Post a photo, any photo

[ibglowin]

Okay, I'll bite. I agree that knowing that the rainbow is a result of reflection, refraction, and dispersion changes your perspective. Does it ruin the wonderment?

Well, let's think. What causes refraction? Yeah, yeah, it is the fact that the phase velocity of light is lower in a medium than in vacuum. Well, why is the phase velocity diminished in a medium? Hmm, obviously it is due to the interaction of the electric field with the polarized subatomic particles in matter. But why would that change the phase velocity of the light? Well, we can approximately understand it classically via an acceleration of the electrons (driven by the incident light), and a re-radiation of that light, but with a phase delay. This is a pretty dang good approximation. However, upon careful inspection this picture does not fully account for the effect. Hmm, it turns out that if we consider quantum effects, i.e., the wave-like nature of the electrons, we can account for some of those discrepancies.

But what about dispersion? Oh, that is "just" the fact that different wavelengths of light have a different index of refraction. But why? Oh, again, that is due to the interaction of the electric field with the polarized subatomic particles in matter. Classically, if you "shake" these electrons at different frequencies, the re-radiated light undergoes a slightly different phase shift depending on the frequency. Why is that? Well, classically, it is because of the retardation due to the finite mass of the electron, although classical physics doesn't really account for the origin of electron mass. Again, there are some discrepancies from the classical theory that you need to invoke simple quantum mechanics to explain. However, to explain the mass of the electron, you have to go beyond simple quantum mechanics and look at quantum electrodynamics (QED).

But wait -- your classical theory predicts that the index of refraction will be less than 1.00 at certain frequencies. That cannot be correct: that would imply that the phase velocity of the light is greater than the speed of light in a vacuum, c . Wouldn't that violate Special Relativity (and, for that matter, General Relativity)? Does quantum mechanics save you this time, too? No, the phase velocity in these situation IS indeed greater than c. But the group velocity, that is, the velocity of a "bundle" of light, is NOT greater than c. This situation does not violate relativity. A "superluminal" phase velocity does not carry any information or energy faster than c, which is all that is required to be consistent with relativity.

You mentioned reflection. Why would the light be reflected? After all, water droplets are clear, not like mirrors. Oh, some of that is due to "Fresnel reflectivity," like when you can see your own image when looking through a window, and some is due to total internal reflection. What is Fresnel reflectivity due to? Oh, that is due to two things: because light is a wave AND because of the boundary conditions that Maxwell's Equations impose on the magnetic and electric fields. Maxwell's Equations require that the perpendicular component of the B-field and the parallel component of the E-field are unchanged across an interface. It turns out that, if you look at the relevant vector fields, a propagating electromagnetic wave CANNOT satisfy this condition unless there is a reflected component of the wave. What about total internal reflection? Oh, that is when (at certain angles) a propagating electromagnetic wave CANNOT satisfy this condition AT ALL, except if 100% of the wave is reflected.

But you invoked Maxwell's equations, quantum mechanics, and Special Relativity to explain these things! Why are THEY true? Umm, err, go ask your mother!

Sorry if I rained on your parade or harshed your mellow. But I think there is still plenty of room for wonderment, even if you "know" what causes a rainbow.

 

[Kraffty]

Okay, I'll bite. I agree that knowing that the rainbow is a result of reflection, refraction, and dispersion changes your perspective. Does it ruin the wonderment?

Well, let's think. What causes refraction? Yeah, yeah, it is the fact that the phase velocity of light is lower in a medium than in vacuum. Well, why is the phase velocity diminished in a medium? Hmm, obviously it is due to the interaction of the electric field with the polarized subatomic particles in matter. But why would that change the phase velocity of the light? Well, we can approximately understand it classically via an acceleration of the electrons (driven by the incident light), and a re-radiation of that light, but with a phase delay. This is a pretty dang good approximation. However, upon careful inspection this picture does not fully account for the effect. Hmm, it turns out that if we consider quantum effects, i.e., the wave-like nature of the electrons, we can account for some of those discrepancies.

But what about dispersion? Oh, that is "just" the fact that different wavelengths of light have a different index of refraction. But why? Oh, again, that is due to the interaction of the electric field with the polarized subatomic particles in matter. Classically, if you "shake" these electrons at different frequencies, the re-radiated light undergoes a slightly different phase shift depending on the frequency. Why is that? Well, classically, it is because of the retardation due to the finite mass of the electron, although classical physics doesn't really account for the origin of electron mass. Again, there are some discrepancies from the classical theory that you need to invoke simple quantum mechanics to explain. However, to explain the mass of the electron, you have to go beyond simple quantum mechanics and look at quantum electrodynamics (QED).

But wait -- your classical theory predicts that the index of refraction will be less than 1.00 at certain frequencies. That cannot be correct: that would imply that the phase velocity of the light is greater than the speed of light in a vacuum, c . Wouldn't that violate Special Relativity (and, for that matter, General Relativity)? Does quantum mechanics save you this time, too? No, the phase velocity in these situation IS indeed greater than c. But the group velocity, that is, the velocity of a "bundle" of light, is NOT greater than c. This situation does not violate relativity. A "superluminal" phase velocity does not carry any information or energy faster than c, which is all that is required to be consistent with relativity.

You mentioned reflection. Why would the light be reflected? After all, water droplets are clear, not like mirrors. Oh, some of that is due to "Fresnel reflectivity," like when you can see your own image when looking through a window, and some is due to total internal reflection. What is Fresnel reflectivity due to? Oh, that is due to two things: because light is a wave AND because of the boundary conditions that Maxwell's Equations impose on the magnetic and electric fields. Maxwell's Equations require that the perpendicular component of the B-field and the parallel component of the E-field are unchanged across an interface. It turns out that, if you look at the relevant vector fields, a propagating electromagnetic wave CANNOT satisfy this condition unless there is a reflected component of the wave. What about total internal reflection? Oh, that is when (at certain angles) a propagating electromagnetic wave CANNOT satisfy this condition AT ALL, except if 100% of the wave is reflected.

But you invoked Maxwell's equations, quantum mechanics, and Special Relativity to explain these things! Why are THEY true? Umm, err, go ask your mother!

Sorry if I rained on your parade or harshed your mellow. But I think there is still plenty of room for wonderment, even if you "know" what causes a rainbow.

 

[sour_grapes]

Let me be clear: It was not my intention to show off my oh-so-grand knowledge. At the end of my knowledge, there lies ignorance. I do not understand many of the things and concepts deeper than the ones that I mentioned. (Hence "Go ask your mother.") I think it is good to keep that ignorance, which we all will encounter if we go far enough, in mind! And we can still be filled with wonder at those things that lie just beyond our ken.

 

[wrongway]

Whooaa whooo Oh God its so bright! So bright! Whooo lol I think he got into my wild mulberry wine!

 

[jswordy]

Jan. 4, 1985. Almost 35 years ago, the day after my birthday. Hampton Coliseum in Hampton, Virginia. Price of admission: $17. Remains the best concert of any kind I have ever seen.

 

[geek]

The Boss..!! [emoji106]

 

[Boatboy24]

Jan. 4, 1985. Almost 35 years ago, the day after my birthday. Hampton Coliseum in Hampton, Virginia. Price of admission: $17. Remains the best concert of any kind I have ever seen.

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Ah, Cellar Door Productions.

 

[bkisel]

Not sure why but but this wild flower framed by the bark of a tree caught my interest. [While out hiking in PA Gamelands #37 the other day.]

 

[Kraffty]

Jan. 4, 1985. Almost 35 years ago, the day after my birthday. Hampton Coliseum in Hampton, Virginia. Price of admission: $17. Remains the best concert of any kind I have ever seen.

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I don't think 17.00 would buy you a beer at a Bruce concert today. But seeing him is still on our bucket list.
Mike

 

[wrongway]

Saw Bruce at Mile High on Sept 28 -85! ELO feb 4-1977. They dont make music like that anymore!

 

[ibglowin]

 

[sour_grapes]

True confessions time. I grew up as a city boy. Due to limited family opportunities, I never really got outside the city while I was growing up. In grad school, I was chatting with my roommate, who happened to be an astrophysicist. The whiskey was flowing, and I was waxing philosophic. We were discussing his research, which focused on spiral galaxy formation. Suddenly, it dawned on me: this picture must be all wrong!!

I said: "Wait, this is all ********! If the galaxy we live in were a spiral, then there would be, like, a bright BAND of stars in the sky, in the plane of the spiral!!"

He looked at me for a long time, not sure if I was serious (I was), and said gently " There is. It is called 'the Milky Way.' Have you never seen it?" I had not ever seen it before!

A couple of years later, I went to a conference in a remote part of New Hampshire, and was gobsmacked by what I had been missing!

On a related note, "the Milky Way Galaxy" is redundant. "Galaxy" means "milky," from the Greek, which is where we get our words "lactose," "lactate," etc.

 

[olusteebus]

At the corner of

 

[ibglowin]

No fear.......

 

[bkisel]

Oops! Sorry, couldn't make video public.

How do I delete this post?

 

[dralarms]

Link don’t work. Brings me to a google sign in sheet

 

[Boatboy24]

Link don’t work. Brings me to a google sign in sheet

I got a 404

 

[geek]

I got a 404

Ditto

 

[ibglowin]

Undersea tunnel between Sweden and Denmark

 

[bkisel]

Okay, posting qith dialared pupols. Will edit in the AM but wanted to share this phot. Rajen this morning while walking/hiking in Hills Creek State Patk. Phot was/is stylized by Giigle Photos, NO I AM NOY DRUNK!