And dust is composed of a lot of organic materials. Mainly dead skin cells.

I believe that the phenomenon known as "photon bunching" could also be described as an exchange interaction (along with the associated anti-bunching effect for fermions). If you consider two points, a and b, in some source that is emitting photons and you set up 2 detectors, A and B, to detect those photons, then for photons (and all bosons) you will see an increase in the probability of simultaneous detection at A&B compared to distinguishable particles and a decrease of simultaneous detection for Fermions: https://en.wikipedia.org/wiki/Hanbury_Brown_and_Twiss_effect

Because photons are non-interacting at the tree-diagram level (that is to say that in the Hamiltonian Lagrangian for QED there is no photon-photon interaction term), this does not lead to the same energy consequences as it does for electrons or alpha particles. Both the Coulomb integral and the exchange integral are proportional to the interaction term in the Hamiltonian, except that for photons there is no interaction term! Metaphorically speaking (because there are technical problems with assigning a wavefunction to single photons), the product basis remains the diagonal basis. As a result, you see interference effects that cause the bunching behavior mentioned earlier, but not the same consequences for energy or spin correlation as with electrons.

A careful reader may object at this point and say, "Ah! But you have neglected the higher-order QED effects. Sure, at tree-level there is no photon-photon interaction, but what about the scattering mediated by virtual electron-positron pains? Surely that gives rise to some interaction which turns out to be either attractive or repulsive." And the careful read is almost correct, almost. There is very weak (starting at 4th order) photon-photon interaction and photon-photon scattering in QED, but it turns out that the effective potential that this interaction gives rise to has zero range (one might describe it as "a delta function" although there are technical problems with making this formulation precise in >1 spatial dimension; a complication that comes up repeatedly in my PhD thesis in the context of ultracold atomic physics) and therefore cannot really be described as attractive or repulsive. To expand, to first order in perturbation theory the interaction terms is quartic in the E and B fields, and if you work out what kind of potential it takes to create that you get an operator proportional to a delta function. Of course this is just the effect at first order, the effects at all higher orders will also give rise to interactions that look like they are "zero range", although if it were possible to do the full resummation and go beyond all orders, you might get a spatially-extended potential. I can't think of any reason that that potential should be always attractive or always repulsive, but who knows. Experimentally speaking, attraction/repulsion between beams of photons has not been observed or measured without coupling them to some massive interacting medium.

In the case of photons, there is a purely classical explanation for all of this. Essentially, because the classical limit of a multi-particle system of photons is not a system of interacting distinguishable particles but rather an electromagnetic wave (a coherent state superposition of all numbers of photons with a well-defined average number of photons and phase), you can do the math and arrive at correct predictions purely from considering the classical problem of detecting the signal from a spatially extended EM source with 2 nearby detectors.

I don't see how this explanation is internally consistent. It is a behavior we see in other types of waves, but in those other cases the wave only appears to slow, and the actual wave proceeds at full speed.

Thank you! I got it now!

Well, let's look at a wave in water. It moves some water around, but in a cyclical pattern that should result in very little actual work being done. The same way that lifting something gives you all the energy back when you drop it.

Maybe you're thinking of this from the perspective of a solid object moving through a medium, where it must spend energy on displacing the medium in order to move? This is where my note regarding the wave being energy is important. It does not have to displace anything to move through the medium, the same way that the heat from your stove doesn't displace your pan in order to heat your food. The energy simply goes through.

Not likely, it was a very very complex event that was highly unlikely but still probable. The event require a very specific set of circumstances and environmental conditions. Unless of course panspermia was the beginning of life on earth. Also highly unlikely but equally probable.

Well the person above said the wave is resisted by the medium, and the wave moves the medium (the ping pong balls) as it passes. That sounds like work in the analogy used at least.

And could a photon not shift to a lower energy wavelength? Different photons have different energy I thought?

Dominance has nothing to do with which genes are expressed. It's not about one allele "recognizing" and shutting off the other. Generally speaking for a gene on an autosomal chromosome, both alleles will be expressed. Dominance is a question of whether the effect of one allele can mask the effect of another. So for example let's say you had an allele that produces a protein which is toxic in some way and thereby causes a disease. Then even in a heterozygous organism the single copy of this toxic allele might be enough to produce the diseased phenotype and therefore that allele would be classified as dominant. The healthy version of the protein would still be present in cells but that doesn't matter. I recommend you read the "molecular mechanism" section on the wikipedia article on dominance for more examples and details.

An armadillo has armor, but it also has an internal skeleton that it uses for running. Reconfiguring muscle attachments to attach to external armor instead of the internal skeleton would require a huge amount of evolution. I don't think that any creature has done it.

My understanding is that the photons are not absorbed and re-emitted. The reason being that absorption and subsequent re-emission (ie the exciting of an atom and subsequent relaxing of the electron via spontaneous emission of a photon) is a random process, in that the photon is emitted in a direction completely uncorrelated to the direction it came in at. This is clearly not what the phenomena of refraction does, this would amount to light being dispersed in the material which is not what we observe.

This problem is actually a lot easier to conceptualise with classical electromagnetic waves. With classical em waves, refraction occurs due to the change in the dielectric constant in the material, which is essentially due to the ability of the molecules in the material to polarise when exposed to an electric field, which kind of "reduces" the effect of the field. Another way to think about it is the molecules in the material are producing their own fields via polarisation in response to the applied field that get summed with the incident wave (simple wave superposition) making it appear to propagate slower. However you want to conceptualise it, mathematically the result is the same, the light appears to propagate more slowly in the medium.

Okay back to photons. Photons aren't classical, but they are waves. Now I'm actually a little shaky on the best way to conceptualise this, and I may be outright wrong since it's been a while since I studied this stuff but I believe we can treat photons exactly as we would treat a classical electromagnetic wave when looking how it behaves as a wave, propagating through space and interacting with other fields. And so all of the above paragraph about em waves applied to photons as well. The only thing we have to keep in mind with photons is that they must come in discrete packets of energy, and they can interact with certain atoms to deposit this energy by exciting an electron in the atom (or more realistically interact with the bulk atom lattice to excite electrons in an essentially continuous band). Except in materials where refraction occurs (ie transparent materials), the bandgap is actually too large to allow this to occur, so absorption is not possible and the photon will not be destroyed, and instead pass through as an electromagnetic wave would.

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With the photon absorption and re-emission model, you’d expect that when a beam of light hits an object, that it would be scattered then

Well, passing through it. I mean, is anything really "free"? Changing the energy from one form (wave) to another doesn't "spend" part of itself?

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When thinking of light moving, don't even think of it as individual photons. Instead, it's a probabilistic wave function, with energy corresponding to one photon and which evolves according to all possible interactions it might have.

As long as the wavefunction interacts with something that is not connected to you, it continues to evolve in its strange quantum way, possibly extending its probabilistic state to other objects. We then call it entanglement.

Finally, that wavefunction will interact with something connected to you (your eye, your detector...) and at that point, we say that wavefunction collapsed and you can count it as a photon. But before that - the only significance of "photon" is that total energy of the function was one photon.

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When I was a kid, I learned that any instances after the one that took would not survive because such instance would be the perfect food, so it would be gobbled up by the life already here.

Accelerating the charges in the material requires absorbing some energy from the light. Emission from the charges (the radiation field) requires depositing some energy back into the light. This is consistent with the photon absorption and re-emission model. Sure, it's not individual photons being absorbed by individual charges, but it's still an exchange of energy and the light is still quantized.

A wave doesn't contain energy, it is energy. And it would only lose that energy by doing work, same as anything else. So what work do you think it is doing when it passes through a medium?

Outbreaks occur in new York still. They passed law in 2015 for water tower maintenance. 50000 violations...

https://www.nytimes.com/2022/11/12/nyregion/nyc-legionnaires-nursing-home.html

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There was an incident in Quebec City where a wet cooling AC was spraying a mist of infected water outside and a lot of citizens became ill.