Why is the sky blue on Earth

[Strange]

3 minutes ago, Dalo said:

Which is, allegedly, something that has to do with our vision.

Allegedly?

3 minutes ago, Dalo said:

The idea that objects effectively, "objectively", become smaller or larger with distance

"subjectively"

 

[StringJunky]

For the purposes of the discussion, the sun is smaller than the Earth because the observers and the area of interest are in the vicinity of Earth.

[John Cuthber]

11 hours ago, Dalo said:

1) It seems to imply that the sun, because of its distance from the earth, becomes actually smaller. Is that what you are saying?

Well, OK, you spotted his sloppy use of language but it does get smaller

https://en.wikipedia.org/wiki/Angular_diameter

 

Apparently this concept is difficult for some people

 

11 hours ago, Dalo said:

Which is, allegedly, something that has to do with our vision. The idea that objects effectively, "objectively", become smaller or larger with distance is certainly metaphysically interesting.

Perspective happens with a pin-hole camera.

It's simple geometry, and nothing to do with our eyes.

[swansont]

17 hours ago, Dalo said:

I was not aware of any relevant experiments I refused to consider. Could you be more specific?

Your refusal to consider a grating in preference to a prism, for example.

Your insistence that one must go to Mars, or to other planets, in order to accept that certain laws of physics apply there.

[Dalo]

1 hour ago, swansont said:

Your refusal to consider a grating in preference to a prism, for example.

Your insistence that one must go to Mars, or to other planets, in order to accept that certain laws of physics apply there.

I admit that I do not equate a grating to a prism, nor do I think that what is considered as valid on earth should automatically be applied to other stars and planets.

I believe, just like you do, that the laws of physics are universal, so, in this spirit I should accept all that Physics teaches us as being simply applicable to Mars. But then, we would be forgetting that we are not talking about the physical laws themselves, but our interpretation of them. We are talking about our physical theories, and they cannot claim the same universality as the laws themselves.

4 hours ago, John Cuthber said:

It's simple geometry, and nothing to do with our eyes.

Indeed. Maybe you should think of it as the first case of relativity Einstein should have dealt with.

Edited November 19, 2017 by Dalo

[John Cuthber]

7 minutes ago, Dalo said:

Indeed. Maybe you should think of it as the first case of relativity Einstein should have dealt with.

It has nothing to do with relativity.

You can, in principle, get an image of the whereabouts of a gun emplacement by  getting a thick wall with a hole in it and seeing  where the shells land on "your side" of the wall.

Perspective is, as I said simple geometry.

9 minutes ago, Dalo said:

I believe, just like you do, that the laws of physics are universal, so, in this spirit I should accept all that Physics teaches us being simply applicable to Mars. But then, we would be forgetting that we are not talking about the physical laws themselves, but our interpretation of them. We are talking about our physical theories, and they cannot claim the same universality as the laws themselves.

Make up your mind.

If I was stood on Mars with the spectrometer, I'd take to Mars exactly the same "interpretation" of the laws as I have here on Earth. If, the machine didn't work on Mars then it wouldn't have worked here on Earth.

So that idea doesn't wash.

This isn't postmodernism. Reality is real.

[Dalo]

20 minutes ago, John Cuthber said:

If I was stood on Mars with the spectrometer, I'd take to Mars exactly the same "interpretation" of the laws as I have here on Earth. If, the machine didn't work on Mars then it wouldn't have worked here on Earth.

So that idea doesn't wash.

I am afraid it is your interpretation of universality that "doesn't wash". Reality, as you very well know, can be very complex. We might think that our explanations cover all bases, until we come up against an exception that compels us to review the most fundamental principles of our theory. As it was the case with Relativity and and Quantum Theory.

 

20 minutes ago, John Cuthber said:

It has nothing to do with relativity.

You can, in principle, get an image of the whereabouts of a gun emplacement by  getting a thick wall with a hole in it and seeing  where the shells land on "your side" of the wall.

Perspective is, as I said simple geometry.

The example you give concerns short distances. It becomes more problematic when we consider, for instance, the sun and earth.

I had posed the same question in my first thread (which was blocked), concerning the light coming from the sun and how begged the following question:

"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."

 @StringJunky said  that the rays diverge before and after they enter the atmosphere. I find that "before" still mysterious (unless we take into consideration Einstein's view that rays can be bent through gravity), since it would also only concern a small portion of all sun rays.

Edited November 19, 2017 by Dalo

[Strange]

1 minute ago, Dalo said:

 @StringJunky said  that the rays diverge before and after they enter the atmosphere. I find that "before" still mysterious

I can't imagine why. The Sun radiates in all directions therefore all the rays are diverging from one another. The light that reaches Earth is very nearly parallel, but still diverging (I'm sure someone worked out the angle for you earlier in the thread, or in another similar thread).

[StringJunky]

1 minute ago, Strange said:

I can't imagine why. The Sun radiates in all directions therefore all the rays are diverging from one another. The light that reaches Earth is very nearly parallel, but still diverging (I'm sure someone worked out the angle for you earlier in the thread, or in another similar thread).

Intensity wouldn't diminish with distance otherwise.

[Dalo]

1 hour ago, Dalo said:

"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."

 

[Strange]

39 minutes ago, Dalo said:

"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."

They are nearly parallel because of the distance.

You get rays from all parts of the surface of the sun, which is why you can see the entire sun.

Luckily, you only receive a tiny fraction of them, otherwise you would burst into flames.

Complicated, I know ...

[Dalo]

16 minutes ago, Strange said:

They are nearly parallel because of the distance.

You get rays from all parts of the surface of the sun, which is why you can see the entire sun.

Luckily, you only receive a tiny fraction of them, otherwise you would burst into flames.

Complicated, I know ...

No, you just make it too simple.

If I remember correctly you are one of the people who think that we see an object because its reflection, the rays emanating from it, enter our eyes. And still we see all those parallel rays.

[John Cuthber]

2 hours ago, Dalo said:

I am afraid it is your interpretation of universality that "doesn't wash". Reality, as you very well know, can be very complex. We might think that our explanations cover all bases, until we come up against an exception that compels us to review the most fundamental principles of our theory. As it was the case with Relativity and and Quantum Theory.

Reality is complex. that's why we have studied the manufacture of spectrometers very carefully. We have tested them both as a QC exercise and also by using them in countless situations for over a hundred years.

The one currently under debate is just on a different rock. Why would it be different from one on the rock we call Earth?

Obviously, there might be something odd happening, but that would breach your own stated view on universality.

 

2 hours ago, Dalo said:

"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."

Nonsense, not least , because it's trivially false.

You don't see the back of the sun.

We see very nearly half of it from here.

You have this idea backwards.

We see roughly half the moon, but only a very little of the earth. If we climb a tower we can see further.

 

The higher you are above the surface of a sphere, the more of it you can see.

 

[Strange]

12 minutes ago, Dalo said:

If I remember correctly you are one of the people who think that we see an object because its reflection, the rays emanating from it, enter our eyes.

Do you have an alternative explanation for sight?

12 minutes ago, Dalo said:

And still we see all those parallel rays.

Well, only the ones that enter the eye (where they are focused to form an image). I'm not sure what you think the problem is with that.

 

[John Cuthber]

55 minutes ago, Dalo said:

If I remember correctly you are one of the people who think that we see an object because its reflection, the rays emanating from it, enter our eyes. And still we see all those parallel rays.

Actually, once they bounce of something they are not (usually) parallel. They get reflected in all directions.

[beecee]

23 hours ago, Dalo said:

That is a central assumption in Physics, just like the idea of universal gravity which is simply a theory and which got an extra empirical confirmation on the Moon by Armstrong.

Therefore, either nothing will change for the theory of light, or, if prisms on Mars give another spectrum, a new theory will have to be devised.

You may think that we already know the answer and I cannot blame your conviction, but that is still not a proof.

You really need to go back to basics. Firstly, science in general does not deal in proofs. In fact science has little to do with "proving" anything. Secondly, you need to research what a scientific theory really is: It is not defined as a "theory" as per the general everyday meaning. In other words it is not a guess. [as is a hypothesis] it is an explanation of some aspect of nature that is supported by empirical  evidence and continues to make successful predictions. Secondly a scientific theory is always open to change based on further observational evidence and data, but by the same token, a scientific theory gains in certainty as it continues to match observations. 

Again if I were you I would do some proper research into science and the scientific methodology and take less notice of daily media reports, and rhetoric. 

Edited November 19, 2017 by beecee

[Strange]

1 hour ago, Dalo said:

If I remember correctly you are one of the people who think that we see an object because its reflection, the rays emanating from it, enter our eyes.

No, I think the brain sends sense rays out through the eyes and these detect the objects in our environment. You know, like bats do with sonar. That is why we can find our way around even when there is no light.

[beecee]

On 11/10/2017 at 2:37 AM, Dalo said:

Yes, that is the explanation usually given. 

I wonder: is it scientifically, empirically, proven that colors do not come from the matter particles themselves? Why assume that something is being stopped or let through, and not assume that different matter reacts differently to em waves?

And the correct explanation. The color of any object in the first instant, depends on the EMR being emitted. Then of course that EMR enters the eye, and the properties and structure of the eye and what part of the spectrum it absorbs or reflects determines what colour we see.

You may well ask, what colour is an Orange in the dark? The real scientifically correct answer to that question, is that the Orange is black...or has no colour as no EMR is falling on it, to either reflect, refract or absorb.

[StringJunky]

9 hours ago, Dalo said:

No, you just make it too simple.

If I remember correctly you are one of the people who think that we see an object because its reflection, the rays emanating from it, enter our eyes. And still we see all those parallel rays.

At any given point on a reflective or illuminating surface, photons are travelling in all directions from it (where they aren't blocked) and one of those lines of photons will strike a point on your retina, as placed by your eye lens. Do that for the whole surface from all positions of the object you  get an (inverted) image of that object on your retina. You don't receive parallel rays, you receive the converging ones from all points of that viewed object. if you ask "How can we see stars as we do?",all you are seeing is a white dot which is a single rod being fired on your retina... it has no spatial dimensional value other than your eye is detecting a single line of photons from that star.

Edited November 20, 2017 by StringJunky

[Dalo]

On 11/20/2017 at 3:47 AM, StringJunky said:

You don't receive parallel rays, you receive the converging ones from all points of that viewed object

This is the biggest mystery of all. And if one thinks about how the world looks like in perspective, and how it does from another perspective, one can only wonder how it it is possible that we see the sun "in its totality", meaning, the parts facing us.

The sun rays can only reach us in a parallel way because of our perspective. If we remember how much larger the sun really is, and we still cling to the idea of parallel rays, then we would be a dust speck on the path of the sun, and the few rays getting bent through the atmosphere would show us nothing but a bright speck.

 

That is the mystery of space, and how we see it and experience it. Before the relativity of time, maybe Einstein should have started with the relativity of space.

[Strange]

17 minutes ago, Dalo said:

This is the biggest mystery of all. And if one thinks about how the world looks like in perspective, and how it does from another perspective, one can only wonder how it it is possible that we see the sun "in its totality", meaning, the parts facing us.

It really isn't as complicated as you seem to be making it. Rays from every part of the surface reach our eye. Therefore we can see all parts of the surface. Where is the mystery in that? You seem to be going out of your way to fail to understand so you can claim it is mysterious.

18 minutes ago, Dalo said:

The sun rays can only reach us in a parallel way because of our perspective. If we remember how much larger the sun really is, and we still cling to the idea of parallel rays, then we would be a dust speck on the path of the sun, and the few rays getting bent through the atmosphere would show us nothing but a bright speck.

That is certainly the case for more distant stars, where we cannot resolve the surface. The Sun is close enough that we can see the whole disk. Draw a digram ... calculate the apparent size ... and maybe it will be less "mysterious".

[Dalo]

Just now, Strange said:

That is certainly the case for more distant stars, where we cannot resolve the surface. The Sun is close enough that we can see the whole disk. Draw a digram ... calculate the apparent size ... and maybe it will be less "mysterious".

Yes, draw a diagram... of the sun, earth, the observer, and keep the same ratios as far as size is concerned.

[Strange]

Just now, Dalo said:

Yes, draw a diagram... of the sun, earth, the observer, and keep the same ratios as far as size is concerned.

It won't help you if I do this. You need to do it in order to understand. 

But why is looking at the Sun any different from looking at a coin you are holding or a painting on the wall?

[Dalo]

- I do not!

- you do too!

[DrP]

9 minutes ago, Dalo said:

- I do not!

- you do too!

Ah!  I see the problem now - you are only about 5 years of age!...  well, you are very intelligent for a junior! Well done for thinking about such things. Ask your teacher to explain it to you and they can show you with a diagram how the suns incident rays on the earth are parallel. If you still don't understand it then re address the topic in a few years when you've grown up a bit, learnt a little science, and you might grasp it then.