Strange Posted February 2, 2018 Share Posted February 2, 2018 1 hour ago, studiot said: Let me remind you of the OP. Posted two years ago and not been back since. I don't think you are going to get any guidance from them. Link to comment Share on other sites More sharing options...
Eise Posted February 2, 2018 Share Posted February 2, 2018 Quote Light: visible or invisible? 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? 1 hour ago, studiot said: Let me remind you of the OP. I have this in mind all the time. Let's just look at the assumption behind the question 'Light: visible or invisible?' It is obvious: the OP's assumption is that we can see objects because they reflect light. If this would be the only meaning of seeing, then light really is invisible. You cannot see light that does not enter your eye, because light does not reflect light. (The same for emitting light: a light beam passing by does not emit light to your eyes. Therefore you cannot see light that does not enter your eyes). But I surely agree with you that it is a rather limited concept of seeing, because we are also used to say that we see light. We perfectly understand when somebody says he is seeing light. As you say, it has multiple meanings. But in the strict sense that the OP is using (seeing1), we cannot see light. In the normal daily sense, of course we can see light (see2). And mostly we do not bother about this distinction, because it seldom leads to confusion. Except you meet a philosopher in a thread about the visibility of light... 1 Link to comment Share on other sites More sharing options...
studiot Posted February 2, 2018 Share Posted February 2, 2018 (edited) 34 minutes ago, Eise said: I have this in mind all the time. Let's just look at the assumption behind the question 'Light: visible or invisible?' It is obvious: the OP's assumption is that we can see objects because they reflect light. If this would be the only meaning of seeing, then light really is invisible. You cannot see light that does not enter your eye, because light does not reflect light. (The same for emitting light: a light beam passing by does not emit light to your eyes. Therefore you cannot see light that does not enter your eyes). But I surely agree with you that it is a rather limited concept of seeing, because we are also used to say that we see light. We perfectly understand when somebody says he is seeing light. As you say, it has multiple meanings. But in the strict sense that the OP is using (seeing1), we cannot see light. In the normal daily sense, of course we can see light (see2). And mostly we do not bother about this distinction, because it seldom leads to confusion. Except you meet a philosopher in a thread about the visibility of light... Yes I agree that the OP restricted his discussion to light which enters the eye. Since that is the only light he discusses, that must be the light he states quite clearly, although you did not underline it, that we never see. So the issue arise of does the light that enters the eye and forms some sort of image on the retinal constitute seeing or was he intending the creation of a mental model to be included. He was not clear and may even have meant something else entirely that neither you nor I have thought of. I have already demonstrated the some complications with the mental model interpretation the most important being the colour blindness tests where the hidden symbol is there and seen at the retinal stage but invisible in the mental model. As a matter of interest, yes this is an old thread and the correct proceedure would have been for the hijacker to have started a new thread, perhaps stating that it was inspired by this one. By coincidence I was asked another technical question in another old thread last night and I am collecting information to do just this and start a new thread in answer. Edited February 2, 2018 by studiot Link to comment Share on other sites More sharing options...
John Cuthber Posted February 2, 2018 Share Posted February 2, 2018 10 hours ago, Eise said: Wrong. You see1 a blue apple. Only observers in the same inertial frame see1 the apple red. There is no objective reason to say that some inertial frame is preferred above anothe The idea of you telling me what I see is absurd- especially when I already told you. 11 hours ago, John Cuthber said: What I "see" is an image of the imperfections in my eye's lens; regardless of the source. Strictly what I see is essentially the point spread function of the eye.https://en.wikipedia.org/wiki/Point_spread_function 10 hours ago, Eise said: And do you see3 that there is a difference between seeing light and seeing objects by means of light? I recognise the terms have different meanings. However, the reason I can tell you what colour the light is, is that I can see it. I can also see objects, but I can't see objects that don't exist- for example, a blue apple. I may mistakenly believe that I see a blue apple. That's faulty perception. A bit like you "see" a line as longer than another line in optical illusions. Link to comment Share on other sites More sharing options...
beecee Posted February 2, 2018 Share Posted February 2, 2018 (edited) 8 hours ago, Eise said: You cannot see light that does not enter your eye, because light does not reflect light. (The same for emitting light: a light beam passing by does not emit light to your eyes. Therefore you cannot see light that does not enter your eyes). Hmmm...We see via the organ that evolution has bestowed on us, called the eye. To see requires light from the visible part of the spectrum to enter the eye via reflection and/or refraction. If no part of the visible spectrum is reflected/refracted to enter the eye, we essentially only then see black...or the absence of any part of the visible spectrum. The nature of any light/photons that are reflected from any object to the eye, are then totally independent of what happens to that object, and are only dependent on the fabric of the framework it is being radiated through, and that we call spacetime. eg 1: photons from distant objects in space appear redshifted due to the framework [spacetime] being stretched. [expanding] eg 2: Also of course if a being on a planet orbiting the star Betelgeuse should observe that star to go supernova, we on Earth would still continue to observe the light that has left that star for another 650 years, before the light from the supernova reaches us. Therefor I conclude that we see at least part of the EMS that we term the visible spectrum via the evolutionary organ we call the eye. Edited February 2, 2018 by beecee Link to comment Share on other sites More sharing options...
John Cuthber Posted February 3, 2018 Share Posted February 3, 2018 4 hours ago, beecee said: Therefore you cannot see light that does not enter your eyes We are back to the idea that China is invisible (because I can't see it from here) which is plainly absurd. You can only see something if it is- or comes from- a place where you can see it. But, if It is in a position to project light into my eyes I can see that light, and I can make deductions from it about the outside world. On 2/22/2016 at 7:41 PM, John Cuthber said: 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. Link to comment Share on other sites More sharing options...
Eise Posted February 5, 2018 Share Posted February 5, 2018 On 03/02/2018 at 1:19 AM, John Cuthber said: The only thing you see is light. Then you cannot see cars, because cars are not light. On 02/02/2018 at 7:55 PM, John Cuthber said: The idea of you telling me what I see is absurd- especially when I already told you. And it is still wrong. You see an apple: but for you it looks blue. So you see1 a blue apple. Of course this is because you see1 the apple because you see2 blue light. And you might guess well that this is due to the Doppler-effect, especially while Scotty's T-shirt looks blue to you too. But nothing in the blue light alone will give you a clue that the light is Doppler-shifted. On 02/02/2018 at 7:55 PM, John Cuthber said: I may mistakenly believe that I see a blue apple. That's faulty perception. A bit like you "see" a line as longer than another line in optical illusions. Literally it is not faulty. As I said, there is objectively no preferred observer frame. Of course it is easiest always to take the restframe of the object under scrutiny and you, the observer, as preferred frame. But when there is no such frame, because the frame move against each other, who is right? Seeing things and seeing light are just different things. And when one reduces the meaning of 'seeing' to 'seeing things', then you cannot see light. And when you reduce seeing to 'seeing light' only, then one cannot see things that reflect light. And if you use both meanings for seeing in one word, then you do not account for the difference between how we see macro objects and light. Which nearly never is a problem... Link to comment Share on other sites More sharing options...
koti Posted February 5, 2018 Share Posted February 5, 2018 30 minutes ago, Eise said: Then you cannot see cars, because cars are not light. I think this is faulty logic Eise. Technically, in the context that we are speaking here, cars that we see are light because they reflect light therefore we see them. If they wouldn't reflect light we wouldn't see them. It's crude and simple and I'm sure I don't need to explain this but that's really all there is to it. Link to comment Share on other sites More sharing options...
studiot Posted February 5, 2018 Share Posted February 5, 2018 (edited) I see no inconsistency. There are many terms where one word can mean the whole or part of something. For instance sheep can refer to one sheep or the whole flock. But if you are looking at a field of sheep, you need the context to distinguish which is meant. Baa Baa Baa Edited February 5, 2018 by studiot Link to comment Share on other sites More sharing options...
StringJunky Posted February 5, 2018 Share Posted February 5, 2018 3 minutes ago, koti said: I think this is faulty logic Eise. Technically, in the context that we are speaking here, cars that we see are light because they reflect light therefore we see them. If they wouldn't reflect light we wouldn't see them. It's crude and simple and I'm sure I don't need to explain this but that's really all there is to it. We see a configuration of the light that represents the object the photons interacted with. Link to comment Share on other sites More sharing options...
studiot Posted February 5, 2018 Share Posted February 5, 2018 5 minutes ago, StringJunky said: We see a configuration of the light that represents the object the photons interacted with. Always? When we see the black sheepdog, What light do our eyes receive from the dog? Yet we correctly 'see' a dog, not an absence of light (can you see an abscence of light?) I think counterexamples can be constructed for any simplified definition. Link to comment Share on other sites More sharing options...
koti Posted February 5, 2018 Share Posted February 5, 2018 6 minutes ago, StringJunky said: We see a configuration of the light that represents the object the photons interacted with. The above might do as a definition of reflected light from the surface of the car but isn’t „reflection” sufficient? Link to comment Share on other sites More sharing options...
studiot Posted February 5, 2018 Share Posted February 5, 2018 Just now, koti said: The above might do as a definition of reflected light from the surface of the car but isn’t „reflection” sufficient? See my post above. Link to comment Share on other sites More sharing options...
StringJunky Posted February 5, 2018 Share Posted February 5, 2018 Just now, studiot said: Always? When we see the black sheepdog, What light do our eyes receive from the dog? Yet we correctly 'see' a dog, not an absence of light (can you see an abscence of light?) I think counterexamples can be constructed for any simplified definition. A black dog is not an absence of light; it is not a perfect absorber Link to comment Share on other sites More sharing options...
studiot Posted February 5, 2018 Share Posted February 5, 2018 Mine is perfect Link to comment Share on other sites More sharing options...
StringJunky Posted February 5, 2018 Share Posted February 5, 2018 (edited) 3 minutes ago, studiot said: Mine is perfect Then all you'll see is a silhouette, the outline from which one might determine is a dog. Edited February 5, 2018 by StringJunky Link to comment Share on other sites More sharing options...
studiot Posted February 5, 2018 Share Posted February 5, 2018 (edited) If I stood at the field gate and said to the farmer "do you see the silhouette", he would rightly think I'd had too much cider. Did you see the recent lunar eclipse? What did you see? Edited February 5, 2018 by studiot Link to comment Share on other sites More sharing options...
StringJunky Posted February 5, 2018 Share Posted February 5, 2018 4 minutes ago, studiot said: If I stood at the field gate and said to the farmer "do you see the silhouette", he would rightly think I'd had too much cider. Did you see the recent lunar eclipse? What did you see? No, I didn't but that is the Moon in the Earth's shadow. Link to comment Share on other sites More sharing options...
koti Posted February 5, 2018 Share Posted February 5, 2018 (edited) 13 minutes ago, studiot said: Mine is perfect You guys crack me up, You know very well that there is no such thing as a perfect light absorbing dog Edit: Here's a near perfect light absorbing material though. Edited February 5, 2018 by koti Link to comment Share on other sites More sharing options...
dimreepr Posted February 5, 2018 Share Posted February 5, 2018 (edited) 15 minutes ago, StringJunky said: Then all you'll see is a silhouette. 11 minutes ago, studiot said: If I stood at the field gate and said to the farmer "do you see the silhouette", he would rightly think I'd had too much cider. Semantics, the reason for eight pages of the obvious. 11 minutes ago, studiot said: Did you see the recent lunar eclipse? What did you see? The light that entered the eye; a silhouette is, the spin a brain puts on the information received. Edited February 5, 2018 by dimreepr 1 Link to comment Share on other sites More sharing options...
koti Posted February 5, 2018 Share Posted February 5, 2018 5 minutes ago, dimreepr said: Semantics, the reason for eight pages of the obvious. The light that entered the eye; a silhouette is, the spin a brain puts on the information received. Whadda you know dimreepr... +1. Link to comment Share on other sites More sharing options...
StringJunky Posted February 5, 2018 Share Posted February 5, 2018 6 minutes ago, dimreepr said: Semantics, the reason for eight pages of the obvious. An ounce of "commonsense" is worth a pound of intelligence in a scientific discussion, eh? Link to comment Share on other sites More sharing options...
dimreepr Posted February 5, 2018 Share Posted February 5, 2018 1 minute ago, StringJunky said: An ounce of "commonsense" is worth a pound of intelligence in a scientific discussion, eh? Feel free to argue my point? Link to comment Share on other sites More sharing options...
Tub Posted February 5, 2018 Share Posted February 5, 2018 4 hours ago, dimreepr said: Feel free to argue my point? On reflection, dim, i see your point............or do i? Link to comment Share on other sites More sharing options...
Strange Posted February 5, 2018 Share Posted February 5, 2018 25 minutes ago, Tub said: On reflection, dim, i see your point............or do i? On reflection, maybe you see it twice. Link to comment Share on other sites More sharing options...
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