All Photons Move at 300,000km/s.... But Don't?

Yes I hope so. Maybe we'll see from the response we get. And maybe, just for fun, rpenner will come in with a more rigorous mathematical commentary, which will tax my little grey cells…..

This is the sort of discussion I enjoy on this forum. It is sadly all too rare.

P.S. my grasp of even QED is pretty shaky. Quantum chemistry is one thing, quantum physics another.

 

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Footnote: I've just found a nice graph of refractive index vs. frequency, showing what happens around a "resonant" absorption line, in this exchange:
http://physics.stackexchange.com/questions/71126/why-does-the-refractive-index-depend-on-wavelength

If readers care to take a quick look at that graph (you have to scroll down a bit), they will see there is obviously an intimate connection between dispersion and absorption even though, as the dialogue on our own thread makes clear, the two things are distinct.

This sort of thing - a deep connection between things one might not have realised had anything in common - is what makes it worthwhile getting out of bed in the mornings.

 

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That stackexchange page lacked only showing both the index and loss curves together. Here you go: http://www.phy.duke.edu/~rgb/Class/phy319/phy319/node50.html

 

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Ah yes, thanks for this.

 

They are indeed. Late last year a group of Canadian physicists showed that wave-particle duality and Heisenberg's Uncertainty Principle were equivalent.

 

Without a discussion of the quantum mechanical (or wave) picture of the propagation of light though bulk materials, the discussion will be limited to toy models and brittle analogies.

This the second video by the same source references the picture in Chapter 31, "The Origin of the Refractive Index", of Feynman Lectures on Physics, Volume I.

Feynman derives from a model where electrons are held to their nuclei by springs, an electron-centric formula for the scattering of light off individual electrons which sums to (in a wave or quantum-mechanical sense) to coherent propagation with refractive index:
\(n = 1 + \frac{N q_e^2}{2 \varepsilon_0 m_e} \sum_k \frac{f_k}{ \omega_k^2 - \omega^2 + i \gamma_k \omega }\)
where \(\omega\) is the (angular) frequency of the light, \(\omega = 2 \pi \nu = 2 \pi f\); \(m_e, q_e\) are the mass and charge of an electron; \(N\) is the electron number per volume, \(f_k, \omega_k, \gamma_k\) are the oscillator strength (ratio of electrons associated with this oscillation mode), associated angular resonant frequency for the bound electrons, and associated damping factor for each kind of bound electron system.

Unlike the toy model of the energy halting in matter for a percentage of the time, this derivation correctly predicts that for some frequencies n is less than 1, which represents a phase velocity faster than c. The question of can you use that FTL phase velocity to send a message faster than light is firmly answered in the negative in chapter 48 of the same volume. Here is what he writes in Chapter 31:

http://www.feynmanlectures.caltech.edu/I_31.html

http://www.feynmanlectures.caltech.edu/I_48.html

// Now I feel silly for typing those quotes by hand from my dead-tree copies when they are nicely on-line. My formula is based on Feynman's 31.20 and the footnote. It is a natural extension of the simpler 31.19 to materials more complex than in the original derivation in sections 31-1 and 31-2.

 

how do you know, did whatever link you clicked on tell you that ?
oh, i see youtube did, it's not like you know from actual experience, correct ?

 

Eh? I thought we had all known this for almost a century. Can you explain what they found that sheds new light on this?

 

It didn't. The question was answered quite correctly in a couple of different ways previously, with no mention of any singularities or wormholes.

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Yup. I think (?) this is saying that the group velocity will be <c, even if the phase velocity of component waves can be >c. You clearly see n<1, i.e. phase velocities >c, in the curves we were exchanging earlier, close to the absorption line.

 

It appears to be an Entropic Uncertainty Relation which is based on a sum of information unknown when an observable has a distribution of outcomes, versus the formulation of uncertainty as a product of variances of continuous distributions.

The paper and some important references:

http://www.jstor.org/stable/2372390 (1957)
https://elearning.physik.uni-frankf...lm_740/res/files/file_1855/wootters-zurek.pdf (1979)
http://www.sciencedirect.com/science/article/pii/0375960188901144 (1988)
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.60.1103 (1988) [this is where the uncertainty relationship in information is derived]
http://www.atomwave.org/rmparticle/...topic/decoherence refs/englert visibility.pdf (1996)
http://arxiv.org/pdf/1403.4687v2.pdf (2014)

 

Yes. To give an example, let us work with radio waves and plasma or equivalently x-rays in carbon where the Feynman model says there are no restoring forces, so \(\omega_k = 0, \gamma_k = 0\) so the formula reduces to:

\( n(\omega) = 1 - \frac{N q_e^2}{2 \varepsilon_0 m_e \omega^2} < 1\)
Thus the phase speed of light is:
\( v_{\textrm{phase}} \equiv \frac{\omega}{k} = \frac{c}{n(\omega)} > c \)

From this we can calculate the wave-number, \( k \equiv \frac{2 \pi}{\lambda} \) :
\( k(\omega) = \frac{\omega}{c} - \frac{N q_e^2}{2 \varepsilon_0 m_e c \omega} \)
From calculus, we have a trivial differentiation:
\( \frac{d k}{d \omega} = \frac{1 + \frac{N q_e^2}{2 \varepsilon_0 m_e c \omega^2} }{c}\)
and from the definition of group velocity:
\(v_{\textrm{group}} \equiv \frac{d \omega}{d k} = \frac{c}{1 + \frac{N q_e^2}{2 \varepsilon_0 m_e c \omega^2} } < c \)

 

Actually it was a very interesting and informative video, and I also have seen it before, at least two or three years ago.
As the Professor says near the end of the video, there are different validated models to describe the passage of light/photons though any medium, and none lays the other "to rest" as was mentioned. All are still validated descriptions of what happens.
It's similar in a way to the headlines a while back re Hawking supposedly saying "BHs do not exist" and which a couple on this forum immediately grabbed hold of for all their worth!
In actual fact all Hawking was doing was giving a possible quantum mechanical description of EHs.

 

rpenner has given a good roundup of previous research, and one from 2014. The article I found, a general discussion of his last reference, is here:
http://www.sciencedaily.com/releases/2014/12/141219085153.htm

Singapore, not Canada. Sorry. I do a lot of reading about goings on at the Perimeter Institute lately.

 

Still feeling stung over your recent drubbing handed out elsewhere? Should I need to re-post your unbelievable "he almost says element 118" absurdity upon absurdity? Just why a loathsome pest such as you was not long ago life banned from this site speaks volumes for general standards. Can you site a single post of yours where anything other than inane insults or banalities came forth? ANY actual useful technical input - just once?

 

hilarious.. yes, yes that's it. it's not like you can actually answer that remark of mine, correct ? but it's obvious the reality is no, you can not.especially after you make a remark as this to another : And, since you dodge my challenge yet again, prove yourself a low-life coward - yet again.(shrugs).

(shrugs) why not, that's fine. but you still do not understand any of it. correct ?, you should post that also.

yes, why would that be ? maybe it's because internet science hero piss-ants can't grasp anything as they run their mouths.(shrugs)

oh wow, this is original. [actually it's typical low level minded flawed thought processing]
actually, probably. i'm on many sites. i have posting histories on them all. under same name. but i'm sure you could not grasp a lot of it. i also hang out on the ISS u stream site more than anything. some there will even tell you i'm not as you say, only because i talk more science there than anywhere. where there's less " Q-reeus ".

shrugs

 

Why are photons (all wavelengths) considered to be instruments of the so-called "electromagnetic force"? So far as I know, please correct me, photons have no electrical charge nor are they influenced by magnetic fields. The term "electromagnetic spectrum" seems to me to be very inappropriate and highly misleading. Perhaps I am missing something? Thank you!

 

This post as well as your other post show you are missing quite a lot.

 

photon is a particle moving at c speed in straight line, does it vibrating? how can a particle has frequency? what frequency is it?

 

I'm pretty sure you've asked these questions before.

The answers haven't changed since then.