Why do Neutrinos weigh less than other fundamental particles?
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since their coupling to Higgs bosons is weak
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Oh boy oh boy oh boy.  Let me tell you.  I'm so excited... I actually work with neutrinos.\n\nOkay.  So there are three different types of neutrinos, corresponding to the three different types, or "flavors" of matter, and they get heavier as you go along: there are electron neutrinos, mu neutrinos, and tau neutrinos, getting heavier from left to right.  Also, for each of these neutrinos, there is an anti-neutrino, for a total of six types of neutrinos.  THE THING IS that some physicists postulate that a neutrino and an anti-neutrino are the same thing, that each neutrino is its very own anti-neutrino.  The jury's still out.\n\nNeutrinos are the smallest particle (for a while, people didn't even think they had mass.  But they do).  To add to their mystery, they don't really interact with matter.  In fact, one can't directly measure a neutrino - it's impossible, because it won't interact with whatever material your detector is made out of.  Rather, physicists study neutrinos by studying the photons and other goodies created when neutrinos randomly decay.\n\nThe most common source of neutrinos on our good ol' planet Earth is our friend the Sun.  Nobody notices it because the neutrinos don't really do anything, but we're bathed in solar neutrinos all the time.
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Neutrinos exist because Quantum physics demands they exist.  In the decay of a Neutron into an Electron and Proton some extra enegry had to be expelled.  Thus Quantum physics created the Neutrinos.\n\nThe neutrino was first postulated in December, 1930 by Wolfgang Pauli to explain the energy spectrum of beta decays, the decay of a neutron into a proton and an electron. Pauli theorized that an undetected particle was carrying away the observed difference between the energy and angular momentum of the initial and final particles. Because of their "ghostly" properties, the first experimental detection of neutrinos had to wait until about 25 years after they were first discussed. In 1956 Clyde Cowan, Frederick Reines, F. B. Harrison, H. W. Kruse, and A. D. McGuire published the article "Detection of the Free Neutrino: a Confirmation" in Science (see neutrino experiment), a result that was rewarded with the 1995 Nobel Prize.\n\nThe name neutrino was coined by Enrico Fermi - who developed the first theory describing neutrino interactions - as a word play on neutrone, the Italian name of the neutron. (Neutrone in Italian means big and neutral, and neutrino means small and neutral.)\n\nIn 1962 Leon M. Lederman, Melvin Schwartz and Jack Steinberger showed that more than one type of neutrino exists by first detecting interactions of the muon neutrino. When a third type of lepton, the tau, was discovered in 1975 at the Stanford Linear Accelerator, it too was expected to have an associated neutrino. First evidence for this third neutrino type came from the observation of missing energy and momentum in tau decays analogous to the beta decay that had led to the discovery of the neutrino in the first place. The first detection of actual tau neutrino interactions was announced in summer of 2000 by the DONUT collaboration at Fermilab, making it the latest particle of the Standard Model to have been directly observed.\n\nA practical method for investigating neutrino masses (that is, flavour oscillation) was first suggested by Bruno Pontecorvo in 1957 using an analogy with the neutral kaon system; over the subsequent 10 years he developed the mathematical formalism and the modern formulation of vacuum oscillations. In 1985 Stanislav Mikheyev and Alexei Smirnov (expanding on 1978 work by Lincoln Wolfenstein) noted that flavour oscillations can be modified when neutrinos propagate through matter. This so-called MSW effect is important to understand neutrinos emitted by the Sun, which pass through its dense atmosphere on their way to detectors on Earth.
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Nope, the magnetic information (not electronic!) doesn't weigh anything, it's all related to the orientation of the "magnetic moment" (up or down) of the atoms i.e. the way atoms are turning (to make it simple). they're not heavier if they turn in one sense than if they does in the other
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In the Standard Model, quarks, electrons and the like are considered to be pointlike. This gives problems at short distances where for instance the electromagnetic force between two of them becomes infinite.\n\nThe basic idea of stringtheory is that the fundamental constituents of matter are strings of a length of order of 10^35 m which vibrate at specific frequencies. However, the simplest string theories give more problems then they solve and consistent theories requires more then four dimensions. \n\nMembranes take the idea even further.  The particles are represented by vibrating surfaces and higher dimensional objects.
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Gravity is the weakest of the four fundamental forces.  If you take the smallest amounts of the quantities that each force depends on (mass for gravity, charge for electromagnetic, etc.) and put them the same distance apart, then gravity is by far the weakest force.   But you have to use a very small distance, because the strong and weak forces are only short-range forces; they don't extend out much beyond the radius of a nucleus.  Consider the interaction between two quarks that are 3 x 10^-17 m apart.  Their strong nuclear interaction is about 100 times stronger than their electomagnetic interaction, about 1,000,000 times stronger than the weak interaction, and about 10^43 times stronger than the gravitational interaction.
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This is a very good question. Ultimately it comes down to being one of the fundamental features of our universe. But it can also be broken down a bit.\n\nLike charges repel, and opposite ones attract because of differences in their electric fields. But the electric fields are really part of the larger electromagnetic force. This force is mediated by photons (light) and, indeed light is a self-propagating electromagnetic wave.\n\nBut there are also three other fundamental forces: gravity, the strong nuclear force and the weak nuclear force. The strong nuclear force is well, strong, but very short range. It holds the protons and neutrons together in a nucleus (otherwise the like charges from the protons would break up every nucleus except hydrogen). The weak nuclear force is sort of a miscellaneous, and comes into play in certain radioactive decay sequences.\n\nIn the 1980s it was shown that the electromagnetic and weak forces are actually the same thing. The difference we observe is that the universe is, relatively speaking, "cold," and these two parts have separated out. It is sort of like having a glass of steam (one thing) which cools down until there is water and ice (two things). The water and ice look a lot different from each other, but are fundamentally the same. In the same way in the very, very early universe when things were a lot hotter, the electromagnetic and weak forces were identical - like the steam in the analogy.\n\nMore recently it was found that the strong force can also be linked to the "electroweak" force in the same sort of manner. The mathematical and physical details are different from "electroweak unification" but the basic principle is the same. It was from this Grand Unification of the electromagnetic, weak, and strong forces the the theoretical notion of quarks came. This GUT has been tested and the experiments show it is right on target.\n\nThe next step is to connect the electro-weak-strong force with gravity. This is a lot harder because the first three are understood in the context of Quantum Mechanics and gravity is understood with General Relativity. QM and GR are not compatible on some basic principles.\n\nOne approach that is being tried to combine QM and GR is with string theory. To make this work the universe is composed of 11 dimensions, the usual 3-spatial and 1-temporal dimentsion, plus 7 very, very small spatial dimensions. If these extra 7 are looped around themselves so that they are vastly "smaller" than a proton, we'd never really notice them.\n\nWhat string theory seems to suggest is that there are just some ways to make stuff in the universe, and one of these ways is to create the "force particles" that mediate the fundamental forces.\n\nSo, extrapolating that, and realizing that string theory is in no sense proven, we can say that "like charges repel" because of the geometry (the 11-dimensions) of the universe.\n\nBut string theory remains far from being complete mathematically, and no one can really make solid predictions yet to test it. So, you can also fall back on the answer in the first paragraph.
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We really don't know the specific neutrino masses. We know that at least one of the neutrinos has a non-zero mass, but it isn't known exactly what that mass is or which neutrinos have mass.\n\nThe problem is that neutrino masses are detected from 'oscillations; between neutrino types. Essentially, massive neutrinos can change types: electron neutrinos can convert into muon neutrinos, etc. The rate of the conversion depends on the *differences* in the masses, not the masses themselves. Because of this, we know that there is at least one neutrino whose mass is at least .1eV. In all likelihood, the masses are about this size for all three types of neutrinos.\n\nAs for how they affect the evolution of the universe, the main influence is that neutrinos are a type of 'dark matter'. They interact so infrequently with other matter that they have the characteristics needed for the cosmological dark matter. However, given the likely size of the neutrino masses and the amount of dark matter we know exists (through gravitational lenses and galactic dynamics), it is likely that neutrinos account for less than 1/4 of the total amount of dark matter.\n\nAnyway, neutrinos were in equilibrium with electrons in the very early universe. later, they 'decoupled' and evolved separately from other forms of matter. So they main way they affect things is through their gravity. Massive neutrinos would help in the formation of galaxies, for example.\n\n http://physicsweb.org/articles/world/11/7/3\n http://www.phys.hawaii.edu/~jgl/nuosc_story.html
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Well, a proton is not an elementary particle.  And the electron is the smallest lepton.  However, an elementary muon will decay to an electron and neutrino when passing from space into an atmosphere
1020906
Quarks are smaller.  Also the string theory says that quarks can be further divided into strings.  Strings are so small that if an atom is the size of our solar system, then strings are only about as big as a tree.
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This looked interesting but I am still very confused ?!?!?!\n\nWeighing the Universe \n\nThere are obvious contributions to the density of the Universe, e.g., planets, galaxies, ... , however, there are also other not so obvious contributions. We need \nrho = rho(baryons) + rho(neutrinos) + rho(photons) + ... \n\nUsing the above, we define \n\nOmega = Omega(baryons) + Omega(neutrinos) + Omega(photons) + ... \n\nSo the issue becomes what are all of these contributions to Omega? \n\nBefore we go on, photons are in there, but why? Aren't photons massless? And what if neutrinos turn out to be massless? Why are they there? \n\n\nAccording to Einstein, E = mc2, and mass and energy are equivalent. They are just different forms of a single entity \n===> mass = Energy / c2 \n\n\nCMBR ===> rho(photons) = 4.7 x 10-34 gm per cubic centimeter << than any reasonable rho(critical) \n\nThe neutrinos are more problematic. \nFor the Cosmic Neutrino Background Radiation (CNBR) \n\n====> rho(neutrinos) = 0.3 rho(photons) and if neutrinos are massless (like photons) then the CNBR does not make a large contribution to the density of the Universe. \n\n\nWhat if neutrinos are not massless? \n\nnumber of neutrinos per c.c. is N(neutrinos) ~ 375 per c.c. ===> rho(neutrinos) ~ 375 m(neutrino) gm per c.c. \n\nTo get an idea about when neutrinos are important, let's use H(now) ~ 25 [km/s] per Million light years ===> rho(critical) ~ 1.2 x 10-29 gm per c.c. ===> rho(neutrinos) > rho(critical) if m(neutrino) > 3.2 x 10-32 gm ~ m(electron)/300,000 (or so). \nNeutrinos can either be important or not depending upon whether they have a significant rest mass. \n\n\nGalactic Masses (Individuals and Groups) \nI will discuss galaxies as probes of the mass of the Universe. In some cases, there will be direct counting of galaxies, in other cases, the galaxies will be used as test particles. Define \n\n\nOmega(gal) = Omega(baryon) + Omega(other?) \nWe will measure Omega(galaxy) using light and dynamical techniques \n\n\nLight Method \nThis is straight-forward. We simply count up galaxies. The complication is that we observe primarily the galaxies which are easy to see. However, there are also many galaxies which are hard to see. These hard to see galaxies are the ones with low surface brightness (which means that they are very hard to see against the pervasive background of the night sky. The number of these low surface brightness galaxies is not yet well-established, however, the current density distribution of galaxies is interesting. But anyway, let's press onward under the assumption that we may be making a factor of 2 error or so by only considering the bright galaxies in our discussion. \n\nRecall, galaxies are divided up into different types: \n\n\n \nThe different types of galaxies have different Mass-to-Light (M/L) ratios. To get a feel for what M/L tells us, consider: \n\n\nA galaxy made of 1011 stars like the Sun. We then have M/L = 1011 M(Sun) / 1011 L(Sun) ===> M/L = 1 M(Sun)/L(Sun). If we measure M/L in units of solar masses to solar luminosities, then this galaxy has M/L = 1. \n\nSuppose that this same galaxy had in addition to its stars, 1011 black holes of mass 1 M(Sun) ===> M/L = 2 x 1011 M(Sun) / 1011 L(Sun) ===> M/L = 2 \n\nSuppose that we had a galaxy composed of 1011 stars of mass 10 M(Sun) and 104 L(Sun) ===> M/L = 1011 x 10 M(Sun) / [1011 x 104 L(Sun)] ===> M/L = 0.001 \n\nThe Mass-to-Light ratio depends on the types of stars that populate galaxies and how much unseen matter exists in the galaxies. \nThe typical M/L for the visible parts of galaxies are: \n\n\nEllipticals: (M/L) ~ 7 - 20 \nSpirals: (M/L) ~ 3 - 5 \n===> Omega(gal,visible) ~ 0.007 (factor of 2 uncertainty) << 1 \n\n\nDynamical Methods \nThe dynamical methods are indirect in the sense that you do not count-up things. You rely on Newton's laws of physics and gravity. The dynamical methods are applied on all scale
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The existence of neutrinos was postulated to explain what was \nobserved when a nucleus undergoes beta decay via electron emission (a neutron \nin the nucleus changes into a proton, and the nucleus emits an electron).  \nObservation seemed to indicate that, in general, neither momentum nor total \nenergy was conserved in such a reaction.  This was, understandably, \ndisturbing.  In 1931 the physicist Pauli proposed that another, unseen \nparticle was also being emitted in the reaction, accounting for the "missing" \nmomentum and mass-energy.  Fermi named this particle neutrino" meaning "little \nneutral one".  The name reflected the assumption that it had no electric \ncharge (so that the law of charge conservation would remain intact); \nadditionally, it was postulated to have zero spin (keeping the law of \nconservation of angular momentum) and to interact only weakly with matter (to \nexplain why it was virtually undetectable). Eventually the neutrino was \ndetected, in the early 1950's, through nuclear reactors (which produce huge \nnumbers of neutrinos).  Currently it is believed that there are three kinds of \nneutrinos (plus their antiparticles, making a total of six) -- the electron-\nneutrino, the muon-neutrino, and the tau-neutrino.  Neutrinos are considered \nto be the force-carriers associated with the fundamental force called the weak \nforce. The weak force is very important -- it contributes to the production of \nelements of higher atomic number, without which life as we know it would be \nimpossible.
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I doubt it.  Even with the vast size of the universe if such a thing could occur it might be very small.  Consider this.  If you can see things in outer space then photons have to be present; even in shadow.  They bounce off of objects and register on your retina.  It has been proven that photons do have mass and are matter.  Also neutrinos are all over the universe and can pass through all matter.
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Yes, it is thought that neutrinos travel faster than the speed of light-In fact, it is thought that the speed of light is the *lower* speed limit for neutrinos.  Thought is not particularly fast,and is measurable at a few hundred miles/hour.  Einstein's theory says that nothing can be accelerated to the speed on light, and only refers to massive particles and objects.  The theoretical connection between particles created together (paired particles) seems to obey no speed limit, and react instantly regardeless of the distance, but we are not sure if this represents somethign traveling between the objects, or a connection that exists in a different plane or dimension.
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Particles called W and Z bosons, which are similar to photons, except for having very large masses (about 80 times heavier than protons)\n\nThe large mass of these particles makes them hard to create out of the vacuum, thus they come into existence much less frequently than the massless photons.
1039705
The cell is still made up of many atoms, thats the only irrefutable link there. And the atom is not the elementary essential of matter, if by elementary essential you are referring to the smallest constituent of a matter. Atom is made of of sub-particles: protons, electrons, neutrons, quarks... And these are further made up of smaller sub-particles (our knowledge are always limited). Proton and nuetron have masses and volumes. Doesnt that mean they are matter too?
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As Mez says, you can't travel at the speed of light and measure any passage of time at all.  Clocks stand still at light speed.\n\nUntil recently, we did not know if neutrinos had rest mass or not.  It was thought they might be massless and travel at the speed of light.  However, observations conducted by neutrino observatories found that some solar neutrinos were switching between neutrino flavors during their flight from sol to the detectors.  This showed they must therefore have an internal clock running (or their initial state would be frozen), confirming they have a (small) rest mass and therefore travel at sub-light speeds.