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Neutrino Oscillations Confirmed
mfg writes "The Sudbury Neutrino Observatory has found evidence that neutrinos can change type between the Sun
and Earth. See the
BBC news story for more details."
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In the "standard model" of particle physics, there are sixteen "elementary" particles, and their anti-particles. Three of these particles are the neutrinos, which come in three different flavors. It's long been known that their masses must be very small, and it's been thought that neutrinos might have zero mass, like the photon. However, neutrino oscillation implies that there is a mass *difference* between neutrino flavors, and a mass difference means that they can't all be zero. Thus this means that neutrinos have mass, and that's a very important theoretical issue!
Fermlab is in the process of building an X million dollar project to send neutrinos 735km to minnesota to see if they oscilatte during the trip... Kinda pointless now. The project is called NuMI, its kinda interesting, they were going to send neutrinos through the ground to an old mine- check out the NuMI web site.
For the people who have no idea what neutrinos oscillating is about - try here. It gives a good overview, made so someone like me could even understand it.
As an ex-member of SNO (my name (N. Tagg) is on the papers) as well as a current member of MINOS (the experiment you're reffering to at Fermilab) I can say that this is simply not true; the experiments are complimentary, not exclusionary.
In fact, there is a large quantity of work going on in this field. Current experiments include KamLAND, Borexino, Opera, NuMI-MINOS, Super-Kamiokande (when they finish their repairs in a year or so), K2K (KEK to Super-K), MiniBOONE the new JHF facility, plus a bunch more I'm forgettting.
There are several reasons for all this activity. First, there are at least two different types of oscillaitions. (The naive and over-simplified theory is that there is nu-electron to nu-mu oscillation, and nu-mu to nu-tau oscillation, the first of which is seen by SNO, the second of which is seen by atmosphereic neutrinos and by the beam experiments). There may be a third mode, which implies a new variety of neutrino (nicknamed 'sterile' for various reasons).
In addition, we're looking to prove that our theory about the oscillations is correct; that they really oscillate in the way we think they do (i.e. change back and forth between flavours on a given time scale that is dependent on energy and suchlike). We want to know the exact parameters in the theory, so the theorists have some hard numbers to much on to make better overarching theories. And, there's always the possibility that something entirely new will crop up in these studies.
(A note on that last: modern neutrino detectors were born out of eariler attempts to build proton decay experiments... but the neutrinos kept getting in the way! On the 'don't beat 'em, join 'em' approach, people started looking at the neutrinos themselves with more interest.)
--Nathaniel, prowling his favourite topic.
No. This is probably the single most common misconception about physical science; but a misconception it is.
A physical "law" is not a "theory that has been proven". The word "law", in physical science, is used to describe relations between independently observable properties of systems that have been detected through experimentation or observation. Thus we have Newton's Law of Gravitation, which relates an external observable property of an object (the force upon it) to intrinsic but observable properties of that object (its mass, the masses of other objects, and the distances between them); this is a physical law even though, strictly speaking, it isn't true (as we now know that it provides only an approximation, which holds reasonably well over certain domains of length and mass scale).
The fact is that theories are never proven to be true in science. A theory can be falsified, but can never be proven true. This is because no matter how much evidence you have collected in favor of a theory, it is always imaginable that tomorrow, someone will observe some phenomenon that contradicts it. We have tons and tons of evidence supporting conservation of momemtum in systems isolated from external forces; but no matter how much evidence we have, it is logically impossible for me to guarantee that tomorrow someone won't do a robust experiment that shows violation of conservation of momentum. I'll bet all the money in the world that won't happen, I'm confident it won't happen; but I cannot logically assert with 100% confidence that it cannot happen. You can never say with logical certainty what will happen in an experiment until you do the experiment; and because of this, scientific theories are not proven true. Instead of being "proven to be true," scientific theories are "supported by the weight of accumulated evidence"; it is the degree to which that accumulates evidence is convincing that determines the statue of the theory it supports.