I mean the beam coming out of the torch. — Hachem

You mean a scene like this? :



There is no beam. Can you show me a specific example of what you're referring to? Fire generally doesn't create "beams" of light, or at least not very strong ones. The fire is illuminated because that's where the photons are coming from.

I meant simply an electric torch to light the way through the dark wood.

Like this?



What you're seeing there are particles (like dust and water vapor) reflecting photons from the "beam" of light that flashlights produce. If the air was perfectly clear (a vacuum) you would not be able to see the beam whatsoever.

Regular atmosphere also reflects photons, but it since it's pretty thin the effect is very minimal (unless we're talking about many kilometers of thickness, which essentially is what causes the greenhouse effect...).

That is the explanation I expected. There are some things which I would like you to explain to me. I know it sounds rather simple, but we are trying to determine where our views diverge, and I hope this will help

The electric torch is shining forward, that is the direction of the beam. When the photons coming out of the torch hit the air particles light is produced that is reflected in all directions. My first question, and let us take it one step at a time, is: how far is the light reflected off the particles?

The electric torch is shining forward, that is the direction of the beam. When the photons coming out of the torch hit the air particles light is produced that is reflected in all directions. My first question, and let us take it one step at a time, is: how far is the light reflected off the particles? — Hachem

You've already made a mistake though. Photons come out of the torch (zillions of them) and a lot of them are sharing similar directions (they're in a "beam"). When individual photons in this beam happen to strike particles (dust, water molecules, etc...) they get "reflected". The reason why "color" is interpretable from the resulting reflected photon is because a portion of it's energy is absorbed (pertaining to R-G-B wavelengths on the light spectrum). One reason why light doesn't reflect off of objects for eternity is because eventually they will be entirely adsorbed by the atoms they collide with. An interesting side note here is that when electrons absorb light energy they become more "excited" which basically translates to heat energy that distributes through it's atomic structure. Black tends to reflect very little visible light (which is why it appears dark) and absorbs much of it. This is why a dark surface will heat up much more quickly when exposed to direct sunlight!!!

So to reiterate, when photons strike particles, they are reflected and a portion of their energy may be absorbed, which can change where that light falls on the color spectrum. New photons are not generated from a single photon striking a surface or particle (not without a "photoelectric effect"), and individual photons are reflected according to the angle that they happen to strike a given surface or particle.

If you understand the above, the answer to your question is that individual photons will keep traveling until they encounter some obstacle or are absorbed by something. I cannot tell you at what distance the photons become too spread out for us to detect, but individual photons themselves will go on until interrupted.

the answer to your question is that individual photons will keep traveling until they encounter some obstacle or are absorbed by something — VagabondSpectre

I will ignore my mistake for now, and plod further. This is a moment of great mystery for me, photons that go on indefinitely unless they are stopped.
I also have great difficulties with the Maxwellian model of electric field creating or calling up a magnetic field, which in turn...
Both these phenomena reek of pepertuum mobile. Don't you think?

I will ignore my mistake for now, and plod further. This is a moment of great mystery for me, photons that go on indefinitely unless they are stopped.
I also have great difficulties with the Maxwellian model of electric field creating or calling up a magnetic field, which in turn...
Both these phenomena reek of pepertuum mobile. Don't you think? — Hachem

So...

If you throw a ball in empty space, why should it slow or stop? If an electromagnetic wave throws a photon into empty space, why should it slow or stop?

Beyond this things get genuinely complicated if you want to understand the behavior of individual photons ("EM waves").

When you create and launch an individual electron or photon, it's "position" can be legitimately described as a wave like function of possible positions. While it's in wave or "photon" form there is no way to describe it as physical. It's a very mysterious thing we sometimes call a "particle-wave". When this wave comes into contact with something, it gets absorbed at a particular spot along an arc or function of possible positions that it could have "appeared" and gotten absorbed at.

While it's in wave or "photon" form there is no way to describe it as physical. It's a very mysterious thing we sometimes call a "particle-wave". — VagabondSpectre

We seem to have left the realm of Physics altogether.

I also have great difficulties with the Maxwellian model of electric field creating or calling up a magnetic field, which in turn... — Hachem

We don't know why moving electrons create large electromagnetic fields and even electromagnetic waves in the form of photons, we just know that they do. (we don't yet really know what an electron is).

We seem to have left the realm of Physics altogether. — Hachem

Yes, and entered the realm of quantum physics (which describes itself as strange, but really it's all physics)...

Well, I suppose we have come to what really separates us. Different metaphysical models. See, I do not believe that photons, whatever they are, go on indefinitely. I think it is just a very convenient thing to postulate. It might of course be true, still I prefer the following test which I presented in the other discussion. The one of two observers, one near earth, and the other on Mars, and how they could communicate with each other through telescopes.
Just to avoid any more misunderstandings: sending light or radio signals would happen at a speed lower or at the most equal to the speed of light.

I thank you for your patience and explanations, but I am afraid that we are just like two religious people with a different faith. However much we learn about the other faith, we still prefer our own.

There is hope though, my faith can easily be declared false, and for that the simple test I described is more than sufficient.

I wonder, what kind of test could possibly prove Quantum Physics wrong?


https://thephilosophyforum.com/discussion/comment/109157

The difference between faith and science is that science yields to evidence...

We currently communicate with satellites orbiting Mars and we understand very well the delay caused by the distance between us... Telescopes aren't magical such as you describe, they're just fancy eyeballs that enhance resolution. I don't understand why you believe your experiment would prove you correct.

I encourage you to seek a more formal education of physics. It shouldn't take too long before you realize just how fundamentally reliable and demonstrable the current model actually is...

If you want to get anywhere in science though, then forget your faith. You need to modify your intuition and theories to fit with what the evidence shows, not with how you think things should be.

Thank you for your advice.

Light Rays, Objects and Vision

Have you ever thought about the fact that we are able to take a picture of the sun, the ultimate source of light?
For that we have to neutralize the light rays overwhelming our sensors.
But what does it mean that we can see behind the light rays?

Light theory would make us believe that it is those rays, that make our cameras and eyes blink, that carry the image of the sun to us. But which rays are we talking about? And is it really just a matter of intensity?

Let us suppose that it is indeed a matter of how strong the light is. If it is too strong, all we see is the light itself.

Remember the burning glass trick? Focus a magnifier in such a way that it can burn through a sheet of paper? But what if you do not want to burn the paper, and aim at projecting an image of the sun instead?

Very simple, you make sure that the rays are (slightly) out of focus on the paper. As we all know, an image of a distant object will appear after the focal point, and will be inverted, its size depending on the focal length of the objective.

Think about that. What is then forming the image if all rays are made by the lens to converge on a focal point? After all, they start diverging right after that until they are too far from each other to be perceived as an image.

Ray tracing glosses magnificently on this annoying fact. It makes us draw lines from the object to the image, but those lines are imaginary lines, while the only lines we can see and make visible are the rays captured by the lens and made to converge or diverge.

Ray tracing is in fact tracing an alternate reality. The image can appear anywhere after the focal point and that makes it very difficult to define what exactly is a focus.

Ray tracing tells us that a point i on the image is in focus when all the rays emanating from a point o on the object converge to i.

But where are those rays, and how come we cannot see them? How come we can see all the light rays converging, or diverging, through a lens, but not the ray tracing rays?

Ray tracing rays, just like light waves, are mathematical constructs that make it possible for us to build a rational image of the visual world, but it would be very difficult, if not impossible, to prove their empirical existence.

All of this simply means that we do not know how images are formed, even if we have a very rational explanation for it. This explanation remains a geometrical fiction, however useful it may be.

Of course, something does not need to be visible to exist. After all, who in this century would dare deny the existence of atoms and sub-particles?
But we are talking about light, something very tangible, and only meaningful, as far as images are concerned, when it can be made visible.

What are light rays, or waves, that are only visible to the mathematician?

Distance, Object Size and Light

I have already discussed of the singular fact that objects become smaller with distance. For that I got treated to an elementary lesson in Optics and spatial perspective, as if that were an explanation in itself.

Here is a puzzle.

When an object is distant we assume that the light rays it propagates become somehow parallel. Just like waves when they are infinitely stretched.
This is a central assumption of Optics. How well is it justified?

We will all agree that the object in the distance has not somehow shrunk to its visible proportions, and we do not doubt an instant that if we were to approach it, it would regain its true size.

Imagine alien observers looking at our Sun from a few hundreds or thousands of light years away. It would appear to them as very small of course.

Think now of the light rays emanating in their direction. How could they ever become parallel with the distance? And if they did, wouldn't that mean that the alien observers would in fact be incapable of even detecting the sun since only a small portion of the parallel rays would be captured by their telescope?

But now that you think of it, if the light rays do not become parallel, how would it be possible at all for these observers to see our Sun? Since the sun is radiating rays in all directions, and these rays, just like Faraday's electromagnetic lines of force, would keep diverging from one another, weakening the light of the sun until it disappears entirely, there will come a moment where the distance between each (invisible) ray would become so great that the largest telescope would not be enough to gather them through the same lens.

No, apparently, the only way for the Aliens to see our Sun would be if our fiery star did shrink with the distance. Only this way could its rays become parallel and enter the alien telescope.

Where is Poisson when you need him?

Poisson, an ardent supporter of Newton's corpuscular theory, had calculated that Fresnel's theory implied that there should be a bright spot at the center of the shadow of a circular object. That, he thought, was ridiculous and proved that Fresnel's analysis was wrong. Arago is supposed to have proven that it was indeed the case.
I could not find any article or fragment by Arago in which he talks of such an experiment. If you know of one, please let me know.

I have taken pictures with a pinhole lens and extension rings, as I have said in another thread. I noticed that the exposure time needed to be longer the more rings I used, that is the longer the focal length became.

I find it very strange for two reasons.

1) The same center of the scene keeps being projected, and should therefore be unaffected by the narrower field of view. Certainly for distant parts of the image.

2) Center rays, those going through the center of the pinhole and the rings in this case, should be completely unaffected by the length of the extension rings. They are after all on a direct and free path to the camera sensor.

This should mean that whatever the aperture, the center of the image should remain as bright, or at least brighter than the rest.

We should always have a Spot of Poisson on every picture ever taken by a camera at small apertures, or every image projected on a wall through a pinhole.

I will be grateful to whomever shall explain to me why that is not the case.

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