3 ms·

From the (captions under photographs) in the article: 'Located 2.1 kilometers underground in the Creighton mine in Ontario, Canada, the Sudbury Neutrino Observa

From the (captions under photographs) in the article: 'Located 2.1 kilometers underground in the Creighton mine in Ontario, Canada, the Sudbury Neutrino Observatory’s detector (left) was filled with “heavy” water, which features deuterium in place of hydrogen atoms. Its findings provided evidence that neutrinos can change, or “oscillate,” between different flavors.' "China’s Jiangmen Underground Neutrino Observatory (JUNO), seen here under construction in 2023, is currently the world’s largest neutrino detector. It began collecting data in August 2025; one of its main goals is to determine the outstanding mystery of how heavy each flavor of neutrino is." The second caption implies that some "flavors" of neutrino may be heavier than other flavors. The first caption says that neutrinos oscillate between different flavors. If the first caption is correct, then wouldn't each flavor of neutrino be just as heavy as the others?

cobbzilla 4mo ago
I also wonder this! Some real physicist tell me what I’m getting wrong here: neutrinos have mass but the magnitude is so infinitesimally small, and the oscillation smaller still, such that you’re bumping up against some fundamental properties of the universe and the oscillation is “borrowing” and “returning” some tiny amount of mass/energy from the vacuum.
- deleted 4mo ago
  [deleted]
- falseprofit 4mo ago
  Not a physicist, but here are a couple Wikipedia excerpts I found: From page “Conservation of mass”: “In general, mass is not conserved. The conservation of mass is a law that holds only in the classical limit.” From page “Neutrino oscillation”: “Neutrino oscillation arises from mixing between the flavor and mass eigenstates of neutrinos. That is, the three neutrino states that interact with the charged leptons in weak interactions are each a different superposition of the three (propagating) neutrino states of definite mass. Neutrinos are produced and detected in weak interactions as flavour eigenstates[a] but propagate as coherent superpositions of mass eigenstates.[23]”
  - cobbzilla 4mo ago
    so it’s changing mass/energy with itself? and the whole thing says constant? I guess that makes sense.
    - falseprofit 4mo ago
      Maybe it isn’t changing mass at all, and what’s changing is just the probability distribution resulting from a hypothetical flavor measurement. If we could measure the mass (collapse to mass eigenstate), I think I understand we would see no oscillation.
Giefo6ah 4mo ago
In 1987 a supernova was observed in the sky. In a great coincidence, just months after being put into operation, a new type of detector meant to study if protons are stable, detected instead the neutrinos coming from the supernova in a way that could be individually timestamped. No other supernova has been visible with the naked eye ever since, or is likely to be seen in our lifetimes. https://sci-hub.st/10.1103/PhysRevLett.58.1494 https://sci-hub.st/10.1103/PhysRevLett.58.1494 The neutrinos arrived 3 hours before the supernova was first seen in the sky. This could mean that neutrinos travel faster than light: that they negative mass. It has not been ruled out yet, but it would take extraordinary evidence for any physicist to admit to a faster-than-light particle. The core of supernovae are predicted to take around 4 seconds to explode, and during that time they release 99% of the energy that was binding the star together as neutrinos. Once this has happened, however, it takes several hours for the explosion to be visible outside. If they had 0 mass, you'd expect the burst of neutrinos to last for about 4 seconds. The detected spread was of around 6 seconds. It was likely that the model for supernovae was missing something. But perhaps neutrinos are slowed down as they interact with other particles on the way here from the supernova. Massless particles always travel at the speed of light, only massive particles can be slowed down. Perhaps neutrinos have mass. In order to test the basic theory of nuclear fusion in stars, the "Homestake experiment" was set up to count neutrinos from the Sun. https://sci-hub.st/10.1126/science.191.4224.264 https://sci-hub.st/10.1126/science.191.4224.264 The experiment consists of a big tank of perchloroethylene. Electron neutrinos (and only electron neutrinos) are expected to collide with the Cl-37 atoms to form Ar-37 in the reverse reaction to that of radioactive beta decay. Then the individual Ar-37 atoms can be separated into a gas and counted. According to the brightness of the Sun, it was expected that around 50 such Ar-37 atoms would be detected every 100 days. Only 17 were observerd, on average. A third of the neutrinos went missing. A new round of experiments was made, culminating in the fantastically sophisticated Super-Kamiokande, which is sentitive to all other "flavours" of neutrinos, and also capable of detecting the direction they are coming from. https://arxiv.org/pdf/hep-ex/9807003 https://arxiv.org/pdf/hep-ex/9807003 It was confirmed that the missing 2/3 of the electron neutrinos expected to come from the Sun had somehow transformed into the other flavours. What's more, muon neutrinos coming from cosmic ray decay in the atmosphere were detected half as frequently in an upwards direction, coming from the other side of the Earth, than in the downwards direction. The conclusion is that neutrinos must change flavour as they move through space. Particle accelerators were built in several sites, pointing towards the Super-Kamiokande across the earth's crust, sending a beam of neutrinos of a known kind to measure this "oscillation". https://arxiv.org/pdf/hep-ex/0606032 https://arxiv.org/pdf/hep-ex/0606032 Since they have mass, the artificial neutrinos are slightly dispersed by their passage through the Earth's crust. Their arrival time forms three different overlapping peaks, corresponding to three different masses. The proportion of each kind changes along the path in a sinusoidal fashion, but the mass peaks remain. The current interpretation is that the mass and the flavour of neutrinos are (almost) "conjugate" properties of the particles, in a similar way to the well-known uncertainty between position and momentum, or between time and frequency in Fourier analysis. As a neutrino moves through space, its mass can be measured more and more accurately from the dispersion in arrival times. The better we know the mass of the particle, the more uncertain we are of its flavour. If because of the great distances the mass is well known, as is the case with the solar neutrinos, then the three flavours are almost completely entangled. On short distances the flavour is well determined but the masses are uncertain.
nxpnsv 4mo ago
They are weirder than you think. They interact with flavor, but these are a superposition of three mass states and it all oscillates. https://en.wikipedia.org/wiki/Neutrino_oscillation https://en.wikipedia.org/wiki/Neutrino_oscillation

cobbzilla 4mo ago

I also wonder this! Some real physicist tell me what I’m getting wrong here: neutrinos have mass but the magnitude is so infinitesimally small, and the oscillation smaller still, such that you’re bumping up against some fundamental properties of the universe and the oscillation is “borrowing” and “returning” some tiny amount of mass/energy from the vacuum.

deleted 4mo ago
[deleted]
falseprofit 4mo ago
Not a physicist, but here are a couple Wikipedia excerpts I found: From page “Conservation of mass”: “In general, mass is not conserved. The conservation of mass is a law that holds only in the classical limit.” From page “Neutrino oscillation”: “Neutrino oscillation arises from mixing between the flavor and mass eigenstates of neutrinos. That is, the three neutrino states that interact with the charged leptons in weak interactions are each a different superposition of the three (propagating) neutrino states of definite mass. Neutrinos are produced and detected in weak interactions as flavour eigenstates[a] but propagate as coherent superpositions of mass eigenstates.[23]”
- cobbzilla 4mo ago
  so it’s changing mass/energy with itself? and the whole thing says constant? I guess that makes sense.
  - falseprofit 4mo ago
    Maybe it isn’t changing mass at all, and what’s changing is just the probability distribution resulting from a hypothetical flavor measurement. If we could measure the mass (collapse to mass eigenstate), I think I understand we would see no oscillation.

Giefo6ah 4mo ago

In 1987 a supernova was observed in the sky. In a great coincidence, just months after being put into operation, a new type of detector meant to study if protons are stable, detected instead the neutrinos coming from the supernova in a way that could be individually timestamped. No other supernova has been visible with the naked eye ever since, or is likely to be seen in our lifetimes. https://sci-hub.st/10.1103/PhysRevLett.58.1494 https://sci-hub.st/10.1103/PhysRevLett.58.1494 The neutrinos arrived 3 hours before the supernova was first seen in the sky. This could mean that neutrinos travel faster than light: that they negative mass. It has not been ruled out yet, but it would take extraordinary evidence for any physicist to admit to a faster-than-light particle. The core of supernovae are predicted to take around 4 seconds to explode, and during that time they release 99% of the energy that was binding the star together as neutrinos. Once this has happened, however, it takes several hours for the explosion to be visible outside. If they had 0 mass, you'd expect the burst of neutrinos to last for about 4 seconds. The detected spread was of around 6 seconds. It was likely that the model for supernovae was missing something. But perhaps neutrinos are slowed down as they interact with other particles on the way here from the supernova. Massless particles always travel at the speed of light, only massive particles can be slowed down. Perhaps neutrinos have mass. In order to test the basic theory of nuclear fusion in stars, the "Homestake experiment" was set up to count neutrinos from the Sun. https://sci-hub.st/10.1126/science.191.4224.264 https://sci-hub.st/10.1126/science.191.4224.264 The experiment consists of a big tank of perchloroethylene. Electron neutrinos (and only electron neutrinos) are expected to collide with the Cl-37 atoms to form Ar-37 in the reverse reaction to that of radioactive beta decay. Then the individual Ar-37 atoms can be separated into a gas and counted. According to the brightness of the Sun, it was expected that around 50 such Ar-37 atoms would be detected every 100 days. Only 17 were observerd, on average. A third of the neutrinos went missing. A new round of experiments was made, culminating in the fantastically sophisticated Super-Kamiokande, which is sentitive to all other "flavours" of neutrinos, and also capable of detecting the direction they are coming from. https://arxiv.org/pdf/hep-ex/9807003 https://arxiv.org/pdf/hep-ex/9807003 It was confirmed that the missing 2/3 of the electron neutrinos expected to come from the Sun had somehow transformed into the other flavours. What's more, muon neutrinos coming from cosmic ray decay in the atmosphere were detected half as frequently in an upwards direction, coming from the other side of the Earth, than in the downwards direction. The conclusion is that neutrinos must change flavour as they move through space. Particle accelerators were built in several sites, pointing towards the Super-Kamiokande across the earth's crust, sending a beam of neutrinos of a known kind to measure this "oscillation". https://arxiv.org/pdf/hep-ex/0606032 https://arxiv.org/pdf/hep-ex/0606032 Since they have mass, the artificial neutrinos are slightly dispersed by their passage through the Earth's crust. Their arrival time forms three different overlapping peaks, corresponding to three different masses. The proportion of each kind changes along the path in a sinusoidal fashion, but the mass peaks remain. The current interpretation is that the mass and the flavour of neutrinos are (almost) "conjugate" properties of the particles, in a similar way to the well-known uncertainty between position and momentum, or between time and frequency in Fourier analysis. As a neutrino moves through space, its mass can be measured more and more accurately from the dispersion in arrival times. The better we know the mass of the particle, the more uncertain we are of its flavour. If because of the great distances the mass is well known, as is the case with the solar neutrinos, then the three flavours are almost completely entangled. On short distances the flavour is well determined but the masses are uncertain.

nxpnsv 4mo ago

They are weirder than you think. They interact with flavor, but these are a superposition of three mass states and it all oscillates. https://en.wikipedia.org/wiki/Neutrino_oscillation https://en.wikipedia.org/wiki/Neutrino_oscillation