# Neutrinos with Mass and Traveling at Light Speed: Explained

• oferar
In summary: Now if you say, "regarding my lab frame as being at rest, for the moment, can I work out the physics that determines what velocity I see the neutros travel?" Yes I can, using the kinetic energy and momentum just as for a Newtonian particle, but remembering to make proper use of the gamma multiplier \gamma = \frac{1}{\sqrt{1 - \frac{v^2}{c^2}}}.The neutrinos have a very small mass, so their speed is close to the speed of light in any experimental situation on earth. However, it is possible to have "slow" neutrinos emitted from particle beams in the backward direction. The beam must be very
oferar
Hello, I recently read about neutrinos having mass > 0.
(http://news.bbc.co.uk/1/hi/sci/tech/4862112.stm) , but also they travel at the speed of light. How can it be possible? If they have mass, their mass should increase with the velocity, and at the speed of light according to special relativity they should have an infinite mass.
Can someone explain what this means? Maybe they should travel slower than light?

Thanks.
fernando

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Well, they travel at a speed that is very close to the that of light.

What decides what velocity a object has since everything is relative?

Essentially, the observer decides... relative to himself.

Jarle said:
What decides what velocity a object has since everything is relative?
However you measure, it should not be greater than c for a particle with nonzero mass.

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but he cannot reach a veloticity "c". so there has to be something that decides the velocity. if he is just below the c level of velocity, another object can't very much faster than that, even though it stands still in his frame. ( if he has the same speed)

Jarle said:
but he cannot reach a veloticity "c". so there has to be something that decides the velocity. if he is just below the c level of velocity, another object can't very much faster than that, even though it stands still in his frame. ( if he has the same speed)

Velocity with respect to what? You are writing as if the neutrinos had an ansolute velocity with respect to some fixed frame of reference. But this is relativity; there is no fixed frame nor any absolute velocity, other than c, either. If I see the moving at v, I can be moving at v in the opposite direction at v and the particle be standing still. Or any combination of its velocity and mine that add up to a relative v between us. As long as $$\frac{v^2}{c^2} < 1$$ it's physically possible.

Now if you say, "regarding my lab frame as being at rest, for the moment, can I work out the physics that determines what velocity I see the neutros travel?" Yes I can, using the kinetic energy and momentum just as for a Newtonian particle, but remembering to make proper use of the gamma multiplier $$\gamma = \frac{1}{\sqrt{1 - \frac{v^2}{c^2}}}$$.

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Neutrinos are usually emitted at high energy (several keV to MeV). Their mass, if it exists, is <1eV, so their speed is close to c for any experimental situation on earth.
In principle, it is possible to have "slow" neutrinos emitted from particle beams in the backward direction. The beam must be very energetic because it has to match the ratio neutrino energy/neutrino mass. Those beams are not available yet and it can be doubted that we would detect slow particles in the mess of a collision or similar events.

## 1. What are neutrinos and how do they differ from other particles?

Neutrinos are subatomic particles that have no electric charge and are almost massless. They are one of the fundamental particles that make up the Standard Model of particle physics. Unlike other particles, neutrinos interact very weakly with matter, making them extremely difficult to detect.

## 2. How do we know that neutrinos have mass?

Experimental evidence from various sources, such as the Super-Kamiokande and the Sudbury Neutrino Observatory, have shown that neutrinos can change between different types, or "flavors", as they travel. This phenomenon, known as neutrino oscillation, can only occur if neutrinos have mass.

## 3. Can neutrinos really travel at the speed of light?

According to the theory of relativity, particles with mass cannot reach the speed of light. However, neutrinos have a very small mass and travel very close to the speed of light. This is why they were initially thought to be massless until the discovery of neutrino oscillation.

## 4. How do neutrinos interact with matter if they have no charge?

Neutrinos can interact with matter through the weak nuclear force, one of the four fundamental forces in the universe. This interaction is very rare and only occurs when a neutrino collides with a nucleus, causing it to change into a different type of neutrino.

## 5. What are the implications of neutrinos having mass and traveling at the speed of light?

The discovery of neutrino mass has significant implications for our understanding of the universe and its fundamental laws. It also has practical applications, such as in the field of astrophysics where studying neutrinos can provide insights into cosmic phenomena and events such as supernovae explosions.

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