Dear Ken,
Your response touched on a few points that I think deserve some more discussion, as I indicated before. The first thing I wanted to address was your reference to Einstein's point, 'that we should be suspicious of "asymmetries which do not appear to be inherent in the phenomena"', which you used to support an argument that the beautiful symmetries we do know of, which allow us to use the same laws in *any* inertial frame, should be telling us something about our universe. In this, you may be presuming that a presentist position would be inconsistent with there being something fundamental about the universe that would lead to the symmetries that appear to be inherent in the phenomena.
I've said before that I think there is strong empirical evidence to support the description of an ultimate cosmic reference frame, and therefore an objective "now". I've also said that I *don't* think space-time is just a superdeterministic solution to an initial value problem. I want to add that I *do* think there is an objective maximally symmetric background metric and that the order of objective temporal passage relates to a maximally symmetric foliation. This isn't something I can justify in a post here, so I'll only add that what I have in mind involves teleparallelism, as I think this background metric (de Sitter space) isn't *really* warped in the presence of mass, but rather the metric isn't conserved in local frames where there is torsion, and that's why space-time is described as being warped in such frames. Therefore, relatively speaking, it's a lot more like SR than GR, although we know that teleparallel gravity and GR are equivalent. The main difference with other approaches along these lines, is in the absolute foliation that I think needs to be assumed, which is the point I'm wanting to discuss with you, so what I'd like to do is press your point of criticism with this in mind.
From your comment to Torsten above, I think your criticism might have been referring to the past-future asymmetry, but then I'd ask how it is that that *doesn't* appear to be inherent in the phenomena? I mean, if all the information we ever receive is *always* about events that occurred in the past, and that is about phenomena that never appear to be influenced by future events, then how does a past-future asymmetry *not* appear to be inherent in the phenomena? On the other hand, the background structure I'm referring to has the same t-symmetry that's usually found in most physical theories.
But I also wonder if you're referring to the asymmetry in the description of a photon moving to the left *actually* getting further away from an inertial body than one that's moving to the right because the body is *actually* moving to the right--even though that body should, in its proper coordinate frame, describe a photon's velocity as being the same constant value in all directions of "space". Such a description is necessary if there's to be objective temporal passage and a constant speed of light, and although from one point of view (which you're arguing for) it may seem a bit contrived to argue for these "tilted" descriptions of reality rather than assuming simultaneously occurring events are synchronous in every inertial frame of reference, I'd argue that the alternative seems *far more* contrived.
To begin that argument, I'd say first of all that the symmetry objection isn't really an objection against my view because I think the apparent symmetry in the phenomena *is* inherent in an objective background structure of space-time. And second of all, I think a *fair* assessment of what's contrived or not--of what we should be "suspicious of" or not--should openly admit concerns with both sides of the issue.
I think many people have been so concerned with trying to accept the implication of a block universe, that they often forget what's so entirely *unacceptable* about it. In fact, I think many have found some way of coming to terms with the idea precisely *because* they've completely missed what is so entirely unacceptable about it. From what I read in your essay and your above reply to Torsten, and even by your argument that our knowledge of space-time symmetry should be taken to indicate something about what's inherent in the phenomena, I don't think you fall into the latter camp. By this, I mean that I don't think you have the wrong idea about an all-at-once block universe, as some people have, who think relativity should be taken to imply something like "all of space-time exists"; but by your argument that you think we should consider our knowledge--our empirically verified description of symmetries, etc.--as indicating something about reality, I think you *are* forgetting just how totally at-odds the all-at-once view is with *what we know*.
I've been thinking a lot about the block universe idea, and particularly about what it can't be taken to mean, which a large part of my essay concentrated on; and I think the best way of getting some clearer idea without sneaking another dimension into the view, is to state its meaning in two ways: (i.) "nothing *exists*", where emphasis is placed on "exists" because the concept of anything existing implicitly assumes a dimension of temporal passage that, in this case, isn't the time-dimension of space-time, but would be another one, of the same form as the time-variable of classical mechanics; and (ii.) "everything doesn't exist", where everything refers to all of eternity, as reality all-at-once, which does not exist. Another way of stating this is that the block universe interpretation of relativity considers that the theory describes reality as all of eternity, but does not describe reality as *being* all of eternity.
Nothing about this view is consistent with what we know of reality. So many people have worked to come to terms with it, only to end up with a view in which all of eternity is supposed to *exist*. They think of the apparent passage of time as an illusion that occurs "as our consciousnesses crawl upwards along the life lines of our bodies", etc. But we know that this sneaks in another dimension that's not there in the physical description; that the dimension that *would* describe existence, as it did in classical mechanics, is already used up in space-time. So nothing can exist. The four-dimensional world all-at-once 'is' temporally singular.
This is why I indicated that in trying to come to terms with, and make use of the block universe theory, I do think you've come to neglect the significance of the issues that there are with it; i.e., because you're arguing that space-time symmetry should be telling us something fundamental about the world, about what "appears to be inherent in the phenomena", and yet you're using this to support a view that's inconsistent with anything existing. And there is nothing more blaringly obvious about reality than the fact that it exists. Things happen as it exists, and we describe those happenings by putting them in order of spatio-temporal occurrence. It *is* an error to then think of that description as something that exists; and I think it's just as wrong to think of reality as that description--as the mathematical model, sliced up as we choose to do because of its symmetry--but with nothing *existing*.
So, I've told you how I think relativity theory can describe existence. I've taken standard arguments that have been given *against* existence--relativistic thought experiments that clearly show the relativity of time, as described from different perspectives--and I've explained how I think it's wrong to define the synchronous events that are described in arbitrary inertial frames as simultaneous.
You asked, "Should I be making these adjustments to my reality every time I design a laboratory experiment? Do the half-lives of radioactive atoms fundamentally change as I drive them around town?" No. The principle of relativity, and therefore relativity theory, allows that we can describe everything from the perspective of an arbitrary frame of reference; in regard to the half-lives of radioactive atoms, I could hop into a spaceship right now and fly for the rest of my life at some relativistic velocity and when I die the Universe would be a heck of a lot older than it will be when I die if I just stay put; but this doesn't mean that there is no ultimate cosmic rest-frame--it just means that you can do physics without knowing what that frame is. But that doesn't mean that there *isn't* an objectively true geometry and actual objective temporal passage; actual existence.
You wrote, "But just because there are situations where such an analysis might be (arguably) more natural, there are certainly situations where it's *far* from natural. I'm concerned you're cherry-picking the former examples in place of the latter". But I've taken standard thought experiments that have been used to show the relativity of simultaneity, and turned them around to show how simultaneity can be taken as an objective relation while synchronicity depends on motion with respect to the objective rest-frame. Recall the above example in which you and I are holed up in the cabin of a ship, which is roughly along the lines of what I wrote in my essay this year. If you were referring to this when you said my analysis might be arguably more natural, I think I should point out that this is *exactly* the type of thought experiment that's usually taken to indicate that the description of time and the synchronicity of events given from different points of view is relative. All I've done is to take the standard thought experiment a step further and explain the paradoxical implication regarding simultaneity from the perspective that something is *actually* in motion, with reference to its surroundings, despite the fact that there aren't any forces acting on it.
Also in my original post above, I wrote that "On my essay page, I've also opened up a discussion involving a thought experiment from Brian Greene's Fabric of the Cosmos, which clearly demonstrates the relativity of synchronicity, and I've described how I think that should be correctly interpreted, and what I see as being wrong with the usual interpretation." This is a standard thought experiment that's stated clearly so that anyone with an interest in the physical world can understand it and be convinced of the relativity of simultaneity, and I've tried to explain how objective simultaneity works in that scenario.
The point is that I'm hardly cherry-picking by considering the same illustrations that others have used to show that there is no objective simultaneity relation, and explaining what I think is the error in their reasoning.
All the issues that have been contrived based on the theory of relativity stem from the simple fact that because everything can be described in isolation, without reference to an external world, people have wanted to conclude that there is no real external world. They've looked at the world through rose-tinted glasses in order to justify calling it red--i.e., they've denied objective reality, which is the one thing through which the whole theory can make sense, and through that denial they've concluded that we live in a paradoxical world, albeit with beautiful symmetries, that makes no sense.
Consider the twins paradox, for example. The reason for all the fuss is that, according to relativity theory, since, by construction, both twins are always in inertial reference frames, one has to admit that either of them must be able to describe himself as always remaining at rest while his brother goes on a journey. But if we situate the twins in reality, there's just no way to reasonably argue against the fact that one twin in particular *actually* hops from one frame of reference to the other *and this completely resolves the paradox* (see, e.g., Schutz's Intro to GR book, at the end of the SR chapter).
When the "paradox" was first contrived, the motions of celestial bodies were thought to be completely random, so there was reason to see some validity in the "paradox"; but even amidst this worldview, when constructing his cosmological model in 1917, Einstein noted that the velocities of the stars are all much less than c--which one wouldn't expect if one thought that random stellar motions should be uniformly distributed on the allowed interval--and used this to support a simplifying assumption that there is a cosmic frame of rest with respect to which the stars all have some small amount of proper motion.
This brings me to cosmology, which everyone who argues for pure relativity seems to want to neglect. Since the ultimate point of debate has to do with the question, "is there, or is there not, a Universal frame of rest?", I simply can't understand how it could be considered justifiable to neglect the cosmological evidence. Since the point is that regardless of whether there is a cosmic rest-frame, relative to which everything in the Universe can be described as "*really* moving", Lorentz symmetry allows us to describe events from whatever frame of reference we'd like, that point can't be used as grounds to claim that there really is no cosmic rest-frame. That really is just like looking at the world through rose-tinted glasses in order to justify claiming that it's tinted red.
Einstein argued that since the theory can be derived without assuming there is an absolute reference frame, the law of parsimony urges that we make no such assertion. All I'm arguing is that he pushed parsimony too far, without initially grasping the implication that this would have for existence, and how badly the theory would conflict with the apparent flow of time and consciousness--and that the assertion that there is no cosmic rest-frame is now perfectly well understood to be at-odds with the empirical evidence.
So, I've gone on to show how the implications of relativity theory that seem at first to be paradoxical can in fact be interpreted in a way that makes sense intuitively, when the assumption of a cosmic rest-frame has been made. And I've argued that the cosmological evidence supports that assumption. For, even neglecting the CMB, it's obvious from galactic redshifts that there is a cosmic frame of rest. The galaxies all have some proper motion, but aside from those that are very close to us, their proper velocities are negligible compared with an isotropic redshift-distance relation. Assuming homogeneity of space (and a natural interpretation of the fact that the redshifts aren't, say, constant, but do increase with distance), we arrive at the conclusion that space is expanding in cosmic time, and we get a very good fit to the data when we do assume that the redshifts are entirely due to this cosmic expansion. But the evidence for a cosmic rest-frame doesn't end there: our interpretation of the detailed anisotropy signature in the CMB is based on the hypothesis that the effects of vacuum fluctuations in the early universe would have expanded along with space--and the model fits very well with the same parameters that have been constrained by other means. Furthermore, although proper motions of galaxies through space (including our own) are negligible in the redshift-distance relation, from the CMB dipole anisotropy we can actually infer precisely how quickly we're travelling through space; i.e. we can go a step beyond the inference from the redshift-distance relation, that there must be *some* cosmic rest-frame, and we can actually measure our own absolute motion--which is something that no one a hundred years ago thought we could ever possibly do.
I'm sorry: I know this is a long post, and I know that my argument conflicts with the basic premiss of your essay; but I think, from your essay, that certain positions I've taken in this argument *are* consistent with your own views, so I'm hoping you'll be willing to fairly consider what I've written. As I said before, from a quantum mechanics point of view I admit that you may have an argument that the block universe is better; but since you based your premiss on relativity, I wanted to explain why I think the points you make in your argument are in conflict with the premiss, as those same points can be used to argue against it.
I respectfully request that you consider my arguments somewhat more carefully, as they not only relate to your essay, but you've even indicated a greater interest in arguments against a block universe on this page. I assure you, as I've said here, that I've made no attempt at "cherry-picking", but have done my best to meet standard thinking about relativity that supports the block universe view head-on.
Thanks for your time,
Daryl
