LIGHT THROUGH A GLASS PANE - NEW MECHANISM
Dottore in Chimica, Emeritus, Universita' di Bologna, Italy
Introduction
A beam of yellow light (sodium lamp) crosses a glass plate - we know two things:
=we see a yellow colour inside the plate: the wavelength of the incident beam inside the plate remains unchanged.
=the light beam inside the plate moves at a constant speed, 'lower' that that of light in vacuum, named 'c'.
The purpose of this short note is concerned with the meaning of this word 'lower'.
Proposed mechanisms and critique
The 'common people' mechanism: 'The light inside the plate travels at a lower speed because the fotons hit the atoms of the medium and loose therefore speed. This mechanism cannot be true: if at every collision the foton would loose speed, the speed of light within the plate would not be constant, it would constantly decrease...
The mechanism proposed by a 'NASA expert' on youtube: The proposed mechanism must explain why within the plate the speed is constant, and 'correct' the previous mechanism.
'The impinging wave generates a NEW WAVE within the plate, and this new wave travels at a lower speed' This implyes that, when exiting the plate, the new wave restores the 'old one'... This mechanism is open to several points of critique:
=1= A lower speed inside the plate means that the frequency of light within the plate is lower, thus the energy associated with the new wave, hv, (v=nu, frequency), is lower! Where is the lost energy going? There is no energy reported to come off the glass plate!
=2= When the light beam exits the plate and the incidient wave is restored, the energy associated with the beam past the plate is equal to its initial value: how is the lost energy recovered? Where should it come from?
=3= When a foton hits the last atom on the plate, how does it 'know' that there are no more atoms ahead and thus it is time to speed up to the initial speed, c ?
A NEW MECHANISM PROPOSED
PLease let me use a metaphor for its introduction.
I have a dancer who plans to cross the dance floor following a straight line and moving at a speed equal to c .
When meeting a lady the dancer dances the waltz with her (1 only 'turnaround') and he proceeds on to the next lady - at a speed equal to c . Let's consider the time involved in dancing the waltz. At the end of his travel you measure a time higher than that you would have measured if he had met no ladies. And you calculate and measure a speed lower tha c. But nowhere during his travel the dancer moved in a straight line at a speed lower than c !
Thus this metaphor should be sufficient to clarify what will happen to a foton when it crosses the glass plate!
The conclusion: during its travel, as concerns the mechanism, the foton 'knows' two states: one 'entangled' with an atom of the medium and one 'moving in a strait line at a speed equal to c'. Of course, the effect of the medium (glass, plastic, water) is felt on the foton only in its entanglement state. The overall result is one in which the foton is observed 'AS IF' it travelled at a speed lower than c, which is not true!
dec. 9 2019
youNOTE -Clarifies the concept embedded in the short article:
velocity of light / new mechanism
The concept that a foton may arrive 'late' where it is expected even when its velocity is unchanged seems counterintuitive, but not necessarily so on second thought...It can arrive late because of an increased length of travel!
This concept removes all theoretical objections that I could think of to the idea offered by other authors, that normally a foton travels through a medium at a steady reduced speed - connecting 'delay' to 'reduced velocity'...
When a foton meets an atom, to an infinitesimal delay 'dt' must correspond an infinitesimal increase in distance 'ds'...without its velodity being affected...
In cosmology they report that galaxies cause delay in the travel of the fotons: this is obvously the work of atoms and molecules that are observed in the gas clouds of said galaxies, the mechanism is the same as that taking place within a glass pane of your picture window...
Amedeo Andreini
25 jan. 2020 / publication 2-3-2020