Lessons from the Block Universe by Ken Wharton

"...there's no objective way to distinguish an initial boundary condition from a final boundary condition without resorting to our time-asymmetric intuitions that don't apply in a block universe."

Nice.

This idea of "introcausality" just may hold the key to the preservation of continuous function physics in a way tractable to machine-computing algorithms, i.e., finite methods.

Intriguing insight, with a clearly defined research path. Thanks, Ken.

Tom

Hi, Tom. Ken's arXiv:0706.4075 was mentioned to me on Friday by David Miller in Sydney, so finding this FQXi essay hours later was a surprise to me, both in timing and, by comparison, in content. In response to your comment, I guess I don't yet see that Ken's research path is clear.

Hi, Ken. I'm sorry to say that I have all sorts of trouble with details of your essay. I've been doing mathematics of quantum fields and of random fields for some time, a small part of which is outlined in my FQXi essay. The mathematics is avowedly set against a block-world Minkowski space -- I s'pose anyone who works in QFT would be s'prised to be told they ain't working in terms of block world /models/.

I note that discussions about placing initial and final conditions on our models are academic, insofar as we only have empirical data about the world-tube in the universe that our world (or, more solipsistically but in a similar world-tube sense, my body) occupies in the block-world. And, at any moment of our effective psychological present, our data is limited to what we actually have gathered and recorded in the past.

I could take issue with almost every paragraph of your paper, but I will instead pick your last paragraph's comment that "physicists would be better off using the block universe to re-envision quantum theory from scratch". This is part of what I would say I have tried to do (you will judge to what extent I've succeeded), however I have no ontological commitment to the block world, it is merely a useful way to organize our empirical data (which is always only about the past, albeit the past is always increasing, and of limited detail), and our approximate predictions about the empirical data we will gather in the future.

Over-briefly, I will say of one detail that your strictures about particle configuration space in quantum mechanics do not apply once we model the world using quantum or random fields, at least on my essentially statistical field-theoretic interpretation. Additionally, however, as soon as we speak of statistics in Physics we have to identify an ensemble, for which we have to identify distinct regions of space-time as measured to be similar enough for them to be put together as an ensemble, but measured to be different enough for the statistics to be nontrivial (interesting and/or useful is good too). This is hard enough if we use a Minkowski space background, but much easier then than if we run experiments against a dynamical curved space background. The point for your view is, I think, that insofar as the experimental verification of a model requires ensembles and statistics, this requires more mathematical structure than a block world has traditionally provided.

To put what I think is a significant question as well as my position rudely, do you see your block world as an ontology or as an effective ordering principle for empirical data? You put your heart on your sleeve for a block world, but to me you don't give a strong enough sense of your philosophical intentions. Feel free to reply expansively; it's your comment thread.

Despite the above, I have commented here because of some common feeling with your essay.

Hi Peter. You write "Hi, Tom. Ken's arXiv:0706.4075 was mentioned to me on Friday by David Miller in Sydney, so finding this FQXi essay hours later was a surprise to me, both in timing and, by comparison, in content. In response to your comment, I guess I don't yet see that Ken's research path is clear."

It's clear to me.

Ken is quite correct that quantum mechanics did not evolve from a block universe model. The relativistic block universe came to us mathematically complete; quantum mechanics was knitted from experimental results. The addition of field theoretical quantum physics (e.g., your model) attempts to restore continuous function analysis to discrete phenomena.

I doubt that the David Miller you mention is the Karl Popper protege and scholar at Warwick U., U.K., with whom I am acquainted, but if he were, he should appreciate Ken's bold conjectural approach toward this problem. I know I do, and although Ken can speak for himself, if it's philosophical intentions you demand, I stand firmly in the Popper camp.

The research direction in Ken's work that I find clear--as I stated--is the possibility of strict computability, i.e., of an algorithm to model discrete phenomena that explains why the universe appears to obey continuous functions.

Tom

Tom, I agree that QM didn't evolve from a block universe model. I think, and I think you accept in your comment, that relativistic quantum fields do, now, largely adopt a block world ground. You know, but Ken presumably doesn't yet, that I work with continuous models not because it's how I think the world must be, but only because /I/ find it convenient, as of now, to do so, even though the finite number of finite accuracy measurements that we can make and record cannot possibly justify a continuous model.

I guess the David Miller I mentioned appreciates something about Ken's work, at least in relation to mine, because he was reminded of Ken's work, and suggested it to me, upon seeing my FQXi essay, which I had asked him and a few others in Sydney to look at. This is a David Miller who wrote "Realism and time symmetry in quantum mechanics", Phys. Lett. A222, 31-36(1996). His web-page in Sydney is at http://www.usyd.edu.au/time/people/miller.htm.

I appreciate the empiricist sentiment that citing Popper claims, but most Physicists and Philosophers of Physics are influenced enough by the devastating mid-century critiques of positivism that it's important to know in what ways they accommodate those critiques. Claiming to be Popperian no longer adequately informs us of your point of view.

I perhaps fail clearly to discern Ken's research path more because of the pairing of Ken's FQXi essay with his arXiv:0706.4075 than because of either of them taken separately. I worry that a block world structure is not a sufficiently strong guiding principle by itself for constructing a new mathematics, and I don't see clearly what other mathematical or physical principles Ken advocates.

Great essay, Ken. As you know from our meeting at Perimeter this fall, we agree on the use of a blockworld for fundamental physics. I've two comments/questions:

"Doesn't this imply that we need to come up with a more expansive view of space-time that is somehow compatible with both quantum theory and relativity? Balderdash. ... GR is the correct tool to ask questions about space and time."

GR has (at least one) temporal pathology, namely closed time-like curves (CTCs) allowing for self-inconsistency, e.g., a particle looping around a CTC segment so that it strikes itself before it entered the CTC segment, thereby keeping it from entering the segment to begin with. How do you propose GR be modified to rectify the existence of such CTCs and how is this incorporated in your formalism?

"So far, the closest approach to the block universe is the 'de Broglie-Bohm Interpretation'."

The Relational Blockworld (Foundations of Physics 38, No. 4, 348 - 383 (2008), quant-ph/0510090) is consistent with your argument that blockworld time be made compatible with quantum physics. The main difference between your approach and RBW is that RBW is fundamentally probabilistic so we don't have "to reinvent every single piece of quantum theory in a block universe framework." On the contrary, quantum physics as it stands makes perfect sense in RBW. [Our essay will be posted this week.]

A BW kindred spirit,

Mark

"Gradually the conviction gained recognition that all knowledge about things is exclusively a working-over of the raw material furnished by the senses. ... Galileo and Hume first upheld this principle with full clarity and decisiveness." --(Albert Einstein, Ideas and Opinions)

Hello Ken,

You write, "Our time-asymmetric intuitions make it difficult to be objective when considering the nature of time. But these difficulties can be overcome by using the framework of the "block universe", where every event is mapped onto a static, four-dimensional structure. In this perspective, time is represented as a spatial dimension, so the block universe can never "change"; there is no additional time dimension for such a concept to even make sense."

Actually Godel had a huge problem with the block universe, as it implies time travel while denying the flow of time. Godel pointed out the paradoxical "timeless" implications of the block universe, as well as its inability to account for time as we experience it, and this problem has largely been swept under the rug, along with curiosities such as quantum entanglement, nonlocality and all the dualities--space/time, energy/mass, and wave/particle. Today we are told that that is "just the way things are" and not to worry about it. Perhaps this helps explains why physics has not really advanced in the past thirty years... for Einstein stated, "curiosity is more importnat than knowledge."

The block universe is an human-constructed artifact of certain interpretations of relativity, as physicists glossed over the fact that x4 or "ict" is very different from the three spatial dimensions, x1, x2, x3. But Einstein and Minkowski had it right there in Einstein's 1912 manuscript: x4 = ict. Ergo, if time moves, so must x4. My paper discusses the fourth expanding in far more detail.

Time as an Emergent Phenomenon: Traveling Back to the Heroic Age of Physics by Elliot McGucken

--http://fqxi.org/community/forum/topic/238

Yes--this block time paradox/problem was swept under the rug on many levels, as well as the EPR paradox, and it is great that fqxi allows a forum to discuss such curious phenomena of our physical reality. MDT's simple principle, celebrating a hitherto unsung universal invariant--the fourth dimension is exapnding relative to the three spatial dimensions--provides a physical model liberating us from Godel's block universe while also accounting for the "spooky" action at a distance in the EPR Paradox.

You should read A World Without Time, by Palle Yourgrau

"For Godel, if there is time travel, there isn't time. The goal of the great logician was not to make room in physics for one's favorite episode of Star Trek, but rather to demonstrate that if one follows the logic of relativity further even than its father was willing to venture, the results will not just illuminate but eliminate the reality of time." -A World Without Time, Palle Yourgrau"

MDT posits that time travel into the past is not possible, as the past does not physically exist--an observation in line with all empirical observations. MDT chooses Godel, Einstein, and Minkowski over Star Trek.

You write, "This essay argues that the block universe is by far the best framework for physical theories, as general relativity is simply incompatible with any alternative."

General Relativity is completely compatible with MDT, as MDT's physical reality underlies all of relativity--indeed, relativity is derived from MDT in my paper. All of quantum mechanics is also completely compatibel with MDT.

You write, "The only part of physics that does not fit into such a "block" picture is quantum theory, as it was not originally developed in a block-universe framework. But far from implying that the block universe is incorrect, I argue that we can instead use lessons from the block universe to reconstruct quantum theory in a manner compatible with general relativity." Quantum gravity exists neither in reality, nor in any consistent theory.

You write, "Balderdash. Looking to quantum theory for answers about space-time is like looking to a roadmap for answers about geology: it's a tool designed for something else entirely."

Every physical measurement made of physical reality is governed by quantum mechanics. So please do not throw out all empirical evidence in contemplating the physical nature of time.

You say, "The solution to this dilemma is not to jettison the block universe; without the block universe we would never be able to make sense of relativity."

Actually, my essay liberates us from the block universe, while providing a *physical* foundation for relativity, while unfreezing time and providing a *physical* mechanism for entropy, nonlocality, quantum entanglement, all the dualities--wave/particle, space/time, mass/energy--and time and all its arrows and assymetries across all realms, as well as the pervasiveness of Huygens' Principle.

You write, "Instead, the solution is to reinvent every single piece of quantum theory in a block universe framework. It's a daunting task, but I'll outline how it might be done after I discuss why quantum theory can't just be "tweaked" into a block universe framework." Is this not what the quantum gravity regimes and string theorists have spent hundreds of millions of dollars trying to accomplish, with naught to show for it? As MDT shows that the block universe does not exist, there is no longer any need to send postdocs and graduate studnets dashing down dead-end roads. Indeed, we live in a strange era where physicits try to advance physics by paying other people to work out the details on their non-theories, raising funding by merely promising that they are on to something big, which oft neglects physical reality as a foundational premise.

You write, "So what happens to the "wasted" information in ø for those unperformed measurements? Well, in the Copenhagen interpretation, much of that information gets erased forever thanks to the "collapse" of the wavefunction. At this point one might ask: What is the point of using a high-dimensional configuration space to encode extraneous information that just gets erased anyway?"

By conducting physics in realms safe from measurement, as well as simple logic and reason and physical reality, one is generally guaranteed a lifetime of funding--a theorem proven time and again by string theory and other anti-theories.

You write, "Counterintuitive though this may be, our intuitions about time are notoriously unreliable. We need to free our intuition from time itself, taking all of our lessons from the static block universe."

Einstein would disagree--"The only real valuable thing is intuition."--Albert Einstein.

To reject *physical* intuition and replace it with the nonsensical block universe MDT does away with seems to go exactly against the spirit by which physics has ever advanced, according to Galileo, Einstein, and other noble physicists.

It seems a preposterous conclusion that quantum mechanics, which works so very well, must be thrown out and reformulated for something which MDT shows there is no need for--the block universe.

"In the long run my observations have convinced me that some men, reasoning preposterously, first establish some conclusion in their minds which, either because of its being their own or because of their having received it from some person who has their entire confidence, impresses them so deeply that one finds it impossible ever to get it out of their heads. Such arguments in support of their fixed idea ... gain their instant acceptance and applause. On the other hand whatever is brought forward against it, however ingenious and conclusive, they receive with disdain or with hot rage - if indeed it does not make them ill. Beside themselves with passion, some of them would not be backward even about scheming to suppress and silence their adversaries. I have had some experience of this myself. ... No good can come of dealing with such people, especially to the extent that their company may be not only unpleasant but dangerous."--(Galileo Galilei)

"my dear Kepler, what do you think of the foremost philosophers of this University? In spite of my oft-repeated efforts and invitations, they have refused, with the obstinacy of a glutted adder, to look at the planets or Moon or my telescope." --Galileo Galilei

We must forver keep physical reality in the front and center, along with logic and reason and *physical* intuition--otherwise progress in physics will grind to a halt, as it has for the past thirty years.

"But before mankind could be ripe for a science which takes in the whole of reality, a second fundamental truth was needed, which only became common property among philosophers with the advent of Kepler and Galileo. Pure logical thinking cannot yield us any knowledge of the empirical world; all knowledge of reality starts form experience and ends in it. Propositions arrived at by purely logical means are completely empty as regards reality. Because Galileo saw this, and particularly because he drummed it into the scientific world, he is the father of modern physics -- indeed, of modern science altogether." --Albert Einstein, Ideas and Opinions

Hi Ken,

This is in answer to your question how RBW differs from your view. First see our essay soon to be posted. Second, read the following:"Why Quantum Mechanics Favors Adynamical and Acausal Interpretations such as Relational Blockworld over Backwardly Causal and Time-Symmetric Rivals" in a focus issue of Studies in the History and Philosophy of Modern Physics on time-symmetric approaches to quantum mechanics edited by Huw Price, Volume 39, Issue 4, pp. 732-747. M. Silberstein, M. Cifone and M. Stuckey. I'll try to attach it.

The general answer however is this: while, like yourself, we take blockworld (BW) as an essential feature of interpreting QM, we don't need to revamp QM, e.g., replace the Schrodinger equation with the Klein-Gordon equation. In the aforementioned paper we argue that retrocausal accounts of QM do not take acausal and adynamical thinking seriously enough and that their retrocausal devices amount to little more than a veiled assertion that in the BW the outcomes of QM experiments are already "there." For example, even Price admits that all such causal talk (retro or otherwise) is merely perspectivial. So the first problem is how to invoke BW in a non-trivial explanatory fashion. We show how to do this with an adynamical and acausal explanation that is fundamental to any dynamical explanation of QM and it involves BW in an essential fashion. Second problem, we show that the experimental set-up known as quantum liar experiment (QLE) is fatal for any purely dynamical time-like or retrocausal account that purports to save locality, while RBW has no problems.

In addition, RBW fully resolves the measurement problem and is fully compatible with special relativity (SR) as it is local while being non-separable and requires no FTL influences or action-at-a-distance. Perhaps most importantly of all, as the essay will elaborate, RBW leads to a completely unique solution to the problem of quantum gravity with profound implications for the various problems of time.

One last minor point. I think you might want to sharpen your claim that QM and BW are inherently incompatible. You seem to think that BW ENTAILS that there is only one outcome for every experiment in M4, while the Hilbert space of QM demands otherwise. But surely this isn't true,after all, Saunders and other Everettians defend the "QM block world" wherein all the outcomes exist in a BW setting. It's true that they must explain why it appears that there are only 3 spatial dimensions or why these 3 dimensions of space emerge from the more fundamental Hilbert space, but there are many such programs. Furthermore, the Everett interpretation squares perfectly with SR and locality. The burden of establishing comparative advantage is especially high for you given your need to radically revise QM.

Another kindred BW spirit.

MichaelAttachment #1: SHPMP557.pdf

Tom,

Thank you for the kind words; I'm glad you found the essay stimulating. As for your discussion with Peter as to whether there is a "clear research path", you're right that certain paths forward are certainly clear, and he's right that this essay (and the arXiv paper) don't exactly make it clear *which* research paths I'm advocating. There are a lot of paths forward, and I'm still not certain which ones are most promising. After all, when going all the way back to 1927 and changing all these fundamental assumptions, the amount of work that needs to be done just to recover known experimental results is truly daunting. (Of course, I have my opinions on how best to proceed, but more on that some other time...)

Concerning your interest in the computability aspect, there's both good news and bad news. The good news (that you point out) is that there's actually something to compute: systems of well-defined equations and well-defined boundary conditions, with solutions of easy-to-interpret classical field values at given points in space-time. The bad news is that by imposing different portions of the boundary conditions at different times, the usual computational technique of starting with the initial solution and then incrementally calculating subsequent time-steps will no longer work. The whole 4D system needs to be solved globally, like a 3D spatial boundary problem. And when one can't solve the equations exactly, it's not at all clear how to proceed computationally. (Ideally, I'd like to "push" the computational uncertainties toward the center of the 4-volume, away from the boundaries.) Any insight on this issue would certainly be appreciated.

Best,

Ken

Peter,

Thanks for your interest -- and no, I certainly don't consider it rude to ask me about my ontology! (More on this in a sec.) By the way, I had already read your recent arXiv paper, and I had been planning to introduce myself once I read up on random fields. This week I'll head over to your own essay and see what I can find out...

>I s'pose anyone who works in QFT would be s'prised to be told they ain't working in terms of block world /models/.

In that case, what's the difference between classical fields, random fields, and quantum fields? As I see it, the moment one takes the classical meaning of the x-coordinate and turns it into an *operator*, one has left the block universe behind. Furthermore, any QFT theorist would admit that many interpretational questions are shunted down to non-relativistic quantum mechanics. (If it were otherwise, QFT theorists could answer all the outstanding quantum mysteries just by taking the non-relativistic limit of QFT.)

>I note that discussions about placing initial and final conditions on our models are academic, insofar as we only have empirical data about the... past.

What about a double-slit experiment that happened back in 2003? Why shouldn't we be able to go back and apply the empirical data as boundary conditions on both the state-preparation stage and the data-acquisition stage of the experiment? That would be a final boundary condition on the intermediate system, but it's all still in the past. (And if that's okay, then we could certainly imagine doing the same thing for possible future outcomes of future experiments as a computational tool for making predictions.)

>insofar as the experimental verification of a model requires ensembles and statistics, this requires more mathematical structure than a block world has traditionally provided.

I wasn't trying to imply that we can get *all* of our answers from the block universe, any more than Einstein was able to derive GR from just the equivalence principle. But I think we can certainly include ensembles and statistics in a block universe; see my next post for more detail.

>do you see your block world as an ontology or as an effective ordering principle for empirical data?

I see the block universe as a framework that is a logical necessity for any physics model that includes space and time. So in that sense it's an ordering principle, but I'm applying it to more than just empirical data. After all, I want to be able to say what happens between quantum measurements, at all points in space-time. The ontology I'm proposing is simply that of classical fields, where all the "quantum weirdness" comes about from the closed-hypersurface boundary conditions on those fields (and a probability that is applied to the whole hypersurface, not just the outcome).

>I worry that a block world structure is not a sufficiently strong guiding principle by itself for constructing a new mathematics, and I don't see clearly what other mathematical or physical principles Ken advocates.

Your worry is well-founded; the block universe is certainly not enough by itself. But in addition to this framework, along with insights concerning space-time from general relativity, the principle that has guided me this far is simply this:

Fundamental physics proposes an underlying ontology to explain empirical data. Einstein taught us the importance of making sure the ontology is consistent when the same empirical data are viewed from different reference frames. I simply want to extend this consistency requirement to time-reversed reference frames.

Every single standard interpretation of quantum mechanics fails on this count; they all give *fundamentally different explanations* for the same empirical data, if simply viewed in the opposite temporal order. Fixing this problem is a very demanding principle, that leads almost inevitably to the type of conclusions that I am drawing. However, I realize that few people feel this type of symmetry is important, so the essay and the arXiv paper each explore different motivations that reach the same conclusions.

Best,

Ken

Hi Mark,

I must apologize for not having written since we met last month; I have your papers on top of a stack of must-read items, but haven't yet been able to devote the necessary time to them this semester. Soon, I promise.

>GR has (at least one) temporal pathology, namely closed time-like curves (CTCs) allowing for self-inconsistency, e.g., a particle looping around a CTC segment so that it strikes itself before it entered the CTC segment, thereby keeping it from entering the segment to begin with.

I think quantum effects save the day here, for two different reasons: one is that we need to replace classical particles with fields, so there's so such thing as an "all or nothing" trajectory (didn't Feynman work out an example like this with a light switch?). The other is that there's no way to prepare the initial state with sufficient accuracy to cause this precise dilemma. In fact, as I see it, the logical necessity of uncertainty principle is that it prevents exactly this sort of paradox. (And these paradoxes would no longer require CTCs if one takes an introcausal perspective where the future is always affecting the past.)

>The main difference between your approach and RBW is that RBW is fundamentally probabilistic so we don't have "to reinvent every single piece of quantum theory in a block universe framework."

I wasn't trying to lump in RBW in with the "established" interpretations; more on RBW after you post your essay.

But I will say that I've given a great deal of thought to how a theory can be "fundamentally probabilistic" and still work in a block universe. I do think it can be done, but not in the way that standard QM's Born Rule is probabilistic: those are *outcome* probabilities, which is a concept of dubious validity in a block universe. The key, I think, is to define probabilities over parameters that are unknown but well-defined. Then, once you know everything, all those probabilities can converge to 1 or 0 (in a block universe, any given event either happens or it doesn't). This is also deeply consistent with a Bayesian interpretation of probability, where probability is just a measure of belief based on available information, not anything fundamental that is somehow "out there" in the static block universe.

Cheers,

Ken

Dr. E,

From your post, and from other very similar posts you've written on other threads, I take it that we are coming at this issue from diametrically opposite philosophical perspectives: you're railing against the block universe, while the block universe is central to my thinking. Apparently the detailed arguments for such a view in my paper have not swayed you, and your post has not swayed me. Perhaps we'll just have to agree to disagree.

Best,

Ken

Hi Michael,

I'm looking forward to your essay... I'll try to carefully read through your papers this week as well.

>...their retrocausal devices amount to little more than a veiled assertion that in the BW the outcomes of QM experiments are already "there."

Wait a sec -- surely if you are using a block picture you must agree that the outcomes are, in a timeless sense, "already there"? I hope your point here is that other approaches merely assert the outcome without giving any tool to determine that outcome's relative likelihood. If so, I have such a tool; a probability measure of the entire hypersurface boundary; it's in the arXiv paper.

>Saunders and other Everettians defend the "QM block world" wherein all the outcomes exist in a BW setting.

I guess I merely dismissed such a picture in my essay without going into details... But I refuse to accept that any Everettian picture is compatible with a block universe until I see their version of general relativity. It would have to explain exactly how all these universes are connected together, something they seem to avoid pinning down. (Actually, I admit that I still probably wouldn't accept it, even then, because it would still violate the guiding principle I spelled out at the end of my earlier response to Peter.)

To me, Everett's Many Worlds Interpretation is the poster child for how awkward it can be to extrapolate non-block-universe concepts to their logical conclusions. Best to start off with block-universe-compatible concepts in the first place.

Cheers,

Ken

Interesting responses to all your commenters. I feel clearer, anyway.

"what's the difference between classical fields, random fields, and quantum fields"

Between the first and the second, classical fields don't work well with probability: if we introduce thermal fluctuations, when we measure the field it will almost certainly be discontinuous (akin to the discontinuous paths of Brownian motion). To accommodate modern physics experiments, however, we *have to have probability* in the mix, which I would /prefer/ to have well-defined. Continuous random fields are the nicest mathematics for introducing probability into a block world of classical fields (at least, I think there's no contest from stochastic methods, such as are used in Stochastic ElectroDynamics, in GRW-type reduction mechanisms, or in Langevin-type equations). Perhaps, although here I am out of my mathematical area, my methods could be called a block world approach to the Fokker-Plank equation.

Continuous random fields are very close to quantum fields, but they are different in commuting instead of being non-commuting at time-like separation. That of course leads to a different measurement theory, which we certainly have to discuss carefully, but so much stays the same that we can feel relatively comfortable with the transition from QFT to continuous random fields. This seems a strong merit for random fields as a mathematics that moves us away from QFT, even if it's only a transition to a better mathematics for fundamental physics.

x,y,z,t are coordinates in QFT and for continuous random fields. The field is an operator-valued distribution, but QFT and random fields are set against a classical manifold. That changes if one moves to the mathematics of non-commutative geometry, but that's not the standard model.

I feel ambivalent about asserting a block world ontology for future events, insofar as I cannot experiment on the future, confined as I am to my psychological present, but a model has to model, aka predict, something about the future.

I'm also looking forward to the RBW essay.

Thanks Ken!

You write, "From your post, and from other very similar posts you've written on other threads, I take it that we are coming at this issue from diametrically opposite philosophical perspectives: you're railing against the block universe, while the block universe is central to my thinking. Apparently the detailed arguments for such a view in my paper have not swayed you, and your post has not swayed me. Perhaps we'll just have to agree to disagree."

There are vast problems with the block universe, including the fact that implies time travel, while offering no mechanism for the arrows of times, nor the assymetries of time. Also, the block universe freezes time, while robbing us of our free will.

These problems are not my mere "opinion," but rather they are realities noted by great minds including Kurt Godel and R. P. Feynman.

MDT resolves these problems, not by ignoring them and glossing over them, but by presenting a hitherto unsung universal invariant--the fourth dimension is expanding relative to the three spatial dimensions at c, distributing locality and fathering time: dx4/dt=ic.

Indeed, MDT finally provides, in Feyman's words, "the thing that makes the whole phenomena of the world seem to go one way."

While begin your essay with, "Our time-asymmetric intuitions make it difficult to be objective when considering the nature of time," Feynman instead embraces physical reality, and sees the ubiquitous presence of time's arrows and assymtries--and MDT agrees with Feynman, that we ought not ignore nature's *physical* reality, and that we need to find "the thing that makes the whole phenomena of the world seem to go one way."

"All knowledge of reality starts form experience and ends in it." --Einstein

And that "thing" is the invariant expansion of the fourth dimension--dx4/dt=ic.

Feynman stated, "Now if the world of nature is made of atoms, and we too are made of atoms and obey physical laws, the most obvious interpretation of this evident distinction between past and future, and this irreversibility of all phenomena, would be that some laws, some of the motion laws of the atoms, are going one way - that the atom laws are not such that they can go either way. There should be somewhere in the works some kind of principle that uxles only make wuxles, and never vice versa, and so the world is turning away from uxley character to wuxley character all the time - and this one-way business of the interactions of things should be the thing that makes the whole phenomena of the world seem to go one way. But we have not found this yet. That is, in all the laws of physics that we have found so far there does not seem to be any distinction between the past and the future. The moving picture should work the same going both ways, and the physicist who looks at it should not laugh."--(The Distinction of Past and Future, from The Character of Physical Law, Richard Feynman, 1965)

MDT also resolves the problems Godel had with a 4D block universe, which allowed time travel, while disallowing the flow of time. Time travel is impossible, because time, as measured on our watches, is an emergent phenomena that arises becase the fourth dimension is expanding relative to the three spatial dimensions at c, or dx4/dt=ic. In his 1912 Manuscript on Relativity, Einstein never stated that time is the fourth dimension, but rather he wrote x4 = ict. The fourth dimension is not time, but ict. Despite this, prominent physicists have oft equated time and the fourth dimension, leading to un-resolvable paradoxes and confusion regarding time's physical nature, as physicists mistakenly projected properties of the three spatial dimensions onto a time dimension, resulting in curious concepts including frozen time and block universes in which the past and future are omni-present, thusly denying free will, while implying the possibility of time travel into the past, which visitors from the future have yet to verify. Beginning with the postulate that time is an emergent phenomenon resulting from a fourth dimension expanding relative to the three spatial dimensions at the rate of c, diverse phenomena from relativity, quantum mechanics, and statistical mechanics are accounted for. Time dilation, the equivalence of mass and energy, nonlocality, wave-particle duality, and entropy are shown to arise from a common, deeper physical reality expressed with dx4/dt=ic. This postulate and equation, from which Einstein's relativity is derived, presents a fundamental model accounting for the emergence of time, the constant velocity of light, the fact that the maximum velocity is c, and the fact that c is independent of the velocity of the source, as photons are but matter surfing a fourth expanding dimension. In general relativity, Einstein showed that the dimensions themselves could bend, curve, and move. The present theory extends this principle, postulating that the fourth dimension is moving independently of the three spatial dimensions, distributing locality and fathering time. This physical model underlies and accounts for time in quantum mechanics, relativity, and statistical mechanics, as well as entropy, the universe's expansion, and time's arrows and assymetries.

Godel had a huge problem with the block universe, as it implies time travel while denying the flow of time. Godel pointed out the paradoxical "timeless" implications of the block universe, as well as its inability to account for time as we experience it, and this problem has largely been swept under the rug, along with curiosities such as quantum entanglement, nonlocality and all the dualities--space/time, energy/mass, and wave/particle. Today we are told that that is "just the way things are" and not to worry about it, nor ask foundational questions. Perhaps this helps explain why physics has not really advanced in the past thirty years... for Einstein stated, "curiosity is more important than knowledge."

"For Godel, if there is time travel, there isn't time. The goal of the great logician was not to make room in physics for one's favorite episode of Star Trek, but rather to demonstrate that if one follows the logic of relativity further even than its father was willing to venture, the results will not just illuminate but eliminate the reality of time." -A World Without Time, Palle Yourgrau"

Too many modern physicists resolve glaring problems these days by completely ignoring them. I think FQXI is sensitive to this--the fact that foundational questions are largely ignored by the modern academy; while those who ponder them are too often snarked.

"Forget time," we are told, while at the same *time* funding is sought for throwing out quantum mechanics and reality, so as to reformulate physics based on the unreal--the human construct of a block universe, while ignoring the real--the ever-flowing movement of time, which emerges because the fourth dimension is expanding relative to the three spatial dimensions at c.

Best,

Dr. E (The Real McCoy)

Thanks for your response, Ken. Hope you're willing to continue this thread until I understand your position.

"I think quantum effects save the day here, for two different reasons: one is that we need to replace classical particles with fields, so there's so such thing as an "all or nothing" trajectory (didn't Feynman work out an example like this with a light switch?). The other is that there's no way to prepare the initial state with sufficient accuracy to cause this precise dilemma. In fact, as I see it, the logical necessity of uncertainty principle is that it prevents exactly this sort of paradox."

I'm talking about classical objects, so the DeBroglie wavelengths are much smaller than the objects themselves. You're not suggesting that such objects be modeled as and exhibit wave characteristics, are you?

Regarding your second point, are you claiming that a classical object won't follow the self-inconsistent CTC simply because that path is highly improbable? If so, what makes it more improbable than any other? What happens when an object follows this improbable path? Or, do you mean impossibility rather than improbability? If so, what makes it impossible?

"(And these paradoxes would no longer require CTCs if one takes an introcausal perspective where the future is always affecting the past.)"

So, are you saying GR needs to be augmented with a self-consistency principle? How is it realized physically? Would I feel a mysterious force pushing the ball out of my hands as I'm about to start it on the self-inconsistent path? Would I suddenly change my mind, asking myself later, "Gee, why didn't I release the ball?"

Thanks again for your patience,

Mark

Ken,

You write "The whole 4D system needs to be solved globally, like a 3D spatial boundary problem. And when one can't solve the equations exactly, it's not at all clear how to proceed computationally. (Ideally, I'd like to "push" the computational uncertainties toward the center of the 4-volume, away from the boundaries.)" I am in full accord.

I envision the computational possibility for a sorting algorithm to perform strongly polynomial time claculations of least path, least energy between t and t' based on your probability calculations of future boundary conditions at t', for any arbitrarily chosen scale. To explain:

My ICCS 2007 paper, necsi.org/events/iccs7/papers/740473b577c92da06ccd77fad70c.pdf, proposes that the flow of information for a random field of complete probable future states to a partially ordered present is indistinguishable--as you have also concluded--from the flow of information past to future.

How about an n-dimensional, 2-point boundary value problem in which the path t to t' is maximally efficient, least action? I compare the classical 2-point boundary, 6 dimension problem of landing a rocket on the moon in shortest path at least fuel cost, with a universal control system in which negative feedback from the future informs the present state. Gravity is, in fact, just such a univeral negative feedback system. In other words, negative feedback informs the present, positive feedback informs the future, and stasis--or neutral feedback--is the aggregated smoothly continuous property of the complex system on the large scale.

As a result, what we call "the present," at an arbitrarily chosen frozen moment of time, is the least of all possible moments. Your block universe is therefore preserved without sacrificing the dynamical properties of an evolving system, and accounting for the closed hypersurface bondary conditions.

Peter, you write "Claiming to be Popperian no longer adequately informs us of your point of view." Fair enough! The philosophy to which I particularly refer is what Popper called "metaphysical realism." (Objective Knowledge; Realism & the Aim of Science.) I think Ken's proposal meets the criteria; future boundary conditions are necessarily metaphysical but not beyond comprehension and indirect measurement.

Tom

Hi Peter,

You may be "ambivalent" about treating the future the same as the past, but I argue it's this precise ambivalence that has let to so many problems when it comes time to reconcile QM with GR. Even though it's counter-intuitive, we need to force ourselves to treat the past and the future on the same footing. After all, *eventually* the future will be past, and we shouldn't have to treat those events differently in our equations once that happens. (Granted, learning about uncertain values makes them more certain, but that sort of thing equally applies to uncertain values both in the past and the future.)

I'll email you with some thoughts concerning random fields and probability... I've recently become interested in a possible overlap between stochastic fields and this two-time boundary framework, and would like to better understand if there's any connection with your own research -- because as you say, there are some common threads between our ideas. (On the other hand, I'm concerned that you're treating probability as a physical substance rather than just a consequence of uncertainty. That doesn't work in a static block universe, because those "real" probabilities must somehow *change* to become some certain outcomes.)

Cheers,

Ken

Hi Mark,

I *am* suggesting that everything is really classical fields, but this is no stranger than a QFT theorist suggesting that everything is really quantum fields -- it's just a question of when you're allowed to approximate those fields as classical objects. (And no fair giving me a far-out scenario, and then appealing to common sense to prevent me from using fields! :-) After all, if one *ever* expects some weird field-like aspect of a macroscopic object to rear its head, it'll be in some sort of outlandish situation like this one...).

I found the Feynman reference -- it was a very similar example addressed in Wheeler/Feynman's 1949 paper (not the 1945 one). Check it out -- they conclude that all these paradoxes rely on an "all-or-nothing" sort of interaction, but once you allow continuous interactions (say, a glancing blow due to a slightly-misaligned trajectory through a CTC) there's always a resolution.

>Regarding your second point, are you claiming that a classical object won't follow the self-inconsistent CTC simply because that path is highly improbable? If so, what makes it more improbable than any other?

Yes, that's almost what I'm claiming. Technically, I'm claiming that the precise initial conditions that would send it on such a trajectory, combined with the precise later conditions on space-time that the CTC exists, have a joint probability distribution that is related to the number of global solutions that satisfy all those conditions. If you postulate that there are no such solutions (as you do), then the probability is exactly zero.

>So, are you saying GR needs to be augmented with a self-consistency principle? How is it realized physically?

Now this question I'm surprised to hear coming from a "Block World Kindred Spirit"... To me, one of the biggest advantages of the block universe framework is that it *is* a consistency principle, in and of itself! Paradoxes can't happen in a block universe, by definition. In a non-block-universe framework, like standard QM, each of these possible paradoxes has to be ruled out, one at a time (although see arXiv: quant-ph/0506141 for David Pegg's excellent take on how QM can do this).

So GR doesn't need any new consistency principle as long as you don't impose so many boundary conditions that there's no solution, and QM wouldn't need one either if we re-build it along the lines I suggest in my essay. I would hope that adding a generic constraint on the allowed boundary conditions would naturally prevent overconstrained problems in classical GR (such as this one).

>Would I feel a mysterious force pushing the ball out of my hands as I'm about to start it on the self-inconsistent path? Would I suddenly change my mind, asking myself later, "Gee, why didn't I release the ball?"

Well, everything's mysterious until you understand it... :-) They've done interference experiments with buckyballs, which are pretty darn big. Is the "force" that keeps those C60 molecules from hitting the dark fringes "mysterious" or not?

Regardless, you wouldn't ever *feel* such a quantum effect; you would just see the end result. That's because if you are measuring one set of parameters (like a force), then Heisenberg says you're losing information about some other parameters, and in my approach it's always in the unknown parameters where the "mysterious" quantum effects would come into play. (After all, the parameters that you measure are imposed as a boundary condition on the system.)

For that last part of your question, it sounds like you're trying to back me into a corner where I have to choose between free will and the block universe. I doubt that such a corner exists, but if it did, I'd come down on the side of the block universe every time. As a well-thought out explanation of why I might feel this way, check out Greg Egan's short story, "The Hundred Light Year Diary" in his collection "Axiomatic".

Cheers,

Ken

Tom,

Thanks for your thoughts on the matter... I'll need to think about how a "sorting algorithm" might do the job. The problem with continuous, classical fields vs. classical particle paths is that the number of options to sort would seem to be much larger in the case of fields. (And don't forget, the field has to consistently solve a set of differential equations throughout the 4-volume. And those are Euler-Lagrange equations that already minimize the action, so that sort of minimization principle doesn't get you anything extra in this case.)

Cheers,

Ken