Light: visible or invisible?

[The_Believer1]

Hello friends!

 

I have a question about light. We all know that we see objects because they reflect light into our eyes. But we never see the actual light. So my question is why can't we see light. Or can we in fact see light. If so, how?

[Sensei]

Light from f.e. Sun, light bulb, stars, LED/LCD, etc. is tremendous quantity of photons. Electric neutral particles.

That are absorbed and emitted by matter.

If photon is absorbed, it's gone from system under observation.

Absorbed photon increases mass-energy of system that absorbed it.

Which often means increase of temperature of object.

Object with higher temperature than environment is emitting black body spectrum at slightly higher shifted range.

 

For human eyes visible spectrum range is between 400 nm to 700 nm.

You can't see UV, x-ray, gamma photon, but can see effects of them on matter.

Like photoelectric effect, fluorescence, ionization, photo-disintegration etc.

Edited February 22, 2016 by Sensei

[Klaynos]

Our eyes are only capable of seeing light. Or brains then do significant data processing on the interactions. This provides us with what you might consider vision, it shows where the light last interacted with something significantly (this isn't a very good way of putting it but will do). Light doesn't strongly interact with light so you don't get the strong interactions to allow you to locate the light (not sure how that sentence would really be any less illuminating but it's the best I can do when this tired).

[swansont]

"Seeing" is a response of photons interacting with molecules in our eyes, and the resulting impulse being sent to the brain to be interpreted. So a lot of this depends on what you mean by "seeing" light.

[Delta1212]

Light is the only thing you can see.

[John Cuthber]

But we never see the actual light.

Yes we do,

Unless we are talking about the idea of "close your eyes and imagine a hippo- how many legs does it have" as seeing, then there's no sensible debate here

The only thing you see is light.

[Ophiolite]

At the heart of the OP seems to be the question, why can we not look at the form and shape of a photon? I think that question has been implicitly answered.

[Furyan5]

Sorry I took so long to reply. You're right. We can't see light. Light is what makes objects visible. The reason most people don't agree is because they believe the reality they perceive exists outside their heads. That's not true. 

When our eyes detect (not see) light, they send electrochemical impulses to our brains visual cortex. Here our brain creates the visual representation we perceive. Our whole lives we perceive this visual representation, not actual reality. Our brain creates images of objects through different visual sensations such as colors and brightness. The light we see is brightness, as opposed to darkness. It's not light (electromagnetic radiation). People confuse the two meanings of light. 

Visible light is not visible. It's light which makes objects visible. 

[Furyan5]

Light is not visible. We don't see light, we feel light. We see through our eyes but we detect light with our eyes. We do not detect light that passes us, only the light that enters our eyes. That's, the light that strikes our retina. Detection through physical contact is called touch, not sight. 

For us to see light, it would have to emit or reflect light. Light is colourless and moves at "the speed of light". Many people confuse light with the actual object emitting or reflecting the light. We don't see light, we see it's source. Light makes objects visible. Light itself is not visible. 

[Phi for All]

!

Moderator Note

A major chunk of discussion, starting where Furyan5 takes us away from physics with the phrase "Physics tries to seperate from subjective experiences", has been split away to here. At that point, the discussion became more about philosophy than the physical nature of light, and friction naturally occured. 

So let's be clear, this thread is in a Physics section, and the other thread is in Philosophy. Sorry for any inconvenience.

 

[studiot]

On 22/02/2016 at 5:24 PM, The_Believer1 said:

Hello friends!

 

I have a question about light. We all know that we see objects because they reflect light into our eyes. But we never see the actual light. So my question is why can't we see light. Or can we in fact see light. If so, how?

 

On 22/02/2016 at 5:46 PM, swansont said:

"Seeing" is a response of photons interacting with molecules in our eyes, and the resulting impulse being sent to the brain to be interpreted. So a lot of this depends on what you mean by "seeing" light.

 

I agree we need a working definition of seeing and in order to have that we need a working model of the process, since seeing is a process, not an object.

So I offer up such a model for discussion and improvement.

Firstly let me observe what seeing is not, since it has been suggested that seeing is synonymous with detection.

I suggest that detection is a much more general process with a variety of outcomes.

Many (most) parts of the body can respond to light in some fashion.
Thus they can be said to detect light.

For instance the action of light on the body produces chemical change resulting in vitamin D production.
Other action produces the melanin tan.
Yet other action synchronises the bioclock or tells us to wake or sleep.

For any of these actions and more, a particular form of light is required so the activity can be said to detect or distinguish that form of light from other forms.
However each interaction is separate from and unconnected to any other interaction.
So one particular UV photon that kicks off a secosteroid production is independent of another such event.

But in the process of seeing our eyes not only form a real (in the optical sense) image of all the light enetering but also generate information signals coding the relationship (if there is one) between all the photons.

Note a modern camera sensor mimics this in a crude way.

So is the process of formation of this image 'seeing' ? Or is there yet more to it?

Well the answer is 'there is more to it', since each of these images is a two dimensional representation of the same thing from a slightly different viewpoint, so can be processed to yield a three dimensional model of what is in front of the viewer.

In animals, including humans, this processing is done by the brain.

But what is this model of?
Is it of an object, as has been suggested?

Well no because the eye will still produce the image and the brain the model if there is no object there.
For instance in a whiteout in snow or fog we will still receive light and 'see' something.

Further, otical illusions of many sorts abound, where the system is tricked into producing a false model.
Or artificial stimulation of part of the chain can also produce false models or block real ones.

 

So is seeing the successful conclusion of the chain of sub processes which make up an overall process?

 

I look forward to comments.

 

[MigL]

I wear one of my many watches at all times Studiot, and in the summertime the interaction of UV light from the sun with my skin forms, after a few days ( I'm Italian and tan easily ), an image of my watch on my wrist.
You could say any interaction is an imaging, or 'seeing', albeit with different sensitivity and speed.

On the other hand my left eye 'sees' perfectly well, and focuses an image on my retina and its detector rods and cones. However the information cannot get to my brain because glaucoma damaged my optic nerve; and I 'see' nothing.

Maybe we need to define what visible and invisible means instead.

Edited January 26, 2018 by MigL

[studiot]

Great stuff MigL, straight to the point.

At what stage can we call 'imaging', seeing ?

There are other processes for creating an image, including ones that cannot be observed by visible light, such as electron microscopy and seismology.

So we need separate terms for imaging and seeing.

As to visible and invisible.
I am happy to pair these with seeing and define invisible as that which can't bee seen and visible as that which can.

 

But does seeing refer to creating the image or the abstracted model?
A camera can create an image. And we use general English to talk of the camera 'seeing' and (in)visible to the camera or the naked eye.

[Furyan5]

3 hours ago, studiot said:

 

 

I agree we need a working definition of seeing and in order to have that we need a working model of the process, since seeing is a process, not an object.

So I offer up such a model for discussion and improvement.

Firstly let me observe what seeing is not, since it has been suggested that seeing is synonymous with detection.

I suggest that detection is a much more general process with a variety of outcomes.

Many (most) parts of the body can respond to light in some fashion.
Thus they can be said to detect light.

For instance the action of light on the body produces chemical change resulting in vitamin D production.
Other action produces the melanin tan.
Yet other action synchronises the bioclock or tells us to wake or sleep.

For any of these actions and more, a particular form of light is required so the activity can be said to detect or distinguish that form of light from other forms.
However each interaction is separate from and unconnected to any other interaction.
So one particular UV photon that kicks off a secosteroid production is independent of another such event.

But in the process of seeing our eyes not only form a real (in the optical sense) image of all the light enetering but also generate information signals coding the relationship (if there is one) between all the photons.

Note a modern camera sensor mimics this in a crude way.

So is the process of formation of this image 'seeing' ? Or is there yet more to it?

Well the answer is 'there is more to it', since each of these images is a two dimensional representation of the same thing from a slightly different viewpoint, so can be processed to yield a three dimensional model of what is in front of the viewer.

In animals, including humans, this processing is done by the brain.

But what is this model of?
Is it of an object, as has been suggested?

Well no because the eye will still produce the image and the brain the model if there is no object there.
For instance in a whiteout in snow or fog we will still receive light and 'see' something.

Further, otical illusions of many sorts abound, where the system is tricked into producing a false model.
Or artificial stimulation of part of the chain can also produce false models or block real ones.

 

So is seeing the successful conclusion of the chain of sub processes which make up an overall process?

 

I look forward to comments.

 

Finally, someone intelligent to chat to. 

3 hours ago, studiot said:

 

 

I agree we need a working definition of seeing and in order to have that we need a working model of the process, since seeing is a process, not an object.

So I offer up such a model for discussion and improvement.

Firstly let me observe what seeing is not, since it has been suggested that seeing is synonymous with detection.

I suggest that detection is a much more general process with a variety of outcomes.

Many (most) parts of the body can respond to light in some fashion.
Thus they can be said to detect light.

For instance the action of light on the body produces chemical change resulting in vitamin D production.
Other action produces the melanin tan.
Yet other action synchronises the bioclock or tells us to wake or sleep.

For any of these actions and more, a particular form of light is required so the activity can be said to detect or distinguish that form of light from other forms.
However each interaction is separate from and unconnected to any other interaction.
So one particular UV photon that kicks off a secosteroid production is independent of another such event.

But in the process of seeing our eyes not only form a real (in the optical sense) image of all the light enetering but also generate information signals coding the relationship (if there is one) between all the photons.

Note a modern camera sensor mimics this in a crude way.

A camera creates a copy of a light pattern, which our eye detects and our brain converts into an image. The camera doesn't create images.

So is the process of formation of this image 'seeing' ? Or is there yet more to it?

Well the answer is 'there is more to it', since each of these images is a two dimensional representation of the same thing from a slightly different viewpoint, so can be processed to yield a three dimensional model of what is in front of the viewer.

In animals, including humans, this processing is done by the brain.

But what is this model of?
Is it of an object, as has been suggested?

Well no because the eye will still produce the image and the brain the model if there is no object there.
For instance in a whiteout in snow or fog we will still receive light and 'see' something.

Further, otical illusions of many sorts abound, where the system is tricked into producing a false model.
Or artificial stimulation of part of the chain can also produce false models or block real ones.

 

So is seeing the successful conclusion of the chain of sub processes which make up an overall process?

 

I look forward to comments.

 

 

[StringJunky]

6 minutes ago, Furyan5 said:

Finally, someone intelligent to chat to. 

Is someone 'intelligent'  who says what you want to  hear?

[Furyan5]

1 minute ago, StringJunky said:

Is someone 'intelligent'  who says what you want to  hear?

No, it's someone who makes logical and relevant comments on a topic. I actually disagree on some points. 

[StringJunky]

2 minutes ago, Furyan5 said:

No, it's someone who makes logical and relevant comments on a topic. I actually disagree on some points. 

'Logical' meaning "it makes sense to me".

[Furyan5]

1 minute ago, StringJunky said:

'Logical' meaning "it makes sense to me".

Does logical have a different meaning?

2 hours ago, MigL said:

I wear one of my many watches at all times Studiot, and in the summertime the interaction of UV light from the sun with my skin forms, after a few days ( I'm Italian and tan easily ), an image of my watch on my wrist.
You could say any interaction is an imaging, or 'seeing', albeit with different sensitivity and speed.

On the other hand my left eye 'sees' perfectly well, and focuses an image on my retina and its detector rods and cones. However the information cannot get to my brain because glaucoma damaged my optic nerve; and I 'see' nothing.

So your eye detects light and you see nothing? How interesting!

 

[Strange]

23 minutes ago, Furyan5 said:

Does logical have a different meaning?

Yes. A lot of people use it as a synonym for common sense or things that are intuitively obvious. I would assume / hope that you know what logic is as you have used a few terms from philosophy. You understand, presumably, that it is a formal system for reaching conclusions based on premises, and that those conclusion must be true if the premises are.

[Furyan5]

47 minutes ago, Strange said:

Yes. A lot of people use it as a synonym for common sense or things that are intuitively obvious. I would assume / hope that you know what logic is as you have used a few terms from philosophy. You understand, presumably, that it is a formal system for reaching conclusions based on premises, and that those conclusion must be true if the premises are.

That's why it makes sense to me. A concept which does not contradict itself is logical. 

Claiming that something smaller than an electron and faster than a bullet is visible, is illogical. 

1 hour ago, Strange said:

Yes. A lot of people use it as a synonym for common sense or things that are intuitively obvious. I would assume / hope that you know what logic is as you have used a few terms from philosophy. You understand, presumably, that it is a formal system for reaching conclusions based on premises, and that those conclusion must be true if the premises are.

That's why it makes sense to me. A concept which does not contradict itself is logical

Claiming that something smaller than an electron and faster that a bullet, is visible, doesn't seem logical. Not to me anyway. 

 

[beecee]

On 2/23/2016 at 4:24 AM, The_Believer1 said:

Hello friends!

 

I have a question about light. We all know that we see objects because they reflect light into our eyes. But we never see the actual light. So my question is why can't we see light. Or can we in fact see light. If so, how?

What is reflected into your eyes is the actual light in the form of photons...When we see beams of light in a dusty room, we see the photons scattered off that dust and so we see an apparent path via the beam of photons scattered off that dust and illuminating the path. We don't say that we see a beam of dust, we say we see a beam of light, albeit light that is reflected off that dust into our eyes. Putting it scientifically, the photons that enter our eyes, strike our retina  and triggers neural signals to our brain. Our brains interpret those signals into a recognised pattern that we recognise as the shape of whatever the object was that reflected those photons into our eyes. It's still photons that we see though.

[Strange]

6 hours ago, Furyan5 said:

A concept which does not contradict itself is logical. 

That is one of the rules of logic, but not very useful by itself.

Quote

Claiming that something smaller than an electron and faster than a bullet is visible, is illogical.

That could only become illogical if you stated the premises and showed that conclusion cannot be derived from them.

You sound as if you are saying "that doesn't make sense to me" which is not the correct use of "logical" (in a philosophy forum).

However, your statement "something smaller than an electron" is meaningless as electrons are zero-sized.

Edited January 27, 2018 by Strange

[studiot]

10 hours ago, Furyan5 said:

Finally, someone intelligent to chat to. 

 

9 hours ago, Furyan5 said:

I actually disagree on some points. 

I'm listening ?

[Furyan5]

8 hours ago, beecee said:

What is reflected into your eyes is the actual light in the form of photons...When we see beams of light in a dusty room, we see the photons scattered off that dust and so we see an apparent path via the beam of photons scattered off that dust and illuminating the path. We don't say that we see a beam of dust, we say we see a beam of light, albeit light that is reflected off that dust into our eyes. Putting it scientifically, the photons that enter our eyes, strike our retina  and triggers neural signals to our brain. Our brains interpret those signals into a recognised pattern that we recognise as the shape of whatever the object was that reflected those photons into our eyes. It's still photons that we see though.

Except for your last sentence, you're right. We see the OBJECT that reflects the photons. Seeing objects provides us with an evolutionary advantage. Our eyes DETECT photons. 

2 hours ago, Strange said:

That is one of the rules of logic, but not very useful by itself.

That could only become illogical if you stated the premises and showed that conclusion cannot be derived from them.

You sound as if you are saying "that doesn't make sense to me" which is not the correct use of "logical" (in a philosophy forum).

However, your statement "something smaller than an electron" is meaningless as electrons are zero-sized.

And seeing something of zero-size is logical?

[Tub]

On 2/22/2016 at 5:24 PM, The_Believer1 said:

Hello friends!

 

I have a question about light. We all know that we see objects because they reflect light into our eyes. But we never see the actual light. So my question is why can't we see light. Or can we in fact see light. If so, how?

If it isn't too far off-topic, i'd like to ask how we " see " dreams: obviously reflected light is not involved so there can't be any photons to be detected, and is it still the visual cortex that is involved? Can anyone enlighten me? ( Sorry ! ).