Thread: Why do things look smaller the farther away they are?

I understand the Euclidean and Optical explanations for the most part and being an occasional artist and photographer, the elements of linear perspective (and other culturally induced visual perspectives) are familiar to me. ….ex. the Renaissance term of Chiaroscuro.

However, I cannot seem to get to the root of any kind of Quantum or Relativistic explanation. What exactly is the answer when considering the motion of photons?

Is the phenomena of photon energy dispersion (Thompson Scattering?) part of the explanation?

(I know dispersion causes Chromatic aberration in optics)

Is this due to gravitational effects and the curvature of space-time? Any insights here are very much appreciated.

Inverse square law? An object A which is twice as far away as an identical object B will take up 1/4 of field of vision that object B does, and likewise reflects 1/4 the light into your eye, but you knew that. Why are you looking for a Quantum or Relativisitic explanation? I'm not trying to be a wise guy, I'm a noob here.

Beyond my understanding, but maybe I have a thought or two.

What is "far away?" I will suppose you mean spatial distance, as that is the first approximation.

So what is distance, or as I prefer to think of it, what is separation? This gets more complicated than one might think.

You probably know about the added dimensions in string and m theories. What happens to our usual idea of distance when more dimensions are added? Maybe an added dimension could provide a means to travel from point a to point b with less separation. Think of a mobius strip, a fundamentally two dimensional object. If a pencil point is not allowed to leave the surface, it can travel around the loop the long way, but if it is allowed to pass through a "hole" in the surface, the separation may be much less, or even zero. Point a and point b may be separated by nothing more than the thickness of the paper. So, what "way" (as in 'Far Away') should we talk about?

Have you considered Richard Feynman's response to the Michealson Morley two-slit phenomena? He concludes that photon behavior can best be thought of as the sum of all possible pathways between a and b. I have his book somewhere here but would have to search for it.

But, one point at a time. I'll wait for a reply rather than drone on endlessly.

You know, i never really thought about it at all until I saw this thread. Because, to be honest, it seemed like a kind of obvious question. Before reading this thread I would have responded "Because it's far away, duh" I never considered something getting smaller in the distance to be an optical "illusion", to me if it stayed the same size while getting further away THAT would be an optical illusion. Its a good question that makes an otherwise "easy" question, very difficult to answer. So, for now heres a bump for this thread, and i'll keep checking back to see if theres a good answer. This kinda blows my mind in the same way the idea of a "holographic 2d" universe does.

Originally Posted by Alamaral

Inverse square law? An object A which is twice as far away as an identical object B will take up 1/4 of field of vision that object B does, and likewise reflects 1/4 the light into your eye, but you knew that. Why are you looking for a Quantum or Relativisitic explanation? I'm not trying to be a wise guy, I'm a noob here.

By parameters of the question, it is an optics question of the observable universe. Relativity is only a factor if there is enough mass between the observed and the observer to warp space enough to act as a gravity lens. Principles of quantum mechanics would imply that there is some effect caused by the observation, but since you are probably looking at a macroscopic object as opposed to a sub-nuclear particle, the effect of QM are essentially swamped out and classical mechanics and electromagnetic theories would apply.

Alamaral basically has it right. It really has nothing to do with Quantum or Relativistic effects but everything to do with the angle of light rays coming from the object entering your eye.



This diagram shows how the light from different points of an object travel through the lens of an observers eye and reaches the back of the retina where one "perceives" the object. The more space on the retina the object covers the "larger" that object appears to the observer.


Now due to the inverse square law as Alamaral mentioned previously, the further an object is away from the observer the shallower the angle will be for the light entering the eye. A lot of the light that was traveling from the object that entered the eye when up close will now miss the eye completely because of the increased distance between them. Only light with much shallower angles or close to parallel will now enter the eye.

.


Here's a rough sketch I tried to make to illustrate this.


Since the refracted image on the retina covers a smaller area as compared to when the object was close up, we perceive it as "smaller". No modern physics needed

Originally Posted by vintster

Alamaral basically has it right. It really has nothing to do with Quantum or Relativistic effects but everything to do with the angle of light rays coming from the object entering your eye.



This diagram shows how the light from different points of an object travel through the lens of an observers eye and reaches the back of the retina where one "perceives" the object. The more space on the retina the object covers the "larger" that object appears to the observer.


Now due to the inverse square law as Alamaral mentioned previously, the further an object is away from the observer the shallower the angle will be for the light entering the eye. A lot of the light that was traveling from the object that entered the eye when up close will now miss the eye completely because of the increased distance between them. Only light with much shallower angles or close to parallel will now enter the eye.

.


Here's a rough sketch I tried to make to illustrate this.


Since the refracted image on the retina covers a smaller area as compared to when the object was close up, we perceive it as "smaller". No modern physics needed

Um. correct me if I'm wrong, but this image is off. The image, (the light) should go through a POINT on the lens. That's what puts it in focus.

no, one usually considers light coming from an infinitely far away source so that all rays are parallel entering the lens. The lens focuses the collection of parallel rays entering it. So if you have a close object, that picture is exactly what is happening. Every point radiates a spherical light propagation. So what you see is the sum of a bunch of solid angles of spheres entering the lens at once.