VParticles and the Gamma Decay of a Neutral Pion

It is shown that the previous theoretical calculations of the lifetime for the gamma decay of the ${\pi }^0$ meson must be subject to an obvious modification because of the presence of new particles recently discovered experimentally. This may be regarded as an example of the fact that, in some cases, the meson-nucleon system cannot be treated as being isolated from the rest of the elementary particles. We cannot give an accurate numerical prediction for the lifetime until sufficient knowledge about the new particles is accumulated. Some features of Pais' theory of the $V$ particles are discussed in connection with this problem.