Online Course Review: "Mysteries of Time" (prof. Sean Carroll, from "The Great Courses")

What is Time? And why does it seem to "flow" in just one direction ("arrow of time")?

Few questions could be more spellbinding - and almost intractable - than that!

In this blog, I'll periodically include detailed reviews of some online courses I've taken.

REVIEW OF ONLINE COURSE "Mystery of Time" (course by Cal Tech prof. Sean Carroll, produced by "The Great Courses" in 2012)

Another fascinating course by Sean Carroll! He's very ambitious to not only tackle the Universe - and the difficult abstract concept of Time's Arrow (direction) - but also to make it accessible (sort of) to a (serious and determined) lay audience.

Speaking of "layperson", even though that's the intended audience, I'd only recommend this course to people who are used to, at the VERY least, watching (and enjoying!) documentaries on topics such as quantum mechanics and relativity.

Let's face it: to seriously tackle the physical concept of Time means bringing out a formidable armada of thermodynamics, classical physics, quantum mechanics, special relativity, general relativity and cosmology, with a sprinkling of string theory, etc. If most of those are new to you, you'll be in for a rough ride, in spite of Sean Carroll's super-human explaining skills! Other courses are vastly better suited to anyone who is just getting their feet wet with Physics...

I have a fairly substantial background in Physics and in Math... and found this course complex: the real complexity is devilishly hidden in the subtlety of many of the arguments, once you get past the initial chapters. For example, can the arrow of time be attributed to the time asymmetry of the weak force... or to the collapse of the wave function? Even stripped of math, these topics are really upper-division college level, if not graduate-level. Reading the course comments, it's sadly clear that this class flew way over the heads of many.

For me personally, my main issue with this course was a certain amount of repetitiousness (though understandable given the immense subject breath and the wish for accessibility to a determined lay audience.)

Nonetheless, I certainly appreciate how Sean Carroll brought it all together, with the patience and dogged determination of a star fictional detective. (The word "Mystery" in the title is appropriate!)
In the detective-story analogy, please be aware that the "whodunit" is not fully revealed because, well, it's not fully understood! So, there is a certain letdown by the end. In particular, our own personal perception of time - probably the most fascinating aspect of time to us - cannot be full grasped because, oops, we don't understand how a physical system such as our brain develops consciousness. (Theoretical Neuroscience is my own research area.)

The partial "whodunit" for the Arrow of Time, namely (SPOILER ALERT!) the increasing entropy and the initial cosmological condition of low entropy, is intellectually interesting but may not be emotionally satisfying. Of course, that's not the professor's fault!

Something else that I felt unsatisfying was a certain amount of "hand waving": for example, the collapse of the wave function, which at face value seems a prime suspect for an arrow of time, is summarily dismissed saying, "the arrow of time is not explained by the time-asymmetry of quantum mechanics. The time-asymmetry of quantum mechanics is explained by the arrow of time" (together with brief reference to work in that area - but not a full explanation.)

Likewise, statements like the following one (taken from the accompanying booklet) beg for more explanation: "In the early universe, there were no black holes; there was just plasma and gas spread uniformly throughout the universe. Ordinarily, we think of that as a high-entropy state, but when gravity is important, things change."

I realize, however, that the breath of the subject matter was staggering and that Sean Carroll was bending backwards to accommodate a general audience - in particular avoiding math - and so it's understandable that some elements just got a passing mention.

Like any good "series", this course ends with a fascinating cliff-hanger: a speculative, but somewhat plausible, mechanism by which a universe that has reached high (even maximum) entropy might spawn off a new "bubble universe". For "Season 2", we'll have to wait for more research!
Meanwhile, I'm planning to buy Sean Carroll's 2010 book, "From Eternity to Here: The Quest for the Ultimate Theory of Time": I bet it'll cast light on the parts I felt were too briefly touched upon in this amazing course!

This is Physics in its Magnificence, and I congratulate Dr. Carroll and the high production value added by The Great Courses!

Link to course, including trailer.

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