When two billiard balls collide in normal situation (on earth) we hear the sound due to their impact. This is a sufficient proof that the collision is inelastic in nature due to loss of energy in the form of sound. But suppose the same collision occured in space, then we will not be able to hear the sound due to collision as there is no medium for sound to propagate. Then can we say in this case that the collsion is elastic since no energy is dissipated? (We assume that the balls do not deform during the collision)