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.
like sands through the hour glass, so are the days of our lives.
+/-
Low entropy beginnings… SBC notes:
“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.”
Is the emergent complexity of life just an effect of turbulence in the march toward an entropic maximum ?
Charge and balance: is technically accurate measurement of the components of our material world capable of becoming an explanation for its stability?
“Time’s direction ” is not contained by or limited to the “arrow” analogy.
I still don’t get how the ‘Arrow of Time’ notion helps to explain time.
It explains an undoubtedly fascinating idea that the universe moves from lower to higher entropy. And, sure, that takes time. That is amazing , no argument.
But does it do anything to explain time?
” “Time” is something that physicists understand quite well.” Ha ha ha ha ha
Sean, honestly, you still need to concentrate more on the word, rather than the concept; get the word, and the understanding will follow. It’s all (ssshhh) – about events. Time is an abstract, remember
Eric,
Please see C.F.T.’s comment in Sean’s most recent blog entry; Morgan, Jon, and the Mystifying Balloons. That’s what I meant.
Brett, you are still being far too coy. I really have no idea what idea you think I was conveying in my remarks or if you agreed with them or vehemently disagreed. I think supersymmetry is generally presposterous in view of the CC and in view of the lack positive results so far at the LHC. I thought I conveyed that but perhaps you did not get that. Did that go over your head and you are attacking me for not believing in supersymmetry? Or did you understand my disagreement with supersymmetry and are attacking me for that? I’m just picking at pieces trying to understand your completely nonunderstandable response.
It seems to me you are acting like a belligerent person in a bar looking for a fight. Sorry, can’t oblige on something as ridiculous and incoherent as your response was.
Whatever, I appreciate Lee’s attitude. Always trying to think out of the box.
Which is IMHO the right aproach for getting out of the mess that theoretical physics is currently in.
Time is nothing but a measurement of human construct, uncertain at best. =
It was a joke Eric, jesus tap dancing christ, I was agreeing and building on your comment,
you: “For every non-snarky comment we must include a snarkladen one to create neutrality and to make us all feel terrible after reading internet comments. It only makes sense!”,
me: “it also has to be convinced of superiority while being factually inaccurate”,
It’s not a critique of you…wow.
Thanks for that. I don’t know you, nor have I followed comments by you on other threads, so there just wasn’t enough information in your original reply or followup to know. On the internet a person is just a disembodied voice with few clues, that’s why I was asking for clarification all along. Which I’m finally getting… It all goes back to snark. Without context there is just far too much snark on the internet. You really have to know someone well before snark works, or is even appropriate.
I’m glad to know your reply wasn’t itself snark. I just didn’t know.
Our observations about the unidirectionality of time — fundamental or not — raises an interesting question about whether the spacelike and timelike dimensions are fully equivalent labelable spaces.
First, thinking of it statically… This is probably an unnecessarily complicated way to think about treatment of the spacelike axes and timelike axis under a rotation…
If we do something along the lines of the ADM-formalism and foliate the spacetime 4-manifold into a series of spacelike surfaces, an object that retains the same spacelike coordinates in each surface (call it x,y,z remaining fixed as measure by a stationary observer at infinity whose clock ticks one second for each second on the t index, for easiness) its worldline is recoverable as a timelike curve when merging the family of surfaces back into the 4-spacetime. “Reusing” (x,y,z) at each of several “t ticks” is pretty natural.
What happens if we instead foliate the 4-spacetime into a 3-spacetime indexed by a spacelike axis, and then try to recover the worldline of a test object held fixed at some (x,y,t)? Is there a plausible observer who can see “reuse” of (x,y,t) at each of several “z ticks”? Physically that would be something like an instantaneous snapshot of a vertical string, I think.
Dynamics seems to expose a derivative of reusability in the form of (a)causality.
In the first case, we can at each tick of the index “t” vary a test object’s position along “x” by some amount “left” and “right”. The recovered worldline is sensible, and is seen all the time in Minkowski spacetime diagrams that use (x, ct), or (x, t) because we want to set c to unity for ease. If we draw (z, t) we see a vertical line. If we draw the whole thing we see a worldline that we expect is timelike for all observers.
In the second case, where we are using z as an index, how do we interpret the resulting Minkowski diagrams if we move the test object “left” and “right” along the x axis? Since t is constant then the we get spacelike intervals in (x,t) and (z,t), and there are probably no observers at all that would see a timelike worldline.
The same happens if we vary y.
We may or may not get something causal out the other end if we vary t. Obviously if our test object is smoothly always-moving and always-futureward at less than the conversion factor, then we wind up with a (z,t) worldline that is timelike, even if we don’t move along t at a constant rate. Eliminating the smoothness of the always-moving produces interesting results, and the results of moving the test object in the pastwards direction seem jarring as the worldline exits the light cone.
But is it so jarring as to be *unphysical*? Isn’t this roughly Wheeler’s electron?
So, is it that “slots” on the timelike axis aren’t really reusable (except via a loop — modulus style — assuming CTCs are OK) whereas “slots” on the spacelike axes are? Or is this something that is a side-effect of a foliation approach, or with recovering a 4-spacetime from the set of 3-hypersurfaces in general?
Or am I just wrong and/or confused? Very likely the latter. 🙂
Scott Aaronson asked similar questions about the reusability of time here, although I am inclined to think that time really is “reusable” as long as one pays attention to symmetries and degrees of freedom ( http://en.wikipedia.org/wiki/One-electron_universe ). I think he thinks too hard about the sign difference in the metric signature and has concluded wrongly that it’s because of something fundamental about the timelike dimension.
http://www.scottaaronson.com/blog/?p=368
I’m sceptical about this whole “ontology” business which motivates all of this. You can apply the time evolution operator to map some initial state to a future state, and then say that the future universe is physically the same thing as the initial universe.
Reading the original writings of Copernicus, Galileo Kepler and Newton, I sometimes have the impression that we’re back into Aristotelian thinking when hearing things like “naturalness” and “fine tuning”. Are these ideas the modern-day equivalents of the “perfect forms” (spheres, Platonic solids, circles) of the Aristotelian days ? Are we looking for the principles of the Mysterium Cosmographicum, based upon the idea that the universe should follow our preconceived ideas of what it ought to adhere to ?
Copernicus was still in that mindset ; Kepler started out in that mindset, and did the amazing thing of letting the data (from Brahe) overrule his preconceptions ; Newton finally rejected it.
Now that we don’t have any data to guide us, are we back to guessing what nature ought to do (not have “unnaturalness” ; not to “fine-tune” ; … ) ?