According to the Heisenberg uncertainty principle, it is not possible to simultaneously determine the exact position and momentum of a particle with absolute precision. The principle states that there is a fundamental limit to the precision with which certain pairs of physical properties, such as position and momentum, can be known.
In the case of a massless particle, such as a photon, its momentum is given by its frequency and wavelength through the relation p = h/λ, where p is the momentum, h is Planck's constant, and λ is the wavelength. Since a massless particle travels at the speed of light, its wavelength is inversely proportional to its frequency (λ = c/f), where c is the speed of light and f is the frequency. Combining these relationships, we have p = hf/c.
Since the momentum of a massless particle is related to its frequency, there is a natural uncertainty in the determination of its frequency, and therefore its momentum. This inherent uncertainty arises from the wave-particle duality inherent in quantum mechanics, where particles can exhibit both wave-like and particle-like properties. Consequently, the uncertainty principle applies to massless particles as well, and it is not possible to precisely determine both the position and momentum of a massless particle simultaneously.
In summary, a massless particle, even though it may have an exact position, would still be subject to the uncertainty principle and would not violate it. The principle sets a fundamental limit on the precision with which certain pairs of properties, such as position and momentum, can be known simultaneously.