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

Pb^208 - Pb^208 collisions and vacuum metastability disasters

  1. Aug 16, 2010 #1
    First off, I'm not in any way anti-LHC. Quite the opposite to be honest. Even so, this speculative disaster scenario (vacuum bubbles) have caught my attention latelly, and I haven't been able to let go off it. Mostly because I find the otherwise brilliant LSAG-report (both actually) to be quite inconclusive on this specific subject. They claim that the RHIC report pretty much covered it all. But they only acknowledge the existence of CR (Fe?) of energies up to 2TeV/COM so how can that analogy be valid when they eventually are going to collide Pb^208 at as much as 5.5TeV (2013-2014?).

    I get the part with us presumably are living in a false vacuum and that a quantum tunnelling (either particle accelerator induced or "natural" occuring) could trigger a phase transition into the true vacuum. Furthermore, I'm aware that Rees & Hut was first with these "concerns", but how did they (a) reach the conclusion that we could be in a false vacuum and (b) that the collisions at particle accelerators could possibly cause this vacuum metastability event?

    And perhaps most importantly, how come people claim that the upcomming Pb^208 collisions at max energy (aprox. 2.80TeV/COM for this year) would be more likelly to produce a universe gobbling vacuum bubble than the proton collisions at 3.5TeV/COM? Isn't the whole process governed by the achieved energy at COM rather than what the collisions consist of?

    If anyone could take the time to straighten this out for me I'd be forever grateful, it has been bugging me for quite a while now=)
  2. jcsd
  3. Aug 16, 2010 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The LHC disaster scenarios that I'm familiar with are strangelets and black holes. Here are a couple of papers on those:


    Do you have papers you can point us to on the scenario you're referring to (preferably ones that are free online)?

    One of the safest, model-independent arguments against all these scenarios is that cosmic-ray collisions could replicate LHC collisions, and they haven't caused any known dramatic events yet. However, these arguments get kind of complicated, and I have often seem them drastically oversimplified (including here on PF). E.g., LHC collisions produce a compound system that is (approximately) at rest, whereas natural collisions don't (usually) do that.
  4. Aug 16, 2010 #3
    I'm sorry that I was a little unspecific in my initial post. Here is a summary of what I was talking about: http://en.wikipedia.org/wiki/False_vacuum. That is a very short summary of Rees & Hut's paper from 1984 which isn't available for free (unfortunatelly).

    (See my previous post reg. details of why I find the LSAG-report inconclusive in regards to this specific scenario=)

    Here are the separate safety reports (both RHIC and LHC):
    RHIC - http://www.bnl.gov/rhic/docs/rhicreport.pdf (p.3)
    LHC - http://lsag.web.cern.ch/lsag/LSAG-Report.pdf (p.5)

    Is there any risk whatsoever that this actually could happen?
  5. Aug 16, 2010 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Reading the LHC report, it looks to me like vacuum bubbles and magnetic monopoles are far more easily dismissed than black holes and strangelets. In all four cases, cosmic rays could mimic LHC collisions.

    For strangelets, the cosmic ray argument is complicated by the fact that strangelets are expected to be relatively fragile, so hypothetical strangelets produced by cosmic rays, at large center of mass velocities, might be harmless because they would break up when they hit something. This concern is not present for vacuum bubbles and magnetic monopoles, which are presumably not fragile. Therefore the cosmic ray argument is more secure for vacuum bubbles and magnetic monopoles then for strangelets.

    For black holes, there is a pesky case with two large extra dimensions, which can't be ruled out based on cosmic rays colliding with Earth, but that would have resulted in the destruction of white dwarfs and neutron stars. This issue is particular to black holes.

    If you provide the reference for the Rees and Hut paper, people here might be able to comment.

    The increases in energy you're talking about probably don't affect the conclusions based on the cosmic ray arguments. Cosmic rays go up to energies many orders of magnitude higher than LHC energies, not just a factor of 2 higher.
  6. Aug 17, 2010 #5
    Here is a very short summary of both papers, and links to them: http://www.sns.ias.edu/~piet/act/phys/vacuum/index.html

    The name of the papers are:

    How stable is our vacuum? by Hut, P. & Rees, M.J., 1983
    Is It Safe to Disturb the Vacuum? by Hut, P., 1984

    Basically, what I wonder is if there is an increased risk of a phase transition in regards to heavy ion collisions (compared to proton ones) since the energy is close to 575TeV/nuclei, which sounds like alot?

    But perhaps it is as you said, vacuum metastability is one of the easier scenarios to dismiss thanks to CR observations. Even so, the RHIC-report mentions an upper limit of heavy ion CR as low as 2TeV/COM which then means LHC will be colliding heavy ions at greater energies than has been observed in CR, or am I overlooking something?
  7. Aug 25, 2010 #6
    Any input whatsoever would be deeply appreciated. I'm really starting to loose sleep over these upcomming collisions. Especially since, to my understanding, they will be colliding Pb^208 at energies higher than observed in CR.

    How can they be sure that the collisions isn't going to cause a quantum tunneling?

    Is there an increased risk for things to go bad when they start to collide heavy ions or is that just another crackpot claim by the LHC-opponents?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook