Tuesday, July 12, 2005
First Aired: 
Tuesday, November 9, 2004

What Is It

Time is the most familiar thing in the world, and yet philosophically one of the most puzzling. Is the present what's left when you subtract what has already happened, and what is yet to happen? Then it seems to vanish into a mere instant.  Are future events completely unreal? Or are they just the things we can't know yet? Is time unreal, as many philosophers have thought? Columbia's Dave Albert joins John and Ken for a fascinating hour. 

Listening Notes

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. 

Is time travel possible? It seems like if you could travel back in time, you couldn't do anything to change the causal history of the world. Kurt Goedel came up a solution to the equations of relativity that says time travel is possible. This leads to the grandfather paradox, that is, if you could travel back in time to kill your grandparents then you would prevent yourself from traveling back in time. Albert describes an interpretation of time as relative change in things. If our perception of time gets at some objective thing in realty, then could there be creatures that cognize time differently than we do? Albert thinks natural selection likely ensures that all creatures worry about arranging future events more than past ones.

  • 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.