My understanding is that a particles, like photons, don't have wave shifts. That's an emergent property of many particles
https://preposterousuniverse.com/wp-content/uploads/grnotes-...
When light is redshifted, it loses energy, therefore the wavelength becomes longer.
Importantly, light very much behaves like a conventional wave in many real experiments - the interferometer experiment being one of the oldest and most well known. It is not a probability wave in that case, but an actual physical wave (now known to be an oscillation in the electro magnetic field, but long assumed to be a mechanical wave in the luminiferous aether).
Classically one can imagine that as if electron was hit by a particle. But then we have light diffraction and interference, which classically is described as a wave. So from a classical point of view light travels as a wave but interact as a particle.
As of nature of the light, then consider that there is a reformulation of a classical electrodynamics that eliminates electromagnetic waves all together. There are only electrons that interacts with each other directly with no waves in between. Feynman spent quite some time trying to develop quantum electrodynamic based on that. He failed. Still the point stands that we never observe light directly but only through its effects on electrons and other charged particles. So it could be that what we call light is a theoretical artifact and there is no light in reality.
And the classical point of view is wrong. Photons resemble classical particles in a few respects, and classical waves in a few others, but at the end of the day they're neither.
> Still the point stands that we never observe light directly but only through its effects on electrons and other charged particles.
This is true of literally everything. "Direct" observation does not exist. Every atom, every cell, every person, every planet, every star - you know them by their effect on your sense-data, or else not at all.
and yes direct observation exists. that's what measurement is. and that's all you can ever "observe" unless you incorporate the wavefunction, which also doesn't "exist".
Although there are those who believe that photons only exist at source and at the detector, there is some experimental evidence which contradicts that (for example, this 2013 paper in which researchers 'read' information from a photon without destroying it, which implies its continued existence between creation and observation: https://doi.org/10.1126/science.1246164).
For what it's worth, I am also of the opinion that your tone was hostile, and yes, 'textual words' can and do have a (metaphorical) tone. Regarding downvoting and critiquing, there's an old adage about if you walk into a room and it smells of dog shit, maybe someone in the room stepped in something on the way in, but if every room you walk into all day stinks, well maybe you should check your own shoes.
and for what it's worth I don't believe the paper you linked says what you think it says.
I have. Srednicki and Weinberg are sitting on my bookshelf right now.
> photons dont exist, dude, except in connection with and at the site of the detector.
Exactly backwards.
Photons fall out of mode-expanding asymptotic EM field states just like any other particle. It's the interaction picture that can't be rigorously built up out of particle states.
what i said is not backwards unless you use the inverse understanding of "exist". and how can photons exist without interaction? they don't. they're localizations by detectors. until then, they only "exist" as the probability wave. that's due to nothing localizing them. that's how i mean "exist". so it's not really meaningful to use that word.
btw "any other particle" doesn't fall out of EM fields.
I very obviously meant that XYZ-particle states fall out of mode expansions of the XYZ-field, not that all particles are EM quanta.
> what i said is not backwards unless you use the inverse understanding of "exist". and how can photons exist without interaction?
Exactly the same way any other field configuration can? The state space of the free EM field simply is the photon Fock space.
The state space of an interacting 4D EM field is unknown and may well not exist, hence the need for perturbative approaches and renormalization - in which particle states again emerge as terms in the perturbation series.
> The state space of the free EM field simply is the photon Fock space.
but I'm not sure what your point in mentioning this is. When people hear things like "particles exist between their emission and measurement", they might get the idea that there could be said to be any reality to the existence of particles in transit. They simply aren't particles the way people think of them - they are probability waves. A great example we could discuss is the HBT experiment in which photon bunching was seen. If the bunched photons were really "particles" by any sense of the word, they wouldn't bunch in time of detection merely by the fact they are entangled with each other. That would be like saying entanglement affects the flight of a particle which is simply not able to be said.
They're not anything the way laymen think of them. They're not classical particles, they're not classical waves, they're not classical anything. They're not really probability waves either, for that matter, or even field configurations - the real object is the algebra of observables. But laymen don't get to dictate the vocabulary of physics, and neither do mathematicians. Fields are the things that would be dual to the observable algebra, were it always equipped with a dual; particles are the things whose creation and annihilation operators would generate it, were there only always such things.
silly downvoters.