Another objection by Olum and Everett is that even if Mallett's choice of spacetime were correct, the energy required to twist spacetime sufficiently would be huge, and that with lasers of the type in use today the ring would have to be much larger in circumference than the observable universe. At one point, Mallett agreed that in vacuum, the energy requirements would be impractical but noted that the energy required goes down as the speed of light goes down. He then argued that if the light is slowed down significantly by passing it through a medium (as in the experiments of Lene Hau where light was passed through a superfluid and slowed to about 17 metres per second), the needed energy would be attainable. However, the physicist J. Richard Gott argues that slowing down light by passing it through a medium cannot be treated as equivalent to lowering the constant c (the speed of light in vacuum) in the equations of General Relativity, saying: