Does the Block Universe of Physics Mean Time is an Illusion?

I have written many Insights (and coauthored an entire book) explaining how the puzzles, problems, and paradoxes of modern physics can be attributed to our dynamical bias and resolved by rising to Wilczek’s challenge [1]:

A recurring theme in natural philosophy is the tension between the God’s-eye [4D] view of reality comprehended as a whole and the ant’s-eye view of human consciousness, which senses a succession of events in time. Since the days of Isaac Newton, the ant’s-eye view has dominated fundamental physics. We divide our description of the world into dynamical laws that, paradoxically, exist outside of time according to some, and initial conditions on which those laws act. … The God’s-eye [4D] view seems, in the light of relativity theory, to be far more natural. Relativity teaches us to consider spacetime as an organic whole whose different aspects are related by symmetries that are awkward to express if we insist on carving experience into time slices. … To me, ascending from the ant’s-eye view to the God’s-eye [4D] view of physical reality is the most profound challenge for fundamental physics in the next 100 years [p. 37].

Thus, while certainly not complete, physics is comprehensive and coherent when adynamical, 4D constraints are considered fundamental to dynamical, (3+1)D time-evolved causal mechanisms. This 4D “block universe” or “blockworld” view of physics sometimes leads people to believe “time is an illusion.” For example, in his video “The Fabric of the Cosmos: The Illusion of Time” Brian Greene states:

Like this river, time seems to flow endlessly from one moment to the next. And the flow of time seems to always be in one direction, toward the future. But, that may not be right. Discoveries over the last century have shown that much of what we think about time may be nothing more than an illusion. Contrary to everyday experience, time may not flow at all. Our past may not be gone. Our future may already exist.

What Greene is referring to as “nothing more than an illusion” are the dynamical temporal experiences of Now, Passage, and Direction. By “the Now,” I mean that my experiences are localized in time, I don’t experience the past (what I experienced according to my memories) or the future (what I anticipate I will yet experience). That temporally localized experience is the Now. “Passage” means that the Now does “move” into the future and “Direction” means the Now does not “move” into the past. In this Insight, I want to distance myself from this claim as we did in our book “Beyond the Dynamical Universe,” which is subtitled “Unifying Block Universe Physics and Time as Experienced.” The bottomline is the block universe view of physics does not entail that time is “nothing more than an illusion,” as I will now explain.

Everyone has a dynamical temporal experience that the 4D spacetime of relativity theory does not capture and this concerned Einstein as noted here by Carnap [2]:

Once Einstein said that the problem of the Now worried him seriously. He explained that the experience of the Now means something special for man, something essentially different from the past and the future, but that this important difference does not and cannot occur within physics. That this experience cannot be grasped by science seemed to him a matter of painful but inevitable resignation [p. 37].

David Mermin recently acknowledged this issue writing [3]:

The experience of the Now does indeed mean something special for me, something essentially different from my past and my future. The apparent absence from physics of this important difference is an artifact of the unwarranted removal of the subject from the story physics is allowed to tell. That the Now appears to be unavoidably missing is a clear indication that the world indeed makes no sense, if I insist on leaving my own experience out of the story I tell about it [p.13].

In other words, Mermin says we need to acknowledge that physics and experience should be related (and he does so via QBism). As I pointed out in this Insight, Einstein himself acknowledged the same in his essay “Physics and Reality” [4]:

The whole of science is nothing more than a refinement of everyday thinking.

On the stage of our subconscious mind appear in colorful succession sense experiences, memory pictures of them, representations and feelings. In contrast to psychology, physics treats directly only of sense experiences and “understanding” of their connection. But even the concept of the “real external world” of everyday thinking rests exclusively on sense impressions.

I believe that the first step in the setting of a “real external world” is the formation of the concept of bodily objects and of bodily objects of various kinds. Out of the multitude of our sense experiences we take, mentally and arbitrarily, certain repeatedly occurring complexes of sense impression (partly in conjunction with sense impressions which are interpreted as signs for sense experiences for others), and we attribute to them a meaning — the meaning of the bodily object.

The second step is to be found in the fact that, in our thinking (which determines our expectation), we attribute to this concept of the bodily object a significance, which is to a high degree independent of the sense impression which originally gives rise to it. This is what we mean when we attribute to the bodily object “a real existence.” The justification of such a setting rests exclusively on the fact that, by means of such concepts and mental relations between them, we are able to orient ourselves in the labyrinth of sense impressions. These notions and relations, although free statements of our thoughts, appear to us stronger and more unalterable than the individual sense experience itself, the character of which as anything other than the result of an illusion or hallucination is never completely guaranteed. On the other hand, these concepts and relations, and indeed the setting of real objects and, generally speaking, the existence of the “real external world”, have justification only in so far as they are connected with sense impressions between them which they form a mental connection.

The very fact that the totality of our sense experiences is such that by means of thinking (operations with concepts, and the creation and use of definite functional relations between them, and the coordination of sense experiences to these concepts) it can be put in order, this fact is one that leaves us in awe, but which we shall never understand.

In guiding us in the creation of such an order of sense experiences, success in the result is alone the determining factor. All that is necessary is the statement of a set of rules, since without such rules the acquisition of knowledge in the desired sense would be impossible. One may compare these rules with the rules of a game in which, while the rules themselves are arbitrary, it is their rigidity alone which makes the game possible.

And Hermann Weyl believed [5]:

Physics is the “Construction of objective reality out of the material of immediate experience” [p. 117].

Accordingly, the “game of physics” is the study of the “bodily objects” of our “sense experiences.” As Einstein pointed out, there are already some assumptions there, so it’s best to start with “all sense experiences.” I am the spatiotemporal origin of “all sense experiences.” I assume a subset of “all sense experiences” represents other perceivers. For example, my perception of you is a subset of my “sense experiences” and I will assume you also have “sense experiences.” In Einstein’s words, “partly in conjunction with sense impressions which are interpreted as signs for sense experiences for others.” Therefore, I am the spatiotemporal origin of “my sense experiences.” I communicate with other (human) perceivers to construct a model of objective reality (the “real external world”) that reconciles the disparate elements of our “sense experiences.” For example, when you view a car from its trunk and I view it from its front, we have two distinct “sense experiences.” We model these disparate perceptions by assuming two perceivers located spatially with respect to one car (thus, the wording of the preceding sentence). This is how we self-consistently model the “real external world” aka our model of objective reality to reconcile our disparate “sense experiences.” In Einstein’s words, “the totality of our sense experiences … can be put in order.” 

We then use this model to explore regularities and patterns in the events we perceive. We mathematically describe these regularities and patterns and explore the consequences (experiments). In Einstein’s words, “operations with concepts, and the creation and use of definite functional relations between them, and the coordination of sense experiences to these concepts.” We then refine our model of physical reality as necessary to conform to our results. This allows us to explain the past, manipulate physical reality in the present (to create new technology, for example), and to predict the future. For his own reasons, Mermin writes [3]:

The special character of my Now is a brute fact of my personal experience, and I conclude from what others tell me that it is also a brute fact of the personal experience of everybody I communicate with. Together we have all deduced, from our direct personal data and the communications of others, an abstract model that we call space-time. The model provides a way for each of us to record our memories, direct and reported, of all these Nows, and our anticipations of subsequent Nows [p. 13].

In other words, physics “models and explores regularities and patterns in the self-consistent collection of shared perceptual information between perceivers” [6, p. 12]. Of course, this does not mean that the 4D spacetime or block universe model of physics includes only what is perceived. Rather, it involves “the class of conceivable observers” per Thomas Ryckman [5]:

The desired conception of a completely impersonal world is only expressible as a geometrical structure. Thus relativity theory (taken as including something like Weyl’s extension of the class of conceivable observers) has completely overturned the older conception of an external world as substance or material [p. 195].

Having established the unavoidable link between physics and experience, we make the assumption that experience and constraints on experience are co-fundamental [6]. In other words, this worldview is grounded in experience and the “laws of physics” are understood to describe the constraints on experience. Mermin writes [3]:

On the basis of my prior experiences I can form expectations for the responses of the world to my actions.

Science can be viewed as a user’s guide to the world. Scientific laws are guides to action, which have proved to be spectacularly successful.

Laws of science are the regularities we have discerned in our individual experiences, and agreed on as a result of our communications with each other. Science, in general, and quantum mechanics, in particular, impose further constraints on my probabilistic expectations. They help each of us place better bets on our subsequent experience, based on our earlier experience [p. 4].

The constraints on experience constitute what we mean by “physical reality” or “objective reality” or Einstein’s “real external world.” This is called “radical empiricism” or “neutral monism” in the language of William James [6]. Mermin writes [3]:

For a QBist empiricism has a strongly personal flavor to it: the knowledge of each one of us derives from our own personal experience. This is close to what William James called ‘radical empiricism’. Different people with different experiences will in general have different knowledge [p. 5].

That immediately renders the so-called “hard problem” or “generation problem” of consciousness a nonstarter. For example, Einstein’s concern that the Now “cannot occur within physics” is a nonstarter because the laws of physics are not fundamental to experience, they are co-fundamental, you don’t have one without the other [6].

You certainly don’t have to subscribe to “radical empiricism” and you can still show the block universe view of physics does not entail that time is “nothing more than an illusion.” For example, Carlo Rovelli has his own reasons to write [7]:

There is nothing in relativity which is in contradiction with our experience of time, or that suggests that our experience is ‘illusory’ [p. 1].

I’m simply summarizing the core idea in our book and recent paper [6] in this Insight.

As it turns out, besides the fundamentality of our experience in terms of “interacting bodily objects,” there is one other constraint on experience that is necessary to reproduce the theories of physics we have today, i.e., the relativity principle aka “no preferred reference frame” [6]. As Arthur Eddington wrote [5]:

physics is about the world from the point of view of no one in particular [p. 195].

This is responsible for the constraint-based approach to physics via the notion of symmetries. Michael Hicks writes [8]:

There are not two worlds in one of which I am here and in the other I am three feet to the left, with everything else similarly shifted. Instead, there is just this world and two mathematical descriptions of it. The fact that those descriptions put the origin at different places does not indicate any difference between the worlds, as the origin in our mathematical description did not correspond to anything in the world anyway. The symmetries tell us what structure the world does not have.

Taken together, these two axioms of physics, i.e., interacting bodily objects plus no preferred reference frame [6], constrain experience in some very counterintuitive ways, as I pointed out in numerous Insights, our book, and most recently in our answer to Mermin’s challenge [9]. Since these constraints are co-fundamental with our dynamical experience, the constraints can in no way negate the validity of dynamical experience to include our dynamical experience of time. Mermin writes [3]:

This model singles out no part of space-time as Now. But to say that Now plays no role in the physical description of space-time is to overlook the crucial fact that my personal Nows constitute the only grounds I have for my physical description of the contents of space-time [p. 13].

In other words, per Mermin [3]:

By identifying my diagram with an objective reality, I fool myself into regarding the diagram as an objective four-dimensional arena in which my life is lived [p. 13].

To represent our actual experiences as a collection of mathematical points in a continuous spacetime is a brilliant strategic simplification, but we ought not to confuse a cartoon that attempts concisely to represent aspects of our experience with the experience itself [p. 14].

So, where does the confusion arise? Let me revisit something that I presented in my Insight, The Relativity of Simultaneity and Blockworld. As stated above, each perceiver (real or possible) is the spatiotemporal origin of “their sense experiences.” Let me refer to a perceptual origin as a PO. I am a PO and when I use my spacetime model to predict or explain my experiences, I use not only my spatiotemporally localized Now, but I use a Now Slice (per Greene), i.e., a spatial hypersurface in my spacetime model. For example, I need the pizza shop to be open Now if I am to call and order a pizza Now. I have essentially extended my Now through a particular spatial hypersurface of my spacetime model so as to include the workers at the pizza shop. I called this spatially extended property ‘realness’ in that Insight (Greene might say I and the pizza shop are “equally real” on that Now Slice). Per Einstein above:

This is what we mean when we attribute to the bodily object “a real existence.” The justification of such a setting rests exclusively on the fact that, by means of such concepts and mental relations between them, we are able to orient ourselves in the labyrinth of sense impressions.

Since the boys and girls in that Insight occupy different reference frames, their Now Slices do not overlap in the composite spacetime model, i.e., the block universe spacetime model of “the self-consistent collection of shared perceptual information between perceivers.” In other words, the boys’ spacetime model is reconciled with the girls’ spacetime model in the composite block universe spacetime model (“block universe model” for short) using the relativity of simultaneity (RoS). Consequently, I wrote in the Insight (as emphasized by Greene):

Finally, notice that at Event 3 Alice shares ‘realness’ with Bob while she shares ‘realness’ with Sara (both T = 0, Figures 4 & 6). However, at T = 0 Sara also shares ‘realness’ with Joe (both at Event 1). Thus, Bob at t = 0 shares ‘realness’ with Bob at t = 0.002s, so the RoS implies the future is as ‘real’ as the present.

This assumes that the property of ‘realness’ is transitive, which is perfectly acceptable for building our block universe model in that it suggests the constraints on dynamical experience might be spatiotemporal rather than dynamic. For example, according to the girls’ dynamical experiences (i.e., data being collected and shared via interactions), the boys’ meter sticks are short and their clocks run slow. But, according to the boys’ dynamical experiences, it is the girls’ meter sticks that are short and the girls’ clocks that run slow. Each set of POs (boys and girls) have their own Now Slices of ‘realness’ which do not overlap in the block universe model, so these facts are rendered perfectly consistent in the block universe model of the constraints on dynamical experience. All of that obtains because of the relativity principle applied to the measurement of $c$. Likewise, as I showed in this Insight, Alice says Bob’s Stern-Gerlach spin measurements must be averaged to satisfy conservation of spin angular momentum for measurements of the Bell spin states, while Bob says the same thing about Alice’s Stern-Gerlach spin measurements. Thus, our conservation principle (constraint) is satisfied only spatiotemporally, i.e., we have a perfectly symmetrical (between reference frames) “average-only” conservation of spin angular momentum. All of that obtains because of the relativity principle applied to the measurement of $h$. However, if I attempt to associate the transitivity of ‘realness’ with the personal spacetime model for some PO, I do obtain a contradiction with the fundamentality of dynamical experience.

To see this, return to the girls and boys and apply transitivity to the ‘realness’ between events on two different Now Slices of the two different spacetime models. Whose dynamical experience does that represent? No one’s. There is no PO with a personal spacetime model that identifies ‘realness’ with that collection of events in the block universe model. If there was such a PO, they would not experience objects moving through space, so their experience would not be dynamical, which contradicts the fundamentality of dynamical experience, i.e., the experience of “interacting bodily objects.” It’s hard to imagine what physical basis might exist for such a “view from nowhen” since we understand quantum transitions are needed to emit and receive the photons required to see something and such transitions are dynamic. So, we see that the basis for confusion resides in the (tacit and false) association of a PO with the transitivity of ‘realness’ in building the block universe model of constraints on dynamical experience.

Of course, the corollary to the fact that the laws of physics cannot negate the reality of our dynamical experience is that laws of physics cannot explain the reality of our dynamical experience either — again, because they are co-fundamental in this view. This has been acknowledged by Max Planck [10]:

Sullivan: Do you think that consciousness can be explained in terms of matter and its laws?
Max Planck: No. I regard consciousness as fundamental. I regard matter as derivative from consciousness. We cannot get behind consciousness. Everything that we talk about, everything that we regard as existing, postulates consciousness.

and Erwin Schrödinger [11]:

Although I think that life may be the result of an accident, I do not think that of consciousness. Consciousness cannot be accounted for in physical terms. For consciousness is absolutely fundamental. It cannot be accounted for in terms of anything else.

and further argued here by Hrvoje Nikolic (aka Demystifier), for their own reasons. If you want to avoid this consequence and assume the laws of physics are fundamental to consciousness (as necessary for them to explain it), you might look at Smolin’s attempt articulated in his recent paper, “On the place of qualia in a relational universe.” In that case of course, the “all-at-once” or “block universe” view of physics is indeed problematic, so he introduces a preferred reference frame.

All of that being said, there is a very real sense in which “time is an illusion,” i.e., in comparing our personal spacetime model with the objective spacetime model of special relativity. See The extraordinary consequences of Einstein’s universe for a presentation of that idea. In conclusion, the simple answer to the title of this Insight is, “No! The 4D spacetime or block universe model of physics does not negate the reality of our dynamical experience to include our dynamical experience of time. However, the objective spacetime model of 4D spacetime does tell us that our personal spacetime models are all missing the equal ‘realness’ of all events.” As Paul Harvey used to say, “And now you know … the rest of the story.”

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References

1. Wilczek, F.: Physics in 100 Years, Physics Today 69(4), 32–39 (2016).
2. Carnap, R.: Carnap’s Intellectual Biography, In: The Philosophy of Rudolf Carnap; Schilpp, P., Ed.; Open Court, 3–84 (1963).
3. Mermin, N.D.: Making better sense of quantum mechanics, Reports on Progress in Physics 82, 012002 (2019).
4. Einstein, A.: Physics and Reality, Journal of the Franklin Institute 221(3), 349-382 (March 1936).
5. Ryckman, T.: The Reign of Relativity, Oxford University Press: New York, New York, (2005).
6. Silberstein, M., and Stuckey, W.M.: Re-Thinking the World with Neutral Monism: Removing the Boundaries Between Mind, Matter, and Spacetime, Entropy 22, 551 (2020).
7. Rovelli, C.: Neither Presentism nor Eternalism. 6 Oct 2019.
8. Hicks, M.: What Everyone Should Say about Symmetries (and How Humeans Get to Say It), Philosophy of Science 86, 1284–1294 (2019).
9. Stuckey, W.M., Silberstein, M., McDevitt, T., and Le, T.D.: Answering Mermin’s challenge with conservation per no preferred reference frame, Scientific Reports 10, 15771 (2020).
10. Sullivan, J.: Interviews with Great Scientists IV. Prof. Schrödinger, The Observer, 15–16  (1931).
11. Sullivan, J.: Interviews with Great Scientists VI. Max Planck, The Observer, 17  (1931).