Is the future real? What happens to the present moment when it becomes past? Does the present depend on thought? Is the flow of time just a human construct? Ken introduces David Albert, philosopher and physicist at Columbia. Albert begins by suggesting that we think of the “now” like we think of “here”, that is, “here” is wherever I am and “now” is whenever I am thinking. Our intuitions say that space and time seem fundamentally different. For example, we have sense experience access to different points in space, but we do not have such access to time.

Ken asks if time could be real in experience but not objectively real. Albert describes the problem of the direction of time in the foundations of physics in terms of billiard balls hitting. Albert points out that most theories of time are symmetric while our experience of time is asymmetric. What it would mean for time to move faster? Rate is measured in terms of time. Albert talks about the import of Einstein's theory of relativity has for understanding time.

时间旅行可能吗?似乎如果你能回到过去，你就无法改变世界的因果历史。库尔特·哥德尔提出了一个相对论方程的解决方案表明时间旅行是可能的。这就引出了祖父悖论，也就是说，如果你能回到过去杀死你的祖父母，那么你就会阻止自己回到过去。阿尔伯特将时间的解释描述为事物的相对变化。如果我们对时间的感知是真实存在的某一客观事物，那么是否存在与我们认知时间不同的生物?阿尔伯特认为自然选择可能会确保所有的生物都更关心安排未来而不是过去的事情。

• Roving Philosophical Report(Seek to 04:36): Amy Standen interviews Doug Williams about movies on time travel such as Twelve Monkeys and Back to the Future.

• Sixty Second Philosopher(Seek to 50:18): Ian Shoales gives a brief history of time, from ancient Greek mythology through Newton and modern physics.