In quantum field theory, particles, such as photons, are not self-sustaining entities in the way you might think of a classical object. Instead, they are excitations or disturbances in their corresponding quantum fields. The energy associated with these particles does not come from some internal reservoir but rather from interactions with the underlying fields and other particles in the universe.
Let's take the example of a photon, which is the quantum of the electromagnetic field. Photons can travel vast distances because they do not experience significant decay or dissipation effects in vacuum. In this case, the energy of a photon comes from its frequency and is related to its quantum mechanical wave nature.
The energy of a photon is determined by its frequency, according to the equation E = hf, where E is the energy, h is Planck's constant, and f is the frequency. As a photon propagates through space, it maintains its energy by preserving its frequency. This conservation of energy is a fundamental principle in physics.
It's important to note that while photons can travel long distances, they can also be absorbed or scattered by interacting with other particles or fields. For example, when a photon encounters matter, it can be absorbed by an atom or molecule, transferring its energy to the absorbing system. Alternatively, a photon can be scattered or refracted when passing through a medium, changing its direction without being absorbed.
In summary, the energy associated with a quantum, such as a photon, does not arise from an internal source but rather from its interaction with the underlying fields and other particles in the universe. The conservation of energy and the preservation of the quantum's frequency allow it to propagate over vast distances.