Now: The Physics of Time

by Richard A. Muller
Norton, 2016, 364 pages
reviewed by T. Nelson

ow, you just know the author of this one is going to say something like “Only now do we have all the physics in hand to understand now.” He doesn't disappoint on that one. But now, as to whether physics understands now now, now that's another matter.

This is an unusual book; even though there are almost no equations (except in the Appendix), Muller clearly had a lot of fun writing it. He's incredibly enthusiastic: it's like listening to the ravings of a math prof who just drunk ten cups of coffee. I just wish I owned the patent on the word “Now”.

Now, this guy is an experimental physicist, so he starts from the assumption that time is a real thing. He says the theory that an increase in entropy causes time has it backwards; it's the flow of time that causes entropy to increase. That's the commonsense view (which, admittedly, doesn't mean as much as it used to), and it pretty much throws any discussion of entropy out the window.

Muller's alternative, which is only presented in the last 15 pages (the rest being a light, nontechnical overview of entropy, relativity, and quantum mechanics), is that time was created in the Big Bang, and its ongoing expansion is the continual creation of new now moments. This sort of makes sense: if the expansion is due to creation of new space, as opposed to stretching the old space, then it stands to reason it's creating new time as well. In the Introduction he writes: “We experience the new moment differently from the preceding ones because it is the only one in which we can exercise choice, our free will, to affect and alter the future.”

But how? The continual creation of new time, he says, is exactly how we experience time. No doubt that feels true, but how are we distinguishing new bits of time from old ones? We experience no such segregation of old and new space; our finest instruments can barely detect the expansion. How can we be surfing on some wave of exciting new time, but still be living in the same old dull space?

When physicists talk about entropy driving time, they usually mean the increasing entropy of spacetime itself due to its expansion, not the thermodynamic statistical entropy in material objects that Muller talks about throughout this book. That's why until recently some of them thought if the universe began contracting, time would run backwards. So it seems a bit unfair to be talking about statistical entropy.

My thinking is the ideas here need more oven time. Instead of being on the verge of understanding time, it seems to me that we're nowhere close. But maybe, as in our passage through time itself, it's the journey that counts.

dec 23, 2016