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The Nobel Prize in Physics 2015

Slings and Arrows

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Slings and Arrows
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The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Physics for 2015 to

Takaaki Kajita
Super-Kamiokande Collaboration
University of Tokyo, Kashiwa, Japan

and

Arthur B. McDonald
Sudbury Neutrino Observatory Collaboration
Queen’s University, Kingston, Canada

“for the discovery of neutrino oscillations, which shows that neutrinos have mass”

The Nobel Prize in Physics 2015 recognises Takaaki Kajita in Japan and Arthur B. McDonald in Canada, for their key contributions to the experiments which demonstrated that neutrinos change identities. This metamorphosis requires that neutrinos have mass. The discovery has changed our understanding of the innermost workings of matter and can prove crucial to our view of the universe...

The discovery led to the far-reaching conclusion that neutrinos, which for a long time were considered massless, must have some mass, however small.

http://www.nobelprize.org/nobel_prizes/physics/laureates/2015/press.html
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"At this moment in this room there are more than a billion neutrinos, which travel almost at the speed of light.

"These elementary particles are the second most abundant in the universe, next to the photons, which are the particles of light.

"There are three kinds of neutrinos. Electron-neutrinos, mu-neutrinos and tau-neutrinos. This year’s prize is awarded to the experimental discovery that neutrinos can change identity. For example, a mu-neutrino can become a tau-neutrino and vice versa. They oscillate."

Scientific American (October 6, 2015)
http://www.scientificamerican.com/podcast/episode/2015-nobel-prize-in-physics/
 
Slings and Arrows said:
"At this moment in this room there are more than a billion neutrinos, which travel almost at the speed of light.

"These elementary particles are the second most abundant in the universe, next to the photons, which are the particles of light.

"There are three kinds of neutrinos. Electron-neutrinos, mu-neutrinos and tau-neutrinos. This year’s prize is awarded to the experimental discovery that neutrinos can change identity. For example, a mu-neutrino can become a tau-neutrino and vice versa. They oscillate."

Scientific American (October 6, 2015)
http://www.scientificamerican.com/podcast/episode/2015-nobel-prize-in-physics/
Click to expand...
There seem to be different estimates, I just read this

About 65 billion neutrinos, produced by nuclear fusion in the Sun, pass through every square centimetre of area on Earth, every second (you could try and calculate that yourself), without doing anything.

Read more at: http://phys.org/news/2015-10-neutrino-great-cosmic-mysteries-nobel.html#jCp

So the number produced every second by the sun is 65 billion times the surface area in centimetres of a sphere of radius 150 milllion kilometres.
 
DuvalHMFIC said:
Hasn't anyone told these immigrating neutrinos that we don't want them here?
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Yes, but they only find out when they arrive. They're actually pretty polite about it, and leave right away without making a fuss.
 
I was listening to a piece the other day that said while travelling through (near?) matter helps the oscillations along (all the neutrinos produced in the core of the sun have been able to oscillate to their final distribution of 1:1:1), these oscillations can happen as it travels through free space as well. But the oscillation depends on movement, a neutrino sitting still wouldn't spontaneously change.

As these are massive objects, there must be some inertial frame where one is at rest. How is it the neutrino in that frame would not be able to change but it can in our frame?

Did I misunderstand something, or were they unclear?
 
BowlOfRed said:
As these are massive objects, there must be some inertial frame where one is at rest. How is it the neutrino in that frame would not be able to change but it can in our frame?

Did I misunderstand something, or were they unclear?
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You've hit on almost exactly the interesting thing about neutrino oscillations. Yes, there are three neutrino mass states---sometimes labeled nu_1, nu_2, and nu_3. All of your intuition about rest frames and relativity and so on is correct if you're thinking about those.

But the three "flavors" are not mass states at all. The "electron neutrino" is a superposition of masses 1,2, and 3, characterized by a particular set of amplitudes and phases. The "muon neutrino" is a superposition with a different set of phases and amplitudes. There is no "rest frame" for the electron neutrino---if you look at it from the rest frame of a nu_1, the phases of the 2 and 3 are getting out of phase because they're moving, if you look at it from the rest frame of the 2 then the 1 and 3 are getting out of phase, etc..

"Oscillations" can only happen if it's possible for originally-electron-neutrino-like phase superposition to look like muon-neutrino phase superposition later, and that only happens when different mass states are mixed together.
 
Samson said:
There seem to be different estimates, I just read this

About 65 billion neutrinos, produced by nuclear fusion in the Sun, pass through every square centimetre of area on Earth, every second (you could try and calculate that yourself), without doing anything.

Read more at: http://phys.org/news/2015-10-neutrino-great-cosmic-mysteries-nobel.html#jCp

So the number produced every second by the sun is 65 billion times the surface area in centimetres of a sphere of radius 150 milllion kilometres.
Click to expand...

If you factor in the interaction cross section with the human body, the average human will absorb about one neutrino over his/her lifetime (maybe two if you're a bit more on the round side...)
 
ben m said:
You've hit on almost exactly the interesting thing about neutrino oscillations. Yes, there are three neutrino mass states---sometimes labeled nu_1, nu_2, and nu_3. All of your intuition about rest frames and relativity and so on is correct if you're thinking about those.

But the three "flavors" are not mass states at all. The "electron neutrino" is a superposition of masses 1,2, and 3, characterized by a particular set of amplitudes and phases. The "muon neutrino" is a superposition with a different set of phases and amplitudes. There is no "rest frame" for the electron neutrino---if you look at it from the rest frame of a nu_1, the phases of the 2 and 3 are getting out of phase because they're moving, if you look at it from the rest frame of the 2 then the 1 and 3 are getting out of phase, etc..

"Oscillations" can only happen if it's possible for originally-electron-neutrino-like phase superposition to look like muon-neutrino phase superposition later, and that only happens when different mass states are mixed together.
Click to expand...

I attended a lecture on this the other day. I'm still trying to wrap my head around it all, but if I understood it correctly, the lecturer stated that it is not known what the mass is of the neutrinos, but they do know the difference in masses. Therefore, it is not impossible that one of the states could be zero mass. A question I had, that I should have asked, was whether the period of this oscillation (muon, tau, electron) is known, and is this a constant? Also, they refer to the speed as a considerable fraction of the speed of light. Is this speed known with any precision?
 
The neutrino might finally be a real world example of something with a mass that has a limit approaching zero...whatever the hell that means.
 
Olowkow said:
I attended a lecture on this the other day. I'm still trying to wrap my head around it all, but if I understood it correctly, the lecturer stated that it is not known what the mass is of the neutrinos, but they do know the difference in masses. Therefore, it is not impossible that one of the states could be zero mass. A question I had, that I should have asked, was whether the period of this oscillation (muon, tau, electron) is known, and is this a constant? Also, they refer to the speed as a considerable fraction of the speed of light. Is this speed known with any precision?
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Neutrinos questioned

A summary:

"Amongst the fathers of quantum mechanics, Bohr, Heisenberg and Pauli each proposed radical explanations for this observation - Bohr, that energy was not exactly conserved; Heisenberg, that space-time was not continuous - but it was Pauli's proposal that won the day."

So the later discovery of this particle seems to me rather a consequence that Pauli once had "won the day" than a consequence of its existence.​

Cheers
Wolfgang
 
...what boils down to "I don't know what you're talking about, but it's controversial!".

Wolfgang, this thread is about why Kajita and McDonald -who belong to a profession you clearly don't- got the Nobel Prize, not about why you will never be allowed even to cater that ceremony. Besides, it is supposed to contain scientific explanations and not story telling, which is what you basically do.
 
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Samson said:
There seem to be different estimates, I just read this

About 65 billion neutrinos, produced by nuclear fusion in the Sun, pass through every square centimetre of area on Earth, every second (you could try and calculate that yourself), without doing anything.
Click to expand...

That's not necessarily a contradictory fact to the claim that there are about a billion neutrinos in the room. One figure is talking about how many pass through a surface at any time, the other is talking about how many occupy a volume. Those 65 billion passing in to a room through every square centimeter are moving at the speed of light about one foot per nanosecond. So for a ten foot wide room only about 700 of those will be in the room with you at any one time. That would be for every square centimeter of the room facing the sun since we're talking solar neutrinos here. In a million square centimeter room (lecture hall sized) you've got almost a billion.
 
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wogoga said:
Neutrinos questioned

A summary:

"Amongst the fathers of quantum mechanics, Bohr, Heisenberg and Pauli each proposed radical explanations for this observation - Bohr, that energy was not exactly conserved; Heisenberg, that space-time was not continuous - but it was Pauli's proposal that won the day."

So the later discovery of this particle seems to me rather a consequence that Pauli once had "won the day" than a consequence of its existence.​

Cheers
Wolfgang
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I'm pretty sure that a lot of ambitious grad students seeking a Nobel would have been unimpeded by Pauli's having "won the day", had they felt even for an instant that conservation of energy was wrong.

I'm not a physicist, but I suppose the best response is that in the end the sciences generally go with the explanation that is best supported by evidence and experiment, and not with the hypothesis promoted by the loudest or most popular or intimidating proponent. There could certainly come a time when it is shown that our understanding of thermodynamics or space-time is flawed, but in the meantime absent evidence to the contrary, current theories seem to satisfy Occam's razor. Ad hoc exceptions just add needless complexity.
 
Olowkow said:
A question I had, that I should have asked, was whether the period of this oscillation (muon, tau, electron) is known, and is this a constant?
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It takes a bit of approximation to be able to say this, but yes there are three natural (constant) frequencies in the system---basically there are three mass states with three de Broglie frequencies, so (in the neutrino rest frame) there are three simple frequency differences which govern the oscillations. When you're in the lab frame and looking at high energy neutrinos, oscillations appear as a function of L/E (distance per energy) which works out to be the neutrino's proper time.

Also, they refer to the speed as a considerable fraction of the speed of light. Is this speed known with any precision?
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The difference between the neutrino speed and the speed of light is (so far) immeasurably small and likely to remain so, even if we get lucky and detect supernova neutrinos again. For a good mental picture of the neutrino mass spectrum, imagine they have something like 0.05, 0.005, and 0.001 eV. Work out the speed needed to give a neutrino 40 MeV of kinetic energy even for the heaviest of those masses.
 
wogoga said:
So the later discovery of this particle seems to me rather a consequence that Pauli once had "won the day" than a consequence of its existence.
Click to expand...

What's the mechanism for that? Is it like in "The Secret" when you wish for something hard enough the Universe rearranges itself to give it to you?

(You've never seen a neutrino experiment, have you, Wogoga?)
 
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