I was thinking, can an object have negative mass? If an object with positive mass needs infinite energy to go at the speed of light, would an object with negative mass need infinitely negative energy (if negative mass were possible, this would be possible too right?) If an object had negative mass, could it go faster than the speed of light? I know that dark matter is supposed to have negative pressure, how does that work? If something can have negative pressure, could it have negative mass? Thanks!