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One of the first things I learned while scratching is that a mirror polishes well, even if it is not aluminized, However, it allows us to make some observations.
Indeed ( someone told me, but I don't remember who
) a shiny glass reflects the 5% of the incident light.
obviously ( I say this ) the remainder 95% it will pass through the glass
After a few years of “deep thoughts” I found myself wondering about this fact which seems absolutely normal and found in everyday experience:
How does a photon decide whether to bounce or pass through glass ? I am trying to say, they come to an agreement among themselves ? kind:” I'll go first, you bounce too…” or someone keeps count of those who cross and then “closes the border” and the rest bounce ?
someone please me “enlighten” !
Hi Massimo, I think I told you that on average glass reflects approximately the 5% of the incident light and it is normal for a small amount to be reflected. I imagine it has happened to everyone that even though you are in front of a window you can see your reflection in it.
When light hits a surface it is partly absorbed, partly transmitted and partly reflected and this depends on how the light bounces within the material itself.
It is explained here quite well:Ok, on a macroscopic and electromagnetic level we agree… But this doesn't give me an answer to my question:
imagine being able to project a single photon perpendicularly on a glass surface. What does the photon do ? bounces , crosses or both ?
I am by no means an expert, I'm not a scholar, I don't have a degree but I like physics, chemistry and geology as well as astronomy, and so I bring up what I have occasionally found myself reading about Richard Feinmann's beautiful writings, often quite indigestible for me as they cannot be explored in depth with my limited training as an expert in industrial electronics.
A photon hitting a surface, it would seem to me that in the collision he might have the probability of crossing it and finding his end elsewhere, or find one's end immediately in being reflected as a particle bounces, or reflected as an electromagnetic wave, perhaps more easily diffracted by an asperity, or absorbed as a particle by some electron of some atom of matter, going to temporarily increase the spin energy, and then return it with the times of the target atom, like the laser does.
But it is said that, although a wave or corpuscular aspect can be measured, there is no possibility of measuring the other possibly contemporary dual aspect….Without perhaps letting Schrödinger's cat die.
Well, good ! we are getting closer
I confess to you that I didn't invent this photon story , I put it there just to try to stimulate curiosity about some aspects of daily glass scratching that seem so normal that we no longer even pay attention to them, but which actually hide in their essence the greatest mysteries of our universe.
In fact, the first to experiment with these quantum effects of light was Richard Feynman , he was responsible for the birth of QED ( quantum electrodynamics ) which is the most complete and exhaustive theory of the interactions between light and matter.Then, always with the aim of stimulating curiosity, I renew my application “embarrassing” in light of Giulio's probabilistic consideration and Mirco's reflection-refraction percentage: assuming that there is a probability of 5% that photons are reflected and del 95% that pass through the glass, how they do it 100 photons to decide which way they should go ? Let's put it another way too, perhaps more correct: why on 100 photons only 5 are reflected and 96 they cross ?
Is’ It was Feinmann himself who explained what Newton had failed to do.
Feinmann was a formidable physicist, especially in teaching his subject. Bought his book , you can't help but buy another one!.
Newton had already noticed that glass plates reflect the 4% of the incident light, and he wondered if it was a feature of the front part of the glass that created that reflection, and for what reason.
In experimenting with glasses of different thicknesses Newton discovered that that 4% varied to arrive unexpectedly until 16%. But then just as unexpectedly it went back down to the 4%. But he couldn't explain why.
Like the rest, as the great precursor he was, it already happened to him due to the failure to explain how the force of gravity works, and how he could act at an infinite distance without a “ether” that would pass it on.Then Grandpa Albert arrived, e “stretched out” its hypothetical network formed by the new space-time dimension (didactically valid image to make oneself understood), to explain that the mass of bodies sinks into it in proportion, curving its surface continuously, and therefore for this reason objects are attracted even at infinite distances.
Well Feinmann in 50 compelling pages within everyone's reach, (and without a formula) explains that the reflection of the front face of a glass, it is conditioned by the refraction of the posterior face, works , with the periodicity given by the wavelength of the light, is added to the previous effect, increasing al 16% his reflection; or he largely elides it by returning to 4%.
Feimnann for his curiosity was , dancer, burglar (while working on the Manhattan Project at Los Alamos), bongo player, amazing teacher, technician who discovered the defect that caused the shuttle to explode on takeoff, and more, it is absolutely worth reading because his books are also published in Italian.
For those more accustomed to English, On YouTube there are some of his filmed lessons which are always very interesting.Now we are really close
I too was fascinated by this great character. Entering the world of quantum electrodynamics and the experiments of the great scientist, popularizer and Nobel Prize winner for physics Feynman you enter a surprising world, simple but at the same time incomprehensible, a world where the absurd is the basis of the understanding of everyday reality in the interaction between light and matter.To answer our question, I report a small excerpt from a beautiful blog article “the infinite theater of the cosmos” by astrophysics professor Vincenzo Zappalà. I invite everyone to dedicate a little’ time reading these articles on Feynman and QED, it's really worth it, where it is explained simply and completely, without resorting to the complex mathematics of quantum mechanics, the “absurdity” of our photon bouncing off the glass
The choice of photon
…All we have to do is enter the world of the absurd and say that it is impossible to know what the single photon decides to do. It can “choose” to go straight or bounce, but it is a decision entirely his that we could never know. However, something can be known, that is, the percentage of photons that return backwards compared to those that advance. We cannot predict which photon makes one choice or the other, but we can say that the 4% go back and the 96% go ahead. You realize what we said? Physics, that science that describes and explains exactly, it is forced to calculate only the probability of an event. In other words, even heavier, Nature only allows us to calculate a probability. Absurd, truly absurd!
However, this result is still nothing compared to what awaits us, complicating the experiment a little…
An interesting collateral phenomenon derived from the behavior of those incident photons, is that, in the example of the mirror, reinforcement or attenuation of the radiation reflected by the 4% to a 16% , depending on the ratio between the wavelength of the radiation, and thickness of the glass plate.
Intuitively, amplification occurs when the reflected wave is exactly in phase with the incident one, so as to strengthen it. And therefore why this occurs, the thickness of the plate should be equal to an integer multiple of the wavelength of the radiation you wish to enhance.
It goes without saying that the rest of the other wavelengths are part of the same light beam, they are destined to undergo a greater attenuation the greater the interference of the destructive reflection given by the phase shift.
On this principle (which is also that of Fabry Perot's interferometer invented in the early 1900s), I had discovered the interference filters that we amateur astronomers also use to make the radiation emitted by the nebulae visible. Interferential filters obtained by depositing on the two faces of the calibrated support glass, one, but generally multiple semi-transparent metallic layers.
“Multiple layers” perhaps because the deposits of different types of metal also “build thickness”, and at the same time they themselves are more or less reflective of certain wavelengths. Hence the fact that a thick filter can have more than one band of passing radiation.
The result is that a photon enters the chamber formed by the thickness of the support between the two semi-transparent mirrors, calibrated to the multiple value of the wavelength to be transmitted enhanced, is reflected zigzag several times, amplifying with each bounce, to finally emerge greatly increased. While vice versa the other wavelengths are gradually attenuated.
The distance between semi-reflective walls for example, in the “etalons” of solar telescopes (ugly French term which means "stallion" in the sense of "precise champion") to transmit only the hydrogen alpha radiation emitted by the Sun, can be “tunable” with a kind of focus to maximize their efficiency.
All of this has no educational claims and is my personal opinion. Is’ that is, what I seemed to have understood when my flammable curiosity caught fire on this topic too.
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