The stillness of Time

IF blog readers, I've reposted the entry below without the original tease about Sean Carroll's appearance at the IdeaFestival. These entries are syndicated; just click the "IdeaFestival blog" link to the left if you are reading this on the web site. "Insider Passes" to hear Carroll - and all the other fantastic presenters - are now available for purchase.


A recent Wired piece interviewed Caltech physicist and author of "From Eternity to Here," Sean Carroll and asked whether "he could explain his theories about time to a layman." 

His reply?

In one very real sense, you are time:

I’m trying to understand how time works. And that’s a huge question that has lots of different aspects to it. A lot of them go back to Einstein and spacetime and how we measure time using clocks. But the particular aspect of time that I’m interested in is the arrow of time: the fact that the past is different from the future. We remember the past but we don’t remember the future. There are irreversible processes. There are things that happen, like you turn an egg into an omelet, but you can’t turn an omelet into an egg.

And we sort of understand that halfway. The arrow of time is based on ideas that go back to Ludwig Boltzmann, an Austrian physicist in the 1870s. He figured out this thing called entropy. Entropy is just a measure of how disorderly things are. And it tends to grow. That’s the second law of thermodynamics: Entropy goes up with time, things become more disorderly. So, if you neatly stack papers on your desk, and you walk away, you’re not surprised they turn into a mess. You’d be very surprised if a mess turned into neatly stacked papers. That’s entropy and the arrow of time. Entropy goes up as it becomes messier.


From a cosmological view, the universe is moving from a highly ordered state to a completely disordered one, from a colossally energetic beginning to a cold end. Although the laws of physics are in theory symmetrical, the arrow of time goes in only one direction. People grow older. Suns eventually exhaust their fuel. It's that passage from energy to lethargy to stillness that we perceive and clock on the way to the next business appointment.

Among other reasons, it's that intuitive association of the passage of time with decreasing energy that makes Salvador Dalí's painting "The Persistence of Memory," pictured here, so startling.

Wayne      alt