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Dalo

Sunny reflections

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14 minutes ago, Dalo said:

The question I am asking is how this obvious fact relates to the idea that light rays, in this case sun rays, are propagated in all directions?

Because only one ray will go from the sun, to the mirror, to the eye. Someone in a different position will see a different ray, that took a different path. It's not that complicated.

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Edited by Strange

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3 minutes ago, Strange said:

Because only one ray will go from the sun, to the mirror, to the eye.

and how do you explain that?

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My apologies for the OT discussion.
I only brought up how sight works as a response to Dalo's reference to Homunculus.

I did suggest that he would have better understanding if he considered the ray going back from his eye, to the object ( and to the light source )
Not the other way around, which generates the multiple reflections.

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2 minutes ago, MigL said:

I did suggest that he would have better understanding if he considered the ray going back from his eye, to the object ( and to the light source )

Agree.

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4 minutes ago, MigL said:

My apologies for the OT discussion.
I only brought up how sight works as a response to Dalo's reference to Homunculus.

I did suggest that he would have better understanding if he considered the ray going back from his eye, to the object ( and to the light source )
Not the other way around, which generates the multiple reflections.

I am not sure I understand what you mean. Maybe you could elaborate?

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7 minutes ago, Dalo said:

and how do you explain that?

Are you joking? It is pretty obvious. There is only one possible line from point A to point B that is reflected from a plane surface. Did you skip basic geometry at school? You know, the properties of straight lines and angles?

If you think this is wrong, then draw a diagram with two different lines from A to B. 

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2 minutes ago, Strange said:

Are you joking? It is pretty obvious. There is only one possible line from point A to point B that is reflected from a plane surface. Did you skip basic geometry at school? You know, the properties of straight lines and angles?

If you think this is wrong, then draw a diagram with two different lines from A to B. 

You are still missing the point I am afraid. Forget about reflection since it seems to confuse the issue. Let us assume that we agree on it as an empirical fact and how it can be explained geometrically.

 

The question is: knowing all that concerning reflection, how can we think that light rays are propagated in all directions? 

The last suggestion is: start from the subject, or his eye, instead of from the light source. I find it a very interesting suggestion and I would like to hear more of it.

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12 minutes ago, Dalo said:

The question is: knowing all that concerning reflection, how can we think that light rays are propagated in all directions? 

Did you ignore the diagram I posted? We know the Sun illuminates objects in all directions. Are you being deliberately obtuse?

15 minutes ago, Dalo said:

The last suggestion is: start from the subject, or his eye, instead of from the light source. I find it a very interesting suggestion and I would like to hear more of it.

Really? Again?

https://en.wikipedia.org/wiki/Ray_tracing_(graphics)

Go ahead. Ignore this answer and ask the same thing again. 

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4 minutes ago, Strange said:

Go ahead. Ignore this answer and ask the same thing again. 

Go ahead and say the same thing again and again.

Imagine a unit circle (in meters). Put statues all around it, placing them on the perimeter. Make sure the circle is illuminated by the sun at some other time but real noon (the zenith). Now measure the angle of each shadow.

 

I will admit that I have never actually performed the experiment, so I am really curious as to what the result would be.

Will each shadow have its own angle (relative to some reference coordinates), or will all statues have shadows at the same angle?

What could we conclude regarding the way sun rays are propagated through space?

 

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5 minutes ago, Dalo said:

I will admit that I have never actually performed the experiment, so I am really curious as to what the result would be.

Maybe you should. You might learn something.

But you don't need to do the experiment. Draw the frigging diagram.

6 minutes ago, Dalo said:

Will each shadow have its own angle (relative to some reference coordinates), or will all statues have shadows at the same angle?

They will all be at a slightly different angle, but so slight that they will appear to be parallel. Why not calculate the angle between them? Then it might make more sense.

Quote

What could we conclude regarding the way sun rays are propagated through space?

In your case, nothing, apparently.

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20 minutes ago, Strange said:

They will all be at a slightly different angle, but so slight that they will appear to be parallel

I admit that I still do not understand, so please bear with me.

If rays were propagated in all directions, shouldn't  the angles differ much more one from the other?  If instead of statues we used thin sticks, wouldn't that make a difference?

Also, a remark I placed earlier. When you look at the reflection of the sun on the water, you get blinded, but stepping aside solves the problem. If rays were propagated in all directions, shouldn't you get blinded wherever you stood.

 

Here is a little "experiment" I made: shine an electric torch on the bathroom mirror. You will see the wide beam illuminating the mirror and its surroundings. You will also see the lamp itself of the torch, as a bright spot. If you move the torch around, the beam will describe a wider circle than the central bright spot of the lamp that will seem almost not to move.

The rays of the beam will all move together in the same direction. Maybe the same thing happens with the sun?

Edited by Dalo

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4 hours ago, Dalo said:

If rays were propagated in all directions, shouldn't  the angles differ much more one from the other? 

What do you you base that "should be" on? Why not work out what the angle should be.

 

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The sun happens to be 150 mill km away, so the rays reaching the Earth are essentially parallel.

I imagine ( hope ) you could calculate the angular difference between the rays subtended by your statues' separation.

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1 hour ago, Dalo said:

I admit that I still do not understand, so please bear with me.

If rays were propagated in all directions, shouldn't  the angles differ much more one from the other?  If instead of statues we used thin sticks, wouldn't that make a difference?

Also, a remark I placed earlier. When you look at the reflection of the sun on the water, you get blinded, but stepping aside solves the problem. If rays were propagated in all directions, shouldn't you get blinded wherever you stood.

 

Here is a little "experiment" I made: shine an electric torch on the bathroom mirror. You will see the wide beam illuminating the mirror and its surroundings. You will also see the lamp itself of the torch, as a bright spot. If you move the torch around, the beam will describe a wider circle that the central bright spot of the lamp that will seem almost not to move.

The rays of the beam will all move together in the same direction. Maybe the same thing happens with the sun?

  

Here's the shadows made by 1 meter high sticks illuminated by a point light source located 3 meters to the right and 3 meters above the plane. They point at different angles

  shadows01.png.7dc710c96f2584781e41e1546a7d7e0b.png

 

Here are the same sticks illuminated by a light source in the same direction but at the distance of the Sun.  They appear nearly parallel.   shadows2.png.4faa7eca8612ddce02da6cebf764d311.png

The reason for the difference is the distance of the light source.  You get shadows at obviously different angles in the first image because the spacing of the sticks is a good sized fraction of the distance to to light source.  In the second image, the light source is so far away (150 million km, as already mentioned.), that the light rays that reach the sticks are very nearly parallel to each other.

This diagram shows what's going on.

On Orange lines are rays of light emitted in many directions by a light source, the red dots are objects casting shadows, and the black lines are the shadows.  Only rays of light heading from the source in the direction of the objects will produce shadows and those shadows will point in the direction of the rays of light the objects block.

In the top image, the light is fairly close and the angles between the shadows wide. In the second image, the light is further away and the angle between the shadows is narrower. 

shadowlines.png.4414207c37ccf6fc1ec31eba59bc7b91.png

 

 

To put this to scale with sun light, imagine that the red dots are 1 inch apart. Then to match sunlight, the light would have to placed 1.8 miles to the right of the dots.  At this distance, the angle difference between the shadows produced would be 0.006 degrees.

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48 minutes ago, Janus said:

  

Here's the shadows made by 1 meter high sticks illuminated by a point light source located 3 meters to the right and 3 meters above the plane. They point at different angles

  shadows01.png.7dc710c96f2584781e41e1546a7d7e0b.png

 

Here are the same sticks illuminated by a light source in the same direction but at the distance of the Sun.  They appear nearly parallel.   shadows2.png.4faa7eca8612ddce02da6cebf764d311.png

The reason for the difference is the distance of the light source.  You get shadows at obviously different angles in the first image because the spacing of the sticks is a good sized fraction of the distance to to light source.  In the second image, the light source is so far away (150 million km, as already mentioned.), that the light rays that reach the sticks are very nearly parallel to each other.

This diagram shows what's going on.

On Orange lines are rays of light emitted in many directions by a light source, the red dots are objects casting shadows, and the black lines are the shadows.  Only rays of light heading from the source in the direction of the objects will produce shadows and those shadows will point in the direction of the rays of light the objects block.

In the top image, the light is fairly close and the angles between the shadows wide. In the second image, the light is further away and the angle between the shadows is narrower. 

shadowlines.png.4414207c37ccf6fc1ec31eba59bc7b91.png

 

 

To put this to scale with sun light, imagine that the red dots are 1 inch apart. Then to match sunlight, the light would have to placed 1.8 miles to the right of the dots.  At this distance, the angle difference between the shadows produced would be 0.006 degrees.

Thank you. I will study this very carefully and welcome any other information.

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@Janus
First, thank you for the drawings, they are very enlightening and impressive. They also show why reflection concerns the projection of one space point onto another single image point. They make  in fact very nicely the abstract laws of reflection visible .

Concerning the point where rays, or rather waves, become parallel with the distance. I think it is a fundamental assumption without which reflection would be unexplainable.

Parallel light rays do create their own problems I am afraid.

Imagine the Sun in all its majesty and... size. Its rays would start all entangled and criss-crossing each other, to slowly disentangle and become parallel. That is of course only possible if we enter the quantic field of wave-particles and forget about the abstraction of "ray" or even "wave". Only then can such an idea become meaningful.

Back to the size of the sun. It is infinitely larger than our circle, and parallel rays/waves/particles can only mean that but a negligible fraction of those light elements, however we may want to qualify them, will reach the circle.
That is also not a problem for our circle. As long as there are enough of them to create shadows we are covered, so to speak.

It becomes more problematic when we want to explain the fact that we can, or at least think we can, see the sun in its totality (with the proper protections). Its sheer size becomes then unsurmountable.

How come we can see the sun if its rays are reaching earth in a parallel fashion?

So, I am afraid that we are back to square one: we have no problem explaining reflection as long as it means a one on one correspondence between object and image.

It is when we abandon this principle that we encounter problems.

Edited by Dalo

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At the risk of going off topic again, your eye ( and any other viewing device ) is equipped with a set of convex lenses which focus the incoming parallel rays to a spot on your retina.

It does not matter how many reflections there are; the only one you 'see' is the one that strikes your eye. So the only way to analyze the situation is by considering straight rays from the eye back to the source. That's why we call it geometric optics.

Leave photons and waves out of this ; they are not suitable for this analysis and would only complicate it unnecessarily.

How many more times and more people need tell you the same thing ?

Edited by MigL

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46 minutes ago, MigL said:

At the risk of going off topic again, your eye ( and any other viewing device ) is equipped with a set of convex lenses which focus the incoming parallel rays to a spot on your retina.

You are referring to the process of image formation through a lens, a process in which rays, however they fall on the lens, cross each other at a focal point.

This is a very understandable and well understood process, the quality of our optical devices from cameras to space telescopes being and undeniable proof of our technical know-how.

You conveniently forget what the central issue is: if the sun rays reach the earth in a parallel way, only a very negligible fraction will reach our eyes, wherever we stand. And still, we see the sun in its totality.

That is the puzzle I would like to see solved.

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2 hours ago, Dalo said:

So, I am afraid that we are back to square one:

!

Moderator Note

No. I was willing to think you were just having a mental block, but after the excellent explanations given (thanks, all), your continued persistence in misunderstanding is indistinguishable from trolling. You seem to be purposely missing the point, so this discussion is over. You aren't allowed to bring it up again unless you do it in the spirit of learning.

Thread closed.

 

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