I fear we have (in the sense of no new particles likely to be found, NOT questions to be asked and answered).
Glad I got out when I did. :-) -- Ernie P. On Oct 19, 2012, at 7:43 AM, [email protected] wrote: > > > > > Science Blogs > Have we reached the end of Particle Physics? > > Posted by Ethan on October 17, 2012 > > > "The particle and the planet are subject to the same laws and what is learned > of one will be known of the other." -James Smithson > > The entirety of the known Universe -- from the smallest constituents of the > atoms to the largest superclusters of galaxies -- have more in common than > you might think. > > > Image credit: Rogelio Bernal Andreo of > http://blog.deepskycolors.com/about.html. > > Although the scales differ by some 50 orders of magnitude, the laws that > govern the grandest scales of the cosmos are the very same laws that govern > the tiniest particles and their interactions with one another on the smallest > known scales. > > > Image credit: R. Nave of > http://hyperphysics.phy-astr.gsu.edu/hbase/particles/expar.html. > > We study these two scales in entirely different ways; the largest scales can > only be studied with great telescopes, using the natural cosmic laboratory of > outer space, while the smallest scales require the largest, most powerful > machines ever constructed here on Earth: particle accelerators! And of all > the particle accelerators ever built by humanity, the Large Hadron Collider > (LHC) is by far the most powerful. > > > Image credit: Maximilien Brice, (c) CERN. > > Although many of us are still hoping that the LHC finds something new, > exciting and unexpected, it was constructed -- first and foremost -- to find > the last missing piece of the Standard Model: the Higgs Boson. There are many > types of fundamental particles in the Universe, but we can divide them into > three general categories: fermions (like quarks and electrons), gauge bosons > (like the photon), and the Higgs, a unique, fundamental scalar particle. > > > Image retrieved from Fermilab, modified by me. > > I don't know whether you followed physics news prior to the LHC, but if you > did, you'll remember that there was wild speculation about what mass the > Higgs Boson was going to have. There's a very good reason for this: all these > particles -- through the physics of quantum field theory -- have dramatic > effects on what we observe in this world. > > > Image credit: DESY in Hamburg, from http://www.desy.de/f/hera/engl/chap1.html. > > For example, we normally think of protons and neutrons as being made up of 3 > quarks apiece, but those three quarks only account for some 2% of the total > mass of those particles; the rest of that mass comes from all the other > particles, interacting via the laws of quantum field theory (QFT). All these > particles are so interdependent on one another that if the top quark -- the > heaviest of all standard model particles (and some 180 times the mass of the > proton) -- were twice the mass it actually is, every proton in the Universe > would be 20% heavier than the protons that actually exist! > > So, too, the mass of the Higgs would be highly dependent on what else is in > the Universe, and what interactions actually happen according to the laws of > QFT. > > > Image credit: David Kaplan. > > The standard model, of course, does not include gravity. But the real > Universe has gravity, and we assume that whatever the full, fundamental > theory of the Universe is, it incorporates all of the known forces, gravity > included. When it comes to gravity, we typically consider General Relativity > as a low-energy, large-scale (compared to the Planck length, at least) > approximation of a more fundamental, fully quantum treatment of gravity, > which is simply beyond the scope of our theoretical tools. > > > Image credit: Jim Mims of Science And Computer Science, from > http://www.alpcentauri.info/. > > At least, it has been for generations. But there is a new idea gaining > traction in recent years when it comes to making a quantum theory of gravity: > asymptotic safety. Without going into any mathematical detail (and with full > disclosure that I myself don't understand it as well as I'd like), you can > think of it as a mathematical trick that allows you to incorporate > gravitation into your QFT. (For a little more detail, see here, and for a lot > more, see the Weinberg original.) > > There's a very important reason we care about this: if we understand how to > incorporate gravity into our quantum field theories, and we've measured the > masses of all the standard model particles except one, we can theoretically > predict what the mass of that one remaining particle needs to be in order for > physics to work properly at all energies! > > > Image credit: Harrison Prosper at Florida State University. > > We can do this because demanding that the Universe be stable constrains that > last free parameter -- the mass of the Higgs boson -- to be one particular > value. If the mass turns out to be that value, then that's indicative that, > if asymptotic safety is a valid idea, there are no new particles in the > Universe that couple to the Standard Model. In other words, there are no new > particles to be found by building colliders in the Universe, all the way up > to Planck energies, some 15 orders of magnitude more energetic than those > probed by the LHC. > > But if we can predict that mass, and the actual mass of the Higgs boson turns > out to be anything else, either higher or lower, then that means there must > be something new in the Universe in order for physics to be self-consistent. > Now, here's the truly amazing thing: that mass was calculated back in 2009, > before the LHC was turned on. > > > Image credit: From Phys. Lett. B's paper by Mikhail Shaposhnikov & Christof > Wetterich. > > You can read the abstract here and the full article here, but what's truly > amazing is that we've now found the Higgs, and we know its mass. Want to see > what this paper, nearly 3 years old now, predicted for the mass of the Higgs? > (Highlights, below, are mine.) > > > Image credit: Mikhail Shaposhnikov & Christof Wetterich. > > Holy. Crap. > > So I want you to understand this correctly, because this could be huge. If > asymptotic safety is right, and the work done in this paper is right, then an > observation of a Higgs Boson with a mass of 126 GeV, with a very small > uncertainty (±1 or 2 GeV), would be damning evidence against supersymmetry, > extra dimensions, technicolor, or any other theory that incorporates any new > particles that could be found by any accelerator that could be built within > our Solar System. > > Fast-forward to this past July, when the discovery of the Higgs Boson -- > confirmed to be a single, fundamental scalar particle of spin-0 -- was > announced. What was its mass, again? > > > Image credit: Vixra blog, of combined CMS/ATLAS Higgs signal. > > According to the combined ATLAS+CMS data (both major detectors), a Higgs of > mass somewhere between 125 and 126 GeV was detected with a (robust) > significance of 6-σ, with an uncertainty of around ±1 GeV. In other words, > those of you who followed the excitement in July may have witnessed the last > fundamental particle physics discovery we will ever make. There still may be > more out there, but the Higgs Boson could have very well been the last > unfound fundamental particle accessible to colliders. > > Yes, there are still more questions to answer, more physics to learn and more > to explore even with the LHC, including questions about dark matter, the > origin of neutrino mass, and the lack of strong CP-violation. But there might > not be anything more to learn -- at least, in terms of fundamental, new > particles -- from doing particle physics at higher and higher energies. > > > -- > Centroids: The Center of the Radical Centrist Community > <[email protected]> > Google Group: http://groups.google.com/group/RadicalCentrism > Radical Centrism website and blog: http://RadicalCentrism.org -- Centroids: The Center of the Radical Centrist Community <[email protected]> Google Group: http://groups.google.com/group/RadicalCentrism Radical Centrism website and blog: http://RadicalCentrism.org
