Essay Abstract

Despite that Minkowski's rigorous arguments for the reality of spacetime impose fundamental limits on our views of the physical world, many papers and books, which deal with the issue of the nature of what exists, completely ignore them as if they did not exist. I am not alone to think that ignoring (and therefore contradicting) such a strict no-go (based on the experimental evidence) is not how science works. That is why, as a case study of this worrying trend, I will discuss Carlo Rovelli's paper "Neither Presentism nor Eternalism" in which he argues that becoming is an objective feature of the world and which is the most recent example of this trend.

Author Bio

One of the founders and current director of the Minkowski Institute. PhD in Physics (Montreal, 1997). PhD in Philosophy of Science (Sofia, 1988).

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Dear Vesselin,

although I disagree with any ideas of reified spaces, your reconstruction of Minkowski's derivation of the necessity of 4D-space is the best and clearest I ever read. And (dephysicalised) it even supports my idea that all frames are equivalent in which the phenomena hold good, i.e. in which the relations between objects (before, behind, within, around, through, along, opposite of, etc.pp.) hold good - not the dynamics of objects!

best,

Heinz

    Dear Vesselin,

    I enjoyed very much to read your essay! Misconceptions about Minkowski's spacetime and his four-dimensional ontology still exist, and even in places where you'd expect better. Your very well explained essay clarifies such misunderstandings. I'm glad to see it here. Indeed, Minkowski spacetime provides a no-go result against absolute time and space, with similar, if not higher importance as other no-go results like Bell's theorem. I wish you success in this contest!

    Cheers,

    Cristi

      Dear Dr. Petkov,

      Your essay clearly accomplishes your goal, arguing that Minkowski spacetime does not allow for objective becoming. However, you seem to accept Minkowski spacetime as settled fact. The only true facts are validated observations. Everything else is interpretation of those observations, based on reasonable and accepted assumptions. But assumptions are not observable, and agreement on reasonable and accepted assumptions, no matter how widespread, is not proof of their truth, as the history of physics has demonstrated time and again.

      In my essay, I start with an empirical model of observations as the starting point for physical description. I then consider various assumptions that underlie various conceptual models of physical reality. I conclude that the most reasonable conceptual model, in fact, does accommodate objective becoming, and that the conventional physical interpretation, on which Minkowski spacetime is based, is an idealized special case that does not in fact exist.

      I hope you will take a careful read of my essay, consider the validity of the implicit assumptions that underlie conventional physical interpretations, and share your thoughts.

      Thanks.

      Sincerely,

      Harrison Crecraft

        Dear Heinz,

        Thanks for your comments and specifically for "I disagree with any ideas of reified spaces." I've done my best to show why Minkowski did not reify his die Welt (the World, i.e. spacetime). First, mathematicians do not have this habit. Second, Minkowski excitedly announced the new radical views of space and time (the excitation is much more intense in the draft version of his 1908 lecture) - even this demonstrated that Minkowski believed his arguments proved the reality of (the four-dimensional) die Welt; otherwise there would have been no reason for excitation - mathematicians do not get excited by a four-dimensional mathematical space.

        But this is, of course, not an argument in the essay. The main point of the essay is that Minkowski's arguments prove the reality because experiments would be impossible if spacetime were not real. In other words, the main point of the essay is that the reality of spacetime is not just assumed (reified), but proved by experiments. Please see my answer to Harrison Crecraft below on whether Minkowski's arguments can be objected by stating that experiment have different interpretations.

        Best wishes,

        Vesselin

        Dear Cristi,

        Thanks a lot! I guess you are aware that such misconceptions are often caused by inadequate views on the nature of physical theories (e.g. one can hear "theories are just descriptions"). Perhaps, the saddest example of how such inadequate views can prevent even great scientists from making a discovery is Poincaré's failure to discover the spacetime structure of the world. He believed that our physical theories are only convenient descriptions of the world and therefore it is really a matter of convenience and our choice which theory we would use. As T. Damour stressed it, it was

        "the sterility of Poincaré's scientific philosophy: complete and utter "conventionality" ... which stopped him from taking seriously, and developing as a physicist, the space-time structure which he was the first to discover."

        (Colleagues, interested in the drama of the discovery of spacetime by Minkowski and Poincaré can find more details on http://www.minkowskiinstitute.org/born.html, including facts which appear to indicate that Minkowski arrived independently at what Einstein called special relativity and spacetime, but Einstein and Poincaré published first.)

        Best,

        Vesselin

        Thanks a lot for your comments and particularly for "Everything else is interpretation of those observations" (although I am not sure I understand what you mean by "The only true facts are validated observations").

        Regarding your comment "you seem to accept Minkowski spacetime as settled fact", please see my answer to H.H.J. Luediger above on what makes me think so. I suspect you may object that, for example, the experiments which confirmed the relativistic kinematic effects (that I wrote would be impossible if spacetime did not exists) have more than one interpretation.

        If you really think so, then you can have a look at the more visualized version of Minkowski's explanation of length contraction (see p. 40 of http://spacetimecentre.org/vpetkov/TheUltimateJudge.pdf); the two figures below are from the article - both the theory and the experiment say that the contracted meter stick (Fig. 1) contains three colours, but this is only possibly if the meter stick exists equally at all moments of its history in time (Fig. 2), which proves the reality of spacetime.

        I believe this thought experiment clearly demonstrates that length contraction (and more generally relativity of simultaneity, because both length contraction and time dilation are specific manifestations of relativity of simultaneity) have a single interpretation.

        Also, I think technology is probably sufficiently advanced to make such an experiment possible. But no one would spend any money on it because it is absolutely certain that any experiment would prove what is depicted on Fig. 1. Unless, a billionaire, interested in science, decides to support such a project....

        Best wishes,

        Vesselin PetkovAttachment #1: BlockU.jpg

        Dear Vesselin,

        I couldn't agree more that the Block-Universe view is not taken seriously enough. However, for the BU view to have any physical consequences, one needs to represent those (extended) world-lines in it or, more generally, the energy-momentum tensor on the r.h.s. of Einstein's field equations. And there is a problem, as Einstein himself was well aware (referring to the r.h.s. as "the wing of the palace made of wood"). But in fact, that problem can be traced to the self-force problem of classical electrodynamics, which has never been properly solved.

        After years of extensive research I can say with reasonable confidence that the combination of the two - the BU view with a properly represented energy-momentum tensor - solves all the major open problems in physics, from the foundations of QM to the dark-matter mystery https://arxiv.org/pdf/1201.5281.pdf .

        Moreover, my proposal can supply you with yet another `weapon' against BU deniers: A proper solution to the self-force problem implies that classical electrodynamics cannot be formulated in terms a Cauchy initial value problem. In other words, the (extended) world-lines of particles are defined globally in the BU (albeit constrained by local relations, namely local energy-momentum conservation and Maxwell's equations).

        One additional radical consequence is explored in my essay.

        Best,

        Yehonatan

          Dear Vesselin,

          I'm confused! What means 'real' to a mathematician? Is space-time reality (like an apple), a model of reality, an idea not contradicting certain observations or an object in mathematicians' heaven? And more important, did space-time exist prior to Einstein/Minkowsk and if yes, in which way?

          puzzled,

          Heinz

          Dear Yehonatan,

          Thanks a lot for all this information. I have already created a folder FQXi 2020 on my computer and, like all colleagues here, will have a lot to read and think!

          I am glad you are also interested in the self-force. Here is an item from the list of new results in my book Relativity and the Nature of Spacetime:

          "The proper description of electromagnetic phenomena in non-inertial reference frames in terms of the anisotropic velocity of light leads to the definition of another overlooked quantity - an anisotropic volume element - which simultaneously solves two problems - it accounts for the factor of 1/2 in Fermi's potential for a charge in a gravitational field and the 4/3 factor in the self-force acting on a non-inertial charge."

          Regarding your results I will definitely have a close look.

          Best wishes and good luck,

          Vesselin

          Dear Vesselin,

          Thank you for your response and further illustration of Minkowski spacetime. You state in The Ultimate Judge "all three relativistic effects have been repeatedly confirmed by experiment." I believe to be more accurate, you should say "all three relativistic effects have been repeatedly shown to be consistent with experiment." I would then agree 100% with you. However, consistency between experimental results and the interpretation of experimental results is not proof of the assumptions underlying the interpretation.

          Observer A and observer B do indeed have different inertial frameworks and perceptions of time. Furthermore, Lorentz transformations can transform one reference to another with no loss of information. This is fact. Minkowski spacetime, however, is based on the assumption that physical reality is independent of any particular inertial reference frame, i.e. that physical reality is non-contextual. Certainly, non-contextuality is consistent with relativity experiments, but again, consistency is not proof.

          Non-contextuality is more difficult to reconcile with quantum experiments, yet most physicists cling to the idea of a non-contextual quantum reality. This difficulty is manifested by the lack of any accepted quantum interpretation. In my essay, I argue that a contextual interpretation is consistent with quantum and relativistic experiments, but it is more general, it is based on empirically consistent and conceptually simple assumptions, and it accommodates objective becoming. I hope you will take to time to read it.

          Sincerely,

          Harrison

          Dear Heinz,

          Regarding "What means 'real' to a mathematician?" I simply wanted to point out the fact that Minkowski saw in the unification of space and time he introduced something more than just another mathematical space. My guess is that if Minkowski had to answer your second question, he would say that his die Welt (spacetime) is a mathematical model of a real four-dimensional world (when people, including myself, say "spacetime is real" we mean precisely that).

          [Instead of asking you to see my answer to another comment, I will repeat it here] Let us look again at the two figures in the attached file - they represent two ontologically sharply different entities (of different dimensions): Fig. 1 depicts the suggested by our senses three-dimensional meter stick (and a three-dimensional world), whereas Fig. 2 represents a four-dimensional entity - the stick's worldtube - (and a four-dimensional world). These figures are definitely not merely different equally good descriptions of the physical reality, because reality is either 3D or 4D. If someone rejects the accepted view and holds that the dimensionality of the world is not a fundamental feature of the world (on equal footing with its very existence), then that should be explicitly stated and arguments, based on the experimental evidence, should be provided.

          Now the question is whether experiment can determine the dimensionality of the meter stick (and therefore of the world). This is precisely what the experimental verification of length contraction did. And I would like to stress it again: I think that is the strongest form of experimental verification - if the meter stick's worldtube were not a real 4D object (depicted in Fig. 2), length contraction would be impossible.

          Best wishes,

          VesselinAttachment #1: 1_BlockU.jpg

          Dear Harrison,

          I read your comments several times and, frankly, do not see on what grounds the experimental verification of length contraction should be downgraded from a "proof" to "consistent".

          Let us look again at the two figures in the attached file - they represent two ontologically sharply different entities (of different dimensions): Fig. 1 depicts the suggested by our senses three-dimensional meter stick (and a three-dimensional world), whereas Fig. 2 represents a four-dimensional entity - the stick's worldtube - (and a four-dimensional world). These figures are definitely not merely different equally good descriptions of the physical reality, because reality is either 3D or 4D. If someone rejects the accepted view and holds that the dimensionality of the world is not a fundamental feature of the world (on equal footing with its very existence), then that should be explicitly stated and arguments, based on the experimental evidence, should be provided.

          Now the question is whether experiment can determine the dimensionality of the meter stick (and therefore of the world). This is precisely what the experimental verification of length contraction did. And I would like to stress it again: I think that is the strongest form of experimental verification - if the meter stick's worldtube were not a real 4D object (depicted in Fig. 2), length contraction would be impossible.

          In your comment you talk more about describing physical reality, whereas Minkowski asked the fundamental question: What is the dimensionality of the physical reality? How to describe it is a separate question.

          Of course, I will read your essay - it is already in my FQXi 2020 folder.

          Best wishes,

          Vesselin

          7 days later

          Dear Vesselin,

          I very much agree with your observation that a conversation about the nature of spacetime is long overdue. I tackle similar territory in my own essay from the perspective of quantum logic, a perspective mind you, when I first heard about it I dismissed as not being logic. I invite you to take a look. I should say though I take a diametrically opposite view to yours and argue for an objective becoming.

          I recently came across a paper by a historian of physics who argued that Einstein did not view his theory as a geometrisation but as the unification of gravity and inertia. I found that quite thought provoking.

          I wish you all the best with the contest.

          Warm wishes

          Mozibur Ullah

          4 days later

          Thank you for your patience. It is very difficult to separate empirical facts from interpretations, based on assumptions. I have focused on quantum interpretations and have concluded that quantum reality is objectively contextual. You have prompted me to examine more closely the empirical evidence and assumptions regarding the physical reality of non-contextual 4D spacetime. Thank you.

          Best,

          Harrison

          Thanks a lot. I read your essay several days ago but need to think a bit more in order to try to provide helpful comments.

          In the meantime, you could think of submitting an article to the forthcoming Minkowski Institute Magazine, if interested (http://www.minkowskiinstitute.org/MIMagazine.html).

          Best wishes,

          Vesselin

          Hi Vesselin,

          Our previous discussion has prompted me to take a deeper dive into empirical measurements, facts, and interpretations.

          The Michelson-Morley experiment demonstrated the truth of statement A: "Whatever inertial reference frame is measured from, the speed of light is the same." We can take A as empirical fact. A underlies the Lorentz transformations, which we can also accept as true. The Lorentz transformations transform the measurements of physical reality from one inertial reference to another, including measurements of time and length.

          Consider the statement B: "Physical reality is non-contextual." In the context of SR, this means that physical reality is independent of the particular inertial reference from which it is measured. Without going into details, I claim that B is logically equivalent to statement C: "Physical reality is described by 4D spacetime." I further claim that (BC) => A. We have accepted A as true. The truth of A is consistent with the truth of B and C, but the truth of A neither proves nor implies the truth of B and C.

          Rejecting B and C does not contradict the Michelson-Morley experiment or the Lorentz transformations. It is simply a question of whether we assume that physical reality is contextual or non-contextual. Insofar as the Lorentz transformation preserves information and given that time in SR is reversible, the contextuality of physical reality in SR is undecidable. It is simply a matter of assumption.

          I do not believe this is the case for quantum mechanics, in which wavefunction collapse is empirically irreversible and information is not conserved. As described in my essay, I believe that quantum mechanics provides a strong case for the fundamental non-contextuality of physical reality. If this is true, unification of quantum mechanics and relativity would require accepting the non-contextuality of relativitistic physical reality, as well.

          Best,

          Harrison