Physicist Sean Carroll is hunting for the ultimate theory; he wants to explain the arrow of time.

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. … 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.

Carroll theorizes there is a “parent universe” that gives birth to multiple universes (a multiverse) through multiple “big bangs”, each with its own unique arrow of time. Each universe begins with some high level of entropy, which is winding down from that point forward. The empty, quiet parent spacetime from which these many other universes emerge is a static unchanging place of low entropy, with just enough quantum fluctuation for the new universes to be born again and again.

Like Alex Vilenkin, Carroll quotes St. Augustine to describe how we have some sense of what time is, even though we find it really difficult to explain what time really is.

Read More: Wired Magazine, February 2010.

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1 Comment on What Is Time?

  1. I highly enjoyed Huw Price’s book, which explores the numerous subtle slips that physicists and philosophers make when trying to explain why the past is different from the future.

    Now that I’ve found that ‘Many Worlds’ QM interpretations are mainstream, I’m really curious if there are any time-symmetric formulations. (I gather one objection to the universe splitting or being duplicated has been where the extra energy comes from.)

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