In my opinion, the quality of a space entirely devoid of matter (vacuum) can be changed by energy (mass) and vice versa (interaction). In this way, if light passes nearby a massive star may get delay rather than the light that it passes nearby the moon because of the higher refractive index of the space (vacuum).

Dear Farhad

You used "Quality of a space", I like it, because Space is not just holder, it has quality that we are ignoring it for long time. I believe Space is smart entity, it does a lot of things that... Article Quantum Intelligent Space

I think there is an important distinction:

• Refraction changes both the speed and direction of light.
• Gravitational warping of space time, induced by mass, changes only the direction of the light - not its speed; 'c' remains constant.

In an astrophysical system that exhibits multiple gravitational lensing of a background source which inherently varies in brightness (e.g. the quasar

RX J1131−1231), an observation showing that the lensed images vary with different time lags might at first be misinterpreted to suggest a variable speed of light; but with repeated observation, the constancy of the time lags between the light curves shows that it is due to different optical path lengths rather than different speeds. Therefore, mass/gravity is not inducing a refractive effect.

Farhad Vedad: We'd need to know more about your experiment where you say you "noticed that the refractive index of the medium increases near an object".

A vacuum does not have a refractive index. The fact that a large mass can warp space and thereby bend the light passing through the vacuum does not represent a refractive index for the vacuum itself, but is instead only a measure of the gravitational effect of the mass on space-time, which would be the same whether the space near it was a vacuum or filled with some transparent material. So treating the bending of light as you are talking about is misplacing the cause of the bending.

Courtney Seligman How can you be so sure? Have you tried to measure the refractive index of the vacuum in an isolated box near a massive star and far from any gravity field to compare the refractive index of the vacuum inside that box in those to conditions and then compare them?

Everyone should see this video https://youtu.be/B_ixkOI4k8c It is about bending light, it is conducted by Dr. Ed Dowdye

Javad Fardaei it is really interesting, however, it may not explain some other issues in my opinion.

Farhad Vedad "Have you tried to measure the refractive index of the vacuum in an isolated box near a massive star and far from any gravity field to compare the refractive index of the vacuum inside that box in those to conditions and then compare them? "

Of course Courtney hasn't done that: nobody could. I don't think it's a fair question to ask.

It's also an unnecessary question to ask, because it is a paradox. Refractive index is a property of a medium. One 'box' of vacuum cannot have a different refractive index to another 'box' of vacuum, since they are the same medium (or as most physicists would regard it, the same absence of a medium). In any true vacuum, you will always find an index of 1.00000....

Ray Butler good at least we have one point in common that we cannot talk so sure about our ideas.

When you talk about medium, do you believe that the medium is just suspending in a empty bowl by the name of space? Are you sure that space and the medium (a colony of atoms, whatever and whatever) do not interact on each other at all? if yes, then which quality of the space has been affected?

But about the number 1.00000... I would say that if and only if my experiments have been done correctly then that number varied. However, I am still developing my works.

I am not pretty sure, but roughly about 100 um.

Refractive index depends on the density and crystal structure of the material media. The origin of refractive index is due to pure quantum mechanical effect.

It's not homogenous. As the distance to the object is closer, light slows down more.

Again I can't say very precise but roughly the time delay was about 50ps for 450nm, 35ps for 520nm and 27ps for 640nm in length of 45cm.

@Thierry "possible that the gravity-bending is a hoax "..." the alleged 'gravitational bending' in galaxy clusters"

"Hoax" and "alleged" are curious choices of words.

"Alleged" implies a level of doubt that doesn't stand up to the fact that we have many observations of the deflection and amplification of light by gravitational lensing. Not just in galaxy clusters, but also in microlensing events involving single stars and even exoplanets.

"Hoax" implies a deliberate falsification by scientists - which is a serious and unjustified charge. Perhaps you only meant "misinterpretation?"

There is a vast difference between a dishonest scientist intentionally misleading others, and an honest scientist putting forward a best-fit current-knowledge model, per the scientific method, which may subsequently be shown (again per the scientific method!) to have been the wrong explanation.

This is my own lab at home where I did the experiment of light speed. The time delay was roughly about 50ps for 450nm, 35ps for 520nm and 27ps for 640nm in length of 45cm.

Thierry De Mees

Seriously? You question the reality of the moon landings, and climate change?! How can a scientist - a person who draws evidence-based conclusions - fall for such Youtube hoax crank nonsense?

There is ample evidence that the Van Allen radiation belts "problem" was no problem at all. Here's one succinct description:

• "the on-board dose counters for the Apollo missions registered average radiation doses to the skin of the astronauts of 0.38 rad. This is about the same radiation dose as getting two CT scans of your head, or half the dose of a single chest CT scan; not too bad, though not something you should do every week".
• Source, with links to the reported data: https://www.forbes.com/sites/jillianscudder/2017/06/16/astroquizzical-van-allen-belts-barrier-spaceflight/

We also know that there was an element of fortunate good timing. The Apollo missions happened to take place around the time of Solar Maximum (peak of its 11 year cycle). Solar Max increases the flux of solar wind particles, but counterintuitively it makes travelling within the Solar System safer in terms of radiation dosage, because the magnetic field of the Heliosphere strengthens and becomes more of a barrier to the external galactic cosmic ray flux. See the figure attached, from:

• Schwadron, N. A., et al. (2014), Does the worsening galactic cosmic radiation environment observed by CRaTER preclude future manned deep space exploration?, Space Weather, 12, 622–632, doi:10.1002/2014SW001084.

This was noted by Young that the light appears to start bending before it reached the surface of a refractive body. Some optics textbooks note this. Also, he noted the light through a slit appears to be more intense near the edges of slits in diffraction experiments as Farhad saw.

Thierry De Mees

1- I did the single slit diffraction under water. Then I noticed that as much as the slot is smaller, the estimation of the refractive index of water is larger since the fringes squeezes more for the shorter wavelength.

This effect can be related to two issues. First, it can be because of the greater attraction of liquid molecules to each other the same as the surface tension and producing a local lens near the slit. However, it can be an unknown effect that it results in increasing the refractive index inside the slit indeed.

2- I lined up 200 single slits (width 0.1mm) along 450mm. Then I aligned a distance meter and a mirror along the axis of the slits either side. The beam of the distance meter would pass through 200 slits and later would be reflected by the mirror to another mirror and in the end back to the sensor of the distance meter. The distance meter showed a tiny longer distance that meant light slowed down.

3 - I did this experiment by using three nano second pulsed laser (450nm, 520nm, and 640nm) at 20 MHz signal generator. The 150 MHz photo detector was connected to oscilloscope and the results as I mentioned before appeared. The air cannot make lens effect as water. So, the only things that was left is that the refractive index inside the slots and subsequently near the surface of an object is getting higher that causes the light slows down.

4- This results get more thinkable when I increase the refractive index of the medium a bit higher than the refractive index of the barriers. I got a tiny bright zero-order fringe only for the red light in the far field but dark fringe in both near field and far field for the green and blue ray.

I hope I explained well.

Ray Butler Dear Ray, I am afraid to say that your topic does not match my discussion. Thank you so much for you understanding.

Thierry De Mees

If the light goes zig-zag that probably it does, then the route will be longer for the longer wavelength and consequently the time delay for the red ray will be more. However in my experiment the red is faster. Probably this is one of the reason that IR is better to be used for telecommunication.