Neutrinos: Fast or Slow? Can We Observe It?

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In summary, neutrinos are typically fast and travel at speeds close to the speed of light due to their small masses. However, they can also be in a state of slowness or rest in a local inertial frame. There have been indirect observations of slow-moving neutrinos, particularly in tritium beta decay, but these cases are very rare. The proposed PTOLEMY detector aims to detect non-relativistic neutrinos from the cosmic neutrino background.
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Can neutrinos also be in a state of slowness or rest?
As far as I know neutrinos are normally fast/ connected with a velocity close to the speed of light. This seems to be characteristic.
Can neutrinos also be in a state of slowness or rest? If yes, has there ever been an indirect observation of such cases?
 
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Since neutrinos are massive, they travel at speeds lower than the speed of light. As such, you can always find a local inertial frame where a particular neutrino is at rest. However, the neutrino masses are very small and this leads to them traveling very close to light speed unless you somehow manage to give them very very little kinetic energy.

Note that there is no such thing as ”being at rest”. You can only be at rest relative to something else.
 
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About 1 in 5 trillion neutrinos from tritium beta decay have an energy below 1 eV assuming small neutrino masses. Maybe 1% of these (so 1 in 500 trillion) would have a speed below 30% the speed of light. Tritium has a very low decay energy - for most beta decays the fraction is much smaller. If the constraints from cosmology are wrong for some reason then the fraction could be larger, but still very small.

Some neutrinos from the cosmic neutrino background can be non-relativistic today. PTOLEMY is a proposed detector to find them.
 

1. What are neutrinos and how do they travel?

Neutrinos are subatomic particles that have no electric charge and very little mass. They are created in nuclear reactions, such as in the Sun, and can also be produced by cosmic rays. Neutrinos travel at almost the speed of light and can pass through matter without interacting with it.

2. Are neutrinos fast or slow?

Neutrinos are considered to be fast because they travel at almost the speed of light. However, compared to other subatomic particles, such as photons, they are relatively slow.

3. How do we observe neutrinos?

Neutrinos are notoriously difficult to observe because they rarely interact with matter. However, scientists have developed specialized detectors, such as large underground tanks filled with liquid, to detect the rare interactions between neutrinos and other particles. These detectors can also determine the energy and direction of the neutrinos.

4. Can we control the speed of neutrinos?

No, we cannot control the speed of neutrinos. Their speed is determined by their energy and mass, which are fixed properties of the particle.

5. What are the implications of observing fast or slow neutrinos?

The speed of neutrinos can provide valuable information about the fundamental properties of these particles and the nature of the universe. Observing faster or slower than expected neutrinos could also lead to new discoveries and advancements in our understanding of physics.

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