I don’t think it would look like a wall, either. It would just look like a big flat floor, only slightly more so. The fact that it is infinite in size really wouldn’t affect its appearance very much at all.
The difference in apparent horizon height between standing at the centre of a 600ft-diameter flat disc suspended in space, and standing at the centre of the OP’s infinite flat plane, is less than 1 degree.
Quick illustration of an observer’s view on a 600ft-wide disc and on an infinite plate (not to scale). The red cross shows the centre point of the field of view.
On a finite floor you’re right but on an infinite floor, you would lose all clues as to distance. No railroad track effect or change in brightness/sharpness of image. Stereoscopic clues are useless. Think of being in a room of uniform whiteness that is perfectly lit. What clues do you have to identify the difference between floor and wall or are the two indistinguishable? I thinks a slimilar effect may work here.
Without texture or atmospheric dimming, etc. it won’t be possible to tell anything much about the groundplane, other than that it occupies the bottom half of the world - this might well cause the mind to perceive it as being a fairly small bowl.
It also means you’d not be able to land an aircraft on it without crashing, using visual cues alone - because there would be no way to (visually) gauge altitude at all
Ok, if this plane is featureless, there’s no way to tell whether you are in a spherical section like bowl, or a section of a cylinder. The ground would just appear to be everywhere beneath your eye level when looking straight ahead. Adding a grid, the ground would appear curved. Obviously there is something (that for some reason isn’t being called a horizon) straight ahead, where light emanating from the ground no longer enters the eye. Everything above that is sky.
There is any easy way to see the results of this. Go outside in Kansas, or on the ocean or a large lake, at night. Stop paying attention to the ground, which is actually curved. Pay attention to everything above the ground. This is the same effect. The sky extends infinitely. Even though the stars are different distances away, you can’t discern that because of the great distances, they will all appear to be the same distance away, on the surface of a great bowl.
The bowl effect occurs because we see things as if they were on the inner surface of a sphere intersected by a cone. Light from nearby locations hits our retinas at distinctly different locations in each eye, giving us depth perception. Far away, the light hits the retinas in the same location, or close enough, that we can no longer distinquish the distance, and everything appears the same distance away. To be equidistant from a point, they would have to be on the inner surface of a sphere, a section of which is the bowl we see.
So, there is a finite bowl of some diameter that has the same ray diagram as an infinite plane for a five foot high eye, if no features are present to give direct scale by natural triangulation.
Both would look like a flat ground and open sky. The brain is where this happens, not the eye.
Lacking features, I’m not sure whether or not you perceive the ground as flat. You perceive the night sky as a bowl because it has features. If it has none, I don’t know.
Sure, if the walls are the same colour as the floor. But I’m assuming that the infinite plane is a different colour from the “sky”.
No, I’m still not having this “bowl” idea when it comes to the ground.
The night sky looks like an inverted bowl above you because, as you say, all the stars are, effectively, at infinity, and so you perceive yourself to be at the centre of a sphere. If you look straight up, you’re seeing “the same distance” as you are if you look 45 degrees up from the horizon, or 10 degrees, or 0.01 degrees.
With a flat plane, that’s not true. If you look straight down, you’re seeing about 5 feet away. If you look down at 45 degrees, you’re seeing a distance along the hypotenuse of right-angled triangle of sides 5 feet, i.e. just over 7 feet*. If you look down at 10 degrees below the horizon, you are looking a distance of about 28.8 feet, and so on.
You can’t compare the “spherical” sky above you to the flat ground below you. I still maintain that the ground will look totally flat, and fail to see where people are getting this curved bowl idea from. If the ground is totally featureless, with nothing for your eyes to fix distance on even at your feet, then you wouldn’t perceive it as flat (it would be a “whiteout” covering half your field of vision), but neither would you perceive it as curved… it would just be… nothingness. I am assuming instead that we are talking about a giant flat car park, or Kansas wheatfield, or something, with enough surface features for your eyes to get a fix on.
*7.07 feet from your eyes diagonally to the ground [sqrt (5[sup]2[/sup] + 5[sup]2[/sup])], but 5 feet horizontally from where you are standing.
Here’s a stock image that illustrates what I mean. This plane appears to be infinite (OK, the algorithm that produced it probably didn’t go quite to infinity, but as I pointed out above, the visual difference between an infinite plane and a simply very big plane is essentially nothing) and it certainly doesn’t look curved or in any way “bowl-shaped” to me, even though it starts off “below my feet” and ends up “at eye level”.
I think the whiteout is correct. By curvature I just meant you would sense that the ground is rising up at some point to form the ‘horizon’, but not necessarily as a smooth curve, it could be perceived as any shape, but the whiteout situation sounds more likely, not flat, but no shape that can be determined.
My last post got lost right at the bottom of the previous page. See this stock illustration. That (minus the cheesy sun effects) is pretty much what I think an infinite plane would look like, if it had surface detail. It looks perfectly flat, as far as the eye can see, and never appears to “rise up” to form the horizon, even though the horizon is clearly “higher” than the ground beneath your feet. There’s no “bowl” illusion at all.
Based on my (admittedly limited) understanding of how we see, our eyes/brain are going to take samples of what we see ahead and form them into a composite image.
The eyes continuously move slightly, so even if we are looking straight forward, perfectly parallel with the ground plane, our eyes will be taking samples at parallel (seeing sky), at 0.000…01° above parallel (again seeing sky) and at 0.000…01° below parallel, seeing ground some finite (if very great) distance away. The brain will paint in the rest of the details, painting in a (straight) horizon between parallel and the nearest measurement below parallel.
My reading of the discussion is that it wouldn’t look like a bowl, just that a featureless bowl would look exactly the same. The bowl would look like an infinite plane. How would you tell the difference between a featureless bowl with a lip at eye level and an infinite featureless plane?
I’m saying that it wouldn’t - it would appear flat.
I’ll allow that a featureless bowl with the rim at your eye level would also look flat, if there were no shadows to give away the curvature, but a bowl with a grid would look very different from a plane with a grid, as in the illustration I just posted.
I’ve had a couple maths teachers who would have told you that trig *is *poetry. Mathematics does strange things to some people. Plaid sleeveless sweaters is the least of them.
What if you’re sandwiched between two infinite planes? Clearly, both would appear to meet at the horizon, and I can see the brain interpreting this as either or both being curved: after all, one is clearly above, the other clearly below you, so in order to ‘meet’, they’ll have to curve. Perhaps the perception of this would change depending on how far you are from either plane – being very close to the ground, it seems about flat, the amount it needs to curve to meet the horizon being negligible; but if you ascend, the horizon stays at your eye level, leading to a greater inferred curvature because of the higher apparent distance between ground and horizon (i.e. your eye level).
My guess would be that, since we’re so used to seeing ground and sky, our brain would process that as the bottom one being flat and the top one being domed.
Well that does have a grid on it, which actually cues the eye to think it’s flat. I think random features would make it more difficult. Again, by curved, I didn’t mean a specific shape. Chronos may be right though, we probably tend to consider the ground flat, no matter how it appears.
If the ground is totally featureless, with nothing for your eyes to fix distance on even at your feet, then you wouldn’t perceive it as flat (it would be a “whiteout” covering half your field of vision), but neither would you perceive it as curved… it would just be… nothingness. I am assuming instead that we are talking about a giant flat car park, or Kansas wheatfield, or something, with enough surface features for your eyes to get a fix on.
