# Questions about neutrinos compared to the nature of light

First question:

Within experimental error all measurements of neutrino and light speed in vacuum are consistent with c,
but one way speed measurement of light is well proscribed,
so is a one way speed measurement of neutrinos also proscribed?

I have more questions, but maybe just clarify this one first.

Nugatory
Mentor
so is a one way speed measurement of neutrinos also proscribed?
There's no problem measuring the one-way speed of neutrinos or anything else (including light) if we're allowed to assume that the one-way speed of light is equal to the two-way speed.

The "proscription" against measuring the one-way speed of light is just saying that the one-way speed of light is something that we have to assume, not something that we can prove experimentally. Any experiment that purports to measure the one-way speed of light will turn out to be somehow based on this assumption.

Of the neutrino and light, can speed of both be measured two way, or just light?
(I'm wondering how to make a neutrino reflect or bounce back to obtain a two way path measure of speed)

Does the two way speed measure of light categorically theoretically extend to everything that moves at c?
(or does each type of thing that moves at c require an independent two way speed measure?)

The "proscription" against measuring the one-way speed of light is just saying that the one-way speed of light is something that we have to assume, not something that we can prove experimentally. Any experiment that purports to measure the one-way speed of light will turn out to be somehow based on this assumption.

It doesn't need to be based on this assumption. It is sufficient if it is based on an equivalent assumption.

• weirdoguy
jbriggs444
Homework Helper
(I'm wondering how to make a neutrino reflect or bounce back to obtain a two way path measure of speed)
In principle, it is easy. You send a friend to stand over there with a neutrino detector and a neutrino gun. You fire a neutrino at him. When he detects it, he shoots one back. You measure the time delay between when you fired your neutrino and when you detected the one from your friend you also measure the distance to where your friend is standing. Compute two times distance over time and you have the two-way speed.

The local flux is about 65 billion per square centimeter per second, so I might have trouble distinguishing which one was shot by my friend. :)

Another question:

If I label a group "c travelers" to include all particles that travel at c and their attributes with respect to c (e.g., relative speed between source and detector not effecting measured speed, no reference frame, etc.), are neutrinos categorically/theoretically "c travelers" yet?

jtbell
Mentor
are neutrinos categorically/theoretically "c travelers"
No. It's well established via neutrino oscillations that neutrinos have mass. Therefore they cannot travel at exactly c.

No. It's well established via neutrino oscillations that neutrinos have mass. Therefore they cannot travel at exactly c.

This suggests to me neutrino travel speed range of 0 to approaching c but all measures are consistent with c. Why no "slow" neutrinos?

ZapperZ
Staff Emeritus
This suggests to me neutrino travel speed range of 0 to approaching c but all measures are consistent with c. Why no "slow" neutrinos?

1. Because there's nothing to slow it down, since it has such a weak interaction with matter

2. You need to be coincidentally, and via very low odds, in exactly the same frame of reference to one of these neutrinos to be able to see it with speed 0.

Neutrinos may have a range of kinetic energies. However, because it has such a minuscule mass, even such a wide range of energies barely deviates significantly from being practically at ~c.

Zz.

jtbell
Mentor
Also, calculate the energy of a "slow" neutrino, using whatever speed you consider to be "slow." What kind of processes might produce such "slow" neutrinos?