Neutrinos have mass. AND they travel at c.
HOW????
Rob
Established Member
Neutrinos have mass. AND they travel at c.
HOW????
Rob
Order of Kilopi
It isn't thought that they do travel at the velocity of light. They can travel at very close to c, however.Originally Posted by robross
I say there is an invisible elf in my backyard. How do you prove that I am wrong?
The Leif Ericson Cruiser
Order of Kilopi
They were thought to travel at c when they were thought to be massless. Now that they're thought to have mass, it's assumed they travel at a little less than c.
Grant Hutchison
Established Member
Itīs that easy!?!
Established Member
... definitely not FTLSo now I find out matter CAN go FTL!
Established Member
See:
http://en.wikipedia.org/wiki/Neutrino#Speed
Definitely NOT faster than light.
Established Member
How could anyone ever have thought that a particle of matter, a sibling to electrons, taus, and muons, could have been massless? Masslessness would have made it something else completely different from matter, something that didn't fit in with electrons and such!
Administrator
In the old days we didn't know whether or not neutrinos were 'matter'. They could have been more analogous to photons that carried a 1/2 spin and lepton number.
Forming opinions as we speak
Administrator
Just so people know, robross ran into one of those quirks with allowed words in titles and did ask for it to be changed, but mods ran into the same issue.So now I find out matter CAN go FTL!
Established Member
If we don't limit ourselves to the vacuum, FTL is possible.
See Cerenkov radiation. Make note it's not true FTL, since c does not decrease as it's defined as 'in vacuo'.
Order of Kilopi
Interesting..
Established Member
Thinking and proving are two different things. It has been very difficult to experimentally pin down the mass of the elusive neutrino experimentally. Until you prove than it has mass, you cannot take it for granted that it does. That's just how science works.
Order of Kilopi
Just adding further, how difficult is it to measure the mass of such a tiny particle (accurately) if its travelling at or very close to "C"? Also how would one measure the position/existence of any object travelling FTL if it was possible?
Established Member
Speed is not the major problem in neutrino investigations. The big problem is the ability of the neutrino to pass through matter -- detectors and even the entire Earth -- with little chance of being detected. Having no electrical charge (in addition to being small and fast) makes them very hard to detect.
Order of Kilopi
yes thanks, i was trying to point out that because they are so small that any form of detection would surely change the precision of the measurement taken of the mass, speed and position, as in the uncertainty principle.
Established Member
"Cosmic Gall,"
by John Updike
From Telephone Poles and Other Poems, Alfred A. Knopf, (1963).Neutrinos they are very small.
They have no charge and have no mass
And do not interact at all.
The earth is just a silly ball
To them, through which they simply pass,
Like dustmaids down a drafty hall
Or photons through a sheet of glass.
They snub the most exquisite gas,
Ignore the most substantial wall,
Cold-shoulder steel and sounding brass,
Insult the stallion in his stall,
And, scorning barriers of class,
Infiltrate you and me! Like tall
And painless guillotines, they fall
Down through our heads into the grass.
At night, they enter at Nepal
And pierce the lover and his lass
From underneath the bedyou call
It wonderful; I call it crass.
Order of Kilopi
Neutrinos are still without putative mass according to the Particle Data Group. Upper limits of putative mass are the bounds from the experiments to date....usually around 0.003 ev. As Wiki says, and was said here years ago, the coincidences during SN1987a at the worldwide detectors, give the velocity as ~ c to about 8 sig figs.
Vulcan Administrator
"light speed" doesn't work, but "c" does.
Everything I need to know I learned through Googling.
Established Member
Why would "light speed" not work?
Established Member
Light 'slows down' when going through 'stuff'.
It can get through glass faster than a diamond. It goes through empty space faster than air. Light speed is a catch-all term for many different things.
C only has 1 value, the speed of light in empty, and flat, space.
Banned
This is the second time in this thread where I need some explanation of comment.. please ?"light speed" doesn't work, but "c" does.
What is this about ? Are you referring to the search function?
Thanks Alainprice... you may have just answered me..
Order of Kilopi
Actually; I believe it was in reference to what words work within thread titles.
I do agree Alainprice's answer does fit as well.
But; maybe it's extremely intelligent board software too.
Established Member
My original *thread* title was written hastily. It was "So now I find out matter CAN travel FTL" when I really had meant "c", not FTL. I was not able to change the thread title after I saved it, I could only change the title of my first *post*. I asked the mods to change the thread title, but they were unable to change "FTL" to "light speed", but they discovered that changing "FTL" to "c" did work.
Why "light speed" is not allowed in a thread title, I have no idea, you'll have to ask the board admins.
Rob
Established Member
But back to the original topic...
So by our current understanding of matter and energy, either neutrinos have mass and travel less than c, or they have no mass and can travel at c.
However, experiments measuring both mass and velocity of neutrinos have determined both that they have mass, and travel at c (within the error margin of the measurement). However, the speed measurement *could* be wrong, and they end up not traveling at c.
But, if they do move at c, and they have mass, this would certainly represent a rule-breaking particle!
Rob
Order of Kilopi
Well, experiments show that they have masses very close to zero, and velocities very close to c: the error margins are small, but accommodate non-zero mass and sub-c velocity.
Theory, meanwhile, requires them to have non-zero mass in order to explain their observed flavour oscillation, and that in turn requires them to have sub-c velocity. So it seems that we probably just need tighter measurements of both mass and velocity, so that we can distinguish between "close to" and "equal to".
Grant Hutchison
Order of Kilopi
My understanding was that we theororize that they have mass because they can change between thier 3 states.
Although; this might be older information, so maybe there are actually mass measurements since I heard it this way. And; I only heard it on PBS (I think it was Nova: ghost particle)
Order of Kilopi
Yes, that's the flavour oscillation I mentioned above.
Grant Hutchison
Established Member
Would be interesting to have both a gravitational wave and neutrino detection for a nearby supernova.
Member
It would, but we'll need to wait a while for the completion of the space interferometer being build by the ESA so that we could directly measure this week gravitational wave
Order of Kilopi
So far, neutrino flavor oscillations have all occurred in matter path/experiments. In these, the Eigenstates of the neutrinos superimpose on the matter Eigenstates, ala MSW matter oscillations, and the massless neutrino can flavor-switch. If the neutrinos are Majorana, and massive, they ought to be able to do that on their own in a vacuum, with no matter path involved. That, as far as I know, has never been seen. Until it is, there is no definitive mass, and the consistency of not violating the Law of Conservation of Lepton Family Number, which also has never been seen, seems to be the consistent guiding principle in interpreting the present results....Majorana mass means you can't tell the difference between a neutrino and an antineutrino in the same family. pete 8 sig figs is pretty good...
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