Need some help with Vacuum metastability disaster scenario

Discussion of the end of the world brought about by ultra high energy colliders.
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rasalhauge
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Need some help with Vacuum metastability disaster scenario

Post by rasalhauge » Thu Aug 26, 2010 8:35 pm

Ok, so I'm writing a short piece in Swedish about the safety of the LHC-collisions and has now written about all scenarios except the most far-fetched of them all, the Vacuum metastability disaster. I know they deal with it it in the LSAG-report but that isn't as conclusive as I would like it to be=) So basically, since alot of smart people frequent here I thought I would ask you for help.

The problem I'm having is partly the conclusion LSAG draws reg. this specific subject, i.e. that no further studies since the safety report on RHIC (Review of speculative disaster scenarios at CERN) was issued. The problem with this is that the RHIC safety report concludes that heavy ion CR has been observed up to 2TeV, thus LHC is going to collide heavy ions at higher energies than has been observed. Or am I missing something here?

2TeV seems like a far to low number for CR, especially since there are theories that predict UHECR to consist of heavy ions (as opposed to lower energies being predominatelly protons). I know the latest HiRes(?) data indicates a majority of CR being p but to my understanding that was only valid for CR-energies up to 10^18eV (GZK-limit?)

What I wonder is this:
1. Has heavy ion CR been observed at 2.8TeV and beyond, or is it only protons that has been observed up to energies magnitudes greater than achieved at LHC?
2. Is there any "mechanism" as to how a particle accelerator induced quantum tunneling might be able to happen? More specific than "high enough energy at small enough space"
3. Is Rees/Hut the only ones that propose that a decay of the false vacuum might be caused by particle accelerators?
4. Could benign vacuum bubbles form, or would all spell doomsday?
5. Finally, why would a vacuum metastability event be more likelly in heavy ion collisions than in pp-collisions? As far as I can see the only mechanism in reg. to vacuum decay is a high enough COM and in that case pp-collisions must be more likelly to cause a vacuum decay, right?

Any kind of answers would be deeply appreciated=)

rasalhauge
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Re: Need some help with Vacuum metastability disaster scenario

Post by rasalhauge » Sat Aug 28, 2010 9:55 pm

Any input here would be deeply appreciated, even if it just address one or a few of my questions. And if I've asked questions that have already been answered, please hint me in the right direction of the answers=)

I am aware that Stephen had a thread on Vacuum metastability, but I couldn't find any answers to my questions there.

Kasuha
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Re: Need some help with Vacuum metastability disaster scenario

Post by Kasuha » Sun Aug 29, 2010 8:23 am

It's hard to prove or disprove hypotheses based on assumptions of existence of physics that weren't observed yet. According to basic logic, in the statement "if A then B" if A is false then the statement is true whatever the B is so that does not tell us anything about whether B is true or false.
As far as I know no false vacuum has been observed yet, not on earth and not in space even though in space and even in earth's atmosphere there are locations where much more violent processes than in LHC take place.
The basic argument is, if the (whatever phenomenon) can be created in LHC, then there is another place in the universe where it would have been created long time ago and we would be able to observe it. If we don't observe it, it either doesn't exist or it's not as violent as some people are trying to suggest us.

rasalhauge
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Re: Need some help with Vacuum metastability disaster scenario

Post by rasalhauge » Tue Aug 31, 2010 5:58 pm

Kasuha wrote:It's hard to prove or disprove hypotheses based on assumptions of existence of physics that weren't observed yet. According to basic logic, in the statement "if A then B" if A is false then the statement is true whatever the B is so that does not tell us anything about whether B is true or false.
As far as I know no false vacuum has been observed yet, not on earth and not in space even though in space and even in earth's atmosphere there are locations where much more violent processes than in LHC take place.
The basic argument is, if the (whatever phenomenon) can be created in LHC, then there is another place in the universe where it would have been created long time ago and we would be able to observe it. If we don't observe it, it either doesn't exist or it's not as violent as some people are trying to suggest us.
Ok, but bottom line; is there in any way an increased risk with heavy ion collisions vs. pp collisions? Not just regarding vacuum metastability, but rather overall. Heavy ion collisions is, to my understanding, messier than proton-proton collisions and thus more things could go wrong, or is that the wrong way to look at it?

But then again, they operate at lower COM-energy so that would be a positive factor, wouldn't it?

Oh sorry, I ramble on reg. this again, just confused. Some say that it's an increased risk with heavy ions, others not. My logic tells me that none should be considered dangerous, but sometimes nutcases like Gorelik gets to me, and the whole vacuum metastability event really scares the crap out of me from time to time. Although, I know, and follow, the line of reasoning that states that no disasters shoule derive from LHC if CR doesn't cause it.

Kasuha
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Re: Need some help with Vacuum metastability disaster scenario

Post by Kasuha » Tue Aug 31, 2010 7:54 pm

As far as I know, heavy ion collisions are a bit like chain crashes on highways - there is a lot of mess all around but all individual car (particle) collisions are not more energetic than when just two cars collide. In the LHC heavy ion runs, per-particle energy will be way lower than in proton runs. One of reasons for that is because lead nuclei have worse ratio of weight to charge (neutrons carry no charge) so with equal field needed to keep them in the ring they cannot give each particle in the nucleus as high energy as if they were all protons.

If you're asking if some kind of collective effects might occur - in fact that is what they are going to look for. But the question if there is "more to go wrong" needs specifying what can go wrong first. According to standard model and all available evidence nothing can go wrong in a way these hypotheses suggest.

The funny thing about these hypotheses is - their proponents don't try to bring proofs of their hypotheses. They don't even try to find ways to verify their hypotheses (i.e. propose experiments that would demonstrate new physics without destroying the universe). All they are doing is trying to prove they cannot be disproved (and they fail at that, too).

The sad thing is that they use the lines which were often used when popularizing LHC - that LHC is so special that the environment in it is unique in the whole universe. There is one point in which this is true, LHC magnets are really colder than almost anything in the universe as that generally cannot fall below relict radiation temperature. But that is completely irrelevant from the particle collisions point of view because in that relative particle speeds count. Not mentioning that collisions occur in safe distance from any of the supraconductive magnets too as they would immediately quench them and make them useless.

rasalhauge
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Re: Need some help with Vacuum metastability disaster scenario

Post by rasalhauge » Wed Sep 01, 2010 6:01 pm

Kasuha wrote:As far as I know, heavy ion collisions are a bit like chain crashes on highways - there is a lot of mess all around but all individual car (particle) collisions are not more energetic than when just two cars collide. In the LHC heavy ion runs, per-particle energy will be way lower than in proton runs. One of reasons for that is because lead nuclei have worse ratio of weight to charge (neutrons carry no charge) so with equal field needed to keep them in the ring they cannot give each particle in the nucleus as high energy as if they were all protons.

If you're asking if some kind of collective effects might occur - in fact that is what they are going to look for. But the question if there is "more to go wrong" needs specifying what can go wrong first. According to standard model and all available evidence nothing can go wrong in a way these hypotheses suggest.

The funny thing about these hypotheses is - their proponents don't try to bring proofs of their hypotheses. They don't even try to find ways to verify their hypotheses (i.e. propose experiments that would demonstrate new physics without destroying the universe). All they are doing is trying to prove they cannot be disproved (and they fail at that, too).

The sad thing is that they use the lines which were often used when popularizing LHC - that LHC is so special that the environment in it is unique in the whole universe. There is one point in which this is true, LHC magnets are really colder than almost anything in the universe as that generally cannot fall below relict radiation temperature. But that is completely irrelevant from the particle collisions point of view because in that relative particle speeds count. Not mentioning that collisions occur in safe distance from any of the supraconductive magnets too as they would immediately quench them and make them useless.
Thank you so much Kashua for taking the time to answer my silly concerns, it really means the world to me. And again, I know that the LHC is more or less foolproof but still there's a part of me that listen to the lunatics. The thing I worry the most about is vacuum metastability (surprise) and the main reason I worry about it is that there is so little known about it, which in my book means that there is an increased risk of stuff going wrong (I know, crazy).

But isn't it true that Rees and Hut failed to propose a mechanism for accelerator induced quantum tunnelling? I mean, isn't the theory that an really energetic particle collision could push us over to a new vacuum? But they didn't manage to give an estimate of how much is too much (i.e. trigger a phase transition) so basically there is just a matter of guesses, right?

To my understanding the LSAG-report seems to have divided the disaster scenarios in two separate groups; the ones that actually could happen (MBH's and Strangelets) and those who really shouldn't be able to happen (Vacuum bubbles and negativelly charged magnetic monopoles). The first group seems to consist of phenomena that is more or less expected according to the standard model, and the last group only possible in special, unproven, circumstances (like us actually living in a false vacuum). Is that more or less correct?

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photino
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Re: Need some help with Vacuum metastability disaster scenario

Post by photino » Wed Sep 01, 2010 7:50 pm

The thing I worry the most about is vacuum metastability (surprise) and the main reason I worry about it is that there is so little known about it
The one thing that is known about it with certainty is that (assuming we were indeed living in a false vacuum state) nothing in the entire history of the universe has been able to trigger a vacuum bubble -- not even once -- because if it had, we wouldn't be here.

This puts really strong bounds on what you might reasonably expect to see happen in an accelerator: For vacuum decay to even be a possibility, the accelerator would have to be doing something unprecedented in the history of the universe.
But isn't it true that Rees and Hut failed to propose a mechanism for accelerator induced quantum tunnelling?
That is not what they set out to do. (After all, there IS no theory that predicts we live in a false vacuum whose decay would be triggered by heavy ion collisions.) Instead, their calculation estimates how many heavy ion collisions of the requisite energy have occured naturally in the entire past history of our planet. This number can then be compared with the number of collisions that are going to be produced at the LHC.

This line of argument is described in detail in the RHIC safety report. It still holds for the LHC - all you have to do is insert the LHC collision energy and ion type into the requisite equation. The argument is still valid for the higher energies of the LHC as available cosmic ray data for iron cosmic rays (which is what is used in the report) has also improved since the RHIC report was written. The conclusion does not change.

A relatively recent review of what is known about cosmic rays at the relevant energies is e.g. http://arxiv.org/PS_cache/arxiv/pdf/090 ... 0725v1.pdf.

Considering ion collisions specifically in addition to the p-p collisions, and considering gold collisions specifically rather than just heavy ion collisions in general, is done to close loopholes which a devil's advocate might pick at - such as "what if there were something about a quark-gluon-plasma that makes triggering vacuum decay more likely? or something about gold collisions that "somehow" makes them problematic where lead collisions of the same energy are safe?".

rasalhauge
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Re: Need some help with Vacuum metastability disaster scenario

Post by rasalhauge » Thu Sep 02, 2010 7:44 pm

So basically we should be safe?=)

There is something that I wonder about though. In the previous post you wrote:
Considering ion collisions specifically in addition to the p-p collisions, and considering gold collisions specifically rather than just heavy ion collisions in general, is done to close loopholes which a devil's advocate might pick at - such as "what if there were something about a quark-gluon-plasma that makes triggering vacuum decay more likely? or something about gold collisions that "somehow" makes them problematic where lead collisions of the same energy are safe?".
I didn't quite understand that part, Devils advocate is that the same as the latin "advocatus diaboli"? Sorry for all the stupid questions, I blame it on the fact that English isn't my main language.

Is there any reason whatsoever to think that the state of QGP could mean an increased risk? Or what did you mean? I thought that the only aspect that mattered when talking about the probability of a transition to another vacuum was the center of mass energy in the collisions, or could there be some collective effects caused by the luminousity? I mean, doesn't the amount of collisions mean that there are more particles in the oncomming collisions than in the first?

And finally, in what way is the QGP formed at 2.80TeV going to be different than when it's formed at 400GeV? I imagine that the increased energy, and the heavier isotope, would mean that the lifetime of the QGP would be increased, right?

rasalhauge
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Re: Need some help with Vacuum metastability disaster scenario

Post by rasalhauge » Thu Sep 02, 2010 7:52 pm

By the way, in the ArXiv article they state that the observed upper limit for Fe is 10^19eV. What would that translate to in TeV?

And yet another stupid question, the Oh-my-God particle that was extremely energetic when it hit the detectors, but isn't it possible that the energy was far less from what it was originally? I.e. lost some energy during travel?

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photino
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Re: Need some help with Vacuum metastability disaster scenario

Post by photino » Fri Sep 03, 2010 12:33 am

Devils advocate is that the same as the latin "advocatus diaboli"?
Yes
Is there any reason whatsoever to think that the state of QGP could mean an increased risk?
No - that's why I said "devil's advocate" ;)

The point of looking at ion collisions specifically is to rule out the possibility that there could be a problem arising from some completely unknown new physics that noone expects, and that conspires to appear only in just these heavy ion collisions (due to unknown "collective effects" of some sort) . It's about closing loopholes.
10^19eV. What would that translate to in TeV?
T=Tera=10^12, so 10^19 eV = 10^7 TeV
the Oh-my-God particle ... isn't it possible that the energy was far less from what it was originally? I.e. lost some energy during travel?
You mean on its way to earth? Unless it encountered something on the way - no. And space is pretty empty...
in what way is the QGP formed at 2.80TeV going to be different than when it's formed at 400GeV? I imagine that the increased energy, and the heavier isotope, would mean that the lifetime of the QGP would be increased, right?
Not necessarily - I don't know. (Part of the answer, I suppose, is that the point of the experiment is to see how it differs at increased energies....)

rasalhauge
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Re: Need some help with Vacuum metastability disaster scenario

Post by rasalhauge » Sun Sep 12, 2010 10:52 pm

I just realized that I never thanked either one of you properly for taking the time to adress my fears. I really appreciate it, so thank you guys=)

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