upon to direct the scientific path to a realistic people benefit oriented funding.

  15. Let me put it in a very simple form :
    Why space bends when energy is included in space ?
    Either there is a mechanism or it is just a fundamental fact irreducible to any simpler facts and where science stop talking .
    That is the question.

    1. Depending on what you mean with “mechanism”, it may be that you will never get the kind of answer you expect from physics. When people ask for a “mechanism”, they often expect that something new is explained to them in terms they already understand. This is usually not what fundamental physical theories achieve. Rather they allow you to understand nature in new terms which you need to learn along with the theory.

      As a simple example take Newton’s famous law F = ma. It tells you that force equals mass times acceleration. No mechanism is implied. Depending on the context, you can choose to interpret the equation such that force “causes” acceleration (for example when you throw a ball) or such that acceleration “causes” force (for example when you catch a fast ball and you feel it press against your hand), but the equation itself says something more basic and general, it just states an equality.

      What we usually call “mechanisms” in everyday language are complex relationships between objects we experience, relationships that we interpret in terms of “cause” and “effect”. This thinking is very useful in everyday live, but it relies on notions that we learned by observing the macroscopic world, and these notions often make no sense on a more fundamental level. In the end you understand mechanisms in terms of equations, not equations in terms of mechanisms.

      That said, physicists sometimes use the word “mechanism” to refer to mathematical or physical relations they understand or want to understand (as in the “Higgs mechanism”). But this is just another way of talking about equations, it does not mean that there really is a relationship of “cause” and “effect” as our common sense is used to assume.

  16. @G.E.N:
    You completely missed my question , ….using your own words then :
    What is the mechanism leading from distribution to geometry ? Knowing that the former IS NOT the later as its causal effector .
    GR equations only describe the geometry — many many ones — but it in no way explain the mechanism that causes distribution to generate geometry.
    That is the question .

  17. As this warping of space-time affects the actual framework of reference that we use to measure things, we measure “curvey” trajectories, but the fact is that we have “warped prototype meters”, “warped chronometers”, “warped scales”, etc.

    This warping is local, affected by the local distribution of energy and momentum.

    So, some regions of space-time might be more “twisted” than others.

    This is what happens around massive objects, like stars, white dwarfs, neutron stars and black holes, just to name a few, but also around not so massive objects, like the Moon, or Earth: the effects are more difficult to measure and detect, but they are there and actual measurements confirm predictions by GR.

  18. @aa.sh: In simple terms, the distribution of energy and momentum affects the geometry of space-time in such a way that the trajectories of macroscopic bodies are the curves that we can see and measure. So gravity is not the end result of a force applied on these bodies, but the result of the bodies following a “straight” trajectory (just as the principle of inertia says) that looks curvey from our point of view. The curves are the result of space-time being warped by this distribution of energy and momentum.

    Kind regards, GEN

  19. I know my gentle teacher that there are many speculations revolving around space in-flow into matter , but my question is concerned with GR where solutions of the equations decribe the configurations , geometry of responses not its mechanism , I am asking about the later.

  20. Matt. , you said that gravity is the response of space-time to energy and momentum , now , does any theory or speculation to date proposed a mechanism by which that response is realized ? Can any theory explain how this response is actualized ?

  21. @MartenVanDijk: by the end of 1907, Einstein himself realized the equivalence of accelarations and gravity within close distances, and a days later, he realized also that gravity might be just the result of the warping of space-time.

    By then, he was convinced of the value of the concept of space-time (raum und zeit) as it was proposed by Hermann Minkowski. Originally, Einstein was not thrilled with Minkowski’s ideas.

    Minkowski himself had been a professor of Einstein’s, and Einstein did not impress Minkowski at that time.

    By 1907, Minkowski was working at Gottingen, and at that time, Einstein was neither thrilled with Gottingen’s mathematicians.

    Kind regards, GEN

  22. Nice article. However I am not as optimistic as you about inflation.
    Right now there are so many models of inflation (see for eg http://arxiv.org/abs/1303.3787, about 370 pages) that one can construct any inflationary model to fit any observations and inflation is no longer easily testable or falsifiable.

    Just to shoot down a couple of points mentioned as “smoking guns” of inflation

    o Inflation is supposed to predict spectral index different from 1. Starobinsly has recently constructed an inflationary model with n=1

    o Back in 90s when we thought universe is open, there were many inflationary models which predicted omega less than 1.

    Note also that scalar field driven inflation is not the only possibility. there are also vector models of inflation.

    Note that sometimes I have also heard this anecdotal statement in some
    high energy physics seminars that “inflation maybe connected to grand unified theories”. Well GUT based inflation is almost ruled out based on
    limits on r. Thus I am no longer sanguine about inflation.

    Also note that single scalar field models of inflation have many conceptual problems (see for eg this paper by Steinhardt and your CFA colleague Avi Loeb http://arxiv.org/abs/1304.2785)

    1. I honestly don’t know how optimistic to be… I’m not enough of an expert. Personally I’m amazed that it was possible to rule out as many models of inflation as we’ve seen so far. I do think it is worth remembering that inflation could easily have been falsified over the 33 years or so since it was invented. That hasn’t happened. However, your skepticism that inflation is still falsifiable given what we already know from our recent data (or that one can use what we will learn soon to narrow in on a small set of plausible examples) is certainly something I’m potentially sympathetic to. [You will notice I have chosen not to work on this subject…] Still, I was surprised that cosmologists came up with so many tools for studying things relevant to inflation, and I can imagine being surprised again. Are we sure that surprising discoveries in gravitational waves or 21 cm line observations couldn’t falsify the theory?

  23. Prof. Strassler: In your opinion, is the Firewall Problem closely related to the measurement problem for the string landscape?

  24. Thank you, Matt, Edwin and Gastón. Your explanations helped clear things up, and I think I understand now. I’ll say again, I hope I live long enough to see gravity and QFT reconciled… or any of the nagging issues of physics.

    It seems sometimes, that after the progress of the early 20th century, physics got a bit stalled. There was some joy at finding the Top and a Higgs (kind of as expected), but I yearn for a game changer!

    1. So do we all. Maybe that will come from a brilliant theorist, maybe it will come from a surprising experiment; but during the past 25 years we have not gotten enough useful clues.

      1. And, of course, all us fascinated amateurs dream of making that one uber-cogent remark that dumbfounds the entire physics field with a massive V8 moment… “Why didn’t we think of that!! How could we have been so blind” 😀

        Sadly theoretical physics isn’t very much like astronomy… 😐

  25. The general consensus is that grativy (GR) and Quantum Field Theory (QFT) are significant in black holes, so, they have to work together and be consistent with each other, but we still do not have a consistent model for these two (GR and QFT) to be able to work together.

    Because of black holes, GR and QFT should not be mutually exclusive, even though in our incomplete current understanding, they are in practice mutually exclusive, since they are inconsistent with each other.

    Kind regards, GEN

  26. At the risk of revealing serious ignorance, are the following two questions known to be 100% false?

    1. Gravity does NOT quantize.
    2. There are no “gravitons”.

    I ask because mutually exclusive duality seems an aspect of reality. There are the dualities in C, P & T. There are the dualities addressed by Heisenberg Uncertainty. In the macro world, the dualities of DNA and gender and other physical systems. The ancient philosophy of Yin/Yang seems to highlight this basic property of existence.

    So is there any possibility that gravity and SM are mutually exclusive, irreconcilable dualities? Or is that known definitely to be a silly idea?

    1. I think it is important to distinguish between “mutually exclusive” and “irreconcilable” aspects. A physical theory T can very well have limits A and B in different regimes that show mutually exclusive properties, yet these properties are perfectly reconcilable in the overarching theory T.

      A well known example is waves and particles: Classical waves and classical particles are mutually exclusive concepts (for example the phenomena of interference and discreteness distinguish them). Yet quantum mechanics, and in particular quantum field theory, teaches us that there are aspects of nature that can exhibit both wave and particle characteristics, depending on how you look at them, and everything is perfectly consistent. It is only the limiting simplifications that we make in different regimes that are seemingly incompatible.

      These kinds of equivalences (e.g. the one reconciling waves and particles) are one of the reasons that mathematics is so important for the description of nature (as we understand it so far), because natural human languages are poor in this respect. Our “common sense” likes to put things in one category or in another, but mathematics and physical insight show that seemingly different things can be actually equivalent due to a deeper underlying structure, and mathematics allows us to state this in precise terms.

      As to the question of whether things could really be irreconcilable: Well, we will never be able to proof (in the mathematical sense) that nature has consistent laws that we can potentially understand and formulate. But you have to admit, that the assumption that such laws do indeed exist has proven enormously successful so far.

      1. Thank you, that is a very good distinction to make, and perhaps it helps me shape my question a bit better. I had meant to mention the wave / particle duality; it’s very close to what I’m reaching for here.

        Is it possible that GR and QFT are mutually exclusive but reconcilable (through an overarching theory “T”) such that my two questions above are NOT both false? It feels like just about everything I’ve read about a “TOE” assumes that the trick involves finding a way to quantize gravity and discovering gravitons.

        I think what I’m really wondering is if we’ve absolutely ruled out the idea that there is a duality, similar to the wave/particle one, that admits a “smooth” gravity along with discrete matter.

        I’ve read about (but not fully comprehended) “background dependent” versus “background independent” … is it possible gravity is a smooth background for QFT?

        (I realize my questions may be laughable to the trained physicist! :))

        1. Edwin’s comment is indeed well put.

          Let’s say it this way: Einstein’s equation says that gravity is space-time’s response to energy and momentum — ALL energy and momentum, including

          1) energy and momentum from gravity itself AND
          2) energy and momentum from other things.

          So how are you going to set up a theory in which one source of energy and momentum isn’t subject to the laws of superposition and uncertainty that arise in quantum mechanics, while the other source is subject to those laws? No one has suggested a clearly consistent way of doing this.

          Where it really gets bad is if you go deep into the guts of quantum theory, and you discover that you actually CANNOT cleanly separate (1) and (2) anyway: the energy and momentum from gravity gets mixed up with the energy and momentum of quantum fluctuations of other fields. The latter contribute to the strength of gravity, so when you measure a gravitational force you can’t even say which is which.

          In short, trying to separate these things just generates a mess. There needs to be a better way of joining them together.

          1. The inconsistency between GTR and QFT on gravity is not solved yet. Nevertheless I absolutely agree that pseudogravity (in an elevator, in a rocket) is formed by energy and momentum.

    2. Regarding gravitons: I would be interested to read an expert’s take on this. May non-expert understanding of the argument is such: We know that nature is quantum mechanical to a very high degree of precision, and we also have a successful field theory (general relativity) of gravity. When put into the quantum mechanical framework, field theories tend to have particles, so there are very good reasons to assume that gravitons are part of a correct description of nature at least in a certain regime. This does not necessarily imply that gravitons are fundamental particles. There are theories with non-fundamental (pseudo-)particles. For example when you describe vibrations and sound in solid materials in the framework of quantum mechanics, you get particles (phonons). In that sense particles are quite a general consequence of quantum mechanics and fields.

    3. Nobody really can make suitable statements about what it would even mean to have non-quantum gravity and no gravitons. Either quantum mechanics is right and you MUST quantize gravitational waves and get gravitons, just like any wave in our world, whether elementary or not, is quantized; OR quantum mechanics is wrong when it comes to gravity and you have to extend your description both of gravity and of everything else too. I don’t think you can come up with any reasonable way to have quantum particle physics as the basis for everything except gravity, and have gravity have its own, independent basis. You can’t even make sense of Einstein’s equations if you try that.

      As for your last questions: I have no idea what this means. It’s words. Give me equations; then we can talk.

      1. I’m afraid I’m not qualified to come up with equations, but perhaps my second comment above helps explain what I’m trying to ask.

        It all boils down to this: for many years I’ve heard about how the SM and GR are incompatible and that one (or both) must be incomplete. I’ve also heard about how both theories are in vast, high-precision agreement with tests.

        So the evidence suggests both are right.

        But they cannot be.

        I’ve wondered for a long time how that will be resolved (and I hope I live long enough to see that resolution). That the solution seems to be so elusive makes me wonder if there might not be an incorrect key assertion somewhere. I have no factual basis, but I do find I lean towards what follows your “OR” above as a hoped for eventual answer.

        1. I doubt that you or I will live to see the resolution.

          When you say “evidence suggests both are right”, that’s not true. Evidence only suggests that both are right within the range of current experiments. But black holes are an example of something where (1) they come into conflict, and (2) there have never been any experiments to help us understand what actually takes place.

          In a similar way, Newton’s laws of motion worked fantastically well; so did Maxwell’s laws of electromagnetic fields. Despite their success in experiments, theorists recognized at some point that they were in conflict. The resolution, of course, was that Newton’s laws were incomplete and Maxwell’s were in good shape. Of course that wasn’t the end of it; Maxwell’s laws were in conflict with thermodynamics, also a very successful theory. There, it was both that needed revision, through the quantum hypothesis and the eventual development of quantum mechanics and quantum field theory. Long story short: attempts to resolve conflicts between two successful theoretical frameworks, each with their own range of validity, has led to many great breakthroughs in theoretical physics.

          1. If it requires exploring at the Planck level to ultimately prove a theory that includes both GR and QFT, can we ever hope to accomplish it? Do “can’t be done, even in principle” limits apply at those energies?

  27. Polchinsky’s “firewalls” are quite natural. The enormous thermodynamical effects in Black Holes due to the enormous time-differences between the insides and outsides of Black Holes, take care of that.
    By the same token singularities cannot exist.

  28. Matt,

    When can we hear about those models which solve the naturalness problem? One other thing, if those models do the trick then they should be also possible TOEs, right? In case of many such models, they should be equivalent. I bet there are not 😉

  29. There is some evidence that indicates that the current value of Lambda is such that the current value of Omega is about 1, that is, close to the critical value, so, we have a universe that is about “flat”.

    BTW, Lambda is not really constant in value, as it varies over time, in line with the Hubble constant, that also varies over time.

    Kind regards, GEN

    1. I think the two statements are false.
      All measurements (black body background radiation, and others) show that the universe is “flat” (that is euclidean, not parabolic or hyperbolic), so Omega appears to be one. This is one reason why “inflation” has been invented, to explain universe is flat, and Omega is One.
      And we know now (from the studies of supernovae, from black body radiation and else), that Lambda (or something that behave like a cosmolical constant), is such that the sum of density of matter (ordinary and black), and dark energy density is one.

      For the second statement, if Lambda is the cosmological constant that Einstein introduced in his equations, it must be indeed a constant (the energy density of vacuum), even if Hubble constant, which measures the rate of expansion of universe varied of course during history.

      Kind Regards, Alain

  30. Matt:
    Only evidence we have so far is for small positive Lambda.Do you have any feeling why people would consider ADS (negative Lambda ) space as any believable model except that it possibly can be solved mathematically and nothing else can be solved mathematically?!!

    1. Many reasons. (Lambda: the cosmological constant.) Black holes of relatively small size are not sensitive to whether the cosmological constant is zero, positive or negative… so the actual value of the cosmological constant is irrelevant to the calculations. Negative Lambda is a theory that can have supersymmetry (remember what I said about supersymmetry earlier? Now many problems become simpler so you have a hope of solving them and gaining insights that apply even in the non-supersymmetric context.) Furthermore, with negative Lambda you can apply the AdS/CFT (more generally string/field) correspondence, and you can take the problems you’re interested and formulate them more precisely in quantum field theory than you can in string theory. So the experimental fact that there is a small positive cosmological constant has no relevance to the study of quantum mechanics and black holes.

    1. One of the logical possibilities for the resolution of the firewall paradox or eg what survives is called strong complementarity, or A ? Rb. This isn’t logically far from the original proposal..

      1. There is no consensus, and honestly I’m tired of 25 years of vague proposals with no math to back them up. This problem needs an influx of precise thinking, or brilliant new insight, if we’re not to keep going round in a big, slowly-rising helix.

  31. Wow, a post covers almost the entire frontier of physics; the quantum gravity, the supergravity, the black holes (including the firewall problem) and cosmic inflation. But, most importantly, it is about the following comments, “Susskind stated clearly his view that string theory, as currently understood, does not appear to provide a complete picture of how quantum gravity works. … It’s remarkable to hear Susskind, who helped invent string theory over 40 years ago, say this so forcefully.” The Apple Boy was truly moved by this comment and had a discussion with his G-grandmother.

    Apple Boy: The M-theory and SUSY were the only two huge trees in the physics forest for the past 50 years. Now, someone (including the original tree planter) finally admit that they have barked up the wrong trees. Especially when this is reported by a great physicist Matt Strassler, it will be truly a genuine news. Hi, G-grandmother, what do you think about this quantum gravity and black hole issues?

    G-grandmother: Oh, they are deeply entangled with the quantum principle, you know. The only way to resolve these issues must first get the bottom of the quantum principle, as I said last time that it is *the* issue. Which one of the two cases below is the correct answer?
    1. Quantum principle (fundamental) causes the nonzero vacuum energy (emergent).
    2. Nonzero vacuum energy (fundamental) causes the quantum principle (emergent).

    Apple Boy: I can obviously see some differences between the two cases. But, what is the big deal?

    G-grandmother: Huge, huge. There are huge differences in three tiers.
    First, in case 1, the size of vacuum energy is controlled by the quantum fluctuations, that is, it can be any size depending upon the moods of the quantum daddy. On the other hand, in case 2, the vacuum energy is set by the fiber-structure of the space-time field, and the quantum fluctuations are the squires of the vacuum energy master.

    Apple Boy: What is the fiber-structure of the space-time field? I have never heard about this before.

    G-grandmother: Oh, this is the second tier huge difference. When we see quantum principle as the fundamental, we block the true fundamental (the space-time field) from our view. It is the *fiber* of the space-time field gives rise to quantum principle.

    Apply Boy: Well, it is great. But, so what? By following your saying, the quantum principle is correct, and it is a great tool for solving physics problems. Do we need to know the fiber of the space-time filed? As far as I know that no one on this Earth knows about it? That is, even if *you* tell us the answer, no one will believe you. How can you convince anyone that your fiber story is correct if you do know the answer?

    G-grandmother: Wow, boy, you really got me. I have never thought about the issue of convincing others. Well, you have been driving for many hours. How far away from home now. I got to take a break for thinking about that challenge.

    Apply boy: Only 14.15 miles from our driveway now, this moment. Just relax, no big deal.

    G-grandmother: Wow, how can you get the distance so accurately?

    Apply boy: GPS. With GPS you know. About 16 satellites orbiting the Earth, and they together can calculate the location of every point on Earth and can give out the precise distance between any points on Earth.

    G-grandmother: Oh, I know, I know now. When I came down from upstairs, I did see some metal balls flying around in space, peeking on some *landmarks*. That is, the landmarks. As long as they know their own position relating to those landmarks, they can calculate the location of every point on Earth. But, it is plagiarism, the violation of the copyrights, you know. It was the precise way that the *Nature-master* used for constructing the fiber-structure of the space-time field.

    Apply boy: Very interesting. There is a landmark for the space-time field. How many landmarks the Nature-master needs for his work? GPS uses many landmarks, you know.

    G-grandmother: One, just one. Nature-master has three crowns; Omnipresent, Omnipotent, Omniscience. So, he needs just one which is eternally accurate, not shakable by any external forces (good or evil).

    Apply boy: Wow, what is it? What is its name? Where is it located?

    G-grandmother: Name? Oh, no name. Nature-master did not give it a name. But, your brother told me a while back, it is called Alpha [α (electron fine structure constant)], a pure number which cannot be changed by any external force. With that eternal landmark, the Nature-master made three *rulers*; ħ (Planck constant), c (light speed) and electric charge. With the reference point anchored (the landmark), he used these three rulers to map out the space-time field. By the way, being very lazy, the Nature-master made two auxiliary landmarks; the Cabibbo and Weinberg angles.

    Apply boy: Well, it is a truly interesting story. But, how can you or the Nature-master convince anyone that it is the correct story.

    G-grandmother: Backward, go backward. Only with the correct fiber structure, one can *calculate* (derive) those landmarks. So, anyone who can derive Alpha is having the correct knowledge of the fiber of the space-time field.

    Apply boy: I just checked the Wikipedia now, and it says that no one is able to calculate the Alpha. After all, we got back to the ground zero. There is no hope of getting any answer for those great issues; the quantum gravity, black holes.

    G-grandmother: Oh, no, no. Your brother showed me an equation about how to calculate the Alpha a while back. I hate math, you know. So, I asked an 8th grader to check that equation out. The number comes out exactly correct. As he knows no physics at all, he won’t even know how to mess up the calculation. So, I am quite confident about that equation. By the way, what is Wikipedia? You seemingly take it as Gospels. Why does it not list that equation?

    Apply boy: You are really outdated. Now is 21st century, you know. A correct equation is often not politic correct, and of course, it cannot be correct. But, I think that there another way to resolve those issues. Now, the dark mass and dark energy are two greatest mysteries in physics. When they two are resolved, all other issues will be resolved too. Don’t you think? By the way, what is the third tier difference?

    G-grandmother: Boy, you are definitely correct. But, they are not mysteries but two pieces great *cakes*. About the third tier difference, embarrassing, very embarrassing…

    1. Tienzen: you said α is a pure number which cannot be changed by any external force. I’m afraid it’s a “running” constant. It varies with energy density. See NIST at http://physics.nist.gov/cuu/Constants/alpha.html :

      “Thus α depends upon the energy at which it is measured, increasing with increasing energy, and is considered an effective or running coupling constant. Indeed, due to e+e- and other vacuum polarization processes, at an energy corresponding to the mass of the W boson (approximately 81 GeV, equivalent to a distance of approximately 2 x 10^-18 m), α(mW) is approximately 1/128 compared with its zero-energy value of approximately 1/137. Thus the famous number 1/137 is not unique or especially fundamental”.

      Sorry about that. I wonder if it’s got something to do unifying gravity and electromagnetism and quantizing gravity myself. Especially when you start looking at α=e²/4πε₀ħc and conservation of charge along with α varying with gravitational potential. But that’s one for another day.

      1. Correct: look at http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-known-forces-of-nature/the-strength-of-the-known-forces/ , Figure 2.

        Trying to unify electromagnetism and gravity [which is what Einstein, not knowing what we know today, wasted 30 years on] would be a mistake. You need to unify at least hypercharge and weak isospin ( see http://profmattstrassler.com/articles-and-posts/particle-physics-basics/the-known-apparently-elementary-particles/the-known-particles-if-the-higgs-field-were-zero/ for their definitions) with gravity if you want to play that game. Most attempts at unification first unify weak isospin and hypercharge with the strong nuclear force (so-called “Grand Unification”) and then at around the same distance, or a bit shorter distances, unify all three with gravity and perhaps other things.

          1. John,
            In case you are interested there is a book: “Nothingness: The Science of Empty Space” by Henning Genz that covers the variation of the electromagnetic force with energy. The physics section of any decent library should have it. Also if you are interested in an actual experiment you might want to check out: “Measurement of the Electromagnetic Coupling at Large Momentum Transfer” in the Physical Review Letters 78, 424-427 (1997) where 1/α was found to be 128.5 +/- 1.8 at 57.77 GeV.

    2. Apple Boy: Hi, G-grandmother, your landmark and the fiber of space-time ideas are not appreciated by a commenter duffieldjohn, he says, “Thus α depends upon the energy at which it is measured, increasing with increasing energy, and is considered an effective or running coupling constant.” Professor Matt Strassler also says that “You need to unify at least hypercharge and weak isospin with gravity if you want to play that game.” What do you say?

      G-grandmother: duffieldjohn’s saying is not wrong. When someone took pictures of me, those pictures are all different. I don’t even recognize that some of them are truly me. I talked about only two points.
      a. The fiber of space-time field is the fundamental while the quantum principle is the emergent.
      b. The fiber-structure of the space-time field was laid out with a landmark as the key reference.
      If they agree with these two points, the other nitty-gritty does not concern me. If the Nature-master used a different landmark, it will be just fine with me. Matt’s comment really hits the point. But, it is so big an issue and cannot be discussed with a few comments, you know. We need to do some preparations for that huge, huge feast. Furthermore, I have heard that gravity was described in many different ways; by Newton, Einstein, quantum gravity, supergravity, etc.. How can gravity be unified with anything else if it itself is a pile of marbles. Thus, first, we must know exactly what gravity is. The dark mass and dark energy play a big part in gravity. So, this unification issue can be started from these two issues. Most importantly, these two issues are more clearly defined by the Planck’s data, that is, there are *numbers* to be checked with, and we won’t go into the tongue in cheek arguing.

      Apple Boy: In the article “Storm in Ice Cube (Résonaances)”, it says that a PeV dark matter candidate was discovered. I think that the dark matter issue will be resolved very soon.

      G-grandmother: Oh, that will be truly nice. Pev x N (numbers in the universe)/visible matter = 5.3526, then they got it. Maybe their model is a bit more complicated than that, but this is the basic idea. The dark matter issue is very simple, you know, as the ratio is known from the Planck’s data to be 5.3526, a very simple number to check with. But, I have peeked into the Nature-master’s file box of the dark matter, I did not see any Pev type dark matter in there. Is any known physics model predicting a Pev dark matter? Or someone has to come up one in a hurry?

      Apple Boy: It sounds simple enough with the ratio known. That the one who can whip up that number in some kind of physics equation must be the winner of this puzzle solving game. But, even that dark matter puzzle is solved, I am still confused about this mass-charge issue. What the heck is the mass-charge anyway? For electric charge, it is unique, only one charge regardless of who is carrying it. Why are here so many mass-charges?

      G-grandmother: What? I never know that. I was told by the Nature-master zillion years ago that there is one and only one mass-charge. Maybe something new has evolved in this universe since my last visit. Can you tell me how many different mass-charges there are?

      Apple Boy: Oh, G-g-mother, you are really outdated. The up-quark is many times heavier than electron, not to say about the e-neutrino. If we use the electron mass as the charge unit, it won’t work for the neutrinos. We just very recently discovered that neutrinos also carry mass-charge, you know.

      G-grandmother: Thanks heaven, boy. I thought that you was talking about something huge and difficult. This is no issue. Those 48 matter particles all carry different masses, but they are not different mass-charges. Those 48 are 48 pimples on the mass-charge. Those pimples weight differently, but the mass-charge which they sit on is all the same. There is only one mass-charge in this universe.

      Apple Boy: Wow, never heard about this before. How can you convince anyone on Earth about your pimple story?

      G-grandmother: The number, the dark mass/visible mass ratio number (= 5.3526), from the Planck data. The Nature master divided his universe into two dominions; the ocean of energy and the continent of mass. Then, this continent of mass was given to his 48 kids (you call them 48 matter particles) *evenly*, exactly measured by the mass-charge, you know. Yet, only the youngest generation who takes up the stage (not back stage which houses their anti-cousins) is horsing around and making a lot of sparks. The two older generations are stay put inside without giving out any lights. By the way, although the neutrino is also out playing, but it does not giving out lights neither, being too shy, you know. So, the dark/visible ratio = [41 x (100 – w) % /7].

      Apple Boy: What is the w in the equation?

      G-grandmother: Statistics, the out-of-bound statistics. Many balls went out of bound and disturbed those old folks who do give out lights when disturbed. According to the AMS02 data, the statistics is about 8 to 10%. If we choose w = 9, then the dark/visible ratio = 5.33, and it fits the Planck data perfectly.

      Apple Boy: How about the mass of W, Z bosons and gluons?

      G-grandmother: Oh, no. The land right in the dominion is only giving to the legitimate kids (the matter particles) of Nature master. Those bosons and gluons are workers, already counted in their landlord’s account. The different mass for the different landlord is as different name tags for his mass-territory, a pimple on the mass-charge, so to speak.

      Apple Boy: Well, even if this is correct, it is only 1/3 of gravity story. How about the dark energy issue? Is it an important part of the gravity? As far as I know, it is a true mystery now.

      G-grandmother: Definitely, dark energy, 2/3 of story. Mystery? Kind of. But, no. But, not today.

  32. Just wondering if theories that maintain that gravity itself reverses at very small distances (on the order of 10^-16m) so that singularities cannot arise and as a mechanism for inflation were discussed or have been eliminated.

    Also wondering if theories that maintain that gravity itself reverses at very large distances (on the order of 10^26m) as a mechanism to explain the accelerated expansion of the universe were discussed or have been eliminated.

  33. To start with, not even the NSA has unlimited computer power.

    Many computational problems for the sets of equations used in cosmology are of the NP (Non Polynomial Time) type.

    In fact, many of these problems are also of the NP-hard kind, which means that they are of the NP-Complete kind actually!.

    Besides all these considerations, we do not completely master the physics of quantum gravity, so, we are not able to design a complete solution to these types of problems, even if we do have enough computing power to spare of these problems.

    Kind regards, GEN

    1. “Unlimited” computer power was meant in the sense as “sufficient computer power to obtain a reasonable numerical approximation of the problem that allows to study the effects in a qualitative manner”. Also, NP-hard problems may have approximations with polynomial behaviour, i.e., much easier and faster to calculate.
      What I have particularly in mind is that in some sciences, such as astronomy, the advances of numerical simulations now allow to study effects that were impossible to investigate some 20 years ago: collisions between two stars or two planets; many-body problems of some 10,000 or 100,000 stars describing the (approximate) evolution of a galaxy; even attempts to simulate an anisotropic supernova.
      The question is now if we may expect similar advances in the field of particle physics and cosmology, or if the problems are more fundamental.

      1. Markus,

        I’m assuming that when Matt speaks of the problems with simulation he is saying the algorithms are of NP or undecideable complexity. Are we talking traveling salesman or halting for the algorithm?

        You are correct that there are approximations for many of these, but they are approximations. We can’t know how good the approximations are. If we could know, the problems would be no more than P complexity so the approximations would not be needed.

        We can simulate an atom bomb and note it looks close to the real thing so have confidence in the simulation. But if you simulate the inside of a black hole with a polynomial approximation, how can you know if you are correct?

        1. Isn´t it a general problem how to know if a description of the “inside of a black hole” is correct? This problem also occurs if you use a set of physical equations, and suppose you can solve them without making any numerical approximations – it is still possible that these equations no longer hold (exactly) true if some kind of new physics comes into play for what happens “inside a black hole”.
          So my guess is the verification, if we talk about experimental data, can only come from effects (for example, outgoing radiation) observed outside the black hole, that by theoretical reasoning are related to its inside. (This approach is clearly limited to the viewpoint of an outside observer; it does not reflect the view of someone falling into a black hole.)
          An approximate numerical model, if it were feasible (and I note that Matt says it is not feasible now), that could roughly reproduce such observed effects could at least serve as a “toy model” helping to understand some aspects. Maybe similar as theoretical models which introduce supersymmetry into the equations, not because it is a proven concept but because the resulting equations are easier to solve, and give some insight in some processes.

          1. A reminder: the classical equations of general relativity tell you that no new physics should be needed inside a black hole until you get to the highly curved region near the singularity. In other words: you cannot evade this problem by saying, “oh, we just need new laws of physics inside the black hole.” That would already contradict **classical** general relativity.

            And you can’t entirely quarantine the problem “inside” the black hole, since the black hole is going to evaporate before long and then you’re left with the problem. Moreover, it’s not even clear how quantum spacetime should be viewed. Is it clear that “inside” and “outside” are precisely defined, once spacetime starts fluctuating?

    2. Gen,
      NP does not stand for Non-Polynomial, rather is stands for Non-Deterministic Polynomial. In other words, these problems (e.g. the Traveling Salesman problem) can be solved by a non-deterministic Turing Machine in polynomial time.

      1. @SomeGuy: you are right. NP stands for Non-Deterministic Polynomial.

        NP problems will demand exponential time (non polynomial time) in a Deterministic Turing Machine, as much as the will demand polynomial time in a non deterministic Turing Machine, as is this second situation that gives name to Non-Deterministic Polynomial.

        Kind regards, GEN

  34. Matt, how do we have to understand your statement “the mathematics required to study these problems is simply too hard — no one has figured out how to simplify it enough […]” Does it mean that the governing physical equations (and initial/boundary conditions) for the problems are known, but it is currently not possible to find a solution of these equations? Or are the equations themselves not yet clear?
    (You wrote something in response to kashyap vasavada and the issue of many particle scattering, but I am asking more in general.)
    The background of my question is: If we had unlimited computer power, it seems likely that we could find a numerical solution to a physical problem if the mathematical equations can be precisely written down. It would be rather an advance in technology and computational algorithms that would put the solution of the problem within reach. On the other hand, if it is not yet clear which equations to solve, having more computer power at hand would not help us.

    1. The computer power that would be required to compute a quantum field theory descriptions of how a black hole forms and evaporates in quantum gravity (which is the only way we know how to set up the computation rigorously) is far, far beyond current computational ability.

      So the only way to try to solve this problem at present is to simplify the problem, and the equations, by making a clever set of assumptions and approximations.

      However, it isn’t even clear that the quantum field theory method that I’ve just described could really answer the question of what happens from the point of view of someone who falls into the black hole.

      So (a) there do exist rigorous equations that we could in principle try to solve, but doing so is out of reach, and (b) we’re not even sure that the solution we’d obtain would be enough to solve the most critical questions, because they might only tell us about what a black hole looks like to an outside observer, and not to an observer who will and then does fall inside… much less how to reconcile the views of different observers.

  35. I think black holes might be a red herring Matt, and would venture to suggest that the necessary insight might be found in classical electromagnetism and how it relates to QED, and then how it relates to general relativity. Take a look at “The role of the potentials in electromagnetism” by Percy Hammond and see this bit near the end note: “We conclude that the field describes the curvature that characterizes the electromagnetic interaction”. I suspect the strong curvature regime isn’t down near a black hole. I suspect it’s right there in electromagnetism. I haven’t read it, but if you can, take a look at “Geometry of Electromagnetic Systems” by Daniel Baldomir and Percy Hammond. I can say more if you’re interested. There’s maybe a clue to it in gravitomagnetism. Meanwhile imagine you pluck a guitar string. Take a high-speed snapshot of the vibrating string. It’s curved.

        1. Insights are not useful if they do not come with equations. I do not mean cocktail party conversation, or conversation at a bar over a beer. Without equations, it’s just blahblahblah. The idea that particles are strings vibrating in different ways means nothing — NOTHING — until someone actually writes down an equation describing how a string vibrates, or how two strings scatter off one another. From there, you can start to make progress. Without those equations, I guarantee you that your guess as to how things work would be wrong. No one, for instance, would have guessed that if you take a loop of string, make it relativistic, and add quantum mechanics, you get a massless spin-two particle — and thus general relativity — as an output. Talk is cheap.

          1. Matt, with respect that’s Catch-22. When some guy writes down an equation (it won’t be me) all those other guys at that conference will be left high and dry. When he’s giving his speech in Stockholm they’ll all be kicking themselves because HE turned the insight into an equation, whilst they rejected it and demanded an equation instead. And when they’ve got it, who needs them?

            1. Usually, when the great person has the great idea and solves the great problem, the solution is built on the work of others. For instance: Einstein solved the puzzle of his day by inventing special relativity, but he could not have done it had he not had the clue of Lorentz and Fitzgerald’s contraction equations. For instance: when ‘t Hooft solved the problem of renormalization of the Standard Model’s equations, he had a lot of prior work behind him that he could build on.

              Alternatively, what often happens is that a large group of people solves a problem collectively, over time. For instance: Quantum mechanics. Planck solves a thermodynamic paradox by introducing some notion of quanta, but doesn’t know what to do with it. Einstein suggests light is quantized. Bohr suggests atomic energy levels are quantized. Lots of other people make progress in other directions. It’s all very confusing. Only over 25 years does the picture start to come into focus. No one person solved quantum mechanics; but each person introduced new equations, new mathematics in some cases, and each generation of ideas built upon the equations of the previous one. No one had the insight that “the world is governed by quantum mechanics” in one step. It wasn’t talk: it was hard work, small insights, new equations, experiments, more hard work, more small insights, more new equations, more experiments, etc…

  36. Matt, could you suggest one or two examples of the following: “But even if it [supersymmetry] is not [true], the solutions to hard problems in supersymmetric theories may provide general insight into what the solution in the real, non-supersymmetric world may qualitatively look like. There are a number of striking examples of success with this approach.”

    1. These examples are quite technical, so that’s why I didn’t just lay them out in a few lines. I’m sure if I think for a while I’ll come up with other examples, but here are a few — not sure of your technical background, but maybe a few of them will make sense.

      1) Insights into “confinement” of quarks (i.e. why you never see quarks, antiquarks and gluons by themselves, but only find them in hadrons) and chiral symmetry breaking (why quarks and antiquarks form a Higgs-like field that, like the Higgs field, has a non-zero value in nature, explaining why pions are light particles.)

      2) Significant insights into the “pomeron” (the effect that governs how hadrons scatter off each other at very high energies and very low angles.)

      3) Significant insights into the ubiquity of conformal [for our purposes, `scale-invariant’ or fractal] quantum field theories in three (and other) spatial dimensions.

      4) Insights into how to view jets of hadrons (experimental manifestations of high-energy quarks and gluons) concerning when they do and don’t arise in quantum field theory.

      5) New insights into how theories with only gluons (“Yang-Mills theories”) work.

      6) At least two possible new solutions to the hierarchy problem (i.e. the naturalness problem of the Standard Model.)

      7) New calculational techniques for making predictions for particle physics experiments.

      8) Insights into how quantum field theories with strong forces work at finite temperature.

      9) Significant insights into subtle tunneling phenomena called “instantons” (discovered by ‘t Hooft, mentioned above, and by Polyakov, this years Fundamental Physics Prize winner)

      10) Possible insights into poorly understood phenomena in solids.

      … I’m sure I haven’t exhausted the list.

      1. Thanks for the list–coming up with 10 items is a thorough reply even if you say there are many more! I have a general idea about some of these problems (I did a B.Sc in Physics, finishing in the early 90s, before switching to another, non-scientific field for graduate work) but I guess what it’s hard to imagine–and what I’d like to be able to imagine–is the nature of the general insight you can get from a solution that is predicated on a particular theory, such that the insight is still valid or useful even in the absence of that theory. (Presumably the insight required the theory–but if the theory ends up not corresponding to reality then I would have thought that the solution it suggested has no better chance of corresponding to the real world solution than a solution generated by any other incorrect theory.)

        1. ” if the theory ends up not corresponding to reality then I would have thought that the solution it suggested has no better chance of corresponding to the real world solution than a solution generated by any other incorrect theory.)”

          On the contrary. Why do biologists study mice? Because they share some common features with humans. Cats, dogs, even flies. Not all lessons learned from mice apply in humans. But many do.

          You probably will only be married once or twice. But you probably dated more than that. Don’t you think that you learned about relationships and kindness and sensitivity and how to interact with others from people you dated for short times, lessons that were (or will be) valuable in your marriage even though they were learned from people you didn’t marry in the end?

          Black holes in string theory, in loop quantum gravity, and in any candidate theory of quantum gravity will have similar features. It is quite possible that if you use the wrong theory to understand how black holes work, the lesson you learn will still apply to all candidate theories of quantum gravity. The only way to find out is to calculate and learn the lesson, and then think about what it means.

          The history of theoretical physics shows very clearly that what you learn from the wrong but calculable theory can be as important as what you learn from the right but impossibly difficult theory. We have learned a great deal about the theory of quarks and gluons in the real world by studying other theories that differ in some ways and are similar in others. Sometimes we learn from the similarities. Sometimes we actually learn from the differences.

          1. You wrote: “You probably will only be married once or twice. But you probably dated more than that. Don’t you think that you learned about relationships and kindness and sensitivity and how to interact with others from people you dated for short times, lessons that were (or will be) valuable in your marriage even though they were learned from people you didn’t marry in the end?”

            Yes absolutely! But the people I dated before marrying were actual, real-life non-fictional people, and to a first approximation we understand why behaviour that is attractive or unattractive to one person will be received similarly by another person–there are fundamental things that are common to most/all people. But if supersymmetry is not based in fact, then I would have imagined the analogy being some loner who got their advice about how to treat their future spouse from his/her interactions with imaginary friends.

            Having written that, though, I can see that the imaginary friends scenario would be better than nothing as an approach to figuring out how to deal with people.

            1. Regarding the imaginary friends: remember, also, that we can often calculate very precisely what happens in imaginary worlds. The precision of the information is important.

              However, it is also true that this approach comes with a caveat — just as it does for biologists studying mice, or a person applying lessons from past relationships to a new one. Proceed With Caution. Not all lessons learned are general ones.

  37. If the history of Physics teaches us any lesson, it is a lesson regarding the fact that nature is “weird” and goes by rules and laws that sometimes are puzzling to are understanding, and we have to accept that and learn the hard way, taking it in strides.

    Kind regards, GEN

  38. It does not surprise me that Susskind is very candid and open regarding his concerns of this problem and how current scientific knowledge and tools are not adequate enough.

    That reminds me of that story about the “Richard Feynman” sandwhich, and how Feynman said that his sandwhich “had a lot of ham but had no baloney”.

    Kind regards, GEN

    1. I’m totally unconvinced. I don’t think anything I’ve heard from anyone on this problem suggests that a solution is close at hand. The basic mathematical problem — even the proper formulation of the basic mathematical problem — remains unsolved.

      Crudely speaking, the AdS/CFT correspondence (the quantum equivalence of field theory and string theory, in appropriate settings) allows you to use quantum field theory to learn a lot (not everything) about black holes from the point of view of someone who remains outside the black hole. It does not help you learn much about the point of view of someone who falls in, or about how the viewpoints of the two are reconciled.

  39. As far as I understand it (not much, actually), The Firewall Problem is related with “how probability is conserved and how different observers view the event”.

    the matter of the famous “Black Hole Wars” is not (completely) resolved yet, in the sense that there is still not an answer to how the information of what happens within the back hole (BH) will not be lost when the BH evaporates.

    Besides this, it is not completely understood what different observers see when an object passes through the event horizon of a BH into it.

    Actually, it is this last problem in particular that the “Firewall” controversy actually describes.

    Kind regards, GEN

  40. I don’t know if there is a simple answer to this question. But let me ask anyway. First, do you agree that gravity in the Einsteinian form comes out “naturally” from string theory (as some claim)? In that case there would be a paradox. If ST is extension of SM and QFT (at least consistent with) then why should there be any problem in quantizing gravity within ST?

    1. Gravity does come out naturally from the consistency of string theory — but in fact it would come out naturally from any consistent theory of a spin-two massless particle, so this isn’t quite as magical as it looks. The magic, in a sense, is that string theory actually has a spin-two massless particle at all.

      There’s no “problem” quantizing gravity within string theory as long as you want to do what string theory calculations do best: give you the results for scattering particles (including gravitons) off each other.

      But there are deeper problems in quantum gravity than simple scattering, and string theory doesn’t tell you how to formulate them. In particular, if you scatter many particles off each other at high energy, so that you can form a black hole, string theory methods — at least, the techniques in string theory that we have learned up to now — don’t tell you enough to figure out what happens next… at least, not completely, and not at the level which allows you to understand the most critical things about how probability is conserved and how different observers view the event.

      1. Thanks. Do I understand that it is not just computational difficulties of many particle scattering in ST but fundamental problem with conservation of probability and black holes etc?

        1. Somewhere in between. It’s not computational difficulty of many particle scattering, because the available techniques for doing particle-scattering are not really the right ones when you have the formation of a black hole horizon. There are, however, other clever techniques that can be applied in this context; these were learned in the 1990s and go under names like “gauge/string duality” (also known as AdS/CFT correspondence). However, powerful as these are (and I myself learned a great deal about quantum field theory using these techniques) and despite the fact that they allow new ways of looking at and studying black holes, they don’t seem to be enough to resolve the key puzzle about black holes and quantum mechanics.

          It’s not merely probability conservation — it’s really the whole structure of quantum mechanics in the context of strong gravitational fields, such as are found near a black hole. How does quantum mechanics work from the point of view of an observer who falls into the black hole after it forms and never comes out? How does quantum mechanics work from the point of view of an observer who remains outside the black hole while it forms and evaporates away to nothing? And most important of all, how does quantum gravity reconcile those two viewpoints, whatever they are? There are fundamental conundrums here, which go back decades; I first heard about them when I was a young graduate student.

      2. What GR is really good at is giving you geodesics in a block universe when supplied stress-energy at every point in spacetime. However, what would be more useful in practice is in giving stress-energy when supplied partial geodesics, and in a way which lets one readily infer the components of that stress-energy and how they evolve. Initial values formulation approaches are a tractable step towards that, but the problem there is that constraints on the evolution of stress-energy have to come from outside GR, for example from the SM. Understanding the mechanism by which a metric is generated gets harder when importing things like uncertainty relations — would one really observe a metric sourced by a huge mass-energy in a superposition where location is the state that is superposed ?

        1. In answer to your last question: yes, I think so. If not, then all the inflation calculations on how structure is formed from quantum fluctuations are wrong. No?

          It’s not the amount of energy that matters. It’s the causal structure of the space. It’s what a black hole does to the causal structure that makes quantum mechanical arguments problematic.

          1. Well, that’s the semiclassical gravity answer, isn’t it? 1/{\sqrt{2}} (|M at location A> + |M at location B>) decoheres into the metric sourced at A with 50% probability and the metric sourced at B with 50% probability, no? The question then becomes how to pick out one of the classical states — where does one find the answer to that?

            The causal structure is a closely related problem – if a particle with evolving internal degrees of freedom (“a clock”) is in a superposition of two locations at different gravitational potentials you get a mess [ arXiv:1105.4531 [quant-ph] ]; if you try to build a superposed metric with nonnegligible curvature you’re unleashing the same problem.

            I’m not sure what you mean in your second paragraph’s first two sentences.
            The causal structure of spacetime is tested and dynamically driven by “clocks” in the most general sense per the GR resolution of Einstein’s hole argument, and background independence more generally, isn’t it? (I think we agree on the final sentence if the black hole is compact energy).

            1. Paragraph 1: the answer is the same as in any measurement, no? It’s all in the correlation of the metric with the observer. That’s how inflation works: what we see is the part of the wave function of the universe with which our existence is correlated.

              Paragraph 2: I can imagine that this is extremely complicated to do technically. But I don’t know if this is a problem of principle… Maybe it is, but if so, that’s an important point.

              Paragraph 3: Not sure I followed you here…

          2. Where curvature is large, you get a situation where for a particular observer A is beyond an event horizon (from black holes, cosmic inflation, or even the metric expansion of space) and B is not, leading to the sorts of questions the firewalls debate is asking. EPR pairs near black holes sharpen questions about censorship arguments, particularly those in which big bang and big crunch (or flipped cosmological arrow of time) singularities are strongly censored and black hole singularities are transient. However the problem is (I think) probably more general, i.e., it applies to accelerated quantum systems where event horizons and EPR = ER arguments are not (or not obviously) involved.

            The third paragraph that was difficult to follow was just late-night defensiveness about doing GR on fibre bundles and not on manifolds.

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