I have no doubt that we will someday develop machines that simulate human behavior so well that they are indistinguishable from humans; thus many will argue they pass the Turing Test. However, as John Searle points out in his Chinese Room argument, a simulation, no matter how accurate and believable, is merely a simulation. The simulated person would lack subjective experience and any true understanding. In short, machines will never be sentient despite how well future engineers will fake it.