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0 pointschemeng6y ago0 comments

They are not the same photons. They are emitted by the electron changing energy states after excitation of the incoming photon. But your intuition that there is some quantum weirdness is correct. Quantum Electrodynamics is the theory you're looking for. It unifies quantum mechanics and special relatively in the context of light/matter interaction. Given you seem to be familiar with Feynman. You're in for a treat! His book on QED is meant to be an accessible explanation.[1]

[1]https://en.m.wikipedia.org/wiki/QED:_The_Strange_Theory_of_L...

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whatshisface6y ago

Hydrogen atoms can't store photons that do not have the same wavelength as any of its spectral lines. Nonetheless, hydrogen gas has an index of refraction that is a continuous function of frequency, and as a result it can reflect light of any wavelength. Therefore, hydrogen does not store any energy for any length of time in the course of typical reflection. Even if the Feynman diagram for reflection looks like a combination of absorption and re-emission, if the absorption and emission process can't occur at separate times, then it is not right to say that one is followed by the other.

boomboomsubban6y ago

Isn't hydrogen gas almost exclusively H2, giving it plenty of possible electrons to interact with photons?

whatshisface6y ago

That's a good catch, but H2's spectral lines are still discrete. It's not that gasses can't absorb photons, it's that they can only do so at very specific frequencies.

To simplify the argument, you could use Helium instead. Here is a (discrete!) list of its spectral lines: https://physics.nist.gov/PhysRefData/Handbook/Tables/heliumt...

And here is a chart of its (continuous!) index of refraction: https://refractiveindex.info/?shelf=main&book=He&page=Mansfi...

BeetleB6y ago

You didn't address the concern. A given atom cannot absorb any photon. They can only absorb photons of certain energy levels/wavelengths. Electrons can occupy only certain energy levels. So they can only absorb photons that match the difference if two energy levels.

empath756y ago

> They are not the same photons.

How do you define "the same" for two photons?

tsbinz6y ago

This is the question that should be higher up in the thread. This whole discussion makes no sense. Photons carry no hidden identity.

zamadatix6y ago

A photon doesn't need to carry a UUID for people to conceptualize a difference between a photon going through free space and being absorbed and re emitted. The parent comment asks the right question, what is being meant by "the same" is required to know before being able to say the discussion makes no sense.

Taking your first literal interpretation as the only way the discussion could have value is no more helpful than this exchange: "I'm going to the store, do you want the same hot dogs we have in the fridge?" "That doesn't make sense, the store can't have the same hot dogs we have in the fridge".

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zelphirkalt6y ago

Who knows, maybe they actually do, but we do not know it yet. I mean, how do you know they do not?

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ngvrnd6y ago

it's all the same photon

hanoz6y ago

For those missing the reference: https://en.m.wikipedia.org/wiki/One-electron_universe

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viklove6y ago

But that's just not true. The electron will only get excited if the incoming photon has a very specific wavelength, so most of the light that hit your house's walls, for example, is reflecting. The photoelectric effect is real, but it only applies in specific circumstances...

chemengOP6y ago

There will be a transfer of energy to the system if there is an interaction, but will only absorb the incident photon at specific energies. In the case of reflection in this classical view, it simply re-emits the energy back out as there are no valid energy transitions. The reality is far more complex and this thread is mixing multiple theories together, wave and particle views and simultaneously comparing single atom mechanics with those of lattices/solids. This is all causing a lot of confusion that's hard to address in comments.

j / k navigate · click thread line to collapse

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whatshisface6y ago

boomboomsubban6y ago

Isn't hydrogen gas almost exclusively H2, giving it plenty of possible electrons to interact with photons?

whatshisface6y ago

That's a good catch, but H2's spectral lines are still discrete. It's not that gasses can't absorb photons, it's that they can only do so at very specific frequencies.

To simplify the argument, you could use Helium instead. Here is a (discrete!) list of its spectral lines: https://physics.nist.gov/PhysRefData/Handbook/Tables/heliumt...

And here is a chart of its (continuous!) index of refraction: https://refractiveindex.info/?shelf=main&book=He&page=Mansfi...

BeetleB6y ago

empath756y ago

> They are not the same photons.

How do you define "the same" for two photons?

tsbinz6y ago

This is the question that should be higher up in the thread. This whole discussion makes no sense. Photons carry no hidden identity.

zamadatix6y ago

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zelphirkalt6y ago

Who knows, maybe they actually do, but we do not know it yet. I mean, how do you know they do not?

2 more replies