How does biological evolution work in the block universe/b-theory of time?

Question

The b-theory of time is often described as a film reel where the whole reel exists, but we can only view one frame at a time.

The problem I have with this analogy is that it starts to feel too theological. Where did the film reel come from? If it all began to exist "simultaneously" then biological evolution cannot explain diversity in nature because the current creatures already existed somewhere in the file, even from the beginning of the playback. I'd have to imagine the film reel being created by a director that builds it frame by frame, then sets it in motion.

I'm hoping that I'm not understanding the idea correctly and am taking the analogy too far. Is there a better way to think about it?

Answer 1

It is a fallacy to consider physical processes such as evolution existing for an observer "looking down" on block time. For that observer there is no such thing as space or time, they are by definition outside of both. The observer thus has no concept of simultaneity outside of a slice through the block map. The idea of the whole map coming into being "simultaneously" has no meaning to them. Whatever way they might appreciate the flow of causality in their higher universe, it will not be the same way the laws of physics work in ours.

Answer 2

Picture a pile of sand, being added to grain by grain. The exact way it piles and slips is unpredictable, and stochastic. Yet, the general behaviour averages to very predictable, forming a pyramid pile in a way related to the specific grains.

When we look at what dimensions are defined as, they are symmetries under transformation, which simplify descriptions, and are directly equivalent to conservation laws (Noether's theorem). We can picture this where say you move a spinning top one metre to the left, and the momentum is the same. But rotate around the axis or around the middle, and the results are different (ie it has rotational but not translational momentum). Same if something has momentum in a spatial direction: there is an assymetry in transformation. This kind of pattern is the core of what we call a dimension. Space and time are sets of transformations and localised properties within them.

Now consider fractional dimensions, fractals. These represent not simple linear or reversing changes as you move across a system (perform a transformation), but fractional changes. The simplest example is the Koch Snowflake, which can be interpreted as niether a line, nor a plane - it has a dimension of 1.26. Fractals occur everywhere in nature, like the branching patterns of trees or alveoli in lungs (you can see a good explanation of how simple rules generate patterns like this here). (my favourite example of behaviour 'simplifying' across a dimension in a fractional way, is blackhole turbulence)

So. In a block universe evolution is a stochastic fractal, pattern. It is a shape, that's all. Like the shapes sandpiles make. Sandpiles have a shape in 3D,and they have an evolving shape in 4D too.

Personally, I'm inclined to see it not as a single 4D block, but a stack of blocks, in 5D. The Holographic Principle, which explains where the information goes when blackholes evaporate, points to this. We could picture quantum event splitting as branching the 4D block, into an additional dimension.

Answer 3

Many philosophers of physics assume The Past Hypothesis, that the universe was extremely low entropy compared to today at the Big Bang, "over and above" (Harvey S. Brown) the laws of physics.

With unitary and symmetric laws of physics, the Big Bang is a necessary prior/initial condition to pick out a direction of time, e.g. the second law.

I say all this because this prior/initial condition is what stands in for the director in your analogy. Instead of director creating a reel of film to set in motion, it is initial conditions + physical laws of evolution that predicts rather than creates one frame to the next. And with symmetric and unitary laws of physics, any frame predicts its adjoining frames in either direction.

For the "setting in motion" part, the B-theorist has to say the feeling of time flowing is a subjective illusion. It's not that this flow of time, this subjective illusion in the brain, is unphysical or dualistic necessarily. Rather it has the same status as any other subjective experience, like colors, warmth, and pain. And B-theorists often say subjective experiences like these will be explained in time by neuroscientists and psychologists.

Why set it up this way instead of just having an objective flow of time? Because the laws of physics are completely symmetric. Thus we have to posit this extra Past Hypothesis to explain why world looks like it does today. So either the laws of physics are wrong/incomplete, or the laws are pretty accurate and it's the initial condition we have to explain.

Finally I can now say, from this block perspective of the laws, there is no privileged present. There is not even a privileged past or future. The Big Bang is just a prior condition, not necessarily an initial one. This equity of the laws, that any "frame" predicts and other frame is very attractive.

So as far as evolution, all we are committed to admitting is that prior conditions were such that together with the laws of physics predicted/created a branching structure of complexity of life. No extra extra commitments to a director, creator, theology, etc. We can happily predict backwards and forwards (within the laws' limits) to our hearts contents. Maybe that's all we can ask of science.

A final analogy from Harvey Brown might help. The laws of physics determine/predict one patch of spacetime to the next in any "direction". This situation is like a patterned rug, where one patch of the rug predicts the patches around it. No objective flow of time, no "creation", just predictions about patches. The psychological flow of time has to be be explained to complete the story, but many are optimistic.

Hopefully all this shows how a B-theorist might hang things together. Creatures evolved later (like us) really just "coexist" with all the other past creatures. There is no privileged present or slice of spacetime. (Again, physicalist minded B-theorists admit the further task of explaining conscious experiences including flow of time, but which philosophy doesn't have to ultimately explain conscious experience at some point).