You are definitely right in saying cosmic rays have been measured for years, but the majority of them consist of protons, and heavy ions are more rare. Cosmic rays consisted of protons are known to reach high energies (10^20 eV), but are there any direct measurements concerning leads ions?

"…because of the low flux of ultrahigh-energy cosmic rays, the mass composition cannot be measured directly. Instead, it is inferred from measurements of the extensive air showers—the cascades of high-energy ions created when incident cosmic rays collide with atoms in the atmosphere."

"All of the natural elements in the periodic table are present in cosmic rays, in roughly the same proportion as they occur in the solar system."

"The safety margins we have derived [for RHIC] would improve by the same factor [for LHC]."

What else do you want? If you want more, try sending your questions to CERN, because you're asking for information that I don't have.

Also, I ask you again, do you have some information concerning these collisions that thousands of scientists don't have? This hysteria has gone on with the public for more or less every single particle accelerator ever built. RHIC was painted as a doomsday machine ten years ago, and LHC has essentially been an encore of that circus (initially spearheaded by the same guys who attacked RHIC).

For a long time these ultra high cosmic rays were thought to be made of iron, but a recent study found them to be protons after all. http://www.insidescience.org/research/scientists_prove_cosmic_rays_are_made_of_protons

Maybe you missed something from that brief article:

"Cosmic rays have energies that can be much higher than anything produced by physicists. HiRes looks at the composition of cosmic rays with energies a million times greater than those generated on Earth, such as in the accelerator at the Large Hadron Collider."

Also, that is brand new information (published less than a month ago), and it by no means suggests that iron-iron or even lead-lead collisions do not or cannot occur in the atmosphere. Even beyond that, lead has been used in collisions for years, so we again go back to: do you have some information concerning lead ions that thousands of scientists don't have?

This bring me back to the RHIC safety report, where the authors claim they can't possibly know which type of collision (proton, iron, lead etc.) is more effective at triggering a vacuum instability event, so they have to make sure there are higher cosmic ray collisions from both types.

Now you might say this document is 11 years old, but since the LSAG said no new information was brought into consideration regarding this particular doomsday scenario, it seems fair for us to make conclusions based on that paper.

The idea of a vacuum instability event is frightening (a lot more than people quoting the bible and Nostradamus), and I want to be absolutely sure we have nothing to worry about.

Just knowing lead ion collisions in cosmic rays suppress 2.76 TeV would make me more calm.

"…because of the low flux of ultrahigh-energy cosmic rays, the mass composition cannot be measured directly. Instead, it is inferred from measurements of the extensive air showers—the cascades of high-energy ions created when incident cosmic rays collide with atoms in the atmosphere."

"All of the natural elements in the periodic table are present in cosmic rays, in roughly the same proportion as they occur in the solar system."

"The safety margins we have derived [for RHIC] would improve by the same factor [for LHC]."

The LSAG safety report, if you've read all of it, also states: "However, if LHC collisions could produce vacuum bubbles, so also could cosmic-ray collisions. This possibility was first studied in [7], and the conclusions drawn there were reiterated in [8]. These bubbles of new vacuum would have expanded to consume large parts of the visible Universe several billion years ago already. The continued existence of the Universe means that such vacuum bubbles are not produced in cosmic-ray collisions, and hence the LHC will also not produce any vacuum bubbles."

I think you're getting confused over what a particular ion is (i.e. lead, gold or iron) versus the centers-of-mass and velocities of particles in a given collision.

Seriously, try asking CERN. Further, try watching this lecture. You can also usually find the e-mail addresses of scientists who author various papers, sometimes on their university web pages. Some scientists welcome random public inquiry about the work, others not so much. Be forewarned. You might additionally have a look at this forum and website. Sadly, even that board has a certain base of users who ask questions, get answers, then claim nobody answered their questions. So I'm becoming increasingly convinced that some people just can't be pacified. Maybe they don't even want to be, because nothing seems good enough for them.

The only alternative to trusting the conclusions of scientists in a particular field, is to become a scientist in a particular field. If you're still worried after that, publish a paper explaining why.

I don't know what else to tell you other than repeat that the information you asked for has been provided. If that isn't sufficient, I apologize, but I can do no more, other than provide the additional sources linked above.

The way I think about it: Everyone values their lives, they all want to do every precaution possible to ensure their safety. It's not like scientists are immortals. Now, rather than being worried about it, let the professionals do the work. I believe their grasp on the severity of the situation is clearer than yours.

For a long time these ultra high cosmic rays were thought to be made of iron, but a recent study found them to be protons after all.
http://www.insidescience.org/research/scientists_prove_cosmic_rays_are_made_of_protons

CERN scientists have been working on lead ion collisions for years. You'll have to be more specific and explain what the problem is relative to the experiments that have been going on for a long time. As I understand, lead and gold are sometimes used because their nuclei provide a reasonable compliment to that of iron, and lead is known to react in a manner perhaps favorable to producing the quark-gluon plasma scientists expect to result from the collisions. Are you aware of some problem in this regard?

This bring me back to the RHIC safety report, where the authors claim they can't possibly know which type of collision (proton, iron, lead etc.) is more effective at triggering a vacuum instability event, so they have to make sure there are higher cosmic ray collisions from both types.

Now you might say this document is 11 years old, but since the LSAG said no new information was brought into consideration regarding this particular doomsday scenario, it seems fair for us to make conclusions based on that paper.

No problem, but I really don't know what else to tell you at this point. I addressed your concern in my first post, but it doesn't seen to have been enough.

I hope I phrased my points more clearly this time (I admit I have a problem making myself clear sometimes). The idea of a vacuum instability event is frightening (a lot more than people quoting the bible and Nostradamus), and I want to be absolutely sure we have nothing to worry about. Just knowing lead ion collisions in cosmic rays suppress 2.76 TeV would make me more calm.

But, according to my understanding, his research is only theoretical at this point and no direct measurement were made confirming that for certain. Do physicists rely solely on this research when addressing the safety concern of a vacuum bubble, or do they have empirical evidence?

Is there something in that article which suggests to you that these collisions have not been measured? From here:

"Cosmic rays have been observed with energies from 10^9 eV to over 10^20 eV."

From here:

"The nature and origin of ultrahigh-energy (>10^18 eV) cosmic rays remain a mystery. Astrophysicists hunt for clues regarding their mass composition, which, along with other properties such as the flux and arrival direction distribution, should help distinguish among the various models of the sources and propagation of cosmic rays. However, because of the low flux of ultrahigh-energy cosmic rays, the mass composition cannot be measured directly. Instead, it is inferred from measurements of the extensive air showers—the cascades of high-energy ions created when incident cosmic rays collide with atoms in the atmosphere."

I'm not exactly sure what you're looking for.

Besides, I recently read that the LHC is mainly going to collide lead ions. Do we have any information regarding that type of collision in nature?

CERN scientists have been working on lead ion collisions for years. You'll have to be more specific and explain what the problem is relative to the experiments that have been going on for a long time. As I understand, lead and gold are sometimes used because their nuclei provide a reasonable compliment to that of iron, and lead is known to react in a manner perhaps favorable to producing the quark-gluon plasma scientists expect to result from the collisions. Are you aware of some problem in this regard?

I don't know how common lead collisions are in nature. Maybe someone else here does, or you can try sending your questions directly to CERN. I will say that all elements are known to appear in cosmic rays, and this includes lead:

"All of the natural elements in the periodic table are present in cosmic rays, in roughly the same proportion as they occur in the solar system."

Once again thanks

No problem, but I really don't know what else to tell you at this point. I addressed your concern in my first post, but it doesn't seen to have been enough.

this has been really bothering me for the past few weeks.

That much is clear, but why?

Besides, I recently read that the LHC is mainly going to collide lead ions. Do we have any information regarding that type of collision in nature?

Once again thanks - this has been really bothering me for the past few weeks.

Because looking at these numbers, there doesn't seem to be a safety argument to guarantee the upcoming collisions in November won't cause the decay of our false vacuum.

2 TeV is the point to which iron-iron collisions had been measured as of September 1999. Scientists have more recently measured iron-iron collisions at up to 100,000,000 TeV, and this happens routinely in cosmic terms. LHC will operate at a tiny fraction of this level of energy.

I was referring to the "Review of Speculative "Disaster Scenarios" at RHIC" .
http://www.bnl.gov/rhic/docs/rhicreport.pdf

Specifically to the "Vacuum Instability" section, where it says the maximum energy observed of iron cosmic rays was 2 TeV per nucleon, while the LHC is going to collide heavy ions at an energy of 2.76 TeV, thus exceeding the cosmic rays limit. Is it possible that I misunderstood that passage? Because looking at these numbers, there doesn't seem to be a safety argument to guarantee the upcoming collisions in November won't cause the decay of our false vacuum.

I'm hoping to find out I was wrong, because this whole thing makes me very uneasy (because the cosmic rays argument is the only real way to make sure we are safe, regarding the possibility of a vacuum metastability event).

1. There's already a heavy-ion collider operating at Brookhaven (granted, at lower energy than LHC). Most of the ionosphere is laden with ions that routinely interact with a variety of high-energy cosmic particles, mostly protons but sometimes helium nuclei.

I'm not sure which safety paper you're referring to, but here is an excerpt from "Will relativistic heavy-ion colliders destroy our planet?" by Dar, De Rujula and Heinz, from September 1999:

At the Large Hadron Collider (LHC) currently being built at CERN, the experiment ALICE [21] will study Pb-Pb collisions at Ebeam ∼ 600 TeV, roughly 30 times higher than at RHIC. At the LHC, the planned number of heavy-ion collisions per year is similar to the corresponding figure at RHIC. To analyze the LHC case in the same spirit with which we have studied RHIC, we have to raise the threshold energy for strangelet production to the LHC energy, even though this assumption was already ultra-conservative for RHIC. Raising the threshold energy, and reusing Eq. (5), we conclude that the safety margin for ALICE is a factor 303.2 ∼ 5.3 × 104 lower than it is for RHIC. This means that, in discussing ALICE, it would presumably be advisable to improve our very safe limits based on the fate of stars and/or to develop considerations that rely more heavily than ours on our understanding of heavy ion collisions. For example, if one were to argue that, at a fixed energy per nucleon, Fe-Fe collisions are as good or better than Pb-Pb collisions at making strangelets, the probability P⋆ in Eq. (5) would increase by about 11 orders of magnitude, due to the smaller equivalent CR energy per nucleus, and the much larger CR abundance of Fe. The safety margins we have derived would improve by the same factor.

Emphasis added.

As for heavy-ion collisions in nature, the same paper notes under the section titled "Heavy-ion collisions in space":

In-flight collisions between cosmic rays are a rare but non-negligible occurrence. In a fraction of these encounters the centre-of-mass system moves sufficiently slowly for the process to be similar to the ones studied at RHIC: the flaw discussed in the previous section is avoided.

What follows is a selection of math that is, I must confess, beyond me.

At any rate, what this passage seems to imply is that the majority of these rare collisions occur at much higher energies.

Bear in mind that CERN's LHC safety conclusions have undergone extensive review at least twice since 1999.

—

2. Whatever that object was, it was a long way off, and I see nothing in that article suggesting that it can affect us in any way, aside from being visible with certain equipment.

Regarding the second question. I don't know all that much about the object in the article, but is stated that it is a loooong way away from us somewhere from around 130 lightyears to 11 billion lightyears away. Hence, I'm 100% sure that this object isn't going to cause trouble for us. Not in the near future, not ever.

1. The LHC is going to start colliding heavy ions at about 2.76 TeV in November. I wanted to find out if there are cosmic ray collisions of the same type at a higher energy than that, so that we can be reassured that the LHC does not poses an additional risk from that aspect. I'm aware of the fact that proton - proton collisions have been observed of up to 10^20 eV, but what about heavy ion ones? In the RHIC safety paper published in 1999 they said they can't know for sure which type of collision can more effectively trigger a false vacuum decay, so they have to check both types. But unfortunately, I can't seem to find any data about heavy ions in cosmic rays. Can anyone help out?

2. Do you supposed this object can appear once again sometime in the near future, and cause trouble for us?
http://www.skyandtelescope.com/community/skyblog/newsblog/28244844.html?pageSize=0