Light: visible or invisible?

[Eise]

1 minute ago, koti said:

I have a 600mW 532nm laser with a decent enough divergence to see the beam even in daylight. So what?

That is great. But you do not see it because of daylight. You see it even better in the dark, right? Exactly the opposite with macro objects: those can be better seen in daylight.

[koti]

7 minutes ago, Eise said:

That is great. But you do not see it because of daylight. You see it even better in the dark, right? Exactly the opposite with macro objects: those can be better seen in daylight.

Right. I’m done here Eise.

[dimreepr]

Sometimes, it's better to acknowledge a good argument, than just try to keep your guns...

[koti]

8 hours ago, dimreepr said:

Sometimes, it's better to acknowledge a good argument, than just try to keep your guns...

Since this thread is in physics I feel I need to point out that Eise’s argument is horribly confusing and in my opinion plainly wrong.  People who are not familiar with light, imaging, optics and the related physics will get badly confused by the 12 pages in this thread and instead of getting a clear answer to the OP they are getting nonsense. Congratulations on luring me out.

8 hours ago, Eise said:

That is great. But you do not see it because of daylight. You see it even better in the dark, right? Exactly the opposite with macro objects: those can be better seen in daylight.

There is so much wrong in your above post that I cant leave it (for reasons I gave above to dimreepr) 

You see or you do not see laser beams at night or in daylight for the exact same reasons that you see or do not see „macro” objects in daylight or at night. „Macro objects” are only adding to the confusion, it doesn’t matter if its a large or small object, the principals of seeing them or not seeing are the same, its always the same. Your statement that „its exactly opposite with macro objects” is yet another level of confusion, its not exactly the opposite, its exactly the same...you see relfected light off of objects and since in daylight the source for this reflection is the sun, its pretty obvious that you see them better when there is a sun which serves as a source for this reflection. It is not revealing that when the sun is not shining on your „macro objects” you dont see the light reflected by these objects (unless ofcourse its the ISS flying above your head at night which reflects sun light therefore you can see your „macro object” at night) FFS there is no distinction which you are trying to create. Your premise that „light doesn’t reflect light” is yet a deeper level of nonsense and confusion adding to this psychosis. Please bare in mind that your philosophical thought experiments in this case are extremely confusing for people who don’t know their physics.

Edited February 18, 2018 by koti

[iNow]

If we’re being pedantic, we don’t see anything...ever. We experience a pattern of chemoelectric activation in our nervous system and call it seeing. Generally, this maps accurately on to the reality around us, but not always. Generally, the experience is shared by multiple observers and consensus is reached, or validated by instruments and measurements, but not always. I could put a magnet by your skull or feed you a psychotropic mushroom and cause you to “see” light in a perfectly pitch black space. But, since as Koti mentions this thread is in the physics forum, we’re talking about reflection of photons and their impact on photoreceptors... or, at least we should be. 

Edited February 18, 2018 by iNow

[John Cuthber]

Can someone explain why anyone is talking about "macro objects"?

http://www.nationalgeographic.com.au/science/how-a-student-took-a-photo-of-a-single-atom.aspx

[StringJunky]

1 hour ago, John Cuthber said:

Can someone explain why anyone is talking about "macro objects"?

http://www.nationalgeographic.com.au/science/how-a-student-took-a-photo-of-a-single-atom.aspx

I found a good close up:

 

[koti]

36 minutes ago, StringJunky said:

I found a good close up:

 

Nice. I wonder what the exposure time was...judging by the distortion in the color it had to be taken at a very high ISO setting too, and several seconds exposure (considering that its a modern DSLR). Which would make sense,in order for us to see it the camera had to emphasize the ridiculously small amount of light which the strontium atom reflected.

Edited February 18, 2018 by koti

[StringJunky]

12 minutes ago, koti said:

Nice. I wonder what the exposure time was...judging by the distortion in the color it had to be taken at a very high ISO setting too, and several seconds exposure (considering that its a modern DSLR). Which would make sense,in order for us to see it the camera had to emphasize the ridiculously small amount of light which the strontium atom reflected.

I think the atom is being excited by UV, so is actually a light source rather than a reflector per se.

[koti]

3 minutes ago, StringJunky said:

I think the atom is being excited by UV, so is actually a light source rather than a reflector per se.

Youre right, seems the atom re-emitted absorbed light rather than reflected it. Same thing though from the point of view of a human observer. Awesome experiment, its astonishing that commercially available cameras are capable of gathering so litte light these days.

[geordief]

"Physicists create new form of light"

http://news.mit.edu/2018/physicists-create-new-form-light-0215

 

Is light "seeing" light here? And can we thus "see" light with light now?

 

Probably h. arsed but is there any relevance to the OP?

[Eise]

On 18/02/2018 at 2:05 AM, koti said:

You see or you do not see laser beams at night or in daylight for the exact same reasons that you see or do not see „macro” objects in daylight or at night. „Macro objects” are only adding to the confusion, it doesn’t matter if its a large or small object, the principals of seeing them or not seeing are the same, its always the same.

I am trying to understand what blocks you from understanding my point.

It seems that you look at what happens in our visual system, eyes, nerves, brain. and there you are right, there is no difference. But there is a plain difference in the physics of seeing objects by reflection, or by seeing light. I'll try a more lively example.

Imagine, you want to steal an expensive artifact from a museum. In the night of course. To be able to see, you take a torch with you. By its reflections on floor, walls etc you find your way. Close by the artifact, you become suspicious: maybe there is laser light crossing the way to the artifact. But you cannot see it. Your torch does not help you. So what do you do to find if there is some photo electric alarm? Luckily enough you are a smoker, and you have your cigarettes with you. So you light one, and blow the smoke in the room between you and the artifact. And yes! Now you see that the smoke is reflecting light, all on a fine straight line. 

So you need two different methods to see what you want to see: all normal objects you see in the light of your torch. The light beam however, you see exactly the opposite way: you add 'objects' (smoke particles) that show you were the laser beam goes through, instead of 'adding light' to see objects.

On 18/02/2018 at 2:05 AM, koti said:

Your premise that „light doesn’t reflect light” is yet a deeper level of nonsense

Well, it is a physical fact. Why is that nonsense?

On 18/02/2018 at 2:05 AM, koti said:

Please bare in mind that your philosophical thought experiments in this case are extremely confusing for people who don’t know their physics.

As soon as most posters here said it is mainly a semantics question, this thread should have been moved to philosophy. So if some administrator wants to do that, please feel free...

[koti]

52 minutes ago, Eise said:

I am trying to understand what blocks you from understanding my point.

It seems that you look at what happens in our visual system, eyes, nerves, brain. and there you are right, there is no difference. But there is a plain difference in the physics of seeing objects by reflection, or by seeing light. I'll try a more lively example.

Imagine, you want to steal an expensive artifact from a museum. In the night of course. To be able to see, you take a torch with you. By its reflections on floor, walls etc you find your way. Close by the artifact, you become suspicious: maybe there is laser light crossing the way to the artifact. But you cannot see it. Your torch does not help you. So what do you do to find if there is some photo electric alarm? Luckily enough you are a smoker, and you have your cigarettes with you. So you light one, and blow the smoke in the room between you and the artifact. And yes! Now you see that the smoke is reflecting light, all on a fine straight line. 

So you need two different methods to see what you want to see: all normal objects you see in the light of your torch. The light beam however, you see exactly the opposite way: you add 'objects' (smoke particles) that show you were the laser beam goes through, instead of 'adding light' to see objects.

Well, it is a physical fact. Why is that nonsense?

As soon as most posters here said it is mainly a semantics question, this thread should have been moved to philosophy. So if some administrator wants to do that, please feel free...

Sure Eise. Acording to you, adding an object in the form of smoke to see a weak laser beam forms a new concept of see2. Lets just disregard that lasers are a form of light which works by manipulation of energized atoms concentrating them into a very narrow space and forcing the subsequent photons to move in a uniform direction thus creating a laserbeam which if not powerful enough and if not within the mid ranges of visible spectrum is difficult to see. Lets just stick to your see1 and see2 concept and keep the psychosis going for all the readers. 

Edited February 19, 2018 by koti

[Eise]

14 hours ago, koti said:

Acording to you, adding an object in the form of smoke to see a weak laser beam forms a new concept of see2

It is not really new. It is just a small ambiguity in the daily meaning of 'to see'. But if you go to the museum, you better be aware that a torch might not be enough. Every professional thief is aware of this ambiguity, and takes his cigarettes with him. ;-)

14 hours ago, koti said:

Lets just disregard that lasers are a form of light which works by manipulation of energized atoms concentrating them into a very narrow space and forcing the subsequent photons to move in a uniform direction thus creating a laserbeam which if not powerful enough and if not within the mid ranges of visible spectrum is difficult to see.

I do not disregard anything. Why would the way the light is produced be of any importance for my distinction? (oh forgot, you never answer questions I ask).

14 hours ago, koti said:

Lets just stick to your see1 and see2 concept and keep the psychosis going for all the readers.

I know only one or two readers who are at the brink of an intellectual psychosis... The rest already accepted that it is semantics. Explicitly working out the semantics seems to confuse you.

 

[Andreas0305]

It is lovely to see how a simple question can turn in to a debate with such a strong energy, even tension  The power of thought is the strongest power and while everyone could be right, everyone could be wrong as well. So, to try to answer the question:

What we can't see, doesn't mean that it is not there (light cant be seen by naked eye traveling across the universe), it is one of the forms of electromagnetic radiation, but the light that we see during the day time is visible to us when reflecting from the smallest particles, like atmospheric elements) and then in space when it reflects from the moon or other celestial bodies, so in vacuum there is nothing to reflect from and this is why we can say that actually we can't see the light traveling, only the source and when it bounces. 

On the other hand, try to look in a light source (don't do it too long with the sun:)), for a certain period of time your brain will "store" a light  and then you can see it without actually seeing it or bouncing from other elements, just a fine imprint.

If there wouldn't be light, there wouldn't be writing :), among other things

[koti]

37 minutes ago, Andreas0305 said:

If there wouldn't be light, there wouldn't be writing :), among other things

Yes there would, and there is.

[Eise]

8 hours ago, Andreas0305 said:

It is lovely to see how a simple question can turn in to a debate with such a strong energy, even tension  The power of thought is the strongest power and while everyone could be right, everyone could be wrong as well. 

Well, I think when one is consistent in the meaning of words one is using, one surely fairs better than using words and shift their meanings. A lot of philosophical problems are caused or amplified by different meanings, in at least two ways:

1. Different persons attach different meanings to a word.
2. One person (slowly) shifts the meaning of a word when building up an argumentation (or jumps back and forth between different meanings).

Both are used more or less intentionally (i.e. in bad faith!) by e.g. creationists ('Evolution is just a theory'; 'Big bang, therefore our God').

8 hours ago, Andreas0305 said:

What we can't see, doesn't mean that it is not there (light cant be seen by naked eye traveling across the universe), it is one of the forms of electromagnetic radiation, but the light that we see during the day time is visible to us when reflecting from the smallest particles, like atmospheric elements) and then in space when it reflects from the moon or other celestial bodies, so in vacuum there is nothing to reflect from and this is why we can say that actually we can't see the light traveling, only the source and when it bounces. 

Yep. That is what I am saying. Just made one word bold to accentuate that one does not necessarily have to say it in this way.

8 hours ago, koti said:

Yes there would, and there is.

Depends on how you define 'writing'... 

Edited February 27, 2018 by Eise

[Furyan5]

On 27/02/2018 at 12:33 AM, Andreas0305 said:

It is lovely to see how a simple question can turn in to a debate with such a strong energy, even tension  The power of thought is the strongest power and while everyone could be right, everyone could be wrong as well. So, to try to answer the question:

What we can't see, doesn't mean that it is not there (light cant be seen by naked eye traveling across the universe), it is one of the forms of electromagnetic radiation, but the light that we see during the day time is visible to us when reflecting from the smallest particles, like atmospheric elements) and then in space when it reflects from the moon or other celestial bodies, so in vacuum there is nothing to reflect from and this is why we can say that actually we can't see the light traveling, only the source and when it bounces. 

On the other hand, try to look in a light source (don't do it too long with the sun:)), for a certain period of time your brain will "store" a light  and then you can see it without actually seeing it or bouncing from other elements, just a fine imprint.

If there wouldn't be light, there wouldn't be writing :), among other things

Does a tree make light visible, or does light make a tree visible? I'm not denying that our eyes detect light, but what do we see?

On 15/02/2018 at 3:21 PM, Eise said:

This is what you said:

What you were describing ('you see only light') fits to my description of 'see2'. With that 'only' you exclude 'see1'.

I put it in your mouth ('Then you must conclude...'), not in mine. I would never agree with your statement that we only see light. Usually I see all kind of things, thanks to their reflection. I see cups on my desk, which I see of course too, my computer screens (OK, these emit light), outside I see cars. If you say we only see light, i.e. 'seeing light' is the only correct use of 'seeing', then you should say I am wrong when I describe my environment, and I should use another word instead of 'seeing', e.g. 'observe by visually means'. But that would be a bit weird, isn't it?

And we had the problem of the 'perfect black dog'. As it neither reflects, nor emits light, one had to say one does not see this dog. Which makes no sense too.

 

 

Started posting before I saw yours. Yep, that is exactly what is going on.

We already have a word for see2. It's called detecting. We detect light. We don't see light. We see objects because our eyes detect light. 

[Strange]

On the subject of writing ... I heard of an interesting experiment on vision. When you look at a page of writing, it all appears to be there, fully formed. But that is an illusion created by the brain. They did an experiment where they used eye-tracking so that only the word you are looking at is displayed, the rest of the text is replaced with X's or nonsense. To the experimental subject, the page of text appears completely normal. To someone looking over their shoulder, it is a page of nonsense, with words being displayed momentarily all over the place. (They did a similar thing with colour, to show that the mind creates a colour image of the full scene before us, even though only the central part of the visual system has colour perception.)

[koti]

9 hours ago, Strange said:

On the subject of writing ... I heard of an interesting experiment on vision. When you look at a page of writing, it all appears to be there, fully formed. But that is an illusion created by the brain. They did an experiment where they used eye-tracking so that only the word you are looking at is displayed, the rest of the text is replaced with X's or nonsense. To the experimental subject, the page of text appears completely normal. To someone looking over their shoulder, it is a page of nonsense, with words being displayed momentarily all over the place. (They did a similar thing with colour, to show that the mind creates a colour image of the full scene before us, even though only the central part of the visual system has colour perception.)

Yes, but I bet the lights were on during both experiments. Nice soothing post though, Strange. 

[StringJunky]

4 minutes ago, koti said:

Yes, but I bet the lights were on during both experiments. Nice soothing post though, Strange. 

The brain does some serious photoshopping. We have a blind spot in each eye with no receptor cells there and we never notice them normally because our brain photoshops  a continuation of whatever is around the blind spot into it.

[koti]

2 minutes ago, StringJunky said:

The brain does some serious photoshopping. We have a blind spot in each eye with no receptor cells there and we never notice them normally because our brain photoshops  a continuation of whatever is around the blind spot into it.

It's actually even more diverse than just photoshopping...the brain processes responsible for perception can cause the light which is fed from eyes to the brain to cause Synesthesia, a phenomenon of perceiving certain letters in certain colors, certain colors as sounds or skin sensations depending on the type of the condition. The lights still need to be on though.

[Furyan5]

1 hour ago, koti said:

It's actually even more diverse than just photoshopping...the brain processes responsible for perception can cause the light which is fed from eyes to the brain to cause Synesthesia, a phenomenon of perceiving certain letters in certain colors, certain colors as sounds or skin sensations depending on the type of the condition. The lights still need to be on though.

Light fed from the eyes to the brain? You believe the eyes send light to the brain?

[StringJunky]

20 minutes ago, Furyan5 said:

Light fed from the eyes to the brain? You believe the eyes send light to the brain?

The impulse created by the photon interacting with a receptor. He could've easily just said 'signal'.  It's not too difficult to work out what he meant.

Edited February 28, 2018 by StringJunky

[koti]

24 minutes ago, Furyan5 said:

Light fed from the eyes to the brain? You believe the eyes send light to the brain?

Retina contains neuron photoreceptors (rods & cones) which translate light into signals which travel through the neural pathways into the brain. So yes, in short - eyes send light into the brain. It’s not my belief, its well established science.

Edited February 28, 2018 by koti