Physicist’s ideas that the universe is some sort of 3D projection from 2D information seems a bit trendy at the moment.
How do we know that they aren’t simply confusing the way the brain recreates 3D from 2D on the retina with something much larger “out there” ?
Given this scheme, is it fair to say that the info of the universe is held in 2D, which is then made to be 3D, which the human eye picks up as 2D and passes to the brain to make 3D again ?
I get the feeling nobody gets this question…
It’s possible. What physicists have discovered is that it’s possible to formulate 2-D laws of physics that give identical answers to our normal 3-D laws of physics. It’s analogous to the relationship between Cartesian and polar coordinate systems. You can perform calculations in either system and get the same answer.
So maybe the universe is “really” 2-D instead of 3-D. And the apparent 3-D nature of the universe is just an artifact of how our brains process sensory information.
I do not understand the physics theories that you alluding to, but I am confident that they are not confused in the way you suggest.
On the other hand, I do know quite a lot about how visual perception works, and I can assure you that the brain does not “recreate” anything 3D from “2D on the retina”. We do not, in any sense, or at any stage of the process of perception, see the retinal image, its 2D nature is of little significance, and it does not, in any useful sense, constitute a “stage” (let alone the first stage) of visual processing. Admittedly, your misconception about its actual role in visual perception is a very common one (and, very likely, one shared by many physicists), but I am confident that even this misconceived view of vision does not have anything to do with some physicists ideas about a “holographic universe” or whatever.
No. The “apparent” 3D nature of the universe is an “artifact” of how our 3D bodies interact with their environment, which, to all relevant intents (and almost all irrelevant ones), actually is (spatially) 3D. Furthermore, at no stage of the process of perception do our senses suggest otherwise.
But anyway, the physicists are talking about something quite different (although I am not competent to explain what).
Possibly my idea is due to being accustomed to seeing simplified diagrams of the eye, in which light comes in and impacts retina, which looks like an image is being made from an admittedly curved but otherwise flat surface. But the retina is multilayered is it not, and cells are not flat ?
Perhaps a better question then would be why we even get the idea of 2D when nothing we can perceive or experience has anything other than 3 dimensions, not even a diagram on paper.
OK, putting that aside, I’ve been chewing over, occasionally, what the origin of the mathematical objects we are accustomed to using in science actually is ?
I’ve got *Visual Intelligence *by Donald Hoffman here, and he explains that the image in your eye is discrete, analagous to a pointilliste painting, but our perception is of a world of continuous surfaces and edges - implying that continuity is our construction.
So, is our geometry, which seems to be predicated on continuous lines, edges and surfaces, a fiction of the brain taken from our perception ?
Seems obvious, but the entire world of physics seems to talk as if this continuous sort of geometry describes the real world in front of our eyes rather than the construction of our brains.
Is the real world actually continuous and the brain simply does it’s best to reconstruct that continuous world from a fragmented reception on the retina ?
I think it has something to do with black holes; if I understand it correctly, the maximum amount of entropy (and conversely, information) that can exist in a region scales with the boundary of a region, not it’s volume.
We really do live in and experience a world with three spatial dimensions. All physicists agree on that. The holographic cosmology models, however, posit that the three-dimensional Universe that we experience is a holographic projection from a two-dimensional universe which is more fundamental. Meanwhile, there are also other models that posit that our Universe is actually just one slice of a higher-dimensional universe of some sort, with some sort of mechanism (there are a variety posited) preventing us from perceiving the extra dimensions.
I watched this by Susskind a couple of times,
The World as Hologram
and he talks about a painting as being really a 2D image, when a painting is really a 3D image notionally taken as 2D. He also talks about the hot fluid around a black hole as being 2D, which seems also to be something 3D to me. I have to take it that he is not really meaning that paint is two dimensional, nevertheless the language used makes it easy to think that he might.
I struggle to get what they really mean by 2D, because as far as I know matter has 3 dimensions and if information is not held as matter then what is it ?
Like this ?
That is not the issue. I am not denying that the retinal image can, for most practical purposes, be regarded as 2D. What I am denying is that it follows from that fact that the brain must then “reconstruct” a 3D representation of the world from a 2D representation that is (or is derived from) the retinal image(s). The problem is not with your understanding of the structure of the retinal image, but of the role that it plays in the overall process of visual perception.
Vision is not a one way flow of information from the world, through the eye (where it gets reduced, by the optics, to a 2D “picture”), into the brain. The eye is, in fact, in constant motion, actively seeking out behaviorally relevant visual information in the environment.
Despite the fact that its optics are rather like those of a camera, the eye’s functional role in vision is not analogous to a video camera, feeding in an image to the brain like a video camera feeds an image to a monitor screen. A better analogy would be the way in which the fingers can find out what an object is by actively moving over its surface, exploring it, and so finding corners, edges, distances between edges, bumps and ridges, soft and hard bits, differences in texture, etc. In the same way, the eye discovers what things are around us, and where, by actively moving, and so exploring the structure and texture of the reflected light in the environment. (We are not conscious of most of the eye movements we make, but the eyes are in practically constant motion nonetheless.) From this perspective, a retinal image is not the crucial representation of the external world, from which an inner understanding must then be recovered by the brain. It is not that any more than the sensations in the fingertips at one particular moment are the unique tactile representation from which the shape and nature of the object in the hands must be reconstructed. In fact, both tactile and visual perception are processes of active exploration carried out over time, and in (3D) space (although, in the case of vision, that time is often - not always - so short that we do not notice it); perception does not depend primarily upon the momentary states of stimulation of sense receptors, but much more on the chronological pattern of changes in such stimulation as the receptors move. (These movements are, of course, directed by the brain, according to its current informational needs, and the brain’s role in directing such exploration is at least as important a part of its role in perception as is any processing it may do on the incoming data stream. Quite considerable areas of the human brain are concerned with directing eye movements.)
This is all, however, a hijack of, and irrelevant to what I take to be the main point of the thread, which was presumably meant to be about theoretical physics, so I should apologize.
Before I shut up, though, I should admit that the account of vision I just gave is, inevitably, greatly oversimplified, and glosses over many important details and qualifications. However, I do think it is a reasonable rough sketch of the reality, whereas the alternative, much better known, rough sketch, which depicts the eyes as rather like video cameras feeding 2D images (or neural descriptions thereof) into the brain, is almost completely wrong, and extremely misleading.
The best analogy here is, well, a hologram (hence the name). You can capture a three-dimensional image on a two-dimensional* piece of film. Now, as a real, physical object, the film of course is not actually perfectly two dimensional, but suppose that, hypothetically, you did have a perfectly 2D film. You could still capture a holographic image on that film. A very high resolution 2D image is enough to capture and reconstruct a lower-resolution 3D image. Real holographic film, despite having a (thin) third dimension, doesn’t actually depend on it.
That’s very interesting, the eye being similar to the sense of touch actively seeking out reality part by part. I’m sure most people think of it as similar to a camera - I did eyes in school biology probably in the same way as most of the world and that’s how I ended up thinking of it, and I would guess how most people think of it.
I understand also that there is no internal cinema with a homunculous in the head watching the projection from the eyes, but the non-existence of a central self isn’t my current subject either.
But… to quote from Donald Hoffman - Donald D. Hoffman | University of California, Irvine
He goes on to elaborate the point that we construct depth from 2D images.
He’s a professor specialising in this field, so isn’t this an authoritative view ?
In a strictly geometric view this is true, but vision as a cognitive mechanism is a complex process, as **njtt **suggests (although I haven’t formally studied it).
The eye is part of an integrated system that works with the brain. The eyes, and in fact the whole body, move interactively with the brain to collect huge amounts of visual information to be interpreted.
We construct depth using multiple things, such as focus and parallax. However, some optical illusions, such as an Ames room, show that the system isn’t perfect.
In the simplest geometric explanation, the two eyes each a slightly different projection of the 3D world onto the 2D retina, and the brain compares these images using the parallax effect to estimate depth. This effect can be exaggerated by moving the head or body into different positions.
One of Hoffman’s points seems to be that a single 2D image can be mapped from an infinite number of 3D environments. The brain makes tacit judgements about what 3D environment is likely, and subconsciously rules out others. For example, a ball can move back and forth in many different ways but still create the same 2D projection. In the linked example, the shadow is added as a cue to the brain for how it should interpret it. Anamorphic drawings also illustrate this idea.
But it’s an oversimplification to say that the phenomenon of vision is a matter of showing the brain two 2D images.
Yeah, like that; thanks for the link!
Hoffman gives the basic example of a straight line, which we can interpret in any number of ways - edge of a circle, pointing any direction etc. His book is really interesting, BTW. njjt doesn’t like to say the eye makes a 2D image, Hoffman seems to use it as a convention - the whole way scientists talk about 2D is quite mangled it seems to me.
It’s conventional to talk about images on paper as 2D when paper and ink marks are obviously 3D objects, so it’s a bit tricky to know how abstract people are being - but I suppose this is a question of what, exactly, a dimension is and how we abstract it from our 3D experience.
Same with a physicist like Susskind - goes on about 2D paintings and their 2D image. I get that it’s a handy convention but I think using such language also tends to mask what’s really going on, and I don’t know what’s really going on !
Actually, and I checked this out, pencil marks on paper have fractal structures - both the graphite and the paper fibres, so it’s not even clear if they fit into the 3D schema at all. Not to me anyway. That’s another debate.
I am a retired (from teaching, but still actively publishing) professor specializing in this field. I do not accept that his view (if it really is his view: see below) is more authoritative than mine.
He is peddling what I consider an outdated and exploded theory, certainly one that is much disputed and does not satisfactorily address a lot of recent (and some older, but formerly ignored) empirical findings and theoretical arguments. It is sadly true that that view is commonly still taught to undergraduates as if it were undisputed fact, and, it is likely to also be generally treated as such at the depth the open internet generally goes into these sorts of things. Very possibly Dr Hoffman actually knows better, and tells his graduate students about it, but the pedagogy (including most, but not all, of the textbooks that undergraduate teachers rely on) and the popularizations, in print and online, have, for the most part, yet to catch up to the cutting edge of the actual science.
Here are a couple of textbooks that explain the more modern theory of vision that I am talking about, but, unfortunately, you will not be able able to access more than a few pages of them online, for free:
Active Vision: The Psychology of Looking and Seeing
Looking and Acting: Vision and eye movements in natural behaviour.
Beyond that, we would have to be getting into the actual technical research literature itself.