Rainbows and wave-particle duality

Main Question or Discussion Point

Correct me if I'm wrong. The wave function of a particle collapses when you observe/measure it? Because that you essentially disturb it. Right?

So how is it that we see rainbows then if it's wave function collapses as we observe it? And how is it that we are able to split white light into different spectrum of light but the wave function doesn't collapse?

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jtbell
Mentor
A rainbow, or any classical optical phenomenon, involves bazillions and bazillions of photons. Each photon "collapses" differently according to a probablity distribution which matches the intensity pattern that you calculate from classical optics/E&M theory.

A rainbow, or any classical optical phenomenon, involves bazillions and bazillions of photons. Each photon "collapses" differently according to a probablity distribution which matches the intensity pattern that you calculate from classical optics/E&M theory.
Wow; interesting.

A bit confused though. So how does this transfer over to the double slit experiment involving "bazillions and bazillions of photons" as you observe/measure it?

Wow; interesting.

A bit confused though. So how does this transfer over to the double slit experiment involving "bazillions and bazillions of photons" as you observe/measure it?
Every photon passes through both slits interfering with itself and is then detected as a single point on the screen. With many photons simultaneously there is no difference, it's just that you have to wait less to see the inteference pattern: with one photon at a time you see one point on the screen, than another in another place, and so on. After having collected a large amount of points, you see the interference pattern.

tiny-tim
Homework Helper
Hi Nano-Passion!

Wave collapse doesn't really come into it …

when a red photon reaches us from a rainbow, loosely speaking it's the same red photon that came from the Sun …

the raindrops don't cause photons of different frequencies (which aren't in superposition anyway) to interfere with each other, they do the exact opposite, they separate them!

Every photon passes through both slits interfering with itself and is then detected as a single point on the screen. With many photons simultaneously there is no difference, it's just that you have to wait less to see the inteference pattern: with one photon at a time you see one point on the screen, than another in another place, and so on. After having collected a large amount of points, you see the interference pattern.
Thank you. =]

Hi Nano-Passion!

Wave collapse doesn't really come into it …

when a red photon reaches us from a rainbow, loosely speaking it's the same red photon that came from the Sun …

the raindrops don't cause photons of different frequencies (which aren't in superposition anyway) to interfere with each other, they do the exact opposite, they separate them!
First, thanks for the warm welcome. :!!)

Red photon? The color of a photon is dependant on its frequency? I thought we interpret photons with color depending on what it bounces of.

So photons come in different colors depending on its frequency? So then according to the doppler effect, it would also be relative to the observer. Correct?

Also, sorry if I'm asking too many questions-- how do raindrops separate photons? I'm interested.

tiny-tim
Homework Helper
Hi Nano-Passion!
Red photon? The color of a photon is dependant on its frequency? I thought we interpret photons with color depending on what it bounces of.
You're thinking of white light (or any mixed colour) …

when it hits something blue, say, mainly the blue bounces off, and so it looks blue.

But an individual photon has a particular wavelength (and therefore a particular frequency) …
that means a particular colour (and there's no such thing as a white photon).
So photons come in different colors depending on its frequency? So then according to the doppler effect, it would also be relative to the observer. Correct?
Yes and yes.
Also, sorry if I'm asking too many questions-- how do raindrops separate photons? I'm interested.
Different frequencies move at different speeds through water.

The amount by which light bends on entering or leaving water depends on the speed, so the colours get separated.

It's the same effect as Newton got through a prism of glass.

Hi Nano-Passion!

You're thinking of white light (or any mixed colour) …

when it hits something blue, say, mainly the blue bounces off, and so it looks blue.

But an individual photon has a particular wavelength (and therefore a particular frequency) …
that means a particular colour (and there's no such thing as a white photon).

Yes and yes.

Different frequencies move at different speeds through water.

The amount by which light bends on entering or leaving water depends on the speed, so the colours get separated.

It's the same effect as Newton got through a prism of glass.
Great, thanks. =D

Well atoms necessarily don't have color but just the one we interpret correct? So how is it that different atoms absorbs some frequencies of photons and reflect back others.

Does this have to do with how many electrons orbiting (or whatever they do) the atom?

It has to do with electron excitation, so yes, it's the number of electrons, but that's linked to protons... and isotopes...

Remember, it's disturbances in the "orbits" of electrons that cause the emission of light. I might help if you look at the example of LASERS, which among other things, can involve pumping, and you'll learn about concepts such as electrons emitting photons as a means of "losing" energy. This all goes back to WHY there is QM in the first place.

http://en.wikipedia.org/wiki/Laser
I think you'll have your current, and many future questions about EM radiation, and how light is emitted in this model. If you imagine a less extreme situation, an electron dumping energy = light, and... well... you'll see.

It's a place to start, but the best point may be at the end:

Wikipedia said:
FoundationsIn 1917, Albert Einstein established the theoretic foundations for the laser and the maser in the paper Zur Quantentheorie der Strahlung (On the Quantum Theory of Radiation); via a re-derivation of Max Planck’s law of radiation, conceptually based upon probability coefficients (Einstein coefficients) for the absorption, spontaneous emission, and stimulated emission of electromagnetic radiation; in 1928, Rudolf W. Ladenburg confirmed the existences of the phenomena of stimulated emission and negative absorption;[8] in 1939, Valentin A. Fabrikant predicted the use of stimulated emission to amplify “short” waves;[9] in 1947, Willis E. Lamb and R. C. Retherford found apparent stimulated emission in hydrogen spectra and effected the first demonstration of stimulated emission;[8] in 1950, Alfred Kastler (Nobel Prize for Physics 1966) proposed the method of optical pumping, experimentally confirmed, two years later, by Brossel, Kastler, and Winter.[10]

(and there's no such thing as a white photon).
I have never heard of "white" photons, infact, but are you sure it's impossible to create an em packet with the appropriate spectrum to appear as white?

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