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piningforthefjords
2010-Jul-26, 07:20 AM
When the LHC was starting up, there were some worries that a collision of two particles could form a bubble of "true vacuum", as opposed to the "metastable vacuum" that the universe is in today. This bubble would then expand outward at the speed of light, annihilating any matter that stood in its way.

Studies later found that cosmic ray collisions, both past and present, took place at energies much higher than those that human-made collisions are capable of, which meant that the LHC is safe.

However, sooner or later, humans will be able to create collisions that are as powerful as, and eventually more powerful than, naturally occurring collisions. Could one of those collisions set off what's known as the vacuum metastability disaster? In other words, could it be that there's a certain energy barrier that naturally-occurring collisions can't overcome but that human-made collisions could overcome? After all, it's not that far-fetched to think that humanity can create collisions that are more energetic than natural collisions. There are several things we can do better than nature.

Ken G
2010-Jul-26, 10:45 AM
However, sooner or later, humans will be able to create collisions that are as powerful as, and eventually more powerful than, naturally occurring collisions.That seems unlikely. Cosmic ray energies are expected to reach a billion times the energies achievable by the LHC. If one scales down the LHC energies by a similar factor, one gets the energies achievable in an X-ray machine in a dentist's office. Will humanity ever build machines that make the LHC seem like something you'd find in a dentist's office? I'm not sure we should expect that will ever be the case, though I could be wrong.


Could one of those collisions set off what's known as the vacuum metastability disaster?Who knows. If our technology continues to advance to that level of power, I'm not sure if our biggest worry will be vacuum metastability! The issue of whether or not our wisdom and responsibility matches our technological accomplishments is already a poignant issue for humanity, and has been basically since the developments that spurred the Nobel peace prize. Your point is that perhaps at some point the issue could shift from our own survival to the survival of the entire universe, but my feeling is that if the vacuum were really so fragile that a single intelligent species could upset it, our universe would never have gotten this far. In any event, ethical issues surrounding vacuum metastability are not currently relevant-- we're a good factor of a billion short of energy there.

Swift
2010-Jul-26, 06:48 PM
Studies later found that cosmic ray collisions, both past and present, took place at energies much higher than those that human-made collisions are capable of, which meant that the LHC is safe.

One small nitpick - the fact that cosmic ray collisions had energies that far exceeded anything even remotely possible for humans was known well before the LHC was even a dream. There is a good history on this website (http://www.telescopearray.org/outreach.html). And there is also more on the wikipedia page (http://en.wikipedia.org/wiki/Ultra-high-energy_cosmic_ray)

The first observation of a cosmic ray with an energy exceeding 1020 electronvolts was made by John Linsley at the Volcanic Ranch experiment in New Mexico in 1962.[1][2]

Cosmic rays with even higher energies have since been observed. Among them was the Oh-My-God particle (a play on the nickname "God particle" for the Higgs boson) observed on the evening of 15 October 1991 over Dugway Proving Grounds, Utah. Its observation was a shock to astrophysicists, who estimated its energy to be approximately 3 1020 electronvolts[3] (300 EeV or 50 joules)—in other words, a subatomic particle with macroscopic kinetic energy equal to that of a baseball (142 g or 5 ounces) traveling at 96 km/h (60 mph).

mugaliens
2010-Jul-27, 04:13 AM
How does this compare to the 1048 J of energy in the core collapse of a Type II supernova which we see as the 10 second neutrino burst? It may be very spread out, but the pressure is enough to cause both electron and neutron degeneracy.

BigDon
2010-Jul-27, 09:17 AM
Think of the Death Ray a stream of OMG particles would make at even flashlight flux levels. (would you get a recoil?) I'm just not sure who I would use it on. Romulans I think. I always hated those smarmy so and so's.

Ken G
2010-Jul-27, 03:17 PM
Think of the Death Ray a stream of OMG particles would make at even flashlight flux levels. (would you get a recoil?) Yes, there would be a whopping recoil. It would be the recoil you'd get from that same number flux of baseballs, reduced by half the ratio of the baseball speed to the speed of light. (Nonrelativistic energy fluxes are turned into momentum fluxes by dividing by v/2, and relativistic energy fluxes are turned into momentum fluxes by dividing by c.) The winds of extremely bright stars are driven by this recoil effect.

(ETA: twice --> half)

BigDon
2010-Jul-27, 11:25 PM
Thanks Ken.

Cougar
2010-Jul-28, 01:06 PM
When the LHC was starting up, there were some worries that a collision of two particles could form a bubble of "true vacuum", as opposed to the "metastable vacuum" that the universe is in today. This bubble would then expand outward at the speed of light, annihilating any matter that stood in its way.

I predict this will never happen. If I'm wrong, you will never know it.