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do phonons have (significant) momentum? do they have rest mass?
A phonon is a quantum of vibrational energy in a crystal lattice. It is the smallest unit of vibrational energy that can exist in a crystal lattice and is considered to be a collective excitation of the atoms or molecules in the lattice.
Momentum is a physical quantity that measures the motion of an object. It is defined as the product of an object's mass and its velocity. In other words, it is the amount of force needed to stop or change the direction of an object's motion.
Rest mass is the mass of an object when it is at rest. It is a fundamental property of matter and is independent of an object's speed or motion. The rest mass of an object is also known as its invariant mass.
Phonons are related to momentum through the concept of wave-particle duality. Just as particles can exhibit wave-like behavior, phonons can also have a momentum associated with them. In fact, the momentum of a phonon is directly related to its wavelength and frequency.
Yes, phonons can have rest mass. This is because phonons, being a quantum of vibrational energy, can have a small amount of mass associated with them. However, their rest mass is generally very small, on the order of 10^-36 kg, and is often neglected in calculations.