Forum Replies Created
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I decided that I’m not only going to vote for Dr Jill Stein, but I’m gonna donate enough to get a t-shirt so I can wear it around town.
Do Greenies make cool Tees? I’ll wear a whack Tee, but it’d obviously be better if it were cooler.
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Yeah, after the Calif result, I guess its time i took down my Bernie sign, and made a big green Jill sign.Maybe I’ll get a Tee shirt too. Or maybe I’ll just get some green textile paint
and a white shirt and make my own. Maybe have a green paint party.bnw has to be loving this — we’re gonna get Trump elected, LoL.
Well, so be it.
w
vI became a boxing fan because of Ali and I stopped being one when he retired. He was the brightest star during the greatest era of heavy weight boxing when Ali, Frazier, Norton and Foreman were contenders.
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same with me, basically. Ali drew me into boxing, and when he retired i really lost interest.Ali, Frazier, Norton, Foreman — i wonder how many total concussions they all had.
I used to assume MMA was more dangerous, but maybe its less dangerous.
There is less of a “constant pounding” I would think. Maybe more danger to knees and joints but less to brains.w
vThis state, known as a quantum spin liquid, causes electrons – thought to be indivisible building blocks of nature – to break into pieces.
The researchers, including physicists from the University of Cambridge, measured the first signatures of these fractional particles, known as Majorana fermions, in a two-dimensional material with a structure similar to graphene…
—————-Majorana particles – Fundamentally confusing
A completely new type of particle is observed for the first time. What does that mean, fundamentally?
https://www.theguardian.com/science/life-and-physics/2014/oct/05/majorana-princeton-particles-fundamentally-confusingYou could define particle physics as the quest to discover the fundamental constituents of nature, and to understand how they interact. The so-called “Standard Model” of physics contains a list of particles which are not made of anything else, and of which everything else is made.
The question of how something can be made of nothing, and specifically how can a fundamental particle have mass, is both basic and deep. The answer – in the Standard Model – is that the mass of fundamental particles comes about because of the way they interact with Brout-Englert-Higgs field. The Higgs boson is the evidence that this works, and the matter particles which get their mass this way are called “Dirac fermions” because they are described by Paul Dirac’s 1928 equation. In the Standard Model, electrons, quarks and neutrinos are all Dirac fermions.
There has been small flurry of physics headlines over the last few days about the discovery, by physicists at Princeton, of a new kind of particle – a Majorana fermion. Proposed by the Italian physicist Ettore Majorana back in 1937 – a while after Dirac, but well before Brout, Englert and Higgs – so-called “Majorana fermions” get their mass via a unique and previously unobserved self-interaction, which is completely different from Dirac fermions, and nothing to do with Brout, Englert or Higgs*.
A consequence of the way this new mass mechanism works is that Majorana fermions must be their own anti-particle. Since particles and anti-particles have opposite electric charge, this can only work for neutral particles. That is to say, an electron has charge -1, so its antiparticle (the positron) has charge +1, and they are distinct from each other, and so cannot constitue a Majorana particle. The only possible candidate for a fundamental Majorana fermion in the Standard Model is the neutrino, since all the other fermions have charge. In fact, many speculative theories that extend the Standard Model – to explain some of the puzzles it doesn’t deal with – contain Majorana neutrinos. There are several highly sensitive experiments around the world searching for evidence, in rare nuclear decays, that neutrinos are Majorana fermions. It is a hot topic.
AdvertisementSo I was excited to read about the new particle, and somewhat diappointed when I did so to find out that it is not a fundamental Majorana fermion, still less a neutrino. A bit of a let-down for me and my particle-physics colleagues. Nevertheless, the result is interesting for a number reasons.
What has been seen is a quantum state in one-atom-thick wire which in a certain energy range behaves like a Majorana fermion. It is not a fundamental particle, it is a composite state, and the behaviour emerges from the interactions of atoms, electrons and photons, described by quantum electrodynamics, in which all fermions are Dirac. The fact that Majorana behaviour has been predicted, and then observed, to emerge as collective behaviour from a “more fundamental” (i.e. higher energy, shorter distance scale) theory is fascinating.
I guess that, given a mathematical principle such as the Majorana mass-mechanism, there are two distinct types of question you can ask. The one particle physicists tend to ask is “Does this appear as part of the basic structure of the universe – does it explain things we already see, answer problems we already have?”. However, one could equally ask “Can we construct a physical system in which this mechanism actually occurs, and if so what can we do with it and what can it teach us?”
The new discovery arises from addressing the second type of question. This kind of approach has yielded results before. For example, studies of emergent supersymmetry in low-energy optical systems continue even while fundamental supersymmetric particles remain elusive. It is also worth remembering that non-relativistic precursers of the Brout-Englert-Higgs mechanism were influential in the development of the Standard Model; and also that there are amazingly interesting (and useful!) phenomena such as superconductivity which arise in such tricky low-energy quantum systems.
AdvertisementI’ve talked about “fundamental particle” a lot in the above discussion, but it is important to be aware that this is just a working definition. The quantum-mechanical principles at play in the complex, composite systems at Princeton are “fundamental” to our understanding of physics, in that they form its foundations, even if the Majorana particle itself is not. When we say that an electron is a fundamental particle, we just mean that we have not been able to see any substructure inside one yet. Or to put it another way, no matter how hard we have tried (and we have tried very hard!) we haven’t broken an electron into pieces yet. It is still possible that we may eventually discover electrons, and even the Higgs boson, to be emergent phenomena of a more fundamental theory, just as these new Majorana fermions emerge from the Standard Model. Each time we look more closely, we have to be ready for surprises; ready to modify what we think of as “fundamental”.
* Nothing to do with this, either, although it does seem to crop up by mistake quite often in conference talks on the subject.
There is a pretty detailed account of the Princeton experiment and its new results here, although regretably the paper itself is not open access.
Jon Butterworth has written a book about being involved in the discovery of the Higgs boson, Smashing Physics, available here . Some interesting events where you might be able to hear him talk about it etc are listed here. Also, Twitter.
