Dear Giuseppe,

Matter doesn't know nor care about photons cruising around.

Matter is made of atoms, atoms are made of electrons stabilized around nuclei.

When an electron is hit by a photon, the energy of the photon is transferred to the electron, which makes the electron jump to an unstable distance farther away from the nucleus.

When the electron looses this energy, it falls back to its initial location, and the lost energy becomes another photon that flies away.

If the 'why' question is meaningful I guess we would be suggesting that in place of equilibrium and loss of equilibrium (energy states etc) we would be considering that some form of homeostasis was in play.

I asked this highly speculative question of Tony Fleming the other day see if considering such things turned anything over! Did we as biological systems come up with homeostasis or was it somehow derived from the universe in some form? Is there some overall state that we are not appreciating that's being maintained?

I am not a believer is God so I guess I should drop this and get my coat!

Dear Andre,

first like to express my heartfelt thanks for the time you take to give me such a clear answer.

Allow me to ask a more specific question:

>> Is there a similar description of the fact, that electrons will only jump to a higher energy state if the photon hitting the electron has an energy which equals the difference between final and initial energy? Or is that just a consequence of quantized energy?

Dear Giuseppe,

You write: ">> Is there a similar description of the fact, that electrons will only jump to a higher energy state if the photon hitting the electron has an energy which equals the difference between final and initial energy? Or is that just a consequence of quantized energy?

"Electromagnetic photons are not quantized as such, which means that the energy that they are made of can have any value in the complete range of possible frequencies.

What is quantized are the frequency levels and related wavelengths of the carrying energy that electrons can stabilize with when captured by atoms."

In Vision-Space the blue sky is an all possibilities field of possible values. There are no surfaces in the sky. It's a medium.

Where there are surfaces the all possibilities values in the field get reduced to a specific value corresponding to the distance that surface is from the locus of fixation.

Note: we are required to the form the fixation.

In other words..this scales! Why would it be otherwise?

Actually it's not so much that it 'scales' as there is a membrane (retina) where either the micro of activity via EMR traverses or is translated to activity performed at the macro scale (mechano or neuronal).

So the underlying mechanics at the micro scale are implicated either directly or by translation within perception (our perceptual structure)?

I realise this may not seem to be strictly 'on message' with respect to the question but I hope it's of interest.

Why does light interact with matter?

You meant why does light interact with matter possessing rest-mass, because light is also material, thought not possessing rest-mass.

Next these two forms of matter interact because SO IS BUILT OUR UNIVERSE, matter interacts with matter by the 4 ftypes of forces.

About your question

"electrons will only jump to a higher energy state if the photon hitting the electron has an energy which equals the difference between final and initial energy? Or is that just a consequence of quantized energy?"

the answer is: the electron would jump even if the photon has a higher energy than the difference ΔE between the two levels in the atom. Part of the photon energy would go on compensating the ΔE, and the rest would remain as kinetic energy of the electron.

Just pay attention: the photon energy cannot be too much greater than the ΔE between the levels. Photons of very high energy may not "see" the atom, the cross-section of interaction with the atom may be very small. For instance, for blocking gamma rays one needs thick walls of leader.

@André Michaud

Deae André,

thanks again for that clear explanation. There is only one part which I do not understand to 100%.

"This is due to the fact that the energy of the electron and of its carrying energy are in resonance states with respect to the proton"

>> What exactly is this carrying energy? What does that mean for the electron? Is it just moving faster than e. g. an electron which was hit by a photon with exactly the energy ΔE? Is there also a counterpart, i. e. too minor energy?

Transational definition :

A photon is a successful transaction between three partners: an emitter, an absorber, and the space, and/or the transparent or half-transparent medium (including eventual optical devices) in between, which transfers by electromagnetic means, a quantum of looping h, and an energy-momentum whose value depends on the respective frames of the emitter and the absorber.

No fuss...

In 1926, Erwin Schrödinger had proved that an emitted (resp. absorbed) photon by an atom is the beat between the intrinsic frequencies of the final state and of the initial state.

Very characteristic in the Mössbauer resonance.

EOT.

Somebody here is confused. The question asked is not "what is the photon", but why does it interact with matter.

Because is not some "another thing", or "another object". The question comes from an ill-made prejudice.

The simple fact that our eyes see, shows that the light interacts with matter.

Dear Giuseppe,

Dear

Your question: Why (not how) does light interacts with matter?, is not simple to answer it fully in post as this one, but let me try to give the main ingredients. Light are electromagnetic fields within a window of 400-700 nm of length wave. The electromagnetic fields (also the photons which their quantization) carry the force between electric charges which are in matter. They are long rank interactions and therefore it is easy to follow that they always are in interaction with matter providing the electric charge.

Photon (quantum of e-m field) interacts with any electrical charge.

So, light interacts with matter because some matter particles are charged.