Horizon: Before the Big Bang

This week the BBC showed a program in their long running “Horizon” series about the question “What came before the Big Bang?”  Here is the gist of the message: A few years back cosmologists accepted that time did not exist before the big bang, so the question did not make sense. The universe along with time itself just started to exist and has been evolving nicely ever since. But now cosmologists are forming all kinds of theories that do put something before the big bang to explain how and why it happened.

So here is a list of the scientists that featured and the theory they adhere to:

  • Andrei Linde: Multiverse inspired eternal inflation
  • Param Singh: Big Bounce due to repulsive gravity at small distances
  • Lee Smolin: Black Holes spawning baby universes
  • Michio Kaku: Vacuum fluctuation from empty space
  • Neil Turok: Colliding Branes
  • Roger Penrose: The future is empty expanding space = a new big bang
  • Laura Mersini Houghton: String cosmology

Each of these ideas has been around for some time and has been worked on by several people. The individuals mentioned here are not necessarily the ones who invented them. The Penrose theory is an exception in that it is a new idea that features in his next book.

In the program each of these scientists was interviewed while they tried to solve one of those  wooden puzzles

The obvious conclusion to draw is that there are a lot of viable theories out there which cannot all be right. Each of the scientists seemed to have quite a strong belief in the theory they supported, but they would all acknowledge that more experimental input is needed to resolve the question. All of them are driven by a philosophical argument that temporal causality must hold absolute so some prior cause of the big bang is needed.

Along with all the theorising and philosophising, a couple of experiments were mentioned which they think might help test these different hypothesis. The first was LOFAR, a low-frequency radio telescope array that may detect background remnants from the big bang. The standard prediction is that it will be white noise, but anything else could be a clue that separates different theories, prepare your predictions in advance please. The second experiment was the more familiar LIGO and its space bound successors LISA. These may be able to detect a gravitational wave remnant from the big bang that could also have a distinctive signature. It is hoped that either of these experiments may see past the wall of last scattering from which the cosmic microwave background emerged to provide information from an earlier time.

Personally, I don’t accept the philosophical need for something before the big bang and I don’t particularly like any of the theories mentioned. I think it is more likely that there was no space or time prior to big bang singularity which itself is a high temperature and density phase with no fixed topology or geometry for spacetime. I am not alone in preferring theories that do not require time to extend before the big bang, but the program has selected those that do. Where was Hawking’s view for example?

I think that explaining the universe requires us to look at ontological causality rather than temporal causality and the big bang is just one feature of the universe, not the reason for its existence. Although the experiments mentioned and others may throw some light on the nature of the big bang, we first need a better understanding of quantum gravity. There is still scope for theoretical developments that may help even before the experiments bear fruit. Even if you favour the string theory/M-theory route to quantum gravity (as I do), a better understanding of their foundations is required before we can hope to answer these questions about cosmology.

Despite that, I don’t think it is wrong to explore a wide range of cosmological ideas of this kind provided they have some good mathematics behind them. It is time for science to start trying to answer such questions. They will have to be looked at from all angles, philosphical, mathematical and experimental if we want to get the right understanding.

For the record I thought this was a good Horizon program, some of their physics/cosmology episodes lately have been a bit empty and ill-conceived. The position was too one-sided, but well researched. I’m glad they did not make the mistake of mentioning the LHC as if it was likely to resolve these questions, but did mention some other experiments that stand a better chance.  

If you missed the program or it is has not yet aired in your country, I dare say you will find it on the web using Google video search. I wont provide any links because I don’t know which if any are legal copies, or how long they will remain available, or whether the same links will work everywhere.

60 Responses to Horizon: Before the Big Bang

  1. David says:

    What I am really interested in is the wooden puzzle featured in the program. What is the name of this 3-D block and where to get one? Thanks!

    • Luboš Motl says:

      It doesn’t seem to have a name but visually it looks like this “wooden puzzle”:


      • Philip Gibbs says:

        I have one that is very similar or perhaps identical to the bigger one on the left, but I’m not sure where I put it. I’ve had it for about thirty years so these things are not new. If I find it I’ll post a picture

        My one is not very difficult to take apart once you spot the key piece, but it is hard to put back together, especially if you forget what it orginally looked like. I think some of the newer versions are harder to take apart. Some of the cosmologists did not seem to be finding it very easy!

  2. Philip Gibbs says:

    There are lots of puzzles of this type. I can’t be sure but it might be the Ramube Octahedron or Dragon Burr but there are many others that look similar. How many pieces do they show when it is taken apart?

  3. Lawrence B. Crowell says:

    Maybe all of these are equivalent. The interior of a black hole near the singularity has an extremely polarized vacuum structure. A string from the perspective of an infalling observer is subjected to an extreme Weyl curvature. This is dual to what an exterior observer sees of the string on the black hole horizon, as it is extended in dual transverse directions. So the NS5~ M2 brane duality with the “black brane” is a dual description of the Smolin hypothesis on BHs spawning cosmologies. The S-dual of the gravitational mass is a NUT parameter, so the dual of a black hole is a Taub-NUT spacetime. Now take this space, make the spatial extent small and draw it into a string — a gravitational analogue of the Dirac magnetic monopole string. Now bolt this onto Dp-branes, and these are the topological indices associated with type II strings attached to these branes which induces their interactions or collisions. So this is an S dual perspective which links the Smolin BH theory with the Turok theory. Now the AdS_n spacetime associated with the brane has this correspondence between the isometries of its boundary and the conformal symmetries of QFT, extending to AdS_nxS^n. The Taub-NUT “bolt” has a discrete winding structure and is a description of AdS_nxS^n/Z_p, which is U dual to AdS_n/Z_p xS^n which describes gravitons on the AdS boundary. These are gravitons in the vacuum — connecting in some ways Turok with Kaku.

    These are possible tools in the toolbox, but these are ways of thinking which makes it likely in my mind that these are all different descriptions of the same basic physics. These rather distinct ways of looking at this problem may reflect the fact we do not yet have the central physical idea in our hands. I do think cosmologies emerge from orbifold winding of dual branes, say the M^4xS^7 with a Lagrangian of the form sqrt{-g}R + (1/4)F^2 + …, or extended superspace in 27 or 57 dimensions with Jordan matrix algebra realizations, where the arrow of time is locally defined. Yet these might emerge from either quantum fluctuations or quantum critical points in a grand Lorentzian manifold. On the other hand the fundamental structure is a Fermi-Dirac field which underlies the quasi-conformal structure of such a theory with AdS hyperbolic structure. For instance the Jordan 3×3 matrix algebra has 27 dimensions, which is reduced to 26 dimensions with a constraint on the 3 scalars on the diagonal. This has some interesting correspondences with the automorphism group of the Fischer-Griess group, or the monster group. The dimension removed by this constrant may be thought of as a second time variable in a grand AdS_(27} spacetime. This is then S dual to a Fermi-Dirac field with some strange associative properties. So the nature of time is very strange, for on the AdS and its conformal boundary perspective time is a global property, but from the S-dual perspective on Fermi-Dirac time may not exist.

    These are again possibilities, which indicate that the frontier of our non-understanding is truly vast. The golden age of discovery in physics and cosmology is before us.

  4. HHu says:

    Phil said “I think it is more likely that there was no space or time prior to big bang singularity which itself is a high temperature and density phase with no fixed topology or geometry for spacetime.”

    Well, there is now Prespacetime Journal. Our ontology (metaphor, if one wishes) is simply:

    Big Bang Singularity = e^i0 = 1 (see, e.g., http://vixra.org/abs/0912.0047)

    There is “no fixed topology or geometry for spacetime” in e^i0=1!


  5. HHu says:

    Oops, I mean http://vixra.org/abs/0912.0047

    Also, I mean there is now Prespacetime Journal dealing with the foundation/ontology of spacetime.


  6. Ik says:

    “The obvious conclusion to draw is that there are a lot of viable theories out there which cannot all be right. ”

    There is only one correct theory, only one Truth.

    *I* created the Universe; I have theoretical proof that *I* came “before” the Big Bang.

    I use quotes around before because it is not theoretically accurate. Before implies time, but, since *I* is Eternal, the concept of time breaks down. Perhaps “without” or “beyond” or “against” – but each of these implies a spatial constraint, and “outside” of spacetime is not theoretically deduced to be space. Sigh. Oh to be Ineffable.

    No wonder it’s been so difficult for Me to find the correct theory – I never included My Self.



    • HHu says:

      About Ik: “Ik got a B.S. at U. of Rochester, did a predoc at NIH, received his Ph.D. from Stony Brook, did a postdoc at Cornell, and is now tenure-track faculty somewhere.”

      It’s very sad to see that the Ik has to hide his ID as a few other commentators here also do.

      The establishment as the “invisible prison” for many so that the ones within may survive and/or feed their family.


    • Ulla says:

      The Universe is “I”?

  7. Sam says:

    Nice post. I don’t understand why the Hartle/Hawking model wasn’t included in the discussion either. It certainly is the longest tenured idea and incorporates the Feynman approach which seems necessary to me if we are ever going to make sense out of the notion of emergent time. I realize that in its initial form, the model made the universe closed, but my understanding is that is not strictly necessary.

    • Philip Gibbs says:

      Sam, you probably know this but just to clarify…

      Whether space is open or closed is still an unresolved question. The spatial part of the metric is near to flat on large scales as far as we can measure. It might have a very slight positive curvature making space closed and finite, or it may have zero, or slightly negative curvature making it open and infinite.

      What we do know now with reasonable certainty is that it will not collapse to a big crunch. It will expand forever at an accelerating rate driven by dark energy. This is assuming standard GR models.

      • Sam says:

        Good point about not knowing the curvature, I brought that up because it’s the first critcism leveled at the Hawking model. But actually, I am confused as to how we can rule out the “big crunch” with reasonable certainity. If dark energy is the cosmological constant, this is obviously the case, but it doesn’t seem like there is any consensus on this point.

      • Philip Gibbs says:

        When I say “assuming standard cosmological models” I mean homogeneous solutions to GR with or without cosmological constant. Many people question whether dark energy in the form of a cosmological constant is right but it fits the data well, up to a point.

    • Lawrence B. Crowell says:

      The original Hawking-Hartle paper computed an estimate for the transition into a de Sitter vacuum. So while the paper involves the 4-dim sphere and the Wheeler-DeWitt equation they also compute a probability for the transition to a de Sitter vacuum. The universe we observe is nearly de Sitter, and the no-boundary condition applies for compact manifolds. So the emergence of the universe from the vacuum by a no-boundary condition probably requires a quantum transition to a de Sitter configuration.

      • Lawrence B. Crowell says:

        I don’t think the Hawking-Hartle wave functional is at all that well established. The state Ψ[g] for a metric geometry g_{ij} is constructed by a path integral

        Ψ[g] = ∫δ[g] exp(-iS[g])

        The metric is a spatial metric for a 3 dimensional space which foliates spacetime of four dimensions in the ADM formalism. The action is then defined according to a canonical quantization procedure, so there is a momentum metric π^{ij} = -iħδ/δg^{ij} and the analogue of the kinetic energy is G_{ijkl} π^{ij} π^{kl} and the kinetic energy term is then given by the Ricci curvature of the spatial surface. So in a general setting the Hawking-Hartle state Ψ[g] is defined on a surface of n dimensions and defines the n + 1 dimensional geometries which have the n dimensional boundary as a boundary. Topologically this boundary is a “cap” which may be contracted to a point, and with the machinery employed this leads to the “no-boundary” formalism.

        This sounds great, so why are people casting about with other ideas? There are a number of weaknesses with this hypothesis. First is that the path integral is euclideanized. This leads to a simplification of calculations where the differential equations have an elliptic complex, or a moduli space that satisfies Cauchy conditions. The hyperbolic case is not so easy to manage. So in effect a lot of physics and relativity has been literally swept under the rug. Another problem is that the contact manifold for the functional differential equations here is not understood well. A third major problem is this does not provide a way of summing over topologies. Quantum gravity likely involves quantum black holes being generated from the vacuum, maybe virtual wormholes and so forth. This approach does not make much sense with respect to topology changes. Of course on this last point debates can run amok of course, where there are different ideas about this and so called quantum foam. The string world sheet acts to valence some of this, and for this reason stringy physics tends to dominate these issues.

    • Luboš Motl says:

      Dear Sam,

      the Hartle-Hawking wave function wasn’t included exactly because it makes sense and it is arguably the only meaningful idea on the market to address these issues.

      The program only focused on the ideas that make no sense. A necessary condition for models to be included was that these models have to agree that there was something before the Big Bang: the Hartle-Hawking model disagrees with this assumption so it is included among the “denier” models (the word “denier” was explicitly used in the TV show as well) and they should be given no space in the media.

      Only diverse nonsense deserves to be mentioned by the BBC – so that there can be a consensus that physics is nonsense which is the only thing they really care about.

      Best wishes

      • Lawrence B. Crowell says:

        I hit the wrong reply button in the post just above. Of course after posting this I see a mis-wording as well. I wrote “… and the kinetic energy term is then given by the Ricci curvature of the spatial surface. ,” where I meant potential energy.

        I would not characterize the HH model as a denier model. I think the problem with HH is it has limitations. The boundary space or metricwhich induces metrics on one dimensions higher may be restricted to a very small value, where topologically it is the boundary of a cap which may be contracted to a point. However, we have other physical considerations as well. The cap can’t be contracted to a pure mathematical point due to Planck length limits or string scaling limits. For instance beneath the string scale the forces involved are larger than the string tension. Physics on a trans-Planckian scale leads to a duality with physics on a sub-Planckian scale. So while the HH wave functional is probably a decent approximation to things

      • Sam says:

        Now that actually makes sense, sadly !

      • Lawrence B. Crowell says:


        I failed to post in the last line! Sometimes this stuff gets annoying.

        Lumo writes on his blog on this feature a lot of stuff that is far more about his emotional state (anger) than much else. Everyone should write to him, “DUDE — CHILL!” Seriously, it is not healthy. I am not sure what his deal is with Smolin, when I find him to be a fairly affable guy IMO. What Penrose says about the exponential expansion of the universe reaching nothing, where there are no “clocks” and this being a singularity of sorts, is something I said 20 years ago. I was called crazy.

        There is one basic reason for doing this stuff, it can be fun. If you can’t have fun with this there is no point in it. This means being able to engage people who have ideas different from your own. For all we know many of these ideas might just be different facets of the same big problem. If you are not having fun with this, then even if you have a degree from a top university it might be best to do something else.

      • Luboš Motl says:

        Dear Lawrence, the problem with Smolin is not he isn’t friendly. He is friendly to others, which included his only quasi-friend at Harvard who could have officially invited him after Smolin had repeatedly invited himself. That was myself. ;-)

        The problem with Smolin is that he is working hard and successfully to transform the institutionalized physics into a pile of postmodern junk.

        Yes, I got a bit upset when watching the program. You can’t make me react differently by some silly pronouncements about chill. This is an automatic reaction that reflects both my knowledge and my emotions. It’s still safe when I can divide the 60-minute program to three 20-minute parts, and do anything pleasant in between.

        It would be harder to be exposed to similar garbage for hours every day, five days a week.

        I don’t claim that the Hartle-Hawking wave function is an established fact of science but your criticism of it makes no sense. It’s the very point of the Hartle-Hawking approach that the beginning of the Universe is presented as a smooth patch of (Euclideanized) spacetime, so the singularity and all the related unknowns of the Planckian regime just disappear. So the problem you *attribute to* the Hartle-Hawking approach is exactly the problem that the Hartle-Hawking wave function solves. Your logic is just upside down – it’s completely absent.

        Physics is not about having “any” kind of fun. Physics is a particular process meant to learn the truth about the most rigorous laws that govern the real world. And there is only one truth, and whenever some evidence becomes relevant for a question, it always makes some answers more likely, and other answers less likely. Any process of learning or collection of evidence leads to old questions being more settled and less ambiguous, while it may open new questions. But if a community is increasingly confused about old questions, it is not making any scientific progress. In some cases, it is not doing science at all.

        So what you propose – random babbling about manifestly incompatible speculations, equipped with absolutely irrational wishful thinking that they’re compatible after all – is exactly what physics is not. Some people may have fun with doing garbage of this kind but it’s not physics and it is extremely important to explain everyone who is capable to understand these matters that it is not physics. In particular, you should close your mouth about physics because you don’t have a slightest idea what it means. You can still have fun anywhere else – you’re a free person – but you and your likes have to be eliminated from science because you don’t know what it is and you have absolutely no respect for it.

        Best wishes

      • CfCS says:

        Lawrence B. Crowell Says:

        There is one basic reason for doing this stuff, it can be fun. If you can’t have fun with this there is no point in it. This means being able to engage people who have ideas different from your own. For all we know many of these ideas might just be different facets of the same big problem. If you are not having fun with this, then even if you have a degree from a top university it might be best to do something else.

        Luboš Motl Says:

        Dear Lawrence [...] Physics is not about having “any” kind of fun. [...] In particular, you should close your mouth about physics because you don’t have a slightest idea what it means. You can still have fun anywhere else – you’re a free person – but you and your likes have to be eliminated from science because you don’t know what it is and you have absolutely no respect for it.

        Richard Feynman wrote once:

        For me, physics is more fun than anything else or I couldn’t be doing it.

      • Luboš Motl says:

        Dear CfCS, exactly, but Feynman was talking about actual physics.

        What was discussed on the BBC program is no physics as he would have indisputably agreed. After all, he attended a cosmological conference in Warsaw in 1962 whose content was pretty much indistinguishable from the BBC program.

        He shared his experiences from the conference with his wife:

        “I am not getting anything out of the meeting. I am learning nothing. Because there are no experiments, this field is not an active one, so few of the best men are doing work in it. The result is that there are hosts of dopes here (126) and it is not good for my blood pressure. Remind me not to come to any more gravity conferences!”

      • Luboš Motl says:

        By the way, the history of general relativity (GR) in the 1960s offers some insightful lessons. It turned out to be a very good decade for GR but it was because of very different advances than what the average people were debating e.g. at the 1962 Warsaw conference.

        You know, in the late 1950s, people would start to write lots of classical formalisms, Hamiltonians for GR, and so on – but most of them really didn’t understand what was physics and what was just mathematical masturbation. Dirac distinguished the first- and second-class constraints but he wasn’t able to say anything about quantum gravity. He actually didn’t know what was hard about quantum gravity. Of course, that’s linked to the fact that Dirac never understood renormalization – which really means that he never understood any beyond-the-classical calculations of quantum field theory.

        It actually needed Feynman to really crack the physics and separate it from meaningless babbling. His irritation by the hosts of dopes in Warsaw in 1962 actually coincided with some basic insights about “where the interesting quantities are hiding”. All the people in Warsaw religiously parroted a particular thing: they thought it was very important to calculate the scattering amplitudes using their canonical Hamiltonian formalism.

        But because it was already realized that the loop amplitudes were divergent, they only meant the tree level amplitudes – without loops. Those folks thought it was important to do lots of work to convert GR to the Hamiltonian form – and then use the Hamiltonian form to deduce the scattering amplitudes. It was Feynman who realized that this “dream” was complete rubbish because what one could get from the tree-level amplitudes was nothing else than classical physics of GR one started with!

        So Feynman realized – and he was the only person to realize – that all this Hamiltonian movement (which, by the way, was later transformed into the loop quantum gravity nonsense – despite the failure in the 1960s) was a completely vacuous masturbation with formalism.

        In fact, it was also Feynman himself who did the critical steps to say something about the non-classical physics of general relativity just a year later. In 1963 (and published one year later), he proved that Gupta’s quantization – just ignoring the unphysical polarizations of the gravity waves, like for photons – was inconsistent for general relativity: it violates unitarity at the loop level. He went beyond this negative conclusion: in fact, he realized that one has to add new fields – today paradoxically known as the Faddeev-Popov ghosts of the BRST quantization – to restore the unitarity at the quantum level.

        Many other key contributions of the 1960s were added by John Wheeler. That includes the concept of quantum foam in 1963, Wheeler-DeWitt equation in 1967, and the term “black hole” also in 1967. So the 126 people at the Warsaw 1962 conference could have had fun but it doesn’t change the historical fact that they were dopes who contributed nothing of lasting value to the physics of general relativity, and it was actually Feynman (an “atypical” participant of that conference) who – together with Wheeler – did the most important contributions to GR in the decade.

        Best wishes

  8. The question what was before Big Bang and the question whether this question has actually any sense relate to the earlier topic of discussion, namely whether energy is conserved in GRT or not. In quantum realm the question is whether conserved Poincare charges exist in GRT as Noether charges or not. If find very difficult to believe that they could.

    Requiring that they do leads to TGD Universe where space-times are 4-surfaces in M^4xCP_2. The outcome is what I call zero energy ontology (ZEO) with causal diamonds (CDs) defined as intersections of future and past directed light-cones (double cones) and highly analogous to Penrose diagrams representing causal units. CDs carry the positive and negative energy parts of quantum states at their boundaries. In ZEO every quantum state can in principle be created from vacuum and evolution is a continual re-creation of the Universe.

    There is a hierarchy of the CDs within CDs. Their unions are possible and they can intersect. CD is geometrically analogous to a big bang followed by big crunch and in cosmological length scales it would correspond to sub-cosmology. The zero energy state associated with sub-CD would be called quantum fluctuation in QFT jargon. In length scale of electron CD corresponds to time scale of .1 seconds which happens to be a fundamental biological rhythm.

    Inflationary scenario is replaced by quantum criticality and flatness fixes the R-W metric apart from a parameter characterizing the duration of the critical period. Therefore the scenario is extremely predictive – as it must be from the fact that critical systems obey universality- as compared to the endless variety of inflationary scenarios. The constraint from imbeddability to M^4xCP_2 would fix cosmological evolution and particle densities would be forced to obey the resulting cosmology as long as criticality prevails.

    There is analogy with multiverse of eternal inflation but the fundamental symmetries are same everywhere and there is no landscape problem.

  9. Ulla says:


    We are living inside a black hole horizon. Energy is conserved. This was very clear. But does it mean that light speed isn’t constant?

    The universe expands such that the square root of its size matches the wavelength of the light from the big bang.

  10. Lawrence B. Crowell says:

    The universe is not a black hole. This can be seen rather simply. As objects approach the interior of a black hole the Weyl curvature increases. This induces a tidal force. So a spherical cloud of particles would be drawn into an prolate ellipsoid, or cigar shape. So we would observe galaxies along an axis at antipodal directions recede away and red shifted. However, galaxies along the equator or 90 degrees from this axis would be moving towards us and be blue shifted. This is clearly not what we observe, for this would be an anisotropy of considerable extent.

  11. CfCS says:

    A few years back cosmologists accepted that time did not exist before the big bang, so the question did not make sense

    Would read “so the question did not make sense for them“, because there was pioneers in the study of time before the BB. A relevant example is the Nobel laureate I. Prigogine, to whom the Prof. Ivanenko invited to write in a scientific memorial at Lomonosoff University, under the phrase written by Dirac. Prigogine wrote that “time precedes existence“.

    He discusses his vision of the cosmos as a giant dissipative structure in a chapter in one of his last books: The End of certainty. Some very early works from him and coworkers in alternative cosmological models are available online:

    Entropy and cosmology

    Thermodynamics of cosmological matter creation

    Research done at our Center seems to point an irreversible origin for time, contradicting all those cosmological models. But this work is still under development and as the other cosmological speculations is unproven.

  12. Randy says:

    I’m not sure what the point of the program was. Most of these ideas seem not much beyond the “hey, I guess it could be this” stage. Or at least that’s how they were presented. I think most people new to these concepts look at this and conclude that any idea, perhaps Genesis, make as much sense. I’d much rather hear back from these people if and when they have (1) physical evidence and (2) a way to explain these things to a wide audience.

    Then I wonder, what is the practical use of knowing what happened before the big-bang-that-possibly-didn’t-happen? Suppose any one of these ideas is actually correct. What good does it do us? Will it secure our future for the next century or millennium? Or is it just something nice to chat about over cocktails? Who is funding this, and why?

    Also I was irked at the misconceptions about math. Math is a symbolic construct that humans created for our own benefit. Infinity is an integral part of math. You can use math without infinity, but infinity (like 0 and 1, pi and e and i) is required to fundamentally understand math. It could be that nothing in nature is infinite. But if you want to change math for that (and replace it with what? something less useful?) you’re going to need to throw out centuries of thinking that depends on infinity to work. We can do that, but there needs to be a convincing benefit.

  13. Luboš Motl says:

    The whole program online and my comments about it:


    The program is really bad.

  14. See also my comments about the ideas represented in the program. Technically the program was elegant but about the standards of the contents one can disagree;-).

  15. Lawrence B. Crowell says:

    I have to confess I find Smolin’s “cosmic Darwinism” suspect. Darwinian evolution applies best to the selection of organisms which have a haploid-diploid meiosis cycle and there is a matching of homologous pairs of chromosomes. It turns out to be difficult to apply to prokaryotes in a strict manner, though selection does apply, where the definition of a species is hazy. It is not clear to me how there is a selection mechanism for cosmologies that might emerge from a black hole singularity, or large vacuum fluctuations on or near them.

    The Euclidean patch is a sort of instanton, and the scale of physics does approach Planckian dimensions. The difficulty seems to be with the scale of this patch, which if small enough, or with a large vacuum energy, strains gravitational physics. The energy scale approaches limits set by the string tension or the α’, which puts to question whether these smoothed singularity and spacetime ideas really work beyond a semi-classical approximation. So the idea of extending this to a “no-boundary” does not appear resolved absolutely, only approximately. So as I see it my statement or question still stands.

    As for new and old questions, to me an old question that should have been junked a long time ago is the matter of hidden variables. Some people seem determined to pursue them, but I think this is banging one’s head against a wall. With quantum gravity I don’t think there are many “old questions.” My main complaint about the BBC presentation is in the definition of the big bang. The CMB clearly indicates there was a hot period of the universe with expansion, a big bang. How this connects up with inflation and further to … , which all may be up for question. I don’t think of the initial event, to use that word, was the big bang. I think of the big bang as the process of reheating when the inflaton potential became quadratic after ~ 60 efolds or so. During inflation the vev was about 15 orders of magnitude lower than the Planck density, and prior to that it might well have been higher. It can be thought of as higher in order to provide the initial KE for the inflaton “ball” to roll along the near flat potential — a sort of scalar field “ski-slope.” So it the vev was higher this brings about a host of questions. I don’t think this theoretical issue is at all resolved.

    As for my “random babbling,” there is nothing serious in what I said there. All I am saying is along the lines of “what if?” Some of these ideas might indeed turn out to be various aspects of the same problem. Others may not. On the other hand I might be completely wrong. I am not committed to any of these, or to the statement I made about this. I just don’t think these people are post modernist idiots.

    As for respect for science, the table could be turned as well. I am not any expert on climatology, but frankly you are playing crank science on that front. In the end you dislike the fact this issue is a fly in the ointment of your political bailiwick, and in other places you call anyone concerned about environmental issues a “terrorist.” The environmental community has its problems, as does anything that becomes political, but calling them terrorists is a bit over the top. This amounts to rubbishing up one branch of science because you hold a certain political ideology to a higher standard.

    As for “Chill,” if people in general don’t chill we are heading into big trouble. When a society becomes besotted by anxiety and enthralled by extremists with mental problems the world is in big trouble. This happened in Europe with Lenin, then Mussolini, and the crowing achievement in insanity with Hitler. Something similar is beginning to happen in our modern world. The media has become filled with manic histrionic personalities of a disturbing nature. Glen Beck went in and out of rehab for addiction issues, and one doctor noted that he might be borderline schizophrenic. The Islamic world is entering a stage of collective insanity, and other parts of the world might be baby stepping in the same direction. Déjà vu all over again, this time with nuclear bombs.

    • Ulla says:

      Best fitted means the least energy level? That is evolution a la Darwin.

      The idea is that the biological principles is only a scaled up variant of the basical physical ones. That’s why the solution to physic, the right and true physic, goes through the explanation of biology :)

      There is no way around this fact.

      By this I don’t mean Darwin was totally right, but the ‘fight for the fittest’ was there and is true in some very basic conditions. Darwinism has even invaded the social science, what is most surprising. But we are more than the darwinian level, as is many other animals.

      This living evolution can also be described in quantum mechanic terms.

      • Lawrence B. Crowell says:

        Biological evolution departs from physics of closed systems. Biological evolution is and works within an open thermodynamic system, which more globally is a subset of a larger system that is closed. Most physical theories are Markovian, which means that fluctuations at one time carry no information into the future. Quantum mechanics is Markovian for instance. Biological evolution is a selection mechanism on mutations of genes, where for randomness as the mechanism for mutations means these do carry information into the future. This is a sub-Markovian system. Such systems are open, such as driven-dissipative systems.

        This is what makes Smolin’s idea of cosmic-selection questionable. That is unless we are to think of the universe (multiverse) as an open system with energy flow from outside that adjusts entropy “flow,” to use that term here. This could be a rather unfortunate state of affairs, for the universe has some physically unaccountable “source” from outside.

      • Ulla says:

        Procaryotes do have a selection mechanism. They start making ‘mistakes’ in the copying, a wast amounts of mistakes, until the most efficient are found. a real chaotic behaviour. This mechanism is far more efficient than any homolog chromosome pairing.

        Human behaviour also start working chaotically in difficult situations.

        This is more like the selection mechanism made by quantum tunnelling. In fact the quantum laws suits the ecology very well.

        In physics one selection mechanism is the lowest energy level.

        Open or closed systems has only with energy transformations to do, entropy. Some say the entropial concept cannot be used in biology, but that is obviously not true. Biology is very much entropic, locally. For Universe the situation is maybe somewhat different. But the universal perspective with a closed system is not important even for elemental particles and their braidings. It is only a theoretical possibility.

        Braidings and matter is also an information that is carried forth. Atoms is an informational structure, as is their relations. In QM the entanglement is information. Every kind of negentropy contains information, not only genes.

      • Lawrence B. Crowell says:

        Prokaryotes do a number of interesting things. They even exchange DNA. Yes they do have mutations and there is a selection process. In fact in the lab that is commonly done, where E coli with a beta-galactosidase gene is selected. The beta-gal has lots of restriction sites which permit one to clone in other genes. The first selection done is against the expression of beta-gal. So this is an artificial selection mechanism, but not that different from what happens naturally. What makes this more fluid than Darwinian selection of generations is that the direct cell divisions remove the role of pairing homologous chromosomes and the gamete-zygote cycle.

        For closed systems the principle of least action is probably closer in analogue to a selection process. Of course there will be those who might holler at this comparison, but for the sake of a short post I would cite that as the most analogous. Systems tend towards low energy when that energy is liberated an no longer available to the system. A photon and atom in a closed cavity will cycle between absorption and emission endlessly in Rabi flopping. Now if you open the cavity and the photons fly out, this is stimulated emission and there is a change in the entanglement entropy of the system, where now it is entangled with the outside world.

      • Ulla says:

        In fact humans also exchange DNA, it is about 10% of our signal system, if I remember right. free DNA is circulating in our body. But with that we also say we know very little about the genome. DNA is only about 5% of it for humans.

        The evolution and Smolin a la Matti (when he don’t comment himself :)) From it you can read what is doing the evolutionary quantum mechanics in biology too.:


        Quote: Lee Smolin represented his idea of cosmological evolution and suggested that the collapse of star to black hole is somehow followed by a creation of new cosmology inside black hole. The idea about natural selection in cosmological scales is quite interesting and I ended up with it fifteen years ago through the p-adic calculations of elementary particle masses. The calculations made one key assumption or better to say observation: elementary particles correspond to p-adic primes which are near to powers of two and Mersenne primes and their Gaussian counterparts turned out to be especially important.

        Zero energy cosmology combined with number theoretical universality can give at least a partial justification for this hypothesis. The proper time distances between the tips of CDs would come as octaves of CP2 time and correspond to what I am used to call secondary p-adic length/time scales. For instance, in the case of electron one obtains .1 second which is fundamental biological length scale! The idea that there is natural selection also in elementary particle length scales selecting p-adic length scales characterized by favored p-adic primes as those for which particles are long lived looks very natural. Also TGD inspired quantum biology and theory of consciousness imply evolution in all length and time scales. Mersenne primes emerge also in quantum information theory as special ones.

      • Lawrence B. Crowell says:

        There is no functional DNA running around the body. DNA is pretty carefully bundled up into packets by histones and supercoiled into chromosomes.

        I can’t comment much on Matti’s ideas. A lot of his ideas about p-adic numbers and connections with nearly everything I have never understood.

      • Ulla says:

        It is called DNA trafficing, Lawrence. You forget I am a biologist :)

        horizontal transfer of DNA does occur between somatic cells [2] as well as germ cells [5] (Epigenetic Inheritance through Sperm Cells, the Lamarckian Dimension in Evolution, SiS 42). In fact, DNA, like RNA, is so readily taken up that it has been widely exploited in ‘gene therapy’, while our regulators continue to ignore the potential hazards of the ever inicreasing range of genetically modified nucleic acids released into the environment [6] (Slipping through the regulatory net, ISIS/TWN publication).

        In fact, most of our genome is old viruses and alike. Mechanisms such as alternative splicing, trans-splicing, and RNA editing, DNA-repair etc. Apoptosis is one source but not the only one. Alu elements and CpG DNA especially interesting. Kind of immune system and cancers.

        Look for DNA trafficking. Here is one ex. http://www.jimmunol.org/cgi/reprint/176/8/5033.pdf

        p-adic and Planck constant hierarchy is about scaling. It can be of almost anything. It is the missing rule behind why something has a special mass or length, size etc. Not any size will do, as Kea has seen with the neutrinos. Also motions, velocity, thermodynamics, etc. Measurements of all kinds. But don’t ask me about the math behind. Certainly you will find it on his website.

      • Lawrence B. Crowell says:

        The website about contains the one sentence paragraph:

        There is current debate as to whether circulating DNA is solely derived from dead cells [12] or whether they are actively secreted by living cells [9, 13].

        I have no problem with the idea that DNA is brought into a cell by phagocytosis. However, until demonstrated otherwise I think it is likely this DNA comes from cells that have undergone apotosis.

      • Ulla says:

        Maybe you should look at the other link too. One only sentence is never enough.

  16. CfCS says:

    To Lubos Motl.

    That is right, both Feynman and Lawrence B. Crowell understood that physics is about fun and that if you do not get fun with physics you would abandon it, whereas you wrote just the contrary “Physics is not about having any kind of fun.” I recommend you to follow their advice.

    The conference in Warsaw was not a “cosmological conference” as you incorrectly say but the 1962 International Conference on Relativistic Theories of Gravitation. Your comparing of it with the BBC program is just ridiculous.

    The letter that Feynman sent to his wife Gweneth and that you quoted above, but evidently truncated at its most interesting parts, is that where Feynman stated his personal (and well-known) dissatisfaction by the geometric formulation of general relativity and specially by the relativist community. As John Preskill and Kip Thorne write:

    Indeed, in spite of his deep respect for John Wheeler, Feynman felt an undisguised contempt for much of the relativity community in the late 50′s and early 60′s. This is perhaps expressed most bluntly in a letter to his wife Gweneth that he wrote from the Warsaw conference in 1962

    Both Feynman and Dirac understood renormalization and both described it with the same perfection. Feynman named it a “dippy process”.

    The problem with Feynman was that he never understood the Hamiltonian formulation of mechanics really. That is why he failed to give a Hamiltonian version of his electrodynamics with Wheeler, in despite that both promised us one. And that is also why Feynman original formulation of QED (the “spacetime formulation”) has been finally substituted by the more standard Hamiltonian formulation for quantum fields. As Weinberg correctly points out the generator of time translations is the Hamiltonian not the Lagrangian.

    It is perfectly possible to build a general relativistic Hamiltonian, what happen is that the relativist community and specially the loop community is confused about basic issues as covariance, backgrounds, generators, causality…

    Of course, this does not imply that string community is doing it better. The string theory is just so wrong, and that Feynman wrote:

    String theorists don’t make predictions, they make excuses

  17. Lawrence B. Crowell says:

    String theory is too good to be true, but at the same time it is too good to be completely wrong. To be honest I am rather impressed by how stringy physics, and even AdS/CFT structures, are showing up in solid state physics. Maybe Smolin does have something with his idea of selection. Biological organisms tend to exhibit genes over and over again. Physics seems to do something similar, such as isospin formalism that occurs in various cases as well as various symmetries.

    As for loop quantum gravity the idea seems so basic as to be almost impossible to fail. Yet there is this Barbero-Immirzi parameter problem with black hole entropy. So there is some serious problem, but the critics of LQG have never put their finger on exactly what that is, or what is required to repair the problem, if it can be repaired. The whole idea is based on general relativity, canonical quantization, and loop connections which are fairly natural appearing extensions of general relativity into a quantum theory. Yet clearly there are some serious problems with the whole program. Whether there is anything to it, such as whether some “stringy” content might fix the problem, is not the main point. If the problem could be precisely identified, instead of finger pointing nonsense, that might be some fairly serious progress. I spent some time reading LQG stuff, and I must confess I could not get interested in it beyond a certain point — to be honest it gets rather boring. Yet maybe reviewing that stuff again might be worth something.

    Time translations are indeed Hamiltonian, but the problem is that a basic formalism of general relativity in Hamiltonian form results in the NH = 0 and N^iH_i = 0 result. The quantum analogue is the Wheeler Dewitt equation HΨ = 0, which has no dynamics. There is no time evolution. Why is it that the diffeomorphism of spacetime is not captured by this? The definition of time according to diffeomorphisms as formulated by the lapse and shift functions is not well understood. There is a really deep question here.

    As for fun, it extends to everything — not just physics. I am dismayed by how over the last couple of decades the social milieu has been increasingly defined by anger, fear or hatred. People are not happy, and there is a sort of industry, aka the media, that is making money by getting people angry. This is not a good development, but it makes some people money and it is a hook for political power. Damned, we can do better than this.

    • CfCS says:

      Lawrence B. Crowell Says:

      Time translations are indeed Hamiltonian, but the problem is that a basic formalism of general relativity in Hamiltonian form results in the NH = 0 and N^iH_i = 0 result. The quantum analogue is the Wheeler Dewitt equation HΨ = 0, which has no dynamics. There is no time evolution. Why is it that the diffeomorphism of spacetime is not captured by this? The definition of time according to diffeomorphisms as formulated by the lapse and shift functions is not well understood. There is a really deep question here.

      That is what I did mean by

      It is perfectly possible to build a general relativistic Hamiltonian, what happen is that the relativist community and specially the loop community is confused about basic issues as covariance, backgrounds, generators, causality…

      The correct general relativistic Hamiltonian is non-zero. It is only when the Hamiltonian method is misunderstood that one gets a meaningless result H=0.

      The problem of time is not a deep problem anymore. And modern generalizations of string and brane theory are free of that problem as well, because physicists are giving correct Hamiltonians.

  18. Philip Gibbs says:

    Feynman had a well known disrespect for authority so I always find it a little ironic when he is quoted as an authority on various topics like string theory or philosophy. He had an opinion on these things, not a devine insight. Let’s not forget that he died in 1988 when string theory was at a very early stage.

    OK, so physics is both fun and serious at the same time. Does anyone here really disagree with that?

    I thought the theories described on Horizon were all very speculative and they were selected to try to make a particular point about there being something before the big bang. Personally I think physicists need to speculate beyond what we currently know. It’s just a series of thought experiments. I should worry that some people watching this program would missunderstand the process that is going on and conclude that all cosmologists are crazy, but perhaps I wont.

    Aside from that I enjoyed the program. For me it underlined the fact that there is a lot of disagreement still on the subjects discussed. The missing Hawking Hartle idea is closer to what I would find philosophically right and the maths possibly a little better, but it is still just another specualtive idea based semi-classical reasoning that we know must break down at some point.

    The real need is to have a working theory of quantum gravity that can be applied to these ideas to see if they are consistent. Ultimately we need experimental tests to determine which quantum gravity theory is right, but so far we dont have any theory of quantum gravity that can be tested.

    Loop Quantum Gravity is interesting in that it highlights some particular mathemtical ideas such as spin networks that might be relevant in some form. As far as I know it does not recover a classical limit. I have heard some talk of its problems being fixed but until I see some phenomenology of quantum grvaity effects I take that with a pinch of salt.

    I prefer string theory but it still lacks a formulation that can be used to understand what happens to spacetime at the Planck scale. Such a formulation must exist, someone just has to find it. The way we see string theory now is very different from how it was seen ten years ago, and then it was very different from how it was seen over twenty years ago when Feynman was around. Who knows what another ten years will bring?

    Meanwhile, please avoid any tones that might be antogonistic :)

    • CfCS says:

      Philip Gibbs Says:

      Feynman had a well known disrespect for authority so I always find it a little ironic when he is quoted as an authority on various topics like string theory or philosophy. He had an opinion on these things, not a devine insight. Let’s not forget that he died in 1988 when string theory was at a very early stage.

      We would explain why he was anti-Establishment. He was very creative and loved to find new ways to look to old stuff. When he shared his novel ideas, from quantum theory to gravitation, he received the hostility of the Establishment. General relativists hate his non-geometrical formulation of gravitation. Electrodynamicians hate his formulation of classical electrodynamics without fields. Quantum theorists hate his formulation of quantum mechanics. For instance Feynman wrote about his experience at Pocono conference.

      [...] My way of looking at things was completely new, and I could not deduce it from other known mathematical schemes, but I knew what I had done was right. [...] For instance,

      take the exclusion principle [...] it turns out that you don’t have to pay much attention to that in the intermediate states in the perturbation theory. I had discovered from empirical rules that if you don’t pay attention to it, you get the right answers anyway [....] Teller said: “[...] It is fundamentally wrong that you don’t have to take the exclusion principle into account.”

      [...] Dirac asked “Is it unitary?” [...] Dirac had proved [...] that in quantum mechanics, since you progress only forward in time, you have to have a unitary operator. But there is no unitary way of dealing with a single electron. Dirac could not think of going forwards and backwards [...] in time

      [...] Bohr [...] said: “[...] one could not talk about the trajectory of an electron in the atom, because it was something not observable.” [...] Bohr thought that I didn’t know the uncertainty principle

      [...] it didn’t make me angry, it just made me realize that [... they ...] didn’t know what I was talking about, and it was hopeless to try to explain it further.

      Regarding string theory, he was one of the pioneers in quantum gravity (recall his famous Caltech lectures) and was against the Establishment. You are right that he knew string theory in the early “glory days”. If Feynman was alive today, knowing the current state of brane, M-theory, landscapes, and all that messy stuff, I am convinced that his criticism had been close to that by Nobel Laureate Laughlin:

      String theory is like a 50 year old woman wearing too much lipstick.

    • Philip Gibbs says:

      Bits of rhetoric like that don’t count for anything in science, no matter who says them.

      • CfCS says:

        One would not forget that the rhetoric is based in underlying physico-mathematical analysis published in journals. As Feynman, Laughlin is also doing some work in quantum gravity and has also showed some of the mistakes done in the field (specially regarding black holes).

      • Philip Gibbs says:

        Hopefully people do not form their opinions based on the number and qualifications of scientists who express a particular view, or on the comic quality of their rhetoric, but rather on the science behind what they say.

        I see from an abstract of one of Laughlin’s papers that he does not believe in Hawking radiation and he thinks that GR breaks down at the event horizon. That puts him at odds with a much larger section of the physics community than just the string theorists.

        There are plenty of well known physicists who don’t like string theory and plenty of others who do. That is because the matter of quantum gravity is not settled yet. I happen to favour string theory but if others don’t then they are welcome to seek alternatives that work better. So far nobody has succeeded.

      • CfCS says:

        It is not a belief, but physico-mathematical analysis. Hawking radiation is a hypothesis based in the existence of the event horizons predicted by GR. However, more detailed analysis, including positive EMT for gravitons and quantum corrections (both lacking in the geometrical classical picture of GR) show that an event horizon never form and that the black holes predicted by GR do not exit.

        Of course, Laughlin is not alone and even Hawking seems to be finally accepting the new picture:

        “[it] seems to be that a true event horizon never forms,” said Hawking, “just an apparent horizon.”

        Physics is not a democracy, and when doing research one would not be worried when one puts himself at odds with a much larger section of the physics community than just the string theorists. The history of physics is full of examples where the majority was plain wrong and a minority completely right.

    • Lawrence B. Crowell says:

      I am not aware of a general relativistic Hamiltonian, outside of string theory, that is a nonperturbative quantization of diffeomorphism-invariant gauge theory. Of course string theory treats gravitation in a less than satisfactory way. The loop variable mavens use a noncanonical formalism, beyond the standard Wheeler Dewitt equation approach, to construct gauge invariant operators that obey a C* algebra. The “loop” comes in because Wilson loops are computed this way, which are thought to lead to a renormalizable theory. So far I am not aware that this has been accomplished.

      Philip, One point of string theory is to valence the Planck scale chaos with the string world sheet. So by its nature string theory is about an order of magnitude larger in scale than Planck units. It is possible that this means string theory is really another effective theory. The Planck scale is a sort of ultimate void of nothingness, and it might be that if theoretical physics derives something underlying string theory that it might also just approach the Planck scale. We may never get a physics really at the Planck scale simply because there is no physics there.

      • CfCS says:

        As said above the WdW equation is wrong. It was obtained from misapplying the Hamiltonian method. As was also said above, adequate and rigorous treatments give a non-zero Hamiltonian and viable Schrödinger-like equations. A good place to start may be the chapter 10 “ON THE RESOLUTION OF TIME PROBLEM IN QUANTUM GRAVITY” in this recent book

        Schrödinger-like equations as 10.14 are, of course, outside the framework of loop quantum gravity, string theory, and similar outdated approaches.

      • Lawrence B. Crowell says:

        It is not hard to get a Schrodinger type of equation from the WdW equation. The wave functional can be extended to include a scalar field Ψ[g, φ]. The scalar field produces a phase term e^{-iEt} so the WdW equation is a Schrodinger-like equation locally. This naïve sort of thing only works in some saddle point approximation, and does not appear workable “globally.” This does suggest holography might work in some way. The AdS boundary is a CFT where gravity emerges. So this might be a way of getting a gravitational Hamiltonian that defines dynamics beyond its role as a Lagrange multiplier.

        I looked at the referenced book on Google books. I could not find the equation you referenced. However, there are some pages which are not presented there.

      • CfCS says:

        Since that the WdW equation is wrong, any attempt to derive a valid Schrödinger equation from it is useless and, evidently, your “phase term” does not give any valid equation (apart from being very naive).

        The equation 10.14, a Schrödinger equation, is globally valid (the Hamiltonian is invariant), and as said above it is not derivable neither from loop theory nor from string or similar wrong and outdated approaches. Indeed, you can see that the author is proposing far reaching generalizations of string and brane theory in his book.

        Note: His theory is not the more general possible. For instance, the Box in the page 7 of the next Perspective about science discusses the approximations needed to derive a Schrödinger equation from the general theory.

        First one may ignore non-deterministic chaos (do not confound it with deterministic chaos), then the f-terms vanish. Next one may ignore the non-unitary terms (e.g. the well-known Lindblad terms), then the remaining equation gives you the evolution in terms of the quantum Liouvillian. The Schrödinger equation (and the Hamiltonian as generator of time translations) are finally recovered in the pure state approximation.

        With all the approximations named above, we obtain a Schrödinger equation, but as 10.14, both are still much more general than anything obtained from outdated loops or strings. Taking the classical limit does not give general relativity but an extension (this is also true for 10.14. The classical limit of 10.14 is an extension of general relativity. The classical limit of 10.14 is described in the well-known monograph by Trump and Schieve).

        After obtaining the classical limit, I would apply about half-dozen of further approximations to obtain general relativity. But this is goinf too large and I stop here.

        Please do not reply me again with outdated, simplified, and wrong stuff as WdW, AdS, Wilsons, and the like.

      • Lawrence B. Crowell says:

        I have not of course read this yet, but only looked at it on Google Books. Unfortunately there are pages omitted, which make it difficult to follow. I will see if I can put this on my book budget for November.

    • Philip Gibbs says:

      String theory has a good stab at aproaching the Planck scale. It’s perturabation series is thought to be finite at all orders and it has target space duality that makes very small distance scales dual to very large scales.

      The problem is that the perturbation series most likely diverges just like they usually do in QFT. As temperatures and densities approach the Planck scale it fails. There are some arguments that suggests a phase transition is approached, but what is beyond that transition, nobody knows exactly. Matrix theory is non-perturbative, but it too fails to answer these questions for other reasons. There are known dualities that tell us a bit more, but still not a complete solution. It is frustrating that there is so much that works but not quite enough to seal it.

      I don’t think string theory is an effective theory for something else. There is no indication of that like there is for some QFTs. It’s more a question of finding the right non-perturbative formulation for string theory, then we can start to look at whether it really solves the quantum gravity problem, and whether the mutiverse of vaccua is real etc.

  19. Lawrence B. Crowell says:

    The phase transition you allude to is probably the Hagedorn. A temperature T = 1/L_{string} is such that at that temperature strings merge into one great “thread.” This has some analogues with the quark-gluon transition to a plasma or fluid. This is one reason to suspect there might be something underlying string theory. The idea was hatched by Scherk as a theory of hadron, and QCD did emerge as a theory of quark confined by gluons in flux tubes. The superstring might in fact be the same thing. We might consider whether it is made of partons or D0-branes with a similar flux tube structure. At the Hagedorn temperature this break down into a type of plasma of these partons. Dp-branes, for p > 1, would then be something analgous to the Fermi-surface.

    • Philip Gibbs says:

      That’s about it. Of course the Hagedorn temperature was first used to describe the temperature of deconfinement in QCD. However it has a generic meaning for systems where the parition function diverges at a certain temperature. Using the same name to refer to the temperature of a phase transition in superstring theory is more recent.

      • Lawrence B. Crowell says:

        This would then complete a QCD and AdS correspondence. The string at the Hagedorn temperature is then equivalent to a QCD theory. The strings at the boundary of the AdS spacetime at the Hagedorn temperature should then be the same as the quark-gluon plasma.

  20. Ulla says:

    Who’s Afraid of a Big Black Hole? This documentary examines the work of astronomers and theoretical physicists who are trying to map a black hole, in the hope of discovering whether they are the key to solving the mystery of what existed before the big bang.


    A comment: Dark matter is a grade of matter associated with a different minimum distance value or Planck length. With a different Planck/ minimum length it also has a different associated Planck constant, so it cannot readily exchange photons/ electromagnetic energy with our matter, hence it is dark to us (but not to itself). Also derived from the minimum distance value is the Gravity constant (G), so dark matter has a different Gravity constant,
    Not said by Matti…


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