# What is the role of the laws of physics in a block universe?

Definition of a block universe - The idea that the whole universe exists simultaneously and time doesn’t flow.

For those who favor this kind of theory (the few of you), what is the role of the laws of physics in such a universe? Are the laws of physics just a reflection/projection determined by the blocked universe? Are there other superior laws that created the block? or was the block created by the laws of physics too? Is it possible to have a glitch in such a block?

I understand that there can be only theories and nothing more, but I am interested in any kind of references.

• I had to look up "block universe" and got apparently contradictory answers. Past, present and future co-exist v past and present do and future doesn't exist. Unless you can travel through forward through time, what difference would either make? Either way, how would either change the role of the laws of physics? – Robbie Goodwin Feb 6 at 23:56
• @Robbie Goodwin Maybe there are some other external superior laws that have created the so call “block” with the laws of physics in it? In the same way that the laws of Biology depend on the laws of chemistry and the laws of chemistry on the laws of physics. Maybe the laws of physics depend on a much more superior set of laws that we are restricted from knowing or understanding? I meant for it to be a soft question, and I apologize if non practical – Isaac Brenig Feb 7 at 0:14
• Thanks and isn't that more about metaphysics, or philosophy? Either way, what difference might a block universe make? Why not ask simply "What is the role of the laws of physics?" (Come to that, why not just ask "What is the role of physics?") – Robbie Goodwin Feb 7 at 0:20
• @Robbie Goodwin most of the articles that I have read on the subject came from physicists (more than philosophers), While they are all speculative, they are pretty interesting and they also help expand my imagination. It is much easier for me to imagine “other superior” laws in a “block” universe than in “regular” universe. So again, I apologize if my question isn’t practical enough – Isaac Brenig Feb 7 at 0:50
• Thanks Isaac You seem to be looking for an extended discussion, in which case someone might link you to a chatty site but it wouldn't belong on SE. If you must risk the wrath of any official noticing you're looking for an extended discussion, why is it easier to imagine “other superior” laws in a “block” universe and how is that different from the “regular” one? – Robbie Goodwin Feb 7 at 22:28

A block universe is simply one in which all the laws of physics are deterministic and reversible. In such a universe, complete and precise knowledge of the configuration of the universe at one point in time (or across one "slice" of the block) contains enough information in principle to determine the configuration of the universe at all past and future times. I emphasise "in principle" because there is nothing that says such a calculation has to be even remotely feasible in practice.

In a block universe there can still be an arrow of time, and so a flow of time in a psychological sense. If the universe starts in a state of low entropy (as our own universe did) then its entropy increases over time due to the second law of thermodynamics, and because of this it is only possible to construct memories in one direction (memories of what we call the "past") and not in the other (we cannot remember the "future"). We could, in principle, predict the future, but an exact prediction would require a level of complete and precise knowledge which would make it unfeasible. Of course, we make approximate predictions of the future all the time - if I go for a walk on a sunny day I predict that is unlikely to rain, so I do not take an umbrella. I also predict that an earthquake, a tidal wave, a volcanic eruption or a shower of frogs are also very unlikely events in the next hour or so.

In a block universe, whether you regard the laws of physics as determining the timeless configuration of the universe, or you regard the configuration as determining the laws of physics is a philosophical question. Like the chicken and the egg, these two aspects of the universe are inextricably linked.

Doubts about whether our universe is a block universe do not arise because it is illogical - the concept is entirely self consistent. Instead, they arise from our observations of the laws of quantum mechanics. The non-reversible nature of quantum measurement (you cannot reconstruct the previous state of a quantum system once it has been measured and its state has "collapsed" into an eigenstate of the measurement operator) seems to rule out the possibility of our universe being a block universe - if you grant the physical reality of wave function collapse.

However, there are interpretations of quantum mechanics, such as the "many universes" interpretation - where wave function collapse is an illusion due to our restricted knowledge - we only have knowledge of one universe from an immense collection of possible universes. The evolution of the collection of all possible universes in a "many universes" scenario could still be deterministic and reversible, so this could still be a block "mega-universe", although we can only ever have knowledge of an infinitesimally small part of it.

Two well known books on this topic are Julian Barbour’s The End of Time (pro block universe) and Lee Smolin’s Time Reborn (anti).

• So in theory the ideas of a block multi universe can be promoted (being caution not to use the word “proved”) by our restricted knowledge of the laws of physics, but our restriction means that we probably can never prove it, since we don’t have access to all the knowledge of the laws of physics, nor to the possible knowledge of other “possible superior” laws. – Isaac Brenig Feb 6 at 22:53
• When I mention other “possible” laws I am referring to how for example the laws of biology depend on the laws of chemistry and the laws of chemistry depend on the laws of physics, maybe the laws of physics depend on some laws that we don’t have access to? – Isaac Brenig Feb 6 at 22:59
• @IsaacBrenig We know that our current understanding of physics is not complete because there are fundamental incompatibilities between general relativity and quantum mechanics. The search for a viable theory of quantum gravity and for a “Theory of Everything” (en.wikipedia.org/wiki/Theory_of_everything) are active areas of research in theoretical physics. – gandalf61 Feb 7 at 9:51
• @IsaacBrenig: don't think about it as of something that needs to be proven, but rather as of a way to describe the universe - the question then is how well this conceptual description fits reality, and where it breaks down. To get a feel for the idea, consider this: a wave can be described by a traveling sinusoidal curve, OR you can imagine it extending out in time to form this sort of undulating pattern, and that we're "along for the ride" on a time slice that travels into the future. The laws just describe relationships between things in both cases. – Filip Milovanović Feb 7 at 14:36
• @IsaacBrenig - sure, but, a few things. At the moment, we don't know what the deeper, more fundamental laws are; when these are discovered, they'd likely be studied within physics (the scientific discipline), and would themselves be considered laws of physics - unless a new discipline/science splits off. These divisions (physics/chemistry/biology) are in a sense arbitrary and are a historical accident - they reflect how humanity went about understanding the world throughout history. – Filip Milovanović Feb 8 at 2:07

What is physics? Physics is the discipline that studies numerically nature and uses mathematical models, the theories, in order to describe the data and , important, predict new situations. Laws (also postulates, principles) of physics are extra axioms to the mathematical axioms in order to pick from the infinity of mathematical relations in the models, the ones that are relevant to fitting the data.

For any new way of looking at data, as is this block you are discussing, the existing laws have to be incorporated so the new theory would fit the data, and in order to be a legitimate new theory it should also make measurable predictions, otherwise it will be just a complicated way to fit the same data.

Take a diamond lattice. It can be geometrically mapped, no laws obvious. Where are the laws? They are in the theory that allows the study of lattices, built in the mathematical model that finally gives the lattice points.

• As for my understanding: there might be superior laws that “created” the laws of physics, But not only it can’t be proved, it also can’t be theorised, since the definition of a physics theory must include the laws of physics ? – Isaac Brenig Feb 6 at 22:14
• A physics theory must have laws. As with mathematical axioms, it is possible that a new formulated theory to describe the data could have these laws as theorems and have new laws for axioms. If the data is described by both we speak of one theroy being and interpretation of the other. A theory to be new, would need to model the same data and predict new effects to be discovered.. It could have completely new axiomatic statements/laws , but the original ones have to be there, in the of the new theory, because the old theories should be embedded in the new because it should fit the old data. – anna v Feb 7 at 5:49

If you think of the block universe as the name suggests, as a "block" of unchanging structure, then the "laws of physics" are simply a compressed representation of the patterns that are etched into that block. Their existence means that the Universe's pattern is, however apparently complex, one that is "just so" as to permit an efficient, small, representation.

It's like if you take an image of the Mandelbrot set. The picture does not change, but that lack of change does not negate that one can describe every detail thereof simply by writing down the following formula:

$$M := \left\{ c \in \mathbb{C}: \exists L \in \mathbb{R} \forall n \in \mathbb{N} |(z \mapsto z^2 + c)^n(0)| < L \right\}$$

You could say that the existence of laws of physics, in effect, is a statement about the Kolmogorov complexity of the universe: the length of the shortest possible text required to completely describe it in some description language. In some sense, it is "simpler" than just an arbitrary, generic block of random patterns, for which no other way exists to represent it in the language than to just painstakingly specify each and every single point.

That said, it is not necessarily absolutely so: we could imagine that parts of it were in effect "chosen at random", while other parts are not - that is what non-determinism would mean in a block universe context. In that case, the actual descriptive complexity will be that much higher, but the existence of "partial" laws will nonetheless drive it down by a factor, i.e. that many fewer zillions of bits, than the case with no laws at all, i.e. a fully, or Kolmogorov-random, universe.

Laws of physics arise from noticing that there are patterns in nature that appear to recur reliably. For instance, Newton's laws of motion and quantum mechanics. These suggest that the universe is not an arbitrary, eternal collection of blocks, but an emergent phenomenon that arose out of some basic principles that produce these patterns.

What would this mean in the context of a block universe? It means that there are rules governing how the could be constructed out of all the blocks. Sort of like the workings of Lego blocks and Lincoln Logs: they can only interlock in certain ways. These rules become visible to us as the patterns that we notice, and physics is the process of discovering these patterns. Perhaps if we keep investigating we might eventually be able to figure out how the blocks themselves are design and why they have these rules. This is the holy grail of physics: a "theory of everything".

But since we're part of the universe, this becomes incredibly self-referential. All our thoughts and actions are encoded in these blocks. How much sense does it make to talk about "discovering" things when the state of having this knowledge is already in the blocks? There's little room for the concepts of free will, randomness, and unpredictability.

What we view as the arrow of time is just a dimension in the block universe. The second law of thermodynamics, which says that entropy always increases in the "forward" direction of time, could be a consequence of the rules of block construction mentioned above.

How likely is it that some basic rules for interlocking blocks could produce the emergent effect of detecting and understanding the patterns produced by those rules? This is not unlike the question of how likely it is that the basic constants of physics are such that we get a stable enough universe to produce stars, planets, and life. We don't know how this happened, and a common, but not very satisfactory, solution is the anthropic principle: if things weren't the way they are, we wouldn't be here asking the question.

Doing physics essentially assumes that all these patterns really exist, and they have some cause. But it could also be an illusion, like the Matrix. Or like biblical literalists who believe that the Earth is only a few thousand years old, and that all the geographic and archeologic evidence scientists use to prove its age were created by God to make it appear older.