Light’s temperature and particle’s temperature from 3000K The universe is estimated to have been in the thermal equilibrium state(3000K) around 380,000 years after its birth. From this, we induce the current temperature of CMB - 2.7K. In case of particles existing outside(example. at Void area) of the cluster of galaxies structure (or, if not affected by local heat source), what is the temperature currently predicted? How can we get the real answer? Is it adiabatic expansion? How can we get the real answer? Have a nice day!