What is time? Today my metaphysics class talk about the duality between time and space. Some philosophers think time and space are inter changable. Both of the measure the relative distance between two points, either in space or in time. The class talked about the problem of time travel as well. The hardest problem is the causation loop, where one event is the cause of itself. I don’t agree that nature of time and time travel is metaphysics, it should be in the realm of science. When preparing for this week’s class, I digged out and read my copy of Stephen Hawking’s A Brief History of Time. Most philosophers without a science backround assume space and time are two different but similiar things. According to Hawking, there exists only one thing call space-time. Space cannot exist indepedent of time, so it is pointless to talk about space alone. I ask this question to the profressor after class, and it seems he dismiss Hawking’s point of view has any philosophical value. What a old fashion philosophy guy! I can see how science will change the field of metaphysics. Many metaphysics assumings philosphers take it for granted for centuaries are being challenaged by quatum physics. Quatum physics shine lights on those old questions and maybe it will lead to a more convincing solution oneday.