Everything is energy so that's a pretty useless description. Plus photons are self-propagating oscillations in the electromagnetic field they aren't mystery balls of energy any more than any other particle is.

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It's not useful to think of individual photons as having "id numbers", because they don't. Photons are accounting devices to keep track of the strength and direction of electromagnetic waves. It's like the dollars in your bank account: they don't have individual identity either.

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"I want to emphasize that light comes in this form-particles. It is very important to know that light behaves like particles, especially for those of you who have gone to school, where you were probably told something about light behaving like waves. I'm telling you the way it does behave- like particles."

Feynman, "QED The Strange Theory of Light and Matter"

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Feynman's book QED, The Strange Theory of Light and Matter is written without math. I highly recommend it if you want to understand light.

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>The photon absorption and re-emission model doesn't hold up as well as Feynman's explanation.

In his book QED, Feynman explained that he favored the photon absorption model but used field mathematics because it was the only method to deal with the vast quantities of photons.

"I want to emphasize that light comes in this form-particles. It is very important to know that light behaves like particles, especially for those of you who have gone to school, where you were probably told something about light behaving like waves. I'm telling you the way it does behave- like particles."

-Feynman, "QED The Strange Theory of light and Matter"

He then went on to explain everything about transmission, refraction and reflection as individual photon absorption and emissions.

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Yes and no. The entanglement will be most certainly lost if it flies through a room temperature chunk of material consisting of billions of atoms.

In a more idealized case of it interacting with just a single cold atom, it can be preserved and will entangle with the atom also.

> "Certainly the electrons in my left hand are not the electrons in my right hand."

You'd be surprised. The states are certainly different, but it makes no sense to talk about electrons, other than the states being filled or not. There is no such thing as "that electron", only "that electron state" and "a electron".

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No - it's generally a good approximation if at the two states, the fluid's properties are approximately the same.

That's not always true for huge differences in temperature and/or pressure.

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