Saturday, September 17, 2016

Making Absolute Time Compatible with Relativity

In my last post I mentioned having read Lee Smolin's Time Reborn. I wanted to mention a couple highlights.

In chapter 4, Smolin introduces a great piece of terminology: "Doing Physics in a Box." By this he means "the method of restricting attention to a small part of the universe" (p. 38). This is a more colloquial way of talking about the "Newtonian paradigm." As Smolin points out, timelessness is baked into the method.

Another valuable contribution is in chapter 14, when Smolin introduces the theory of shape dynamics. He points out that cosmology on the largest scales gives a preferred cosmic clock and a preferred state of rest. These are the local standards of rest, for which the cosmic microwave background radiation is isotropic (a red or blue shift to one side or the other would indicate motion with respect to the local standard). But on smaller scales, the temporal free-for-all of general relativity obtains.

General relativity, it turns out, can be reformulated in a beautiful way as a theory with a preferred notion of time. This reformulation is just another way to understand general relativity, but it reveals a physically preferred synchronization of clocks throughout the universe. Furthermore, the choice of that preferred synchronization depends on the distribution of matter and gravitational radiation throughout the universe, so it is not a throwback to Newton's absolute time. Nor can it be discovered by any local measurements, so it is completely compatible with the relativity principle for small subsystems of the universe.

The theory that enables this reversal of perspective is called shape dynamics. Its main principle is that all that is real in physics is connected with the shapes of objects, and all real change is simply changes in those shapes. Size means nothing, fundamentally, and the fact that objects seem to us to have an intrinsic size is an illusion. (pp. 167-168)

"Intrinsic size is an illusion" seems a high price to pay! But it turns out that the theory is only claiming that objects that aren't close by each other can't be compared in size, similar to how in relativity theory, events that are far apart have no unique ordering in time. The example he gives is of a mouse and a box: it doesn't make sense to ask if the mouse is smaller than the box if they exist in different galaxies, since there's no way to try to fit the mouse into the box.

Names Smolin associates with shape dynamics: Julian Barbour, Niall Ó Murchadha, Sean Gryb, Henrique Gomes, and Tim Koslowski.

Lee Smolin's Time Reborn: From the Crisis of Physics to the Future of the Universe (Boston: Houghton Mifflin Harcourt, 2013).

Henrique Gomes, Sean Gryb, and Tim Koslowski, "Einstein Gravity as a 3D Conformally Invariant Theory," arXiv:1010.2481v2 [gr-qc] (2011).

Sunday, September 11, 2016

Lee Smolin and Time

I recently finished Lee Smolin's Time Reborn: From the Crisis of Physics to the Future of the Universe (2013). Smolin is my favorite among the prominent theorists who write for a popular audience. He's an excellent writer, nearly as good as Leonar Susskind (The Cosmic Landscape) at explaining, though at the end of the day, the string theories Susskind explains so well are nonsense. (Smolin made the latter point so well in his The Trouble with Physics, which I also enjoyed.)

Time Reborn was a worthwhile, educational read. What sets Smolin head and shoulders above the rest is that he's an iconoclast and doesn't mind taking an unpopular view. So among other causes, he's sympathetic to Bohmian mechanics(!), and (much more importantly) very clear that there must be a universal reference frame and a single time that unifies the entire cosmos.

Smolin is full of good insights and clearly sees some of the great weaknesses of modern physics, and especially with the field of cosmology and fundamental forces. Smolin sees very clearly that time has been flattened to a spatial dimension, or even a mere parameter, in physics. His discussion here is excellent.

While Smolin is the most philosophical of any physicist who writes for a popular audience, he's definitely not a philosopher. The major problem with the book is that he doesn't consistently apply his own critique to himself—not that that has stopped any modern philosopher from being a philosopher. (Come to think of it, maybe Smolin is a philosopher!) Smolin's ambition is to restore the meaningfulness of time back to physics. A great ambition! But he baffles himself by not having a clear philosophical account of what time is, so he cannot know what it means to restore time, still less can he know whether his ambition is even possible.

His idea is to do away with "timeless" physical laws, so he posits that cosmic laws are evolving and over time come to assume an habitual form. Thus earlier on, things are less determined and they grow more determined as the universe gets older. But if you take a step back, you notice that that this principle is itself a "law" and somehow it escapes Smolin's ban on "timeless laws." He grudgingly acknowledges as much in a later chapter, but doesn't (and can't) do anything to fix the problem.

Actually Smolin's quest for timeless laws is something of a fool's errand. (Not that Smolin is a fool; I think he's just working with a diminished set of principles since he's constrained to the twelve-tone system, so to speak, of modern philosophy, and simply lacks the full pallet of expression.) The point of our thinking philosophically/scientifically is to come up with laws that are always true, that is to say, timeless. But they're timeless in a way that's different from the timelessness that Smolin rightly rails against.

Modern thought patterns itself after Descartes, so without abandoning the sandbox of modern thought, one simply lacks the tools to think about time in the right way. That would be to come to conclusions about time that are always true (i.e., in a properly timeless way), but while capturing time's true nature, a way that is true to the "becoming" of time and the unfolding of real novelty in the universe. Tragically Smolin, as great as he is, is like the proverbial fish who can't notice the medium in which he swims.