Dear Edwin:
I hope you don't mind, but I'm copying a comment that I just left on Johathan Kerr's topic over here because it draws on parts of this current discussion. Also, Edwin, Jonathan, and Georgina, thanks for the interesting and insightful discussion. Georgina, I really like those last Edward de Bono quotes.
Dear Jonathan:
I like your essay. I think you present an interesting analysis of a concept that is very muddled. In particular, I was glad to see you repeatedly bring up the problem with the supposed illusion of time in a block universe. You might like my favourite quotation from Milic Capek, which I think expresses this problem beautifully:
"We shall deal only briefly with an extremely serious epistemological difficulty which arises when time is deprived of an ontological status and reduced to a mere appearance. For in relegating time into the phenomenal world an intolerable dualism is created between the realm of appearances, occurring in time, and the realm of timeless noumena. All static systems from Parmenides to Bradley and McTaggert are plagued by the same problem: If true reality is timeless, *where does the illusion of succession come from?* If time has no genuine reality, why does it appear to be real?
"No solution can be found which would not introduce surreptitiously the reality of time *somewhere*. If the illusory reality of time is nothing but a gradual rising of the curtain of ignorance which separates our mind from the complete and timeless insight, then at least *this process of rising is still a process which unfolds itself gradually without being given at once*; but, by conceding this, we admit the reality of time either in our mind or *between* our mind and the allegedly timeless reality."
For it is this surreptitious element of "time" that enters into the description of a block universe that leads to the intolerable dualism that you've also discussed, which leads to all kinds of paradoxes in working with and interpreting the theory. As you've correctly noted, "in taking that view, the number of phenomena that must be demoted to unreal is large. It amounts to anything that could be called a *process*, and that includes a lot of our world."
But, for this reason, I also think that your description of a block universe doesn't get all the way down to the heart of the issue with it, although I'm certain you do know what that issue is. You described: "The universe is a motionless 4-dimensional block, with no moment called 'now' moving through it anywhere. Instead it has many events and equally important 'now' moments, all sitting alongside each other in a static spacetime grid. This unchanging object it is just *there*." But the thing is, that although we can't avoid the use of verbs in describing what a thing "is", every verb that is used in describing a block universe actually falsely represents it. It's a true dilemma, and I'm not saying anyone could describe a block universe better than you have, but I think that any description of a block universe, which will inevitably require words like "is", needs to be supplemented by saying something like "although we say that a block universe physically 'exists' in its absolute entirety, from the beginning to the end of all four dimensions of spacetime, 'existence' is clearly the wrong word to use in describing a block universe, because although it contains within it a timelike dimension, it no more 'exists' in a temporal sense than a block of wood that comes in and out of existence in an instant; it is temporally singular."
And this is really why any attempt to reconcile the illusion of time with the block universe, as in perdurantism, is a false-start. And it's also the biggest indication that the block universe theory has to be incorrect, because no matter how we try to avoid it, we do commonly get a sense of temporal existence that can't really be reconciled with that singular block. Since the requirement of a block universe can be deduced directly from special relativity theory, something must be wrong at the heart of the theory.
This is all very closely related to the problem that's at the heart of the essentially paradoxical notion of time travel, in which science fiction writers begin with the idea of things actually existing throughout spacetime, (sort of) as in a block universe, but then allow that the events in that "spacetime" are also able to change. Clearly, the notion of a physically existing spacetime that changes requires another temporal dimension---and this is where that surreptitious Newtonian concept of an absolute time comes in; i.e., because the changes that are thought to be able to occur within spacetime, due to a time traveller's influence, are also thought to simultaneously effect all of spacetime. If you could go back in time and kill your grandfather before he met your grandmother, then you never would have been born, so you clearly can't do that---a well-known paradox. But as I see it, my grandfather doesn't exist before he met my grandmother: the event is no longer real. What's real is my typing this right now, which will be past, and therefore unreal, when you come to read it.
Elsewhere on this blog, you've made comments that indicate to me that you think I haven't carefully thought this problem through, and that you think I've been too quick to suggest what I think lies at the heart of the problem with the relativistic implication of a block universe, when I say it is the problem that, along with the assumption that there can be no privileged observers, it is the interpretation that synchronous events, described by constant values of the time-coordinate in any frame, truly occur simultaneously according to observers who remain at rest in those frames---which is what leads directly to the *inference* "that an event can be both past and future in two different viewpoints". Or else, when I say that there must instead be an absolute (global) simultaneity-relation amongst *all* observers in a three-dimensional enduring (i.e., flowing) universe.
This is a difficult stance to argue for, which involves not only having to reconcile with the principle of relativity and the relativity of simultaneity, but also having to justify the need to forsake the principle that there can be no privileged observers (which seems to agree so well with both the principle of relativity and the Copernican viewpoint), and show that the scientific evidence does actually support this.
This is what I concentrated on accomplishing in my essay; but I assure you that I have subjected the problem of the nature of time to rigorous analysis, dedicating nearly eighty pages of my (184 page) thesis to an analysis of the historical, philosophical, epistemological, and physical factors associated with this great problem. Although it may appear that I have presented something that simply works (I can hope you at least saw it that way), I have by no means simply chosen, without a great deal of thought, to reload assumptions that were previously cast off with good (but I think imperfect) reason. This is my response to your remark that "In relativity I'm often suspicious of views in which the weirdness in the theory is removed by pointing out errors that everyone else failed to see for a century. Usually when physicists allow a theory to be weird for that long, it's because they couldn't go anywhere else, and not from lack of trying."
You also wrote to Edwin: "I felt that unlike many, you were grasping at an underlying reality by looking at the clues. That's what makes a paper of interest to me these days, if it's looking for ways forward for physics - it's not enough for it to be trying to rejig existing theory into something it wasn't before. Like you, in my essay I'm grasping at an underlying reality by looking at the clues, and the real clues are external things like observations, not internal things like elements of existing theory.
"To me, for an approach to be relevant in the present situation it also has to be open to there being bits of the jigsaw missing, that we haven't yet found. Many of the essays I've read have implied within them the idea that the pieces we have are enough to finish the puzzle, if we can only organise them in the correct way. And yet a careful look at the clues shows that this idea is unavoidably wrong - new conceptual elements are needed."
I agree with you here, except for the part where I fear you're considering me with the "many" who are unlike you. To use your analogy, if we think of physics as closing in on the completion of one area of a puzzle (say, just for instance, with about ten pieces left to put together), you know that without fitting the remaining loose pieces into the puzzle correctly you can only jam about half (say, five or six) of them in the remaining space. These few pieces are all connected at points, and touch on the completed part that surrounds them in a number of places, but the picture is obviously imperfect and sparse. However, the pieces that have not been carefully fit into their right places *can* be put there by taking a careful look at their shape; but this may require one or two of the other pieces that were set aside because they didn't fit when the first five or six were jammed in without enough care.
Just because I have, in my essay, attempted to take a piece of the puzzle that I think was out of place, and fit it into its correct spot, that should not be taken to indicate that the argument has implied within itself "the idea that the pieces we have are enough to finish the puzzle." To my notion, space-time is, by the definition I've given of an enduring three-dimensional universe, *not* real. It is a graduating map of the events that occur in the universe, which contains within it the effects of things that occurred in the (absolute; purely *ideal* or mental) past. Now, in general relativity, space-time is described as a four-dimensional physical field that is moulded by mass which in turn follows geodesics, so that there is a reciprocal interaction. "Space and time are now dynamic quantities: when a body moves, or a force acts, it affects the curvature of space and time---and in turn the structure of space-time affects the way in which bodies move and forces act. Space and time not only affect but are also affected by everything that happens in the universe."
In my opinion, this quotation from A Brief History of Time poses just as paradoxical a notion as the theory of time travel---which Hawking also considered realistic enough, according to standard relativity, that in 1992 he invented the chronology protection conjecture. For the idea is the same: four-dimensional space-time exists, and bodies dynamically move through it, shaping it moment-by-moment in their presence. Since it is in fact space-time that's warped in the presence of gravitational mass according to general relativity theory, then according to the cosmological interpretation of relativity that I've discussed in my essay, all that might actually be warped is the perception of that unreal coordinated map of events.
If we choose to postulate absolute time in place of the postulate of the absolute world (according to Minkowski, since the relativity-postulate "comes to mean that only the four-dimensional world in space and time is given by phenomena..., I prefer to call it the *postulate of the absolute world*"), at the sake of having to accept that there *is* a fundamental rest-frame in our Universe, as cosmology came to demand anyway, many of our previous notions will have to fall. But the empirical facts still have to remain the same, so it's true that we will still have to reconcile the physical theory---our interpretation of the mathematics---with the evidence. Therefore, this requires a certain amount of "re-jigging" in order to maintain consistency.
I hope you don't mind this long note: I've found both your essay and your comments to be thought provoking, and I had a lot that I wanted to say in response. I hope you've found my comments to be thoughtful, and that we can continue to have intelligent discussion if you've got anything to add or criticise in response. I think we do have a common goal in mind; therefore, for now, I'd like to leave you with a quotation from Bertrand Russell, which I included in my thesis as an epigraph to the chapter "Against Einstein's Relativity: A Doxographical Analysis":
"I cannot believe---and I say this with all the emphasis of which I am capable---that there can ever be any good excuse for refusing to face the evidence in favour of something unwelcome. It is not by delusion, however exalted, that mankind can prosper, but only by unswerving courage in the pursuit of truth."
Daryl