How do we know light exists???

[The Rebel]

Seems like a simple question, cos we can see it?

 

I'm not sure what sort of answers I'm gonna get, "cos it does, stupid", "cos einstein says so" or a link to another thread.

 

My problem is in accepting light as a stream of particles (photons) that "travel" from one place to another. My preception is that as an energy change takes place, like fusion in the sun, and electrons get excited, it produces an EM field as oppose to creating a photon travelling away from the source. This EM field effects other surrounding matter, a bit like an iron filing is affected by a magnet.

 

An example would be a cars headlights. From the side we can't see the "beam" of light (unless it is scattered in our direction by particles in the air), it merely hits the ground and the matter in ground reacts to it, upon which we see this "excitement" by receptors in our eyes, being stimulated by the new EM wave from the ground.

 

If light were made of photons then wouldn't we see the beam from the side?, you can't say only one side of the photon is visible (the "front").

 

I guess my question is do photons actually exist or are they just theoretical models of whats happening. Some may say well certain experiments have detected a photon, but then anything that is a measuring a system, affects the system. The measuring instrument is merely in the EM field, and being affected, it isn't necessary picking up a "photon".

 

Thanks.

[Johnny5]

My preception is that as an energy change takes place, like fusion in the sun, and electrons get excited, it produces an EM field as oppose to creating a photon travelling away from the source. This EM field effects other surrounding matter, a bit like an iron filing is affected by a magnet.

 

Can you show me what you mean in formulas please. In quantum theory, light is emitted by a hydrogen atom when an electron changes energy levels. Is that what you mean by "energy change."

 

Regards

[5614]

If light were made of photons then wouldn't we see the beam from the side?' date=' you can't say only one side of the photon is visible (the "front").

[/quote']

 

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.

 

If a car's headlight shoots photons forward they are not going to hit your eye unless the 'bounce' off something, this happens in laser because the photons are so densely packed enough photons bounce off the air to see them... you would probably not see a single photon by itself, its not enough to trigger the electrical impulse to your brain.

[swansont]

I guess my question is do photons actually exist or are they just theoretical models of whats happening. Some may say well certain experiments have detected a photon' date=' but then anything that is a measuring a system, affects the system. The measuring instrument is merely in the EM field, and being affected, it isn't necessary picking up a "photon".

[/quote']

 

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?

[Nevermore]

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

[Cadmus]

My problem is in accepting light as a stream of particles (photons) that "travel" from one place to another.

Excellent point. I do not think that it is extermely useful to consider light as a stream of particles. Instead, light is stream of waves. The word photon can be thought of as the name of the interaction that occurs when light waves interact with space-time in their path.

[5614]

I do not think that it is extermely useful to consider light as a stream of particles. Instead, light is stream of waves.

I would disagree, understanding photon physics thinking of them as purely a wave would get very confusing... 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).

[Johnny5]

I would disagree, understanding photon physics thinking of them as purely a wave would get very confusing... 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).

 

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

 

Regards

[Cadmus]

I would disagree, understanding photon physics thinking of them as purely a wave would get very confusing... 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).

How would your understanding of the effect of photons differ if you were to consider photons as a quantization of the interaction that occurs when light waves interact with space-time in their path.

[swansont]

The very fact that this discussion is even taking place' date=' proves conclusively that physics needs a better photon model.

[/quote']

 

Or that trying to use macroscopic concepts to decribe atomic-scale phenomena gives a model that is lacking.

[5614]

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

Nah, I totaly disagree... I could explain that 5x2=10 to a 2 year who can't even do addition yet and he wouldn't understand, does that mean that mathermatics and multiplication isn't good?

 

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

 

In fact if they thought it was no good they wouldn't be trying to learn it!

 

How would your understanding of the effect of photons differ if you were to consider photons as a quantization of the interaction that occurs when light waves interact with space-time in their path.

The thing is that you can't have a wave which when it interacts with space-time randomly changes to a particle.... I'm not saying its not a good way of visualising light, it's just that I think that surely viewing it as a wave/particle all at once simplifies things, with QM's wave-particle duality I think its just easier to view everything as both at once, that way you don't get confused as to when it's what and how it interacts, its both, it acts as both, view it as both... at the same time whatever works for you... and I suppose looking back at what The Rebel said maybe your way is better in this case.

[Cadmus]

The thing is that you can't have a wave which when it interacts with space-time randomly changes to a particle.

I agree. I would do away with the particle completely. When a tsunami wave crashed into Indonesia, Thailand, Somalia, etc., in each case it was the exact same wave (set of waves). Different parts of the wave front hit different locals. The various land forms were subjected to an imparting of a large amount of energy. If we consider that in the case of light this energy takes specific quanta, why could we not consider that Indonesia, etc. absorbed, or were hit by, photons of water. In other words, when a light wave front encounters space-time, it imparts energy. That energy is quantized. That quanta can be called a photon. However, why must that photon refer to a particle at all? It could simply be a name given to the quantum of energy imparted by interaction with the wave front. Why is the concept of an independent particle object even necessary?

[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.

 

If you find this subject interesting a lot chemical instrumentation (thats my area of training) is based on the properties of light ... if you ever run into a good book on spectroscopy pick it up.

 

http://fuse.pha.jhu.edu/~wpb/spectroscopy/spec_home.html ... click on the basics of light.

 

I hope that helps you out ... I may have repeated information you already know.

[5614]

Why is the concept of an independent particle object even necessary?

Because as Technologist said photons can behave as partciles. The photoelectric effect is indeed a big proof of this. As Max Plank found out when he made his E=hf formula light seems to come in chunks, rather than a continuous wave, these chunks are photons.

[syntax252]

I guess my question is do photons actually exist or are they just theoretical models of whats happening. Some may say well certain experiments have detected a photon' date=' but then anything that is a measuring a system, affects the system. The measuring instrument is merely in the EM field, and being affected, it isn't necessary picking up a "photon".

 

Thanks.[/quote']

 

Well one thing seems clear: Something is there, else why and how would light sensitive organs (eyeballs) have evolved?

[Cadmus]

On what possible basis might you make such an assumption?

[Cadmus]

As Max Plank found out when he made his E=hf formula light seems to come in chunks, rather than a continuous wave, these chunks are photons.

Does this demonstrate that light comes in chunks, or that light interaction with objects in space-time is quantized. These are two different things.

[Technologist]

Much of what I've read in astronomy suggests that the concentration of matter in space is largely diluted. There is not enough material (medium) to transmit waves. If I recall correctly this is why scientists invented the mysterious ether. Is this incorrect?

[swansont]

Much of what I've read in astronomy suggests that the concentration of matter in space is largely diluted. There is not enough material (medium) to transmit waves. If I recall correctly this is why scientists invented the mysterious ether. Is this incorrect?

 

They assumed that the light waves needed a medium in which to propagate. The trouble arises when you discover that we are neither stationary nor moving with respect to the proposed medium.

 

So the conclusion is that EM waves do not need a medium through which to propagate.

[5614]

Does this demonstrate that light comes in chunks, or that light interaction with objects in space-time is quantized. These are two different things.

It showed that light came in chunks.... are you proposing that it travels as a constant stream of energy and then when it interacts with space-time randomly changes into chunks? (Or were you just asking?)

[J.C.MacSwell]

They assumed that the light waves needed a medium in which to propagate. The trouble arises when you discover that we are neither stationary nor moving with respect to the proposed medium.

 

So the conclusion is that EM waves do not need a medium through which to propagate.

 

Is that your conclusion/you agree fully with it?

[swansont]

Is that your conclusion/you agree fully with it?

 

I can't think of a third option. The concept does seem to allow for c being constant in all inertial frames.

[dsjgenius]

well if you can not disprove there is such a thing called light, it does not mean that there is such a thing as light (or photons for that case) so i agree with johhny5 in that physics does need a more conclusive model of light and photons as the currrent model of light as photons is too abstract and vague for some people to understand

[Cadmus]

It showed that light came in chunks.... are you proposing that it travels as a constant stream of energy and then when it interacts with space-time randomly changes into chunks? (Or were you just asking?)

I am proposing that light travels in waves, and when the wave front interacts with space-time, it imparts an effect that can be quantized. This quantization is not a particle, but rather the particle concept is merely a way to symbolize the quantization of the interaction of light waves with space-time.

[swansont]

well if you can not disprove there is such a thing called light, it does not mean that there is such a thing as light (or photons for that case) so i agree with johhny5 in that physics does need a more conclusive model of light and photons as the currrent model of light as photons is too abstract and vague for some people to understand

 

Models are measured by how well they explain and predict behavior, not by how readily people can understand them. Occam's razor aside, some things about nature are just not very simple.