Is the speed of light constant between galaxies?

Yes, it does. But in the pseudo-Riemannian geometry of 4d space-time, there are different types of path for massive and massless particles - we call these time-like geodesics and null (or light-like) geodesics. In our everyday Euclidean geometry, there is only type of path (or geodesic) so this is unfamiliar behaviour.

But you offer no proof, nor any reason to believe what you say. You just recite stuff and then make up more nonsense when you are caught in an error.How about giving us one observation that your proposal explsins that is not explained by standard cosmology?

When you say "massive particle", is that any particle with mass?Do the different paths through Reimannian space correspond to different paths in Euclidean space? In other words, we can observe massive and massless particles following these different paths?--Percy

Is the wikidepdia article on Geodesics helpful? The GR I've picked up from watching Susskind's video series on General Relativity only dealt with timelike geodesics.Geodesics in general relativity - Wikipedia

Massive particle is indeed any particle with mass.The different paths in spacetime followed by massive and massless particles will be visible to us as the particles following different paths through space.As cavediver said, this is what makes geometry with a time dimension very different to purely spatial geometry. When all the dimensions are spatial there is only one type of path, our normal intuitive idea. When there is a time dimensions there are three separate types of paths.Edited by Son Goku, : Small addition.

Then I'm going to guess that you are either a looney or a troll.

Yes, no matter how small a mass. Yes, though I don't think we'd ever be able observe the difference without some decent source of curvature, such as a black hole. I have mentioned this photon orbit that exists half again as far from the centre of Schwarzschild black hole as the event horizon. Photons will zip around on this circular orbit quite happily, but anything with mass will spiral into the event horizon.ABE: ah, SG beat me to it - that's what happens when you write a post then forget to submit it for several hours Edited by cavediver, : No reason given.Edited by cavediver, : write not right as it was written right.

NN, SG and CD,Thanks for the info, one more question. CD's answer about needing "some decent source of curvature" hints that we don't yet have experimental or observational confirmation of massive and massless particles following different paths - is that true?--Percy

If dark matter is anti matter, matter and light would be pushed away,
but also light(photons) are in effect there own anti particle, which would mean when a photon comes into contact with dark matter it would be both a photon and an anti photon, the photon would be pushed away in the opposite direction and the anti-photon which would then pass through dark matter, where upon leaving dark matter it would then again be a photon and also send an anti photon back into the dark matter.

Sticks and Stones, i am only trying to put to words what i see, think of me as you will, i mean no offense to anyone, or there beliefs,
I can understand why you may call me a "looney or a troll",
I myself think of many "humans" as "one dimensional entities" who may live in this world but never really understand what is in front of them, being unable to see beyond their conditioning.It is hard enough trying to put how i see this small part, so if i jumped to beyond this, you would not be the only one calling me a looney, as there is yet no "science" around that comes close to explainning,
There are a few of us who are no longer held, who can move between these boundaries.
We had to find new ways to still exsist in this "human reality", This is one of mine, Trying to understand the science behind it all.
It keeps me from losing myself completely, so i may carry on being a father and grandad.

No they wouldn't. It would produce copious amounts of photons as matter and anti-matter annhialite. It would be the most luminous matter in the universe, the very opposite of dark matter.You might also read about positron emission tomography, otherwise known as PET scans. This technique acutally uses anti-matter to produce photons.Also, anti-matter absorbs light just like regular matter, so again we have the problem if scattered or absorbed light which is not seen.

It seems as if you are just making it up as you go. Reference to evidence in the real world would be very helpful at this point. It would appear that person is you because you simply don't understand how reality works. Instead, you have a fantasy that you have invented which you "see", but can never evidence. You have made it abundantly clear that you don't understand what the science actually is, nor the current state of the evidence.

Almost certainly true - we don't have observational confirmation of this. I think you would need a handy black hole and some distant oribital platforms to house a laser, a particle accelerator, and a couple of detectors.

I do understand how reality works, i am just trying to understand how light behaves with dark matter, i know light is bent around high gravitational masses, but i also know that light travels through dark matter, the evidence is there, but it as been interpreted wrong,
physics first went off tracks when the "big bang" theory was put forward, at roughly the same time as the universal background radiation was detected, because they seemed to fit each other it became excepted by most, which as threw science back decades, now all "evidence" is made to fit into this big bang theory.There is nothing in the big bang theory that does not fit better in a free falling expanding universe in lower d space,
it explains dark matter, blackholes, gamma ray bursts , gravity , galaxy formation, and much more.The evidence is there, it is how it is interpreted, YOU WILL ALWAYS BELIEVE WHAT YOU HAVE BEEN "TAUGHT".You have not got the ability to see a complete picture.We are argueing over a wheel nut and missing the car.

What is this evidence you are talking about? Lemaitre proposed the Big Bang in 1927. The CMB was not detected until 1964. The CMB was a prediction of the BB model for almost 40 years before it was finally discovered. The Big Bang was first proposed because of the observed correlation between distance and redshift for distant galaxies. Umm, no. The model is changed to fit the evidence. The latest evidence demonstrates that the expansion is accelerating, so this has been incorporated into the BB model. What evidence is there for "lower d space"? Apparently not since you have dark matter being made up of ions which just doesn't work.