Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS

Sean Carroll on Time

  • By David Levin
  • Posted 11.10.11
  • NOVA
Listen

Physicist Sean Carroll says there's no such thing as past or future in the elementary laws of physics.

Transcript

SEAN CARROLL ON SPACE AND TIME

Posted November 10, 2011

The words past and future do not appear in the laws of physics. There is no difference between one direction of time and the other in the ultimate elementary laws of physics. What we do is we assign the words past and future to the direction of lower entropy and higher entropy.

Entropy is a way of measuring the disorderliness of any system—whether it is the universe or a cup of coffee or anything like that. So if things are precisely organized, in particular if they’re segregated so that your cream is over here and your coffee is over here, that’s low entropy, that’s a high amount of organization. Then you mix them together and the entropy goes up. And it’s a law of nature if you leave things by themselves entropy always goes up. Things go from being orderly, very delicately organized, to being messier, to being more disorganized.

And so we tend therefore to associate time with not just change, but a certain directed kind of change. The direction of time in which the entropy was lower we call the past. The direction of time in which entropy is increasing we call the future. That’s what defines the arrow of time. And all of that is part of this underlying dynamic caused by the fact that the universe started very organized and is becoming ever more disorganized as it expands and cools and things happen.

Credits

AUDIO

Produced by
David Levin
Original interview by
Randy MacLowery

IMAGE

(Sean Carroll)
© WGBH Educational Foundation 2011

Major funding for "The Fabric of the Cosmos" is provided by the National Science Foundation and the Alfred P. Sloan Foundation.

Additional funding for this program is provided by the Arthur Vining Davis Foundations.

Related Links

  • The Fabric of the Cosmos

    Acclaimed physicist Brian Greene reveals a mind-boggling reality beneath the surface of our everyday world.

  • Janna Levin on Space and Time

    Physicist Janna Levin says that Einstein and Newton had very different ideas about what space and time really are.

  • Leonard Susskind on Space

    Physicist Leonard Susskind says that Einstein’s equations show that space exists, but they don’t explain what it is.

  • Putting Relativity to the Test

    Nearly a century after Einstein published his general theory, experiments continue to confirm its every prediction.

Close

You need the Flash Player plug-in to view this content.