Class debate: Everything we see is a result of reflected light

In summary: Just the reverse. The light we see is from photons that did a lot of bouncing.. That's why they are at kilokelvins and not megakelvins.In summary, the two photons are considered to be the same because they are Compton scattered.
  • #1
TL;DR Summary
Light, optics, debate,
Everything we see is a result of reflected light.
True or False
We had an all out war over this question. The question is not as easy as it seems. There are many valid arguments.
It would be interesting to see any opinion or contribution to this argument.
 
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  • #2
Intel Xeon said:
TL;DR Summary: Light, optics, debate,

Everything we see is a result of reflected light.
True or False
We had an all out war over this question. The question is not as easy as it seems. There are many valid arguments.
It would be interesting to see any opinion or contribution to this argument.
False. You see direct, non-reflected light when you stare at at illuminated lightbulbs, candle flames, stars, etc. (But avoid doing this with the sun please.)
 
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  • #3
What about looking at a flame?
 
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  • #4
However when a ray of light is emitted from a source the photons gets reflected on the small particles and doesnt directly reach our eye. its has some reflections on the particles. The sky appears blue to us as a result of this
 
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  • #5
Whacky6414 said:
However when a ray of light is emitted from a source the photons gets reflected on the small particles and doesnt directly reach our eye. its has some reflections on the particles. The sky appears blue to us as a result of this
I would distinguish between diffraction and reflection.
 
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  • #6
Whacky6414 said:
The sky appears blue to us as a result of this....
The blue color of the sky is caused by the scattering of sunlight off the molecules of the atmosphere. This scattering, called Rayleigh scattering, is more effective at short wavelengths (the blue end of the visible spectrum).

From: http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html
 
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  • #7
Intel Xeon said:
TL;DR Summary: Light, optics, debate,

Everything we see is a result of reflected light.
True or False
We had an all out war over this question. The question is not as easy as it seems. There are many valid arguments.
It would be interesting to see any opinion or contribution to this argument.
Actually, everything you see is a result of *absorbed* light. Your rods and cones must absorb light in order to generate a nerve signal.
 
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  • #8
Everything you see is the output of your brain's processes. Much of it is a rendition of the environment around you; not all of it is.

  • Stick your finger in your eye. You'll see stuff that didn't come from the environment, or any light thereof.
  • Get a migraine; you'll see stuff in your vision that is not out there in the environment (it's coming from your compressed optic nerve.)
 
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  • #9
Whacky6414 said:
However when a ray of light is emitted from a source the photons gets reflected on the small particles and doesnt directly reach our eye. its has some reflections on the particles. The sky appears blue to us as a result of this
That's usually called "scattering", not reflection. If you want to use non-standard definitions of words I can't stop you, but it's a pointless argument. In any case, not all light is scattered (not anywhere near all) which is why we see the Sun as a bright disc and not just a glowing blue sky everywhere.
 
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  • #10
Ibix said:
If you want to use non-standard definitions of words I can't stop you, but it's a pointless argument
With an unfortunate username like "Whacky", it is especially unlikely to be fruitful.

I might exclude stars, because the light in stars has spent thousands of years bounching around the interior, but most of the other examples are good.
 
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  • #11
Intel Xeon said:
Everything we see is a result of reflected light.
True or False
What about watching an LED television?
 
  • #12
Vanadium 50 said:
I might exclude stars, because the light in stars has spent thousands of years bounching around the interior, but most of the other examples are good.
The light emitted by the star's surface is made of photons who did no bouncing inside the star. The gamma photons emitted by the thermonuclear reactions don't reach the surface. Even if they did, we won't see them.
 
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  • #13
To the contrary! A photon from a star was bouncing back and forth a lot before it made it out to the surface. E.g. a photon which leaves our Sun has been trapped inside the hot plasma for around 100'000 years before it came out.
 
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  • #14
nasu said:
The light emitted by the star's surface is made of photons who did no bouncing inside the star.
Just the reverse. The light we see is from photons that did a lot of bouncing.. That's why they are at kilokelvins and not megakelvins.

However, the OP seems to have tossed his stink bomb and left the thread,
 
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  • #15
The energy carried by the initial gamma photons reaches the surface after a long time. But the photons themselves? How do you tell that the visible photons are the same as the initial gamma photons? Are the two photons involved in Compton scattering, for example, the "same" photon or are they "different"? It may be just a matter of convention. I don't have any reason to argue either way but I would consider them rather than two photons. This was the reason for my previous post. @vaneesh71 @Vanadium 50.
 
  • #16
I don't think "is that the same photon with a different energy or a different photon entirely" is an answerable question. I think most people understood what is meant by what I and @vanhees71 said.
 
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  • #17
Then why propagate this image of a photon bouncing like a pinball ball towards the surface and eventually escaping into space?
Not all the processes contributing to the opacity of the solar interior are ellastic scattering where you may argue that is the same photon but with the lower energy. There is actual absorption by different mechanisms, on diferent types of ion-electron systems. So many "primary" photons , if any, never reach the surface. But their energy does, eventualy. This is what takes a long time to reach the surface, heat it and result in emission of (close to) blackbody radiation.
By the same picture, the IR photons emitted by a hot stove are actually the visible photons emitted by the fire after they travel through the walls of the stove and loose some energy?
 
  • #18
nasu said:
Then why propagate this image of a photon bouncing like a pinball ball towards the surface and eventually escaping into space?
Because it helps people understand. Apparently not you, but at least classroom upon classroom f stellar interiors students.
 
  • #19
I am trying to find this description in astrophysics textbooks but did not find it so far. Do you have a reference to textbook on stellar interior describing this bouncing of photons through the solar/stellar interior?
My original post was based on the suspicion that this is just a pop science model. So far, did not find a clear answer in the books I looked at. But as you say that it is used to teach students, you may have some reference in mind. I would appreciate a source. Thank you.
 

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