Photons, which are particles of light, can undergo Bose-Einstein condensation due to several factors:

Symmetric Wavefunctions:
The first reason is that photons have wavefunctions that are symmetric with respect to particle exchange. Bose-Einstein statistics apply to particles with integer spin, such as photons, which have a spin of 1. According to Bose-Einstein statistics, particles with symmetric wavefunctions can occupy the same quantum state. This means that multiple photons can occupy the same energy level, forming a condensate.

Overlapping Wavefunctions:
Another reason is that photons can have overlapping wavefunctions. In order for Bose-Einstein condensation to occur, particles must have the ability to occupy the same quantum state. This requires the wavefunctions of the particles to overlap. Photons, being massless particles, can have wavefunctions that extend over large distances, allowing for significant overlap. As a result, photons can occupy the same energy level and form a Bose-Einstein condensate.

Zero Chemical Potential:
The third reason is that the chemical potential of photons is zero. The chemical potential is a measure of how the energy of a system changes with the addition of particles. For Bose-Einstein condensation to occur, the chemical potential must be sufficiently low. In the case of photons, their zero rest mass and the fact that they are not subject to gravitational forces leads to a zero chemical potential. This allows for the formation of a Bose-Einstein condensate.

Combination of Factors:
All of the above factors - symmetric wavefunctions, overlapping wavefunctions, and zero chemical potential - contribute to the ability of photons to undergo Bose-Einstein condensation. The combination of these factors allows for the formation of a macroscopic population of photons occupying the lowest energy state, which is the hallmark of Bose-Einstein condensation.

In summary, photons can undergo Bose-Einstein condensation because they have wavefunctions that are symmetric with respect to particle exchange, they can have overlapping wavefunctions, and their chemical potential is zero. These factors enable multiple photons to occupy the same quantum state and form a condensate at low temperatures.