Neurinos are massless paricles

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Discussion Overview

The discussion revolves around the nature of neutrinos, specifically whether they are massless particles and the implications of this on their kinetic energy. Participants explore concepts related to mass, energy, and the relativistic framework, as well as the definitions and usefulness of kinetic energy in this context.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question whether something with no mass can possess kinetic energy, leading to a rephrasing of the question regarding the existence of particles with no rest energy.
  • One participant notes that massless particles can have momentum, suggesting that having kinetic energy is not far-fetched.
  • Another participant emphasizes that kinetic energy is not particularly useful in a relativistic framework, advocating for the use of rest energy and total energy instead.
  • There is a discussion about the terminology of "covariant" in relation to quantities and equations, with some participants clarifying their understanding of how four-momentum transforms between frames of reference.
  • One participant asserts that neutrinos are not massless and have a rest mass, contrasting this with photons, which are massless but still possess energy.

Areas of Agreement / Disagreement

Participants express differing views on the mass of neutrinos, with some asserting they are massless while others claim they have a rest mass. The discussion remains unresolved regarding the implications of mass on kinetic energy and the definitions of relevant physical concepts.

Contextual Notes

There are limitations in the discussion regarding the definitions of mass, energy, and the applicability of classical versus relativistic concepts. The terminology used by participants may lead to misunderstandings, particularly around the concept of covariance.

colinr
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I've heard that it is thought that Neurinos are massless paricles, but I'm now hearing that they have kinetic energy.

Can something with no mass have kinetic energy?
 
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Kinetic energy is a classical concept that has little use in a relativistic framework. Good quantities to use are rest energy (Lorentz invariant) and total energy (Lorentz covariant). The difference (total - rest) corresponds to the classical kinetic energy (the classical formula only picks up the lowest order term). However, since it is neither absolutely conserved nor an invariant quantity, it is not a terribly useful concept.
So the question can be restated as "Can something exist that has no rest energy?". The answer to that is yes. Such particles are required by SR to have no rest mass and to always move at the speed of light. Examples are photons and gluons, but apparently not neutrinos, since they are no longer considered massless due to observed oscillation effects.
 
massless particles can have momentum, so having kinetic energy is not far from it.
 
zefram_c said:
Kinetic energy is a classical concept that has little use in a relativistic framework. Good quantities to use are rest energy (Lorentz invariant) and total energy (Lorentz covariant). ...

Hi there.

Could you tell me what you mean by a quantity being "covariant"?

I thought that "covariant" made only sense when referring to an *equation*, not a quantity. An equation is covariant when the two sides transform the same way under Lorentz transformations (in SR) or general coordinate transformations (in GR). On the other hand, a quantity may be invariant or not. But I don't know what it would mean for a quantity to be "covariant". A quantity may transform as a vector, a spinor, a tensor of a certain rank, etc. In that case it is not invariant, but I have never seen (or I did not notice) the adjective "covariant" used in that context.

Pat
 
nrqed said:
Could you tell me what you mean by a quantity being "covariant"?

I thought that "covariant" made only sense when referring to an *equation*, not a quantity. An equation is covariant when the two sides transform the same way under Lorentz transformations (in SR) or general coordinate transformations (in GR).
Ooops, sorry. My terminology was very sloppy on that one. I meant that the four-momentum transforms as a Lorentz vector between frames of reference. This would not be true for the kinetic energy, which would transform in a more complicated manner.
 
Last edited:
colinr said:
I've heard that it is thought that Neurinos are massless paricles, but I'm now hearing that they have kinetic energy.

Can something with no mass have kinetic energy?

Neutrinos are definitely not massless, they have a rest mass. Particles with no rest mass, for example photons, DO have energy, which can be calculated by using the equation...

E = h \nu Where E is the energy, h is plank's canstant and \nu is frequency of the light.
 

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