Alan Alda and Curvature in Space-Time

Actor Alan Alda appears with mathematician Bob Osserman in a video of a Berkeley Repertory Theatre conversation sponsored by the Mathematical Sciences Research Institute. It is a wonderful conversation between two very intelligent and curious individuals. Here I want to comment on Alda’s implicit, unanswered question:

          What is meant by curvature in space-time?In space alone, e.g. in the Euclidean plane, a path is straight if it has constant slope, never getting more or less steep. In space-time, a path is straight if it has constant velocity, i.e., if it never changes slope or speed. Galileo observed that in free space, objects move in straight lines at constant speed, i.e., move in straight lines in space-time. They do not “curve” in space-time by speeding up or slowing down or changing direction. Gravity, however, causes a ball thrown in the air to deviate from such straight lines and continually change speed and direction. In this sense, gravity causes objects to curve in space-time, to change speed as well as direction.

Of course as Osserman explains, Einstein’s Theory of General Relativity (see also my books on applied real analysis and Riemannian geometry) is fundamentally deeper than this, but this is something I wished I could have told Alda first. 

 

One Comment

  1. Jonathan '05:

    Hi Frank! It’s Jonathan ’05, directed here by ephblog. Thanks for teaching me something within my grasp but previously unrealized. You might be happy to know also that Matt and I are planning to play in a bridge tournament at Harvard on the 10th. I don’t play much at all these days, though I occasionally teach some students here at Cornell, but Matt and I do the Bridge Bulletin hands together when we can and find that we still have the same style and approaches. I look forward to playing again with him.

Leave a Reply

Your email address will not be published.