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No mini b/h at LHC because h/e/p collide with earth every day?

  1. Jan 10, 2010 #1
    I'm not fully able to comprehend the argument that allegedly proves, that no mini b/h can emerge at CERN - that we witness collions at higher energies everyday and no b/h has occured so far - besides the prediction that such objects would immediately decay and disintegrate because of Hawking-radiation.
    Latter asummption aside, how can one possibly compare h/e interstellar particles collisions with the experiment conducted at CERN? If we were talking about the same issue here, physicists wouldnt have had to build the LHC but just put CMS somewhere in the wild, waiting for the next interstellar particle to cause an event. It's simply not the same. The situation is completly different, the conditions under which the experiment is conducted are differend and the whole outcome is complicated, subjected to chaos (especially any unpredicted and unintended follow-up events inside or outside the detector, irrespective of how much energy is still in them) and - most important - IS, IN FACT, counting on "new physics".

    That said, from the most simple and unphysicistic standpoint and with bare reasoning, how can anyone be more than 60% (let's say) sure, that no mini b/h or even worse will occur? Not panicing, just curious.
     
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  3. Jan 10, 2010 #2

    bcrowell

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    There is in fact a branch of experimental particle physics that does exactly that. The reason it can't do the same thing as the LHC is that the events are spread out over many cubic miles, and the rates are very low.

    Two useful papers on this topic: http://arxiv.org/abs/0806.3414 http://arxiv.org/abs/0806.3381
     
    Last edited by a moderator: Apr 24, 2017
  4. Jan 10, 2010 #3

    Vanadium 50

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    Also, ignoring the difficulty of flying a 10,000 ton object like CMS in the upper atmosphere, there is a more fundamental problem - how do you steer it to the place where an energetic cosmic ray interaction is going to happen?
     
  5. Jan 10, 2010 #4

    diazona

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    When they say "new physics" they're talking about things that haven't previously been observed in experiments, not things that have never happened on Earth. All these "new physics" events happen routinely in cosmic ray collisions etc., but as the previous posters mentioned, we have such a hard time analyzing natural events (like cosmic rays) that there are almost certainly some interesting things that have evaded our detection so far.
     
  6. Jan 10, 2010 #5
    The first and most important facts that I wish you would realize, is that the production of BH at LHC is
    1) very speculative and not the purpose of LHC. The purpose of LHC is to investigate electroweak symmetry breaking.
    2) the evaporation stems from very general principles for which no serious physicist doubt. Believing that BH will be produced but not evaporate is self-contradictory : one can not coherently believe the speculative side of a theory and reject the robust side.

    As has already been said, the reason we built a laboratory to study those collisions is because we want to have things tightly under control, in terms of modifying one parameter of the collision at a time, in terms of having complex detectors gathering all details, and most importantly in terms of reproducing many many times the same collisions in order to gather statistics.

    The fact remains that the LHC experiment has already taken place many times in the upper atmosphere without us gathering the data, and the Earth is still here.

    We are not talking about 60% certainty, we are talking about safety much more certain than the vast majority of activities all human beings undertake everyday without even thinking about it. Walking the streets of any major city nearby dangerous traffic is less safe. Even sneezing in a closed room could cause a disruption in the air equilibrium, and trigger a shock wave possibly killing one's relative. This the kind of likelihood we talk about when we say the LHC could destroy the Earth : it goes against all basic understanding of thermodynamics.
     
  7. Jan 10, 2010 #6

    bcrowell

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    I think this is a considerable overstatement of the security with which we can predict radiation from microscopic black holes. It is after all a wild extrapolation into a realm that is completely untested by experiment. But in any case, there are many arguments in addition to this one that are just as strong, and *all* of these arguments would have to be wrong for microscopic black holes to cause disaster. It's very, very hard to cook up a disaster scenario that would not have already led to either the destruction of the earth or the destruction of neutron stars and white dwarfs by naturally occurring microscopic black holes. There's also the possibility of strangelets, but again, it's just very hard to come up with any plausible disaster scenario.

    If people want to worry about technology producing the end of the world, a much higher-probability possibility to worry about is nuclear winter caused by a nuclear exchange between India and Pakistan.
     
  8. Jan 10, 2010 #7
    Either you use conventional theories, then you can come up with numbers, and this is not an overstatement. Or you want to use exotic scenarios, in which case it is impossible to come up with likelihood in the space of "physical theories".
     
  9. Jan 11, 2010 #8

    Vanadium 50

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    To produce them mini-BH's at colliders requires their coupling with matter to be larger than predicted. For them to be stable against Hawking radiation requires their coupling with matter to be smaller than predicted. I'm willing to believe either one - but not both simultaneously.
     
  10. Jan 12, 2010 #9

    bcrowell

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    This is basically a statement that the decay rate is related to the production rate, which is a secure statement based the fundamental properties of quantum mechanics. But we know that the fundamental properties of quantum mechanics are incompatible with gravity. It's been proposed, for example, that the black hole information paradox implies that one needs to throw unitarity overboard in order to get a theory of quantum gravity. I'm not saying I'm worried about LHC doomsday scenarios. I just don't think it's a good idea to overstate one's case, since we're extrapolating into unknown physics. The relationship between decay rate and production rate is one of a list of four or five very strong arguments against the doomsday scenario, each of which would have to fail in order to get the end of the world. I would actually feel very worried if there were only *one* such argument that had to fail.
     
  11. Jan 12, 2010 #10
    There still remains the experimental fact that cosmic rays did not blow us up, despite the fact that many more collisions have occurred without us watching. Unless of course cosmic rays were switched on right before we found them.
     
  12. Jan 12, 2010 #11

    bcrowell

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    This is an oversimplification, since cosmic rays don't produce their products at rest with respect to the earth. These two papers spell out the correct arguments in detail:

    http://arxiv.org/abs/0806.3414

    http://arxiv.org/abs/0806.3381
     
  13. Jan 12, 2010 #12
    Please forgive me, but this is not an oversimplification, since the decay products in LHC collisions are NOT at rest : the collision takes place at the parton level, partons have ZERO probability to carry the entire momentum of the proton, and zero squared is still zero.

    Not even to mention the fact that, given a mini BH size, the upper bound on its cross section would allow it to sit at the center of the Earth for longer than the Earth lifetime.
     
    Last edited: Jan 12, 2010
  14. Jan 12, 2010 #13

    bcrowell

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    There's a five-page appendix (appendix F) in http://arxiv.org/abs/0806.3381 discussing this point, so I don't think it's as trivial as you claim.

    This is a different argument than the one that I criticized as an oversimplification. I agree with you that that there are many different, strong arguments against the LHC doomsday scenario. However, this argument is also not quite as solid and straightforward as you claim. See section 4 of the same paper, especially the final paragraph that summarizes the section. Their final conclusion is that they can't rule out certain scenarios with shorter lifetimes.

    Both of your two arguments quoted above can be made simpler and more secure by focusing instead on the constraint imposed by the fact that white dwarfs and neutron stars haven't been destroyed by cosmic rays. See sections 6-8 of the paper.
     
    Last edited: Jan 12, 2010
  15. Jan 12, 2010 #14
    The fact that there are five pages to slowly and simply report numerical investigations does not mean that it is not obvious to somebody with a modest experience in back-of-the-envelope order of magnitude estimation. This appendix is full of equations and plots, would you care to estimate the number of lines ?
     
  16. Jan 13, 2010 #15

    Vanadium 50

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    I think that you are throwing the baby out with the bathwater.

    It's true we don't have a quantum theory of gravity. It's also true we haven't needed one - there is no observation that we have made than cannot be explained by GR or QM+Newton. Any deviation between what we can calculate and the real world is too small to measure.

    Also, the linking of the decay and production rates is ultimately a statement about CPT, which requires only three things - locality, causality and Lorentz invariance. Not to mention that this has been tested time and again to extremely high accuracy.

    Finally, we're not talking about a 1% difference in production and decay couplings - we're talking about something like 1080.
     
  17. Jan 13, 2010 #16

    bcrowell

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    If you asked David Finkelstein or Roy Kerr about this in 1960, they would have explained to you very patiently that this line of reasoning is fundamentally flawed, that even though the field equations of GR have time-reversal symmetry, the event horizon of a black hole nevertheless acts like a perfect unidirectional membrane. Stuff goes in. Stuff doesn't come out. This appears to contradict the time-reversal symmetry of GR, but it doesn't.

    Okay, it's fifty years later, and we think we have a much better handle on the black hole information paradox, some approximate ways of handling the interface between GR and quantum mechanics, etc. The answer that Finkelstein or Kerr would have given in 1965 is probably wrong. However, the more recent ideas about black hole radiation have not been "tested time and again to extremely high accuracy" the way CPT has in particle physics. The arguments are very persuasive, but there is absolutely no empirical evidence.
     
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