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

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Discussion Overview

The discussion revolves around the potential risks associated with Pb208 collisions at the LHC, specifically focusing on the speculative scenario of vacuum metastability disasters. Participants explore the implications of these collisions in the context of existing theoretical frameworks and previous reports, questioning the validity of comparisons with cosmic-ray collisions and the conclusions drawn by safety reports.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant expresses concern over the LSAG report's inconclusiveness regarding vacuum bubbles and questions the validity of comparisons with cosmic-ray collisions, which reportedly only acknowledge energies up to 2TeV/COM.
  • Another participant mentions that cosmic-ray collisions, which can replicate LHC collisions, have not resulted in any known catastrophic events, suggesting a model-independent argument against disaster scenarios.
  • There is a discussion about the fragility of strangelets produced in cosmic-ray collisions compared to vacuum bubbles and magnetic monopoles, with some arguing that vacuum bubbles are less likely to be dismissed based on cosmic-ray arguments.
  • One participant raises the question of whether the increased energy of heavy ion collisions (up to 575TeV/nuclei) poses a greater risk for triggering a phase transition compared to proton collisions.
  • Concerns are voiced about the implications of colliding Pb208 at energies higher than those observed in cosmic rays, questioning the safety and the potential for quantum tunneling events.

Areas of Agreement / Disagreement

Participants express a range of views, with no consensus on the safety of the upcoming Pb208 collisions or the validity of the arguments presented in existing reports. The discussion remains unresolved regarding the likelihood and implications of vacuum metastability disasters.

Contextual Notes

Participants note limitations in the existing reports, including the scope of cosmic-ray energy comparisons and the assumptions underlying the conclusions about vacuum stability. The complexity of the arguments surrounding the risks of vacuum bubbles and other disaster scenarios is acknowledged.

malm1987
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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" occurring) 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=)
 
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The LHC disaster scenarios that I'm familiar with are strangelets and black holes. Here are a couple of papers on those:

http://arxiv.org/abs/0808.4087
http://arxiv.org/abs/hep-ph/9910471

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

http://arxiv.org/abs/0808.4087
http://arxiv.org/abs/hep-ph/9910471

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.

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?
 
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.
 
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 a lot?

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?
 
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?
 

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