How do we know light exists???

[The Rebel]

Quite a lot of posts to get through, but here goes.

 

5614: It doesn't quite work like that, a photon has to hit the receptors in your eye which triggers an electrical impulse to your brain which is how you see.... the key point being that the photon has to go into your eye for you to see it.

Ok so the model of a photon was possibly taken out of line there, in that light is not evident until it interacts with something (like the eye). Try this one, there was a thing I read in a QED book once that talked about how light is reflected through glass. It mentioned how light was reflected off the front and rear surfaces differently depending on the thickness of the material, some kind of percentage or something. It made you think if light were particles how would each photon know whether to bounce of the front surface without knowing the thickness of the material fist. I concluded it has to be that energy fields are involved and NOT that light is a stream of particles that change as and when they come into contact with the surface.

 

Swansont: EM energy is quantized, and that's what we call a photon. You can also view it as a vibrational mode of the EM spectrum. What's the difference between the model and reality, if the model explains how reality behaves?

So then what is a photon a particle?, a unit of energy?, a wave? The problem is the number of models we have. Each sit perfectly within their context but in abstract form I’m struggling to decide what a photon is, how its created, what the interaction is between emitting and receiving, i.e. by particle movement, by energy waves, etc.

 

Nevermore: Light is a notion produced by the human brain. Without an eye, there is no light. Only photons.

I disagree. Something is there, as Syntax252 says. Whether its a cluster of particles or an energy field. The eye is just an instrument to measure the light. It’s like saying there is no voltage on a power supply until you put your fingers in it.

 

Cadmus: I do not think that it is extermely useful to consider light as a stream of particles

It is useful, but it has flaws, especially in abstract.

 

5614: I prefer to think of light, or EM radiation as particles travelling in a wave. So (I've said this before) but just as a dolphin swims jumping in/out of water, so a dolphin (particle) jumping up and down (a wave).

Are you saying light consists of both a carrier wave AND a particle. That a photon rides a wave until it hits something? That’s an interesting concept, I’d have to consider.

 

Johnny5: The very fact that this discussion is even taking place, proves conclusively that physics needs a better photon model.

One that can be derived out of context, and then have the equations applied to it to put it back in to explain all related sciences involving light.

 

5614: Just because someone doesn't understand does not mean that the thing they are trying to understand is no good.

In their individual forms the models of the photon are very good, and helpful for their application. It is the combination of these and defining how what light is itself that is causing the problems.

 

Technologist: Light has a dual nature. It can show characteristics of both a wave and a particle. Experiments on reflection, refraction, and diffraction clearly show that light displays wave like properties similar to waves of water or sound. On the other hand light shows characteristics of a particle. Assuming that the space between earth and the sun lacks enough material to transmit a wave, then how would light reach us if it wasn’t a particle? The photoelectric effect is evidence of the particle nature of light.

 

All these are examples of how I find it difficult to imagine what a photon is. All the concepts that involve light like curving around a stellar mass, photoelectric effect, reflection, diffraction, absorption, constancy, mass-energy relationship, why doesn’t it drag when in motion, nature around black holes, how its created (e.g. light bulbs, transmitters), if photon is particle then what is it physically doing when it leaves a radio aerial?, its effects on particular chemicals (e.g. fading, sunburn, microwaving), polarisation, what the ether is and how it travels, why we can’t see it unless we are in direct view, reactions in different material thicknesses, etc, etc.

 

I’m trying to understand what light is to provide a commonality across all of these, and not simply in example of photoelectric effect consider light as a particle, in reflection light is a wave, and have so models for the same thing just try to explain a particular concept.

[J.C.MacSwell]

 

I’m trying to understand what light is to provide a commonality across all of these' date=' and not simply in example of photoelectric effect consider light as a particle, in reflection light is a wave, and have so models for the same thing just try to explain a particular concept.[/quote']

 

Noone has succeeded yet.

[jdurg]

I have always thought of light as a stream of particles (photons) which move in a wavelike pattern. Depending on how you are viewing the light, it will either look like a wave to you or a bunch of quantized particles. (I believe someone else had looked at it like this before). Think of it like drawing a wave on a piece of paper but instead of using one continuous line, you use a bunch of VERY closely spaced dots. From a distance and from most angles, it would look like a solid line. But when you get really close to the paper, you see that the solid line is actually composed of a bunch of same sized dots. These 'dots' would be the photons.

 

The Rebel: I think you misinterpreted that thing about the glass. I believe what it was saying was that if a beam of light goes through the glass, it gets reflected/diffracted internally based upon the thickness of the glass. So the light goes through the front of the glass and is bent due to the interaction with the glass. How far the overall bend is depends on the thickness of the glass. On a very thin piece of glass, there isn't a whole lot of 'stuff' to interact with so the light goes right through the other side and isn't bend a whole lot. On a thick piece of glass, there's a large amount of matter to slow down the light beam and cause it to bend substantially. If it's thick enough, the light loses its energy and is completely blocked.

 

This is why I too believe in the bunch of particles moving in a wave pattern type of theory. As these 'particles' move through the glass, they interact with the glass and lose some energy. As a result, the wave pattern changes and the light appears differently than it did before.

[The Rebel]

No this wasn't to do with refraction. It was 5-6 years ago I picked this book up and I can't remember what its called or who its by, it was just QED stuff.

 

It talked about how light reflects and transmits on front and rear surfaces of a glass block. For example 4% are partially reflected of the front surface, leaving 96% to transmit to the rear surface, which in turn reflects 4%. I was doing A-level physics at the time and so I'm fairly certain it was not relating to basic refraction stuff.

 

It also mentions particle-wave duality and refered to photons as wavicles. It was good because it focused on light itself as a whole, instead of pin-pointing specific areas of physics.

 

I'll see if I can find the book and spend some time reading it, maybe then I can get a better understanding of answering the concepts in my post above.

[Silencer]

Everyone knows that lightbulbs don't actually give off light, but collect dark.

 

You can see this because when you put your hand underneath the bulb the dark starts to collect under your hand.

 

And when it "burns out" that really means that it is filled up with dark!

[ydoaPs]

lol. thats goin into the best quote thread.