Light: visible or invisible?

[MigL]

The information the violet photon carries, John, is not related to itself but to its last scattering, or, temperature of its emitter.
The information itself is 'altered' in some situations. Light coming up out of a gravity well is red-shifted. The car's color doesn't change. The information getting to the detector ( eyes ) does.

( Wait a minute, is that argument in my favor, or against ? Damn, I hate this definition stuff. )

[beecee]

33 minutes ago, MigL said:

The information the violet photon carries, John, is not related to itself but to its last scattering, or, temperature of its emitter.
The information itself is 'altered' in some situations. Light coming up out of a gravity well is red-shifted. The car's color doesn't change. The information getting to the detector ( eyes ) does.

( Wait a minute, is that argument in my favor, or against ? Damn, I hate this definition stuff. )

I was once involved in a debate re "what colour is an Orange in the dark. It was eventually agree after a long drawn out debate that in the dark [no photons of light] the Orange is black...that is it has no colour. In other words the colour of any object depends on the wavelength of the visible part of the EMS that falls on it. If photons are not reflected into the eye, the eye and its transmitters have nothing to determine.

I see that favouring the position that light/photons are visible. 

 

2 hours ago, Furyan5 said:

Exactly what I've been saying all along. Pity it isn't as obvious to everyone.

This is a debate re the nature of light. There are so far two reasonable opinions. You again need to accept that. Either [1] You are wrong. [2] Your argument is solely based on semantics and pedant and philosophical in nature, or [3] You are putting your argument rather poorly and acting the same way. I suspect it is a combination of the first two.

Quote

You really don't get it, do you? You see cars, because your eyes detect light. The color of the car depends on the type of light your eyes detect. You can't see light, because light doesn't emit light. If something doesn't emit light, it can't be seen. 

You see cars because your eyes detect light...yes, if there was no light, you would not see your car. Then you say you can't see light! ???

 

[John Cuthber]

10 hours ago, Furyan5 said:

 

Exactly what I've been saying all along. Pity it isn't as obvious to everyone. 

You really don't get it, do you? You see cars, because your eyes detect light. The color of the car depends on the type of light your eyes detect. You can't see light, because light doesn't emit light. If something doesn't emit light, it can't be seen. 

If someone shines a beam of yellow light at me I can see that it is yellow .

I know what colour the light is because I can see it.

One possible source of that yellow light is an electric arc in sodium vapour.

Sodium vapour is blue, so the yellow colour I see is clearly not  because I see the source of the light- that's the wrong colour.

How can I tell the light is yellow if it's invisible?

 

 

[geordief]

 

Is there a distinction between  visible and detected ? 

If light is not detected then  it seems ("previously")  invisible but  with the right apparatus it can be detected at any point of our choosing and so  then it becomes "visible".

The retina is just one physical point amongst any** where the light can be detected (ie "seen")?

 

I am not clear as to what happens to the signal between the time it meets the retina and the time it is finally processed by the brain.

 

Does it remain "em based" all this time . Are all mental processes fundamentally em processes?

 

** any point  between the emitting source and an observer

 

ps is it just me or is this an incredibly slippery  subject?

Edited January 28, 2018 by geordief

[Strange]

12 minutes ago, geordief said:

Does it remain "em based" all this time . Are all mental processes fundamentally em processes?

Only in as much as chemistry is em based because it involves the movement of electric charges, etc.

But nerves communicate and transmit "electrical" signals by chemical processes, not in the same way as say a piece of wire or a transistor. (But this is where we get into semantics again; is it still an "electrical" signal even though it is generated by a sequence of chemical processes?)

 

22 hours ago, Strange said:

That's an interesting example. Although the difference is in whether the eyes respond to the light of that colour or not.

A contrasting example is people with synesthaesia who see numbers as different colours - they are measurably quick at finding a particular number from a crowded page of numbers because the different colour makes it stand out. But that colour is entirely generated in the brain, not from the eye.

Another example that occurred to me is the phenomenon of blind-sight. Some people who having working eyes and optic nerves but have a defective/damaged visual system in the brain (and so are totally blind) are able to navigate around obstacles even though they cannot (consciously) see them.

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

 

[studiot]

37 minutes ago, geordief said:

ps is it just me or is this an incredibly slippery  subject?

 

Yes I think it is a very slippery subject to which there is no one or right answer.

This is why it needs to be taken in context and problems arise when the promoter does not supply sufficient context.

 

I was just looking at my digital clock. What did I see?

12:01 or was it 12 01 or was it 1201 ?

The colon is flashing, and not part of the time so my mental image is of the numbers only.

Further processing from the eye has taken place.

I am also used to tech drawings so when I see the standard three view layout I do not see a sheet of paper with lines, square, rectangles triangles etc on it.
I see the 3D object they are depicting. But that skill only came with practice, it is developed not inherent.

[geordief]

43 minutes ago, Strange said:

Only in as much as chemistry is em based because it involves the movement of electric charges, etc.

 

 

Feels like scratching an itch but does this movement of charges in the brain also produce em radiation of any kind?

 

Do (moving) electic fields exit without em radiation? (am I OT now?) 

[studiot]

8 minutes ago, geordief said:

Feels like scratching an itch but does this movement of charges in the brain also produce em radiation of any kind?

 

Do (moving) electic fields exit without em radiation? (am I OT now?) 

If a uniform field moves, then the actual values of say the electric field remain constant at any point.

There is no uniform field in the vicinity of an electric charge.

So if the electric charge moves the actual values of the field at any point vary, and the change of values moves along with the charge.

This is therefore a propagating disturbance in the electric field. Which is another name for EM radiation.

Equally if a nonuniform field moves then the value of the elctric field at any point is changing as the field moves.
Which again is another name for EM radiation.

 

Does this help?

 

[geordief]

5 minutes ago, studiot said:

If a uniform field moves, then the actual values of say the electric field remain constant at any point.

There is no uniform field in the vicinity of an electric charge.

So if the electric charge moves the actual values of the field at any point vary, and the change of values moves along with the charge.

This is therefore a propagating disturbance in the electric field. Which is another name for EM radiation.

Equally if a nonuniform field moves then the value of the elctric field at any point is changing as the field moves.
Which again is another name for EM radiation.

 

Does this help?

 

Well it seems (perhaps naively) to mean that the brain does produce secondary em radiation of some kind as the electric charges move along its  neural pathways ** even though these are chemical processes.

 

Maybe  this  radiation (another word for "light"?)   is unprocessed and escapes as inconsequential  "waste". and of no bearing on how the brain sees (processes light)

 

Unless  the  speed of movement of the charges is  too low  to produce any em radiation at all ?

 

** hope I am not parroting medical jargon

[Strange]

35 minutes ago, geordief said:

Feels like scratching an itch but does this movement of charges in the brain also produce em radiation of any kind?

They must do. But I'm not sure if it can be easily detected or not. EEG works by measuring the voltages on the skin created by brain activity.

[John Cuthber]

12 hours ago, MigL said:

The information the violet photon carries, John, is not related to itself but to its last scattering, or, temperature of its emitter.
The information itself is 'altered' in some situations. Light coming up out of a gravity well is red-shifted. The car's color doesn't change. The information getting to the detector ( eyes ) does.

So the information it carries is related to the path it took, rather than the source.

Surely that's information about the photon's "history" and, thus about the photon itself?

(I realise that photons don't have history, but...).

A different photon, from the same source, having taken a different path would be a different  colour, so it isn't information about the sourse.

It's information about the photon as it reaches my eye.

It hardly matters. I can only access that information because I see the light.

How could I tell you what colour the light was  if I couldn't see it?

[studiot]

12 minutes ago, John Cuthber said:

How could I tell you what colour the light was  if I couldn't see it?

Well I certainly see ( )that you are using a particular context for the word see, and nothing wrong with that.

 

But, as I have already noted, there other cells in your body capable of 'detecting' certain wavelengths of light via other chemical reations than the ones in your eyes.

 

So context is vital.

 

 

[John Cuthber]

Mine eyes have seen the glory of the coming of the photons.

 

And, for added amusement value, my eyes saw light from the same lamp as being different colours if I moved towards it or away from it.

In those circumstances I'm the only thing that changes (I accelerate in one direction or the other) and what I see changes.The source stays the same, so it's not changing colour.

What I see is different colours of light and, since I can tell you what colour that light is, I must  be able to see that light.

[swansont]

2 hours ago, geordief said:

 ps is it just me or is this an incredibly slippery  subject?

Slippery and especially so when nobody defines their terms.

12 hours ago, MigL said:

The information the violet photon carries, John, is not related to itself but to its last scattering, or, temperature of its emitter.

Not all photons are from a thermal source, or have scattered. We can, after all, identify elements from their emission spectrum.

 

[Eise]

17 hours ago, MigL said:

The point I'm trying to make is that light, or photons, are the information carriers. And while we 'see' by interacting with the information carriers, a photon itself cannot transmit any information about itself ( it would need to radiate light ) for us to be able to 'see' it.
I.E. photons are invisible.

 everything else is semantics.

I think you nailed it, MigL. 

When it is dark in a room, I can see things by turning on the light: they reflect photons. But I cannot do the same with photons themselves. If there is a light beam in the further dark room, I cannot see the light beam. I still cannot see it if I turn on the light (it becomes even worse...)

If we 'see' light, we mostly mean we see something that emits light. If I look into a beam of a torch I do not see light: I see the torch. But if we do not recognise the source of the light, it is very usual to say 'I see some light'. 

But I fully agree that it is semantics. It is clear that if photons are detected by our eyes, we see 'something'. So it is very understandable that we say we can see light. In my opinion however, the question is not of much importance. So I have no idea why the emotions are cooking so high. I do not see how deciding for the correct semantics any important scientific or human problem is cleared of solved.

[swansont]

1 minute ago, Eise said:

 If we 'see' light, we mostly mean we see something that emits light. If I look into a beam of a torch I do not see light: I see the torch.  

I don't think you see the torch. To borrow from John's point above, what color is the torch?

[Tub]

4 hours ago, swansont said:

I don't think you see the torch. To borrow from John's point above, what color is the torch?

 

4 hours ago, Eise said:

.

If we 'see' light, we mostly mean we see something that emits light. If I look into a beam of a torch I do not see light: I see the torch. But if we do not recognise the source of the light, it is very usual to say 'I see some light'. 

 

Just a few moments ago, i went into a large, darkened room with a small torch i have on my key-ring; i held the torch up to eye-level and to the  right side of my head, pointing it directly across my eyes, and at a wall to my left, and switched it on........now, moving my eyes slightly to my right, i could see the lit bulb in the torch and then glancing to my left i could see a patch of light on the wall about 2 metres from where i was standing but between the wall and the bulb i didn't see anything - no beam of light at all, just darkness! I find that very puzzling.

[swansont]

6 minutes ago, Tub said:

Just a few moments ago, i went into a large, darkened room with a small torch i have on my key-ring; i held the torch up to eye-level and to the  right side of my head, pointing it directly across my eyes, and at a wall to my left, and switched it on........now, moving my eyes slightly to my right, i could see the lit bulb in the torch and then glancing to my left i could see a patch of light on the wall about 2 metres from where i was standing but between the wall and the bulb i didn't see anything - no beam of light at all, just darkness! I find that very puzzling.

You don't interact (via vision) with photons if they're not hitting your eye

[Tub]

25 minutes ago, swansont said:

You don't interact (via vision) with photons if they're not hitting your eye

Aha. Thanks

[koti]

Light bouncing off of stuff is visible to humans in ~390nm-700nm wavelength region, period.
The rest is overthinking. 

[John Cuthber]

5 hours ago, Eise said:

If we 'see' light, we mostly mean we see something that emits light.

No

We mostly see things that reflect light.

[beecee]

2 hours ago, koti said:

Light bouncing off of stuff is visible to humans in ~390nm-700nm wavelength region, period.
The rest is overthinking. 

Bingo!!

 

[Eise]

12 hours ago, John Cuthber said:

No

We mostly see things that reflect light.

Sorry, had to express me a bit clearer. If we say 'I see a light', we mostly mean that we see something emitting light: lights of a car, or a torch, or whatever. But there are some other cases, e.g. if you see light at the end of a tunnel.

But generally you are right, we see things because they reflect light.

18 hours ago, swansont said:

I don't think you see the torch. To borrow from John's point above, what color is the torch?

The colour of the light bulb? Of course a torch doesn't light itself.

[Furyan5]

On 28/01/2018 at 3:48 AM, beecee said:

I was once involved in a debate re "what colour is an Orange in the dark. It was eventually agree after a long drawn out debate that in the dark [no photons of light] the Orange is black...that is it has no colour. In other words the colour of any object depends on the wavelength of the visible part of the EMS that falls on it. If photons are not reflected into the eye, the eye and its transmitters have nothing to determine.

I see that favouring the position that light/photons are visible. 

 

This is a debate re the nature of light. There are so far two reasonable opinions. You again need to accept that. Either [1] You are wrong. [2] Your argument is solely based on semantics and pedant and philosophical in nature, or [3] You are putting your argument rather poorly and acting the same way. I suspect it is a combination of the first two.

You see cars because your eyes detect light...yes, if there was no light, you would not see your car. Then you say you can't see light! ???

Yes, I say again, we can't see light. We see objects. But, this is the part which you, and many others, are not getting. We do not see the actual object. When the light from an object strikes our eye, our brain creates a visual representation of that object. 

When you look around you, you are NOT seeing 'the world' with your eyes. Your consciousness is becoming aware of the 'internal' representation of the world. Grasping this is vital to comprehending that light itself is not visible. As long as you believe you 'see' with your eyes, you will believe you 'see' light. 

 

1 hour ago, Eise said:

Sorry, had to express me a bit clearer. If we say 'I see a light', we mostly mean that we see something emitting light: lights of a car, or a torch, or whatever. But there are some other cases, e.g. if you see light at the end of a tunnel.

Too much light can blind us. Over stimulation of the light receptors results in the perception of brightness. But brightness is a subjective visual sensation resulting from over stimulation. It's not a property of light. 

Try this experiment. But use a 40watt globe to prevent damage to your eyes. When you first look at the globe, you only see brightness. But, if you fix your gaze on one spot, your eyes adjust and you actually see the element, which is the source of the photons. 

I will from now on use the word photons as light 'photons' and light (the opposite of dark) are two different things. We do see light, but we can't see photons. 

But generally you are right, we see things because they reflect light.

The colour of the light bulb? Of course a torch doesn't light itself.

 

12 hours ago, beecee said:

Bingo!!

 

No it's not. The object reflecting the light is visible. Light is detectable. Big difference. Some eyes detect light while the person sees nothing. 

Check mate

15 hours ago, swansont said:

You don't interact (via vision) with photons if they're not hitting your eye

Because? Photons are not visible? 

Yes, we know.

21 hours ago, studiot said:

If a uniform field moves, then the actual values of say the electric field remain constant at any point.

There is no uniform field in the vicinity of an electric charge.

So if the electric charge moves the actual values of the field at any point vary, and the change of values moves along with the charge.

This is therefore a propagating disturbance in the electric field. Which is another name for EM radiation.

Equally if a nonuniform field moves then the value of the elctric field at any point is changing as the field moves.
Which again is another name for EM radiation.

 

Does this help?

 

Do you get it now? The fruit bowl you see is 'the image created inside your brain'. When you look up at the sky, you see, 'the representation created by your brain'. When you hold your hand up in front of your face, you see, 'the representation of your hand, created by your brain'. 

You never see the 'outside' world. You only ever see the 'representation'. 

You don't see direct reality, you see indirect reality. Subjectively. 

[studiot]

1 hour ago, Furyan5 said:

Do you get it now? The fruit bowl you see is 'the image created inside your brain'. When you look up at the sky, you see, 'the representation created by your brain'. When you hold your hand up in front of your face, you see, 'the representation of your hand, created by your brain'. 

You never see the 'outside' world. You only ever see the 'representation'. 

You don't see direct reality, you see indirect reality. Subjectively. 

 

Yes thank you, I have never not 'got it'.

That is why I credited you with introducing the end user viewpoint (the brain) from the outset and did not immediately take issue with this view.

In fact my first response was to assert that although  you wish to simplify, Nature is that much more complicated and will thwart you.

You must have accepted this at some point because you yourself said that the meaning of words crucial to the discussion depends upon the context.

My problem with the simple statement that what you see is the model constructed by the brain is that this model is constructed not only from the visual information received by the eyes but also from other information known to the brain and personal directives and controls guiding the creation of the mental model. Some of this additional information is voluntary, some is involuntary.

In contrast the image on the retina is as faithful a reproduction as the laws of Nature allow (although there are also issues with this that we have not discussed).

Edited January 29, 2018 by studiot