Young Australian Skeptics

My post last month attracted a nice little comment:

“One of the big fears at CERN is that the large Hadron collider would produce black holes that would eventually swallow the earth. Please comment on the plausibility of this fear (justification for or against)”

Ah yes, those dastardly black holes. This, I thought, was a nice springboard into a new post.

But I’ll come back to black holes in a moment. First, some background. What really goes on at the Large Hadron Collider?

What are the questions that it actually seeks to answer? Let’s begin by outlining these questions, and the core areas of interest that will be investigated by the various detector experiments at LHC.

The Higgs mechanism: Can the Higgs boson be empirically detected? What if it doesn’t actually exist?
There is some mechanism responsible for doing the things that we often ascribe to the Higgs field, that is, what is known as electroweak symmetry breaking, even if it isn’t actually the Higgs mechanism.

Even if a Higgs boson is not found, at the TeV-​​scale energies being probed here, there will be an extremely good chance of getting some insights into whatever interesting mechanism really is responsible.

A bit of trivia about the Higgs boson: When Nobel laureate “particle hunter” Leon Lederman wrote his book The God Particle, and coined that phrase, which journalists love and scientists are wary of, he apparently originally wanted to call it the goddamn particle, but the publisher wouldn’t allow it.

CP-​​violation: How was CP-​​violation established in the primordial universe, to the degree that it was? What mechanism is responsible for the CP-​​violation, and the resultant amount of matter in the cosmos?

An entire book (or many) could be written on each and every one of these things. For now, though, I’ll elaborate a little on just one of these areas of interest — CP-​​violation and its connection to cosmology.

One of the great open problems in physics at the moment is the question of why the Universe has so much matter in it, and essentially no antimatter.

If matter and antimatter (quarks and antiquarks, fundamentally) were created in equal amounts following the Big Bang, then all the matter and antimatter would annihilate, and the matter-​​filled Universe we see would not exist.

Something that we might expect, perhaps somewhat naively, from laws of physics is CP-​​symmetry — that is, that the laws of physics are ‘symmetrical’ under CP-​​transformation (CP– as in a combination of both Charge and Parity operators.) In other words, basically, the laws of physics are “symmetrical” between matter and antimatter, since CP-​​symmetry is the symmetry between matter and antimatter. We might expect particles and antiparticles should behave “symmetrically” in every way.

However, as per the above, this isn’t true. At least, it’s not always true. There exists some mechanism whereby CP-​​symmetry is perturbed, just a tiny bit — it was perturbed just enough in the early universe to create the universe that we see. This is CP-​​violation, an example of a symmetry violation in physics.

The CP operator is the product of two operators: C for charge conjugation, which transforms a particle into its antiparticle, and P for parity, which creates the mirror image of a physical system, if you will. The strong interaction and electromagnetic interaction seem CP-​​invariant, but a slight degree of CP-​​violation is observed in weak interactions under certain conditions.

The greater the degree of CP-​​violation present in the early Universe, the greater the amount of matter left in the Universe. Thus, the understanding of CP-​​violation plays an important role in cosmology, in explaining the amount of matter in the universe, which is a rather important quantity, from the point of view of physical cosmology.

A B⁰ meson, for example, is made up of a down (d) quark, and an anti-​​bottom (b-​​bar) quark. The corresponding antiparticle, an anti-​​B⁰, is comprised of an anti-​​down and a bottom. These mesons can ‘oscillate’ back and forth — with a particle spontaneously turning into the antiparticle, and vice versa. They’re electrically neutral, and don’t have any charge or other quantum numbers that are non-​​zero that would have to be non-​​conservative when this happens.

But the transitions between particle and antiparticle and between antiparticle and particle don’t occur at quite the same rate — because of the CP-​​violating term!

Whilst CP-​​violation was first experimentally discovered, it was discovered in neutral Kaon interactions — but today, most experimental studies of CP-​​violation deal with the B-​​mesons.

Two of today’s best known particle physics experiments investigating CP-​​violation in the decay of B-​​mesons are the Belle and BaBar experiments — where B mesons are produced in electron-​​positron collisions using particle accelerators — the latter at the Stanford Linear Accelerator, and the former at an electron-​​positron synchrotron collider at KEK in Japan. The interaction points are surrounded by optimised detectors to watch the decay of the B-​​mesons created. When, say, a B⁰ decays into some stuff, say a K⁰ and a couple of leptons, the anti-​​reaction, an anti-​​B⁰ decaying into the corresponding antiparticles, will occur, but at a different rate.

The observation of these decay events inside these detector experiments helps to provide insights into the mechanism by which the symmetry is broken to the degree that it is.

The LHCb detector experiment on the LHC is intended to be very similar in nature to these existing experiments — with similar goals.

Dark matter: It’s quite well accepted today that there is indeed “dark matter”, and it is comprised of weakly-​​interacting particles that have a significant amount of mass, but no charge, electromagnetic interaction, or any other type of significant interaction with their environment; much like the weakly interacting and elusive neutrino, which you may have heard of.

Exactly what are these particles? Could the lightest supersymmetric particles, such as the neutralino, if they exist, be consistent with the dark matter? Could we learn more about the mysterious particles making up dark matter if we are able to artificially create some of these candidate weakly interacting massive particles in the collider?

Quark matter and Quark-​​Gluon Plasmas: When large, heavy nuclei with many nucleons, such as gold or lead, are collided together with high energies under certain conditions, an unusual form of matter known as a quark-​​gluon plasma can be formed, which is an extremely high temperature, thin “soup” of the most fundamental sub-​​components of nuclear matter, quarks and gluons, with these quarks and gluons freed from their usual confinement within the nucleons in the extremely high temperature “fireballs” created in these collisions.

When the popular science headlines say that LHC will “re-​​create the conditions of the universe just after the Big Bang”, it is these Quark-​​Gluon Plasmas that they’re referring to; it is this extremely hot, fundamental, structureless form of matter that was present in the earliest moments of the universe, before it cooled down and particles such as protons began to form.

Supersymmetry: If supersymmetric particles can be observed, what is the mechanism responsible for supersymmetry breaking, making the supersymmetric (SUSY) particles so massive, compared to the familiar standard model particles? (A predicted consequence of supersymmetry is the existence of weakly interacting, high mass “supersymmetric partner” particles corresponding to known Standard Model particles.) Can the existence of supersymmetry explain the strength of gravity, or the composition of dark matter as being made up of supersymmetric particles?

The Hierarchy Problem: Why is gravity such a very weak force, compared to the other fundamental forces? Is the answer related to higher spatial dimensions, or to supersymmetry?

Higher dimensions: Can we empirically “see” evidence of higher spatial dimensions in the universe in high-​​energy particle interactions? What are those dimensions like? What are their properties?

Every one of these areas is potentially going to be answered, or research is going to be considerably furthered, by work at the LHC.

Anyhow; black holes, strangelets and LHC-​​induced apocalypse.

Could collisions in the LHC produce black holes?
The answer is… just barely possibly, maybe. There is some remote chance. However, if these black holes were produced, they would be microscopic, fleeting, quantum black holes which will decay quite rapidly.

No, any black holes potentially produced in the LHC aren’t going to kill you, eat Geneva, or destroy the Earth. If those microscopic black holes were to be formed, it will be really quite fantastic, and it will represent everything that we’ve hoped for from LHC and more, in terms of exciting insights into new physics.

To recapitulate; Production of microscopic black holes in LHC collision events would be awesome.

Here’s why.

If the centre-​​of-​​mass energy of two colliding elementary particles (a maximum of 14 TeV for proton-​​proton collisions in the LHC) reaches the Planck scale, Ep, and their impact parameter, b, is smaller than the corresponding Schwarzschild radius, RH [Ideally, we’d have some subscripts around here, but unfortunately the WordPress installation doesn’t seem to want to do subscripts for me], then a black hole will indeed be produced. However, the energy corresponding to the Planck scale, E_p ~ 10²⁸ eV, is a lot of energy, if you’re an experimental physicist. Such energies are entirely outside the reach of the experimental physicist — so, surely, generation of microscopic black holes at the Large Hadron Collider (LHC) has got to be impossible — doesn’t it?

According to the Standard Model of Particle Physics, black hole generation in a particle collider is indeed impossible at the TeV-​​scale energies associated with the current generation of high energy experimental particle physics endeavors, such as the LHC. The much-​​publicised speculations regarding the possibility of micro-​​black hole formation at the LHC are based on speculative hypotheses derived from theoretical models of cosmology and particle physics beyond the standard model (“new physics”).

Certain models put forward some years ago by theoretical physicists offer a seemingly neat and efficient lead into answering the questions, such as those of the hierarchy problem, of interest to particle physicists, and involve the existence of higher spatial dimensions.

The novelty of these higher-​​dimensional models lie in the fact that it is no longer necessary to assume that these dimensions are of sizes close to the Planck length (~ 10^–35 m). Rather, large extra dimensions could be as large as around a millimetre, if we suppose that the “fields of matter” — those fields of relevance to electroweak interactions and QCD, for example — ‘live’ in the 3+1 dimensional hyperplane of our 3-​​brane  — our familiar 3+1 dimensional world — and that only the gravitational field can interact across the higher-​​dimensional universe. Experiments involving the direct measurement of Newtonian gravity put upper bounds on the size of extra dimensions to a value of less than a few hundred microns.

Stay tuned for the conclusion to this post in Part 2… hopefully the first part hasn’t put you to sleep. Sorry, many of us here at the Young Australian Skeptics are a little busy with exams at the moment, but we hope to have more content for your enjoyment over the coming weeks.

This entry was posted on Monday, June 15th, 2009 at 2:00 pm and is filed under Luke Weston, Skeptic. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.