When worlds collide

A reader emailed me to ask if I had any opinion on the Large Hadron Collider (LHC). I didn't, so he sent me a link to a forum that discusses concerns about the project's safety. I spent a little time over there, and while I am far, far from being an expert on these issues, my layman's impression is that the pro-LHC people know what they're talking about, and the anti-LHC people seem to be rather confused.

The biggest fear cited by the anti-LHC crowd is that a micro black hole will be created by the collider, and this MBH will stayed lodged in the Earth until it eventually devours the planet. The usual comeback is that cosmic rays are interacting all the time in the Earth's atmosphere, and no planet-killing MBHs have been created so far. Naysayers respond that a MBH created outside the Earth's gravitational field would speed harmlessly away, while one created within the Earth's gravitational field would stay with us and gobble us up.

There are at least two problems with this argument. The first is it doesn't matter where the particle collisions take place. As one poster - a physicist working on the LHC, with the screen name "North of the North Pole" - wrote,

[T]here is absolutely nothing different between hadron collisions in the center-of-mass frame that you happen to be sitting in, and the center-of-mass frame that is moving with respect to you. (Don't believe me? Listen to Albert Einstein who showed it was true over 100 years ago).

I'd be happy to view over some of [the critics'] more eloquent theories as to why special relativity happens to be violated in this particular case, whereas a hadron-hadron collision produced at rest with respect to the third rock from our average yellow sun [is] somehow different than hadron-hadron collisions produced with some velocity with respect to us.

The other problem is that any MBHs produced by cosmic-ray collisions would almost certainly disappear in a split second. If they did not - if they instead went careering through the universe - they would eventually be attracted to the powerful gravitational field of a neutron star, and would swallow up that star. Under even the most conservative projections, there would be enough wandering MBHs to snap up any given neutron star after (at most) 100 million years. Thus, 100 million years would be the upper limit of a neutron star's lifespan. In fact, however, neutron stars that are a billion years old have been identified.

In short, even if MBHs are produced by cosmic radiation - or by the kinds of collisions taking place in the LHC - they will wink out almost instantly. Moreover, it should be pointed out that there is no certainty that MBHs even exist, much less that they can be produced at the LHC's energy levels.

Another concern is that the collider will produce strangelets, which will convert our planet to "strange matter." The problem with this view is that there is another collider already in operation, the Relativistic Heavy Ion Collider or RHIC, which would be more likely to produce strangelets than the LHC. The RHIC has been running since 2000, with no ill effects.

The RHIC is less powerful than the LHC, so why would it be more likely to create strangelets? A poster explains:

[T]he production of strangelets is not directly correlated to the power of the accelerator. It is actually inversely proportional to it....

The theory behind strangelets determines that, if they are actually real, they will be produced at greater rates if there is a greater baryon density.... So, the higher the baryon density, the higher the probability of these strangelets forming because you will actually have the particles you need lying around. Another thing essential for the formation of strangelets is that they actually need to form; meaning that the dissociation energy of the strangelet (the energy needed to break up the strangelet) has to be greater than the kinetic energy in the collisions. Otherwise they wouldn't be stable, and any particle colliding into it would provide enough energy for the system to simply dissolve. Now, with the LHC, the energies are greater ..., and this means that the kinetic energy will be greater than that at the RHIC. Thus, because the RHIC has not produced any strangelets, the LHC will be even less likely to. Going back to our earlier point; the baryon density will also be lower. Even assuming an equal amount of baryons, the volume of the LHC is much bigger than the RHIC. So, you have the same amount of baryons over a greater volume, giving less baryon density and thus a smaller probability of producing strangelets.

Yet another concern is voiced by those who fear that the LHC will be "re-creating the Big Bang," as some media outlets have claimed. Re-creating the Big Bang certainly sounds dangerous, but the reality is that the LHC will be re-creating only certain conditions believed to be associated with the Big Bang. It does not have anything near the power of the actual Big Bang, of course.

Some of the critics seem to be quite ignorant of even high school physics. One befuddled person, when informed that cosmic ray collisions are going on all the time, for instance in the sun and moon, responded:

But there isn't gravity on the moon and sun...

Oops! Yeah, there is. Any object with mass exerts gravitational pull.

Trying to rescue his credibility, the poster follows up:

I meant there was far less than there is on earth, haha...

Ha ha, yourself, but you're still wrong. The sun has far more mass than the Earth, and thus a stronger gravitational field, which is why the Earth orbits the sun and not vice versa.

Another poster cites a supposed "expert" who said:

[C]osmic rays have a limit of 10^12 GeV, while the collider will produce 1.4 х 10^13, i.e. more than one order higher.

Prompting this response:

10^12 GeV = 10^21 eV

The LHC operates at 14 TeV = 1.4 X 10^14 eV.

Someone's units are way off.

In other words, the so-called expert's argument is like saying that a book weighing 32 ounces is heavier than a boulder weighing 16 tons. After all, 32 is bigger than 16! The energy level of the LHC is 14 tera electron volts, which is far lower than the energy level found in cosmic radiation.  (10^14 is much less than 10^21.)

Then there are the people who fret because scientists refuse to affirm that the LHC is 100% safe - that there is absolutely no possibility of something going wrong. What these folks don't realize is that scientists are trained to think in terms of probabilities, not absolutes. There is a nonzero possibility of almost anything happening, but most of these nonzero possibilities are so remote as to be effectively impossible. For instance, there is a nonzero possibility that a spaceship will land on the White House lawn and Donald Duck will waddle out. But the actual chance of such a thing happening is so small that it's hardly a possibility at all except in a theoretical sense.

Overall, it seems to me (again, purely from a layman's perspective) that the Large Hadron Collider poses no real risk, and that media alarmism and Internet scare stories have created a phony issue.

A good summary of the LHC experiments, emphasizing safety aspects,  is found here.

Comments

[Ronnie]

I'm glad you wrote this. I think some people are overly paranoid over the LHC.

[zerdini]

Renowned British astrophysicist Stephen Hawking has bet 100 dollars (70 euros) that a mega-experiment this week will not find an elusive particle seen as a holy grail of cosmic science, he said Tuesday.

In the most complex scientific experiment ever undertaken, the Large Hadron Collider (LHC) will be switched on Wednesday, accelerating sub-atomic particles to nearly the speed of light before smashing them together.

"The LHC will increase the energy at which we can study particle interactions by a factor of four. According to present thinking, this should be enough to discover the Higgs particle," Hawking told BBC radio.

"I think it will be much more exciting if we don't find the Higgs. That will show something is wrong, and we need to think again. I have a bet of 100 dollars that we won't find the Higgs," added Hawking, whose books including "A Brief History of Time" have sought to popularise study of stellar physics.

On Wednesday the first protons will be injected into a 27-kilometre (16.9-mile) ring-shaped tunnel, straddling the Swiss-French border at the headquarters of the European Organisation for Nuclear Research (CERN).

Physicists have long puzzled over how particles acquire mass. In 1964, a British physicist, Peter Higgs, came up with this idea: there must exist a background field that would act rather like treacle.

Some scientists were however more optimistic.

Hubert Reeves, the French astrophysician, told the Swiss daily Le Matin that the invention could bring "unexpected results" that would change the world of particle physics forever.

"This machine will probably bring unexpected results that could turn particle physics on its head," Reeves said.

"It's a really impressive tool. It can go as deep underground as the length of a cathedral," he said.

Particles passing through it would acquire mass by being dragged through a mediator, which theoreticians dubbed the Higgs Boson.

The standard quip about the Higgs is that it is the "God Particle" -- it is everywhere but remains frustratingly elusive.

While questioning the likelihood of finding Higgs Bosons, Hawking said the experiment could discover superpartners, particles that would be "supersymmetric partners" to particles already known about.

"Their existence would be a key confirmation of string theory, and they could make up the mysterious dark matter that holds galaxies together," he told the BBC.

"Whatever the LHC finds, or fails to find, the results will tell us a lot about the structure of the universe," he added.

Hawking, the 66-year-old Lucasian Professor of Mathematics at Cambridge University, was diagnosed with the muscle-wasting motor neuron disease at the age of 22.

He is in a wheelchair and speaks with the aid of a computer and voice synthesiser.

[Ben]

I hadn’t been keeping up with this, but if Hawking is opting for String theory, the standard model must be in big trouble.

I'm surprised there is a serious debate about MBHs. I thought the threat from them was an invention of fundamentalist Christians, who like to look for as many ways as they can to end the world.

[Wax Frog]

Allowing that I am another layman, I'm hoping they find something that shoots all their theories to heck! There are a few fundamaterialist bubbles out there in need of bursting :oD

[pmprescott]

Very well summarized piece of information.
By the time you get this far into the sciences most lay people are out of their depth and have a tendency to be very fearful of any expanded knowledge. Isaac Asimov called this the Frankenstein Reaction. If many people had their way we'd still be riding horses, dying of small pox and burning witches.

[steve from brisbane]

Michael, I had been following the argument for a couple of years. What annoys me about it is that those who are saying that mini black hole danger is a "ridiculous" suggestion don't acknowledge that the point about neutron stars as a conclusive argument against the danger was only published in June 2008! Prior to that, the initial safety reviews were mainly based on the assumption that Hawking Radiation would mean mini black holes evaporate instantaneously. Some people (like me) complained that this is not a safe assumption, as it has never been observed, and at least a couple of physicists from time to time had questioned whether it might exist at all.

Finally, they got around to doing the work to show that neutron stars indicate that they must not be danger. Fine, but don't now go calling those who brought up the issue a bunch of idiots (as some science journalists, and some physicists, have.)

I personally still doubt that the physicists involved have considered all possible sources of danger. I think the mini black hole eating the planet idea probably has been conclusively answered, but I note that Rainer Plaga, a well published astrophysicist, wrote in August that under some models, Hawking Radiation could make a mini black hole work like an atomic bomb. The CERN physicists came back and said he made a fundamental mistake; I emailed Plaga and he says he is working on a response. He appears not to be readily acknowledging a mistake. I don't think he is a nutter, and trust him more than Rossler, who is the only scientist who continues to argue that micro black holes may eat the earth on a time scale that matters.

Even if Plaga is proved wrong, I have read at arxiv that "naked singularities" might also be produced by the LHC, and their behaviour seems unknown, as far as I can tell. (Of course, the argument that some may be being produced naturally by cosmic rays and aren't blowing up stars and planets could also be the answer, but it still makes me a little uncomfortable if a slow moving one was created near earth.)

The nagging worry that I have is that the LHC, or its successor, might be capable of intermittently creating something that is dangerous just at a planetary level, and if so this level of technology might be a very handy explanation for the Fermi paradox.