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Comment by javajosh | Hacker News Reader

I think it would be funny if we discover that refraction is caused by the slowing of light in close proximity to mass. That is, one of the most common and observable phenomena in physics is a quantum gravity phenonema! (The usual explanation for refraction is that light as an EM wave causes sympathetic vibration in the electrons (and the protons, a little) which slows it down. But what if light's proximity to protons were caused a multitude of miniature Shapiro delays [0]?)

0 https://en.wikipedia.org/wiki/Shapiro_time_delay

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This can be refuted by observing that the refractive index isn't proportional to density, but is accurately predicted by charge mobility. Also, how refractive index changes with wavelength is related to the resonant frequencies of electrons.

Yeah, I was thinking about it and also lasers wouldn't work if it was 100% mini-Shapiro delays. I was thinking that maybe there's a small GR component to refraction, but the experiment would be tricky. You'd need to pin the electrons in the refractor down in a strong magentic field and then shoot some high energy photons at it, probably at least X-rays, and see if they still refract. (The high energy photons would be necessary to bring their wavelength closer to the diameter of the nucleus).

Refraction is well understood. It is caused by interactions of the incoming wave and electron clouds of atoms.

https://en.wikipedia.org/wiki/Ewald%E2%80%93Oseen_extinction...

Ah, perhaps you are inclined to stop reading when you come across open parenthesis?

Ok, I confess that I didn't read the entire comment. But you have a second problem, as you should explain why the conventional explanation does not hold or is canceled by your theory.

I'm already convinced[0] the effect is small, if it exists at all. However I thought of another experiment that might be easier to perform, to see if there is any effect at all: take two crystals, as similar in depth as one can make them, with two different isotopes, and measure the difference in index-of-refraction. Silicon (28 and 30?) would probably be good for this, as would laser interferometry. (Maybe the Gravity Probe B people have some extra pure isotope wafers they'd be willing to lend?) If I'm right then the Si-30 sample will have a slightly larger index of refraction than the Si-28 sample. Someone needs to do the math though because if the effect is far less than like one layer of atoms, or a few impurities here and there, then the experiment isn't worth doiong.

0 - https://news.ycombinator.com/item?id=36671605

Isotopes are not 100% chemically equivalent and they form chemical bonds with different vibrational resonances because the vibrating masses are different. You can see those differences in spectroscopic line shapes including in refraction (which is related to absorption by the Kramers-Kronig relation). My guess is that those effects would swamp out any relativistic ones by a lot, and because you can't tune the isotopic mass you wouldn't be able to isolate a gravitational effect.

In fact it appears that the isotopic dependence for silicon isotopes is known,

https://arxiv.org/abs/1105.0822

and the refractive index of Si 30 is lower than Si 28 in the IR, because of the different absorption lines.

Perfectly applicable paper, thanks! I skimmed it, but I didn't see an explanation for the lower refraction index for the heavier isotope. It had the lower RI at all wavelengths they looked at. I think it's useful to ignore the "phonon resonance" wiggle in the middle of their tested range on page 4, around 600nm, if looking for some other effect. (it's crazy that an electron that weighs like 10^-31 kg could actually jiggle a crystalline lattice to the point you can see it at all, but I suppose there's a lot of electrons, and Tacoma Narrows bridge reminds me of how powerful resonance effects can be).

The off-resonance curves look exactly like what you expect from the Kramers-Kronig relations

https://en.wikipedia.org/wiki/Kramers%E2%80%93Kronig_relatio...

which have very far reaching effects in term of refraction (the real part of the permittivity decays as 1/w).

In term of resonances, it's important to note that the nuclei themselves are not neutral either. In the IR, the time dependence of the field is slow enough that the nuclei can follow it resonantly. Those fields are much below electronic resonances so the electrons aren't even contributing much beyond making the crystal stable!

Now I'm curious: does the refraction that happen within our eyes has anything to do with the processing and the consequent experience of sight in a way that it utilizes quantum mechanics that we don't understand?

In theory it could but in practice there isn't much about the optical portion of the eye that we do not understand, the boundary of that understanding is well behind the optical nerve. What sort of an effect is it that you are getting at?

If I understand you correctly, Ive long thought about this as well!

Note you should clarify that by "slowing of light" you mean a lowering value of the absolute speed of light.

While Einstein assumed it was constant, yet said speed and time we're changing. It's actually simpler to say the opposite; speed and time change because speed of light (c) changes .

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