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Physics, Astronomy & Cosmology / Re: Acceleration of light?
« on: 25/04/2023 03:38:03 »
Hi.
I completely missed the bit about transitions to different mediums, well spotted @geordief .
Here's a pleasant Physics expert talking about why or how light slows down in glass for a YouTube video produced by Sixty Symbols, it lasts about 15 minutes and you might as well listen to him rather than read some waffle I produce.
So here's 4 different answers, which are are more or less bullet points summarising that video as I saw it:
1. Light can travel more slowly in different mediums but photons don't. Don't ask, live with it.
Be aware that many of the old and popular explanations are wrong.
2. A photon is a particle that is only readily identified in a vaccum. Inside a dense medium which is some regular lattice structure of atoms, what you will actually have is a different particle (sometimes called a quasiparticle) which is known as a "polariton". These polaritons travel at less than the speed of light.
So the photon wasn't accelerated or ever travelling at less than the speed c, instead it was just changed into a polariton once inside the dense medium.
3. The photon is a quantum mechanical object. It can take all possible paths through the medium and some of those involve an interaction with other QM objects like electrons and nucleons that are present in the dense medium. The sum of all the possible paths is such that the overall wave description looks like a photon that has been delayed (travelling at less than c).
There are similarities between the Quantum Mechanical model and the explanation using classical electromagnetic waves. With the classical model, an e-m wave passing close to an atom will cause charged particles like the electrons of the atom to oscillate. However, oscillating electrons will produce their own electromagnetic waves. So these will interfere with the main wave that was passing through. (For the QM model, we have that one photon takes mutiple paths so it is all the wave you need on its own and also the interactions with electrons are "like" the classical interaction in some broad sense).
4. I'm not actually certain I can really articulate a 4th answer. I'm just fairly sure you could find one if you tried.
Best Wishes.
I completely missed the bit about transitions to different mediums, well spotted @geordief .
Here's a pleasant Physics expert talking about why or how light slows down in glass for a YouTube video produced by Sixty Symbols, it lasts about 15 minutes and you might as well listen to him rather than read some waffle I produce.
So here's 4 different answers, which are are more or less bullet points summarising that video as I saw it:
1. Light can travel more slowly in different mediums but photons don't. Don't ask, live with it.
Be aware that many of the old and popular explanations are wrong.
2. A photon is a particle that is only readily identified in a vaccum. Inside a dense medium which is some regular lattice structure of atoms, what you will actually have is a different particle (sometimes called a quasiparticle) which is known as a "polariton". These polaritons travel at less than the speed of light.
So the photon wasn't accelerated or ever travelling at less than the speed c, instead it was just changed into a polariton once inside the dense medium.
3. The photon is a quantum mechanical object. It can take all possible paths through the medium and some of those involve an interaction with other QM objects like electrons and nucleons that are present in the dense medium. The sum of all the possible paths is such that the overall wave description looks like a photon that has been delayed (travelling at less than c).
There are similarities between the Quantum Mechanical model and the explanation using classical electromagnetic waves. With the classical model, an e-m wave passing close to an atom will cause charged particles like the electrons of the atom to oscillate. However, oscillating electrons will produce their own electromagnetic waves. So these will interfere with the main wave that was passing through. (For the QM model, we have that one photon takes mutiple paths so it is all the wave you need on its own and also the interactions with electrons are "like" the classical interaction in some broad sense).
4. I'm not actually certain I can really articulate a 4th answer. I'm just fairly sure you could find one if you tried.
Best Wishes.
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