71 votes
Accepted

Where are all the slow neutrinos?

Strictly speaking, it is indeed incorrect that neutrinos travel at "close to the speed of light". As you said, since they have mass they can be treated just like any other massive object, like ...
Sentry's user avatar
  • 1,533
50 votes

Why do the neutrinos (with mass) from a supernova arrive before the light (no mass)?

The situation with supernova is not about speed of flight but about time of emergence. A type IIa supernova candidate is big, even with the vastly powerful explosion of the core it takes hours to blow ...
dmckee --- ex-moderator kitten's user avatar
46 votes

Why was the neutrino thought to be massless?

I thought the particle was hypothesised in order to maintain the conservation of momentum in a beta-decay. If it was massless, this would have no effect, right? This is where you are confused. Having ...
StephenG - Help Ukraine's user avatar
43 votes

Neutrinos passing through black hole

No, you have a wrong understanding of the Wikipedia statement. Wikipedia says only "Gravity is extremely weak" on a subatomic scale. It does not say "neutrinos are not affected by gravity". They ...
enumaris's user avatar
  • 4,049
42 votes

What is the evidence for 'billions of neutrinos pass through your body every second'?

The existence of the neutrinos was established using energy and momentum conservation in neutron decays. There have been experiments with neutrino and antineutrino beams both at Cern and Brookhaven ...
anna v's user avatar
  • 234k
41 votes
Accepted

Why was the first discovered neutrino an anti-neutrino?

To maintain lepton number as a conserved quantity. Consider, in detail, what's going on in a beta decay (well, I'm going to ignore the nuclear context). The reaction is then $$ n \longrightarrow p^+ + ...
dmckee --- ex-moderator kitten's user avatar
39 votes
Accepted

Can neutrinos "hit" electrons?

Yes, neutrinos "hit" electrons all the time inside the sun, on their way to getting out, which results into the resonant conversion of their flavor, predicated on the changing effective index of ...
Cosmas Zachos's user avatar
37 votes

Sun light takes 1,000/30,000/100,000/170,000/1,000,000 years bouncing around inside to then reach the Earth

The idea that an identifiable photon "bounces around" inside the Sun and emerges some time later is incorrect. The photons that are produced in nuclear fusion reactions or indeed by other ...
ProfRob's user avatar
  • 131k
35 votes

Mass of All the Neutrinos

The neutrino mass, as you have defined it, will not be part of any calculation of the visible mass of the universe. There will indeed be a very large number of $>$MeV neutrinos whizzing about that ...
ProfRob's user avatar
  • 131k
31 votes

Why was the neutrino thought to be massless?

An interesting aspect not touched on by existing answers at the time of writing. What was observed about beta decay is that for the same change in the atomic nucleus, the emitted electron (which, ...
Andrew Steane's user avatar
28 votes

Why do Neutrinos pass through us but photons can't pass through us?

Light rays are a combination of oscillating electric and magnetic fields, and both fields interact strongly with charged particles. That's why light rays are strongly scattered by matter. The ...
John Rennie's user avatar
28 votes

Why, precisely, is argon used in neutrino experiments?

There are many different types of neutrino detectors, using various techniques to turn a neutrino interaction into an electrical signal. Detectors that use a large quantity of water or oil, like Super-...
probably_someone's user avatar
28 votes

Why was the neutrino thought to be massless?

Why did he figure it couldn't be detected? Because the neutrinos interact so weakly that it was for some time believed that it will not be possible to detect. E.g. in the 1934 paper by Bethe and ...
OON's user avatar
  • 8,334
28 votes
Accepted

How can neutrinos be solely left-handed if they have mass?

Yep. You're right. Since neutrinos have mass, they cannot be purely left handed if they are the same kind of fermion as everything else in the standard model. This idea - that neutrinos were purely ...
AXensen's user avatar
  • 7,337
27 votes

Where are all the slow neutrinos?

The experimental detection of slow neutrinos is indeed a big problem, but one that is very important. The cosmic neutrino background is at a temperature of around 2K and likely to consist of non-...
ProfRob's user avatar
  • 131k
27 votes

A thought experiment about neutrinos

This is the question about neutrino masses. If you outrun a left-handed neutrino, and the right-handed particle interacts like an antineutrino, then the neutrino is its own antiparticle. If you outrun ...
rob's user avatar
  • 89.7k
26 votes

Can neutrinos "hit" electrons?

Can neutrinos “hit” electrons? Yes, e.g., Image credit
Alfred Centauri's user avatar
25 votes
Accepted

What does the cosmic neutrino background look like today, given that neutrinos possess mass?

As far as theory goes, the Cosmic Neutrino Background (CvB) was created within the first second after the Big Bang, when neutrinos decoupled from other matter. Nevertheless, while the universe was ...
Sentry's user avatar
  • 1,533
24 votes
Accepted

Should Beta Minus decay put an upper limit on the mass of a neutrino?

This has been attempted, however the energy released in a neutron decay is a shade under a MeV and the neutrino masses are probably below $0.1$ eV. The energy of the neutron decay simply cannot be ...
John Rennie's user avatar
23 votes

How do neutrinos pass through the sun so quickly?

Light takes a long time to escape not because the sun is particularly large but because they run into a lot of electrons and protons on the way. So the light is taking a path that is more like a ...
Sean E. Lake's user avatar
  • 22.5k
22 votes

What is the difference between a neutrino and an electron neutrino?

As commented by Knzhou, neutrinos come in three different types: electron-, muon-, and tau- neutrinos. Each is paired with the particle it is named for in the sense that it is involved in particle ...
niels nielsen's user avatar
22 votes
Accepted

What is the evidence for 'billions of neutrinos pass through your body every second'?

As others have noted, the neutrinos come from the sun. Given that, there are two broad ways of estimating the flux of neutrinos: one is theoretical, and the other is experimental. The theoretical ...
Richter65's user avatar
  • 1,058
21 votes

Why does matter/antimatter only produce gamma rays?

At tree level, a matter-antimatter annihilation reaction doesn't just produce gamma rays, nor can you exclude neutrinos in the final state. Even the simplest such reaction can—given enough energy—...
dmckee --- ex-moderator kitten's user avatar
21 votes

Should Beta Minus decay put an upper limit on the mass of a neutrino?

Here is the KATRIN experiment: The KArlsruhe TRItium Neutrino (KATRIN) experiment, which is presently being assembled at Tritium Laboratory Karlsruhe on the KIT Campus North site, will investigate ...
anna v's user avatar
  • 234k
21 votes
Accepted

Neutrinos passing through black hole

neutrinos are not affected by gravity on the subatomic scale Where do you get this idea? It's not a part of mainstream physics. One of the main ideas behind general relativity is that gravity isn't ...
Mike's user avatar
  • 15.3k
20 votes
Accepted

Why do we not know whether or not neutrinos are their own antiparticles?

We know that neutrinos and antineutrinos exist, and it's possible to tell the difference between them. For example in a charged current detector electron neutrinos produce this reaction: $$ \nu + n \...
John Rennie's user avatar
18 votes

Could Hawking radiation have a lot of neutrinos and dark matter?

Yes. Hawking radiation is universal: the black hole is a modification of spacetime geometry, and the quantum fields, which manifest particles, are residents of that spacetime. Thus they are all ...
The_Sympathizer's user avatar
17 votes
Accepted

How much of neutrinos pass through a neutron star?

Quick answer: Neutron stars are transparent to their own thermally produced neutrinos and any other neutrinos of energies below a few MeV once they have cooled to highly degenerate states at ...
ProfRob's user avatar
  • 131k

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