Jump to content
Science Forums

How do neutrinos do it?


freeztar

Recommended Posts

I just read the wiki on neutrinos (what I could absorb anyways) and I was left with the basic question of, "How do neutrinos pass through mass seemingly unaffected?".

Speed would seem logical, but not when you consider the fact that neutrinos travel "near" the speed of light and are not affected by the collapse of a massive star, whereas photons are.

Optical photons can be obscured or diffused by dust, gas and background radiation. High-energy cosmic rays, in the form of fast-moving protons and atomic nuclei, are not able to travel more than about 100 megaparsecs due to the GZK cutoff. Neutrinos can travel this distance, and greater distances, with very little attenuation.

Neutrino - Wikipedia, the free encyclopedia

 

So then I considered mass. And this quote from the same wiki entry threw me off:

In particle physics the main virtue of studying neutrinos is that they are typically the lowest mass...

 

"Typically"?

This implies that there are other fermions that are sometimes less massive.

 

Then I just turned to the simple explanation and thought that it must be because they are so small that they pass through atomic structures themselves as if traveling through a multitude of solar systems. But then how come they are not affected by electro-magnetic fields?

 

I'm stumped.

 

Does the scientific community have an explanation for "why" neutrinos flow through the earth virtually unimpeded?

Link to comment
Share on other sites

I just read the wiki on neutrinos (what I could absorb anyways) and I was left with the basic question of, "How do neutrinos pass through mass seemingly unaffected?".

Speed would seem logical, but not when you consider the fact that neutrinos travel "near" the speed of light and are not affected by the collapse of a massive star, whereas photons are.

 

Neutrinos ARE effected by gravity in pretty much the same was photons. The thing that makes neutrinos different is that they don't interact at all with photons, and so other then a direct collision there is no way for any other fermion to mess with them.

 

The reason photons aren't a great probe for things like stars is that stars are often composed of vast amounts of ionized material. The photons interact and get scattered by these charged particles.

 

"Typically"?

This implies that there are other fermions that are sometimes less massive.

 

Neutrinos ARE the least massive fermions, but as you get a particles energy/momentum higher and higher its mass becomes less and less relevant. Hence, sometimes its a good approximation to think of an electron as massless. Its almost always a good approximation to think of a neutrino as massless.

 

Then I just turned to the simple explanation and thought that it must be because they are so small that they pass through atomic structures themselves as if traveling through a multitude of solar systems. But then how come they are not affected by electro-magnetic fields?

 

The reason they aren't effected by electro-magnetic fields is quite simple: they are neutral particles. Given that atomic structure is mostly empty space, its pretty unlikely the neutrino can directly collide with another fermion and, being neutral, the electric fields don't mess with it at all.

-Will

Link to comment
Share on other sites

Great replies!

I get it now and reviewing the wiki article, I found this obvious pointer:

Because it is an electrically neutral lepton, the neutrino interacts neither by way of the strong nor the electromagnetic force, but only through the weak force and gravity.

 

I like the simple eloquence of Jay-q's response and the thoughtful and inspiring (...me to research other aspects of the ideas presented...) post by Erasmus00!

 

My questions are cleared up for now, but I'm sure I'll have more once I sit on it for a little while. :)

Link to comment
Share on other sites

Can you elaborate?

 

i would really like to.

but first a poem by pablo neruda

March days return with their covert light,

and huge fish swim through the sky,

 

vague earthly vapours progress in secret,

 

things slip to silence one by one.

 

 

 

Through fortuity, at this crisis of errant skies,

 

you reunite the lives of the sea to that of fire,

 

grey lurchings of the ship of winter

 

to the form that love carved in the guitar.

 

 

 

O love, O rose soaked by mermaids and spume,

 

dancing flame that climbs the invisible stairway,

 

to waken the blood in insomnia’s labyrinth,

 

 

 

so that the waves can complete themselves in the sky,

 

the sea forget its cargoes and rages,

 

and the world fall into darkness’s nets.

Link to comment
Share on other sites

ok,im back,what do you want me to elaborate on.What makes a sea of virtual particles.Howw long they remainin this universe.what makes them blink on and off.i too have so many questions

 

I don't expect an answer explaining the universe. Rather, I would wish upon an explanation that clarifies the "blinking" of neutrinos. In other words, a credible source documenting this "behavior" would be most appropriate. :)

 

PS Neruda Rocks!

Link to comment
Share on other sites

i think they blink on and off with a strange periocity.like viertual particles,they only have a tendency to exist
To the best of my knowledge, neutrinos are not virtual particles. They don’t blink in and out of existence, or tunnel, more than other leptons, such as the electron.

 

The do appear to oscillate, shifting through the three “flavors” of neutrinos at they travel. This phenomena has become the leading explanation for the solar neutrino problem, a shortage in the observed number of electron neutrino predicted by particle physics to be produced in greatest numbers by the Sun. Most theorists now accept that we detect too few electron neutrinos, because many of them have oscillated into muon or tau neutrinos by the time they reach Earth. New detectors capable of detecting all 3 neutrino flavors support this explanation, finding muon and tau neutrinos that can only be explained as having been electron neutrinos when they were created by nuclear fusion in the Sun.

Link to comment
Share on other sites

...and the oscillation phenomenon is the indication that their mass cannot be exactly zero.

 

The answer to the question is that a neutrino participates only in weak interactions, apart from it's tiny conjectured mass. This is why it has an exceedingly low cross section in traversing matter because weak interactions are, as their name suggests, very weak indeed.

 

The only point on which I disagree with Will is in talking about direct collision. The way they travel clean through Earth indicates their cross-section is tiny even for collisions with atomic nuclei. In layman terms this means they can go straight through even the heaviest nucleus with a low probability of interaction. This is not so for electrons, due to electric charge, even less for hadrons; DIS and hadronic diffraction have non negligible cross-section.

Link to comment
Share on other sites

I don't expect an answer explaining the universe. Rather, I would wish upon an explanation that clarifies the "blinking" of neutrinos. In other words, a credible source documenting this "behavior" would be most appropriate. :D

 

PS Neruda Rocks!

 

well,i was reasoning that because nuetrinos didnt interact with matter they must be akin to dark matter in that only gravity is shared between they and this plain of spacetime.and since they do interact occasionally,they must also be akin to virtual paticles that only have a tendancy to exhist.if i were you ide go with craig d.s explination.but,i would like to now know if he means if they have flavors like quarks do and when he says they occilate between these three flavors,where does the symmetry of the other two flavors go.where is that information now manifest

Link to comment
Share on other sites

well,i was reasoning that because nuetrinos didnt interact with matter they must be akin to dark matter in that only gravity is shared between they and this plain of spacetime …
One speculative explanation of the “missing mass” problem proposes that some to nearly all of the missing mass can be accounted for by either a huge number of low mass neutrinos, or a slightly greater average neutrino mass, which could result from many complicated causes. Because neutrinos interact only via gravity and the weak force (W and Z bosons), not via photons, they are by definition “dark”. The questions, which I believe are unresolved, is if there are enough neutrinos, and/or what the actual proportion of the 3 flavors of neutrinos (which have very different masses) is. These are difficult questions, made more so by how difficult it is to experimentally observe neutrinos.

 

... i would like to now know if he [CraigD] means if they have flavors like quarks do and when he says they occilate between these three flavors,where does the symmetry of the other two flavors go.where is that information now manifest
This is a complicated “quantum weird” subject, which I think sources like this wikipedia article do a better job of presenting than I can.

 

The short answer, though, is yes, I mean neutrinos have flavors, but no, their flavors (electron, muon, and tau) are not much like the 6 quark flavors (up, down, charm, strange, top, and bottom). Quark of different flavors have different masses and different charges, while neutrino of different flavors have different masses, but all have the same, zero charge.

Look up the standard model of particle physics.
Qfwfq is, I think, right (as he usually is about Math and Physics). Studying the standard model, even without the more advanced mathematical parts, is a great help in discussions of this kind. It’s full of nifty diagrams and cool-sounding names, but has fewer particles than many comic strips have characters, so is not prohibitively time consuming to achieve some level of mastery in a fairly short amount of study time.
Link to comment
Share on other sites

will do on that standard model.also,i remmber seeing many times where they went to the bottom of some salt mine and fillied a cavity with widex.
There have been, are, and are planned, many neutron detectors, using mediums varying from dry cleaning fluid to liquid or frozen water to stacks of steel plates, with matching sensors varying from photomultiplier arrays to chemical detectors to calorimeters. Many neutrino detectors are placed far underground, to eliminate a major source of “noise” – high energy radiation from space, which is almost completely absorbed by the shielding earth, while neutrinos are almost completely unaffected by it. Other detectors are not shielded, but use reliable techniques for distinguishing “noise” – events triggering the detector’s sensors not caused by neutrinos – from authentic neutrino interactions. The wikipedia article section “Neutrino experiments, neutrino detectors” has a partial list – it doesn’t list small detectors, such as the first ones in the 1950s.
if i remmeber wronly,please excuse.was this an attempt to polorize a filter to their "low cross section"?
AFAIK, neutrinos are circularly, or “not” polarized. Thouh some experiments involving lenses, diffraction grates and similar techniques (like all particles, neutrinos have a wave nature, so, even though they only weakly interact with ordinary matter, can be manipulated optically) have examined neutrino polarization, I don’t think any of the major detectors have, or would gain any advantage by doing so.

 

The design and building challenge of a neutrino detector is not to get neutrinos to interact, which they do with a very small but non-zero probability with practically any material (I recall reading somewhere that a human body has many neutrino interactions over their lifetime), but detecting the interactions, and distinguish them from other interactions that produce similar effects.

 

An interesting, practical application of neutrino detectors is the Supernova Early Warning System. Though intended to provide astronomers with a heads-up to observe supernovae, the system (a collaboration of neutrino detector facilitues, which hasn’t yet detected any supernova) could be the first warning of a nearby supernova, which could be an “extinction level event”. In such an event, people would want to take measures to shield themselves from the ensuing high-energy photon and massive particle “storm”, hopefully assuring that such an event would not be the extinction of our species.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...