Comments on: How To Define Distance In An Expanding Universe

By: Brian Koberlein

Brian Koberlein — Mon, 29 May 2017 20:50:22 +0000

The expanding universe model uses general relativity, not special relativity, which does apply to both accelerating and non-accelerating reference frames.

By: GenialityOfEvil

GenialityOfEvil — Mon, 29 May 2017 20:20:54 +0000

I don’t think gravity affects the speed of light at all, since the lower speed in a denser medium is because the photons interact with the atoms on their way through.
The early universe part’s an interesting one. I guess it depends on the sensitivity of the telescope. I don’t know what altitude sunlight starts bending in our atmosphere to a measurable degree, but there would be a density point where we wouldn’t detect it anymore. So you can measure how much it bends at a given altitude to sea level.
I don’t imagine the ratio would be any differently in the early universe, I don’t think atoms reflect light any differently if they already emit light.

By: Mr Jan David Fisher

Mr Jan David Fisher — Mon, 29 May 2017 19:01:21 +0000

This article re-enforces a question that I have. While the speed of light is independent of the direction it is traveling, it is dependent on the density of the media that it is traveling through. From the big bang to some point, the density of the universe was high and with expansion dropping. What would the effect of the density be on measuring distances, determining the age of the universe, and what is the effect of gravity on the speed of light since it can bend light? Big multi-question and I expect a bigger set of answers–thank you!

By: Garry Short

Garry Short — Mon, 29 May 2017 18:27:38 +0000

I’m deeply perplexed by this discussion.
I wonder about the validity of assuming ‘C’ in Gravitationally bound, Dark Matter vacuum (Minkowski space), to be the same as ‘C’ in the Dark Energy driven expanding vacuum (De Sitter space) between Galaxies.
Lorentz and Einstein himself, declared that Special Relativity ONLY applies in non-accelerating reference frames, so it seems to me that light in that accelerating expansion of De Sitter space, should not be considered to be bound by the same constraints as it might be in non-expanding Minkowski space.

The ^CDM model rounds off far too much for my liking, trying to quantify non-fixed variables with constant values, only ONE of which is the “speed” of light, whilst another glaring problem is the variation in our best estimates of the expansion rate itself. These estimates vary by just over 9% and all three appear to be equally valid.
However the one factor which can be clearly defined as a difference in the methods used is the supposed time frame between events observed/measured. This time lag should have been analysed as evidence of the changed rate of expansion over time, but alas, appears to get swept under some kind of cosmic carpet and we persist with our insistence that the expansion can be offset with a fixed constant value.

There’s more, but this broadly sums up my confusion.

By: Stephen Osborn

Stephen Osborn — Mon, 29 May 2017 12:50:27 +0000

We love that you take the effort to explain things as clearly as possible Brian. It’s not easy!!

By: JIHarmer

JIHarmer — Sun, 28 May 2017 22:47:34 +0000

Thanks for explaining this. Either I’ve just had a Krell brain boost, or this is the best explanation of co-moving distance that I’ve heard….!