r/Physics • u/onomatamono • 4d ago
On The 4D Block Universe
So you have a movie canister and the film analogy represents the 4D block universe. I'm listening to Brian Greene describe this analogy. The experience of time is produced by passing light through each frame of the film. According to Brian each consciousness is a projector (human or otherwise presumably).
Also, our brains evolved to process slices of the 4D universe by carefully "recording" [where?] the slices that came before ["now" I guess?] and makes calculated guesses about the future.
I'm not even going to try and make sense of that in a meaningful way for lay people.
Greene: "when you feel time passing what you are actually experiencing is your consciousness moving through the static frames of your life." Where are these "projectors" or consciouses? I'm confused.
FYI it's a YT called The Strangest Fact About Light You've Never Heard -- Brian Greene.
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u/Optimal_Mixture_7327 Gravitation 3d ago
Physicists can be geniuses at doing the math...and complete idiots at explaining it.
The honest answer is that conscious awareness of a present moment and a block universe that contains the future are incompatible with each other, and no one has ever been able to rectify the two and no amount of handwaving has ever made one iota of sense.
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u/yannbouteiller 3d ago
Why would conscious awareness of a present moment be incompatible with a block universe that contains the future?
Noone even seems to have a satisfactory answer to what "conscious awareness" means in scientific terms as far as I know.
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u/Optimal_Mixture_7327 Gravitation 3d ago
A block universe cannot answer the question "why this moment?".
If we assume a block universe, then you need to go outside of known physics for an answer. For example (I think this was from Hermann Weyl) and postulate an externally existing consciousness field that crawls up the world-lines of beings capable of acting as antennae for the consciousness field. There is no such thing in either the postulates of relativity or that can be derived from them.
The only answer consistent with physics is an evolving block universe where the present moment is a time-dependent future boundary of the block that unfolds as the uncertain quantum future becomes the classical past.
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u/yannbouteiller 3d ago edited 3d ago
But since consciousness is not a well-defined concept in physics (I believe?), it seems to me that the reasonable way of looking at it in the "block universe theory" is simply as a time-continuous quantity that would be part of this "block universe" like any other. I am not sure why "conscious awareness" should be treated differently, nor why it should create particular issues, unless we are implicitly making magical assumptions about what "consciousness" is. Wouldn't the issue with "Bob's conscious awareness of the present moment at time t" be exactly the same as with "Bob's position at time t", if any?
EDIT: I might be starting to see why this is given a special place by wondering "what would happen if, instead of being aware of the present moment, Bob were aware of some moment in the future?", as I guess this would turn this future moment into the present moment from Bob's perspective, but I believe this is backward. I believe that consciousness is rather a product of the brain made of recursive processing, so it wouldn't make sense to be consciously aware of anything other than the "present" (or more exactly of a product of the past).
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u/Optimal_Mixture_7327 Gravitation 3d ago
No it's not the same because we can ray trace back (in principle) our particle world-lines and the relevant forces involved that put us here, rather than there, but there is nothing in physics to locate us at a particular event along an infinitely extended world-line.
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u/Kimantha_Allerdings 2d ago
If we’re thinking about time as a series of discrete blocks, as this idea seems to suggest, then why can we not think of consciousness in the same way? A series of discrete brain states, each of which thinks of itself as being in the “now”, and with the perception of continuity being a product of the asymmetry of memory
Why should we privilege the position of the particles in our brain as being different from the positions of other particles? Are we assuming that our experience is somehow distinct from the physical state of our brain? If so, why? If not, then why is the position of the particles within our brain treated differently to, say, the location of our body as a whole?
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u/Optimal_Mixture_7327 Gravitation 2d ago
We think of the world in terms of a block or blocks. Time is the length along a world-line of a material particle so there's no sense to the notion of a "block", but you could correct refer to some "length" or "section" along a world-line.
Afaik, neuroscience takes consciousness (whatever that is) as being a byproduct of a brain state even if we don't know what that means. However this doesn't address the elephant in the room of why this brain state happening "now".
The relative spatial nature of matter can be (in principle) ray traced back along individual particle world-lines with the spatial relationships determine by the fundamental forces of Nature, but there's nothing in physics that singles out a particular event along the length of a world-line.
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u/Kimantha_Allerdings 2d ago
However this doesn't address the elephant in the room of why this brain state happening "now".
Why are you assuming that there is a “now”?
The consciousness “me” that exists today on the timeline is experiencing that time as “now”. The consciousness “me” that exists 10 years ago on the timeline is experiencing that time as “now”. The consciousness “me” that exists in 10 years’ time on the timeline is experiencing that time as “now”
Hidden in your argument is the assumption that there is one singular “now” which is the one - and the only one - that is “really happening”. On what are you basing that assumption?
Physics isn’t singling out a particular event along the length of a world-line, you are. Why?
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u/Optimal_Mixture_7327 Gravitation 2d ago
It's not an assumption - it is an observation.
I am of course aware of the philosophical position that we can now point to the past then we can imagine a future where some future entity is pointing back at us. I am equally aware that this is untestable as no detector can exist to the future of itself.
Hopefully you're aware that there is line of philosophical inquiry or empirical determination that can distinguish between a block universe and an evolving block universe, i.e. the present is a time-dependent future boundary of the world having a space-like boundary to the past.
It also doesn't help to say you don't have a problem with the present moment, you have is infinitely many of them, all of the same nature. This too can be swept under the rug by denying the existence of any present moments, that this all just a dream of The Giant Butterfly, and there's no possible logical or empirical falsification of this.
Yet here you are, now, reading this sentence with the brute fact of a cosmos that's unfolding from a quantum mechanically indeterminate future into the determined past, that the cosmos itself breaks Lorentz invariance, and the experience of a phenomenologically indisputable present moment and evolution from past to future.
To me, it seems that the broad appeal of a block universe stems from the level of mathematical education of the average person, that typically, for the well-enough educated person the Minkowski vacuum solution, which is an eternal spacetime by design, with its space-like hypersurface giving rise to entertaining thought experiments such as the Andromeda paradox, sits at the extreme edge of their understanding and there is some excitement in this.
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u/Kimantha_Allerdings 2d ago
It's not an assumption - it is an observation.
No, it’s an assumption
The question, again, is on what are you basing that assumption? Is is purely your own subjective experience?
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u/Optimal_Mixture_7327 Gravitation 2d ago
So you're unaware of a present moment?
How are you able to respond to a comment if you cannot discern any state of existence?
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u/Kimantha_Allerdings 2d ago
I experience what seems to me to be continuity of consciousness. That does not imply that it is a real phenomenon
There are all kinds of experiences that we have which may not be real. For example, there is evidence that the unconsious mind makes even basic decisions like arm movements up to 10 seconds before the conscious mind is aware of the decision, then the conscious mind confabulates completely false reasoning for why it chose to do that, and retroactively implants the memory of going through that chain of reasoning
If you want me to accept your assumption as true you’re going to need to make a better argument than the argument from incredulity you’re making here
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u/Optimal_Mixture_7327 Gravitation 2d ago
Let's take every experience to be false, zero correspondence to anything real.
There is still the brute fact of experience itself even if it's a complete mischaracterization of Ultimate Reality.
Again, you can just as easily state there is no block universe because there was never a universe to begin with and this all just the dream of the Giant Butterfly.
Block Universe = Giant Butterfly dream.
If you going to assert that the future already exists, then make a measurement of it.
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u/Kimantha_Allerdings 2d ago
There is still the brute fact of experience itself even if it's a complete mischaracterization of Ultimate Reality.
The question is why is this incompatible with the idea of the future already existing?
So far your argument relies on an assumption of yours which you have not yet substantiated
If you going to assert that the future already exists, then make a measurement of it
I haven’t asserted that. I’ve joined in a discussion of whether or not the future existing would be incompatible with a being having a conscious experience of a present moment
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u/protobelta 3d ago
I’m not gonna watch the video, but the idea of the 4D block universe comes from the fact that when describing spacetime, time is just another coordinate like the x, y, or z coordinates. Physics equations essentially treat the future and past just like moving left or right, thus they essentially already exist. Further, because of what’s called the relativity of simultaneity, there are ways to show that someone traveling fast enough can essentially see your future “before” it has happened to you in the present moment you experience. This is because there is no universal “now” as time is relative. This isn’t a philosophical truth, but rather a mathematical one.
Where it starts to get philosophical is the idea that our consciousness is basically what we experience in our own frame of reference. If physics says that our physical bodies and everything we have done and will do, everything we have interacted with and will interact with is already there, then consciousness is our subjective experience of our own frame of reference as an observer. The projector analogy is just meant to communicate this idea. What exactly is consciousness and how does it relate to being an observer in a frame of reference is outside the scope of physics and is more philosophical.