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Science

Experiment Shows Neutrinos Have Mass 233

Posted by michael from the good-time-to-be-a-textbook-writer dept.
Tuzanor writes: "Physicists have found the most convincing evidence yet that neutrinos, subatomic particles that were thought to have no mass whatsoever, actually do have a very tiny mass after all. The story is at Yahoo!" We mentioned the experiment yesterday, but this is big news. The New York Times has a thorough article on the whole experiment and its meaning.
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Experiment Shows Neutrinos Have Mass More

Experiment Shows Neutrinos Have Mass

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  • Not reall true, it's a different thing! (Score:2)

    by Anonymous Coward
    It sounds good, but this doesn't 100% jive with other experimentation and the theory of what we call the "neutrino".

    Back around 1993, John Edwards, et al, came to the conclusion that neutrinos have no mass after a 10 year, $100 million neutrino mass experiment funded by the nuclear energy commission.

    The theory still holds that a neutrino with a detectable mass significantly smaller than the new clamined mass would in fact be detected in the apparatus. The apparatus used
    for mass detection was, in terms of mass detection, more accurate to the one described in the article above.

    A possible explaination is that Neutrinos sometimes have mass.

    But it is more likely that there are two types of "neutrinos", one rare type with mass (so called mneutrinos), and one much more common type without mass (neutrinos). The theory behind each are very very different!

    For more information, see http://www.autodynamics.org/new99/Neutrino/NeutDel i.html
  • I have so much crap on my desk as it is. Now you tell me I have more?!?
  • Here in the South (Austin, TX, anyway), it seems pretty common to use the word "jive" in place of "jibe." This is for two reasons, 1) standard linguistics... 'b' corrupts to 'v' and 2) the meaning of "jive" which is "to swing" (think Swing dancing) bears a connotation of mutual agreement. Thus, the two things in question dance together, they swing, they jive.

    This defense brought to by the guy who is trying to explain to his 5 year old that "ain't", as used by his redneck mother, is less acceptable than "isn't" or "aren't".

    cheers,
    -l
  • Of course.


    The largest part of the 'mass' (energy) of the neutrino still comes from its kinetic energy. What has been found in the experiment is that it also has a *rest* mass (ie. a mass at zero velocity).

  • How do they know that?

    Maybe they invent particles to make their theories look good - said theories having been proposed vaguely enough to encompass almost anything - then coalesce the theories down around the data as it arrives, calling anything which doesn't fit ``anomalous'' (note the perspective: reality doesn't fit the theory, so reality must be the anomaly, not theory!), then either delete the few offending data from their datasets because it's anomalous, or occasionally when it can't be swept under the carpet, declare it to be a great and rare mystery then set about making a special-case patch to the theory in the hope of eventually having it all work.

    Want a clear, real-world example of this? Try radio-isotope dating.

  • ...shielding it from cosmic radiation would be a problem.

    The only obvious way to shield is very expensive: use several, and go mining on Mercury and maybe Mars (both totally hostile environments) to bury many tonnes of delicate instruments a mile or so down. I'd like to see the budget for that!
  • Here is a site that has a rebuttal that makes sense.

    Yah, that does explain a lot more. And here's another with a slightly different angle [electric-universe.de].
    This is just another case of scientific BELIEF rewriting scientific FACT.

    Uh, I think that would be ``reframing an observation.'' There's no shortage of exciting and imaginitive - and, unfortunately, bankrupt - explanations proposed for ``anomalies'' in orthodox theories, rather than cleanly rewriting the theories as should be done. Just ask J Harlan Bretz [ccrh.org] about that.

  • Re:Not just that they have mass... (Score:5)

    by Sheridan ( 11610 ) on Tuesday June 19, 2001 @07:05AM (#141177) Homepage
    smitty825 quoth:
    If they have mass, then we must include that mass in all calculations, but for some reason they don't want to :-)
    The current standard model does not predict the masses of neutrinos, but its equations are simpler if neutrinos have no mass.
    That's like saying calculating the velocity of an object is easier to calcuate if we don't count friction!

    Just because physically observed particles have mass, it is not necessarily required that the theory has particle masses in its bare Lagrangian form from which the perturbation theory Feynman rules are determined. (And I'm not talking about the Standard Model's Higgs Mechanism for mass generation by spontaneous symmetry breaking - which is another thing altogether...)

    Non-perturbative calculations using the Schwinger-Dyson equations, Ward identities and renormalisability constraints show that masses can be generated dynamically through interactions of massless fields.

    Some (8-10 year old) references can be found via this [dur.ac.uk] HEPDATA query. Note that this is not talking directly about neutrinos, but rather about generating masses for electrons in a simplified version of QED in which electrons start out massless.

    There are almost certainly some newer papers that you could find either at HEPDATA or SPIRES.

    (Full Disclosure: Mike Pennington was my Ph.D. Supervisor, although I didn't work in the non-perturbative SD equations field myself except for a short while at the start)
    --

  • In supernova 1987, the neutrino pulse was only
    seconds before the radiation brightening.
    Not much notice.

    If neutrinos have mass, they'd travel a little
    slower than the speed of light. So you'd expect
    some delays in that 1987 was about 150K light
    years away.
  • This is just another example of them teaching something as fact and then finding out that they were wrong and throwing it away and replacing it with something else.

    Umm... this pretty much is the definition of science. No scientist worth his or her salt would ever present a theory to you as fact. A fact is an observation - "When I let go of this ball, it falls to the earth." The theory is the attempt to explain the fact, and any scientist should tell you, quite cheerfully, that you can never prove a theory, you can only disprove it.

    Now, if you want to disparage the educational system for forgetting to teach this important distinction; or the media for conveniently overlooking it in order to present a sensationalist story; or the socialists and athiests who use it in place of religion; or the politicos who use it to ram through purely political agendas like the Kyoto treaty... well, then you've got a case for being disgusted. Don't mistake the medium for the message, though.

  • The problem is that right now, it would be very hard to come up with a way to give a neutrino low kinetic energy. The excess energy available for kinetic energy of the reaction products is on the order of MeV, while the limits on the mass of an electron neutrino [cupp.oulu.fi] is on the order of eV. The way the physics of nuclear reactions works makes it very difficult for the neutrinos to get a million times less kinetic energy than the other reaction products. In fact, due to the conservation of momentum, its more favorable for the low mass products to get more kinetic energy than the high mass products.

    Even if you could get low energy neutrinos ( less than an eV), you'd still have to collimate a beam them. That would be very difficult to do, since they react so little.

    So yeah, its not impossible to measure the mass of a neutrino directly. But I'd be very surprised if we find a direct way to measure the mass of a neutrino anytime soon. Indirect will have to be good enough for a while.

    --
    I hope we shall crush in its birth the aristocracy of our monied corporations ...

  • Re:what about the velocity? (Score:5)

    by gorgon ( 12965 ) on Tuesday June 19, 2001 @06:54AM (#141185) Homepage Journal
    Well, the mass of neutrinos is so small and they interact with other matter so sparing that its almost impossible to tell the difference between their speed and c. The typical total energy of a neutrino is going to be at a thousand times (and probably a lot more) times its rest mass. A particle with a total energy 1000 times its rest mass has a speed of about .9999995 c, which as you can imagine, is pretty hard to differentiate from 1.0 c .

    So, neutrinos don't travel at c, but its pretty darn close.

    --
    I hope we shall crush in its birth the aristocracy of our monied corporations ...

  • About 18 percent of all the "dark matter" in the universe may now be made up of neutrinos.

    Anyone care to elucidate on this part?

  • Neutrinos have a little mass, so they can't be quite moving at the speed of light. Therefore, when we see a Supernova go off, the light ought to arrive a little ahead of the neutrino burst.

    As I recall, on the big, nearby Supernova 1987A, a neutrino burst was detected. My question is, did anyone get the timing nailed down from this event well enough toconfirm that the neutrinos were a little late?

  • Hey, you with from John? I did some work on SKAT 2 years ago for him.
  • I had an office two doors down (Abby Normal). I did work in the lab accross his office th summer before SKAT got shipped to SuperK.
  • Like the poster below said about the universe weights more than we can observe. On example of this is how galaxies spin. While obviously early on the center spun faster than the core, currently the center and the outside go around the center and the same time, which totally defies concepts of orbits. So its hypothesises that there is alot mass (more at the edges less in the center) creating this effect. But, we can't seem to see this mass, so we just called it dark matter. The new theory is that its now neutrenos. Shrugs.
  • Yes and no. This is a new story, making the front pages of newspapers here in Toronto. But apparently others have claimed to have proved that neutrinos have mass before now. Perhaps the findings of the previous experiment were not known, or discounted.

  • Sure, but we ignore relativity when doing simple physics in high school, pretending that F = m*a, and that mass, length and time are all constants. The fact is, for the most part Newtonian mechanics are pretty much correct, even if they're mathematically wrong. The equations are just simpler if the speed of light isn't a limit.

  • I honestly don't see what creationism has to do with particle physics. Even IF God created all that is in its current form (no big bang, no evolution, and potentially... and some (but not all) creationists actually believe this... no dinosaurs (they were planted by God to test the faith of "scientists")). Even IF we presuppose all of this as absolute truth, that has no bearing whatsoever on whether or not neutrinos have mass. The whole point is that we THOUGHT neutrinos had no mass, and now we've OBSERVED that they MUST have mass. I'm Christian but scoff at almost all creationist logic, and it really runs the gamut... but we're talking about objective observations of the rules of God's universe, with which, if we recall Einstein, God does not play dice with. God did not intend the Bible to be a crutch to be used to ignore science, or batter it into submission.

    - StaticLimit
  • The underground observatory is also part of the supernova early warning systems that will alert the world to the next celestial storm generated by a supernova...

    EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE!

    This is a test of the Supernova Early Warning System. This is only a test. If there had been an actual supernova within a hundred light years of Earth, you would have been instructed to...

    Ummmm...

  • I find these indirect indications of neutrino mass quite amusing, as they seem to be tiptoeing around some odd results found about a decade ago. I originally read about this in a science fact column [washington.edu] by physicist John G. Cramer in Analog magazine. Some experiments were run that measured the square of the neutrino rest mass. The initial experiments had an error bar that overlapped zero, but was mostly negative. Later experiments had an error bar that lay entirely below zero. That is, within experimental error, they had measured a negative squared rest mass for the neutrino, implying an imaginary rest mass for the neutrino, which would mean that neutrinos are in fact tachyons. (Tachyons are hypothetical particles that can only go faster than light, and the higher their energy, the slower they go, so that high-energy tachyons approach the speed of light from above.)

    Cramer quotes an anonymous source as saying that if the sign of these numbers had been reversed (positive instead of negative), there would have been a big press conference announcing that they had shown the neutrino to have a nonzero rest mass.

    I sent email to Cramer maybe five years or so later, asking what had happened with these results. He told me that nothing had happened; there has been no followup, and nobody has shown them to be wrong.

    The super-Kamiokande experiment seems to have been carefully designed to show nonzero rest mass for at least one kind of neutrino while yielding no information on the actual value of the squared rest mass (in particular, its sign.) This experiment measured only the difference in squared rest masses between two types of neutrinos. (If this difference is nonzero, then one of the two neutrino types must have a nonzero squared rest mass.) It is consistent with either a positive or negative squared rest mass.

    This latest result also carefully avoids the issue of the actual value (and sign) of the squared rest mass. It appears that everybody wants to get their Nobel for showing that the neutrino has a nonzero rest mass, but nobody wants to be labeled as a crank for presenting data that would indicate the neutrino has an imaginary rest mass!

  • They can't even make a decent beer.

    Can't make a decent beer? Try Sleeman's [sleeman.com] or Granville Island Brewery or some other microbrew. Hell, even Kokanee isn't too bad.

    I can't believe that someone from the United States, home of beer with alcohol content so low it has to be expressed in scientific notation, is insulting Canadian beer.

    I find it hard to believe that Canada has the scientific know how to be trusted

    In certain areas, such as some types of condensed matter physics (Mu-SR, beta-NMR), superconductor research, and some other fields, Canada leads the world. Our research programs are not as large as the US (since we're a smaller country, population-wise), but they're top-notch.
  • Uh, first of all, which U of A? The University of Alberta [ualberta.ca] is also known as the U of A, and it's definitely in Canada. I'm guessing that's not the one you mean.

    At UBC [www.ubc.ca], Dr. Hardy [physics.ubc.ca]'s lab grows the world's highest-quality YBCO superconductors in the world. (YBCO is the common abbreviation for them--yes, I know the proper name, but it's too ugly in HTML). He is part of a larger Superconductivity Research Group [physics.ubc.ca] at the University of British Columbia [www.ubc.ca]. That group also works closely with the Muon Spin Rotation Group [triumf.ca] based at UBC and nearby TRIUMF [triumf.ca]. Disclaimer: I'm part of the Muon Spin Rotation Group.

    We're also in the process of commissioning a Beta-Nuclear Magnetic Resonance apparatus and beamline at TRIUMF, which will be very useful for probes of the local magnetic fields within superconductors (and other condensed matter physics applications).

    This is by no means an exhaustive list of the areas in which Canada leads in physics--it's just what I'm familiar with. I know we also recently opened a (privately funded) institute for theoretical physics, and they pay very generous salaries. We've also managed to recruit a few key quantum computing people up from the US.

    I'm not trying to say Canada is the best in the world at everything, but we do have some very solid, well-respected programs in physics.
  • Is this the same Dr. Hardy who was at the U of Arkansas about ten years ago working with Dr. Sheng? If it is, and I'm not saying it is, I always got the impression that he was a public relations guy and Sheng was the real horsepower.

    Nope. Hardy has been at UBC for decades, and has won a shitload of awards. Take a look at his bio, which I linked to in my last message. Also, producing highest-Tc superconductors is mostly a game right now, since it's all very small incremental improvements. The real research involves growing and studying high-quality single-crystal samples to learn how they work, so we can make the next big leap. That's where Canada leads.
  • I always thought those wily bastards were full of crap when they said that neutrinos had no mass. I thought common sense would tell you that they'd have to. (Using the logic that, "If A has a mass of X, then the complete mass of the particles in A is X as well.")

    -------
    Caimlas

  • The idea of relativistic mass simply isn't useful, and can lead to a lot of misconceptions.
    Don't you need relativistic mass for gravity calculations? (Isn't that how they confirmed E=mc using Mercury's orbit?)
    --
  • Are you sure that's sqrt(r)? I thought the square of the period was proportional to the cube of the distance. That would make it r^(-3/2).
    --

  • what about the velocity? (Score:5)

    by Mr. Slippery ( 47854 ) <tms&infamous,net> on Tuesday June 19, 2001 @06:38AM (#141210) Homepage

    So this this mean that:

    • neutinos have a non-zero rest mass, and previous ideas that they travel at c are incorrect,
    • neutinos have a non-zero rest mass, and travel at c, screwing up special relativity, or
    • neutinos are some special case, they somehow have a mass but not rest mass

    Please, some physics geek tell us how to resolve "neutrinos has mass" with "neutrinos travel at c.

    Tom Swiss | the infamous tms | http://www.infamous.net/

  • > What has been found in the experiment is that [the neutrino] also has a *rest* mass (ie. a mass at zero velocity).

    Great, all I need is a piece of lead several light-years thick, and I can then melt it down and extract the at-rest neutrinos to make neutrinonium (as long as I'm fantasizing, I wonder if a lump composed of neutrinos at rest would shimmer or somehow change color as the component neutrinos oscillated between three states ;-)

    (Seriously, mad props to the SNO guys. I remember hearing about the Solar Neutrino Problem years ago, and hoping that Sudbury would get the funding to actually carry the experiment through to its conclusion.)

  • > As I recall, on the big, nearby Supernova 1987A, a neutrino burst was detected. My question is, did anyone get the timing nailed down from this event well enough toconfirm that the neutrinos were a little late?

    I don't think we really knew when we SN1987A visibly started brightening - IIRC we saw it after the fact.

    In any event, given that neutrinos could pass through the shell of the star faster (i.e., almost the speed of light) than the star could tear itself apart (i.e. minutes/hours), I'd expect the neutrino burst to be observed before the light from the supernova.

    (That is, the light travels faster than the neutrinos, but the neutrinos get out of the supernova before the shock wave hit the star's surface.)

    Come to think of it, if I were running SNO or Super-Kamiokande, and I saw multiple events all within a few seconds of each other, I'd eliminate the possibility of detector error ASAP, and then look at the angle of incidence (all the neutrinos would appear to be coming from a point source) and start phoning every telescope operator on (and off :) the planet to look in that general direction for something going boom.

  • The sun produces only one type of neutrino. But there are two other kinds that the earliest neutrino detectors could not see, and some of the ones made by the sun turn into those other types on their way to Earth.

    How do they know that? I mean how do they know what type of neutrinos are coming out of the sun since their detectors are on the earth?
  • Thanks to everyone who responded to my query. I guess my problem is that the standard model is said to be somewhat flawed because it not only failed to predict the mass of the neutrino, it also failed predict whether or not the neutrino has any mass. Yet physicists seem confident that the model is good enough to predict that only massive particles can change type in transit and that the sun can only emit electron type neutrinos. I don't know about others but there seems to be a catch-22 whereby a partially flawed model is used to detect its own flaw. Maybe one of you can explain the reason why there is such a high confidence in one facet of the standard model and not the other.
  • so yes, you are correct in saying that the standard model was flawed. but only one assumption of the model was flawed, not the fundamental theories used to explain the model. Those theories, and not the entire standard model, were used to correct the flawed part of the model.

    Thanks for the excellent explanation. I think I need to find out why particle theory insists that only massive particles can oscillate.
  • From the posted link: Folks call this hypothetical process "neutrino oscillation". For it to happen, the neutrinos need to have a nonzero mass. After all, a massless particle moves at the speed of light, so it doesn't experience any passage of time - thanks to relativistic time dilation. Only particles with mass can become something else while they are whizzing along minding their own business.

    Ah. The assumption seems to be that, between the time that massless particles like photons are emitted by the sun and the time they arrive here on earth they will not change because they are traveling at c in "empty" space. However, it is my understanding that neutrinos are created from deep inside the sun and must travel huge distances at speeds lower than c within the sun's body before they make it to outerspace. It appears that there are plenty of opportunities for the neutrinos to interact with other particles of matter and possibly change their state. After all, even massless photons can change their "spin" during interactions.

    It seems to me that a better way to determine whether or not neutrinos are massless might be to calculate their speed to determine if they travel at c. One way to do that might be to detect whether an observed solar explosion or flare is accompanied by a conincident surge in the number of detected neutrinos. Just a thought.
  • Ok. Thanks for the reply. If neutrinos have mass they should travel at different speeds and even come to relative rest. There is no reason to suppose they always have to travel as fast as they do. Why do they appear to always travel at c?
  • Since their rest mass is so tiny, even a small amount of additional energy is enough to boost them immeasurably close to c. It's very unlikely that a process will give them a kinetic energy in our frame that yields speed relative to us that's perceptibly less than c.

    Makes sense. One last question. Why is it so hard for neutrinos to interact with ordinary matter?
  • Thanks for the reply. It seems to me that if neutrino does not have an electric charge, it would not interact with the weak force either since the weak and the EM forces are unified.
  • Electric charge is really just the electromagnetic component of the "unified charge" (I forget what it's really called) that appears in electroweak theory. Neutrinos still have "weak charge". (Hypercharge?)

    This sound a little weird to me because I learned that the weak and EM charges could not be separated according to the electroweak theory. I guess I'll have to leave it at that for the time being. Thanks for taking the time to reply to all my questions.
  • Yeah, SNO is definitely playing this up more than it should. We've known that some neutrinos have mass since Super-K - specifically that there was a mass difference between muon and tau neutrinos.

    However, there had been no direct evidence for oscillations of electron neutrinos, which are the neutrinos produced by the sun and which are by far the most numerous neutrinos in the universe. The number of electron neutrinos detected from the sun was 1/3 of what solar models predicted. The SNO result shows that the total number of neutrinos of all flavours coming from the sun matches the solar models, and so the other 2/3 that were missing are oscillating into other flavours. So there must be a mass splitting between electron neutrinos and whatever neutrinos they're oscillating into. Therefore, those neutrinos must have mass.

    So this is a new and significant result, but this is not the first direct piece of evidence for neutrino mass.

    [TMB]
  • I need some more convincing that neutrinos are changing on their way to Earth. A good way to give more credence to this idea would be to place both types of detectors at several points in the solar system and actually determine a rate factor.

    Maybe Dubya could unificate the world to put some of these "new treeno" detectors up in the sky.

  • Finally an article that... (Score:3)

    by Webmoth ( 75878 ) on Tuesday June 19, 2001 @06:14AM (#141228) Homepage
    Finally, a Slashdot article that carries some weight!

    Can you imagine the gravity of this situation?
  • never found out whether anyone has actually done it!

    Using speed differences from a bright neutrino source to estimate their mass was done ages ago -- assuming you accept that Supernova 1987A [google.com] is bright enough. The data showed an upper bound of 20eV, but couldn't rule out masslessness.

  • They mean the rest mass.

    I though neutrinos traveled at the speed of light, is that wrong? Otherwise, the total mass would be m0/sqrt(1-v^2/c^2) which goes to infinity as v->c. What's wrong with this reasoning?
  • The me, whether or not neutrinos travel at (exactly) the speed of light sounds about as important as whether or not they have a rest mass (well, I guess the two are linked anyway since I think you cannot have a particle with no rest mass traveling below the speed of light).

    If it doesn't need to travel at the speed of light, that means you could theoreticaly stop one (which you cannot do with a photon, at least in vaccum). I wonder what a 1 kg "ball" of neutrinos would look like...
  • Not only that, but the different neutrino flavours must have different masses in order to oscillate.

    But what's REALLY exciting, is they'll probably figure out how to use this in the first episode of Star Trek Enterprise as some sort of new kind of weapon or something.

    "Lieutenant, fire the Neutrino Cannon!!!"

    "I am sir, but it doesn't seem to be having any effect on the ship. It's almost as if the neutrinos are just passing right through it."

    Okay, stupid, I know. Sorry.

  • Neutrinos don't ordinarily react with matter, but...obviously they have to interact on occasion to be measured at all. I wonder if there would be any way of significantly artificially enhancing the reaction rate?
  • Well, light is doing pretty well without mass.
  • ... "job security for particle physicists." Every time they answer a weird question, it raises a bunch of new, weirder questions.

    I'm not sure if this is cool or depressing.
  • awhile back /. had an article on the Space (ie. Pioneer 10/11) not moving as fast and as far as expected when they were leaving the galaxy. Could the Neutrino's be the reason?
  • Oscillation is not decay, decay is one way process where one particles changes into two or more other (less massive) particles, oscillation is a reversible process were a beam of particles transforms back and forth from one type to another.

    More technically the oscillations is caused because the faviour eigenstates of neutrinos as not the mass eigenstates.

    I'll decode the technical jargon for you there. When neutrinos are create or destroyed (by the weak interaction) a neutrinos is formed/destroyed as one of three flavours: electron, muon or tau, (named because of the particle it must be created/destroyed with). However when a neutrino travels it does so as one of three types (call them A, B and C) which each has a different mass, these are the mass eigenstates (Eigen is german for same).

    The strange thing is that A, B and C are actually each mixtures of E, mu and tau neutrinos. and because different massed particles (given a fixed ammount of momentum and energy) will travel a slightly different distance in a given time: if you look at a beam of neutrino that started out as one particular flavour, at each distance in the beam you'll see a different mixture of the different flavours.

    All of this is very strange, and probably wouldn't have been believed if neutral K mesons hadn't been observed in great detail doing the same thing.

    Physists write the numbers that describe how much of each mass eigenstate (i.e. the A, Bs and C), make up each flavour of neutrino as a 3 by 3 matrix known as the Maki-Nakagawa-Sakata matrix.

    The down, strange and bottom quarks 'mix' the same way and the here the matrix is known as the Cabbibo-Kobayashi-Maskawa matrix.

    Finally Lepton number conversation does still apply: the total ammount of Leptons minus the ammount of anti-Leptons always stays the same. However the Lepton flavour numbers i.e. Number of electrons and electronic neutrinos - (numbers of anti electrons + electronic anti neutrinos), which was thought to be conversed, is voliated by neutrino oscillation.

  • Nope. The neutrino has a whole bunch of energy, though. That energy "looks like" mass because of E = mc^2. A lot of the mass in a proton or a neutron comes from the energy holding them together, and the neutrino takes some of that away in the reaction you're talking about.

    So in that sense, a neutrino has mass, in that it has energy. But this result is saying a neutrino has rest mass -- if you were to (somehow) stop the neutrino, so that it had no kinetic energy, it would still have mass, just like an electron.

    -Erf C.

  • Electrons are light enough that they travel at the speed of light at relatively low momenta. The experiment [ualberta.ca] I'm working with will do most of its work at 30 MeV, and for all intents and purposes the electrons (which have a mass of 0.5 MeV) are moving at c (well, 0.99986*c). So basically they move at the speed of light in the vast majority of accellerators, with the exception of picture tubes. :)

    -Erf C.
  • Nobody's "carefully avoiding" anything with either the SuperK or SNO results. These experiments were designed to measure neutrino oscillations. There's no way they could have designed these experiments to measure the absolute mass of a neutrino.

    There isn't some great conspiracy to cover up funny results, either. If it was shown that neutrino mass was imaginary, to a high degree of certainty (and having error bars not covering zero doesn't cut it by itself), physicists would go "huh, that's funny", try and measure it again, and if it was shown true just accept it and move on. The rest of quantum mechanics is so weird, I don't think anyone would have that much trouble buying the idea of imaginary mass...

    -Erf C.

  • Ah, yes -- protons with as much energy as a thrown baseball... :)

    These things are really really cool. You may be interested in the ALTA [ualberta.ca] project -- they're putting cosmic ray detectors on the tops of high schools across Alberta, and letting the students there run them. The idea is to have a huge area over which to detect these things; they're pretty rare.

    They're pretty mysterious, too. Nobody's really sure what sort of mechanism would throw off particles with this much energy. And it's not like we can just look up in the direction they came from, either -- the galaxy has a very slight magnetic field (but we don't know it that well), which bends the paths of charged particles (most cosmic rays), so the direction they hit the Earth from isn't the direction they really came from...

    -Erf C.

  • Re:Not just that they have mass... (Score:3)

    by ErfC ( 127418 ) on Tuesday June 19, 2001 @06:49AM (#141258) Homepage
    They don't want to include neutrino mass in the calculations because it really does make things easier. And it works incredibly well -- which is why it was so hard to prove they have any mass at all. Hell, most of the time we assume electrons are massless. Protons, sometimes, too... Actually, you'd be rather surprised how big something's mass can be before we're forced to say "that has mass" in some of these calculations.

    In physics, almost everything is an approximation. :)

    -Erf C.

  • See SNO's homepage for more (Score:5)

    by ErfC ( 127418 ) on Tuesday June 19, 2001 @06:06AM (#141259) Homepage
    The Sudbury Neutrino Observatory [queensu.ca] homepage has their own article [queensu.ca] about the results. The full paper [queensu.ca] that they submitted to Physical Review Letters is also avilable online.

    -Erf C.

  • Re:Not just that they have mass... (Score:5)

    by ErfC ( 127418 ) on Tuesday June 19, 2001 @06:29AM (#141260) Homepage
    Furthermore, it is this transformation that proves that they have mass.

    Not only that, but the different neutrino flavours must have different masses in order to oscillate. The fact that they have mass at all is the most exciting bit, of course, but the fact that they're all different is pretty cool, too.

    -Erf C.

  • Umm, yeah (Score:5)

    by aozilla ( 133143 ) on Tuesday June 19, 2001 @06:17AM (#141267) Homepage
    "On June 5, 1998, the Super-Kamiokande collaboration announced [uci.edu] discovery of evidence for neutrino mass at the Neutrino '98 conference, held in Takayama, Japan."

  • poetic license? (Score:5)

    by aozilla ( 133143 ) on Tuesday June 19, 2001 @06:29AM (#141268) Homepage
    Neutrinos, they are small.
    They have no charge, they have no mass.
    They do not interact at all.
    The Earth is just a silly ball

    to them through which they simply pass
    Like photons through a sheet of glass
    Or dustmaids down a drafty hall.
    They snub the most exquisite gas,
    Insult the stallion in his stall,
    Cold-shoulder steel and sounding brass
    And pass, like tall and painless guillotines,

    through you and me into the grass.
    At night they enter Nepal
    And pierce the lover and his lass

    from underneath the bed.
    You call it wonderful? I call it crass.

    - John Updike
  • This result means neutrinos do have masses but we don't know what they are. We only know what the mass differences are (which determines the probability that they will have oscillated by the time they reach the detector) and that they must be small. What causes these masses to be small (new particles, extra dimensions...) is the next big question...

    ISTR that they were able to put a fairly solid cap on the rest mass of the neutrino based on some observations made during the big 1987 supernova. They detected a neutrino "pulse" (IIRC they only detected 7 neutrinos, but that is a lot for an event taking place that far away) just a few hours after the supernova was first apparent. That let them calculate a lower bound on the ratio of kinetic energy to rest mass for the neutrino and hence (since they can measure the kinetic energy) an upper bound on the rest mass.

  • My god did you butcher that poem! This is the slashdot--haven't you learned to cut and paste?? Take away this guy's poetic license and his karma whoring license both!

    Reader, you are much more likely to enjoy an unaltered transcription of Updike's Cosmic Gall [www.hut.fi]. (Actually, I'm not sure it is unaltered, but it's at least as good as my memory, and it has the indentation. Depressingly, most versions I found on the web are wrongly formatted and have at least one obvious textual mistake.)

  • There was an interesting article [canoe.ca] I found yesterday on the end of the Universe. Turns out the Universe will expand forever. I think a self renewing Universe would have been more interesting. The article also talks about the theory of flatness in space. The proof seems to be in that the Universe is flat-as-in-paper and not curved as thought. It's all got to do with the amount of Dark Matter in the Universe.
  • In modern parlance, "mass" means "rest mass". Photons, which can never be at rest (since the speed of light is c for all observers), have no rest mass.

    More technically, the rest mass of an object can be found through:

    (m c^2)^2 = E^2 - (pc)^2
    with E the energy and p the momentum. For photons, where E=pc, it's clear that m = 0. For a long time we thought the same thing applied to neutrinos, but apparently not...

    If you're jumping up and down saying, "But mass increases with velocity", you're using an outmoded lexicon. The idea of relativistic mass simply isn't useful, and can lead to a lot of misconceptions.

  • You're entitle to your beliefs, of course, and I doubt either of us will be able to convince the other. But you are making a classic mistake made by many others who have problems with Big Bang cosmology, evolution, etc.

    Science is not about knowledge. Science is about a carefully quantified ignorance. Properly done, and properly presented, science is more about what we don't know than what we do.

    Science is not a collection of facts. Science is a process of validation.

    We sacrifice "certainty" on many many things so that we can claim true certainty on what remains. Science is a severe filter with rigorous standards of what can be accepted as "proven". Eveything that is "proven" is done so provisionally, because scientists understand that we cannot ever have the whole truth. All we can be sure of is further approximations to the ultimate truth.

    It sort of irks me when creationists (not necessarily the poster, but others) point to the process of scientific refinement as "evidence" that, say, the Big Bang is "just" a theory. I teach high school physics, and around May 1, we begin modern physics -- relativity and quantum mechanics. There is always a student or two who throw their arms up in frustration: "Why'd we bother learning that other stuff if it isn't true? What good is a theory if it can be overturned later?"

    But very few theories are actually overturned and discarded. What usually happens is that their regime of applicability shrinks. Newtownian theory is "true", for human-scale objects moving not too quickly. Sure, Relativity is true for those objects, too, and more besides: it's a more accurate, more general theory. But for the sorts of objects

  • I believe that this data was taken, and has been used to put an upper limit on neutrino mass. But I'll be darned if I have a reference handy... :(
  • Having just written an AP Physics solution for my students on just this topic, I'm relatively sure. Here's the reasoning:

    The centripetal force, Fc, must be provided by gravity alone, Fg. So

    Fc = Fg

    m v^2/r = GMm / r^2

    v^2 = GM/r

    v proportional to 1/sqrt(r)

    QED

    You might be thinking of Kepler's Third Law, which says that the square of the period is proportional to the cube of the distance. We can get there from here if we recall that
    v = dist/time = 2 pi r / T
    where T is the period. Plugging that in above we'd have
    (2pi r/T)^2 = GM/r

    4pi^2 r^2 / T^2 = GM/r

    T^2 = (4pi^2/(GM)) r^3

    QED

    Ta-da!
  • Tensors are the things mathematicians use to scare their children into behaving... :)

    OK, more technically correct, tensors are like a generalization of vectors. They can be defined through the way they behave under rotations. And you're right: tensors are often represented through matrices.

    In this forumulation, a scalar is a tensor of rank 0, a vector is a tensor of rank 1, and so on. Tensors are real bears to deal with. I went through an undergraduate program in Physics and never encountered them... they only really popped up in a class on General Relativity. Ugh.

  • Re:Proofs? (Score:3)

    by gilroy ( 155262 ) on Tuesday June 19, 2001 @09:16AM (#141280) Homepage Journal
    Blockquoth the poster:
    I wonder how long it will be before we debunk all quantum mechanics?
    Well, first we'd sort of have to start debunking any of quantum mechanics...

    I don't recall ever seeing anything that threw the fundamental basis of QM (OK, really, QED) into doubt. Indeed, quite the opposite -- things like the Aspect experiments, the stuff about Bell's inequality, and even the "teleportation" stuff seem to say, the Universe is actually as weird as QM makes it out to be.

  • Dark matter v. anti matter (Score:4)

    by gilroy ( 155262 ) on Tuesday June 19, 2001 @08:56AM (#141281) Homepage Journal
    Anti-matter: matter with opposite spin, helicity(? I think), and especially, charge. (Other quantum numbers, such as baryon number, are reversed, too.) Anti-matter particles are like mirror images of "normal" matter. As far as we know, no large sources of anti-matter occur in the Universe (although we can make some on Earth and some decay processes -- like the potassium in your banana -- create some).

    "dark" matter: Matter that, for one reason or another, is not luminous. There is growing evidence that we cannot see all the matter in the Universe. The best evidence, IMHO, comes from studies of galaxy rotation, which show that galaxies are not rotating in a so-called "Keplerian" manner. A collection of particles orbiting a central mass should have a velocity that falls off (as 1/sqrt(r)) with distance. Saturn's rings do this, for example, which was how they were proven not to be solid.

    It turns out that galaxies (which are rotating systems) do not obey this relation, as one might expect (since most of the luminous matter is contained near the center). This implies that there is something else "adding" mass as we travel out from the center of a galaxy. We can't see it, so it must be dark.

    There are also cosmological arguments for dark matter. Most especially, there's a paramter (called Omega) which is the ratio of the Universe's density to "critical density". If Omega 1, the Universe will eventually collapse under the gravitational attraction of its elements. Observation of luminous matter indicates that Omega = 0.1. For a long time people had a bias that Omega should be exactly, leading to the claim that 90% of the matter must be "dark". Since that number agrees reasonably well with the one from galaxy rotations, people saw these as mutually supporting each other. (For the record, I find the cosmological evidence quite unconvincing.)

    So, once you believe there is dark matter, you start to wonder what it's made of. In essence there are three classes of candidates:

    1. Regular, but cold, baryonic matter. This could be gas clouds, failed stars, burnt-out embers, etc. After all, things only glow if they're hot enough. Observed stars, etc. ("luminous baryonic matter") seem to have Omega_luminous about 0.01. Limits from Big Bang nucleosynthesis (the formation of elements in the creation of the Universe) seem to limit all "normal" matter to Omega_baryonic = 0.1.
    2. Neutrinos. We can estimate the flux of comsic neutrinos in the sky independently of their mass. Now that they've been shown to have some, we can estimate the total mass of neutrinos zipping around the Universe. According to the article, Omega_neutrinos is about 0.18.
    3. WIMPs: weakly-interacting massive particles. Since they're weakling interacting, they'd be hard to detect. These would be new particles, so far undiscovered, and they would involve that highest of objects, new physics. Candidates include axions, supersymmetric partners, and other more esoteric items.
    No matter what the "dark matter" is, it will likely consist of anti-matter conjugates as well.
  • About 18 percent of all the "dark matter" in the universe may now be made up of neutrinos.
    The value of 18% is an upper limit on the neutrino mass contribution to the total mass of the Universe, not to the dark matter. The lower limit quoted in the paper is 0.1%, so I think it is inaccurate to say that neutrinos make up "about" 18% of the Universe's mass.
  • Since (as was pointed out by another poster) the neutrinos arrive before the main light, this can't be done exactly as you describe.

    However, an upper limit on the neutrino mass could be made based on the spread in arrival times for the neutrinos. If the higher-energy neutrinos arrive before the lower-energy ones, then there might be a mass.

    Of course, all this is complicated by the supernova itself, which might eject higher-energy neutrinos first, but, given that our models of supernovae are correct, then the spread in arrival times put a limit on the electron neutrino mass of about 19 eV or so.

    Terrestrial experiments have put an upper limit on the electron neutrino mass of about 3 eV.

    The best guess for the electron neutrino mass from the SNO results is much, much smaller; probably it is less than .01 eV.

  • Re:Neutrino IMAGINARY rest mass shown a decade ago (Score:5)

    by daknapp ( 156051 ) on Tuesday June 19, 2001 @09:48AM (#141285)
    The initial experiments had an error bar that overlapped zero, but was mostly negative. Later experiments had an error bar that lay entirely below zero. That is, within experimental error, they had measured a negative squared rest mass for the neutrino, implying an imaginary rest mass for the neutrino, which would mean that neutrinos are in fact tachyons.

    As one of the authors of the result to which you refer, I can authoritatively say that Cramer managed to get it almost completely wrong.

    In fact, there was a paper written by Stephenson that showed that the result could not come from tachyonic neutrinos. In that case, we would have seen a completely different signature.

    The most likely physical explanation for the result would have been another unknown particle. Lobashev still believes in that, but I think the evidence has accumulated that there is no significant excess at the endpoint of the tritium spectrum.

    Of course, it is worth pointing out that nobody has ever found any error in the original data, and we spent something like 2 years trying to find problems before we published it in the first place!

  • Autodynamics? Hee hee hee hee. Oh...I needed a good laugh.

    For those who don't know, the autodynamics crowd seems to think that the physicists of the last 100 years are too corrupt and stupid to notice that Special Relativity is completely false. Not only can't the autodynamics crowd perform a simple derivation, but they choose to ignore the thousands of experiments, measurements, and papers written and peer reviewed, in order to come to their loony conclusion. They misrepresent and misunderstand almost all of modern physics, from condensed matter to particle physics to astrophysics, in coming to their unsupportable conclusion.

    But like I said, thanks for the post! I needed a good laugh :-)

  • You have to admit that what we call quantum mechanics today doesn't much resemble the quatum mechanics of the 1930's. But in the 1930's the perception was that physics had been "solved".

    That's not even close to true. The QM you might study as an undergraduate physicist today is IDENTICAL to the QM derived in the 1930s. What HAS changed is not the theory, but the models the theory is applied to. And there were few physicists in the 1930s (nor today!) that would have claimed physics was "solved" as you put it; that sort of misunderstanding is usually based on popular accounts of cutting edge research, misunderstood and misinterpreted for nonscientists by other nonscientists. When trying to transfer knowledge to the nonscientist, things often have to be simplified, not only to explain it to a non-technical crowd, but also to simply fit it into the time allotted (it takes six or seven years of training and study to get to the point where you can even begin to understand the theories of modern physics at the level necessary to do research ... you can't transfer all that detailed knowledge to a non-scientist is a few minutes or hours, so something has to give).

    As for how much of modern theory will be around in 50 years, just think of how much of modern theory existed 50 years ago: almost all of it! It's only the models, not the derivable theory, that has changed dramatically.

  • Wow! I'm amazed! You've given me a good laugh TWICE in one day! First Autodynamics, and now the CCRH!

    CCRH is the same organization that requires its members to take an oath that they won't accept ANY scientific evidence that contradicts a strictly literal interpretation of the Bible. They are REQUIRED to REJECT evidence that DOESN'T fit their preconceived notions of the planet. And you are holding them up as a paragon of scientific thought and developer of scientific theories?

    Wow...I'm really thankful for all the humor you have injected into my day!

  • I did my undergraduate work at the University of Hawai'i. Ended up the sole student in a supervised senior survey in particle physics/cosmology with him, my last semester. Quite good, but required an extreme degree of self-direction. Given the rest of the university, it's amazing that UH has such a decent physics program.

    Where were you doing SKAT work?
  • The Yahoo (and to a lesser degree, the NYT) article was terribly dismissive of the results from the Super Kamiokande experiment, which had reduced the possibilities to two types of neutrino interaction - to-sterile neutrino oscillation, or to-tau/mu neutrinos... and made the sterile option terribly unlikely. This isn't an utterly new, wow-we-never-suspected sort of discovery - just a refinement of the data. More people (physicists) will find it credible, the degree of certainty has massively increased - but this isn't on scale with the confirmed discovery of a new particle. "We've solved a 30-year-old puzzle of the missing neutrinos of the Sun," the article quotes. Well, perhaps, but like the announcement from the Super-K (there was a huge, boastful quote from my dear old particle physics prof John Learned that was all over the papers), this is mostly hype. Still, got to keep yourself stimulated if you want to survive in academia...
  • And answer this... why are the majority of our beer sales shipped to bars in the states?

    They use it to water down the good beer. :)

    ---
  • Since one of the other options was that the sun was in an unstable phase which would end with a nova or other major solar event in the next few thousand years. Clarke based one of his books on it, and it's also mentioned in McGervey's Quantum Mechanics.



  • It's not the first time somebody has claimed that their experiment shows neutrinos to have mass. The last time this happened, there was a big group that claimed that "our experiment shows that neutrinos have mass". The nest article in the paper was written by a single researcher on the same group, and his conclusion was "nah, it doesn't".

    It is interesting to see if there is solid statistics behind this, or if it is just about making sure to hype it up to get more funding. (one shouldn't have to over-hype good research to get good grants, but those who sitting on the money don't care about science).

  • Not just that they have mass... (Score:5)

    by garett_spencley ( 193892 ) on Tuesday June 19, 2001 @06:12AM (#141305) Journal
    but the experiment also proves that electron neutrinos can also transform into other forms of neutrinos.

    One of the biggest astronomical mysteries was why the sun was not producing anywhere near the predicted amount of electron neutrinos. This experiment proves that it is in fact producing them, but that 60% of them transform into other neutrinos before reaching the earth.

    Furthermore, it is this transformation that proves that they have mass.

    From the article:

    But on Monday, representatives of the Sudbury Neutrino Observatory in Canada announced that neutrinos made by nuclear reactions in the sun's core change from one type to another during their 93-million-mile journey to Earth. And only particles with mass can change form.

    --
    Garett

  • Wrong Category (Score:3)

    by sulli ( 195030 ) on Tuesday June 19, 2001 @07:47AM (#141307) Journal
    Jeez, can't Slashdot get the categories right? Clearly this should be in the Sun [slashdot.org] category.
  • How do they know that? I mean how do they know what type of neutrinos are coming out of the sun since their detectors are on the earth?

    What I took from the article was that the sun doesn't produce enough energy to create the other two particles, muon neutrinos and tau neutrinos, only electron neutrinos. It would take the energy of a supernova or equivalent to produce the other two.

  • Thanks. I wasn't saying the articles were too complex, I just thought it would be useful to cut out the "Why does this matter?" and sum it up for the readership.

    As for your complaints about the +5, I agree. The mod system on Slashdot is far from balanced, and always favors the newest posts over later ones. It's worked against me, IMO, far more often then it's worked to my advantage.

  • Summary, for the non-physicists: (Score:5)

    by mblase ( 200735 ) on Tuesday June 19, 2001 @06:17AM (#141312)
    • A thirty-year-old theory about how fusion takes place in the center of our Sun has been validated.
    • About 18 percent of all the "dark matter" in the universe may now be made up of neutrinos.
    • The standard model held by particle physicists, which up until now assumed neutrinos were completely massless, will have to be revised.
  • You have *perfectly* described science, my anonymous friend.

    The big problem then is that if you choose to ignore science and it's many approximations, you lose out on the wonderful things we get out of it...

    Like cars, watches, computers, TVs, radios, plastic bottles, aluminum alloy wheels, titanium golf clubs, etc.

    With each refinement of science we get ever more unexpected observations, and with each new observation we get new opportunities in which to create new and unexpected devices.

    As we refine the neutrino and the elementary particles we can eventually devise gadgets that rely on the characteristics that these neutrinos have.

    Seriously, what would you have us do? Decide "Physics, chemistry, and science is done. No more research, everything is finished."

    Science is the process by which we try to deduce the pattern, the weave, the weft, of creation, and to satisfy your set of beliefs, the underlying structure as given to us by God. Without science we would have no understanding. Science is constrained to be an approximation, to use heretical thoughts, because the Universe and God is unknowable; we can get infinitely close without ever reaching our destination.

    Geek dating! [bunnyhop.com]
  • This is a tricky question.

    It is energy and momentum that are related, not energy and mass. There is a fine line between the two. For instance, when calculating reactions, you must conserve energy (a scalar quantity) and momentum (a vector quantity), not energy and mass.

    Some confusion arises from people quoting the equation
    E=mc^2
    but this is an abridged version, and many people leave out some critical subscripts. In actual fact, it should be
    E^2 = (p^2)(c^2) + (m_0^2)(c^4)
    where p is the momentum of the quanton, and m_0 is its REST mass. Thus, for photons with no rest mass, take the square root of both sides and substitute p = mv, where v=c, the speed of light, and
    E = mc^2

    It is also from this simplified equation that we can substitute the energy of a wave (E = hc/lambda) and get the deBroglie relationship
    h/lambda = mc = p

    Now, back to the subject at hand, both of you are kind of correct. Light has no rest mass, but light with any amount of energy does have momentum (which can be interpreted as it having mass, but only loosely). If light bends because it is travelling in a straight line through curved space-time, it is only travelling in that straight line because it has momentum, and that momentum is being conserved.
  • I've been reading Slashdot for month's, but I've never posted. Well, today is important enough, and so to you, gentle reader, I say:

    I've been to the SNO! Nyah nyah nyah!! There are no public tours, but I got it!

    Heck, I even got a t-shirt (really!)

    But, to be serious, the whole project is really quite impressive. It's 6800 feet down in the Creighton Mine, which is an active Nickel mine that extends to about 7200 feet (it's something like the 2nd deepest in the world). Being surrounded by so much dense rock means that very little radiation other than Neutrinos reaches the Heavy Water (s/Hydrogen/Deuterium/) tank.

    The ambiant air temperature (outside the air-condition and pressure-sealed lab area) is somewhere aroung 25-30 degrees C (it gets hotter the deeper you dig).

    The Heavy Water (1000 tons) is on loan from various Canadian nuclear power plants. I believe that Canada is the world's biggest producer of Heavy Water (Fact: ~.05% of the water you drink is Heavy!)

    If you're ever in Sudbury, visit Science North, which has some great displays about SNO.
  • Light has no mass. But is has momentum and energy. E=mc^2 doesn't work for light for obvious reasons. If I gave you a photon of some arbitrary energy value, you can't determine its mass with that equation. Neutrinos on the other hand DO have mass (not thanks to the Canadians but the Japanesse 1996 IIRC). Sure they might get most of their mass from relativistic effects, but so what, they have mass. Don't get me wrong, I don't think the experiment above is wasting its time. Why something on the order of 30% of our universe is neutrinos, so I would expect many significant contributions from all of the neutrino experiments in operation. But proving the neutrino has mass isn't a contribution of this experiment. It's probably just the obligitory paper, following up with a "me too". Maybe this would be "News for Nerds" is the title was "Another experiment...." Maybe I should get a hobby.
  • I'm not sure if this is a troll or not. I strongly suspect it is, that said, I'm going to ignore my better judgement.

    Light does not have mass. Light does respond to the curvature of spacetime, as does everything. But this in no way even hints that light has mass. Which is why I'm pretty sure this is a troll. I could almost buy into that someone might mistake radiation pressure and the fact light has momentum as proof light has mass, but not this.

    However, should my estimation be wrong, I have a few suggestions.

    Relativity by Albert Einstein, Wings books ISBN 0-517-029618 (cloth) -025302 (paper)

    Modern Physics by Tipler, Worth Publishers ISBN 0-87901-088-6

    Relativity is actually pretty light on math, short and easy to read. I'd say one could read it easily in an evening. Tipler's on the other hand is my old text book, it's solid in that respect, but not particularly enthralling.

    The gravitational lensing which you describe is mearly the result of light following a straight line on spacetime (which is curved). As such it's totally independant of whether or not light has mass.

  • anti-neutrinos (Score:3)

    by bps300 ( 260675 ) on Tuesday June 19, 2001 @07:35AM (#141342)
    If neutrinos have mass, does this mean that anti-neutrinos have pagan rituals? hmmm...
  • I guess the Italian sounding name should have clued me in.
  • I understood the article, and I'm a filmmaker. If this stuff needs to be made so patronizingly simple, I suppose that "nerd" doesn't imply much beyond someone who likes star trek (but doesn't understand cosmology) and who plays video games (but can't necessarily code them). What is this, USA today?

    I guess I just think it's odd that someone can get a plus 5 for regurgitating completely obvious information, with no take on it at all.

    Now maybe if you'd thrown in some colored bar graphs with neutrino icons, you'd be on your way toward a serious journalistic career in this country...

  • An empirical proof has only traditionally been accepted as valid if it can be replicated. Scientists are a sceptical bunch. They don't want to be told what's so, they want to be told how to prove to themselves that it's so. Otherwise they're just taking it on faith.

    And this neat high/low energy stuff requires such specialised equipment that it's largely a case of doing the experiment, publishing the results and saying "Believe it or not..."

    Are we coming full circle on the whole religion/science thing? I mean, how many of us have personally and quantifiably verified that E=mc^2, let alone the tricky stuff? ;)

    • Neutrinos don't ordinarily react with matter, but...obviously they have to interact on occasion to be measured at all. I wonder if there would be any way of significantly artificially enhancing the reaction rate?

    There must be. I mean, Geordi did it all the time on Next Gen. He could even see "neutrino streams" scattering from the side. And that was years ago! Think what we should be able to do now.

    Uhhh, wait, my beeper's going off. I have to take a pill. Don't go away...

    • This is a test of the Supernova Early Warning System. This is only a test. If there had been an actual supernova within a hundred light years of Earth, you would have been instructed to...
    • Repent your sins.
    • Cram in as many sins as possible (for choice, cramming them into a Natalie Portman lookalike.)
    • Cowboy Neal.

  • Proofs? (Score:3)

    by GusShultz ( 456458 ) on Tuesday June 19, 2001 @07:01AM (#141379)
    Does anyone else get the impression that we keep "proving" our physical observations which are incredibly limited by current technology only to revise as our technology gets better? I wonder how long it will be before we debunk all quantum mechanics?

  • Re:m or m0? (Score:3)

    by Dave Bailey ( 458519 ) on Tuesday June 19, 2001 @07:00AM (#141385) Homepage
    They mean the rest mass. The total energy (rest mass + kinetic energy) is over 1000000 times larger than any rest mass electron neutrinos coming from the sun could have...

  • Re:Summary, for the non-physicists: (Score:4)

    by Dave Bailey ( 458519 ) on Tuesday June 19, 2001 @06:54AM (#141386) Homepage
    A few quick physics for the non-physicists points:
    • The Dark Matter problem gets far more fun than this: This result shows that between 0.1 and 18% of the critical density of the universe (i.e. what is needed so the universe just expands for ever - more than this and it will collapse...) can be neutrinos. What we can see (stars mainly), makes up 10% of this. The big question still is, what is the rest... (see here [harvard.edu] and references contained within for further information.)
    • This result means neutrinos do have masses but we don't know what they are. We only know what the mass differences are (which determines the probability that they will have oscillated by the time they reach the detector) and that they must be small. What causes these masses to be small (new particles, extra dimensions...) is the next big question...
    • If neutrinos have mass, then, according to special relativity, they can't travel at the speed of light. However, if they are very light (which they are) and have a much higher energy than their mass (which they do), they will travel very close to the speed of light.
    Oh yes, maybe Canadians' don't make decent beer but at least they don't try to pass "lager" (weak fizzy pale stuff) off as beer. Give me an Old Peculier any day... ;)

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