Invisible Neutrino: Newsletter Challenge (June 2016)

Good point. Publish or perish, as they say.

On the other hand, the dynamics of a star going nova may not generate the neutrinos at the same time as the shock wave. Does anyone know the timing of the shock wave vs. when the neutrinos are generated? When does the shock wave actually hit the core of the sun and when does Earth actually get destroyed?

The accepted theory is that the flood-flux of Neutrinos is the agent that rips the star apart. That implies that as the current of Neutrinos is streaming through the shell of the star, the *tiny* rate of collisions between the neutrinos and the normal matter tends to sweep the mass out and away, like a garden hose rinsing hard clay off the sidewalk. It takes a lot of flow to make the dirt move a little at a time. But with the core implosion releasing energy on the order of 10^51 ergs, even if only one in a billion-billion Neutrinos strikes a nucleon, there is power to spare!

Does the flood of neutrinos also affect the earth?

Only if the dam is out, and it is high tide in neutrino world. In bizarre old world, not so much.

This neutrino cascade is probably the result of stellar fusion using up all the hydrogen it can get, then trying to heat up more and switch over to other fuels, then the pressure inside the star goes postal.

There is a 99.99% chance our sun will not kill planet Earth that way, but some other star could. Our sun will burn out of hydrogen before all the alternate reaction pathways kick in that make too much of the heavies. At some point the ablation of outer gases overcomes the gravitational bottle, and Sol will expand as a red giant.

When our star expands to a red giant, the orbit of the Earth will be inside this red giant. Sol will be a lot cooler than it is now but the Earth will not be very habitable at all inside this red star.

diameter of earth-orbit to the sun is more than 100 times the diameter of the sun, the volume of the red giant is more than a million time the volume of the sun and the density of the red giant is a millionst of the dense of the sun.

is this denser than earths atmosphere?

I'm not sure if Sol's density, when it envelops the Earth, will be denser than today's atmosphere. However since the surface temperature of a red giant is typically 5000 K I'm sure it will be denser than the Earth's atmosphere at the time it envelops the Earth.

this is the mean-value, density in the center should be much greater than in peripheral.

The obvious answer would be that the neutrino either loses a lot of energy on its way throught the sun - or indeed that it is absorbed in transit
(and I'd really like to see the physics of this hypothetical detector)

BTW, if this were instead the kinetic energy of a neutron (rest mass about 1GeV), the neutron would have had about 98% probability of decaying during the hour it took to reach the earth.

Notes:
. The oscillation hypothesis would be valid if the question limited the detector to electron neutrinos, but the question is specific "all neutrinos of that energy"

. Water baths are used to detect neutrinos via the interaction with the nuclei. Assuming that the dominant interaction is with oxygen and for simplicity that the trajectory sees only the average density of the sun, we find that the neutrino leaving the centre of the sun sees the equivalent of
. sun-density/oxygen-mass-proportion-in-water*mass-concentration-in-sun*path-length, or
. 0.25*1/8*0.001(?)*700,000 = 20km water-equivalent.
That's 500x the absorption length of a large subterranean neutron detector, and there's plenty of other stuff that can interact with neutrinos (I've failed to find cross-section numbers to allow estimation of the proportion of neutrons that interact).
. The energy required to release a charged lepton dependson the interaction, and similarly I've failed to find numbers. But the question was specific, so even a signle low-end 0.1-MeV interaction could take the neutrino outside the 100% range.

There is no doubt therefore that this could explain the failure to detect the single neutrino described in the question. But we would need much better information than I've been able to access to determine what proportion of neutrinos would escape detection. The success of much smaller water-bath detectors and the large path length suggests it might be the majority. (Maybe even the asking of the question in this form would support such a guess)

BTW, I rated Canary's answer as good. This is my attempt at explanation based on the alternative interpretation that "path" implies the neutron actually goes through the earth.

Sorry to keep answering myself, but I found "accepted" numbers for oxygen concentration in the sun as being between 0.75% and 1% by mass, except for the core (unstated). As oxygen constututes about 8/9 of the mass of water, the interaction with oxygen is equivalent to 9/8*0.0075*average-s.g.-through-path*path-length. The non-uniform density means the 0.25 average sg is a gross underestimate, so we can use 1500-km of water as a lower bound for the effective interaction length. That certainly increases the probability of interactions with oxygen (i.e. that involve significant energy loss). BTW, the threshold for interaction with water is about 5MeV,so the neutrinos that are detected by water are the (0.1%) 8B neutrinos with energy up to about 15-MeV and the very rare (0.01%) hep neutrinos. Unfortunately I have still not managed to find information that is suitable to estimate the interaction probability in the 40m deep Super-Kamiode water-based detector; however, the mere fact that energy loss is not mentioned in any of the general-interest journals suggests that the proportionate effect is small; however, the challenge wording refers to a single event, so there is no need for it to be a frequent occurrence.
(I'm assumming that the challenger is not imagining a super-narrowband 14MeV sensor that would be disabled by the energy loss due to the sun's gravity)

14 MeV neutron corresponds to what temperature if that is the K.E. only? Would that be considered a "cold" neutron?

No, definitely not cold! https://en.wikipedia.org/wiki/Neutron_temperature

As you will see, the numbers needed for the expression of particle energies as temperature are often quite absurd.

the neutrino didn't pass the detector

Anti-social neutrino? I mean, what is the neutrino's motivation?

Capable of Detecting != Certainty of Detecting.

In order to detect the Neutrino, it *MUST* interact (collide) with another particle. Neutrinos are very good at avoiding any interaction with anything made of normal matter placed in their path.

So the short answer is is simply missed every single particle in its path and passed through the Earth completely undetected.

Longer answer: The cross section of Neutrinos is vanishingly small, the mass of particles along the path of the Neutrino present a cross section to the Neutrino that can be envisioned as a a gossamer web. The probability of a collision is proportional to the product of those areas, the product is woefully insufficient to expect the likelihood a collision.

That's not to say the detector didn't intercept another Neutrino that was travelling parallel to the first, but unless there were a billion or more Neutrinos in the bunch, chances are that all missed the screen. It's a little like using a steel rebar cage to keep gnats out of the house.

Have I (or the sun, for that matter) ever been dense?

Even the slightest interaction with matter would be sufficient to change the path of the neutrino, and all that is needed is 90-micro-radians. The ~1-Mm oscillation length of a neutrino is significantly reduced in the solar environment, meaning that the majority of neutrinos would show significant interaction with the solar environment.

Thus, although the neutrino was originally headed to pass through the Earth, it will most likely have been diverted by the time it reaches the chromosphere.

We are good at overanalyzing things.

The problem states that a 14MeV neutrino is emitted from a fusion reaction in the core of the sun and travels on a path through earth.

The question also says that the detector is perfect for detecting neutrinos at that energy. If that means specifically 14 MeV, then the simplest answer is that the neutrino wasn't still at 14MeV when it passed through the earth.

"An ideal neutrino detector capable of detecting every neutrino of that energy passing through Earth fails to detect it."

It says the detector is capable of detecting every neutrino of that energy, not that it absolutely does....so the neutrino passed though undetected....

Good point.

IDNHAC on anything further to add.

"Capable of detecting every neutrino of that energy" must mean that it does "detect every such neutrino" when it is fully active. According to this line of reasoning the "simplest and most elegant" answer is that the detector happened to be switched off at the time this particular neutrino passed through the Earth. Obvious, and to my mind so facile as to be normally not worth mentioning (though given the other answers in the thread I'm surprised I didn't spot it already). (BTW, the CR4 moderators can't be perfect, but they don't often let such things pass for "Challenges", though you wouldn't believe it reading the threads.) In any case, even if the detector is switched off 99% of the time, more particles will miss the Earth than would pass through the detector when it is switched off, so (as you wrote) the "simplest and most elegant answer" would in isolation only account for a small proportion fo the cases.

On the subject of the "only allowable answer relating to the energy", I think the wording is capable of a different interpretation. It only says "travels on a path directly through Earth". The A1 in England is a road that runs from London to Edinburgh. If I travel on the A1 it does not mean I follow it as far as Edinburgh. Similarly, the neutrino travelling allong a path that goes through the Earth does not mean it stays on that path. So (avoiding facile answers) we do have the choice: does the neutrino miss the Earth or does the energy reduce sufficiently as to be undetected. The vast majority of particles whose energy is reduced at all will miss the Earth, so I take this to be the best answer (though it took me a stupidly long time to realise).

On the other hand, having some experience of CR4 challenges and having become rather cynical, "The Answer" I am expecting is that the neutrino will have oscillated to a different flavour, which changes its energy; this answer would actually be incorrect, because the things that change during vacuum oscillations are the velocity and the rest mass, but not the total energy.

Does a leaf fall in the woods if there is no observer present?

I don't mind the legal system or several other systems being anthropocentric. However "the woods" almost by definition do not care (and often prefer) if human beings are around to watch the woods in action.

You are not as important as you think.

The woods do not care if a leaf gets transferred into "the getaway car", the legal system does care a great deal about such things, especially if the tree is not native to the area in logical question, to the point that finding the tree = finding the murder scene, etc.

I am not important at all, except to God, me, my dog, my employer, and my wife, mostly in that order on any given day. I know I am important to God (and so are you the same amount), since He took up a cross while being beaten, and carried it up a hill, and let Roman soldiers nail him to it, just for me (and you). He also came back alive after three days with power.

Don't give up on me (or you) doing something great today, it can happen.

And, if a man speaks in the woods where no woman can hear him: is he still wrong?

Only he can miss being heard is if he does not cuss. Wife will always hear.

The answer to that question is so simple,I will let my chauffeur answer it.

The flavor of a neutrino does not effect the neutrino's energy or mass.

"An ideal neutrino detector capable of detecting every neutrino of that energy passing through Earth fails to detect it."

Please be consistent with the given conditions.

It's probably because this ideal detector requires a special AAA battery, and it ran down to below the threshold volts, waiting for the errant neutrino to arrive. The detector is still functional, but the battery let them down.

Each neutrino flavor has a different mass. As the flavor of a neutrino changes, the neutrino's mass changes.

See this article for more on neutrino flavors and masses: http://www.scientificamerican.com/article/nova-experiment-neutrino-mass-mystery/

The total energy is the sum of the rest mass and the kinetic energy. Total energy is independent of the flavour of the neutrino. This certainly invalidates neutrino flavour as an answer to the challenge; I also believe that this is what redfred's comment meant, although I can understand that the comment coud be subject to misinterpretation.

Ok,here's my chauffeur's take on the question,as worded.

Since the neutrino passes "directly through the Earth",it was not detected.

In order for it to be detected,it had to collide with the sensor (H20,etc.) of the detector and would not complete the journey through the Earth.

Your chauffeur should read the semi-technical* descriptions of neutrino detectors more carefully, as he would find that neutrino sensors only extract a proportion of the neutrino's energy. (Insofar as a neutrino has identity it would indeed continue its passage through the Earth.)
*Or, if he is a graduate in nuclear physics doing chauffeuring while wating for postdoctoral funding, he should make a critical reading of the subject as a whole during his "sitting around" time. In that case CR4 denizens would definitely be interested to see his full sumary for the layman.

P.S. I asked my chauffeur, and he said I should buy organic chicken breasts, hammer them flat with a rolling pin so they did not present too deep a target for solar neutrinos, season and and fry in olive oil for 2-1/2 minutes on each side (or until the inside was no longer pink).

My chauffeur,hereafter referred to as "Justin"",replies that the keyword is "directly",meaning without deflection or interruption.A sensor would deflect or interrupt the path of the neutrino,albeit in a small manner.

Semantics, the bane of CR4!

But if you are going to 'do' semantics:

a) Your chauffeur's interpretation would make the challenge question self-contradictory, as it also states that ALL suitable particles are detected.
b) Paths do not necessarily have zero dimensions; as a rambler, I can perfectly well pass other people or stop for a chat and then continue on my way without deviating from the path.

Changing topic slightly:
Since about the middle of c18, individual chauffeurs (and chaffeuses) have generally been referrenced as "James", no matter how they are addressed in person. The name by which they are directly addressed is accepted only when the use of "James" would result in unacceptable ambiguity.
James was concerned that the wrong neutrino flavour would spoil the chicken.
The confidentiality agreement that all our staff sign means that James would never appear publicly in his professional capacity.
It would appear that Mr. Thyme has also realised that his appearance was "out of order", because when I tried to follow your U-tube link I got an apology that the video was not available.

Justin is a very formal gentleman and insists on NOT being called "James" because it puts him in a generic class of ordinary chauffeurs.

He made several appearances on the tv series"The Beverly Hillbillies" in 1964,and is reliving the past,I suppose.

He is getting quite old now,and can't do as much as he once could,so I bought a log splitter to give his back some relief,arthritis and all, you know.

He was offended at first,but finally settled into using it.

However he still insists on felling the trees himself with a double bit axe,just to "keep in shape" as he says.

He carries a set of scissors in his pocket to catch any errant twigs on the topiaries of the estate.

"A stitch in time." and all that.

He only does 50 laps a day in the pool now in the afternoon,so he can be refreshed in time to prepare the dining room for dinner.

It won't be long till he will have to retire,and he will be hard to replace.

I am giving him the Benz when he leaves,since he has driven and cared for it from his first day on the job.

Good help really is hard to find nowadays.

PS:Try the link again,it works fine from my site,and I have to use a sat link to connect.

Allow me to introduce my chauffeur:

https://www.youtube.com/watch?v=bK9VoToteGU

This means Baskin Robbins may have flavors we are not aware of!

Incomplete information again. The original description was of an instrument "capable of detecting every neutrino of that energy". "Flavor" was not mentioned, and (AFAIK) there is no change in energy associated with the changes of flavour.

A Customer complains that a TV I sold him is not working,even though it is capable of over 100 channels.

A visit to the residence reveals it is not turned on.

Such may be the case with the neutrino detector.

Is it turned on,plugged in, etc?

Rather ambiguous question as worded.

Is it OK for me to say that he 'official' answer is a pretty poor one?

IMO: as an answer to the specific challenge question, it's about as good an answer as "because that day was cloudless"

in case of panic - keep quiet

This blog is getting too serious.

A more important question has been bothering scientists all over the world for years:

https://www.youtube.com/watch?v=vXp0i7Y1eVo

... every neutrino of that energy ...

Already been pointed out (and ignored).