[helene_t]

Disclaimer: I'm not smoking obnoxious substances, as Ron would say. I might suffer from mild fever halouscinations, though.

For some reason the following thought just struck my mind: Photons are naughty particles as it takes a scale variable (frequency) to describe a photon while other particles merrily have discrete state variables (spin and such). Thinking a little more about I realized that other particles have a whole vector in their phase space (velocity) for which photons only have a direction. That brings a photon back to 2+1=3 coordinates (plus location) just like other particles. But what's the unifying coordinate system that describes the phase of a photon as well as that of another particle? Eureka! It's momentum, of course! Thnk about it: a photon has a three-dimensional momentum, just like any other particle.

So momentum and rest mass are the fundamental state properties, while velocity is derived from those. Quite unlike what I learned at hi school. Does this make sense?

Btw, what about polarization of light? Is that a discrete coordinate like spin? If not, have other particles anologue properties? And what about light traveling through chicken soup instead of vaccum?

Then I thought about the problem with the mass of the neutrino. My first thought was that it's quite obvious that neutrinos do have rest mass since otherwise they would come in different colours just like photons, But that can't be true of course since if it was that easy, CERN wouldn't have spent billions on Euros and Swiss Francs on the issue. And of course. if two neutrinos have different momentum it may not be easy to determine if it comes to difference in speed or difference in ... in what? Suppose you don't believe in the neutrino rest mass, what extra coordinate would you assign to neutrinos, then? Something like frequency?

Another Eureka moment: It follows from de Broglier's equation that if two neutrinos have different momentum, then they have different wavelengths as well. This is true whether they have rest mass or not.

This finallybrings me to this idea: Relativity requires particle-wave duality. Since without particle-wave duality their would be no unifying frasmework for describing positive-rest-mass and zero-rest-mass particles in the same way!

[DrTodd13]

Is there any debate now that neutrinos have rest mass? I thought without rest mass it would be impossible for neutrino oscillation and that with rest mass neutrinos must oscillate and that since oscillation has been observed that neutrinos must have rest mass.

On a side note, do neutrinos emitted near the core or near the edge have galactic escape velocities?

[hotShot]

Photons have spin!

[Gerben42]

Quote

So momentum and rest mass are the fundamental state properties, while velocity is derived from those. Quite unlike what I learned at hi school. Does this make sense?

On the first day of my university physics lectures the professor visually painted a huge cross through everything learned in highschool. You're right. Velocity is just a derived variable.

Physics is all about conservation laws. Momentum conservation, charge conservation, spin conservation, etc.

Quote

Btw, what about polarization of light? Is that a discrete coordinate like spin? If not, have other particles anologue properties? And what about light traveling through chicken soup instead of vacuum?

Polarization is not discrete but has to do with the spin. I'll leave it up to experts to explain it, though... And yes, other particles have polarization also.

Quote

On a side note, do neutrinos emitted near the core or near the edge have galactic escape velocities?

Yes. Neutrinos travel at highly relativistic speeds and will travel outside of the galaxy. In fact they can be used to detect supernovae since in this event the star is optically thin for the neutrinos and optically thick for photons, meaning that we detect the neutrinos from the event about 1 hour before the photons.

Quote

Photons have spin!

Photons are spin-1 particles, right.

[mike777]

Photons, those are the thingys that act as a wave and a particle depending on who is watching them? That 2 hole experiment whatever? One photon goes through 2 spaced holes at exactly the same time....2 different places at exactly the same time.

[helene_t]

DrTodd13, on Feb 16 2007, 02:30 AM, said:

Is there any debate now that neutrinos have rest mass? I thought without rest mass it would be impossible for neutrino oscillation and that with rest mass neutrinos must oscillate and that since oscillation has been observed that neutrinos must have rest mass.

Correct, the issue is not controversial anymore. I was refering to a debate that took place until a couple of years ago. I should have clarrified that.

[bid_em_up]

You lost me at "Disclaimer"

[Al_U_Card]

Perhaps dark energy and dark matter are of greater import. These issues are comparable with the famour "ether" or "caloric" questions back in the Newtonian days.

[DrTodd13]

With regard to observing neutrinos before photons from supernovae, this certainly has to be the case for intragalactic supernovae, not intergalactic ones. Across inter-galactic distances wouldn't you expect photons to catch up to slower than light speed neutrinos?

The reason I ask about escape velocity is that at one point they thought neutrinos might be a substantial fraction of dark matter but dark matter seems to be gravitationally bound to galaxies and if neutrinos have escape velocity you would expect a gradient of neutrino flux at the core of a galaxy extending outward with density inversely proportional to the cube of the distance. If neutrinos didn't have escape velocity you would expect a sharp boundary at the "edge" of the galaxy.

[Gerben42]

Quote

With regard to observing neutrinos before photons from supernovae, this certainly has to be the case for intragalactic supernovae, not intergalactic ones. Across inter-galactic distances wouldn't you expect photons to catch up to slower than light speed neutrinos?

Sure, but we would not detect neutrinos from too far away supernovae since there would be too few of them. Otherwise this would be a GREAT way to measure their velocity which we cannot possibly distinguish from light speed...

Let's see, the best detector would get 20000 neutrinos for a supernova (see here: http://cupp.oulu.fi/...ino/nd-sn.html) near the galactic center. This reduces with the square of the distance, burying a supernova in the nearest big galaxy, M31, in random noise...

The escape velocity from the Milky Way is about 0.2% of light speed, btw.
Galaxies are small enough not to bother neutrinos and photons a lot, but big enough to create gravitational lenses. Galaxy clusters do even better, of course.

[luke warm]

bid_em_up, on Feb 16 2007, 11:55 AM, said:

You lost me at "Disclaimer"

hahahahah... me too