Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is a black hole an elemenatry particle?

  1. May 30, 2010 #1
    I'd appreciate any insights or online references that discuss the following:

    In THE BLACK HOLE WAR (2008) Leonard Susskind says (beginning pg 368) that in the early 1990's Gerard 'T Hooft conjectured that Planck mass was NOT the end of the elementary particle spectrum.

    't Hooft argued that the spectrum of particles extends on to indefinitely large mass in the form of black holes...that these are fundamentally no different from an elementary particle.....and that only certain discrete masses are possible there....

    Explanation and comments

    I suspect the last part....discreteness...relates to the discrete nature of the information on the horizon....via the holographic principle, so the mass is 'practically continuous'....but not quite.

    Susskind mentions that the smallest diameter a one kilogram object can occupy is not Planck size, but rather a black hole of that mass....He mentions the horizon of such a black hole is about 100 million Planck lengths, but even that is a trillion times smaller than a proton....meantime the singularity at the center is essentially a point mass. So I guess even the massive black holes (singularities) at the center of galaxies are smaller than the common elementary particles.

    We know any black hole can be completely described via mass, charge, angular momentum, and they seem to carry information/entropy....sounds like they might be a "particle".

    Have 't Hooft or anyone else taken this idea further??
  2. jcsd
  3. May 30, 2010 #2


    User Avatar
    Science Advisor

    In a sense a BH in LQG seems to be equivalent to one vertex, so it should be something like a huge "space atom".

    As far as I understood the quantum isolated horizon correctly, the interior of a BH from which the outgoing edges (carrying the area) penetrate the horizon can be treated as one huge intertwiner instead of a huge spin network inside the BH. Both treatments should be equivalent.
  4. May 31, 2010 #3
    Susskind says if EVERYTHING is made of strings, then so are black holes.

    Same book: pg 377
    These ideas and those in my first post were the basis of lectures that Susskind gave at Rutgers and Princeton Universities in NJ, summer 1993: HOW STRING THEORY CAN EXPLAIN THE ENTROPY OF BLACK HOLES. .
  5. May 31, 2010 #4
    Elementary particles are point particles as well, that is they have no size / internal structure by definition. It makes no sense to compare the size of a singularity to a particle since for both it is zero.

    The Schwarzchild radius of course defines a size but it shouldn't be interpreted as something physical, its a critical volume that a given mass distribution could occupy before collapsing into a singularity. The radius of an event horizon also is not a physical object.

    Also, I'd not heard of that book. Clearly there's a couple of you that have read it, would you recommend it?
  6. May 31, 2010 #5


    User Avatar
    Science Advisor

    frankly speaking: as Susskind had these vague ideas it's up to him to elaborate ...
  7. May 31, 2010 #6
    not so....you are referring to a classical mathematical idealization.....

    I'm reading the book for the second time....parts of it for the third time...lots of insights....

    "...as Susskind had these vague ideas it's up to him to elaborate..."

    He subsequently describes related work by others..like Cumrum Vafa....I'll post if I find further insights...it's a good point because he's describing mid 1990's developments in a 2008 book.....I assume he would NOT do so if those led to an utterly dead end....
    Last edited: May 31, 2010
  8. May 31, 2010 #7


    User Avatar

    Not to engage in string reasoning but...
    The analogy isn't that bad, but I'd prefer to reflect upon this without relation to ST.

    Given that electrons orbiting the atomic nucleus in stable configurations made no sense in terms of classical electromagnetism, and was not made sense of until the advent of quantum theory, one can similarly argue that since we don't yet have a QG theory, we really do not know how microscopic black holes would have like. On one hand, it's believed that they would be unstable and radiate and thus evaporate quickly and have short lifetimes, so one would think that this makes no sense. So it makes about as much as sense as an stable orbit of a negative particle around the nucleus did ;-)

    The interesting question is; how would a "black hole" look like, as it's COMPLEXITY (ie. mass) is SCALED down to zero. We don't know that, but I would think the chances are that there might be explanations that explains stability, because the "continuum picture" that DOES make sense to a macroscopic black hole, might BREAK down and become invalid for really small black holes; and I think it's not just about quantized areas, I think it could be that a smooth no-hair black hole symmetry is not viable when the complexity drops.

    But I think the idea is justified since there is alot of reason to doubt that the continuum based expected general properties of black holes, will stay valid when the continuum isn't.

    But I have no opinon yet of at what scale this happens. If it's planck scale or far below even. The observed mass, vs "bare masses" due to effects of polarization and organisation of the environment is still an issue. So I wouldn't jump into too fast conclusions to reject the general idea of a connection.

    But this idea is IMO not ST specific. I don't even think ST helps analysing it at all.

  9. May 31, 2010 #8


    User Avatar
    Science Advisor

    The problem with black holes is that - yes - they share some properties with elementary particles, namely mass, spin and charge; but that there are major differences as well:
    - black holes signal the breakdown of the theory which predicts them (general relativity)
    - there is no quantization procedure for black holes
    - all claculations regarding black holes rely on approximations:
    (Hawking radiation = QFT in curved but classical backgrounds; string theory with extremal BPS states = unrealistic black holes; LQG w/o matter interaction; ...)

    therefore it's a nice but still vague idea ...
  10. May 31, 2010 #9


    User Avatar
    Science Advisor

    The analogy is more about blackholes, that are almost but not quite evaporated. There, and only there, does the analogy make sense. At that point 'T Hooft and others showed that you can treat them using a scattering matrix approach.

  11. May 31, 2010 #10
    I think if you take the analogy with particles seriously there are two length scales associated to a black hole. The radius r=2GM which one can think of "the size of the black hole" and the Compton wavelength l~1/M which is "the size of the singularity". So for large black holes the singularity is essentially a point but if M is of order the Planck scale the singularity would appear to get larger than the horizon and then its not clear that one can think of the body as a black hole. Note that since all elementary particles have a larger Compton wavelength than their event horizon they are not black holes on the other hand all classical point particles of finite mass must be black holes since there size is zero by defintion.
  12. May 31, 2010 #11


    User Avatar

    I think this is hard to argue with :) But alot of things around the QG speculations are generally quite vague.

  13. May 31, 2010 #12


    User Avatar
    Science Advisor

    Rearding new ideas and approaches is science it's hard to predict how much speculation you need upfront and how much detailed and mathematically sound analysis is required. My feeling is that after some decades of speculation there are a lot of fruitful new approaches which can be investigated in more detail (LQG, asymptotoc safety, NCG, CDT to name a few; perhaps even some results from ST).

    In the very end all successful theories were never based on such speculations. That's why I am a bit cautious ... but of course I am not in the position to question ideas from Susskind et al.
  14. May 31, 2010 #13


    User Avatar

    Yes, in any evolution there is a need for balance between diversity and conservatism to make sure we get some stability, but I guess I also mean to say that there are two kinds of vagueness and neither is better than the other one:

    1) "mathematical vagueness" that's common when you go into almost pure philosophical endavours.

    2) "physical/conceptual vagueness" that's common when you get into almost pure mathematical constructs that are almost like mathematical toy models of physics, but where the exact conection to observed reality is often extremely vague.

    I see this as somewhat analogues to precision vs accuracy. Sometimes a less precise statement may be more accurate. I guess the most accurate statement is often that "we don't know for sure", but that's also not very useful, so there are I think an optimum balance between mathematical vagueness and conceptual vagueness for maximum fitness.

    A pure philosopher would get stuck and never computer a single number to quantify reality.
    But a mathematicians could easily creat landscapes of possible numbers but still make no connection to reality.

    This is why I think measurement theory and it's mathematical and physical foundations (which I connect to this discussion) are paramount. When this is ignored as it often is, this is to me "physical/conceptual" vaugness that I find strongly disturbing.

  15. Jun 1, 2010 #14
    In the pages following my original quote, Susskind pursues his main theme: information loss,ala Hawking, or lack thereof (his firm belief), in black holes...not much more about the "paticle" nature of black holes

    So when reading for the first time or two I barely noticed the brief passages about black holes maybe 'being particles'....he does not develop the idea much further in this book that I can see, sticking with an historical story about information loss, but there are some interesting subsequent passages that Susskind does not relate to this particle idea..for example, page 382:

    This sounds a lot like an electron cloud surrounding a nucleus...

    Vafa and separatelty, Ashoke Sen did work with this concept of charged black holes during this period, and developed 'extremal black holes'.."..a perfect balance between gravitational attraction and electrical repulsion..."

    Oddly, at least some of these are at absolute zero, so do not radiate....Sen was apparently the first (1994) to "..put together an extremal black hole and test string theory of black hole entropy.." in which he computed the entropy of a new class of extremal black holes....but could not complete the calculations ...

    This seems to POSSIBLY relate to particle theories that have called for the disintegration of of certain particles....., maybe the proton(??)..... which has been theorized, but never observed.
  16. Jun 1, 2010 #15
    I'm not sure I agree with either, but it's a very interesting observation....
  17. Jun 1, 2010 #16
    "- there is no quantization procedure for black holes"

    I assume you mean in the relativity framework?? Otherwise, don't Beckenstein, Hawking and the Holographic principle pretty well confirm the Planck scale quantization of the horizon...an information bit per unit area....
  18. Jun 1, 2010 #17


    User Avatar

    Mmm I guess the discussion is quite broad and I didn't meant to advocate susskind. I never read any of susskinds full books, and I'll also don't share his view to see unitary as a unquestionable starting point.

    I just thought I commented on the analogy of a system bounded by a horizon and that such a syste - when scaled down in complexity - ie. when it's evaporated almost completely but not fully, may take on distinguishable finestructure. Maybe even associating black hole remnants with elementary partlces. The point would just be that, a really small remnant might not be like a "small big black hole", but due to the low complexity discrete effects not only in mass, but also it's action forms may appear? or - who can deny the possibility?

    It seems from the article that Sussind(the article haelfix referred to) are not fond of thinking of BH remnants, but OTOH I personally don't think that

    - microscopic BH "remnants"

    - radiation contains information

    - apparent non-unitarity for general observer. I share the non-unitarity view for static observer that themselves aren't gaining mass, but this is a speical case only.

    in any way are mutually exclusive explanations. I think all three could possible play roles.

  19. Jun 1, 2010 #18


    User Avatar

    > - radiation contains information

    A very intuitive argument to see this is to compare with pseudo random numbers or cryptation.

    A complex cryptation technique requires a much more complex decoder to hack the cryptation. At some point, a suffciently "simple" decoder cold NEVER implement a working decoding algorithm if the cryptation is too complex. So it will be indistinguishable from a true random code or just nosie contaiing no information.

    This can explain why radiation from a large black hole will, relative to simple observer necessarily appear truly random or void of information. But this no longer holds when the complexity of the blakc hole drops (or if the mass of the observer grows).

    Similarly, it would seem impossible from a light system to implement or code a very complex action. So one might expect in that sense a unification of all actions in the sense that when the complexity drops (like happens to the individual parts in high energy experiments) the freedom for the possible action is stronlgy constrained = unification.

    This was what I had in mind, so I apologize if this was somewhat not on the originakl topic. This is as far as I think, nothing that susskind is thinking about.

  20. Jun 1, 2010 #19


    User Avatar
    Science Advisor

    Yes, I mean the quantization of GR of geometry as you like. Bekenstein's and Hawking's results are indication that there is something intrinsically quantized, but they do not show what is quantized. It's like Planck's ideas regarding his famous black body radiation. Planck was not think that black body radiation is quantized, but only that the interaction of the volume with the atoms in the body are quantized. It was Einstein who finally came to the conclusion that the radiation itself is quantized. Look the Hawkings arguments: geometry is not qantized at all.
  21. Jun 3, 2010 #20
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook