Lee Smolin has a new book out, Time Reborn: From the Crisis in Physics to the Future of the Universe. His previous subtitle lamented “the fall of a science,” while this one warns of a crisis in physics, so you know things must be pretty dire out there.
I’m not going to do a full-fledged review of the book, which gives Lee’s argument for why “time” needs to be something more than just a label on spacetime or a parameter in an evolution equation, but a distinct fundamental piece of reality with respect to which the laws of physics and space of states can change. (Sabine Hossenfelder does offer a review.) There are also suggestions as to how this paradigm-changing viewpoint gives us new ways to talk about economics and social problems.
Over at Edge, John Brockman has posted an interview with Lee, and is accumulating responses from various interested parties. I did contribute a few words to that, which I’m reproducing here.
Time and the Universe
Cosmology and fundamental physics find themselves in an unusual position. There are, as in any area of science, some looming issues of unquestioned importance: how to reconcile quantum mechanics and gravity, and the nature of dark matter and dark energy, to name two obvious ones. But the reality is that particle physicists, gravitational physicists, and cosmologists all have basic theories that work extraordinarily well in the regimes to which we have direct access. As a result, it is very hard to make progress; we know our theories are not absolutely final, but without direct experimental contradictions to them it’s hard to know how to do better.
What we have, instead, are problems of naturalness and fine-tuning. Dark energy is no mystery at all, if we are simply willing to accept a cosmological constant that is 120 orders of magnitude smaller than its natural value. We take fine-tunings to be clues that something deeper is going on, and try to make progress on that basis. Sadly, these are subtle clues indeed.
“Time” is something that physicists understand quite well. Quantum gravity remains mysterious, of course, so it’s possible that the true status of time in the fundamental ontology of the world is something that remains to be discovered. But as far as how time works at the level of observable reality, we’re in good shape. Relativity has taught us how to deal with time that is non-universal, and it turns out that’s not such a big deal. The arrow of time—the manifold differences between the past and future – is also well-understood, as long as one swallows one giant fine-tuning: the extreme low entropy of the early universe. Given that posit, we know of nothing in physics or cosmology or biology or psychology that doesn’t fit into our basic understanding of time.
But the early universe is a real puzzle. Is it puzzling enough, as Smolin suggests, to demand a radical re-thinking of how we conceive of time? He summarizes his view by saying “time is real,” but by “time” he really means “the arrow of time” or “an intrinsic directedness of physical evolution,” and by “real” he really means “fundamental rather than emergent.” (Opposing “real” to “emergent” is an extremely unfortunate vocabulary choice, but so be it.)
This is contrary to everything we think we understand about physics, everything we think we have learned about the operation of the universe, and every experiment and observation we have ever performed. But it could be true! It’s always a good idea to push against the boundaries, try something different, and see what happens.
I have two worries. One is that Smolin seems to be pushing hard against a door that is standing wide open. With the (undeniably important) exceptions of the initial-conditions problem and quantum gravity, our understanding of time is quite good. But he doesn’t cast his work as an attempt to (merely) understand the early universe, but as a dramatic response to a crisis in physics. It comes across as a bit of overkill.
The other worry is the frequent appearance of statements like “it seems to me a necessary hypothesis.” Smolin seems quite content to draw sweeping conclusions from essentially philosophical arguments, which is not how science traditionally works. There are no necessary hypotheses; there are only those that work, and those that fail. Maybe laws change with time, maybe they don’t. Maybe time is fundamental, maybe it’s emergent. Maybe the universe is eternal, maybe it had a beginning. We’ll make progress by considering all the hypotheses, and working hard to bring them into confrontation with the data. Use philosophical considerations all you want to inspire you to come up with new and better ideas; but it’s reality that ultimately judges them.